JP3933062B2 - Wavelength division duplexer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a demultiplexer for low-density wavelength division multiplexing optical transmission (CWDM), and more particularly to a wavelength division demultiplexer using a diffraction grating.
[0002]
[Prior art]
With the development of the information society in recent years, large-capacity communication has progressed, the transmission medium has also shifted from electrical signals to optical signals, and communication systems using optical wavelength multiplexing technology have begun to be used. In particular, in the trunk line system, a terabit-class high-speed network is being put into practical use by high-density wavelength division multiplexing (DWDM). This communication system uses a temperature-controlled wavelength tunable laser as a light source, and transmits several tens of wavelength-multiplexed lights in one cable by an optical multiplexer for bundling a plurality of wavelengths. At the destination of transmission, the multiplexed light is passed through an optical demultiplexer and separated into the original one-wave light, and then a signal is obtained by photoelectric conversion. However, in order to reduce the oscillation wavelength shift due to the temperature of the laser, precise temperature control is required, resulting in an expensive system.
[0003]
On the other hand, low-density wavelength division multiplexing (CWDM, Coarse Wave Division Multiplexing), which has a lower wavelength multiplexing density, is being studied downstream of trunk systems such as access systems and LAN systems. This system uses an optical device corresponding to a wavelength shift due to a temperature variation of a light source as a constituent element, does not require temperature adjustment for stabilization, and can construct a network at a low cost. In low-density wavelength division multiplexing optical communication, generally, the wavelength interval is required to be about 20 nm, and the wavelength shift width of the light source is required to be about 5 nm, and the duplexer needs to cope with this wavelength shift. Furthermore, since it is used downstream rather than the trunk line system, it is necessary to cope with an MM (multi-mode) optical fiber in addition to the mainstream SM (single mode) optical fiber. Therefore, a duplexer such as an AWG (Arrayed Waveguide Grating) using a phase difference mainly used in the DWDM system cannot be used.
[0004]
A method using a filter has been proposed as a duplexer corresponding to low-density multiplexed optical communication, but an expensive multilayer filter of the same number as the number of wavelengths or one less than the number of wavelengths is required, There is a problem that both the mounting cost and the manufacturing cost become expensive.
[0005]
On the other hand, a duplexer using a diffraction grating can demultiplex several wavelengths with a single diffraction grating, and is less expensive than a multilayer filter system. Thousands to tens of thousands of fine grooves are formed on the surface of the diffraction grating, and diffracted light interferes with each other, so that a specific wavelength can be emitted in a specific direction. Further, since a replica can be formed by a transfer technique using a master manufactured as a diffraction grating, this system is suitable for mass production.
[0006]
FIG. 6 shows a configuration example of a conventional duplexer (Patent Document 1).
[0007]
The duplexer shown in FIG. 6 includes a diffraction grating 4, lenses 3 and 6, and a waveguide array 2. The signal light incident on the optical fiber array (light incident portion) 1 is converted into parallel light by the lenses 3 and 6 and is incident on the diffraction grating 4. Then, the optical signal is diffracted in the direction corresponding to the wavelength by the diffraction grating 4. The diffracted light then enters the lenses 3 and 6 again and is guided to a light receiver (not shown) arranged according to the optical path of each wavelength.
[0008]
The light that is incident on the incident portion and further incident on the diffraction grating 4 is spread with angular dispersion and enters the diffraction grating 4, so that the spot diameter on the diffraction grating 4 is increased, and the diffracted light is also spread. The amount of incident light is reduced, and the insertion loss of the duplexer is increased.
[0009]
In order to suppress the spread of the light and reduce the insertion loss of the duplexer, it is necessary to use the lenses 3 and 6 to make parallel light.
[0010]
In this conventional example, as a combination of lenses 3 and 6, parallel light is obtained by a combination of one selected from a Luneburg lens, a geodesic lens, or a two-dimensional lens and a cylindrical lens 6 having a semicircular cross section. It is disclosed.
[0011]
[Patent Document 1]
Japanese Patent Laid-Open No. 09-043440 [Patent Document 2]
JP 2000-171660 A [Patent Document 3]
JP 2000-284141 A [0012]
[Problems to be solved by the invention]
However, there is a problem that the use of a combination of two different lenses increases the cost.
[0013]
Moreover, as what is disclosed as another conventional technique, there is one in which a single spherical lens is used as parallel light (Patent Documents 2 and 3).
[0014]
However, when a spherical lens is used, there is a problem that the size in the thickness direction increases when the loss in the diffraction grating is reduced. Further, there is a tolerance between the lens and the diffraction grating or an optical component such as an optical fiber during assembly. In addition, there is a problem that it is not easy to arrange a small spherical part and a planar part with the optical axis matched.
[0015]
In addition, since these systems do not have a temperature correction mechanism that can cope with wavelength shifts due to temperature fluctuations of the light source, it cannot be expected to satisfy the above-mentioned required specifications for low-density wavelength multiplexing optical communication. It is difficult to use in correspondence with multiplexed optical communication.
[0016]
Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, have a simple structure and is inexpensive, does not require high-precision alignment during assembly, has a large tolerance, and the wavelength of the signal light has changed. Even in such a case, it is an object to provide a wavelength multiplexing demultiplexer capable of accurately demultiplexing signal light.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, a wavelength multiplexing demultiplexer according to the present invention diffracts a wavelength division multiplexed signal light incident on a light incident portion and the light incident portion, and divides the wavelength multiplexed signal light for each wavelength. In a wavelength multiplexing demultiplexer having a diffraction grating to be waved and a waveguide to guide the signal light demultiplexed by the diffraction grating, the diffraction grating is a direction of engraving of the diffraction grating of the signal light to be demultiplexed A divergence angle reducing means for reducing a divergence angle in a direction orthogonal to the divergence angle, the divergence angle reduction means having a chirp shape in which the grating pitch of the diffraction grating is continuously changed, and the diffraction grating and the A cylindrical lens that makes the wavelength-multiplexed signal light parallel to only the engraving direction is disposed between the light incident portion and the signal light separated by the diffraction grating is engraved between the diffraction grating and the waveguide. Condensed light only in the line direction Command helical lens is disposed, said waveguide, and wherein said diffraction grating by demultiplexed waveguide width toward the direction of propagation of the condensed signal light by the cylindrical lens is a tapered waveguide to reduce To do.
[0018]
The duplexer of the present invention includes a light incident part, a diffraction grating that diffracts the wavelength multiplexed signal light incident on the light incident part, and demultiplexes the wavelength multiplexed signal light for each wavelength, and the diffraction grating In the wavelength multiplexing demultiplexer having a waveguide for guiding the signal light demultiplexed by the diffraction grating, the diffraction grating reduces a spread angle of the demultiplexed signal light in a direction perpendicular to the engraving direction of the diffraction grating. The divergence angle reducing means is configured such that the shape of the diffraction grating is an arc, and the wavelength-multiplexed signal light is engraved between the diffraction grating and the light incident portion in the direction of engraving. A cylindrical lens that is only parallel light is disposed, and a cylindrical lens that condenses the signal light demultiplexed by the diffraction grating only in the engraving direction is disposed between the diffraction grating and the waveguide. By the diffraction grating Wherein the waveguide width toward the direction of propagation of the condensed signal light waves by the cylindrical lens is a tapered waveguide decreases.
[0019]
In the present invention, as a means for reducing the divergence angle in the direction perpendicular to the engraving direction of the diffraction grating, a diffraction grating having a continuously changing grating pitch or a circular arc-shaped diffraction grating is used. Since the diffraction angle of the signal light in the direction orthogonal to the line direction can be reduced by these diffraction gratings, it is not necessary to use a spherical lens for condensing. It is sufficient to use only a cylindrical lens that performs the diaphragm in the direction of the engraving line of the diffraction grating, and this makes it possible to reduce the size of the duplexer in the thickness direction. In the present invention, the cross-sectional area toward the direction of propagation of the by the diffraction grating demultiplexed signal light is shall use the tapered waveguide to decrease. Due to a wavelength shift caused by a temperature change of the light source, a position shift of the focal point after diffraction occurs on the diffraction grating. In order to correct this misalignment and narrow the signal light toward the light receiver, a tapered waveguide with a reduced cross-sectional area is effective. The tapered waveguide in the present invention is a planar optical waveguide, and it is also advantageous in that the alignment with the rod-shaped cylindrical lens is easier than the spherical lens.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
[0021]
An embodiment using the chirped diffraction grating (spreading angle reducing means) of FIG. 2 is shown in FIGS. 1 (a) and 1 (b), and the embodiment using the arc-shaped diffraction grating (spreading angle reducing means) of FIG. FIG. 4 (a) and FIG. 4 (b) show the form.
[0022]
In these embodiments, the light incident portion 11, the cylindrical lens 12, the tapered waveguides 14 and 54, and the light receiver 15 are configured.
[0023]
The signal light incident on the light incident portion 11 is converted into parallel light 43 in one axis (inscribed direction: Y direction) by the cylindrical lens 12 (FIG. 3) and is incident on the diffraction gratings 13 and 53. The diffraction gratings 13 and 53 are diffracted in directions corresponding to the respective wavelengths of the signal light. The diffracted signal light enters the cylindrical lens 12 and is condensed on the incident end face 61 on the cylindrical lens 12 side of the tapered waveguides 14 and 54. Further, the diffracted signal light enters the tapered waveguides 14 and 54 arranged in consideration of the condensing position of each wavelength, as will be described later, and then is narrowed down to each port for each wavelength. 15 is taken in.
[0024]
When the chirped diffraction grating 13 (FIG. 2) in which the grating pitch of the diffraction grating continuously changes or the diffraction grating 53 (FIG. 5) having an arc shape is used as the divergence angle reducing means, the direction of the marking line It is sufficient to use only the cylindrical lens 12 that makes parallel light in one axial direction without using a lens that collects light in a direction orthogonal to the direction (zx direction). In this case, the types and number of lenses can be reduced, and the alignment of the light when assembling the duplexer can be facilitated as compared with the case where a spherical lens is used. In addition, both of these diffraction gratings 13 and 53 can be manufactured by a transfer technique or injection molding suitable as a mass production method, and are suitable for mass production.
[0025]
In the diffraction gratings 13 and 53, when the incident wavelength is shifted, the direction of diffraction is changed, and the emission position is moved. In order to correct the deviation of the emission position and to narrow the signal light to the light receiver 15, it is suitable to use the tapered waveguides 14 and 54. Further, by making the incident end faces of the tapered waveguides 14 and 54 wider than the range of the wavelength shift, it is possible to increase the tolerance when mounting the wavelength multiplexing demultiplexer, and the mounting can be easily performed. .
[0026]
That is, when the tapered waveguides 14 and 54 are used, as shown in FIG. 1B and FIG. 4B, not only the wavelengths 18 and 58 when there is no wavelength shift, but also when the wavelength of the light source is shifted. Even the wavelengths 19 and 59 can be guided to the same light receiver 15 without causing crosstalk.
[0027]
The shape of the tapered waveguides 14 and 54, such as the length and the angle of the tapered portion, can be optimized so that the loss at the tapered portion is minimized.
[0028]
Further, the tapered waveguides 14 and 54 can be manufactured by using a low-cost polymer material and using a method with a low manufacturing process such as photolithography. Furthermore, the tapered waveguides 14 and 54 have a planar shape, and the rod-shaped cylindrical lens 12 has fewer alignment positions when being fixed than a spherical lens or the like. There is also.
[0029]
Further, since the waveguide widths of the tapered waveguides 14 and 54 are made narrower as they approach the emission end face 62, the total reflection angle of the optical signal decreases accordingly. For this reason, the amount of light leaking in the radiation mode increases as the distance from the emission end face increases, and the loss may increase. In order to prevent this, it is necessary to increase the confinement of light in the waveguide. The clad layer is not provided in the tapered waveguides 14 and 54, and an air layer having a small refractive index is used instead of the clad layer. It is also possible. Furthermore, an increase in loss due to reflection can be prevented by providing an antireflection film on the end faces of the tapered waveguides 14 and 54.
[0030]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
[0031]
Example 1
FIG. 1 shows the overall configuration of this embodiment.
[0032]
Details of the diffraction grating 13 used in this embodiment are shown in FIG. 2A shows the upper surface of the diffraction grating 13, and FIG. 2B shows the front surface thereof.
[0033]
In this embodiment, the MM optical fiber 11 having a core diameter of 62.5 μm as the light incident portion, the width as the diffraction grating is 11 mm, and the grating pitch 63 is changed from 1.0 to 4.0 μm, and accordingly the blaze angle is 10 to 50 °. varying chirped diffraction grating 13 (FIG. 2), as the spread angle reducing means about the direction towards the rulings 65 of the diffraction grating, a cylindrical lens 12 of focal length lens end face 0.4 mm, the wavelength shift correction means for entering Using a tapered optical waveguide 14 made of polymer as a material and having a length of 8 mm and a core diameter of 60 μm, and a polymer material, a light receiving section 15 having a pitch of 250 μm and an incident diameter of 70 μm is used as a low density. Requirement specifications for multiplexed optical communication: 4 waves in the 1300 nm band (center wavelengths 1275.7 nm, 1300.2 nm, 1324.7 nm, 1349.2 nm), between wavelengths 24.5 nm, to prepare a wavelength-multiplexed demultiplexer corresponding to a wavelength shift ± 5.7 nm.
[0034]
When the plane chirped diffraction grating 13 is used, the respective condensing positions of the emitted light are not aligned perpendicularly to the light beam direction, and the light beams as shown in the long wavelength condensing position 16 and the short wavelength condensing position 17 are used. Tilt diagonally to the direction. Therefore, in order to cope with this inclination, a tapered waveguide 14 having an incident position 64 inclined obliquely as shown in FIG. 1B is used.
[0035]
The shape of the tapered waveguide 14 such as the length and the angle of the tapered portion is optimized so that the loss at the tapered portion is minimized.
[0036]
The focal position of the cylindrical lens 12 is the incident end face 61 to the tapered waveguide, and the focal position of the diffraction grating 13 and the incident position 64 of the tapered waveguide 14 are arranged to overlap.
[0037]
Most of the wavelength division multiplexers can be passively mounted, and can be manufactured at a lower cost than when a spherical lens is used.
[0038]
The characteristics of the mounted wavelength demultiplexer achieved a loss of 3 dB or less in the wavelength range of 1270 to 1281.4 nm, 1294.5 to 1305.9 nm, 1319.0 to 1330.4 nm, and 1343.5 to 1354.9 nm. Achieved flat loss characteristics in the transmission wavelength band.
[0039]
(Example 2)
FIG. 4 shows the overall configuration of this embodiment.
[0040]
Details of the diffraction grating 53 used in this embodiment are shown in FIG.
[0041]
5A shows the upper surface of the diffraction grating 53, and FIG. 5B shows the front surface thereof.
[0042]
In this embodiment, the MM optical fiber 11 having a core diameter of 62.5 μm as the light incident portion, the arc pitch diffraction grating 53 having a grating pitch 63 of 3.0 μm, the blaze angle continuously changing, and the radius of curvature of the arc of 12 mm, as divergence angle reducing means with in the direction of the ruling 65 of the grid, one focal length of the shaft lens end face 0.4mm of the cylindrical lens 12, 8mm length as a wavelength shift correction method of incident, with core diameter 60 [mu] m, the light-receiving Using a polymer taper type optical waveguide 54 that narrows toward the receiver, and a receiver array 15 having a pitch of 250 μm and an incident diameter of 70 μm as a light receiving section, the required specifications for low-density multiplexed optical communication: 4 waves in the 1300 nm band (center wavelength 1275. 7nm, 1300.2nm, 1324.7nm, 1349.2nm), wavelength interval of 24.5nm, wavelength multiplex corresponding to wavelength shift ± 5.7nm To prepare a vessel.
[0043]
When the curved diffraction grating 53 is used, the condensing position is different from that of the first embodiment by setting the vicinity of the vertex of the Roland circle as shown in the long wavelength condensing position 56 and the short wavelength condensing position 57. Therefore, as shown in FIG. 4, a tapered optical waveguide 54 having an incident end face 61 perpendicular to the light ray direction and having an incident position 64 parallel to the incident end face 61 is used.
[0044]
The shape of the taper waveguide 54, such as the length and the angle of the taper portion, is optimized so that the loss at the taper portion is minimized.
[0045]
Most of the duplexers can be passively mounted, and can be manufactured at a lower cost than the case of using a spherical lens.
[0046]
The characteristics of the mounted duplexer achieved a loss of 3 dB or less in the wavelength range of 1270 to 1281.4 nm, 1294.5 to 1305.9 nm, 1319.0 to 1330.4 nm, and 1343.5 to 1354.9 nm, and transmitted. Flat loss characteristics were achieved in the wavelength band.
[0047]
In addition, the light incident part used in Example 1 or 2 is not limited to the MM optical fiber, but may be an SM optical fiber, an optical waveguide, or other incident part via a lens system.
[0048]
The wavelength band to be used can be used in the 1500 nm band and the 850 nm band by changing the design of the grating pitch and blaze angle of the diffraction grating and the shape design of the tapered waveguide.
[0049]
The wavelength multiplexing demultiplexer of the present invention can be applied to, for example, a demultiplexer and an optical transceiver compatible with both SM and MM, such as 10G Ethernet standard LX4. Furthermore, the present invention can also be applied to an optical demultiplexer or an optical transceiver conforming to ITU-T649.2 with a wavelength interval of 1270 to 1610 nm and an interval of two wavelengths of 20 nm.
[0050]
【The invention's effect】
In short, according to the present invention, the signal light is accurately demultiplexed even when the wavelength of the signal light is changed even if the wavelength of the signal light is changed because the simple structure is inexpensive and high-precision alignment is not required at the time of assembly and the tolerance is large. Thus, it is possible to provide an excellent effect that it is possible to provide a wavelength division multiplexer that can be used.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of the present invention.
FIG. 2 is a diagram showing details of the chirped diffraction grating in FIG.
3 is a diagram showing an optical system of a cylindrical lens in FIGS. 1 and 4. FIG.
FIG. 4 is a diagram showing another embodiment of the present invention.
5 is a diagram showing details of an arc-shaped diffraction grating in FIG. 4; FIG.
FIG. 6 is a diagram showing a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fiber array 2 Waveguide array 3 Lens 4 Diffraction grating 5 Lens fixing block 6 Cylindrical lens 11 Optical fiber (light incident part)
12 Cylindrical lens 13 Diffraction grating 14 Tapered waveguide 15 Receiver array (receiver)
16 Long wavelength condensing position 17 Short wavelength condensing position 18 Demultiplexed wavelength light 19 without wavelength shift of the light source 19 Demultiplexed wavelength light 43 with wavelength shift of the light source 43 Parallel light 53 Diffraction grating 54 Tapered waveguide 56 Long wavelength condensing Position 57 Short wavelength condensing position 58 Demultiplexed wavelength light 59 with no wavelength shift of the light source 59 Demultiplexed wavelength light 61 with a wavelength shift of the light source 61 Entrance end face 62 Exit end face 63 Lattice pitch 64 Incidence position 65 Mark

Claims (2)

A light incident part; a diffraction grating that diffracts the wavelength-multiplexed signal light incident on the light incident part and demultiplexes the wavelength-multiplexed signal light for each wavelength; and guides the signal light demultiplexed by the diffraction grating. in wavelength division multiplexing demultiplexer having a waveguide for said diffraction grating comprises a spread angle reducing means for reducing the divergence angle in the direction perpendicular to the ruling direction of the diffraction grating of the signal light to be demultiplexed, the spread The angle reduction means has a chirped configuration in which the grating pitch of the diffraction grating is continuously changed, and the wavelength-multiplexed signal light between the diffraction grating and the light incident portion is parallel light only in the engraving direction. A cylindrical lens is disposed between the diffraction grating and the waveguide, and a cylindrical lens that condenses the signal light demultiplexed by the diffraction grating only in the engraving direction is disposed. On the lattice Wavelength multiplexing demultiplexer, wherein the demultiplexed to waveguide width toward the direction of propagation of the condensed signal light by the cylindrical lens is a tapered waveguide decreasing Ri. A light incident part; a diffraction grating that diffracts the wavelength-multiplexed signal light incident on the light incident part and demultiplexes the wavelength-multiplexed signal light for each wavelength; and guides the signal light demultiplexed by the diffraction grating. And a divergence angle reducing means for reducing a divergence angle of the signal light to be demultiplexed in a direction perpendicular to the direction of the engraving line of the diffraction grating. The angle reduction means has a configuration in which the shape of the diffraction grating is an arc shape, and a cylindrical lens is disposed between the diffraction grating and the light incident portion so that the wavelength multiplexed signal light is parallel light only in the engraving direction. A cylindrical lens for condensing the signal light demultiplexed by the diffraction grating only in the engraving direction is disposed between the diffraction grating and the waveguide, and the waveguide is demultiplexed by the diffraction grating and cylindrical Wavelength multiplexing demultiplexer, wherein the waveguide width toward the direction of propagation of the condensed signal light is tapered waveguide decreasing in's.

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