CN105759348A - Silica-based double-section type groove waveguide polarization rotator and polarization rotation method - Google Patents

Abstract

The present invention proposes a silicon-based two-stage slot waveguide polarization rotator and polarization rotation method, including a slot waveguide and first to fourth strip waveguides with the same size; the first and second strip waveguides form a first In the polarization rotation area, the third and fourth strip waveguides form a second polarization rotation area as a group, and the first and second polarization rotation areas are connected in sequence; two waveguides forming a group are placed on both sides of the slot waveguide, and The first and third strip waveguides are located on the same side of the slot waveguide, and the second and fourth strip waveguides are located on the other side of the slot waveguide; the top surfaces of the first and fourth strip waveguides are flush with the top surface of the slot waveguide; 2. The bottom surface of the third strip waveguide is flush with the bottom surface of the slot waveguide. For an input optical signal containing any polarization state, after passing through the first and second polarization rotation regions of the device, another polarization state optical signal orthogonal to it can be output at the output end, thereby realizing the function of polarization rotation.

Description

A silicon-based two-stage slot waveguide polarization rotator and polarization rotation method

technical field

The invention relates to the technical field of integrated optics, in particular to a silicon-based double-section slot waveguide polarization rotator and a polarization rotation method.

Background technique

Photonic integrated circuit technology has developed rapidly in recent years, especially based on the silicon-on-insulator (SOI) material platform, which has received great attention in the construction of on-chip ultra-compact, high-performance, low-power, and low-cost optical integrated devices and systems. received extensive attention from researchers. However, the inherent high refractive index difference of SOI materials will inevitably bring obvious structural birefringence effects to the design of devices and systems, resulting in strong polarization dependence, which will greatly limit the application of photonic integrated circuits in on-chip optical communication. Large-scale commercial application. To this end, an on-chip polarization diversity scheme is proposed to achieve polarization transparent transmission, and polarization beam splitters and rotators are essential components. For polarization rotators, researchers have proposed many device solutions, including asymmetric directional couplers, asymmetric inclined waveguides, sub-wavelength slits, photonic crystal structures, and electro-optical/magneto-optical materials, etc., to change the structure or The vertical symmetry of the material realizes the function of polarization state rotation. At this stage, there are still some problems in the polarization rotator, especially the large size, low polarization rotation efficiency and high requirements on the process. Therefore, it is necessary to find new methods to effectively improve the overall performance of the device. In order to achieve high-density polarization independent on-chip transmission and high-speed polarization multiplexing transmission to lay the foundation.

Recently, a novel waveguide structure—slot waveguide was proposed. Based on its special structure, it can obtain significant field enhancement effect and local field distribution characteristics. Today, such waveguides have been used in a variety of active and passive devices, including: organic hybrid optical modulators, directional couplers, microring resonators, multimode interference couplers, beam splitters, and sensors. In these devices, the field enhancement effect mode of the slot waveguide is mainly used to effectively improve the sensitivity, coupling efficiency, and working bandwidth of the device. Considering that the slot waveguide is also a polarization-sensitive structure, its polarization dependence is even stronger than that of ordinary silicon-based nanowires. Therefore, when using slot waveguides to construct on-chip photonic integrated circuits, polarization management is a key issue that needs to be solved urgently. In practical applications In , we need to convert the other polarization mode of the slot waveguide into a mode with field enhancement effect, so that its advantages in functional devices are more obvious. Accordingly, for the slot waveguide, it is very important to design a polarization rotator with small size, large working bandwidth, high polarization rotation efficiency and low insertion loss.

Contents of the invention

Purpose of the invention: In order to solve the above technical problems, provide a polarization rotator with small size, large working bandwidth, high polarization rotation efficiency and low insertion loss. This invention proposes a silicon-based double-stage slot waveguide polarization rotator and method.

Technical scheme: in order to realize above-mentioned technical effect, the technical scheme that the present invention proposes is:

A silicon-based double-section slot waveguide polarization rotator, which includes a slot waveguide and a first strip waveguide 4, a second strip waveguide 5, a third strip waveguide 6, and a fourth strip waveguide 7 of the same size; The elongation direction of the slot waveguide is divided into an input slot waveguide 1, a transmission slot waveguide 2 and an output slot waveguide 3; the transmission slot waveguide 2 is equally divided into two sections along the length direction: the first transmission section and the second transmission section, wherein, the first transmission section and the second transmission section A first strip waveguide 4 and a second strip waveguide 5 opposite to each other are respectively arranged on both sides of a transmission section, the top surface of the first strip waveguide 4 is flush with the top surface of the transmission groove waveguide 2, and the second strip waveguide 5 The bottom surface of the second transmission section is flush with the bottom surface of the transmission slot waveguide 2; the third strip waveguide 6 and the fourth strip waveguide 7 opposite to each other are respectively arranged on both sides of the second transmission section, and the bottom surface of the third strip waveguide 6 is in line with the transmission slot waveguide 2 are flush with the bottom surface, and the top surface of the fourth strip waveguide 7 is flush with the top surface of the transmission slot waveguide 2; the first strip waveguide 4 and the third strip waveguide 6 are located on the same side of the transmission slot waveguide 2, and the second strip waveguide The strip waveguide 5 and the fourth strip waveguide 7 are located on the other side of the transmission slot waveguide 2 .

Further, the groove waveguide is composed of two parallel silicon-based nanowires, and a microgroove is formed between the two silicon-based nanowires.

Further, the width of the silicon-based nanowires is 200nm, the width of the microgrooves between two silicon-based nanowires is 100nm-120nm, and the lengths of the first to fourth strip waveguides are 3.0μm-3.6μm.

Further, a substrate 8 and a cladding 9 are also included, and the slot waveguide and the first to fourth strip waveguides are all arranged on the substrate 8 and wrapped between the substrate 8 and the cladding 9 .

The present invention also proposes a polarization rotation method, the method comprising steps:

(a) construct any silicon-based double-section slot waveguide polarization rotator as claimed in claims 1 to 4; the first transmission section of the transmission slot waveguide 2, the first strip waveguide 4 and the second strip waveguide 5 Constitute the first polarization rotation region; the second transmission section of the transmission slot waveguide 2, the third strip waveguide 6 and the fourth strip waveguide 7 constitute the second polarization rotation region;

(b) The transverse magnetic mode/transverse electric mode optical signal is input from the input groove waveguide 1, and passes through the first polarization rotation area and the second polarization rotation area in sequence; wherein, the first polarization rotation area changes the direction of the optical axis of the input optical signal along the Clock rotation angle Form the first polarization rotation signal; the second polarization rotation zone rotates the first polarization rotation signal counterclockwise The direction of the optical axis is rotated counterclockwise relative to the initial input optical signal The second polarization rotation signal of the output slot waveguide 3 is output from the output slot waveguide 3; if the signal input from the input slot waveguide 1 is a transverse magnetic mode optical signal, the signal output from the output slot waveguide 3 is a transverse electric mode optical signal; The signal input by the waveguide 1 is a transverse electric mode optical signal, and the signal output by the output slot waveguide 3 is a transverse magnetic mode optical signal.

Further, the

Beneficial effect:

1. Low insertion loss and high polarization rotation efficiency. The present invention adds two strip waveguides on both sides of the slot waveguide in an up-and-down manner, and introduces two sections of cascaded waveguide structures in the longitudinal direction (the positions of the two waveguides in the second section are exactly the same as those in the first section) on the contrary). Due to the small size of the added strip waveguide, it is only used to change the direction of the optical axis of the mode field, and the length of the waveguide is short (only 3.0 μm to 3.6 μm for a single section), so that the insertion loss of the device is low. In addition, through the optimized design of the double-segment structure, the input polarization state can be rotated by 90° at the output end, which has the advantage of high polarization rotation efficiency.

2. Small size and short polarization rotation region length. As mentioned above, the length of the polarization rotation region of the entire device is only 6.0 μm to 7.2 μm, which is conducive to the realization of compact design and on-chip dense integration of the device.

3. Device manufacturing is relatively easy. The feature size (minimum size) of the device of the present invention is 100nm, that is, the width of the microgroove in the middle of the groove waveguide, which is fully compatible with the size permit of the current CMOS process line, and the device can be manufactured relatively easily and efficiently with the help of a mature CMOS process line.

Description of drawings

Fig. 1 is the structural representation of the embodiment of the present invention;

2 is a cross-sectional view of a slot waveguide structure in an embodiment;

3 is a cross-sectional view of the structure of the first polarization rotation region in the embodiment;

Fig. 4 is the cross-sectional view of the structure of the second polarization rotation region in the embodiment;

Fig. 5 is a change diagram of the polarization state optical axis direction after passing through the first polarization rotation region in the embodiment;

Fig. 6 is a change diagram of the polarization state optical axis direction after passing through the second polarization rotation region in the embodiment;

Fig. 7 is a graph showing the relationship between the polarization rotation efficiency and insertion loss of the device in the embodiment and the working wavelength.

In the figure: 1. input slot waveguide, 2. transmission slot waveguide, 3. output slot waveguide, 4. first strip waveguide, 5. second strip waveguide, 6. third strip waveguide, 7. fourth strip waveguide Shaped waveguide, 8, substrate, 9, cladding.

detailed description

The present invention will be further explained below in conjunction with the accompanying drawings.

Figures 1 to 4 are structural diagrams of a silicon-based two-stage slot waveguide polarization rotator according to an embodiment, which includes a slot waveguide composed of two silicon-based nanowires and a first strip waveguide 4 of the same size. , the second strip waveguide 5, the third strip waveguide 6, and the fourth strip waveguide 7; the slot waveguide is divided into an input slot waveguide 1, a transmission slot waveguide 2 and an output slot waveguide 3 along the length direction; the transmission slot waveguide 2 divided into two sections along the length direction: the first transmission section and the second transmission section, wherein the first transmission section is respectively provided with a first strip waveguide 4 and a second strip waveguide 5 opposite to each other, and the first The top surface of the strip waveguide 4 is flush with the top surface of the transmission slot waveguide 2, and the bottom surface of the second strip waveguide 5 is flush with the bottom surface of the transmission slot waveguide 2; the two sides of the second transmission section are respectively provided with third strips opposite to each other. waveguide 6 and the fourth strip waveguide 7, the bottom surface of the third strip waveguide 6 is flush with the bottom surface of the transmission slot waveguide 2, and the top surface of the fourth strip waveguide 7 is flush with the top surface of the transmission slot waveguide 2; The strip waveguide 4 and the third strip waveguide 6 are located on the same side of the transmission slot waveguide 2 , and the second strip waveguide 5 and the fourth strip waveguide 7 are located on the other side of the transmission slot waveguide 2 .

In the above structure, the first transmission section of the transmission slot waveguide 2, the first strip waveguide 4 and the second strip waveguide 5 constitute the first polarization rotation region; the second transmission section of the transmission slot waveguide 2, the third strip waveguide 6 and the fourth strip waveguide 7 constitute the second polarization rotation region. The width of the silicon-based nanowires is 200nm, the width of the microgrooves between two silicon-based nanowires is 100nm-120nm, and the lengths of the first to fourth strip waveguides are 3.0μm-3.6μm.

The transverse magnetic mode optical signal input from the input slot waveguide 1, after passing through the first polarization rotation region and the second polarization rotation region, outputs the transverse electric mode optical signal at the output end of the output slot waveguide 3; based on the centrosymmetry of the overall structure of the device The characteristic is that the transverse electric mode optical signal input from the input slot waveguide 1 can output the transverse magnetic mode optical signal at the output end of the output slot waveguide 3 after passing through the first and second polarization rotation regions.

Specifically, the transmission characteristics of the optical signal in the silicon-based two-stage slot waveguide polarization rotator with the above structure are as follows: The incident optical signal containing the transverse magnetic mode (TM) enters from the input slot waveguide 1, and then enters the first polarization rotation region of the transmission slot waveguide 2, due to being subjected to the first polarization rotation region in the rotation region, the first strip waveguide 4 and the second strip waveguide 5 Due to the common influence of the input TM mode optical signal, the direction of the polarization axis of the optical signal changes, and after passing through the first polarization rotation region, the direction of the corresponding polarization axis changes by 45°. Next, the optical signal enters the second polarization rotation region, where the additional strip waveguides are located just opposite to those in the first polarization rotation region, that is, the third strip waveguide 6 and the fourth strip waveguide 7, due to the structure Due to the influence of vertical and horizontal asymmetry, the mode of the optical signal will be further rotated and output from the output slot waveguide 3 . Therefore, a polarization rotation angle of 90° can be obtained at the output end, corresponding to the output optical signal of the transverse electric mode (TE), thereby realizing the function of polarization rotation. The structure of this rotator is simple, and its principle can be analyzed by simply changing the direction of the polarization axis, as shown in Figures 5 and 6, where the direction of the mode axis of the first/second polarization rotation zone is different from the horizontal/vertical direction The included angle is (By optimizing the size of the strip waveguide on both sides of the groove waveguide, the direction of the optical axis of the polarization rotation zone mode can be changed to achieve the required angle value where the model is computed using a numerical model solver). After the input TM mode optical signal passes through the first polarization rotation region, the polarization angle rotates clockwise Then after passing through the second rotation zone, due to the change of the optical axis direction of the eigenmode (reverse rotation ), causing the polarization angle to rotate counterclockwise A net rotation relative to the initial TM To achieve a 90° polarization state rotation, that is but This is also the goal of optimizing the dimensions of the two-shaped waveguide in the polarization rotation region (so that the angle between the optical axis of the eigenmode in the polarization rotation region and the horizontal or vertical direction is 22.5°). Compared with the traditional single-segment polarization rotator, the present invention introduces a double-segment polarization coupling region structure, which can theoretically output an optical signal mode containing any polarization rotation angle (between 0° and 90°) at the output end, which can be used For designing compact on-chip optical waveplates. Considering the actual situation, for the slot waveguide, in this embodiment, we only output the TE mode optical signal, which corresponds to realizing a polarization rotation angle of 90°. In addition, the device has a small insertion loss and a high polarization rotation efficiency, which can be Polarization control for on-chip compact slot waveguide devices.

Figure 2 is a cross-sectional view of the slot waveguide in this embodiment. Two silicon-based nanowires (about 200 nm in width) forming the slot waveguide are separated by a microgroove in the middle, and the width of the microgroove is 100 nm to 120 nm. Boundary value relationship, the mode field will have a significant enhancement effect in the microgroove, corresponding to the field enhancement mode of the groove waveguide, that is, the output mode of the polarization rotator designed in the present invention. Fig. 3 is a cross-sectional view of the waveguide in the first polarization rotation region. The first and second strip waveguides are respectively located on both sides of the two silicon-based nanowires forming the slot waveguide, arranged one above the other. The symmetry of the original structure can be broken by using two waveguides on the basis of the slot waveguide. By further optimizing the size of the strip waveguide, the polarization mode corresponding to the required optical axis angle can be obtained at the output end. Figure 4 is a cross-sectional view of the waveguide in the second polarization rotation region. Its structure is similar to that of the first polarization rotation region. The only difference is that the arrangement of the strip waveguides on both sides is upside down, so as to change the light of its eigenmode. axis direction (as shown in Figures 5 and 6), and then change the polarization state optical axis direction of the transmitted optical signal.

FIG. 7 shows the relationship between the polarization rotation efficiency, insertion loss and working wavelength of the silicon-based double-stage slot waveguide polarization rotator in this embodiment. It can be seen from the figure that the device has a large working bandwidth. When the working wavelength is between 1.45 μm and 1.64 μm, the polarization rotation efficiency is always greater than 90%, especially at 1.55 μm, the polarization rotation efficiency is even higher than 97.5%. . At the same time, the insertion loss is less than 0.4dB in the calculated wavelength range, showing better spectral characteristics. Since the silicon-based double-segment slot waveguide polarization rotator has a centrosymmetric structure, the input TE mode optical signal can also output the TM mode optical signal at the output end after passing through the first and second polarization rotation regions. In addition, by adding an active control structure in the first or second polarization rotation region, the polarization rotation angle can be properly adjusted, and then an optical modulator or optical switch based on the polarization state can be obtained at the output end. Finally, the dual-stage slot waveguide polarization rotator solution provided by the present invention can also be used to design polarization rotators for other types of waveguide structures (such as silicon-based nanowires, hybrid plasmonic waveguides, photonic crystal waveguides, etc.).

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (6)

1. a silica-based two section type groove waveguides polarization rotator, it is characterised in that include groove waveguides and equivalently-sized first to fourth slab waveguide (4,5,6,7)；Described groove waveguides is divided into input slot waveguide (1), transmission slot waveguide (2) and output magazine waveguide (3) along its length；Transmission slot waveguide (2) is divided into the two sections: first span line and the second span line along its length, wherein, first span line is respectively provided on two sides with relative the first slab waveguide (4) in position and the second slab waveguide (5), the end face of the first slab waveguide (4) and transmission slot waveguide (2) end face flush, the bottom surface of the second slab waveguide (5) and transmission slot waveguide (2) bottom surface flush；Second span line is respectively provided on two sides with relative Article 3 shape waveguide (6) in position and Article 4 shape waveguide (7), the bottom surface of Article 3 shape waveguide (6) and transmission slot waveguide (2) bottom surface flush, the end face of Article 4 shape waveguide (7) and transmission slot waveguide (2) end face flush；First slab waveguide (4) and Article 3 shape waveguide (6) are positioned at the same side of transmission slot waveguide (2), the second slab waveguide (5) and Article 4 shape waveguide (7) and are positioned at the opposite side of transmission slot waveguide (2).

2. the silica-based two section type groove waveguides polarization rotator of one according to claim 1, it is characterised in that described groove waveguides is made up of two parallel silica-based nanowires, forms microflute between two silica-based nanowires.

3. the silica-based two section type groove waveguides polarization rotator of one according to claim 2, it is characterized in that, the width of described silica-based nanowire is 200nm, width of mini longitudinal channels between two silica-based nanowires is 100nm～120nm, first to fourth slab waveguide (4,5,6,7) length is 3.0 μm～3.6 μm.

4. the silica-based two section type groove waveguides polarization rotator of one according to claim 1, it is characterized in that, also include substrate (8) and covering (9), described groove waveguides and first to fourth slab waveguide (4,5,6,7) it is arranged at substrate (8) above and to be wrapped between substrate (8) and covering (9).

5. a polarization spinning solution, it is characterised in that include step:

A () builds the silica-based two section type groove waveguides polarization rotator of any one as described in Claims 1-4；First span line of transmission slot waveguide (2), the first slab waveguide (4) and the second slab waveguide (5) constitute the first polarization Rotary District；Second span line of transmission slot waveguide (2), Article 3 shape waveguide (6) and Article 4 shape waveguide (7) constitute the second polarization Rotary District；

B TM mode/transverse electric mode optical signal is inputted by () from input slot waveguide (1), sequentially pass through the first polarization Rotary District and the second polarization Rotary District；Wherein, the first polarization Rotary District is by the optical axis direction dextrorotation gyration of input optical signalFormed and polarize rotating signal for the first time；Second polarization Rotary District is by first time polarization rotating signal rotated counterclockwise by angleForm optical axis direction and have rotated angle counterclockwise relative to the optical signal of initial inputSecond time polarization rotating signal and from output magazine waveguide (3) export；If the signal inputted from input slot waveguide (1) is TM mode optical signal, then the signal that output magazine waveguide (3) exports is transverse electric mode optical signal；If the signal inputted from input slot waveguide (1) is transverse electric mode optical signal, then the signal that output magazine waveguide (3) exports is TM mode optical signal.

6. a kind of polarization spinning solution according to claim 5, it is characterised in that described in