[go: up one dir, main page]

WO2014030576A1 - Élément à guides d'ondes optiques - Google Patents

Élément à guides d'ondes optiques Download PDF

Info

Publication number
WO2014030576A1
WO2014030576A1 PCT/JP2013/071845 JP2013071845W WO2014030576A1 WO 2014030576 A1 WO2014030576 A1 WO 2014030576A1 JP 2013071845 W JP2013071845 W JP 2013071845W WO 2014030576 A1 WO2014030576 A1 WO 2014030576A1
Authority
WO
WIPO (PCT)
Prior art keywords
waveguide
sub
optical
main
mode
Prior art date
Application number
PCT/JP2013/071845
Other languages
English (en)
Japanese (ja)
Inventor
裕幸 日下
憲介 小川
一宏 五井
Original Assignee
株式会社フジクラ
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 株式会社フジクラ filed Critical 株式会社フジクラ
Publication of WO2014030576A1 publication Critical patent/WO2014030576A1/fr

Links

Images

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/125—Bends, branchings or intersections
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/14—Mode converters
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
    • G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure
    • G02F1/2255—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure controlled by a high-frequency electromagnetic component in an electric waveguide structure
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G02B6/2808—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using a mixing element which evenly distributes an input signal over a number of outputs
    • G02B6/2813—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using a mixing element which evenly distributes an input signal over a number of outputs based on multimode interference effect, i.e. self-imaging
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G02B6/2821—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29346—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by wave or beam interference
    • G02B6/2935—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
    • G02F1/212—Mach-Zehnder type
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
    • G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure
    • G02F1/2257—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure the optical waveguides being made of semiconducting material

Definitions

  • the present invention relates to an optical demultiplexer and an optical waveguide device including a mode splitter.
  • the present invention also relates to an optical waveguide device including a mode splitter.
  • the other modes are called n-order modes corresponding to the number of modes n.
  • modes of n ⁇ 1 are collectively referred to as higher order modes.
  • Si optical waveguides having silica (SiO 2 ) as a cladding and silicon (Si) as a core can be miniaturized using a high refractive index difference (Si / SiO 2 ), and Si -It is attracting attention and expectation because it can be manufactured relatively inexpensively using existing manufacturing equipment for LSIs (Large Scale Integrated Circuits).
  • an optical demultiplexer splitter
  • MMI multi-mode interferometer
  • Y demultiplexer Usually, the optical demultiplexer is used to divide the fundamental mode light into a desired branching ratio.
  • Patent Document 1 discloses that a sub-waveguide having a taper structure is placed along a main waveguide assuming a silica-based glass waveguide, and a higher-order mode is removed from the main waveguide by adiabatic transition.
  • Non-Patent Document 1 As one of the prior arts related to the Si / SiO 2 waveguide, Non-Patent Document 1 (2.2, 3.2, FIG. 1, FIG. 4, etc.) has a thickness of 200 nm, a width of 400 nm, and an interval of 480 nm. Using a polarization splitter (PS) using a directional coupler (DC) consisting of two Si waveguides, polarization modes can be separated with a length of about 10 ⁇ m. It is disclosed that there is.
  • PS polarization splitter
  • DC directional coupler
  • the relative refractive index difference of the Si / SiO 2 waveguide is much larger than the relative refractive index difference of the LiNbO 3 or quartz-based waveguide.
  • the effective refractive index is reduced and the higher-order mode is removed before the duplexer as in Patent Document 1, for example, a cladding
  • the core width must be 450 nm or less.
  • the waveguide loss is about 0.16 dB / mm when the core width is 500 nm, whereas the waveguide loss is about 0.40 dB / mm when the core width is 400 nm.
  • the waveguide loss when the core width is 400 nm is about 2.5 times the waveguide loss when the core width is 500 nm. That is, the narrower the core width, the higher the waveguide loss, and the easier the waveguide characteristics to deteriorate due to the surface roughness.
  • Patent Document 1 discloses, as means for reducing the effective refractive index, not only the change of the waveguide width but also the change of the impurity concentration in the waveguide and the waveguide depth.
  • an increase in impurity concentration causes an increase in optical loss, and a change in waveguide depth is difficult in the manufacturing process.
  • the technique disclosed in Patent Document 1 is used, the loss of the fundamental mode is increased, or the manufacturing is difficult.
  • Example 1 of Patent Document 2 it is disclosed that a taper length of 2 mm is necessary for a wavelength of incident light of 1.5 ⁇ m.
  • a device with a large relative refractive index difference such as a Si / SiO 2 waveguide has a great advantage in downsizing an optical device by a device of the ⁇ m order using a high refractive index difference. It is not possible to incorporate a device having a size of mm.
  • Patent Document 2 since the fundamental mode light and the primary mode light are separated by adiabatic transition, the interval between the two waveguides needs to be extremely small with respect to the waveguide width.
  • Non-Patent Document 1 discloses a device capable of separating polarization modes, but a device capable of separating propagation modes having different mode numbers n (for example, separation between a fundamental mode and a higher-order mode). Is not disclosed.
  • an object of the present invention is to provide an optical waveguide device including a mode splitter capable of mode separation.
  • a mode splitter capable of mode separation from the optical waveguide of the previous stage of the optical demultiplexer is provided. It is an object to provide an optical waveguide device.
  • the optical waveguide device includes an optical demultiplexer that demultiplexes one input light into a plurality of output lights, and guides the input light and the output light, and includes at least two types of optical waveguide elements.
  • a main waveguide capable of guiding propagation modes having different propagation orders, and a coupling portion arranged in parallel to the main waveguide at a certain distance from the main waveguide so as to constitute a directional coupler;
  • One or more mode splitters having a sub-waveguide capable of separating at least one of the two or more types of propagation modes from the main waveguide; and the main waveguide and the sub-waveguide.
  • N core / n clad which is the refractive index ratio between the core and the clad, is in the range of 101 to 250%.
  • the difference between the width of the main waveguide and the width of the sub waveguide in the directional coupler may be within ⁇ 10%.
  • the difference between the thickness of the main waveguide and the thickness of the sub waveguide in the directional coupler may be within ⁇ 10%.
  • the sub-waveguide may further include a start portion that is continuous with the front end portion of the coupling portion, and may gradually approach the main waveguide as the start portion approaches the front end portion.
  • the sub-waveguide may further include an end portion that is continuous with an end portion at the rear stage of the coupling portion, and may gradually move away from the main waveguide as the end portion moves away from the end portion at the rear stage.
  • the mode splitter may be provided in the optical waveguide that guides the input light.
  • the optical demultiplexer and the mode splitter may be continuously provided in a cascade type.
  • the optical waveguide device further includes an optical multiplexer that multiplexes two demultiplexed lights into one output light, and an optical modulator, and the optical demultiplexer converts one input light into the two demultiplexed lights.
  • the optical waveguide element includes a plurality of the mode splitters, and a difference between the width of the main waveguide and the width of the sub waveguide in each directional coupler is within ⁇ 10%, The distance between the coupling portion and the main waveguide and the length of the coupling portion of the sub waveguide may be equal among all the directional couplers.
  • the optical waveguide element includes a plurality of the mode splitters, and the difference between the width of the main waveguide and the width of the sub waveguide in each of the directional couplers is approximately the same as the main waveguide within ⁇ 10%.
  • the optical demultiplexer may be an MMI type optical demultiplexer.
  • the optical demultiplexer may be a Y-type optical demultiplexer.
  • the core material may be Si, and the clad material may be SiO 2 .
  • the sub waveguide may separate a higher order mode from the main waveguide.
  • the optical waveguide element may further include a light absorption layer disposed at a tip of the end portion of the sub waveguide and doped with impurities at a high concentration.
  • the optical waveguide element may be further disposed at the end of the end portion of the sub-waveguide, and further include a light receiving element and an electric wiring for taking out a current of the light receiving element.
  • the optical waveguide device includes a main waveguide capable of guiding at least two types of propagation modes having different propagation orders, and a constant waveguide from the main waveguide so as to constitute a directional coupler.
  • n core / n clad which is a refractive index ratio between the core and the clad constituting the main waveguide and the sub waveguide, is within a range of 101 to 250%.
  • the difference between the width of the main waveguide and the width of the sub waveguide in the directional coupler may be within ⁇ 10%.
  • the difference between the thickness of the main waveguide and the thickness of the sub waveguide in the directional coupler may be within ⁇ 10%.
  • the sub-waveguide constituting the directional coupler further includes a starting portion that is continuous with an end portion of the previous stage of the coupling portion, and the main waveguide gently moves as the starting portion approaches the end portion of the preceding stage. You may approach.
  • the sub-waveguide may further include an end portion that is continuous with an end portion at the rear stage of the coupling portion, and may gradually move away from the main waveguide as the end portion moves away from the end portion at the rear stage.
  • the optical waveguide element includes a plurality of the mode splitters, and a difference between the width of the main waveguide and the width of the sub waveguide in each directional coupler is within ⁇ 10%, The distance between the coupling portion and the main waveguide and the length of the coupling portion of the sub waveguide may be equal among all the directional couplers.
  • the optical waveguide element includes a plurality of the mode splitters, and the difference between the width of the main waveguide and the width of the sub waveguide in each of the directional couplers is approximately the same as the main waveguide within ⁇ 10%.
  • the core material may be Si, and the clad material may be SiO 2 .
  • the sub waveguide may separate a higher order mode from the main waveguide.
  • the optical waveguide device may further include a light absorption layer provided at a tip of the end portion of the sub-waveguide and doped with impurities at a high concentration.
  • a light receiving element and an electric wiring for taking out a current of the light receiving element may be further provided at the end of the end portion of the sub waveguide.
  • mode separation is possible by the mode splitter. Further, according to the optical waveguide device according to the aspect of the present invention, in the optical waveguide device in which the waveguide capable of guiding two or more kinds of propagation modes is connected to the front stage of the optical demultiplexer, Mode separation is possible from the preceding optical waveguide by a mode splitter.
  • FIG. 1B is a partially enlarged plan view showing the MMI type optical demultiplexer of FIG. 1A.
  • FIG. 1B is a partially enlarged plan view showing the mode splitter of FIG. 1A. It is sectional drawing which follows the SS line
  • (A)-(c) are the simulation results which show an example of the propagation state of the primary mode light in various mode splitters. It is a graph which shows an example of the relationship between the branching ratio in a some curvature radius, and a linear part. It is a graph which shows an example of the relationship between a branching ratio and the curvature radius of a curve part. It is a simulation result which shows an example of the mode of propagation of fundamental mode light in a mode splitter.
  • 1A to 1D show an optical waveguide device according to the first embodiment of the present invention.
  • the optical waveguide device 10 includes an optical waveguide having a core 2 and a clad 3 on a substrate 1.
  • 1A to 1C only a portion corresponding to the core 2 is illustrated and described as an optical waveguide.
  • an optical waveguide device 10 includes an optical demultiplexer 14 that demultiplexes one input light into a plurality of output lights, and a mode splitter provided in the preceding stage on the input side of the optical demultiplexer 14. 20.
  • the output light of the mode splitter 20 is injected into the optical demultiplexer 14 via the incident side waveguide 11. Further, the plurality of output lights demultiplexed by the optical demultiplexer 14 are injected into the plurality of output-side waveguides 12 and 13, respectively.
  • the optical demultiplexer (splitter) is not particularly limited, and examples thereof include an MMI type demultiplexer, a Y type demultiplexer, and a directional coupler.
  • Waveguides (main waveguides) 11, 12, and 13 connected to the optical demultiplexer 14 are multimode waveguides that guide light in multimode.
  • waveguides 11, 12, and 13 it is preferable to use waveguides having a wide core width, such as multimode waveguides, because the waveguide characteristics are hardly deteriorated due to surface roughness.
  • the mode splitter 20 includes a main waveguide 21 connected to the incident-side waveguide 11 of the optical demultiplexer 14 and a sub-waveguide 22 provided away from the main waveguide 21.
  • the main waveguide 21 is desirably a waveguide capable of guiding at least two types of propagation modes having different propagation orders.
  • a waveguide having a wide core width such as a multimode waveguide is used as the main waveguide 21
  • the waveguide characteristics are hardly deteriorated due to surface roughness.
  • the sub waveguide 22 separates at least one propagation mode having different propagation orders from the main waveguide 21 among at least two propagation modes having different propagation orders that can be guided by the main waveguide 21.
  • the main waveguide 21 and the sub-waveguide 22 have coupling portions 21b and 22b that are placed in parallel to each other with a certain distance therebetween, and the directional coupler having a length L 0 by these coupling portions 21b and 22b. Is configured.
  • the mode splitter 20 in the illustrated example has the main waveguide 21 and the sub-waveguide 22 gently from each other from the start portions 21a and 22a in front of the coupling portions 21b and 22b constituting the directional coupler to the coupling portions 21b and 22b. It has a structure that approaches.
  • the mode splitter 20 has a structure in which the main waveguide 21 and the sub-waveguide 22 are gently separated from each other from the coupling portions 21b and 22b to the end portions 21c and 22c at the subsequent stage of the coupling portions 21b and 22b.
  • the sub waveguide 22 may be a waveguide capable of guiding at least two types of propagation modes having different propagation orders.
  • a directional coupler can be formed by placing the sub-waveguide in parallel at a position close to the main waveguide. Forming a directional coupler generally couples any mode of the main waveguide with the mode of the sub-waveguide.
  • the strength of coupling from the main waveguide mode to the sub-waveguide mode is represented by a coupling coefficient ⁇ 21 shown in the following equation (1).
  • C is a constant including a normalization constant
  • n core is the refractive index of the core
  • n clad is the refractive index of the cladding.
  • Subscripts 1 and 2 represent the eigenmodes (E1 and E2) of the main waveguide and the subwaveguide, respectively.
  • x and y are the width direction and thickness direction of the waveguide, and the integration range is in the core cross section of the sub-waveguide.
  • the magnitude of the coupling coefficient depends on how much the electromagnetic field distribution of the eigenmode of the main waveguide extends within the core cross section of the sub-waveguide.
  • the fundamental mode propagates in the center of the core, whereas the higher order mode propagates outside the waveguide as compared with the fundamental mode (for example, Example 1 described later).
  • FIG. 10A and FIG. 10B Therefore, it is expected that higher-order modes such as the first-order mode are more easily coupled to the sub-waveguide than the fundamental mode.
  • the distance between two waveguides forming the directional coupler for example, see the distance w 0 in FIG.
  • the coupling coefficient decreases in both the fundamental mode and the higher-order mode.
  • the coupling coefficient of the fundamental mode is drastically reduced as compared with the coupling coefficient of the higher-order mode such as the first-order mode (see, for example, FIG. 11 of Example 1 described later). Therefore, by appropriately selecting the interval between the two waveguides forming the directional coupler, the difference in the coupling coefficient ⁇ 21 is sufficiently increased between two or more types of propagation modes that can be guided by the main waveguide. be able to.
  • the coupling coefficient ⁇ 21 is proportional to n core 2 ⁇ n clad 2 with respect to the refractive index n core of the core and the refractive index n clad of the cladding. For this reason, in order to increase the difference in coupling coefficient between modes, it is preferable to employ a waveguide structure having a large difference in refractive index.
  • n core / n clad is preferably in the range of 101 to 250%.
  • the core material is Si (refractive index of about 3.475) and the cladding material is SiO 2 (refractive index of about 1.444)
  • a semiconductor material such as an SOI (Silicon On Insulator) substrate is used as a waveguide material. Since it can be used for, it is preferable.
  • the core material include SiO x (refractive index: 1.47), SiON, SiN, and non-silicon based semiconductor materials (compound semiconductors).
  • the maximum power transfer rate is 100% if the two waveguide structures (material, dimensions, shape, etc.) are perfectly symmetrical. Conversely, when the two waveguide structures are different and the mode propagation constants are different, the maximum power transfer rate is less than 100%. Therefore, when efficiently transferring a higher-order mode such as the primary mode from the main waveguide to the sub-waveguide, the waveguide structures (material, dimensions, shape, etc.) of the main waveguide and the sub-waveguide should be made as much as possible. desirable.
  • the main waveguide width and the sub waveguide width is preferably a substantially identical.
  • an old-generation exposure device using KrF (248 nm) as a light source should be used in order to manufacture it inexpensively.
  • a general method for forming a waveguide core there is a possibility that an error caused by alignment accuracy of an exposure mask or etching accuracy may occur. Therefore, when there is no intentional change in the waveguide width (core width) such as a taper shape (see the prior art), for example, the difference between the main waveguide width and the sub-waveguide width is within ⁇ 10%. It is preferable.
  • the difference between the thickness of the main waveguide and the thickness of the sub waveguide is preferably within ⁇ 10%, for example.
  • the length of the directional coupler required until the power shift from the main waveguide to the sub waveguide is maximized is called a coupling length.
  • the bond length depends on the strength of the coupling coefficient ⁇ 21 . In general, the smaller the coupling coefficient ⁇ 21 is, the longer the coupling length is (see, for example, FIGS. 11 and 12 of Example 1 described later). For example, under the condition that the coupling length of the fundamental mode is sufficiently longer than the coupling length of the higher-order mode, the length of the directional coupler is shortened (for example, the length of the directional coupler is set as the coupling length of the higher-order mode).
  • the specific higher order mode (for example, the first mode) is sub-guided from the main waveguide.
  • a mode splitter having a structure that can be separated into waveguides can be realized.
  • the length of the directional coupler is longer than the coupling length of the higher-order mode, the higher-order mode shifts alternately between the main waveguide and the sub-waveguide. Therefore, for example, when the length of the directional coupler is set to be approximately the same as the coupling length of the fundamental mode and the ratio of the higher-order mode shifting to the secondary waveguide is reduced, the fundamental mode is changed from the primary waveguide to the secondary waveguide.
  • a mode splitter having a structure that can be separated into a waveguide is considered.
  • a directional coupler is formed by disposing a sub-waveguide having substantially the same width as the main waveguide in parallel with the main waveguide at a position close to the main waveguide connected to the duplexer. Furthermore, the length of the directional coupler and the interval between the main waveguide and the sub-waveguide are appropriately selected and set by utilizing the fact that the coupling constant is remarkably different between the fundamental mode light and the higher-order mode light.
  • the sub-waveguide 22A has a coupling portion 22b that is a portion constituting the directional coupler and an end portion 22c that extracts the light of the mode separated by the coupling portion 22b.
  • the sub-waveguide does not have the start portion (reference numeral 22a in FIG. 1C) of the structure in which the sub-waveguide approaches the main waveguide gently.
  • the main waveguide 31 is entirely linear from the start portion 31a through the coupling portion 31b to the end portion 31c.
  • the sub-waveguide 32 of the mode splitter 30 includes a start portion 32a having a structure in which the sub-waveguide gently approaches the main waveguide, a coupling portion 32b that is a portion constituting the directional coupler, and a mode separated by the coupling portion 32b. And an end portion 32c for extracting the light.
  • the main waveguide 31 is entirely linear from the start portion 31a through the coupling portion 31b to the end portion 31c.
  • the sub-waveguide 32A of the mode splitter 30A has a coupling portion 32b that is a portion constituting the directional coupler and an end portion 32c that extracts the light of the mode separated by the coupling portion 32b. There is no starting portion (reference numeral 32a in FIG. 2B) of the structure gently approaching the waveguide.
  • the same devices as the mode splitters 20A, 30, and 30A shown in FIGS. 2A to 2C may be used for each mode splitter.
  • the main waveguide 21 is a straight line and the sub-waveguide 22 is a curve.
  • the main waveguide 21 may be a curve and the sub-waveguide 22 may be a straight line.
  • the main waveguide and the sub-waveguide have a symmetrical planar shape as shown in FIG. 1C at least at a position close to the directional coupler.
  • the influence of the symmetry between the main waveguide and the sub-waveguide is determined by a finite-difference time domain (FDTD) method in Example 2 to be described later (particularly, a comparison between FIGS. 18A and 18B). It has been compared by electromagnetic field simulation. 2B is obtained by bending the end portion 31c of the main waveguide of the mode splitter 30A of the optical waveguide element shown in FIG. 2C with the same bending structure as that of the end portion 32c of the sub-waveguide.
  • FDTD finite-difference time domain
  • the start portion 31a of the main waveguide of the mode splitter 30 of the optical waveguide device shown in FIG. 2B is bent with the same bending structure as the start portion 32a of the sub-waveguide, and the end portion 31c of the main waveguide is the end portion of the sub-waveguide.
  • the mode splitter 20 having the symmetry shown in FIG. 1C is obtained by bending with a bending structure similar to that of 32c.
  • the intermediate line of the coupling portions 21b and 22b constituting the directional coupler is set as the symmetry center line (symmetric axis), and the main waveguide start portion 21a and the sub-waveguide start portion 22a are led.
  • the coupling portion 21b of the waveguide and the coupling portion 22b of the sub waveguide, and the end portion 21c of the main waveguide and the termination portion 22c of the sub waveguide are provided so as to be symmetrical.
  • the curvature radius of the curved portion (21a, 21c) of the main waveguide is equal to the curvature radius of the curved portion (22a, 22c) of the sub waveguide, or the curvature radius of the curved portion (21a, 21c) of the main waveguide is the sub waveguide.
  • the radius of curvature of the curved portions (22a, 22c) is larger than the radius of curvature of the curved portions (21a, 21c) of the main waveguide or smaller than the radius of curvature of the curved portions (22a, 22c) of the sub waveguide Is possible.
  • the waveguide can be extended or bent so as to have a desired arrangement on the substrate. Further, the direction and length of the waveguide can be freely set.
  • the widths of the main waveguide and the sub-waveguide can be made substantially the same as a whole as well as the position close to the directional coupler.
  • the sub-waveguide has a start portion of a structure that gently approaches the main waveguide because loss can be further reduced.
  • the influence of the sub-waveguide on the fundamental mode of the main waveguide is compared and examined by electromagnetic field simulation using the FDTD method (described above) in Example 2 (particularly, comparison of FIGS. 18B and 18C).
  • . 2B is obtained by bending the start portion of the sub-waveguide of the mode splitter 30A of the optical waveguide element shown in FIG. 2C in the same bending structure as the end portion 32c of the sub-waveguide. It is done.
  • the mode splitter 20A of the optical waveguide element shown in FIG. 2B by bending the start portion of the sub-waveguide of the mode splitter 20A of the optical waveguide element shown in FIG. 2B with the same bending structure as the end portion 22c of the sub-waveguide, the mode splitter having a gentle approach portion shown in FIG. 1C. 20 is obtained. If the sub-waveguide appears discontinuously in the vicinity of the light passing through the main waveguide, light reflection or disturbance is likely to occur, and the loss of light increases. These losses can be further reduced when the sub-waveguide approaches the main waveguide gently. Similarly, when the sub-waveguide has an end portion of a structure that is gently separated from the main waveguide, it is preferable because the loss of light can be further reduced.
  • the structure in which the main waveguide and the sub waveguide are gradually approached or separated is configured along a curve such as an arc, an elliptical arc, a parabola, or a hyperbola.
  • the curvature radius of the curve is preferably 10 ⁇ m or more, for example. Since the curvature radius of the straight line is ⁇ , there is no particular upper limit to the curvature radius for continuously connecting the straight line portion and the curved portion, but the curvature radius of the curved portion adjacent to the straight line portion is, for example, several tens to Several hundred ⁇ m can be mentioned.
  • the bisector perpendicular to the coupling portions 21b and 22b constituting the directional coupler is set as a symmetry center line (symmetric axis), and the main waveguide start portion 21a and the main waveguide end portion 21c.
  • the start portion 22a of the sub-waveguide and the end portion 22c of the sub-waveguide are provided symmetrically. It is possible to select whether the radius of curvature of the start portion is equal to the radius of curvature of the end portion, whether the radius of curvature of the start portion is larger than the radius of curvature of the end portion, or whether the radius of curvature of the start portion is smaller than the radius of curvature of the end portion It is.
  • FIG. 3 shows a second embodiment of the optical waveguide device.
  • the optical waveguide device according to the present embodiment is formed by providing the optical waveguide device 10 constituted by a combination of the optical demultiplexer 14 and the mode splitter 20 similar to FIG.
  • the optical waveguide device 10 is configured with a 1 ⁇ 2 duplexer (1 ⁇ 2 duplexer), whereas the optical waveguide device of FIG. 3 is configured with a 1 ⁇ 4 duplexer.
  • a 1 ⁇ N (1 input N output) demultiplexer such as a 1 ⁇ 8 demultiplexer, 1 ⁇ 16 demultiplexer, or 1 ⁇ 32 demultiplexer can be configured by overlapping a plurality of stages. It is.
  • the sub-waveguide 22 of each optical waveguide element 10 is shifted to the sub-waveguide 22 at a position sufficiently away from the main waveguide 21, and the separated propagation mode (for example, higher order mode) is absorbed or radiated in a direction away from the main waveguide. . Thereby, recombination to the main waveguide 21 can be suppressed.
  • the separated propagation mode is absorbed in the substrate, for example, a light absorption layer 23 (see FIG. 5) described later is provided at the tip of the end portion 22 c of the sub-waveguide 22.
  • the end portion of the sub waveguide 22 can be extended to the peripheral edge of the substrate and radiated toward the outside of the substrate.
  • FIG. 4 shows a third embodiment of the optical waveguide element.
  • an optical demultiplexer 42 that demultiplexes one input light into two output lights, and a light modulation unit 45 in a subsequent stage on the side where the optical demultiplexer 42 outputs light.
  • a Mach-Zehnder type optical modulator 40 composed of an optical multiplexer 46 that multiplexes two input lights into one output light.
  • One output light of the optical demultiplexer 42 is input to the optical multiplexer 46 via the waveguide 43 having the optical modulator 45, and the other output light of the optical demultiplexer 42 does not have the optical modulator 45.
  • the light is input to the optical multiplexer 46 via the waveguide 44.
  • the light injected into the optical demultiplexer 42 from the optical waveguide 41 in the previous stage of the optical demultiplexer 42 is demultiplexed into two and propagates through different waveguides (arms) 43 and 44, respectively.
  • the light modulator 45 is generally a phase modulator.
  • the optical multiplexer 46 combines them.
  • the waved light is modulated according to the phase difference. For example, switching between the on state and the off state of the optical signal is controlled by the phase difference between the two lights injected into the optical multiplexer 46.
  • the Mach-Zehnder optical modulator 40 When two lights are injected into the optical multiplexer 46 with the same phase, the combined light propagates in the optical waveguide 47 in the subsequent stage in the fundamental mode, and the optical signal is turned on. On the other hand, when two lights are injected into the optical multiplexer 46 with opposite phases, the combined light propagates in the first-order mode to the optical waveguide 47 in the subsequent stage, and the optical signal is turned off.
  • the Mach-Zehnder optical modulator 40 By connecting the optical waveguide 41 before the optical demultiplexer 42 of the Mach-Zehnder optical modulator 40 to the main waveguide 21 of the mode splitter 20 and separating the primary mode light into the sub-waveguide 22, the Mach-Zehnder optical modulator is obtained. Deterioration of the extinction ratio of 40 can be suppressed.
  • the MMI demultiplexer 14 may be used as the optical demultiplexer 42.
  • the relationship between the MMI type duplexer 14 and the mode splitter 20 can be configured in the same manner as the optical waveguide device 10 in FIG. 1A.
  • the optical demultiplexer 42 and the optical multiplexer 46 of the Mach-Zehnder optical modulator 40 are not particularly limited.
  • the MMI type demultiplexer or multiplexer, the Y type demultiplexer or multiplexer, or the direction Examples include sex couplers.
  • the front stage (waveguide 41) which is the input side of the optical demultiplexer 42, the rear stage (waveguide 47) which is the output side of the optical multiplexer 46, or the optical branch It can be provided at one or more locations selected from the inside (waveguides 43, 44) between the wave multiplier 42 and the optical multiplexer 46. That is, the mode splitter 20 can be provided in at least one of the waveguides 41, 43, 44, and 47 that guide the input light, the demultiplexed light, and the output light in the Mach-Zehnder optical modulator 40.
  • FIG. 5 shows a fourth embodiment of the optical waveguide device.
  • the optical waveguide device according to the present embodiment includes a light absorption layer 23 doped with impurities at a high concentration at the end of the end portion of the sub-waveguide 22 of the mode splitter 20.
  • a light absorption layer 23 is provided at the end of the end portion of the sub-waveguide 22. Also good.
  • FIG. 6 shows a fifth embodiment of the optical waveguide device.
  • a light receiving element (PD: Photo Detector) 24 and an electric wiring 25 for taking out the current of the PD 24 are provided at the tip 22d of the end portion 22c of the sub-waveguide 22 of the mode splitter 20.
  • PD Light receiving element
  • an electric wiring 25 for taking out the current of the PD 24 are provided at the tip 22d of the end portion 22c of the sub-waveguide 22 of the mode splitter 20.
  • the PD 24 By installing the PD 24, it is possible to monitor the light amount of the higher-order mode light branched to the sub waveguide 22. By this monitoring, it is possible to detect a shift in operation due to, for example, aged deterioration or an environmental change such as temperature during driving.
  • the optical demultiplexer 14 is incorporated in the Mach-Zehnder type optical modulator 40 (see FIG.
  • the PD 24 and the electric wiring 25 are provided at the end of the end portion 22c of the sub-waveguide 22. It may be provided.
  • the control unit uses the monitoring result using the PD 24 to operate the optical modulator 45 (for example, an applied voltage in the case of electric control). ) Can be fed back.
  • the PD is preferably arranged on the substrate, the PD may be mounted on the substrate.
  • the PD can be integrated as a semiconductor element on the same substrate as the optical waveguide.
  • Examples of PDs that can be integrated on a Si substrate having a Si / SiO 2 waveguide include group IV semiconductor PDs such as germanium (Ge) PD, indium phosphide (InP) -based PDs, or gallium arsenide (GaAs). Examples include III-V compound semiconductor PD.
  • group IV semiconductor PDs such as germanium (Ge) PD, indium phosphide (InP) -based PDs, or gallium arsenide (GaAs).
  • Examples include III-V compound semiconductor PD.
  • two electric wirings 25 can be provided on the substrate (via an insulating layer if necessary), for example, two in parallel for each PD 24.
  • the sub-waveguide 22 and the main waveguide 21 have end portions 21c and 22c having a structure in which they are gently separated from each other. The radius of curvature of the tip 22d of the end portion 22c of the sub-waveguide gradually increases toward the PD 24, and finally the linear waveguide
  • the bending loss of the higher-order mode light at the end portion 22c of the sub waveguide can be reduced by increasing the radius of curvature at the end portion 22c of the sub waveguide. it can.
  • the end portion 22c of the sub waveguide a straight line while leaving the curved portion of the end portion 21c of the main waveguide 21.
  • the directional coupler has no symmetry and the higher-order mode removal rate from the main waveguide 21 is reduced, but the bending loss of the separated higher-order mode light can be reduced.
  • the end portion 22c may be extended on the extension line of the coupling portion 22b while the start portion 22a of the sub waveguide is bent as shown in FIG.
  • a portion close to the coupling portion 22b is bent to some extent away from the main waveguide 21, and a portion away from the main waveguide 21 to a certain extent is a straight line to the PD 24 (the extension of the coupling portion 22b). It is also possible to incline against).
  • the end portion of the sub-waveguide 22 is substantially the same until reaching the light absorption layer 23 or PD 24. It is preferable that the width is formed. As a result, the light absorption layer 23 or the PD 24 can be disposed at a desired position on the substrate, and higher-order mode light branched to the sub waveguide 22 can be prevented from leaking from the sub waveguide 22 into the substrate. As shown in FIG. 3, FIG. 7A, FIG. 7B, and FIG. 8, when the optical waveguide device has two or more sub-waveguides 22, at least one of the end portions of the sub-waveguides 22 has light at the end thereof.
  • An absorption layer 23 or a PD 24 can be provided. It is possible to arbitrarily design, for example, by providing the light absorption layer 23 at the end of the end portion of any sub-waveguide 22 and providing the PD 24 at the end of the end portion of another sub-waveguide 22.
  • FIG. 7A shows a sixth embodiment of the optical waveguide device.
  • the optical waveguide device according to the present embodiment there are two or more sub-waveguides 22 at different positions in the longitudinal direction of the main waveguide 21 in the front stage of the optical demultiplexer 14, and the width of each sub-waveguide 22 is the main The difference from the width of the waveguide 21 is within ⁇ 10%, which is substantially the same as the width of the main waveguide 21.
  • the distance between the sub waveguide 22 and the main waveguide 21 (interval w 0 in FIG. 1D) and the length of the portion where the sub waveguide 22 is placed in parallel with the main waveguide 21 (the length of the coupling portions 21b and 22b in FIG. 1C).
  • L 0 L 0
  • the removal rate of light (for example, primary mode light) to be separated into the sub-waveguide 22 can be increased.
  • FIG. 7B shows a seventh embodiment of the optical waveguide device.
  • two or more sub-waveguides 22 are provided at different positions in the longitudinal direction of the main waveguide 21 in the front stage of the optical demultiplexer 14, and the width of each sub-waveguide 22 is The difference from the width of the main waveguide 21 is within ⁇ 10%, which is substantially the same as the width of the main waveguide 21.
  • the distance between the sub-waveguide 22 and the main waveguide 21 or the length of the portion where the sub-waveguide 22 is placed in parallel with the main waveguide 21 is different, and each sub-waveguide 22 is in a portion along the main waveguide 21.
  • Mode splitters 20 and 200 having different wavelength characteristics are formed.
  • the wavelength band from which light (for example, primary mode light) to be separated into the sub-waveguide 22 is removed can be expanded.
  • the mode splitter 200 has a larger distance between the sub waveguide 22 and the main waveguide 21 than the mode splitter 20, but the present invention is not particularly limited to this.
  • two or more sub-waveguides 22 are provided at different positions in the longitudinal direction of the main waveguide 21 in the previous stage of the 1 ⁇ 2 (one input and two output) optical demultiplexer 14. It is a configuration. However, when the mode splitter 20 is provided before the 1 ⁇ N (1 input N output) optical demultiplexer (see FIG. 3, FIGS. 9A and 9B described later), and the optical demultiplexing of the Mach-Zehnder optical modulator 40 Similarly to other embodiments, such as when the mode splitter 20 is provided in front of the wave filter 42 (see FIG. 4), two or more sub-waveguides 22 can be provided at different positions in the longitudinal direction of the main waveguide 21.
  • the width of each sub-waveguide 22 is preferably within ⁇ 10% of the width of the main waveguide 21.
  • the removal rate of light for example, primary mode light
  • the wavelength band removed by the sub-waveguide 22 can be widened.
  • FIG. 8 shows an eighth embodiment of the optical waveguide device.
  • the optical waveguide device according to the present embodiment has the same configuration as that of the optical waveguide device 10 in FIG. 1A except that each optical waveguide 12 and 13 provided at the subsequent stage of the optical demultiplexer 14 also has a mode splitter 20.
  • the optical waveguides 11, 12, 13 at the front stage and the rear stage of the optical demultiplexer 14 constitute the main waveguide 21, and the mode splitter 20 is provided at each of the optical waveguides 11, 12, 13.
  • the mode splitter 20 according to each of the embodiments of the present invention is not limited to the case where the mode splitter 20 is provided in the preceding optical waveguide 11 of the optical demultiplexer 14 as shown in FIG.
  • each optical waveguide 12 in the subsequent stage of the optical demultiplexer 14 , 13 can also be provided. Further, the present invention is not limited to the case where it is provided in both the optical waveguides 12 and 13 in the subsequent stage of the optical demultiplexer 14, and can be provided in only one of the optical waveguides 12 and 13 in the subsequent stage of the optical demultiplexer 14.
  • FIG. 9A shows a ninth embodiment of the optical waveguide device.
  • the optical waveguide device according to the present embodiment has the same configuration as that of the optical waveguide device 10 of FIG. 1A except that it has a Y-type demultiplexer 15 as an optical demultiplexer.
  • the Y-type demultiplexer 15 can be used instead of the MMI-type demultiplexer 14.
  • a Y-type demultiplexer and multiplexer can be used as the optical demultiplexer 42 and optical multiplexer 46 of the Mach-Zehnder optical modulator 40 shown in FIG. 4 a Y-type demultiplexer and multiplexer can be used.
  • FIG. 9B shows a tenth embodiment of the optical waveguide device.
  • the optical waveguide device according to the present embodiment has the same configuration as that of the optical waveguide device 10 of FIG. 1A except that the optical demultiplexer includes a 1 ⁇ 3 (1 input 3 output) MMI type demultiplexer 16. .
  • the optical demultiplexer includes a 1 ⁇ 3 (1 input 3 output) MMI type demultiplexer 16.
  • a 1 ⁇ 3 MMI duplexer 16 is used instead of the 1 ⁇ 2 MMI duplexer 14. Can be used.
  • FIG. 9C shows an eleventh embodiment of the optical waveguide device.
  • the optical waveguide device according to the present embodiment has a 1 ⁇ N (1 input N output) MMI demultiplexer 17 (where N ⁇ 4) as an optical demultiplexer, except that the optical demultiplexer of FIG.
  • the configuration is the same as that of the optical waveguide element 10.
  • a 1 ⁇ N MMI duplexer 17 is used instead of the 1 ⁇ 2 MMI duplexer 14. Can be used.
  • the cladding region was formed of SiO 2 and the core region was formed of Si.
  • the thickness of the waveguide core region (see t 0 in FIG. 1D) was 220 nm, and the width of the waveguide core region (see w 1 and w 2 in FIG. 1D) was 500 nm. Clads were provided above and below the core to prevent light from touching the substrate and air, respectively.
  • the thickness of the clad (see t 1 and t 2 in FIG. 1D) was 2 ⁇ m above and below the core, respectively.
  • the clad was also formed on the side of the core and between the waveguides.
  • the electromagnetic field distribution in the fundamental mode and the primary mode when the above optical waveguide is arranged alone was analyzed by simulation.
  • the analysis results of the electromagnetic field distribution are shown in FIGS. 10A and 10B. It was found that the fundamental mode shown in FIG. 10A propagates in the center of the core, whereas the higher-order mode shown in FIG. 10B propagates outside the waveguide compared to the fundamental mode.
  • An MMI demultiplexer was used as the optical demultiplexer.
  • the width of the MMI duplexer (see WMMI in FIG. 1B) was 1.5 ⁇ m, and the length (see LMMI in FIG. 1B) was 1.7 to 1.9 ⁇ m.
  • one waveguide is coupled to the incident side of the MMI duplexer, and two waveguides are coupled to the exit side opposite to the incident side.
  • a waveguide on the front stage (incident side) of the optical demultiplexer was used as a main waveguide, and a sub-waveguide was placed in parallel with and spaced from the waveguide.
  • the waveguide width of the sub-waveguide was made the same as that of the main waveguide. If the interval between the main waveguide and the sub-waveguide (waveguide interval) is too close, the coupling of the fundamental mode from the main waveguide to the sub-waveguide becomes strong, and the loss of the fundamental mode light increases. Conversely, if the sub-waveguide is too far away from the main waveguide, the coupling of the primary mode from the main waveguide to the sub-waveguide becomes weak, and a very long sub-waveguide length is required.
  • the coupling coefficient was calculated from the result of mode analysis by the finite element method for the directional coupler in which the two optical waveguides are arranged, and the coupling length was calculated from the coupling coefficient.
  • the waveguide interval was set every 0.05 ⁇ m within the range of 0.15 to 0.85 ⁇ m. This setting was applied to all mode analyzes shown in FIGS.
  • FIG. 11 shows the result of determining the relationship between the coupling coefficient and the waveguide interval. As the waveguide spacing increases, the fundamental mode and primary mode coupling coefficients ⁇ both decrease, but the fundamental mode coupling coefficient ⁇ decreases more rapidly than the primary mode coupling coefficient ⁇ . It turns out that. Further, FIG.
  • the waveguide 12 shows the result of obtaining the relationship between the coupling length and the waveguide interval.
  • the coupling length of the fundamental mode is 504 ⁇ m, but the coupling length of the primary mode is 16 ⁇ m. Since the coupling efficiency and the coupling length of the fundamental mode and the primary mode are determined by the waveguide interval, the length of the portion where the sub waveguide is parallel along the main waveguide (sub waveguide length) is the coupling length of the primary mode. It was equal to. Assuming that the main waveguide and the sub-waveguide are symmetrical, the primary mode light can be transferred to the sub-waveguide 100% if the sub-waveguide length is equal to the coupling length of the primary mode.
  • the relationship between the intensity of the fundamental mode light and the sub waveguide length at a plurality of waveguide intervals was obtained.
  • the result is shown in FIG. In FIG. 13 and FIG. 14 described later, the numerical value displayed in the right frame indicates the waveguide interval ( ⁇ m). From this result, it was found that when the waveguide interval is 0.4 ⁇ m or less, the fundamental mode is strongly coupled to the sub-waveguide, resulting in a large waveguide loss.
  • the reason why the maximum power transfer efficiency is small when the sub-waveguide length is short is considered to be due to the influence of asymmetry at the start and end points of the sub-waveguide.
  • the coupling becomes small, and the transition to the sub-waveguide is not seen unless the sub-waveguide length is increased.
  • the waveguide interval is preferably larger than 0.4 ⁇ m. Therefore, in Example 1, the waveguide interval (see w 0 in FIG. 1D) was set to 0.5 ⁇ m (500 nm), and the sub-waveguide length was set to 16 ⁇ m. As a result, when the primary mode light was injected, the light remaining in the main waveguide with respect to the light transferred to the sub-waveguide was ⁇ 12.5 dB. Further, when the fundamental mode light was injected, the light transferred to the sub-waveguide with respect to the light remaining in the main waveguide was ⁇ 25 dB.
  • the directional coupler is used as the preceding mode splitter, the change in characteristics due to the wavelength change was verified. Further, the wavelength dependence of the power of the first-order mode light immediately before the optical demultiplexer was calculated by changing the incident wavelength under the above-mentioned conditions (waveguide interval 0.5 ⁇ m, sub-waveguide length 16 ⁇ m). The results (wavelengths 1.53 to 1.61 ⁇ m) are shown in FIG. On the long wavelength side, a reduction in the removal rate of the first-order mode light by the sub-waveguide is observed, but the first-order mode light is still removed up to ⁇ 18 dB or less, and 1 in the entire C-band and L-band.
  • a bent portion that is gently separated from the main waveguide is provided at the end of the sub-waveguide so that the primary mode light transferred to the sub-waveguide does not return to the main waveguide again. If the curvature radius of the bent portion is small, the first-order mode light leaks from the sub-waveguide and may recombine with the main waveguide via the cladding. Therefore, the radius of curvature of the bent portion is set to 100 ⁇ m so that leakage of the first mode light is reduced.
  • FIG. 17 shows the state of light propagation when primary mode light having 2% power is mixed with fundamental mode light.
  • A is a case where a mode splitter is not provided
  • b is a case where a mode splitter is provided.
  • the ratio of the power of the left arm to the right arm from the duplexer was -2.77 dB due to mixing of only 2% of the first-order mode light.
  • the power ratio between both arms was 0.42 dB, which was confirmed to be almost uniform.
  • the loss of light due to the addition of the sub-waveguide is 0.11 dB including the loss due to the removal of the primary mode light, and it was found that the loss is sufficiently low.
  • Example 2 Also in Example 2, the same optical waveguide structure as in Example 1 was adopted. Specifically, the cladding material is SiO 2 , the core material is Si, the core thickness is 220 nm, the core width (waveguide width) is 500 nm, and the cladding thickness is 2 ⁇ m above and below the core.
  • the cladding material is SiO 2
  • the core material is Si
  • the core thickness is 220 nm
  • the core width (waveguide width) is 500 nm
  • the cladding thickness is 2 ⁇ m above and below the core.
  • FIG. 18 shows how light propagates when primary mode light is injected into the mode splitter.
  • FIG. 18A shows a mode splitter having a structure in which the main waveguide (left side in the figure) is linear, the sub-waveguide (right side in the figure) is the end point side, and the sub-waveguide is gently separated from the main waveguide. Indicates.
  • FIG. 18B shows a mode splitter having a structure in which the main waveguide and the sub-waveguide are gently separated from each other at the end points.
  • FIG. 18C shows a mode splitter in which the main waveguide and the sub-waveguide have a structure that gently approaches the other side on each start side and a structure that gently leaves the other side on each end side. .
  • the first-order mode light is transferred to the sub-waveguide.
  • the first-order mode light remaining in the main waveguide is slightly recognized in FIG. In FIG. 18B, the primary mode light remaining in the main waveguide is very small, and in FIG. 18C, the primary mode light remaining in the main waveguide cannot be confirmed at all.
  • FIG. 19 shows the result of studying how the branching ratio changes with respect to the length of the straight portion along which the main waveguide and the sub waveguide are parallel to each other in the structure shown in FIG. .
  • the branching ratio here is a value obtained by decibel (dB) display of the ratio between the power of the primary mode light that shifts to the sub-waveguide and the power of the primary mode light that remains in the main waveguide.
  • FIG. 20 shows the results of examining the relationship between the optimized branching ratio and the radius of curvature of the curved portion for the three types of structures shown in FIGS. 18 (a), (b), and (c).
  • the curvature radius of the curved portion 3 to 4 types were selected from 20 ⁇ m, 40 ⁇ m, 60 ⁇ m, and 100 ⁇ m.
  • the results show that the branching ratio is improved by setting (b) as compared to (a) and further by setting (c).
  • the “optimized branching ratio” refers to the branching ratio when the length of the straight line portion is optimized for each structure. Therefore, the branching ratio shown in (c) of FIG. 20 is the same value as the “optimized branching ratio” shown in FIG.
  • the propagation state of the fundamental mode light in the mode splitter in FIG. 18C in which the length of the straight line portion is 2 ⁇ m and the curvature radius of the bent portion is 100 ⁇ m is shown. investigated. The result is shown in FIG. In this result, the fundamental mode light that shifts to the sub-waveguide is completely invisible, and all the fundamental mode light propagates through the main waveguide. Specifically, the branching ratio (loss) was ⁇ 30.5 dB, which was very low loss.
  • a waveguide and an optical demultiplexer were configured with SiO 2 as the cladding region and Si as the core region.
  • the core thickness was 220 nm, and the core width (waveguide width) was 500 nm. Clads were provided above and below the core to prevent light from touching the substrate and air, respectively. The thickness of the clad was 2 ⁇ m above and below the core. The clad was also formed on the side of the core and between the waveguides.
  • An MMI type demultiplexer was used as the optical demultiplexer.
  • the duplexer width W MMI was 1.5 ⁇ m, and the length L MMI was 1.8 ⁇ m.
  • the interval between the parallel waveguides was set to 0.3 ⁇ m.
  • a waveguide on the front stage (incident side) of the optical demultiplexer was used as a main waveguide, and a sub-waveguide was placed in parallel with the waveguide (see FIG. 1A).
  • the waveguide width of the sub-waveguide is set to the same width as that of the main waveguide. Based on the examination of Examples 1 and 2, the distance between the sub waveguide and the main waveguide was set to 0.5 ⁇ m (500 nm).
  • the approach and separation are gentle.
  • the higher-order mode coupling is performed in the approaching portion and the distant portion, although it is weak. Therefore, it is not appropriate to make the approach and separation between the main waveguide and the sub-waveguide too smooth. Therefore, based on the examination of Example 2, as shown in FIG. 18C and FIG. 21, the radius of curvature of the approaching portion and the separating portion is set to 100 ⁇ m in each of the main waveguide and the sub-waveguide, The length was 2 ⁇ m. As a result, the higher-order mode can be efficiently transferred from the main waveguide to the sub-waveguide, and the fundamental mode can be almost eliminated.
  • a waveguide and an optical demultiplexer were configured with SiO 2 as the cladding region and Si as the core region.
  • the core thickness was 220 nm, and the core width (waveguide width) was 600 nm. Clads were provided above and below the core to prevent light from touching the substrate and air, respectively.
  • the thickness of the clad was 2 ⁇ m above and below the core.
  • the clad was also formed on the side of the core and between the waveguides.
  • An MMI type demultiplexer was used as the optical demultiplexer.
  • the width W MMI of the MMI type duplexer was 1.7 ⁇ m, and the length L MMI was 2.4 ⁇ m.
  • the interval between the parallel waveguides was set to 0.3 ⁇ m.
  • a waveguide on the front stage (incident side) of the optical demultiplexer was used as a main waveguide, and a sub-waveguide was placed in parallel with the waveguide (see FIG. 1A).
  • the optimum waveguide interval was examined even with a waveguide width of 600 nm.
  • the interval between the sub-waveguide and the main waveguide was set to 0.5 ⁇ m (500 nm). Further, as shown in FIG. 18C and FIG.
  • the optimum length of the straight portion is obtained by simulation. It was determined to be 9 ⁇ m.
  • the higher-order mode can be efficiently transferred from the main waveguide to the sub-waveguide, and the transition from the fundamental mode to the sub-waveguide can be almost eliminated.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Nonlinear Science (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Electromagnetism (AREA)
  • Optical Integrated Circuits (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

La présente invention concerne un élément à guides d'ondes optiques qui comprend : un filtre de dérivation optique divisant une seule lumière d'entrée en une pluralité de lumières de sortie ; un guide d'ondes principal réalisant le guidage d'ondes de la lumière d'entrée et de la lumière de sortie, et permettant le guidage d'ondes pour au moins deux types de mode de propagation qui ont un ordre de propagation différent ; ainsi qu'au minimum un séparateur de mode possédant une section de couplage située parallèlement au guide d'ondes principal à une distance prédéfinie dudit guide d'ondes principal afin de concevoir un coupleur directif, et comportant un guide d'ondes auxiliaire qui, parmi les deux types de mode de propagation ou plus, peut séparer au moins un type de mode de propagation du guide d'ondes principal. Le rapport d'indice de réfraction (ncore/nclad) entre le cœur et la gaine constituant le guide d'ondes principal et le guide d'ondes auxiliaire est de 101 à 250 %.
PCT/JP2013/071845 2012-08-22 2013-08-13 Élément à guides d'ondes optiques WO2014030576A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2012-183305 2012-08-22
JP2012183305A JP5702757B2 (ja) 2012-08-22 2012-08-22 光導波路素子

Publications (1)

Publication Number Publication Date
WO2014030576A1 true WO2014030576A1 (fr) 2014-02-27

Family

ID=50149885

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2013/071845 WO2014030576A1 (fr) 2012-08-22 2013-08-13 Élément à guides d'ondes optiques

Country Status (2)

Country Link
JP (1) JP5702757B2 (fr)
WO (1) WO2014030576A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9705630B2 (en) 2014-09-29 2017-07-11 The Royal Institution For The Advancement Of Learning/Mcgill University Optical interconnection methods and systems exploiting mode multiplexing

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP5747004B2 (ja) * 2012-08-22 2015-07-08 株式会社フジクラ 光導波路素子
JP5702756B2 (ja) * 2012-08-22 2015-04-15 株式会社フジクラ 光導波路素子
WO2016052344A1 (fr) * 2014-09-30 2016-04-07 株式会社フジクラ Élément de guide d'ondes optique de type substrat
JP6356254B2 (ja) * 2014-09-30 2018-07-11 株式会社フジクラ 基板型光導波路素子及び基板型光導波路素子の製造方法
JP6681456B1 (ja) * 2018-11-26 2020-04-15 沖電気工業株式会社 偏波分離素子
JP2023040871A (ja) 2021-09-10 2023-03-23 富士通オプティカルコンポーネンツ株式会社 光導波路素子および光集積回路

Citations (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04213407A (ja) * 1990-12-10 1992-08-04 Nippon Telegr & Teleph Corp <Ntt> 分岐合波光導波回路
JPH05164926A (ja) * 1991-12-16 1993-06-29 Sumitomo Electric Ind Ltd 光分岐結合器
JPH095549A (ja) * 1995-06-19 1997-01-10 Sumitomo Electric Ind Ltd 光回路及びその作製方法
JP2002014242A (ja) * 2000-06-28 2002-01-18 Oki Electric Ind Co Ltd 光導波路装置
JP2002286952A (ja) * 2001-01-18 2002-10-03 Furukawa Electric Co Ltd:The 導波路型光カプラおよび該導波路型光カプラを用いた光合分波器
JP2002539464A (ja) * 1997-11-29 2002-11-19 ブックハム テクノロジー ピーエルシー 迷光を吸収するための方法および光集積回路
JP2005181748A (ja) * 2003-12-19 2005-07-07 Fdk Corp Ｙ分岐光導波路デバイス
JP2006505812A (ja) * 2002-11-04 2006-02-16 ティーム、フォトニクス 光集積回路内における２対ｎ構成の光分波器
JP2006091785A (ja) * 2004-09-27 2006-04-06 Matsushita Electric Works Ltd 光導波路板
WO2006090863A1 (fr) * 2005-02-22 2006-08-31 Ngk Insulators, Ltd. Modulateur optique
JP2006235380A (ja) * 2005-02-25 2006-09-07 Nippon Telegr & Teleph Corp <Ntt> モードスプリッタおよび光回路
JP2007127748A (ja) * 2005-11-02 2007-05-24 Alps Electric Co Ltd 光導波路を有する光学部品
JP2008089875A (ja) * 2006-09-29 2008-04-17 Sumitomo Osaka Cement Co Ltd 光導波路素子
WO2010113921A1 (fr) * 2009-03-31 2010-10-07 住友大阪セメント株式会社 Modulateur optique
JP2010266628A (ja) * 2009-05-14 2010-11-25 Sumitomo Osaka Cement Co Ltd 光制御素子
JP2010281899A (ja) * 2009-06-02 2010-12-16 Mitsubishi Electric Corp 光フィルタ
JP2011158730A (ja) * 2010-02-01 2011-08-18 Nippon Telegr & Teleph Corp <Ntt> 温度無依存光回路
JP2011257634A (ja) * 2010-06-10 2011-12-22 Fujitsu Optical Components Ltd 光導波路、光変調器、および、光カプラ
JP2012027199A (ja) * 2010-07-22 2012-02-09 Fujitsu Ltd 光半導体装置及びその駆動方法
WO2012043694A1 (fr) * 2010-09-30 2012-04-05 住友大阪セメント株式会社 Elément de guide d'ondes optiques
WO2012056507A1 (fr) * 2010-10-25 2012-05-03 住友大阪セメント株式会社 Élément de commande de lumière
JP2012154980A (ja) * 2011-01-24 2012-08-16 Fujitsu Ltd リブ型光導波路デバイス及びその製造方法

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH11248949A (ja) * 1998-02-27 1999-09-17 Hitachi Cable Ltd 光波長合分波器
JP5715072B2 (ja) * 2012-01-24 2015-05-07 日本電信電話株式会社 高次モード平面光波回路
JP5747004B2 (ja) * 2012-08-22 2015-07-08 株式会社フジクラ 光導波路素子
JP5702756B2 (ja) * 2012-08-22 2015-04-15 株式会社フジクラ 光導波路素子

Patent Citations (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04213407A (ja) * 1990-12-10 1992-08-04 Nippon Telegr & Teleph Corp <Ntt> 分岐合波光導波回路
JPH05164926A (ja) * 1991-12-16 1993-06-29 Sumitomo Electric Ind Ltd 光分岐結合器
JPH095549A (ja) * 1995-06-19 1997-01-10 Sumitomo Electric Ind Ltd 光回路及びその作製方法
JP2002539464A (ja) * 1997-11-29 2002-11-19 ブックハム テクノロジー ピーエルシー 迷光を吸収するための方法および光集積回路
JP2002014242A (ja) * 2000-06-28 2002-01-18 Oki Electric Ind Co Ltd 光導波路装置
JP2002286952A (ja) * 2001-01-18 2002-10-03 Furukawa Electric Co Ltd:The 導波路型光カプラおよび該導波路型光カプラを用いた光合分波器
JP2006505812A (ja) * 2002-11-04 2006-02-16 ティーム、フォトニクス 光集積回路内における２対ｎ構成の光分波器
JP2005181748A (ja) * 2003-12-19 2005-07-07 Fdk Corp Ｙ分岐光導波路デバイス
JP2006091785A (ja) * 2004-09-27 2006-04-06 Matsushita Electric Works Ltd 光導波路板
WO2006090863A1 (fr) * 2005-02-22 2006-08-31 Ngk Insulators, Ltd. Modulateur optique
JP2006235380A (ja) * 2005-02-25 2006-09-07 Nippon Telegr & Teleph Corp <Ntt> モードスプリッタおよび光回路
JP2007127748A (ja) * 2005-11-02 2007-05-24 Alps Electric Co Ltd 光導波路を有する光学部品
JP2008089875A (ja) * 2006-09-29 2008-04-17 Sumitomo Osaka Cement Co Ltd 光導波路素子
WO2010113921A1 (fr) * 2009-03-31 2010-10-07 住友大阪セメント株式会社 Modulateur optique
JP2010266628A (ja) * 2009-05-14 2010-11-25 Sumitomo Osaka Cement Co Ltd 光制御素子
JP2010281899A (ja) * 2009-06-02 2010-12-16 Mitsubishi Electric Corp 光フィルタ
JP2011158730A (ja) * 2010-02-01 2011-08-18 Nippon Telegr & Teleph Corp <Ntt> 温度無依存光回路
JP2011257634A (ja) * 2010-06-10 2011-12-22 Fujitsu Optical Components Ltd 光導波路、光変調器、および、光カプラ
JP2012027199A (ja) * 2010-07-22 2012-02-09 Fujitsu Ltd 光半導体装置及びその駆動方法
WO2012043694A1 (fr) * 2010-09-30 2012-04-05 住友大阪セメント株式会社 Elément de guide d'ondes optiques
WO2012056507A1 (fr) * 2010-10-25 2012-05-03 住友大阪セメント株式会社 Élément de commande de lumière
JP2012154980A (ja) * 2011-01-24 2012-08-16 Fujitsu Ltd リブ型光導波路デバイス及びその製造方法

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9705630B2 (en) 2014-09-29 2017-07-11 The Royal Institution For The Advancement Of Learning/Mcgill University Optical interconnection methods and systems exploiting mode multiplexing

Also Published As

Publication number Publication date
JP5702757B2 (ja) 2015-04-15
JP2014041253A (ja) 2014-03-06

Similar Documents

Publication Publication Date Title
JP5747004B2 (ja) 光導波路素子
JP5702756B2 (ja) 光導波路素子
JP6365855B2 (ja) 一連のベンドを備える導波路型偏光子のための装置および方法
WO2014030576A1 (fr) Élément à guides d&#39;ondes optiques
EP3317704B1 (fr) Polariseur sur puce intégré
JP6011719B2 (ja) 偏波分離器、及び光デバイス
US10838146B2 (en) Single mode waveguide with an adiabatic bend
US8078021B2 (en) Waveguide connecting structure
JP2017504830A (ja) 導波路偏光スプリッタ兼偏光回転子
JP2007072433A (ja) 光集積素子及び光制御素子
CN111796360B (zh) 弯曲波导构造
Tee et al. Numerical investigation on cascaded 1× 3 photonic crystal power splitter based on asymmetric and symmetric 1× 2 photonic crystal splitters designed with flexible structural defects
WO2019171649A1 (fr) Dispositif photonique de conversion de modes optiques de faisceaux optiques
CN113777708A (zh) 模变换器
US9557485B2 (en) System and method for manipulating polarizations of optical signal
EP3203282B1 (fr) Guide d&#39;ondes optique du type à nervure et multiplexeur/démultiplexeur optique l&#39;utilisant
Zamhari et al. Large cross-section rib silicon-on-insulator (SOI) S-bend waveguide
JP6397862B2 (ja) 光導波路素子
US11662522B2 (en) Optical waveguide device operated as mode converter
WO2006073194A1 (fr) Guide d&#39;ondes optiques, dispositif optique et dispositif de communication optique
JP6991259B2 (ja) 光導波路素子
Molina-Fernandez et al. New concepts in silicon component design using subwavelength structures
Shrestha et al. Silicon nitride waveguide router enabling directional power transmission
Teng Design and characterization of optical fiber-to-chip edge couplers and on-chip mode division multiplexing devices
Zamhari et al. Optik-International Journal for Light and Electron Optics

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 13830970

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 13830970

Country of ref document: EP

Kind code of ref document: A1