WO2018235200A1

WO2018235200A1 - Optical waveguide, optical circuit and semiconductor laser

Info

Publication number: WO2018235200A1
Application number: PCT/JP2017/022882
Authority: WO
Inventors: 敬太望月
Original assignee: 三菱電機株式会社
Priority date: 2017-06-21
Filing date: 2017-06-21
Publication date: 2018-12-27
Also published as: JPWO2018235200A1

Abstract

An optical waveguide (1) includes a core (12) through which light in a plurality of waveguide modes propagates between a first end face (13) and a second end face (14). When the width of the core in a second direction perpendicular to a first direction from the first end face toward the second end face is denoted by W, the height of the core in a third direction perpendicular to the first direction and the second direction is denoted by H, the refractive index of the core is denoted by n, and the wave number of the light propagating through the core is k0, the length of the core in the first direction falls within the range of 0.98-1.02 times the length of an integral multiple of 2k0nW2/π and an integral multiple of 2k0nH2/π.

Description

Optical waveguide, optical circuit and semiconductor laser

The present invention relates to an optical waveguide, an optical circuit, and a semiconductor laser for propagating light in a multimode.

In optical communication devices, techniques for integrating functional components on a semiconductor substrate are known. The functional component including the optical waveguide includes a reduction in light intensity, that is, a coupling efficiency due to optical coupling between the optical waveguide, the optical element that causes light to enter the optical waveguide, and the optical element that receives the light emitted from the optical waveguide. It is desirable that the decrease can be reduced. As the miniaturization or integration of the optical communication device is promoted, the loss of coupling efficiency due to a slight positional deviation between the optical waveguide and the optical element becomes remarkable.

In Patent Document 1, the optical multiplexer / demultiplexer, which is a functional component including an optical waveguide for propagating light in a multimode mode, relieves the tolerance of the positional deviation between the optical waveguide and the optical element in the direction parallel to the surface of the semiconductor substrate. The technology to make it happen is proposed. The width of the core of the optical waveguide in the direction parallel to the plane of the semiconductor substrate is expanded to allow light to propagate in multimode. The length of the optical waveguide is set such that the intensity pattern of each waveguide mode at the time of incidence to the optical waveguide is reproduced at the time of emission from the optical waveguide. When eccentricity occurs in the distribution of light at the incident end face of the optical waveguide, the distribution including the eccentricity is reproduced at the output end face of the optical waveguide. The optical multiplexer / demultiplexer can reduce the loss of coupling efficiency by correcting the eccentricity with the optical element that receives the light emitted from the optical waveguide.

JP, 2012-242654, A

In the technology of Patent Document 1, the height of the core of the optical waveguide in the direction perpendicular to the surface of the semiconductor substrate is set to propagate light in a single mode. In the direction perpendicular to the surface of the semiconductor substrate, it is difficult for the functional component to obtain high coupling efficiency because the positional deviation allowed between the optical waveguide and the optical element is extremely small.

The present invention is made in view of the above, and an object of the present invention is to obtain an optical waveguide that can realize high coupling efficiency in a functional component including the optical waveguide.

In order to solve the problems described above and to achieve the object, an optical waveguide according to the present invention comprises a first end face and a second end face, and a plurality of optical waveguides are provided between the first end face and the second end face. The core in which the light of the guided mode propagates. The width of the core in a second direction perpendicular to the first direction, which is a direction from the first end face to the second end face, is W, and in a third direction perpendicular to the first direction and the second direction Assuming that the height of the core is H, the refractive index of the core is n, and the wave number of light propagating through the core is k ₀ , the length of the core in the first direction is an integral multiple of 2k ₀ nW ² / π and 2k ₀ nH It is included in the range of 0.98 times to 1.02 times the length which is an integral multiple of ² / π.

The optical waveguide according to the present invention has an effect that high coupling efficiency can be realized in a functional component including the optical waveguide.

The figure which shows the structure of the optical circuit concerning Embodiment 1 of this invention. FIG. 6 is a diagram showing an example of electric field distribution of light by propagation simulation for the optical waveguide according to the first embodiment. The figure which shows the propagation distance dependence of the overlap integral of the electric field of the light which propagates the optical waveguide in Embodiment 1, and the electric field of incident light. The figure which shows the example of the effective refractive index in the core of the light of the waveguide mode of each order calculated by the propagation simulation shown in FIG. 2, and the propagation constant calculated from the effective refractive index The figure which shows the structure of the optical circuit concerning the modification 1 of Embodiment 1. The figure which shows the structure of the optical circuit concerning the modification 2 of Embodiment 1 The figure which shows the structure of the optical circuit concerning the modification 3 of Embodiment 1 The figure which shows the structure of the optical circuit concerning the modification 4 of Embodiment 1 The figure which shows the structure of the semiconductor laser concerning Embodiment 2 of this invention. FIG. 6 shows a configuration of a semiconductor laser according to a first modification of the second embodiment. FIG. 16 shows a configuration of a semiconductor laser according to a second modification of the second embodiment. A diagram showing a configuration of an optical multiplexer / demultiplexer as an optical circuit according to a third embodiment of the present invention The figure which expanded a part of reflection type grating shown in FIG. 12

Hereinafter, an optical waveguide, an optical circuit, and a semiconductor laser according to an embodiment of the present invention will be described in detail based on the drawings. The present invention is not limited by the embodiment.

Embodiment 1
FIG. 1 is a diagram showing the configuration of an optical circuit 10 according to a first embodiment of the present invention. The optical circuit 10 includes an optical waveguide 1, a light emitting element 2 which is a first optical element for causing light to be incident on the optical waveguide 1, and a condensing lens which is a second optical element for receiving light emitted from the optical waveguide 1. 3 and an optical fiber 4. The optical circuit 10 is a functional component that includes the optical waveguide 1.

The optical waveguide 1 is a multimode optical waveguide that propagates light of a plurality of guided modes. The optical waveguide 1 includes a semiconductor substrate 11, a columnar core 12 through which light propagates, and a cladding formed around the core 12. In FIG. 1, illustration of the clad is omitted. In one example, Si is used as the material of the core 12. As a material of the cladding, SiO ₂ which is a material having a refractive index lower than that of the core 12 is used. The light incident on the core 12 propagates in the core 12 by repeating total reflection at the interface between the core 12 and the cladding.

In one example, in the optical waveguide 1, the core 12 is disposed on the surface of the semiconductor substrate 11 which is a clad. In addition to this, the optical waveguide 1 may be provided with a lower cladding layer which is a cladding and an upper cladding layer. The lower cladding layer is provided between the semiconductor substrate 11 and the core 12. The upper cladding layer covers the core 12 on the lower cladding layer. The optical waveguide 1 may have a flat core 12, and the core 12 may be sandwiched between the lower cladding layer and the upper cladding layer. In FIG. 1, the lower cladding layer and the upper cladding layer are not shown.

The core 12 has a first end face 13 and a second end face 14 which are both ends of a light propagation path in the optical waveguide 1. In the core 12, light of a plurality of guided modes propagates between the first end face 13 and the second end face 14. An AR (Anti-Reflection) coating, which is an anti-reflection film, is applied to the first end face 13 and the second end face 14. In FIG. 1, the illustration of the AR coating is omitted.

The light emitting element 2 is a semiconductor laser. The light emitting element 2 causes the light 15 to be incident on the first end face 13. The condenser lens 3 converges the light 16 from the second end face 14 into the optical fiber 4. The optical fiber 4 propagates the light 16 incident from the condenser lens 3. The optical fiber 4 is a single mode optical fiber. The materials and shapes of the semiconductor substrate 11, the core 12, and the cladding of the optical waveguide 1 are not limited to those described in the first embodiment, and are arbitrary. The positional relationship among the optical waveguide 1, the light emitting element 2, the condensing lens 3, and the optical fiber 4 is not limited to that shown in FIG. 1 and is arbitrary.

In FIG. 1, the direction from the first end face 13 to the second end face 14 is a z direction which is a first direction. The z direction is parallel to the surface 17 of the semiconductor substrate 11 on which the core 12 is provided. Further, a direction perpendicular to the z direction and parallel to the surface 17 and indicated by an arrow in the drawing is taken as an x direction which is a second direction. A direction perpendicular to the z direction and the x direction and indicated by an arrow in the drawing is a y direction which is a third direction. The y direction is the direction perpendicular to the surface 17.

The width of the core 12 in the x direction is expanded compared to the case of a single mode optical waveguide that propagates light of a single guided mode, and light of a plurality of guided modes in the direction parallel to the plane 17 It is possible to propagate. Further, the height of the core 12 in the y direction is expanded as compared with the case of a single mode optical waveguide, and light of a plurality of waveguide modes can be propagated in the direction perpendicular to the surface 17.

In the first embodiment, the length L of the core 12 in the z direction satisfies the following equation (1).

In Equation (1), n is a parameter indicating the refractive index of the core 12. k ₀ is a parameter indicating the number of waves of light propagating through the core 12. In the first embodiment, k ₀ is the wave number in vacuum of the light emitted from the light emitting element 2. Assuming that the wavelength in vacuum is λ ₀ , k ₀ = 2π / λ ₀ holds. N is an arbitrary natural number.

In f (W ² , H ² ), it is assumed that x = W ² and y = H ² are substituted for a certain function f (x, y) having x and y as variables. The function f (x, y) represents the minimum value of Sx and Ty when Sx = Ty is satisfied, where S and T are arbitrary natural numbers. When x and y are integers, the value of the function f (x, y) is the least common multiple of x and y. Also, to give an example, when x = 0.5 and y = 0,2, when S = 2 and T = 5, Sx and Ty become minimum, and f (0.5, 0.2 ) = 1.0. When x = 1.2 and y = 1.8, Sx and Ty are minimum when S = 3 and T = 2, and f (1.2,1.8) = 3.6 .

Moreover, in Formula (1), W is a parameter which shows the width | variety of the core 12 in ax direction. H is a parameter indicating the height of the core 12 in the y direction. The width W is an effective width including a range in which an evanescent component of light propagating through the core 12 occurs. The width W is an average value of virtual widths including a range in which evanescent components of light of a plurality of guided modes occur in the x direction. The height H is an effective height including the range in which the evanescent component of the light propagating through the core 12 occurs. The height H is an average value of virtual widths including a range in which evanescent components of light of a plurality of guided modes occur in the y direction.

Equation (1) has a length L is, indicating that a _2k 0 nW ² / an integral multiple and _2k 0 nH ² / an integral multiple length of [pi of [pi. By satisfying the formula (1), the optical circuit 10 can reduce the decrease in coupling efficiency due to the positional deviation between the optical waveguide 1 and the light emitting element 2.

Next, the principle by which the decrease in coupling efficiency can be reduced by the optical waveguide 1 will be described. When light from the light emitting element 2 is incident on the first end face 13 of the optical waveguide 1, the electromagnetic field distribution φ (x, y, z) of the light is conducted for each order as shown in the following equation (2) Base expanded to wave mode.

In equation (2), φ _i (x, y) represents the electromagnetic field distribution of the guided mode of order i. β _i is the propagation coefficient in the z direction of the guided mode of order i. a _i is an amplitude coefficient of the guided mode of the order i. θ _i is a parameter indicating the initial phase of the guided mode of order i. j represents an imaginary unit.

The relationship between the propagation coefficient β in the z direction and the wave number k _x in the x direction is expressed as shown in the following equation (3).

When a width W indicating an effective width including a range in which an evanescent component occurs is used, the wave number k _x is π (i + 1) / W in the guided mode of the order i. The propagation coefficient β in the z direction in the guided mode of order i is expressed as shown in the following equation (4-1). Equation (4-2) is a variation of equation (4-1) using Taylor expansion. In the equation (4-2), higher order terms are omitted.

The electromagnetic field distribution φ (x, y, L) of the light having propagated the length L from the first end face 13 is obtained by substituting the equation (4-2) into the equation (2) above, and the following equation (5) It is expressed as shown in). The electromagnetic field distribution φ (x, y, L) represents the electromagnetic field distribution of light when propagating through the optical waveguide 1 by the length L.

In Formula (5), when all the phase differences of each waveguide mode are integral multiples of 2 (pi), the phase relationship of the light of all the waveguide modes becomes the same as the time of incidence to the 1st end face 13. FIG. The same light distribution as the incident light appears in the optical waveguide 1. The condition of the length L at that time is expressed as shown in the following equation (6).

In Formula (6), i and j are integers greater than or equal to 0, and M is an arbitrary integer. Expression (6) is a condition under which the distribution of the same pattern as the incident light appears. In the optical waveguide 1, a distribution of a pattern symmetrical to the incident light may appear. The phase difference of the light of each guided mode need not be 2π × M, and the odd function mode which is a guided mode when i is an even number and the even function which is a guided mode when i is an odd number All the phase differences between the modes should be 2π × M. Therefore, the length L may be determined so that all phase differences between the odd function mode and the even function mode are 2π × M + π. The length L is expressed as shown in the following equation (7).

When the length L of the optical waveguide 1 satisfies the equation (7), the distribution of light in the x direction of the first end face 13 is reproduced at the second end face 14. The wave equation can be considered in the y-direction as well as in the x-direction, since variable separation is possible. Using the height H which is the effective height including the range in which the evanescent component occurs, the length L is expressed as shown in the following equation (8).

Also in the case where the length L of the optical waveguide 1 is an integral multiple of the value represented by the equation (7), a pattern identical or symmetrical to the light distribution in the x direction of the first end surface 13 at the second end surface 14 Is reproduced. Also in the case where the length L of the optical waveguide 1 is an integral multiple of the value represented by the equation (8), a pattern identical or symmetrical to the light distribution in the y direction of the first end face 13 at the second end face 14 Is reproduced. Therefore, when length L is determined to be an integral multiple of the value shown in equation (7) and an integral multiple of the value shown in equation (8), that is, length L satisfies equation (1) In this case, the optical waveguide 1 can reproduce the same or symmetrical pattern as the light distribution in the x direction and the y direction. Note that equation (1) has a length L is, indicating that a _2k 0 nW ² / an integral multiple and the length is an integer multiple of _2k 0 nH ² / π of [pi.

The light emitting element 2 emits light having a unimodal distribution. The second end face 14 reproduces the distribution of light having a single peak. When eccentricity occurs in the distribution of light at the first end face 13 due to the positional deviation between the light emitting element 2 and the optical waveguide 1, the distribution of light including such eccentricity is reproduced at the second end face 14 Be done. The optical circuit 10 can correct eccentricity by active alignment of the condenser lens 3 and the optical fiber 4. Thus, the optical circuit 10 can reduce the loss of coupling efficiency.

As a comparative example, in the case where a single mode optical waveguide provided on a semiconductor substrate and a light emitting element are directly optically coupled, when the positional deviation between the optical waveguide and the light emitting element is about 0.5 μm, the coupling efficiency is − It falls below about 3 dB. On the other hand, when a multimode optical waveguide is used, for example, when the width of the optical waveguide is 15 μm, even if the positional deviation between the optical waveguide and the light emitting element is about 10 μm, the light of the light emitting element is almost lossless Can be incident on the optical waveguide.

In the first embodiment, the optical waveguide 1 reproduces the distribution and eccentricity of light having unimodality at the first end face 13 at the second end face 14. When the light emitted from the second end face 14 is condensed by the condensing lens 3 and the light is made incident on the optical fiber 4, the emission of the light at the second end face 14 if unimodality can be ensured. Even if the positional deviation is about 10 μm, the coupling efficiency is about -3 dB. Thereby, the optical circuit 10 can obtain the effect of reducing the loss of the coupling efficiency, as in the case where the displacement amount of the incident position of the light on the first end face 13 is 10 μm.

The optical circuit 10 can reduce the positioning accuracy of the optical waveguide 1 and the light emitting element 2. The incident position of the light from the light emitting element 2 on the first end face 13 may vary depending on the accuracy of crystal growth or polishing at the time of manufacturing the semiconductor substrate 11. In addition, the variation in the incident position on the first end face 13 may occur depending on the mounting position accuracy when mounting the optical waveguide 1 and the light emitting element 2. Since the positioning accuracy of the optical waveguide 1 and the light emitting element 2 can be relaxed, the accuracy of the semiconductor substrate 11 can also be relaxed.

Further, in the first embodiment, the width and height of the core 12 are expanded as compared with the single mode optical waveguide. As the xy cross section of the core 12 is enlarged, the evanescent component decreases. In the optical waveguide 1, the roughness of the surface of the optical waveguide 1 due to the manufacturing process has less influence on the light propagating through the optical waveguide 1 as compared with the single mode optical waveguide. Thereby, the optical waveguide 1 can reduce the loss of light when propagating the optical waveguide 1.

Next, when the length L satisfies the equation (1), a calculation example will be described regarding the operation and effect that the distribution of incident light to the first end face 13 is reproduced at the second end face 14. FIG. 2 is a view showing an example of an electric field distribution of light by propagation simulation for the optical waveguide 1 according to the first embodiment. Here, the optical waveguide 1 is an optical waveguide of PLC (Planar Lightwave Circuit) which uses Si and SiO ₂ as materials. The refractive index of the core 12 of the optical waveguide 1 is 1.466, the refractive index of the cladding is 1.46, and the width W and height H of the core 12 are 46.5 μm. The vertical axis in FIG. 2 represents the position in the x direction, and the horizontal axis represents the position in the z direction. The light incident on the first end face 13 of the optical waveguide 1 is a Gaussian beam whose full width at half maximum (FWHM) is 15.0 μm. In the description of FIG. 2, the position of incident light indicates the position of a Gaussian peak. The pattern of the electric field distribution may be referred to as "field pattern" as appropriate.

In FIG. 2, when the position of the incident light indicated by the arrow in the figure coincides with the center position O of the core 12 of the optical waveguide 1, that is, the deviation between the incident light and the center position O is 0 μm. The case and the case where the shift between the incident light and the center position O is 5 μm, 7.5 μm, and 10 μm are shown.

According to FIG. 2, regardless of the amount of deviation of the incident light from the center position O, a field symmetrical to the field pattern at the position P0 at the position P1 which is 9.68 mm ahead in the z direction from the position P0 of the first end face 13 A pattern has appeared. The same field pattern as the incident light appears at a position P2 which is 19.36 mm ahead in the z direction from the position P0. In the first embodiment, similarly to the relationship between the x direction and the z direction, the field pattern at the position P0 is also in the relationship between the y direction and the z direction regardless of the amount of deviation of the incident light from the center position O. A symmetrical field pattern appears at position P1, and the same field pattern as the field pattern at position P0 appears at position P2.

FIG. 3 is a diagram showing propagation distance dependency of overlap integral of the electric field of light propagating through the optical waveguide 1 and the electric field of incident light in the first embodiment. The vertical axis in FIG. 3 represents overlap integration, and the horizontal axis represents the propagation distance in the z direction from the position P 0 of the first end face 13. Similar to FIG. 2, FIG. 3 shows the case where the shift amount between the incident light and the center position O is 0 μm, 5 μm, 7.5 μm, and 10 μm. In the propagation distance dependencies of 0 μm, 5 μm, 7.5 μm, and 10 μm, the upper end of the vertical axis represents that the overlap component is 100% at the time of incidence.

In FIG. 3, it is not clear where the field pattern symmetrical to the field pattern at the time of incidence is reproduced. The position where the same field pattern as the field pattern at the time of incidence is reproduced is shown as a clear peak of the overlap integral, as indicated by the circle in the relation of 0 μm, 5 μm, 7.5 μm, and 10 μm. There is. Regardless of the amount of deviation of the incident light from the center position O, the overlap integral becomes 96% at the time of incidence at the position P2 at a distance of 19.36 mm from the position P0, and becomes maximum. This indicates that 96% of the light on entry is obtained on exit. Also, the loss of coupling efficiency is 4% (−0.18 dB) of the intensity of incident light, which is a minimum.

FIG. 4 is a view showing an example of the effective refractive index in the core 12 of light of the waveguide mode of each order i calculated by the propagation simulation shown in FIG. 2 and the propagation constant calculated from the effective refractive index . Substituting the width W, which is the effective waveguide width obtained from the average of the effective refractive indices for all the waveguide modes shown in FIG. 4, into the above equation (7), the same field pattern as the field pattern at the time of incidence is reproduced The length L is 19.34 mm, and it can be seen that it matches well with the result of the above-mentioned propagation simulation.

In this case, when the shift amount of the length L is in the range of about ± 0.376 mm, the overlap integral in each propagation distance dependency shown in FIG. 3 is 0.5 or more. In this case, in the optical waveguide 1, 50% of the light at the time of incidence will be obtained at the time of emission, and there is no problem in practical use. This corresponds to the fact that the length L can tolerate an error of ± 2% from the value obtained by the equation (1) above. Accordingly, the

optical waveguide

1, _2k 0 nW ² / _π integer multiples and _2k 0 nH ² / _π length L to be within the range of 0.98 times the length of 1.02 times the integral multiple of By being set, the loss of coupling efficiency can be reduced, and high coupling efficiency can be obtained.

The width W and height H of the core 12, the refractive index of the core 12, and the refractive index of the cladding are not limited to those described above. If the length L can be set to the value obtained by the above equation (1) or a value within the range of 0.98 times to 1.02 times the value obtained by the equation (1), the width W and H and each refractive index can be set arbitrarily. The optical waveguide 1 is not limited to one included in the PLC, and may be included in an optical circuit other than the PLC.

The optical waveguide 1 may include bending or bending between the first end face 13 and the second end face 14. In this case, the z direction is a direction along the center position O of the core 12. Not only when the optical waveguide 1 has a linear shape, but also when it has a shape including bending or bending, the loss of coupling efficiency can be reduced, and high coupling efficiency can be obtained.

The optical waveguide 1 is not limited to the case of a PLC optical waveguide including Si that is the core 12 and SiO ₂ that is the cladding. The material of the semiconductor substrate 11, the core 12 and the cladding constituting the optical waveguide 1 is not limited to Si or SiO ₂ , and semiconductor materials such as SiN, SiON, GaAs, InP, dielectric materials LiO ₃ Nb, or polymer materials It may be

The width W and the height H of the core 12 may satisfy the relationship of W ² = m 1 × H ² or H ² = m ² × W ² . m1 and m2 are arbitrary natural numbers. In other words, the square of the width W is an integral multiple of the square of the height H, or the square of the height H is an integral multiple of the square of the width W.

By way of example, if W ² = 0.5 and H ² = 0.2, then f (0.5,0.2) = 1.0, as described above. Also, if W ² = 0.5 and H ² = 0.25, and if W ² is twice H ² , then S × W ² and T × H ² when S = 1 and T = ^2. Is the minimum, and f (0.5, 0.25) = 0.5. From the above equation (1), the length L becomes smaller as f (W ² , H ² ) becomes smaller. Thus, the W ² integral multiple of H ^2, or of H ² by an integral multiple of W ^2, it can be designed shorter length L of the core 12.

Next, a modification of the optical circuit 10 according to the first embodiment will be described with reference to FIGS. 5 to 8. In each modification, the combination of the first optical element and the second optical element is different from the example shown in FIG. 5 to 8 show the first optical element, the second optical element, and the core 12 of the optical waveguide 1 when the optical circuit 10 is viewed from the y direction, and the semiconductor substrate 11 is not shown. . Also, the description of the components common to the components shown in FIG. 1 will be omitted as appropriate.

FIG. 5 is a diagram showing the configuration of the optical circuit 10 according to the first modification of the first embodiment. The optical circuit 10 includes an optical fiber 5 which is a first optical element, a condenser lens 3 which is a second optical element, and an optical fiber 4. The light 15 having passed through the optical fiber 5 is incident on the first end face 13. The light 16 emitted from the second end face 14 passes through the condenser lens 3 and enters the optical fiber 4.

FIG. 6 is a diagram showing the configuration of the optical circuit 10 according to the second modification of the first embodiment. The optical circuit 10 includes a light emitting element 2 which is a first optical element, and an optical fiber 4 which is a second optical element. The configuration of the modification 2 is the same as the configuration shown in FIG. 1 except that the condenser lens 3 is omitted. The optical fiber 4 and the second end face 14 are directly optically coupled. By causing the light from the optical waveguide 1 to directly enter the optical fiber 4, the number of parts of the optical circuit 10 can be reduced, and the manufacture can be facilitated and the cost can be reduced.

FIG. 7 is a diagram showing the configuration of the optical circuit 10 according to the third modification of the first embodiment. The optical circuit 10 includes an optical fiber 5 which is a first optical element, and a light receiving element 6 which is a second optical element. The light receiving element 6 is an element for detecting light, and one example is a photodiode (PD). The light 15 having passed through the optical fiber 5 is incident on the first end face 13. The light 16 emitted from the second end face 14 is incident on the light receiving element 6.

FIG. 8 is a diagram showing the configuration of the optical circuit 10 according to the fourth modification of the first embodiment. The optical circuit 10 includes a light emitting element 2 which is a first optical element, and a light receiving element 6 which is a second optical element. The light 16 emitted from the second end face 14 is incident on the light receiving element 6. In the third modification and the fourth modification, the condenser lens 3 may be provided between the second end face 14 and the light receiving element 6.

Thus, the first optical element includes one of the light emitting element 2 and the optical fiber 5. The second optical element includes one of the optical fiber 4 and the light receiving element 6. The second optical element may include a condenser lens 3 between the second end face 14 and the optical fiber 4. The

optical fibers

4 and 5 may propagate light by either single mode or multi mode. The first optical element and the second optical element may include optical waveguides other than the optical fiber instead of the

optical fibers

4 and 5.

According to the first embodiment, the optical waveguide 1, the length L of the core 12 in the first direction, _2k 0 nW ² / an integral multiple and _2k 0 nH ^2/0 the length of an integer multiple of π for π By including in the range of .98 times to 1.02 times, loss of coupling efficiency can be reduced. As a result, the optical waveguide 1 has an effect of being able to realize high coupling efficiency in the functional components including the optical waveguide 1. The optical circuit 10 can realize high coupling efficiency by including the optical waveguide 1.

Second Embodiment
FIG. 9 is a view showing the configuration of a semiconductor laser 20 according to a second embodiment of the present invention. The semiconductor laser 20 is an optical waveguide 1, an optical amplifier 21 which is a first optical element for causing light to be incident on the first end face 13, and a second optical element for receiving the light reaching the second end face 14. And a mirror 22. The semiconductor laser 20 is a functional component provided with the optical waveguide 1. The same parts as those in the first embodiment described above are denoted by the same reference numerals, and redundant description will be omitted.

The optical amplifier 21 amplifies light in a certain wavelength range, and emits the amplified light 23 to the first end face 13. The optical amplifier 21 receives the light 23 from the first end face 13 and uses the received light 23 for amplification. The optical amplifier 21 amplifies light by current injection or light excitation. The end face 25 of the optical amplifier 21 optically coupled to the first end face 13 is provided with an AR coating for reducing the reflection of the light 23 from the optical waveguide 1. Alternatively, a structure for preventing reflection may be provided on the end face 25. One example of a structure for preventing reflection is a structure including a surface inclined to the chief ray of light 23. In FIG. 9, illustration of the AR coating and the structure for preventing reflection is omitted.

The optical amplifier 21 includes a partially transmitting mirror provided at the end face 26 opposite to the end face 25. The partially transmitting mirror transmits a part of the incident light and reflects the other light. The optical amplifier 21 emits the light 24 transmitted through the partial transmission mirror from the end face 26. In FIG. 9, illustration of the partially transmitting mirror provided on the end face 26 is omitted.

In one example, the mirror 22 is a layer of highly reflective material and is provided at the second end face 14. The mirror 22 has a high reflectance for light in a wide wavelength range. The material of the mirror 22 is gold, silver or aluminum which is a highly reflective metal material. The mirror 22 is formed by vapor deposition of a metal material on the second end face 14. The material of the mirror 22 may be a highly reflective material other than a metal material. The mirror 22 may be formed by a method other than vapor deposition. Note that other examples of the mirror 22 will be described later.

The light 23 emitted from the end face 25 of the optical amplifier 21 enters the first end face 13. The light propagating through the core 12 from the first end face 13 to the second end face 14 reaches the second end face 14 and is reflected by the mirror 22. The light reflected by the mirror 22 propagates in the core 12 from the second end face 14 toward the first end face 13. The light 23 emitted from the first end face 13 enters the end face 25 of the optical amplifier 21. Part of the light propagated inside the optical amplifier 21 is reflected by the partially transmitting mirror. The light reciprocating between the mirror 22 and the partial transmission mirror of the optical amplifier 21 is amplified inside the optical amplifier 21. The semiconductor laser 20 emits the light 24 transmitted through the partial transmission mirror of the optical amplifier 21 among the amplified light.

Also in the second embodiment, as in the first embodiment, the length L is set to satisfy the above equation (1). That is, the length L is an integer multiple of _2k 0 nW ² / an integral multiple and _2k of π 0 nH ² / π. Alternatively, the length L is set to be in the _2k 0 nW ² / an integral multiple and _2k 0 nH ² / an integral multiple of the length range from 1.02 times 0.98 times the π of π . The optical waveguide 1 can reduce the loss of coupling efficiency, and can obtain high coupling efficiency.

As in the first embodiment, the semiconductor laser 20 can reduce the loss of light to be reciprocated by reducing the influence of the surface roughness of the optical waveguide 1 on the light propagating through the optical waveguide 1, and the efficiency is high. Can emit light. Further, the semiconductor laser 20 can reduce the current supply to the optical amplifier 21 by reducing the gain required for laser oscillation. Thereby, the semiconductor laser 20 can reduce power consumption. The shape and material of the optical waveguide 1 are arbitrary as in the case of the first embodiment. Also, as in the first embodiment, the square of the width W of the core 12 is an integral multiple of the square of the height H, or the square of the height H is an integral multiple of the square of the width W. Also good.

By making the mirror 22 a layer of a highly reflective material, it is possible to form the mirror 22 having high reflectance for light in a wide wavelength range relatively easily and inexpensively. The mirror 22 is not limited to being a layer of highly reflective material. The mirror 22 may be a wavelength selection mirror that selectively reflects light in a specific wavelength range. The mirror 22 absorbs or transmits light other than light of a specific wavelength range. For the wavelength selection mirror, a reflective grating, a ring resonator, or a dichroic mirror is used. By providing the mirror 22 which is a wavelength selection mirror, the oscillation wavelength of the semiconductor laser 20 can be limited.

Next, a modification of the semiconductor laser 20 according to the second embodiment will be described with reference to FIG. 10 and FIG. 10 and 11 show the first optical element, the second optical element, and the core 12 of the optical waveguide 1 when the semiconductor laser 20 is viewed from the y direction, and the semiconductor substrate 11 is not shown. Do.

FIG. 10 is a view showing the configuration of a semiconductor laser 20 according to the first modification of the second embodiment. In the first modification, the first optical element includes the optical fiber 5 provided between the optical amplifier 21 and the first end face 13. The light 23 emitted from the end face 25 of the optical amplifier 21 enters the optical fiber 5. The light 23 having passed through the optical fiber 5 is incident on the first end face 13. The light 23 emitted from the first end face 13 passes through the optical fiber 5 and then enters the end face 25 of the optical amplifier 21.

According to the first modification, with the optical fiber 5 provided, the semiconductor laser 20 can install the optical amplifier 21 and the optical waveguide 1 at mutually separated positions. Thereby, the semiconductor laser 20 can improve the degree of freedom of the arrangement of the optical amplifier 21 and the optical waveguide 1.

FIG. 11 is a view showing the configuration of a semiconductor laser 20 according to the second modification of the second embodiment. In the second modification, the second optical element includes a mirror 27 and a light receiving element 6. The mirror 27 is a partially transmitting mirror that transmits part of the light reaching the second end face 14 and reflects the other light.

The light propagating through the core 12 from the first end face 13 and entering the second end face 14 enters the mirror 27. A part of the light incident on the mirror 27 is reflected by the mirror 27 and propagates toward the first end face 13 through the core 12. The light 28 transmitted through the mirror 27 is incident on the light receiving element 6. The light receiving element 6 detects the light 28. The semiconductor laser 20 can monitor the intensity of light reciprocating within the optical waveguide 1 and the optical amplifier 21 from the intensity of the light 28 detected by the light receiving element 6. Between the mirror 27 and the light receiving element 6, a wavelength filter that transmits light in a specific wavelength range may be provided. Thereby, the semiconductor laser 20 can monitor the oscillation wavelength. In the second modification, the optical fiber 5 may be provided as in the first modification.

According to the second embodiment, the semiconductor laser 20, a core length of 12, _2k 0 nW ² / an integral multiple and _2k 0 nH ^2/1 from 0.98 times the length of an integer multiple of [pi of [pi. By including in the range of 02 times, the loss of coupling efficiency can be reduced. As a result, the semiconductor laser 20 has an effect that high coupling efficiency can be realized.

Third Embodiment
FIG. 12 is a diagram showing the configuration of an optical multiplexer / demultiplexer 30 which is an optical circuit according to the third embodiment of the present invention. The optical multiplexer / demultiplexer 30 comprises a plurality of first optical waveguides 31 for propagating a plurality of optical signals in different wavelength regions, a second optical waveguide 32 for propagating a multiple wavelength signal, and a multiple wavelength signal from a plurality of optical signals. And an optical multiplexing / demultiplexing unit 33 for demultiplexing the multiplexed or multiplexed wavelength signal into a plurality of optical signals. The optical multiplexer / demultiplexer 30 is a functional component that includes the first optical waveguide 31, the second optical waveguide 32, and the optical multiplexer / demultiplexer 33. The same parts as those in the first embodiment described above are denoted by the same reference numerals, and redundant description will be omitted.

The optical multiplexer / demultiplexer 30 includes a plurality of light emitting elements 2 as a first optical element optically coupled to the first end face 13 of the plurality of first optical waveguides 31 and a second optical waveguide 32. A condenser lens 3 and an optical fiber 4 which are second optical elements optically coupled to the end face 14 of the second lens 2 are provided. The plurality of first optical waveguides 31 and the plurality of second optical waveguides 32 are multimode optical waveguides for propagating light of a plurality of waveguide modes.

The optical multiplexing / demultiplexing unit 33 is formed in the slab optical waveguide 35 connected between the plurality of first optical waveguides 31 and the second optical waveguide 32 and the slab optical waveguide 35, and diffracts the plurality of optical signals by diffraction. And a reflection type grating 34 for reflecting and emitting a multiple wavelength signal or reflecting a multiple wavelength signal by diffraction and emitting a plurality of optical signals. The slab optical waveguide 35 is a multimode optical waveguide that propagates light of a plurality of guided modes. The slab optical waveguide 35 includes a flat core 12 sandwiched between an upper clad layer and a lower clad layer which are clads. The second end faces 14 of the plurality of first optical waveguides 31 are connected to the slab optical waveguide 35. The first end face 13 of the second optical waveguide 32 is connected to the slab optical waveguide 35. The plurality of first optical waveguides 31, the second optical waveguide 32, the light coupling / splitting unit 33, and the plurality of light emitting elements 2 are provided on the semiconductor substrate 11.

Similar to the optical waveguide 1 of FIG. 1, the first optical waveguide 31, the second optical waveguide 32, and the slab optical waveguide 35 include a core 12 and a cladding through which light of a plurality of waveguide modes propagate. The optical multiplexer / demultiplexer 30 is configured as a PLC made of Si and SiO ₂ .

The optical multiplexer / demultiplexer 30 can function as any of an optical multiplexer that multiplexes a plurality of optical signals in different wavelength bands and an optical demultiplexer that divides the multiplexed optical signal according to the difference in wavelength bands. It is a circuit. In the third embodiment, mainly, the case where the optical multiplexer / demultiplexer 30 is an optical multiplexer is taken as an example. The input and output of the optical signal in the optical demultiplexer are opposite to the input and output of the optical signal in the optical multiplexer.

When the optical multiplexer / demultiplexer 30 is an optical multiplexer, light incident on the slab optical waveguide 35 from the plurality of first optical waveguides 31 propagates through the plurality of propagation paths 36 in the slab optical waveguide 35. The light propagating through the plurality of propagation paths 36 is reflected by the reflective grating 34 and is incident on the first end face 13 of the second optical waveguide 32. On the other hand, when the optical multiplexer / demultiplexer 30 is an optical demultiplexer, light incident on the slab optical waveguide 35 from the second optical waveguide 32 is reflected by the reflective grating 34 and propagates through a plurality of propagation paths 36 . The light propagated through the plurality of propagation paths 36 is incident on the second end face 14 of the plurality of first optical waveguides 31.

In the third embodiment, the light emitting element 2 includes four light emitting

elements

2A, 2B, 2C, and 2D that emit light signals having different wavelength ranges. The first optical waveguide 31 includes four first

optical waveguides

31A, 31B, 31C, and 31D into which optical signals from the four

light emitting elements

2A, 2B, 2C, and 2D enter for each wavelength range. The plurality of propagation paths 36 include four

propagation paths

36A, 36B, 36C, and 36D. The number of first optical waveguides 31 and the number of light emitting elements 2 are not limited to four, and may be two, three, or five or more.

FIG. 13 is an enlarged view of a part of the reflective grating 34 shown in FIG. The reflective grating 34 is a sawtooth-shaped diffraction grating structure formed on the side surface of the slab optical waveguide 35. By setting the shape of the groove based on the wavelength range of the plurality of optical signals, the reflective grating 34 reflects the plurality of optical signals from the plurality of propagation paths 36, and The light is collected on the end face 13 of FIG. Thus, the optical multiplexing / demultiplexing unit 33 multiplexes a plurality of optical signals. Further, in the case of performing optical demultiplexing, the reflective grating 34 reflects the multi-wavelength signal and distributes the plurality of optical signals to the plurality of propagation paths 36. Thus, the optical multiplexing / demultiplexing unit 33 divides the multiple wavelength signal into a plurality of optical signals.

In the third embodiment, the length L1 of the _first

optical waveguides

31A, 31B, 31C, 31D satisfies the following equation (9).

In the equation (9), W is a parameter indicating the width of the core 12 of the first

optical waveguides

31A, 31B, 31C, 31D. n is a parameter indicating the refractive index of the core 12. k ₀ is a parameter indicating the number of waves of light propagating through the core 12. In the third embodiment, k ₀ is the wave number in vacuum of the light emitted from the light emitting element 2. Assuming that the wavelength in vacuum is λ ₀ , k ₀ = 2π / λ ₀ holds. M ₁ is an arbitrary natural number.

Further, the length L2 of the _second optical waveguide 32 satisfies the following equation (10).

In the equation (10), W is a parameter indicating the width of the core 12 of the second optical waveguide 32. n is a parameter indicating the refractive index of the core 12. k _ave is an average of wave numbers k ₀ in vacuum of light emitted from the

light emitting elements

2A, 2B, 2C, 2D. M ₂ is an arbitrary natural number.

In the equations (9) and (10), the width W is an effective width including the range in which the evanescent component of the light propagating through the core 12 occurs. The width W is an average value of virtual widths including the range in which evanescent components of light of a plurality of guided modes occur.

Furthermore, the propagation path lengths L ₁ + L _slab + L ₂ of the plurality of optical signals in the first

optical waveguides

31A, 31 B, 31 C, 31 D, the optical multiplexing / demultiplexing unit 33 and the second optical waveguide 32 The expression (11) of The length _L 1 _{+ L} slab + _{L 2,} the first

optical waveguide

31A, 31B, 31C, and the length _{L 1} of the 31D,

propagation path

36A, 36B, 36C, and the length _{L slab} of 36D, a second optical waveguide 32 is the sum of the length _{L 2.}

In Formula (11), H is a parameter indicating the height of the core 12 in the first

optical waveguides

31A, 31B, 31C, 31D, the second optical waveguide 32, and the slab optical waveguide 35. n is a parameter indicating the refractive index of the core 12. k ₀ is a parameter indicating the number of waves of light propagating through the core 12. M ₃ is an arbitrary natural number. The height H is an effective height including the range in which the evanescent component of the light propagating through the core 12 occurs. The height H is an average value of virtual widths including the range in which evanescent components of light of a plurality of guided modes occur.

As shown in equation (9), the length L ₁ is set to an integral multiple of 2k ₀ nW ² / π. Further, as in the first embodiment, since there is no practical problem even if an error of ± 2% is allowed, the length L ₁ is 0.98 times the integral multiple of 2k ₀ nW ² / π. It may be set to be included in the range of 1.02 times.

As shown in equation (10), the length L ₂ is set to an integral multiple of ² k _ave n W ² / π. Further, as in the first embodiment, since there is no practical problem even if an error of ± 2% is allowed, the length L ₂ is ² k _ave n W ² / π as in the first embodiment. It may be set to fall within the range of 0.98 times to 1.02 times the integral multiple.

As shown in equation (11), the length L ₁ + L _slab + L ₂ is set to an integral multiple of 2k ₀ nH ² / π. Further, as in the first embodiment, there is no practical problem even if an error of ± 2% is allowed, so that the length L ₁ + L _slab + L ₂ is ₂ k ₀ nH as in the first embodiment. It may be set to be included in the range of 0.98 times to 1.02 times the length of integer multiple of ² / π. As a result, the loss of coupling efficiency of the first

optical waveguides

31A, 31B, 31C, 31D, the second optical waveguide 32, and the slab optical waveguide 35 can be reduced, and high coupling efficiency can be obtained. .

The width and height of the core 12 of the plurality of first optical waveguides 31 and the second optical waveguide 32 are expanded as compared to a single mode optical waveguide. In the slab optical waveguide 35, the height of the core 12 is expanded compared to a single mode slab optical waveguide. The expanded width and height or height of the core 12 reduces the evanescent component. Since the surface roughness of the plurality of first optical waveguides 31, the second optical waveguide 32, and the slab optical waveguide 35 has less influence on the propagating light, the optical multiplexer / demultiplexer 30 The loss of wave or demultiplexed light can be reduced.

Next, the operation and effect of the lengths L ₁ , L _slab , and L ₂ by satisfying the above formulas (9), (10), and (11) will be described. When the length L ₁ satisfies the equation (9), the eccentricity of the distribution of light generated due to the positional deviation between the respective first optical waveguides 31 and the respective light emitting elements 2 in the direction parallel to the surface 17 Is reproduced at the incident position from each first optical waveguide 31 to the slab optical waveguide 35. When light having a single peak is incident on the slab optical waveguide 35, light incident on the second optical waveguide 32 from the slab optical waveguide 35 also has a single peak. The light having a single peak of each wavelength range emitted from each light emitting element 2 is input to the second optical waveguide 32 while maintaining the distribution including the eccentricity.

When the length L ₂ satisfies the equation (10), the second optical waveguide 32, like the first optical waveguide 31, distributes the light at the first end face 13 at the second end face 14. to recreate. In the equation (10), the wave number k _ave of the core 12 of the second optical waveguide 32 is an average of the wave numbers k ₀ of a plurality of optical signals, whereby the second optical waveguide 32 can be obtained after multiplexing. For light, the distribution of light can be reproduced.

On the other hand, in the direction perpendicular to the surface 17, by satisfying the equation (11), the eccentricity of the distribution of light generated due to the positional deviation between each first optical waveguide 31 and each light emitting element 2 is It is reproduced at the second end face 14 of the second optical waveguide 32.

Thereby, the optical multiplexer / demultiplexer 30 has a distribution of light generated due to the positional deviation between the respective first optical waveguides 31 and the respective light emitting elements 2 in the direction parallel to the surface 17 and in the direction perpendicular to the surface 17. The eccentricity of the second optical waveguide 32 can be reproduced at the second end face 14 of the second optical waveguide 32. The optical multiplexer / demultiplexer 30 can correct eccentricity by active alignment between the condenser lens 3 and the optical fiber 4. Thereby, the optical multiplexer / demultiplexer 30 can reduce the loss of coupling efficiency.

In the third embodiment, the optical multiplexer / demultiplexer 30 has a distribution of light having unimodality at the first end face 13 of the first optical waveguide 31 at the second end face 14 of the second optical waveguide 32. Reproduce eccentricity. When the light emitted from the second end face 14 of the second optical waveguide 32 is condensed by the condensing lens 3 and the light is made incident on the optical fiber 4, if the unimodal property can be secured, the second The coupling efficiency is about -3 dB even if the deviation of the light emission position at the end face 14 is about 10 μm. As a result, the optical multiplexer / demultiplexer 30 has the effect of reducing the loss of coupling efficiency, as in the case where the amount of deviation allowed for the incident position of light at the first end face 13 of the first optical waveguide 31 is 10 μm. You can get

The plurality of first optical waveguides 31 and the second optical waveguides 32 may include a curve or a bend between the first end surface 13 and the second end surface 14. The plurality of first optical waveguides 31 and the second optical waveguide 32 can reduce the loss of the coupling efficiency not only in the case of the linear shape but also in the case of the shape including the bending or bending, thereby achieving high coupling efficiency. You can get it. The shape of the slab optical waveguide 35 may be a shape other than the shape shown in FIG.

Values obtained by the above formulas (9), (10), (11), or values within the range of 0.98 times to 1.02 times the values obtained by the formulas (9), (10), (11) The width W and height H of the core 12, the refractive index of the core 12, and the refractive index of the cladding can be arbitrarily set as long as the lengths L ₁ , L _slab and L ₂ can be set to The plurality of first optical waveguides 31, the second optical waveguide 32, and the slab optical waveguide 35 are limited to the optical waveguides of PLC including Si as the core 12 and SiO _{2 as the} cladding. Absent. As materials of the plurality of first optical waveguides 31, the second optical waveguide 32, and the slab optical waveguide 35, semiconductor materials such as SiN, SiON, GaAs, InP, dielectric materials LiO ₃ Nb, and polymers are used. Any of the materials may be used.

The plurality of light emitting elements 2 are not limited to those individually formed on the semiconductor substrate 11, but may be integrated on one substrate. When a plurality of light emitting elements 2 are integrated, the same amount of positional deviation with the first optical waveguide 31 occurs in all of the plurality of light emitting elements 2. It becomes possible to make the eccentricity amount in the 2nd end face 14 of 2nd optical waveguide 32 equal.

As in the modification of the first embodiment, the optical multiplexer / demultiplexer 30 may include the optical fiber 5 which is the first optical element, and the condenser lens 3 may be omitted. In addition, the optical multiplexer / demultiplexer 30 may include the light receiving element 6 which is a second optical element. The first optical element includes one of the light emitting element 2 and the optical fiber 5. The second optical element includes one of the optical fiber 4 and the light receiving element 6. The

optical fibers

4 and 5.

According to the third embodiment, the optical multiplexer / demultiplexer 30 has a plurality of first optical waveguides of a length included in 0.98 times to 1.02 times the length which is an integral multiple of 2k ₀ nW ² / π. 31 and a second optical waveguide 32. In addition, the lengths of the propagation paths of the plurality of optical signals in the plurality of first optical waveguides 31, the second optical waveguide 32, and the optical multiplexing / demultiplexing unit 33 are integer multiples of 2k ₀ nH ² / π. It is included in the range of 0.98 times to 1.02 times the length. As described above, by setting the propagation path lengths of the plurality of first optical waveguides 31, the second optical waveguide 32, and the optical multiplexing / demultiplexing unit 33, the optical multiplexer / demultiplexer 30 has a coupling efficiency of It is possible to reduce the loss. As a result, the optical multiplexer / demultiplexer 30 has an effect that high coupling efficiency can be realized.

The configuration shown in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and one of the configurations is possible within the scope of the present invention. Parts can be omitted or changed.

DESCRIPTION OF SYMBOLS 1 optical waveguide, 2, 2A, 2B, 2C, 2D light emitting element, 3 condensing lens, 4, 5 optical fiber, 6 light receiving element, 10 optical circuit, 11 semiconductor substrate, 12 core, 13 1st end face, 14 first 2, end faces 15, 16, 23, 24, 28 light, 17 faces, 20 semiconductor lasers, 21 optical amplifiers, 22 mirrors, 25 and 26 end faces, 30 optical multiplexers / demultiplexers, 31, 31A, 31B, 31C, 31D 1 optical waveguide, 32 second optical waveguide, 33 light combining / splitting parts, 34 reflective grating, 35 slab optical waveguides, 36, 36A, 36B, 36C, 36D propagation paths.

Claims

A core for propagating light of a plurality of guided modes between the first end face and the second end face,
The width of the core in a second direction perpendicular to the first direction, which is the direction from the first end face to the second end face, is W, perpendicular to the first direction and the second direction Let H be the height of the core in the third direction, n be the refractive index of the core, and k 0 be the wave number of light propagating through the core
The length of the first of said core in the direction contained in the 2k 0 nW 2 / an integral multiple and 2k 0 nH 2 / range 0.98 times the length of an integer multiple 1.02 times the π of π An optical waveguide characterized by
The optical waveguide according to claim 1, wherein the width and the height are the width and the height of the core including a range in which an evanescent component of light of the plurality of guided modes is generated.
The optical waveguide according to claim 1 or 2, wherein the square of the width is an integral multiple of the square of the height.
The optical waveguide according to claim 1 or 2, wherein the square of the height is an integral multiple of the square of the width.
An optical waveguide including a core through which light of a plurality of guided modes propagates between the first end face and the second end face;
The width of the core in a second direction perpendicular to the first direction, which is the direction from the first end face to the second end face, is W, perpendicular to the first direction and the second direction Let H be the height of the core in the third direction, n be the refractive index of the core, and k 0 be the wave number of light propagating through the core
The length of the first of said core in the direction contained in the 2k 0 nW 2 / an integral multiple and 2k 0 nH 2 / range 0.98 times the length of an integer multiple 1.02 times the π of π An optical circuit characterized by
A first optical element for causing light to enter the first end face;
The optical circuit according to claim 5, further comprising: a second optical element that receives the light emitted from the second end face.
The optical circuit according to claim 6, wherein the first optical element includes a light emitting element.
The optical circuit according to claim 6, wherein the first optical element includes an optical fiber.
The optical circuit according to any one of claims 6 to 8, wherein the second optical element comprises an optical fiber.
The optical circuit according to claim 9, wherein the second optical element includes a lens between the second end face and the optical fiber.
The optical circuit according to any one of claims 6 to 10, wherein the second optical element includes a light receiving element that detects light.
An optical waveguide including a core through which light of a plurality of guided modes propagates between the first end face and the second end face;
The width of the core in a second direction perpendicular to the first direction, which is the direction from the first end face to the second end face, is W, perpendicular to the first direction and the second direction Let H be the height of the core in the third direction, n be the refractive index of the core, and k 0 be the wave number of light propagating through the core
The length of the first of said core in the direction contained in the 2k 0 nW 2 / an integral multiple and 2k 0 nH 2 / range 0.98 times the length of an integer multiple 1.02 times the π of π Semiconductor laser characterized by
A first optical element for causing light to enter the first end face;
13. The semiconductor laser according to claim 12, further comprising: a second optical element that receives the light that has reached the second end face.
The first optical element includes an optical amplifier that receives the light emitted from the first end face, amplifies the light from the optical waveguide, and emits the amplified light.
The semiconductor laser according to claim 13, wherein the second optical element includes a mirror that reflects the light that has reached the second end face.
15. The semiconductor laser according to claim 14, wherein the mirror is a layer of a highly reflective material provided on the second end face.
The semiconductor laser according to claim 14, wherein the mirror is a mirror that selectively reflects light in a specific wavelength range.
The mirror is a mirror that transmits part of the light reaching the second end face and reflects the other light,
The semiconductor laser according to claim 14, wherein the second optical element includes a light receiving element that detects light transmitted through the mirror.
A plurality of first optical waveguides including a core through which light of a plurality of guided modes propagates, and a plurality of optical signals of different wavelength regions propagating;
A second optical waveguide including a core through which light of a plurality of guided modes propagates, and through which a multiple wavelength signal which is the plurality of multiplexed optical signals propagates;
An optical multiplexer / demultiplexer configured to multiplex the plurality of optical signals into the multiple wavelength signal or to split the multiple wavelength signal into the plurality of optical signals;
The width of the core is W, the height of the core is H, the refractive index of the core is n, and the wave number of light propagating through the core is k,
The length of the core of the plurality of first optical waveguides and the length of the core of the second optical waveguide are 0.98 times the length which is an integral multiple of 2k 0 nW 2 / π. The propagation path length of the plurality of optical signals in the plurality of first optical waveguides, the second optical waveguide, and the optical multiplexing / demultiplexing unit included in the range of 02 times is 2 k 0 nH An optical circuit characterized by being included in a range of 0.98 times to 1.02 times the length which is an integral multiple of 2 / π.
19. The optical circuit according to claim 18, wherein the wave number of the core of the second optical waveguide is an average of wave numbers of the plurality of optical signals.
A first optical element optically coupled to first end faces of the plurality of first optical waveguides;
20. The optical circuit according to claim 18, further comprising: a second optical element optically coupled to a second end face of the second optical waveguide.
The optical multiplexing / demultiplexing unit
A slab optical waveguide connected to a second end surface of the plurality of first optical waveguides and a first end surface of the second optical waveguide;
A reflection type grating formed in the slab optical waveguide, and reflecting the plurality of optical signals by diffraction to emit the multiple wavelength signal, or reflecting the multiple wavelength signal by diffraction to emit the plurality of optical signals; 21. A light circuit as claimed in any one of claims 18 to 20 comprising.