JP5751008B2 - Optical multiplexer / demultiplexer and optical multiplexing / demultiplexing method - Google Patents

Description

  The present invention relates to an optical technique, and more particularly to an optical multiplexer / demultiplexer and an optical multiplexing / demultiplexing method for multiplexing or demultiplexing light.

  Conventionally, there has been known a spot size conversion element that converts a spot size by changing the cross-sectional shape of the optical waveguide in order to reduce the coupling loss between the semiconductor optical waveguide and the optical fiber whose spot size is reduced to the submicron order. (For example, Patent Document 1).

JP-A-5-249331

  However, in the conventional spot size conversion element disclosed in Patent Document 1, in order to prevent high-order waveguide modes other than the optical fundamental waveguide mode from being excited, the spot size is gently converted to reduce the light Since the length of the waveguide becomes long, for example, when the optical multiplexer / demultiplexer integrated on the semiconductor substrate is applied to the optical waveguide, the size of the entire device is reduced even though the optical multiplexer / demultiplexer is small. There was a problem of becoming larger. In addition, since the spot size on the input side of the conventional spot size conversion element is as small as submicron, the tolerance of the coupling efficiency against the positional deviation between the optical waveguide of the optical multiplexer / demultiplexer and the input side of the spot size conversion element is also small. There was also a point.

  The present invention has been made to solve the above-described problems. For example, in an integrated small-sized optical multiplexer / demultiplexer, an external size is not increased as in the conventional spot size conversion element. An object of the present invention is to improve the optical coupling efficiency with the optical element and to improve the tolerance of the coupling efficiency with respect to displacement.

The optical multiplexer / demultiplexer according to the present invention includes an optical multiplexer / demultiplexer that multiplexes light having different wavelengths into wavelength-multiplexed light or demultiplexes wavelength-multiplexed light into light having different wavelengths. A plurality of optical elements that are optically connected between a plurality of optical elements and the optical multiplexing / demultiplexing unit, and have a length corresponding to each of the different wavelengths, and the plurality of lights are respectively guided in a multimode. The wavelength multiplexed light is optically connected between a mode optical waveguide, a single optical element that propagates light in a single mode, and the optical multiplexing / demultiplexing unit, and has a length corresponding to the different wavelengths. And a multimode optical waveguide to be guided.

  According to the present invention, in the optical multiplexer / demultiplexer, the tolerance of the coupling efficiency against the positional deviation can be improved without increasing the size.

1 is a block diagram showing an optical multiplexer / demultiplexer according to Embodiment 1 of the present invention. Explanatory drawing for demonstrating the optical multiplexer / demultiplexer by Embodiment 1 of this invention Explanatory drawing for demonstrating the optical multiplexer / demultiplexer by Embodiment 1 of this invention Explanatory drawing for demonstrating the optical multiplexer / demultiplexer by Embodiment 1 of this invention Configuration diagram showing an optical multiplexer / demultiplexer according to Embodiment 2 of the present invention Configuration diagram showing an optical multiplexer / demultiplexer according to Embodiment 3 of the present invention Configuration diagram showing an optical multiplexer / demultiplexer according to Embodiment 4 of the present invention

Embodiment 1 FIG.
1 is a block diagram showing an optical multiplexer / demultiplexer according to Embodiment 1 of the present invention. In each figure, the same numerals indicate the same or corresponding parts. In FIG. 1, this optical multiplexer / demultiplexer is connected to a semiconductor substrate 1 as the same substrate, multimode optical waveguides 101 to 104 formed on the semiconductor substrate 1, and multimode optical waveguides 101 to 104. A slab optical waveguide 11, a reflective grating 12 formed on the end face of the slab optical waveguide 11, and connected to the slab optical waveguide 11 and optically coupled to the incident multimode optical waveguides 101 to 104 via the reflective grating 12. The multimode optical waveguide 105 is configured.

  In FIG. 1, light emitting elements 21 to 24 as a plurality of optical elements that are optically coupled to multimode optical waveguides 101 to 104, respectively, and emit a plurality of lights having mutually different wavelengths on a semiconductor substrate 1. Is formed. An optical lens 31 for condensing the light emitted from the multimode optical waveguide 105 and a single mode optical fiber 32 as one optical element to which the light condensed by the optical lens 31 is coupled are provided. ing.

  In FIG. 1, the propagation paths 41-44 in the slab optical waveguide 11 of each light radiate | emitted from the light emitting elements 21-24 are shown notionally. Actually, the light in the slab waveguide spreads in a fan shape and propagates, and when reflected by the grating, this time it propagates while converging in a fan shape, but the propagation paths 41 to 44 are representative optical paths. It is extracted and shown conceptually.

The semiconductor substrate 1 is a substrate made of Si as a constituent material, for example. The multi-mode optical waveguides 101 to 105 and the slab optical waveguide 11 are formed on a semiconductor substrate 1 as a three-layer structure (not shown) with a single-layer core made of Si as a constituent material, and the core sandwiched in the vertical direction. is one having a cladding of two layers as a constituent material of low SiO _2, so-called, is configured as a PLC (Planar Lightwave Circuit).

  In the multimode optical waveguides 101 to 105 and the slab optical waveguide 11, light propagates in the 0th-order waveguide mode, that is, in the single mode because the core thickness is thin in the direction perpendicular to the layer due to the above-described three-layer structure. In the direction horizontal to the layer, since the core width is wide, light propagates in a higher-order waveguide mode in addition to the 0th-order waveguide mode, that is, in a multimode.

  As shown in the enlarged view of FIG. 1, the reflective grating 12 has a sawtooth diffraction grating structure formed on the concave side surface of the slab optical waveguide 11, and the wavelength and reflection defined by the structural parameters are as follows. The light propagating through the slab optical waveguide 11 at an angle is reflected by diffraction. The slab optical waveguide 11 and the reflective grating 12 constitute an optical multiplexing / demultiplexing unit.

  The light emitting elements 21 to 24 are, for example, semiconductor lasers having InGaAsP / InP compound semiconductor mixed crystals as constituent materials, that is, LDs (Laser Diodes), and have wavelengths of 1.295 μm, 1.300 μm, 1.305 μm, Laser light of 1.3 μm wavelength band of 1.310 μm is emitted and output. Each wavelength corresponds to each reflection wavelength of the reflective grating 12.

  Next, the operation will be described. In FIG. 1, each light emitted from the light emitting elements 21 to 24 enters the multimode optical waveguides 101 to 104, respectively. Each light as a plurality of lights having different wavelengths guided in the multimode through the multimode optical waveguides 101 to 104 enters the slab optical waveguide 11.

  When each light incident on the slab optical waveguide 11 is reflected by the reflection type grating 12, by appropriately setting the structural parameters of the reflection type grating 12, four lights having mutually different wavelengths are transmitted via the propagation paths 41 to 44. It becomes possible to condense at the same position. By arranging the end portion of the multimode optical waveguide 105 at this condensing point, light from the propagation paths 41 to 44 in the slab optical waveguide 11 is made incident on the multimode optical waveguide 105. The wavelength multiplexed light that is guided in the multimode through the multimode optical waveguide 105 and emitted from the end face thereof is condensed by the optical lens 31 and enters the end face of the single mode optical fiber 32.

  Based on the above operation principle, the optical multiplexer / demultiplexer according to the first embodiment multiplexes four lights as a plurality of lights having different wavelengths inputted from the light emitting elements 21 to 24 as a plurality of optical elements. The combined wavelength multiplexed light can be output to a single mode optical fiber 32 as one optical element.

Here, in Embodiment 1, the length z _m of the multimode optical waveguide m (where m = 101 to 104) is set so as to satisfy Expression (1).

However, in the formula (1), k _m is the wave number in vacuum of the light propagating multimode optical guide in waveguides m, respectively, is expressed as 2 [pi / lambda _m using the wavelength lambda _m in vacuum. n _m is the refractive index at a wave number k _m of the core of the multimode optical waveguide m, W is the average value of the virtual core width including up evanescent component of Zenshirubeha mode, N is the is a natural number .

Similarly, in the first embodiment, the length z ₁₀₅ of the multimode optical waveguide 105 is set so as to satisfy Expression (2).

However, in the formula _{(2), k ave} is the average value of the wave number _{k m} in vacuum of the light emitted from each light emitting element 21 to 24. n _ave is the refractive index at the wave number k _ave of the core of the multimode optical waveguide 105.

  At this time, when the length of the multimode optical waveguides 101 to 104 satisfies the formula (1) and the length of the multimode optical waveguide 105 satisfies the formula (2), the light emitting elements 21 to 24 and the multimode light guide The coupling tolerance due to the positional deviation with respect to the waveguides 101 to 104, that is, the allowable positional deviation between the light emitting element and the incident optical waveguide with respect to the optical coupling is improved.

  In the following, the operating principle for improving the coupling tolerance will be described. The electromagnetic field distribution of the light incident on the multi-mode optical waveguide is expanded to the next guided mode and expressed by Equation (3).

Where φ _i (x, y) is the electromagnetic field distribution of the _i- th waveguide mode, β _i is the propagation constant in the z direction of the _i- th waveguide mode, a _i is the amplitude coefficient of the i-th waveguide mode, and θ _i is This is the initial phase of the i-th waveguide mode. The z direction is the light propagation direction, and the x direction is the cross-sectional direction of the optical waveguide. For simplicity, a two-dimensional system is assumed here.

On the other hand, the relationship between the propagation constant β _{i in} the propagation direction and the wave number k _{x in} the cross-sectional direction of the optical waveguide is expressed by Expression (4).

However, _{k 0} is the wave number in vacuum of the light propagating in the multimode optical waveguide, respectively corresponding to the multi-mode optical waveguide 101 to 104 in _k m (m = _101~104), the multi-mode optical waveguide 105 Then, it corresponds to k _ave . n ₀ is the core refractive index of the multimode optical waveguide, which corresponds to n _m (m = 101 to 104) in the multimode optical waveguides 101 to 104, and corresponds to n _ave in the multimode optical waveguide 105, respectively.

In addition, since the effective optical waveguide width W including the evanescent component is used and the wave number k _x = π (i + 1) / W at the mode order i, the propagation constant β _i in the propagation direction is obtained from the equation (4). It is represented by Formula (5). Note that Taylor expansion is used for the transformation from the upper equation to the lower equation in Equation (5), and higher-order terms are omitted.

  From equations (3) and (5), the electromagnetic field distribution of light when propagating through the multimode optical waveguide by the distance L is expressed by equation (6).

  In Formula (6), if all the phase differences of each mode are integer multiples of 2π, the phase relationship of all modes is the same as that at the time of incidence, and the same light distribution as the incident light is present in the multimode optical waveguide. Appear. The condition of the length L at that time is expressed by Expression (7).

  Here, i and J are integers of 0 or more, and M is an arbitrary integer. Expression (7) is a condition for the same pattern as the incident mode to appear. However, since a single-peak pattern is not a problem, a condition that is symmetrical to the incident mode may be used. The conditions at this time are that the phase differences of each mode are not all 2π × M, but the phase differences between the odd function mode (i is an even number) and the even function mode (i is an odd number) are all 2π × M, L may be determined so that the phase differences between the odd function mode and the even function mode are all 2π × M + π, which is expressed by Expression (8).

Thus, when the length L of the multimode optical waveguide satisfies the equation (8), the light distribution on the incident end surface is reproduced on the output end surface of the multimode optical waveguide. Note that L and _{z m,} the _{k 0} and _{k m,} if the _{n 0} and _{n m,} equation (8) is the formula (1), and the L and _{z 105,} the _{k 0} and _{k ave, n 0} Is n _ave , Equation (8) becomes Equation (2).

  Therefore, when the multimode optical waveguides 101 to 104 satisfy the expression (1), when each light emitted from the light emitting elements 21 to 24 is unimodal, it is output from the multimode optical waveguides 101 to 104 to be slab light. The light incident on the waveguide 11 is also unimodal. When the light emitting elements 21 to 24 and the multimode optical waveguides 101 to 104 are displaced from each other, the eccentricity of the incident light with respect to the multimode optical waveguides 101 to 104 is also reproduced when entering the slab optical waveguide 11.

  At this time, if the incident light to the slab optical waveguide 11 is unimodal, the light emitted from the slab optical waveguide 11 to the multimode optical waveguide 105 is also unimodal. Thereby, in the multimode optical waveguide 105, the unimodal light of each wavelength emitted from the light emitting elements 21 to 24 preserves the eccentricity between the light emitting elements 21 to 24 and the multimode optical waveguides 101 to 104. Incident at.

  When the multimode optical waveguide 105 satisfies the expression (2), the light distribution at the incident position is reproduced at the emission position, as in the multimode optical waveguides 101 to 104. The same phenomenon occurs for this. That is, from the multi-mode optical waveguide 105, the light-emitting elements 21 to 24 and the multi-mode optical waveguides 101 to 104 are converted into wavelength-multiplexed light from the unimodal light beams emitted from the light-emitting elements 21 to 24. It is emitted while preserving the eccentricity.

  Usually, when a single mode optical waveguide formed on a semiconductor substrate and a light emitting element are directly optically coupled, the coupling efficiency is about -3 dB when the amount of positional deviation between them is about 0.5 μm. On the other hand, when a multi-mode optical waveguide is used, for example, when the optical waveguide width is 15 μm, the light of the light emitting element is incident on the multi-mode optical waveguide with almost no loss even when the positional deviation between them is about 10 μm.

  In the case of the first embodiment, the unimodality and the positional deviation in the distribution of light incident on the multimode optical waveguides 101 to 104 can be reproduced at the emission position of the multimode optical waveguide 105. When the light emitted from the multimode optical waveguide 105 is collected by the optical lens 31 and enters the single mode optical fiber 32, if the unimodality is ensured in this way, the emission point position shift is about 10 μm. The coupling efficiency is about -3 dB. Thus, the allowable positional deviation amount between the light emitting elements 21 to 24 and the optical waveguides 101 to 104 is synonymous with about 10 μm, and the coupling tolerance is improved.

  Next, calculation examples will be described. 2 to 4 are explanatory diagrams for explaining the optical multiplexer / demultiplexer according to Embodiment 1 of the present invention. When the length of the multimode optical waveguide satisfies the equation (8), the distribution of incident light is shown in FIGS. It is a figure which shows the example of a calculation about the effect which reproduces in an output position. In each figure, the same numerals indicate the same or corresponding parts. In this calculation example, the multimode optical waveguide is a PLC optical waveguide having a core refractive index of 1.466, a cladding refractive index of 1.46, and a core width of 46.5 μm. The incident light is Gaussian having a wavelength of 1.300 μm and a full width at half maximum FWHM of 15.0 μm.

  FIG. 2 shows an electric field distribution of guided light by a propagation simulation. The vertical axis is the x direction, and the horizontal axis is the z direction. In FIG. 2, when the incident position of Gaussian coincides with the center position of the optical waveguide (indicated by “incident position 0 μm” in the figure, the same applies hereinafter), and when shifted by 5 μm, 7.5 μm, and 10 μm from the center position. The calculation was performed. Regardless of the incident position of Gaussian, a field pattern symmetrical to the incident light is reproduced at L = 9.68 mm, and the same field pattern as the incident light is reproduced at L = 19.36 mm.

  FIG. 3 shows the propagation distance dependence of the overlap integral between the field pattern of guided light and the field pattern of incident light. The vertical axis is the overlap integral, and the horizontal axis is the propagation distance. In FIG. 3, the symmetrically reproduced position is not clarified, but the position where the same field pattern as the incident light is reproduced is clearly shown as a peak, and the overlap is maximum at L = 19.36 mm at any incident position. 96%, that is, 4% (= −0.18 dB) with the minimum loss. This indicates that 96% of the incident light is reproduced at this particular position.

  FIG. 4 summarizes the effective refractive index of each guided wave mode calculated in the above-described propagation simulation and the propagation constants that can be calculated therefrom. In FIG. 4, when the effective optical waveguide width derived from the average value of the effective refractive indexes of all waveguide modes is substituted into the equation (8) as the core width W, the propagation length L at which the field pattern is the same as the incident light is 19. It can be seen that it is 34 mm, which is in good agreement with the results of the above-described propagation simulation.

  As described above, in the optical multiplexer / demultiplexer according to the first embodiment of the present invention, four light beams having different wavelengths input from the light emitting elements 21 to 24 are converted into a multimode optical waveguide having a length of Expression (1). Each of the multimode optical waveguides 101 to 104 is guided in multimode, and is multiplexed by the slab optical waveguide 11 on which the reflective grating 12 is formed. The multiplexed wavelength multiplexed light is a multimode optical waveguide having a length of the formula (2). The light is guided in multimode by 105 and output to the single-mode optical fiber 32 through the optical lens 31. Accordingly, the optical coupling efficiency with the light emitting elements 21 to 24 can be improved without increasing the size including the multi-mode optical waveguides 101 to 105, and the tolerance of the coupling efficiency with respect to these positional shifts can be improved. There is an effect of being able to.

Embodiment 2. FIG.
As described above, the optical multiplexer / demultiplexer according to Embodiment 1 of the present invention has a coupling efficiency with respect to a positional deviation between the slab optical waveguide in which the reflective grating is formed and the light emitting element in the configuration for realizing the multiplexing function. However, the optical multiplexer / demultiplexer according to the second embodiment of the present invention is a modification of the first embodiment, and in the configuration for realizing the demultiplexing function, The tolerance of the coupling efficiency with respect to the positional deviation between the slab optical waveguide in which the reflective grating is formed and the light receiving element can be improved.

  FIG. 5 is a block diagram showing an optical multiplexer / demultiplexer according to Embodiment 2 of the present invention. In each figure, the same numerals indicate the same or corresponding parts. In FIG. 5, the configuration is the same as that of the optical multiplexer / demultiplexer according to the first embodiment of the present invention except that light receiving elements 21 a to 24 a as a plurality of optical elements are arranged instead of the light emitting elements 21 to 24. Yes, the description is omitted. Note that the propagation paths 41 to 44 conceptually indicate the propagation paths in the slab optical waveguide 11 of each light incident on the light receiving elements 21a to 24a. Needless to say, the length of the multimode optical waveguides 101 to 104 satisfies the formula (1), and the length of the multimode optical waveguide 105 satisfies the formula (2).

  The light receiving elements 21a to 24a are, for example, PDs (Photo-Diodes) composed of InGaAs / InP compound semiconductor mixed crystals, and have wavelengths of 1.295 μm, 1.300 μm, 1.305 μm, and 1.310 μm. Each of the laser beams in the 1.3 μm wavelength band is received, converted into an electrical signal, and output. Each wavelength corresponds to each reflection wavelength of the reflective grating 12.

  Next, the operation will be described. In FIG. 5, wavelength multiplexed light in which four lights having different wavelengths are multiplexed is emitted from the single mode optical fiber 32, condensed by the optical lens 31, and incident on the end face of the multimode optical waveguide 105. . The wavelength multiplexed light that has entered the multimode optical waveguide 105 propagates through the multimode optical waveguide 105 in multimode and enters the slab optical waveguide 11.

  Here, when the wavelength multiplexed light incident on the slab optical waveguide 11 is reflected by the reflective grating 12, the reflection angle at the reflective grating 12 is set for each wavelength by appropriately setting the structural parameters of the reflective grating 12. Are shifted to the different multimode optical waveguides 101 to 104 via the propagation paths 41 to 44 to realize the wavelength demultiplexing function. The four lights having different wavelengths propagated through the multimode optical waveguides 101 to 104 in the multimode are respectively incident on the light receiving elements 21a to 24a and received.

  Based on the above operation principle, the optical multiplexer / demultiplexer according to the second embodiment demultiplexes the wavelength multiplexed light input from the single mode optical fiber 32 as one optical element via the optical lens 31, and the demultiplexed signals are different from each other. Four lights as a plurality of lights having wavelengths can be output to the light receiving elements 21a to 24a as a plurality of optical elements, respectively.

  At this time, as in the first embodiment, the length of the multimode optical waveguides 101 to 104 satisfies the formula (1), and the length of the multimode optical waveguide 105 satisfies the formula (2). The coupling tolerance due to the positional deviation between the elements 21a to 24a and the multimode optical waveguides 101 to 104, that is, the allowable positional deviation between the light receiving element and the outgoing optical waveguide with respect to the optical coupling is improved.

  As described above, in the optical multiplexer / demultiplexer according to the second embodiment of the present invention, the wavelength multiplexed light input from the single mode optical fiber 32 through the optical lens 31 is converted into the multimode light having the length of the formula (2). The multi-mode wave is guided by the waveguide 105, demultiplexed by the slab optical waveguide 11 on which the reflective grating 12 is formed, and the demultiplexed four lights having different wavelengths are expressed by the multi-length of the formula (1). The optical waveguides 101 to 104 are respectively guided in multimode and output to the light receiving elements 21a to 24a. As a result, as in the first embodiment, the optical coupling efficiency with the light receiving elements 21a to 24a can be improved without increasing the size including the multimode optical waveguides 101 to 105, and coupling with respect to misalignment can be achieved. There is an effect that the tolerance of efficiency can be improved.

Embodiment 3 FIG.
As described above, the optical multiplexer / demultiplexer according to Embodiment 1 of the present invention has a coupling efficiency with respect to a positional deviation between the slab optical waveguide in which the reflective grating is formed and the light emitting element in the configuration for realizing the multiplexing function. However, the optical multiplexer / demultiplexer according to the third embodiment of the present invention has an AWG (Arrayed Waveguide Grating), a light emitting device, and a light emitting device in a configuration for realizing a multiplexing function. Thus, the tolerance of the coupling efficiency with respect to the positional deviation can be improved.

  FIG. 6 is a block diagram showing an optical multiplexer / demultiplexer according to Embodiment 2 of the present invention. In each figure, the same numerals indicate the same or corresponding parts. In FIG. 6, in place of the slab optical waveguide 11 and the reflective grating 12, the optical coupling according to the first embodiment of the present invention is configured except that a slab optical waveguide 11a, a slab optical waveguide 11b, and a single mode optical waveguide array 12a are arranged. The configuration is the same as that of the duplexer, and the description is omitted. The slab optical waveguides 11a and 11b and the single mode optical waveguide array 12a constitute an AWG as an optical multiplexing / demultiplexing unit. Note that the propagation paths 41 to 44 conceptually indicate the propagation paths in the slab optical waveguide 11a of each light emitted from the light emitting elements 21 to 24. Needless to say, the length of the multimode optical waveguides 101 to 104 satisfies the formula (1), and the length of the multimode optical waveguide 105 satisfies the formula (2).

Further, the multimode optical waveguides 101 to 105, the slab optical waveguides 11a and 11b, and the single mode optical waveguide array 12a are formed on a semiconductor substrate 1 as a three-layer structure (not shown) with a single-layer core made of Si as a constituent material. The core is sandwiched between upper and lower layers, and has a two-layer clad composed of SiO ₂ having a lower refractive index than that of the core, and is configured as a so-called PLC. In the single mode optical waveguide array 12a, a plurality of optical waveguides having a thin core thickness and a narrow core width capable of propagating only the 0th-order waveguide mode, that is, the single mode, are arranged in parallel in an array.

  In the slab optical waveguides 11a and 11b, due to the above-described three-layer structure, in the direction perpendicular to the layer, the core thickness is thin, so that light propagates in the 0th-order waveguide mode, that is, in single mode, and the direction is horizontal to the layer Then, since the core width is wide, light propagates in the higher-order waveguide mode in addition to the zero-order waveguide mode, that is, in multimode.

  Next, the operation will be described. In FIG. 6, each light emitted from the light emitting elements 21 to 24 enters the multimode optical waveguides 101 to 104, respectively. Four lights as a plurality of lights having different wavelengths guided through the multimode optical waveguides 101 to 104 in the multimode are incident on the slab optical waveguide 11a.

  The four lights incident on the slab optical waveguide 11a propagate while diffusing in the slab optical waveguide 11a, and reach the connection position with the single mode optical waveguide array 12a. At this time, since the incident points to the slab optical waveguide 11a are different in the propagation paths 41 to 44, the relationship of the initial phase of the single mode optical waveguide array 12a is different for each light.

  Here, by appropriately setting the lengths of the plurality of optical waveguides of the single mode optical waveguide array 12a, and making the phase relationship of the light incident on the slab optical waveguide 12b uniform for all the light, The multimode optical waveguide 105 can be coupled. Wavelength multiplexed light propagating through the multimode optical waveguide 105 in multimode and emitted from the end face thereof is collected by the optical lens 31 and enters the end face of the outgoing single mode optical fiber 32.

  Based on the above operation principle, the optical multiplexer / demultiplexer according to Embodiment 3 multiplexes four lights as a plurality of lights having different wavelengths inputted from the light emitting elements 21 to 24 as a plurality of optical elements. The combined wavelength multiplexed light can be output to the single mode optical fiber 32 as one optical element.

  At this time, as in the first embodiment, the length of the multimode optical waveguides 101 to 104 satisfies the formula (1), and the length of the multimode optical waveguide 105 satisfies the formula (2). The coupling tolerance due to the positional deviation between the elements 21 to 24 and the multimode optical waveguides 101 to 104, that is, the allowable positional deviation between the light emitting element and the incident optical waveguide with respect to the optical coupling is improved.

  As described above, in the optical multiplexer / demultiplexer according to the third embodiment of the present invention, four lights having different wavelengths input from the light emitting elements 21 to 24 are converted into a multimode optical waveguide having the length of the formula (1). Waveguides 101 to 104 are guided in multimode, multiplexed by AWG, and the multiplexed wavelength multiplexed light is guided in multimode by the multimode optical waveguide 105 having the length of the formula (2). Is output to the single mode optical fiber 32 via the. As a result, as in the first embodiment, the optical coupling efficiency with the light emitting elements 21 to 24 can be improved without increasing the size including the multimode optical waveguides 101 to 105, and the positional shift between them. There is an effect that the tolerance of the coupling efficiency with respect to can be improved.

Embodiment 4 FIG.
As described above, the optical multiplexer / demultiplexer according to Embodiment 3 of the present invention can improve the tolerance of the coupling efficiency against the positional deviation between the AWG and the light emitting element in the configuration for realizing the multiplexing function. However, the optical multiplexer / demultiplexer according to the fourth embodiment of the present invention is a modification of the third embodiment, and in the configuration for realizing the demultiplexing function, the optical multiplexer / demultiplexer is adapted to the positional deviation between the AWG and the light receiving element. It is intended to improve the tolerance of coupling efficiency.

  FIG. 7 is a block diagram showing an optical multiplexer / demultiplexer according to Embodiment 4 of the present invention. In each figure, the same numerals indicate the same or corresponding parts. In FIG. 7, the same configuration as that of the optical multiplexer / demultiplexer according to the third embodiment of the present invention is used except that light receiving elements 21a to 24a similar to those in the second embodiment are arranged instead of the light emitting elements 21 to 24. Therefore, the description is omitted. Note that the propagation paths 41 to 44 conceptually indicate the propagation paths in the slab optical waveguide 11 of each light incident on the light receiving elements 21a to 24a. Needless to say, the length of the multimode optical waveguides 101 to 104 satisfies the formula (1), and the length of the multimode optical waveguide 105 satisfies the formula (2).

  Next, the operation will be described. In FIG. 7, wavelength multiplexed light in which four lights having different wavelengths are multiplexed is emitted from the single mode optical fiber 32, collected by the optical lens 31, and incident on the end face of the multimode optical waveguide 105. . Then, by the same operation as in the third embodiment, the optical multiplexer / demultiplexer according to the fourth embodiment demultiplexes the wavelength multiplexed light input from the single mode optical fiber 32 as one optical element via the optical lens 31 by the AWG. Then, the demultiplexed four lights as a plurality of lights having different wavelengths can be output to the light receiving elements 21a to 24a as the plurality of optical elements, respectively.

  At this time, as in the first embodiment, the length of the multimode optical waveguides 101 to 104 satisfies the formula (1), and the length of the multimode optical waveguide 105 satisfies the formula (2). The coupling tolerance due to the positional deviation between the elements 21a to 24a and the multimode optical waveguides 101 to 104, that is, the allowable positional deviation between the light receiving element and the outgoing optical waveguide with respect to the optical coupling is improved.

  As described above, in the optical multiplexer / demultiplexer according to the fourth embodiment of the present invention, wavelength-division multiplexed light input from the single mode optical fiber 32 via the optical lens 31 is converted into multimode light having the length of Expression (2). Waves are guided in a multimode by the waveguide 105, demultiplexed by the AWG, and the demultiplexed four lights having different wavelengths are respectively multimoded by the multimode optical waveguides 101 to 104 having the length of the formula (1). The light is guided and output to the light receiving elements 21a to 24a. Accordingly, as in the third embodiment, the optical coupling efficiency with the light receiving elements 21a to 24a can be improved without increasing the size including the multimode optical waveguides 101 to 105, and the coupling with respect to the positional deviation can be achieved. There is an effect that the tolerance of efficiency can be improved.

  In the first to fourth embodiments, the configuration is not limited to the numerical values, shapes, materials, positional relationships, and the like as described above. For example, an example in which the number of different wavelengths, the number of optical elements, and the number of multi-mode optical waveguides on the input side is four is shown, but two or three may be used, or four or more. Also good. In addition, a plurality of optical elements, multi-mode optical waveguides, and optical multiplexing / demultiplexing units are preferably arranged on the semiconductor substrate 1 to facilitate manufacturing by position adjustment or the like, but are not limited thereto, and are not limited thereto. You may make it fix to.

In the above-described first to fourth embodiments, since the average value k _ave of the wavelength multiplexed light in equation (2) is used, the effect of improving the coupling tolerance can be enhanced, which is preferable. For example, a value corresponding to the wave number of the wavelength multiplexed light, such as the median value of the wave number range of the wavelength multiplexed light or the representative value of the wave number of the wavelength multiplexed light, may be used. Has an effect.

In the first to fourth embodiments described above, the multimode optical waveguides 101 to 105 are configured as PLCs using Si / SiO ₂ as a constituent material. However, the present invention is not limited to this. For example, A semiconductor material, dielectric material or polymer material such as SiN, SiON, GaAs compound semiconductor mixed crystal, InP compound semiconductor mixed crystal, LiNbO ₃ crystal or polyimide may be used as a constituent material, and the core refractive index. The numerical values of 1.466, clad refractive index 1.46, and core width 46.5 μm are not limited thereto.

Further, the slab optical waveguide 11 and the reflective grating 12 are shown as those configured as PLCs with Si / SiO ₂ as a constituent material. However, the present invention is not limited to this. For example, SiN, SiON, GaAs compound semiconductors are used. A semiconductor material, dielectric material or polymer material such as mixed crystal, InP-based compound semiconductor mixed crystal, LiNbO ₃ crystal or polyimide may be used as a constituent material. In short, since the spot size is small, its position Any optical multiplexing / demultiplexing unit having a small coupling efficiency tolerance against the shift can be applied as the first and second embodiments.

In addition, the slab optical waveguides 11a and 11b and the single mode optical waveguide array 12a have been configured as PLCs using Si / SiO ₂ as a constituent material. However, the present invention is not limited to this. For example, SiN, SiON, A semiconductor material, dielectric material or polymer material such as GaAs compound semiconductor mixed crystal, InP compound semiconductor mixed crystal, LiNbO ₃ crystal or polyimide may be used as a constituent material. In short, the spot size is small. Therefore, any optical multiplexing / demultiplexing unit that has a small coupling efficiency tolerance against the positional shift can be applied as the third and fourth embodiments.

  In addition, the light emitting elements 21 to 24 are not limited to the above-described configuration. For example, a 1.5 μm wavelength band, a solid-state laser, or the like may be used. In short, in the multiplexing / demultiplexing wavelength of the optical multiplexing / demultiplexing unit. Embodiments that emit light for realizing an optical system such as desired optical communication are applicable as the first and third embodiments.

  In addition, the light receiving elements 21a to 24a are not limited to the above-described configuration, and may be, for example, a 1.5 μm wavelength band or a 0.8 μm wavelength band, or a Ge semiconductor crystal, a Si semiconductor crystal, or the like. In short, what receives light for realizing an optical system such as desired optical communication at the multiplexing / demultiplexing wavelength of the optical multiplexing / demultiplexing unit is applicable as the second and fourth embodiments.

  In the first to fourth embodiments described above, the optical elements such as the light emitting elements 21 to 24 and the light receiving elements 21a to 24a are not limited to individual elements, but are integrated on, for example, one semiconductor substrate as the same substrate. It may be in the form. In this case, since all the optical elements have the same positional deviation from the multimode optical waveguides 101 to 104, there is an effect that the amount of eccentricity of the light in the multimode optical waveguide 105 can be made uniform. In particular, since the light emitting elements 21 to 24 are formed on the same substrate at equal intervals, the multimode optical waveguides 101 to 104 and the eccentric amounts of the respective lights emitted from the light emitting elements 21 to 24 all match. The single-peak positions appearing in the multimode optical waveguide 105 are all coincident, and there is an effect that the wavelength multiplexed light condensed by the optical lens 31 can be coupled to the single mode optical fiber 32 with high efficiency. If a semiconductor substrate on which a plurality of optical elements are formed is arranged on the semiconductor substrate 1, it is preferable that the manufacturing is facilitated by position adjustment or the like, but the present invention is not limited to this. The semiconductor substrate on which the optical waveguide is formed and the semiconductor substrate 1 on which the optical multiplexing / demultiplexing portion and the multimode optical waveguide are formed may be separately fixed.

  In the first to fourth embodiments described above, the optical element that inputs / outputs light to / from the multimode optical waveguides 101 to 104 is not limited to a light emitting element or a light receiving element, but is an optical fiber, for example. Alternatively, a combination of an optical lens and a single mode optical fiber, a single mode optical fiber alone, or a multimode optical fiber alone may be used. In this case, since all the constituent elements can be passive elements, there is an effect that the optical multiplexer / demultiplexer can be easily used.

  In the first to fourth embodiments, the optical element optically coupled to the multimode optical waveguide 105 is not limited to the combination of the optical lens 31 and the single mode optical fiber 32. Light may be directly emitted from the waveguide 105 to the single mode optical fiber 32, or a single multimode optical fiber may be used instead of the single mode optical fiber. Direct emission to the optical fiber has the effect of reducing the number of members and facilitating manufacturing. In particular, when a multi-mode optical fiber is used, the tolerance of the coupling efficiency with respect to misalignment is widened, so that the effect of facilitating the production is obtained.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 11, 11a, 11b Slab optical waveguide 12 Reflective grating 12a Single mode optical waveguide array 21-24 Light emitting element 21a-24a Light receiving element 31 Optical lens 32 Single mode optical fiber 101-105 Multimode optical waveguide

Claims (10)

A plurality of lights having different wavelengths are multiplexed into the wavelength multiplexed light, or the wavelength multiplexed light is split into a plurality of lights having different wavelengths;
A plurality of multimode light beams that are optically connected between a plurality of optical elements and the optical multiplexing / demultiplexing unit and have lengths corresponding to the different wavelengths, respectively, and the light beams are guided in multimodes. A waveguide,
Optically connected between one optical element in which light propagates in a single mode and the optical multiplexing / demultiplexing unit, and having a length corresponding to the different wavelengths, the wavelength multiplexed light is guided in a multimode. Two multimode optical waveguides;
An optical multiplexer / demultiplexer characterized by comprising:   2. The optical multiplexer / demultiplexer according to claim 1, wherein the one multimode optical waveguide has a length corresponding to an average value of wave numbers for the different wavelengths. When L is a length corresponding to each of the different wavelengths or a length corresponding to the different wavelengths, k ₀ is a wave number, n ₀ is a refractive index, W is a core width, and N is a natural number,
L = (2k ₀ n ₀ W ² / π) × N
The optical multiplexer / demultiplexer according to claim 1, wherein: The optical multiplexing / demultiplexing unit is
A slab optical waveguide optically connected between the plurality of multimode optical waveguides and the one multimode optical waveguide;
A reflection type formed on the side surface of the slab optical waveguide, in which a plurality of lights having different wavelengths are reflected by diffraction as wavelength multiplexed light, or a wavelength multiplexed light is reflected by diffraction as a plurality of lights having different wavelengths. The grating,
The optical multiplexer / demultiplexer according to claim 1, further comprising:   The optical multiplexer / demultiplexer according to claim 1, wherein the optical multiplexing / demultiplexing unit is an AWG (Arrayed Waveguide Grating).   2. The optical multiplexer / demultiplexer according to claim 1, wherein the optical multiplexing / demultiplexing unit, the plurality of multimode optical waveguides, and the one multimode optical waveguide are formed on the same substrate. The optical multiplexer / demultiplexer according to claim 1, wherein the plurality of optical elements are light emitting elements or light receiving elements, and the one optical element is a single mode optical fiber.   The optical multiplexer / demultiplexer according to claim 7, wherein the plurality of optical elements are formed on the same substrate.   The optical multiplexer / demultiplexer according to claim 1, wherein the plurality of optical elements and the one optical element are optical fibers. An optical multiplexing / demultiplexing step in which a plurality of lights having different wavelengths are multiplexed into the wavelength multiplexed light or the wavelength multiplexed light is split into a plurality of lights having different wavelengths;
A plurality of lights having different wavelengths combined in the optical multiplexing / demultiplexing step are guided in multimodes at lengths corresponding to the different wavelengths, or are mutually demultiplexed in the optical multiplexing / demultiplexing step. A plurality of multi-mode optical waveguide steps in which a plurality of lights having different wavelengths are guided in a multi-mode through a length corresponding to each of the different wavelengths;
One optical element in which wavelength multiplexed light combined from a plurality of lights having different wavelengths in the optical multiplexing / demultiplexing step is guided in a multimode for a length corresponding to the different wavelengths, and light is propagated in a single mode multiwavelength light demultiplexed into a plurality of light corresponding to a wavelength that is different for the each other with mutually different wavelengths at one input from the optical element and the optical demultiplexing step of light propagates in the output to Luke or single-mode One multimode optical waveguide step guided in multimode length;
An optical multiplexing / demultiplexing method comprising:

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