JP2009265419A - Optical wavelength multiplexing/demultiplexing circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical wavelength multiplexing/demultiplexing circuit with an excellent reflection characteristic, which improves a reflection attenuation amount and a directivity characteristic, in an athermal array waveguide grid (AWG) of a structure in which a thermal compensation material is inserted in a slab waveguide path. <P>SOLUTION: The groove disposed in a first slab waveguide path 102 is divided into six parts 106A to 106F, and they are arranged respectively to have the same width in a progressing direction of the light wave, arranged with a constant interval, that is 60 μm here, of the center line of each groove. In the athermal AWG of the embodiment, ϕ>0 for all net angles ϕ in which each of the grooves 106A to 106F makes to an axis line vertical to a progressing direction of the light wave transmitted from an array waveguide path 103. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical wavelength multiplexing / demultiplexing circuit, and more particularly to an arrayed waveguide diffraction grating type optical wavelength multiplexing / demultiplexing circuit.

  Research and development of a planar lightwave circuit (PlC) composed of a silica-based glass waveguide formed on a silicon substrate has been actively conducted. An arrayed waveguide diffraction grating (AWG) using such PLC technology is a circuit that realizes optical wavelength multiplexing / demultiplexing, and plays an important role as a component for optical communication.

  The AWG has temperature dependency on the transmission wavelength of the light to be multiplexed / demultiplexed. This is because the effective refractive index of the silica-based glass waveguide constituting the AWG has temperature dependence. Therefore, in a normal AWG, it is necessary to add a temperature adjusting device in order to keep the wavelength transmission characteristic constant.

  In order to omit the temperature control device additionally required for the AWG, a method for reducing the temperature dependence of the transmission wavelength of the AWG has been developed. This method is disclosed in Patent Documents 1 and 2. An AWG with reduced temperature dependence of the transmission wavelength is called “temperature-independent AWG” or “athermal AWG”. The athermal AWG is a material having a refractive index temperature coefficient different from the temperature coefficient of the effective refractive index of the waveguide by forming a partially cut groove in each optical path (array waveguide or slab waveguide) in the AWG. This is realized by inserting a “temperature compensation material” hereinafter. The temperature compensation material cancels the optical path length difference change caused by the temperature change in the arrayed waveguide. In particular, the configuration in which the groove is formed in the slab waveguide has an advantage that the circuit area does not increase as compared with the non-athermal AWG.

  FIG. 9 is a plan view showing a configuration of an athermal AWG of a type in which grooves are formed in the slab waveguide. Here, 901 is a first input / output waveguide, 902 is a first slab waveguide, 903 is an arrayed waveguide, 904 is a second slab waveguide, 905 is a second input / output waveguide, and 906 is a groove. The groove 906 is filled with a temperature compensation material. 9A shows a case where a groove is formed in the first slab waveguide 902, FIG. 9B shows a case where a groove is formed in the second slab waveguide 904, and FIG. The case where a groove is formed in the slab waveguide is shown. FIG. 10 is a cross-sectional view taken along line XX of the athermal AWG in FIG. Here, 906 is also a groove, 908 is a silicon substrate, 909 is a waveguide core, and 910 is a clad. The groove 906 is formed by removing a part of the waveguide core 909 and the clad 910 and divides the waveguide core 909. Also in the athermal AWG having the configuration shown in FIGS. 9B and 9C, the cross-sectional configuration of the groove 906 is the same as that shown in FIG.

Each groove is divided into a plurality of grooves. This is because radiation loss can be reduced more than a single groove. In FIGS. 9A to 9C, the optical path length L _i of the _i -th arrayed waveguide is expressed as L _i = L _i + (i−1) · ΔL, and is designed to be sequentially increased by a certain amount ΔL. ing. Accordingly, the length L _i ′ in which the light wave passing through each arrayed waveguide is divided by the groove 906 in the first slab waveguide 902 and the second slab waveguide 904 is L _i ′ = L _i ′. It is expressed as + (i−1) · ΔL ′, and is shaped so as to become longer sequentially by an amount ΔL ′ proportional to ΔL. The transmission center wavelength λ _o in these AWGs is
λ _o = {n _a · ΔL−n _s · ΔL ′ + n ′ · ΔL ′} / M
It is expressed. Here, n _a is the effective refractive index of the arrayed waveguide, n _s is the effective refractive index of the slab waveguide, n ′ is the refractive index of the temperature compensation material, and M is the diffraction order of the AWG. At this time, n 'is close to n _s, the refraction angle of light wave in the groove is assumed to be sufficiently small. In the athermal AWG, ΔL ′ / (ΔL−ΔL ′) = − α / α ′, that is, ΔL ′ = ΔL / (1−α ′ / α) is designed, and the temperature dependence of the transmission center wavelength is compensated. . Where α is the effective refractive index temperature coefficient of the arrayed waveguide and slab waveguide (α = dn _a / dT = dn _s / dT), and α ′ is the refractive index temperature coefficient of the temperature compensation material (α ′ = dn ′ / dT). ).

  As the temperature compensation material, a material in which α ′ has a different sign from α and | α ′ | is sufficiently larger than | α | is particularly preferable. As a material under such conditions, there is, for example, a silicone resin which is an optical resin, and α ′ to −35 × α.

International Publication No. WO 98/36299 Pamphlet Japanese Patent No. 3498650

  When the wavelength multiplexing / demultiplexing circuit is operated in an actual transmission system, it is necessary that the transmission characteristics satisfy a predetermined specification and the reflection in the circuit is suppressed to a predetermined level or less. This is to prevent the operation of these devices from becoming unstable due to the reflected light entering an optical transmitter or optical amplifier installed adjacent to the wavelength multiplexing / demultiplexing circuit. In a wavelength multiplexing / demultiplexing circuit, when a light wave is input from a certain input / output waveguide, the ratio of the light wave power that returns to its own waveguide due to reflection in the circuit is called “reflection loss”. The ratio of the light wave power output to the output waveguide is called “directivity”. In a general WDM transmission system, attenuation of 40 to 45 dB is required for both return loss and directionality. However, in the conventional athermal AWG, there are cases where the required specifications for the return loss and the directivity cannot be satisfied.

  FIG. 11 is a graph showing the temperature dependence of the effective refractive index of the silica-based glass waveguide constituting the AWG and the temperature dependence of the refractive index of the temperature compensation material. Here, the waveguide is a slab waveguide with a relative refractive index difference (Δ) of 1.5% and a core thickness of 4.5 μm, and the temperature compensation material has a refractive index close to that of quartz glass (approximately 1.4 at room temperature) and is refracted. A silicone resin having a rate temperature coefficient of about -35 times that of quartz glass is used. FIG. 12 is a graph showing the calculation results of Fresnel reflection occurring at the interface between the waveguide and the optical resin in FIG. As the refractive index difference between the two, the amount of reflection tends to increase. In the conventional athermal AWG of FIGS. 9A to 9C, when the athermal AWG is used in a wide temperature range of −40 to 80 ° C. at the interface between the groove filled with the silicone resin and the slab waveguide. Causes a maximum of -31 dB Fresnel reflection.

  Here, as shown in FIG. 9A, the reflection characteristics of the athermal AWG in which the groove 906 is formed in the first slab waveguide 902 will be specifically considered. It is assumed that the athermal AWG is designed with a wavelength channel number of 40 and a wavelength channel interval of 0.8 nm (100 GHz) manufactured by a waveguide of Δ1.5%, core width × core thickness 4.5 μm × 4.5 μm. At this time, the number of arrayed waveguides 903 is 150, ΔL is about 30 μm, and ΔL ′ is 1 μm. The groove 906 is divided into a plurality of groove portions. This is because the light waves radiated in each of the divided grooves interfere with each other and have an effect of suppressing radiation loss as a whole. Here, the main path of reflection in which the light wave input from a port of the second input / output waveguide 905 of the athermal AWG returns to its own port or the port of another wavelength channel is the second slab waveguide 904, the array waveguide. The first slab waveguide 902 is reached via the waveguide 903, Fresnel reflection is generated at each interface of the divided grooves, and the second input / output is coupled to the arrayed waveguide 903 again via the second slab waveguide 904. It reaches the waveguide 905. As described above, when the athermal AWG is used in a wide temperature range of −40 to 80 ° C., Fresnel reflection of up to −31 dB occurs at each interface of the groove, so that the loss on the other path is considered to be about 4 dB. Even so, the return loss or directivity characteristic is approximately 35 dB at maximum.

  Such reflection characteristics in the conventional athermal AWG may make the operation of the optical transmitter and the optical amplifier in the transmission system unstable in some cases, which may greatly restrict the design of the transmission system. Therefore, it has been desired to improve the return loss and the directivity characteristics of the athermal AWG.

  The present invention has been made in view of such a problem, and an object of the present invention is to improve the reflection attenuation amount and the directivity characteristic in the athermal AWG having a configuration in which the temperature compensation material is inserted into the slab waveguide. An object of the present invention is to provide an excellent wavelength multiplexing / demultiplexing circuit.

  In the present invention, attention is paid to the coupling efficiency when the light wave reflected at the interface between the temperature compensation material and the slab waveguide is coupled to the array waveguide again. A plane wave propagating through the slab waveguide is coupled to each arrayed waveguide which is a channel waveguide with a certain coupling efficiency. FIG. 13 is an enlarged view of a connection portion between the first slab waveguide 902 and the arrayed waveguide 903 in the athermal AWG of FIG. 9A. FIG. 14 is a graph showing the relationship between the coupling efficiency of the plane wave propagating through the slab waveguide to the arrayed waveguide and the slope θ of the plane wave. Here, the waveguide has Δ1.5% and a core thickness of 4.5 μm. Assume that the interval between adjacent arrayed waveguides is 9 μm, the core width of the connecting portion with the slab waveguide is 7 μm, and the core width is converted to 4.5 μm by the tapered waveguide. It can be seen that the coupling efficiency deteriorates as the plane wave is inclined with respect to the arrayed waveguide. Therefore, if the reflected light wave is inclined with respect to the arrayed waveguide, coupling to the arrayed waveguide is suppressed, and as a result, the return loss and the directivity are considered to be improved.

  FIGS. 15A to 15C show a method for arranging a plurality of divided grooves in a conventional athermal AWG in which a groove 906 is formed in the first slab waveguide 902 as shown in FIG. 9A. Three examples are shown. Here, it is assumed that the groove is divided into six portions 906A to 906F. FIG. 15A shows a method of arranging the grooves so that each groove has an equal width with respect to the traveling direction of the light wave, and the interval between the center lines of each groove is constant. The arrangement method disclosed in Patent Document 2 It is. Here, the interval between the center lines of the grooves is 60 μm. FIG. 15B shows a method in which each groove has the same width as in FIG. 15A and the width of the waveguide left between the grooves is constant. It is considered that the effect of suppressing the radiation loss due to interference is more remarkable than the above arrangement. Here, the width of the waveguide left between the grooves is 30 μm. FIG. 15C shows a method in which the width of the waveguide left between the grooves is constant, as in FIG. It is considered that the radiation loss can be further reduced compared to the arrangement shown in FIG. 15B by making the radiation relatively small at the end groove where the effect is small. Here, the width of the waveguide left between the grooves is 30 μm, and the ratio of the six groove widths is 1: 1.5: 2: 2: 1.5: 1. 15A to 15C, it is assumed that the groove 906 is disposed near the center of the first slab waveguide 902.

  FIGS. 16A to 16C show the inclinations φ of the interfaces of the grooves 906A to 906F in the arrangements of FIGS. 15A to 15C with respect to the light wave propagating from the arrayed waveguide 903, respectively. is there. Here, as shown in FIGS. 15A to 15C, the inclination φ is an angle with respect to an axis perpendicular to the traveling direction of the light wave. If the inclination φ is inclined toward the arrayed waveguide 903 side, φ> 0, If it is inclined toward the input / output waveguide 901, φ <0. In each interface, the interface on the first input / output waveguide 901 side of the corresponding groove is represented by (1), and the interface on the arrayed waveguide 903 side is represented by (2). FIGS. 16A to 16B also show the coupling efficiency when the light wave reflected at each interface is coupled to the arrayed waveguide 903 again. Here, since the light wave reflected at the groove interface with the inclination φ is considered to be a plane wave incident on the arrayed waveguide 903 with an inclination of θ = | 2φ |, the coupling efficiency is derived from the result of FIG. In the arrangement shown in FIG. 15A, the coupling efficiency of light waves reflected from all groove interfaces to the arrayed waveguide is as high as 66%. In the arrangement shown in FIGS. Although there are interfaces with low coupling efficiency, the coupling efficiency is as high as 76% at the interface (2) of the groove 906C and the interface (1) of the groove 906D. Thus, in the conventional athermal AWG, the coupling efficiency of the light wave reflected at at least a part of the groove interface to the arrayed waveguide is high. This is because the maximum / minimum difference of φ does not increase due to the characteristics of the groove arrangement, and φ is distributed positively and negatively across 0 degree. Further, even when φ at each interface is distributed over a relatively wide range as shown in FIGS. 15B and 15C, the most important thing to determine the return loss and directivity characteristics of the athermal AWG is the array guide. It is a light wave that is reflected at the interface having the highest coupling efficiency to the waveguide, that is, the smallest | φ |. Therefore, in order to improve the reflection characteristics of the athermal AWG, it is considered effective to make | φ | large for all the interfaces where reflection occurs.

  Based on the above considerations, the invention according to claim 1 is directed to an arrayed waveguide having waveguides that become longer sequentially with a predetermined optical path length difference, and a first slab guide connected to both ends of the arrayed waveguide. A waveguide and a second slab waveguide; a first input / output waveguide connected to the first slab waveguide; and a second input / output waveguide connected to the second slab waveguide. An arrayed waveguide diffraction grating type wavelength multiplexing / demultiplexing circuit comprising: at least one of the first slab waveguide and the second slab waveguide, a change in optical path length caused by a temperature change in the arrayed waveguide The temperature compensation material that cancels out the wave is disposed so as to intersect the traveling direction of the light wave, and the boundary line of the temperature compensation material is perpendicular to the traveling direction of the light wave in the slab waveguide surface where the temperature compensation material is disposed. Same for axis And characterized in that it finite angle inclined orientation.

  According to a second aspect of the present invention, there is provided an arrayed waveguide having waveguides that become longer sequentially with a predetermined optical path length difference, a first slab waveguide connected to both ends of the arrayed waveguide, and a second slab waveguide. An arrayed waveguide comprising: a first slab waveguide; a first input / output waveguide connected to the first slab waveguide; and a second input / output waveguide connected to the second slab waveguide. A diffraction grating type wavelength multiplexing / demultiplexing circuit, wherein at least one of the first slab waveguide and the second slab waveguide is provided with a groove that intersects the traveling direction of the light wave and divides the waveguide. The groove is filled with a temperature compensation material having a refractive index temperature coefficient different from the temperature coefficient of the effective refractive index of the slab waveguide in which the groove is disposed, and an optical path length caused by a temperature change in the arrayed waveguide. The difference change is offset and the groove is In the slab waveguide in the road surface which is the boundary line of the groove, to the traveling direction perpendicular to the axis of the light wave, characterized in that it is a finite angle inclined all in the same direction.

  According to a third aspect of the present invention, in the second aspect, the groove includes a plurality of grooves arranged in the traveling direction of the light wave.

  According to a fourth aspect of the present invention, in the second or third aspect, the arrayed waveguide, the first slab waveguide, the second slab waveguide, the first input / output waveguide, and the The second input / output waveguide is made of quartz glass, and the temperature compensation material filled in the groove is an optical resin.

  The invention according to claim 5 is characterized in that in any one of claims 1 to 4, the finite angle inclination is 4 degrees or more.

  The invention described in claim 6 is characterized in that, in claim 5, the finite angle inclination is 6 degrees or more.

  According to the present invention, the boundary line of the temperature compensation material arranged in the slab waveguide is inclined at a finite angle in the same direction with respect to the axis perpendicular to the traveling direction of the light wave, so that the athermal AWG type light In the wavelength multiplexing / demultiplexing circuit, the return loss and the directivity can be improved, and the wavelength multiplexing / demultiplexing circuit having excellent reflection characteristics can be realized.

[First Embodiment]
An athermal AWG type optical wavelength multiplexing / demultiplexing circuit according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a plan view showing a circuit configuration. Here, 101 is a first input / output waveguide, 102 is a first slab waveguide, 103 is an arrayed waveguide, 104 is a second slab waveguide, 105 is a second input / output waveguide, and 106 is a first input / output waveguide. 1 is a groove formed on one slab waveguide 102 and filled with silicone resin as a temperature compensation material. The optical path length L _i of the i-th waveguide of the arrayed waveguide 103 is expressed as L _i = L _i + (i−1) · ΔL, and is designed to be sequentially increased by a certain amount ΔL. In response to this, the length L _i ′ at which the light wave passing through each arrayed waveguide is divided by the groove 106 in the first slab waveguide 102 is L _i ′ = L _i ′ + (i−1) · ΔL. It is expressed as “,” and is shaped so as to gradually increase by an amount ΔL ′ proportional to ΔL. Each waveguide is a silica glass waveguide having a relative refractive index difference of 1.5% and a core thickness of 4.5 μm, and the core width of the input / output waveguides 101 and 105 and the arrayed waveguide 103 is 4.5 μm. . The circuit has characteristics of 40 wavelength channels and a wavelength channel spacing of 0.8 nm (100 GHz). The number of arrayed waveguides is 150, ΔL is about 30 μm, and ΔL ′ is about 1 μm.

  FIG. 2 is an enlarged plan view showing the first slab waveguide 102 and its vicinity in FIG. In the present embodiment, the groove is divided into six portions 106A to 106F, and each groove is arranged to have the same width with respect to the traveling direction of the light wave, and the interval between the center lines of each groove is constant. Yes. Here, the interval between the center lines of the grooves is 60 μm. In the athermal AWG of this embodiment, the angles φ formed by the interfaces of the grooves 106A to 106F with respect to the axis perpendicular to the traveling direction of the light wave propagating from the arrayed waveguide 103 are all φ> 0. Features. In other words, the boundary lines of the temperature compensation material are all inclined at a finite angle in the same direction with respect to the axis perpendicular to the traveling direction of the light wave.

  Here, the reflection characteristic of the athermal AWG of the present embodiment is determined by the reflection at the groove interface where the absolute value | φ | of the angle described above is minimized. This minimum value is represented as | φ | min. FIG. 3 shows the distribution of φ at each groove interface when it is designed so that | φ | min = 4 degrees. Here, for each groove interface, the interface on the first input / output waveguide 101 side of the corresponding groove is represented by (1), and the interface on the array waveguide 103 side is represented by (2). FIG. 3 shows that φ> 4 degrees at all interfaces. FIG. 4 shows the coupling efficiency of the light wave reflected at the groove interface to the arrayed waveguide 103 at | φ | min = 0, 4, 5, 6 degrees. FIG. 4 also shows the return loss or directionality of the athermal AWG under the same conditions. In these reflection characteristics, the amount of Fresnel reflection at the groove interface is −31 dB, and the first slab waveguide 102, the arrayed waveguide 103, the second slab waveguide 104, and the second input / output waveguide 105. The loss of the light wave that passes once each is 2 dB. Here, the case of | φ | min = 0 ° corresponds to the configuration of the conventional athermal AWG, and the case of | φ | min = 4, 5, 6 ° is a configuration example of the present invention. As shown in FIG. 4, in the conventional configuration, the return loss or directionality is 36 dB, whereas in the present invention, the angles φ are all φ> 0, that is, | φ | min> 0. The quantity or direction is improved. For example, it is 43 dB at | φ | min = 4 degrees, 51 dB at | φ | min = 5 degrees, and 63 dB at | φ | min = 6 degrees. Therefore, according to the present invention, it is possible to provide an optical wavelength multiplexing / demultiplexing circuit that realizes an athermal AWG having excellent reflection characteristics and satisfies the reflection characteristic specifications required in the WDM transmission system.

[Second Embodiment]
An athermal AWG type optical wavelength multiplexing / demultiplexing circuit according to a second embodiment of the present invention will be described. The configuration of the athermal AWG of the present embodiment is the same as that shown in FIG. The arrayed waveguide 103 is designed to become longer by a certain amount ΔL sequentially, and accordingly, the length by which the light wave passing through each arrayed waveguide is divided by the groove 106 is an amount ΔL ′ proportional to ΔL. It has a shape that becomes longer gradually. Each waveguide is a silica-based glass waveguide having a relative refractive index difference of 1.5% and a core thickness of 4.5 μm, and the core width of the input / output waveguide and the arrayed waveguide is 4.5 μm. The circuit has characteristics of 40 wavelength channels and a wavelength channel spacing of 0.8 nm (100 GHz). The number of arrayed waveguides is 150, ΔL is about 30 μm, and ΔL ′ is about 1 μm.

  FIG. 5 is an enlarged plan view showing the first slab waveguide 102 and the vicinity thereof in the second embodiment. In the present embodiment, the groove is divided into six portions 106A to 106F, each groove has an equal width with respect to the traveling direction of the light wave, and the width of the waveguide left between the grooves is constant. Are arranged as follows. Here, the width of the waveguide left between the grooves is 30 μm. In the athermal AWG of this embodiment, the angles φ formed by the interfaces of the grooves 106A to 106F with respect to the axis perpendicular to the traveling direction of the light wave propagating from the arrayed waveguide 103 are all φ> 0. Features.

  Here, the absolute value of the angle φ described above is expressed as the minimum value | φ | min. FIG. 6 shows the distribution of φ at each groove interface when it is designed so that | φ | min = 4 degrees. It can be seen that | φ | = | φ | min at the interface (1) of the groove 106A, and φ> 4 degrees at all interfaces. In this embodiment, when | φ | min = 0, 4, 5, 6 degrees, the coupling efficiency of the light wave reflected at the groove interface to the arrayed waveguide 103 and the reflection of the athermal AWG under the same conditions The amount of attenuation or directivity is exactly the same as in FIG. However, the amount of Fresnel reflection at the groove interface is assumed to be −31 dB, and the first slab waveguide 102, the arrayed waveguide 103, the second slab waveguide 104, and the second input / output waveguide 105 are each once. The loss of the wavelength of light passing through is assumed to be 2 dB. As shown in FIG. 4, in the conventional configuration, the return loss or directionality is 36 dB, whereas in the present invention, the angles φ are all φ> 0, that is, | φ | min> 0. The quantity or direction is improved. For example, it is 43 dB at | φ | min = 4 degrees, 51 dB at | φ | min = 5 degrees, and 63 dB at | φ | min = 6 degrees. Therefore, according to the present invention, it is possible to provide an optical wavelength multiplexing / demultiplexing circuit that realizes an athermal AWG having excellent reflection characteristics and satisfies the reflection characteristic specifications required in the WDM transmission system.

[Third Embodiment]
An athermal AWG type optical wavelength multiplexing / demultiplexing circuit according to a third embodiment of the present invention will be described. The configuration of the athermal AWG of the present embodiment is the same as that shown in FIG. The arrayed waveguide 103 is designed to be sequentially longer by a certain amount ΔL, and accordingly, the length by which the light wave passing through each arrayed waveguide is divided by the groove 106 is an amount ΔL ′ proportional to ΔL. It has a shape that becomes longer gradually. Each waveguide is a silica glass waveguide having a relative refractive index difference of 1.5% and a core thickness of 4.5 μm, and the core width of the input / output waveguide and the arrayed waveguide is 4.5 μm. The circuit has characteristics of 40 wavelength channels and a wavelength channel spacing of 0.8 nm (100 GHz). The number of arrayed waveguides is 150, ΔL is about 30 μm, and ΔL ′ is about 1 μm.

  FIG. 7 is an enlarged plan view showing the first slab waveguide 102 and the vicinity thereof in the third embodiment. In this embodiment, the groove is divided into six portions 106A to 106F, and the width of the waveguide left between the grooves is constant, and the groove located at the end is arranged so that the groove width is narrower. Yes. Here, the width of the waveguide left between the grooves is 30 μm. In the athermal AWG of this embodiment, the angles φ formed by the interfaces of the grooves 106A to 106F with respect to the axis perpendicular to the traveling direction of the light wave propagating from the arrayed waveguide 103 are all φ> 0. Features.

  Here, the minimum absolute value of the angle φ is represented by | φ | min. FIG. 8 shows the distribution of φ at each groove interface when it is designed so that | φ | min = 4 degrees. It can be seen that | φ | = | φ | min at the interface (1) of the groove 106A, and φ> 4 degrees at all interfaces. In this embodiment, when | φ | min = 0, 4, 5, 6 degrees, the coupling efficiency of the light wave reflected at the groove interface to the arrayed waveguide 103 and the reflection of the athermal AWG under the same conditions The amount of attenuation or directivity is exactly the same as in FIG. However, the amount of Fresnel reflection at the groove interface is assumed to be −31 dB, and the first slab waveguide 102, the arrayed waveguide 103, the second slab waveguide 104, and the second input / output waveguide 105 are each once. The loss of the wavelength of light passing through is assumed to be 2 dB. As shown in FIG. 4, in the conventional configuration, the return loss or directionality is 36 dB, whereas in the present invention, the angles φ are all φ> 0, that is, | φ | min> 0. The quantity or direction is improved. For example, it is 43 dB at | φ | min = 4 degrees, 51 dB at | φ | min = 5 degrees, and 63 dB at | φ | min = 6 degrees. Therefore, it is possible to provide an optical wavelength multiplexing / demultiplexing circuit that realizes an athermal AWG excellent in reflection characteristics according to the present invention and satisfies the reflection characteristic specifications required in the WDM transmission system.

[Summary]
From the above three embodiments, it has been confirmed that the return loss or the directivity is improved in the optical wavelength multiplexing / demultiplexing circuit of the present invention as compared with the conventional example. As a result, according to the present invention, it is possible to obtain a wavelength multiplexing / demultiplexing circuit having excellent reflection characteristics.

  In the present invention, the minimum value | φ | min of the absolute value of the inclination angle φ of each groove interface is preferably 4 degrees or more. If | φ | ≧ 4 degrees, the coupling loss of the reflected light wave with the arrayed waveguide is 10 dB or more, and the reflection attenuation amount and directionality of the optical wavelength multiplexing / demultiplexing circuit are the attenuation attenuation at the groove interface. This is because at least 10 dB should be better than the amount, and it is considered that most reflection characteristic specifications can be satisfied. However, when extremely excellent reflection characteristic specifications are required, | φ | min is more preferably 6 degrees or more. If | φ | ≧ 6 degrees, the coupling loss of the reflected light wave with the arrayed waveguide becomes 30 dB or more, and the reflection attenuation amount and the directivity of the optical wavelength multiplexing / demultiplexing circuit are the attenuation attenuation at the groove interface. This is because it is considered that an extremely excellent reflection characteristic can be obtained because at least 30 dB should be better than the amount.

  On the other hand, | φ | min is particularly preferably 30 ° or less. If | φ | ≦ 30 degrees, the coupling loss of the reflected light wave with the arrayed waveguide is 50 dB or more, and the reflection characteristics of the optical wavelength multiplexing / demultiplexing circuit are sufficiently good. Further, if | φ | min is designed to be larger than necessary, the transmission characteristics of the optical wavelength multiplexing / demultiplexing circuit may be deteriorated.

  In all the embodiments, the configuration in which the groove is formed in the first slab waveguide and the temperature compensation material is filled is shown. However, the scope of the present invention is not limited to this configuration, and the groove is formed in the second slab waveguide. The same effect can be obtained in the configuration formed in the slab waveguide and the configuration formed in both the first and second slab waveguides.

  In all the embodiments, the relative refractive index difference, the core width, and the core thickness of the waveguide are limited to specific values, but the scope of application of the present invention is not limited to these values.

  In all the embodiments, the design parameter of the AWG is limited to a specific value, but the scope of application of the present invention is not limited to this parameter.

  In all the embodiments, the number of groove divisions is limited to a specific value, but the scope of application of the present invention is not limited to this number.

  In all the embodiments, the case where φ> 0 is shown at all the groove interfaces, but the scope of application of the present invention is not limited to this condition, and is the case where φ <0 at all the groove interfaces. The effect can be obtained similarly. The boundary line of the temperature compensation material only needs to be inclined at a finite angle in the same direction with respect to the axis perpendicular to the traveling direction of the light wave.

  In all the embodiments, a silicone resin is used as the temperature compensation material. However, the scope of the present invention is not limited to this material, and the refractive index temperature dependency is different from the effective refractive index temperature dependency of the waveguide. In the athermal AWG to which the material having the above is applied, the same effect can be obtained. As the temperature compensation material, use of an optical resin such as an epoxy resin or a fluororesin can be considered.

  In all the embodiments, a form in which the temperature compensation material is filled in the groove formed on the slab waveguide is shown. However, the scope of the present invention is not limited to this form, and the slab waveguide is divided. Thus, the same effect can be obtained in all athermal AWGs in which the temperature compensation material is inserted between them.

It is a top view which shows the structure of the optical wavelength multiplexing / demultiplexing circuit which concerns on the 1st, 2nd and 3rd embodiment of this invention. FIG. 2 is an enlarged plan view showing a groove 106 in FIG. 1 and its vicinity in the optical wavelength multiplexing / demultiplexing circuit according to the first embodiment of the present invention. In the optical wavelength multiplexing / demultiplexing circuit according to the first embodiment of the present invention, it is a diagram showing the distribution of φ at each groove interface when | φ | min = 4 degrees. In the optical wavelength multiplexing / demultiplexing circuit according to the first embodiment of the present invention, the coupling efficiency of the light wave reflected at the groove interface to the arrayed waveguide 103 when | φ | min = 0, 4, 5, 6 degrees FIG. 5 is a diagram showing a return loss amount or directivity of a circuit under the same conditions. FIG. 5 is an enlarged plan view showing a groove 106 in FIG. 1 and its vicinity in an optical wavelength multiplexing / demultiplexing circuit according to a second embodiment of the present invention. In the optical wavelength multiplexing / demultiplexing circuit according to the second embodiment of the present invention, it is a diagram showing the distribution of φ at each groove interface when | φ | min = 4 degrees. FIG. 7 is an enlarged plan view showing a groove 106 and its vicinity in FIG. 1 in an optical wavelength multiplexing / demultiplexing circuit according to a third embodiment of the present invention. In the optical wavelength multiplexing / demultiplexing circuit according to the third embodiment of the present invention, it is a diagram showing the distribution of φ at each groove interface when | φ | min = 4 degrees. (A) is a top view which shows the structure of the athermal AWG of the type which forms a groove | channel in the 1st slab waveguide in a prior art, (B) is the type which forms a groove | channel in a 2nd slab waveguide. It is a top view which shows the structure of this athermal AWG, (C) is a top view which shows the structure of the athermal AWG of the type which forms a groove | channel in both slab waveguides. It is sectional drawing along the XX line of the athermal AWG of FIG. 9 (A). It is a figure which shows the temperature dependence of the effective refractive index of the silica type glass waveguide which comprises AWG, and the temperature dependence of the refractive index of a temperature compensation material. It is a figure which shows the calculation result of the Fresnel reflection which arises in the interface of the waveguide of FIG. 11, and optical resin. It is the figure which expanded the connection part of the 1st slab waveguide 902 and the array waveguide 903 in the athermal AWG of FIG. 9 (A). It is a figure which shows the relationship between the coupling efficiency of the plane wave which propagates a slab waveguide to the arrayed waveguide, and inclination (theta) of a plane wave. (A) shows a conventional athermal AWG in which grooves are formed in the first slab waveguide. Each groove has an equal width with respect to the traveling direction of the light wave, and the interval between the center lines of the grooves is constant. FIG. 6B is a diagram showing a configuration in which a plurality of divided grooves are arranged, and FIG. 5B is a diagram illustrating an athermal AWG of the type in which grooves are formed in a first slab waveguide in the prior art. It is a figure which shows what has arrange | positioned the groove | channel divided | segmented into several so that the width | variety of the waveguide left between each groove | channel may be constant, (C) is a 1st slab in a prior art. In a type of athermal AWG in which grooves are formed in the waveguide, a plurality of divided grooves are arranged so that the width of the waveguide left between the grooves is constant and the groove width is narrower toward the groove located at the end. FIG. (A) to (C) are inclinations φ of the interfaces of the grooves 906A to 906F in the arrangements of FIGS. 15A to 15C with respect to the light waves propagating from the arrayed waveguide 903, and the light waves reflected at the interfaces. FIG. 8 is a diagram illustrating coupling efficiency when coupled to the arrayed waveguide 903 again.

Explanation of symbols

107, 907 Wavelength multiplexing / demultiplexing circuit 101, 901 First input / output waveguide 102, 902 First slab waveguide 103, 903 Array waveguide 104, 904 Second slab waveguide 105, 905 Second input / output Waveguide 106, 906 Groove 908 Silicon substrate 909 Waveguide core 910 Clad

Claims (6)

An arrayed waveguide having waveguides that are sequentially lengthened with a predetermined optical path length difference;
A first slab waveguide and a second slab waveguide connected to both ends of the arrayed waveguide;
A first input / output waveguide connected to the first slab waveguide;
An arrayed waveguide diffraction grating type wavelength multiplexing / demultiplexing circuit comprising a second input / output waveguide connected to the second slab waveguide,
At least one of the first slab waveguide and the second slab waveguide is provided with a temperature compensation material that cancels out the optical path length difference caused by the temperature change in the arrayed waveguide so as to cross the traveling direction of the light wave. And
In the surface of the slab waveguide in which the temperature compensation material is arranged, the boundary line of the temperature compensation material is all inclined at a finite angle in the same direction with respect to an axis perpendicular to the traveling direction of the light wave. Optical wavelength multiplexing / demultiplexing circuit. An arrayed waveguide having waveguides that are sequentially lengthened with a predetermined optical path length difference;
A first slab waveguide and a second slab waveguide connected to both ends of the arrayed waveguide;
A first input / output waveguide connected to the first slab waveguide;
An arrayed waveguide diffraction grating type wavelength multiplexing / demultiplexing circuit including a second input / output waveguide connected to the second slab waveguide,
At least one of the first slab waveguide and the second slab waveguide is provided with a groove that intersects the traveling direction of the light wave and divides the waveguide,
The groove is filled with a temperature compensation material having a refractive index temperature coefficient different from the temperature coefficient of the effective refractive index of the slab waveguide in which the groove is disposed, and an optical path length difference caused by a temperature change in the arrayed waveguide. The change is offset,
In the slab waveguide surface in which the groove is disposed, the boundary line of the groove is inclined at a finite angle in the same direction with respect to an axis perpendicular to the traveling direction of the light wave. Demultiplexer circuit.   3. The optical wavelength multiplexing / demultiplexing circuit according to claim 2, wherein the groove is composed of a plurality of grooves arranged in the traveling direction of the light wave. The arrayed waveguide, the first slab waveguide and the second slab waveguide, and the first input / output waveguide and the second input / output waveguide are made of silica glass,
The optical wavelength multiplexing / demultiplexing circuit according to claim 2 or 3, wherein the temperature compensation material filled in the groove is an optical resin.   5. The optical wavelength multiplexing / demultiplexing circuit according to claim 1, wherein the finite angle inclination is 4 degrees or more.   The optical wavelength multiplexing / demultiplexing circuit according to claim 5, wherein the finite angle inclination is 6 degrees or more.

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