JP2005326468A - Optical wavelength multiplexer/demultiplexer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a temperature-independent type optical wavelength multiplexer/demultiplexer which can suppress diffraction loss at a groove even when a specific refractive index difference between a core and a clad is made large and which is small-sized and has low loss. <P>SOLUTION: In an array waveguide type optical wavelength multiplexer/demultiplexer 10 constituted of an input channel waveguide 12, an input side slab waveguide 13, an output channel waveguide 15, an output side slab waveguide 16, and a phase shifting channel waveguide 14, a core thick-wall section 21 which is thicker than a core main body 20 forming the waveguide is formed at the input side slab waveguide 13, a taper section 24 in which thickness of the core continuously changes is formed between the core main body 20 and the core thick-wall section 21, and a groove 22 is formed at the core thick-wall section 21 and the groove 22 is filled with an optical resin 23. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to the field of optical communication, and more particularly to an optical wavelength multiplexer / demultiplexer used for performing wavelength division multiplexing transmission.

  In the field of optical communication, a wavelength division multiplexing system in which a plurality of signals are placed on different wavelengths and transmitted through a single optical fiber to increase information capacity has been studied. In this method, an optical wavelength multiplexer / demultiplexer that multiplexes / demultiplexes light of different wavelengths plays an important role. In particular, an optical wavelength multiplexer / demultiplexer using a Mach-Zehnder interferometer or an arrayed waveguide diffraction grating is advantageous in that it can realize multiplexing / demultiplexing at narrow wavelength intervals and easily increase the communication capacity.

  As shown in FIG. 5, a conventional arrayed waveguide grating type optical wavelength multiplexer / demultiplexer 50 includes an input channel waveguide 41, an input side slab waveguide 42 connected to the input channel waveguide 41, An output channel waveguide 43, an output slab waveguide 44 connected to the output channel waveguide 43, and a plurality of phase shift channel guides connected to the input slab waveguide 42 and the output slab waveguide 44. And a waveguide 45.

  The light wave input from the input channel waveguide 41 propagates in the input-side slab waveguide 42 and enters a plurality of phase-shifting channel waveguides 45. The light wave undergoes a phase change when propagating through each phase-shifting channel waveguide 45 and propagates to the output-side slab waveguide 44. Light waves in the output-side slab waveguide 44 interfere with each other and reach each output channel waveguide 43. Here, since the interference pattern of the light wave varies depending on the wavelength, an optical multiplexing / demultiplexing function is realized.

  Here, when an optical wavelength multiplexer / demultiplexer is configured using a conventional material, when the temperature changes, the refractive index of the material changes due to the thermo-optic effect, and the equivalent refractive index of the phase shift channel waveguide 45 changes. To do. Furthermore, the length of the phase-shifting channel waveguide 45 also changes due to thermal expansion. As a result, the amount of phase change received by the light in the phase-shifting channel waveguide 45 changes depending on the temperature. Since this change differs depending on the wavelength, the output demultiplexing wavelength changes as a result. Here, considering the case where it is made of a quartz material as an example, the change of the demultiplexing wavelength due to the temperature in the vicinity of 1.55 μm which is the wavelength band for optical communication is 0.01 μm / ° C. Therefore, for example, when used at an ambient temperature of 0 to 60 ° C., the maximum wavelength of 0.6 μm is shifted. For this reason, it cannot be used in a practical system as it is, and it is necessary to control the temperature of the optical circuit.

  Therefore, as a method of making the temperature independent, a groove is provided in a part of the optical wavelength multiplexer / demultiplexer, in which a temperature coefficient of refractive index is filled with a material different from the material forming the optical wavelength multiplexer / demultiplexer, There is a method for compensating the wavelength dependence of a phase change due to temperature (for example, see Non-Patent Document 1).

  In general, since there is no light confinement structure in the groove, a large diffraction loss occurs. Therefore, a method of reducing the diffraction loss of the entire groove by dividing the groove into a plurality of pieces and reducing the diffraction loss per step of the groove and further causing the grooves to collect light at the groove with the optimum groove interval. Is often used (see Non-Patent Document 2, for example).

  When a groove is formed in a rectangular waveguide, diffraction occurs in both the vertical and horizontal directions with respect to the substrate in the groove, and even if this method is used, the loss cannot be sufficiently reduced. There is an example in which a wedge-shaped groove is provided.

  For example, as shown in FIG. 5, a plurality of wedge-shaped grooves 46 are formed in the input-side slab waveguide 42, and the grooves 46 are filled with an optical resin 47, and the refractive index is reduced by the optical resin 47. Compensation of the temperature dependence of In the input-side slab waveguide 42, only the diffraction in the vertical direction with respect to the substrate affects the loss. Therefore, the loss can be reduced as compared with the case where a groove is formed in the channel waveguide (see, for example, Non-Patent Document 3). .

  On the other hand, by increasing the relative refractive index difference Δ between the core material and the clad material constituting the optical waveguide, there is generally a method for reducing the radius of curvature of the bent waveguide and realizing miniaturization and cost reduction of the element. Yes (see Non-Patent Document 4, for example).

Y. Inoue et al., “Athermal silica-based arrayed-waveguide grating (AWG) multiplexer”, ECOC 97 Technical Digest, 1997, p.33-36 A.Kaneko et al., “Athermal silica-based arrayed-waveguide grating (AWG) multiplexers with new low loss groove design”, OFC '99 Technical Digest ( OFC'99 Technical Digest), 1999, TuO1, p.204-206 Maru et al. “Athermal and Center Wavelength Adjustable Arrayed Waveguide Grating”, OFC 2000 Technical Digest Hida et al., “Fabrication of low-loss and polarization-insensitive 256 channel arrayed-waveguide grating with 25 GHz spacing using 1.5% Δ waveguide grating with 25GHz spacing using 1.5% Δ waveguides) ”, Electron. letter. (Electron. Lett.), 2000, Vol. 36, No. 9, p.820-821

  However, when the relative refractive index difference Δ of the array waveguide diffraction grating type optical wavelength multiplexer / demultiplexer 50 that is made temperature independent is increased, a groove 46 is formed in the input-side slab waveguide 42 to sufficiently There was a problem that the radiation loss at 46 could not be suppressed.

  For example, as shown in FIGS. 6A and 6B, in each of the optical wavelength demultiplexers with Δ = 0.8% and 1.5%, with the same groove width, the groove arrangement interval at which the loss is minimized. Comparing the losses, the optical fiber multiplexer / demultiplexer with Δ = 1.5% has increased the minimum loss. Accordingly, an object of the present invention is to solve the above-described problems and to reduce the diffraction loss in the groove even when the relative refractive index difference Δ between the core and the clad is increased, and to achieve a small and low-loss temperature-free. It is to provide a dependent type optical wavelength multiplexer / demultiplexer.

  To achieve the above object, the invention of claim 1 is directed to at least one input channel waveguide, an input side slab waveguide connected to the input channel waveguide, and at least one output. An arrayed waveguide type comprising a channel waveguide, an output-side slab waveguide connected to the output channel waveguide, and a phase-shifting channel waveguide connected to the input-side slab waveguide and the output-side slab waveguide In the optical wavelength multiplexer / demultiplexer, a thick core portion thicker than the core main body portion forming the waveguide is formed in a part of the input side slab waveguide, and a groove is formed in the thick core portion. In this optical wavelength multiplexer / demultiplexer, the groove is filled with an optical resin.

  According to a second aspect of the present invention, the thickness of the core main body is adjusted so as to satisfy the single mode condition, and the core main body and the thick core are continuously formed. The optical wavelength multiplexer / demultiplexer according to claim 1, wherein the optical wavelength multiplexer / demultiplexer is adiabatically coupled via a taper portion that changes in size.

  According to a third aspect of the present invention, each boundary between the core main body part, the core thick part, and the taper part has an arc shape, and the center of curvature of the arc is the input channel waveguide and the 3. The optical wavelength multiplexer / demultiplexer according to claim 2, located near the boundary of the input side slab waveguide.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the core and the clad formed around the core are formed of a quartz-based material, and the relative refractive index difference between the core and the clad is 1.0% or more. It is an optical wavelength multiplexer / demultiplexer of description.

  According to the present invention, it is possible to achieve an excellent effect that a temperature-independent type optical wavelength multiplexer / demultiplexer can be reduced in size and loss can be reduced.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a plan view showing a preferred embodiment of an optical wavelength multiplexer / demultiplexer according to the present invention.

  As shown in FIG. 1, an optical wavelength multiplexer / demultiplexer 10 is manufactured on a quartz substrate 11, and an input channel waveguide 12 and an input side slab waveguide 13 on the quartz substrate 11 are different in length by a certain value. This is an arrayed waveguide diffraction grating type optical wavelength multiplexer / demultiplexer including a plurality of phase-shifting channel waveguides 14, a plurality of output channel waveguides 15, and an output-side slab waveguide 16. The input channel waveguide 12, the phase shift channel waveguide 14, and the output channel waveguide 15 are waveguides having a rectangular cross-sectional structure, and the input side and output side slab waveguides 13 and 16 are light only in the film thickness direction. This is a waveguide having a flat plate structure having a confinement effect.

  The input-side slab waveguide 13 and the output-side slab waveguide 16 are connected via a phase-shifting channel waveguide 14, and the input-side slab waveguide 13 is connected to the input-channel waveguide 12 at the other end, and the output-side slab waveguide The other end of the waveguide 16 is connected to the output channel waveguide 15. The input-side and output-side slab waveguides 13 and 16 are formed in a sector shape in which a plurality of phase-shifting channel waveguides 14 are coupled in an arc shape, and the center of curvature of the arc is the same as that of the input and output channel waveguides 12 and 15. It is located near the boundary with the input and output side slab waveguides 13 and 16. The optical wavelength multiplexer / demultiplexer 10 is formed by a core having a refractive index of 1.48, and the periphery of the core is buried by a clad 17 having a refractive index of 1.457 (relative refractive index difference Δ = 1.5%).

  As shown in FIG. 2, the cores of the waveguides 12, 13, 14, 15, and 16 constituting the optical wavelength multiplexer / demultiplexer 10 of the present embodiment are 4.3 μm, but the input side slab waveguide 13, a core thick portion 21 region having a core thickness of 10 μm is formed with respect to the core body portion 20 having a core thickness of 4.3 μm.

  The core thick part 21 is formed at the center of the core body part 20, and the input channel waveguide 12 side and the phase shift channel waveguide 14 side of the input side slab waveguide 13 are formed by the core body part 20. Between the core thick part 21 and the core body part 20, a tapered part 24 in which the core thickness continuously changes is formed. Therefore, the core main body portion 20 and the core thick portion 21 are adiabatically coupled by the tapered portion 24.

  That is, the light incident from the input channel waveguide 12 is guided through the core main body portion 20, the taper portion 24, the core thick portion 21, the taper portion 24, and the core main body portion 20 to each phase-shifting channel waveguide 14. The core of the input side slab waveguide 13 is formed so as to be incident on.

  The boundary between the thick core portion 21 and the taper portion 23 and the boundary between the taper portion 23 and the core body portion 20 are arcuate, and the center of curvature 25 of the arc is the input channel waveguide 12. And in the vicinity of the boundary between the input side slab waveguide 13.

  Further, a plurality of wedge-shaped grooves 22 are formed in the thick core portion 21, and all the grooves 22 are filled with the optical resin 23.

  The greater the refractive index of the optical resin 23 filled in the groove 22 is from the refractive index of the material constituting the optical wavelength multiplexer / demultiplexer 10, the more effective the temperature dependence of the optical wavelength multiplexer / demultiplexer 10 becomes. . When the optical wavelength multiplexer / demultiplexer 10 is made of a quartz-based material, the temperature dependency of the refractive index takes a positive value. Therefore, as the optical resin 23, silicone having a negative temperature dependency of the refractive index is used. System optical resin, epoxy optical resin, or the like is used.

  Next, a manufacturing procedure of the optical wavelength multiplexer / demultiplexer 10 of this embodiment will be described. FIG. 4 is a process cross-sectional view along the line AA in FIG.

  As shown in FIG. 4A, a core material 32 is deposited on the quartz substrate 11 serving as a base. The core material 32 forms the pattern of the core body 20.

  Next, as shown in FIG. 4B, after forming the shadow mask 33 on the substrate, the core material 34 is formed. The unmasked portion 33 a of the shadow mask 33 forms the pattern of the core thick portion 21, and the flange portion 33 b of the shadow mask 33 forms the pattern of the tapered portion 24.

  References relating to processes using shadow masks include, for example, Ito et al., “Ultra-low loss arrayed waveguide grating using 1.5% -Δ waveguide”, IEICE Technical Report, OPE2002-16, 2002, p. 27-30.

  Next, as shown in FIG. 4C, the shadow mask 33 is removed, and a waveguide pattern is formed by photolithography and etching techniques. The pattern to be formed is the input side slab waveguide 13, but at the same time, the output side slab waveguide 16, the input and output channel waveguides 12 and 15, and the phase shift channel waveguide 14 are also formed. Thereafter, the clad 17 is formed by chemical vapor deposition, and all the waveguides 12, 13, 14, 15 and 16 are covered with the clad 17.

  Finally, as shown in FIG. 4 (d), a wedge-shaped groove 22 is formed at the location of the core thick portion 21 of the input-side slab waveguide 13, and the groove 22 is filled with an optical resin 23 to obtain the optical wavelength. The multiplexer / demultiplexer 10 is obtained.

Next, the operation of this embodiment will be described.
Light waves input from the input channel waveguide 12 are split in the input side slab waveguide 13, and each light wave propagates to the output side slab waveguide 16 via the phase shift channel waveguide 14. Here, since each of the phase-shifting channel waveguides 14 is different in length, the light wave propagating in the phase-shifting channel waveguide 14 causes a phase change, and the respective light waves interfere in the output-side slab waveguide 16, An optical demultiplexer function is realized by collecting light waves having different wavelengths individually in the output channel waveguide 15.

  In the optical wavelength multiplexer / demultiplexer 10 of this embodiment, a groove 22 filled with an optical resin 23 is formed in the input-side slab waveguide 13 to make the optical wavelength multiplexer / demultiplexer 10 temperature independent. The refractive index temperature coefficient of the optical resin 23 is different in sign from the refractive index temperature coefficient of the quartz-based material constituting the optical wavelength multiplexer / demultiplexer 10, so that the refractive index of the core or the clad 17 changes due to temperature change. Even if a phase change occurs in the propagating light, the phase change can be compensated by the refractive index change of the optical resin 23. Thereby, temperature independence of the optical wavelength multiplexer / demultiplexer 10 can be realized.

  However, since the groove 22 does not have a light confinement function, a diffraction loss occurs. The smaller the core thickness, the larger the loss. Therefore, the thickness of the core of the input side slab waveguide 13 in which the groove 22 is formed is made larger than the thickness of the core satisfying the single mode condition of the arrayed waveguide having the conventional structure. Specifically, the core thick part 21 is formed. Thereby, the diffraction loss in the groove | channel 22 can be reduced significantly.

  FIG. 3 shows the relationship between the groove arrangement interval and loss when the groove width is a parameter in the groove 22 in the input-side slab waveguide 13 of the optical wavelength multiplexer / demultiplexer 10 of the present embodiment. By increasing the core thickness to 10μm, the loss is greatly reduced compared to the conventional optical wavelength multiplexer / demultiplexer with a relative refractive index Δ = 1.5% and a uniform core thickness on the input side slab waveguide. It can be seen that is reduced.

  Since the core body 20 and the core thick part 21 are adiabatically coupled by the tapered core material 23 in which the core thickness continuously changes, the core body part 20 is incident on the core thick part 21. Light can be coupled to the fundamental mode of the core thick portion 21 without loss. Even when the higher-order mode is generated in the groove 22, the core body 20 satisfies the single mode condition, so that the higher-order mode can be attenuated by the core body 20 and the cross-section due to the influence of the higher-order mode can be obtained. Talk degradation can be suppressed.

  Since the propagation constant of the fundamental mode is different between the core main body 20 and the core thick part 21, the region shape of the core thick part 21 causes an aberration in the input-side slab waveguide 13, and the optical frequency characteristics. May deteriorate. However, in the optical wavelength multiplexer / demultiplexer 10 of the present invention, the boundary between the region of the core thick portion 21 and the taper portion 23 is an arc shape, and the center of curvature 25 of the arc is the input channel waveguide 12 and the input side slab. It is located near the boundary of the waveguide 13. For this reason, light that is incident and diffracted from the input channel waveguide 12 to the input side slab waveguide 13 propagates through the core thick portion 21 by an equal distance in any radiation direction in the input side slab waveguide 13. In other words, it is possible to prevent the occurrence of a phase difference due to the difference in propagation direction, and it is possible to prevent the occurrence of aberration as a result.

  Therefore, the temperature-independent type optical wavelength multiplexer / demultiplexer 10 made of a medium having a relative refractive index difference of 1.5% for miniaturization of the optical circuit is formed with a thick core of the input side slab waveguide 13. By doing so, the diffraction loss in the groove 22 filled with the optical resin 23 can be reduced, and the core thick portion 21 is joined to the core body portion 20 in a tapered shape, and the boundary is formed in an arc shape. Thus, aberrations are prevented from occurring in the light incident on the phase-shifting channel waveguide 14, and an optical wavelength multiplexing / demultiplexing function that provides excellent optical characteristics is provided.

It is a top view which shows the optical wavelength multiplexer / demultiplexer which is one Embodiment of this invention. It is the sectional view on the AA line of FIG. It is a figure which shows the relationship between the groove arrangement | positioning space | interval and loss in the optical wavelength multiplexer / demultiplexer of FIG. FIG. 3 is a cross-sectional view illustrating a manufacturing process of the optical wavelength multiplexer / demultiplexer of FIG. It is a top view which shows the conventional optical wavelength multiplexer / demultiplexer. FIG. 6 is a diagram showing the relationship between the groove arrangement interval and loss in the optical wavelength multiplexer / demultiplexer of FIG. 5, (a) is a diagram when the relative refractive index difference Δ is 0.8%, and (b) is a diagram. FIG. 5 is a diagram when the relative refractive index difference Δ is 1.5%.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical wavelength multiplexer / demultiplexer 11 Quartz substrate 12 Input channel waveguide 13 Input side slab waveguide 14 Phase shift channel waveguide 15 Output channel waveguide 16 Output side slab waveguide 20 Core main part 21 Core thick part 22 groove 23 optical resin 24 taper part 25 curvature center

Claims (4)

  At least one input channel waveguide, an input side slab waveguide connected to the input channel waveguide, at least one output channel waveguide, and an output connected to the output channel waveguide An array waveguide type optical wavelength multiplexer / demultiplexer comprising a side slab waveguide and a phase-shifting channel waveguide connected to the input side slab waveguide and the output side slab waveguide. A core thick part thicker than the core main body part forming the waveguide is formed in part, a groove is formed in the core thick part, and an optical resin is filled in the groove. Optical wavelength multiplexer / demultiplexer.   The core body is formed by adjusting the thickness so as to satisfy the single mode condition, and the core body and the core thick part are formed with a tapered part in which the core thickness continuously changes. The optical wavelength multiplexer / demultiplexer according to claim 1, wherein the optical wavelength multiplexer / demultiplexer is adiabatically coupled to each other.   Each boundary between the core main body part, the core thick part, and the taper part has an arc shape, and the center of curvature of the arc is the boundary between the input channel waveguide and the input side slab waveguide. The optical wavelength multiplexer / demultiplexer according to claim 2, which is located in the vicinity. The optical wavelength multiplexing / demultiplexing according to any one of claims 1 to 3, wherein the core and a clad formed around the core are formed of a quartz-based material, and a relative refractive index difference between the core and the clad is 1.0% or more. vessel.

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