JP6109002B2 - Optical waveguide element - Google Patents

Description

  The present invention relates to an optical waveguide device, and more particularly to an optical multiplexer / demultiplexer used for an optical integrated device in optical fiber communication.

  In recent years, with a dramatic increase in communication demand, a wavelength division multiplexing communication system that multiplexes a plurality of signal lights having different wavelengths and enables large-capacity transmission using a single optical fiber has been put into practical use.

  For example, in recent years, a method (100 Gbit Ethernet (registered trademark)) that performs communication at a transmission rate of 100 Gbit / s by combining four wavelengths in the 1.3 μm wavelength band has been standardized and is becoming popular. In such a communication system, the optical transceiver module is required to have a function of multiplexing / demultiplexing multiple wavelengths. As an optical waveguide element including an optical multiplexer and an optical demultiplexer, an optical multiplexing / demultiplexing element module integration technique is required. Development is active.

  In addition, in the variable wavelength light source used for the phase modulation optical communication system, a combination of arrayed DFB-LD (Distributed Feedback Laser Diode) and refractive index control by temperature adjustment or current injection, or a special having a plurality of reflection peaks. A wavelength tunable LD that can cover the entire wavelength band used in communication by wavelength selection using a distributed DBR (Distributed Bragg Reflector) mirror pair has also been developed.

  Furthermore, an optical integration that integrates a wavelength tunable LD (Laser Diode) and an external modulator such as an electro absorption (EA) optical modulator or a Mach Zehnder (MZ) optical modulator on the same substrate. Devices are also being developed.

  Multi-mode interference (MMI) type optical multiplexing / demultiplexing elements that are relatively small in wavelength dependence and suitable for monolithic integration are widely used in the optical multiplexing / demultiplexing sections used in the above-mentioned optical integrated elements. .

  As an optical multiplexing / demultiplexing device, a light intensity multiplexing / demultiplexing device that multiplexes / demultiplexes light intensity with a constant transmission efficiency independent of wavelength, and a transmission efficiency higher than that of an optical intensity multiplexer / demultiplexer for light of specific wavelengths There is an optical wavelength multiplexing / demultiplexing element that multiplexes and demultiplexes at a wavelength.

  Conventionally, the wavelength dependence of the multiplexing characteristics of the optical multiplexing / demultiplexing element has been improved by providing an extending portion having a shape corresponding to a predetermined input wavelength on the input end face of the rectangular optical multiplexing / demultiplexing element An optical wavelength multiplexing / demultiplexing device is disclosed (for example, see Patent Document 1).

Japanese Patent No. 4208366

  In a conventional rectangular optical multiplexing / demultiplexing device, optical signals having different wavelengths are transmitted from an input optical waveguide to an optical multiplexing / demultiplexing portion (a portion of the optical multiplexing / demultiplexing device excluding the input optical waveguide and the output optical waveguide, hereinafter referred to as an MMI portion). When input, the longer the wavelength of the input light is, the more the light converges on the near side of the light propagation direction. Therefore, if the input wavelength is greatly different from the optimum wavelength, the output end face of the MMI unit is output to the output optical waveguide. There was a problem that the light coupling deteriorated and the transmission characteristics deteriorated.

  In addition, due to manufacturing variations of optical multiplexing / demultiplexing elements, there is a problem in that the light convergence position varies, the light coupling from the output end face to the output optical waveguide deteriorates, and the transmission characteristics deteriorate.

  As a countermeasure against such a problem, in Patent Document 1, an extending portion that is wider than the input optical waveguide and narrower than the MMI portion is provided between the input optical waveguide and the MMI portion, and each input optical waveguide is provided. It has been proposed to determine the input wavelength (see, for example, FIG. 4 of Patent Document 1). However, even in such a case, there is a problem that transmission characteristics deteriorate due to a shift in the optimum wavelength of wavelength multiplexing / demultiplexing characteristics due to manufacturing variations of optical multiplexers / demultiplexers.

  Even if an optical multiplexer / demultiplexer with small manufacturing variations is obtained, clear transmission characteristics can be obtained if the wavelength difference of the input light (the difference between the wavelength of the input light and the optimum wavelength) is small. If the wavelength difference of the input light increases, the length of the extending portion needs to be increased accordingly. Therefore, the light input to the MMI portion is undesirably affected by multimode interference in the extending portion, and transmitted. There is a problem that characteristics deteriorate.

  The present invention has been made to solve these problems, and an object of the present invention is to provide an optical waveguide element having good optical multiplexing characteristics or optical demultiplexing characteristics.

In order to solve the above problems, an optical waveguide device according to the present invention includes at least one input optical waveguide connected to an input end face, and at least one input optical waveguide connected to an output end face. And an output optical waveguide that is not one at the same time as the waveguide, and is a multimode interference optical waveguide element having at least one function of optical multiplexing and optical demultiplexing, wherein the input optical waveguide is more than the center of the input end face. It is located on the end side and is inclined so that the connection position with the input end face escapes further toward the end side with respect to the center, and is connected to the input end face. The connection position between the input optical waveguide and the input end face is the same as that of the input end face. center and said position der Rukoto not included in the input optical waveguide.

According to the present invention, at least one or more input optical waveguides connected to the input end face and at least one or more output optical waveguides connected to the output end face and not one at the same time as the input optical waveguide are provided. A multimode interference optical waveguide element having at least one function of optical multiplexing and optical demultiplexing, wherein the input optical waveguide is located on the end side with respect to the center of the input end face, and with the input end face The connection position is inclined so that it escapes further toward the end with respect to the center, and is connected to the input end face. The connection position between the input optical waveguide and the input end face is a position where the center of the input end face is not included in the input optical waveguide. Oh because, it can have good optical multiplexing properties or optical demultiplexing characteristics.

It is a figure which shows an example of a structure of the optical demultiplexer by Embodiment 1 of this invention. It is a figure which shows an example of the cross section of the optical demultiplexer by Embodiment 1 of this invention. It is a figure which shows the calculation result of the light intensity distribution in the optical demultiplexer by Embodiment 1 of this invention. It is a figure which shows the calculation result of the light intensity distribution in the optical demultiplexer by Embodiment 1 of this invention. It is a figure for demonstrating the light intensity distribution in the output end surface vicinity of the optical demultiplexer by Embodiment 1 of this invention. It is a figure for demonstrating the light intensity distribution in the output end surface vicinity of the optical demultiplexer by Embodiment 1 of this invention. It is a figure which shows the dependence of the length of the MMI part of the coupling efficiency of the optical demultiplexer by Embodiment 1 of this invention. It is a figure which shows the dependence of the length of the MMI part of the coupling efficiency of the optical demultiplexer by Embodiment 1 of this invention. It is a figure which shows the wavelength dependence of the coupling efficiency of the optical demultiplexer by Embodiment 1 of this invention. It is a figure which shows an example of a structure of the optical multiplexer by Embodiment 2 of this invention. It is a figure which shows an example of a structure of the optical multiplexer by Embodiment 2 of this invention. It is a figure which shows an example of a structure of the optical multiplexer by Embodiment 3 of this invention. It is a figure which shows an example of a structure of the optical multiplexer by Embodiment 3 of this invention. It is a figure which shows the wavelength dependence of the coupling efficiency of the optical demultiplexer by Embodiment 3 of this invention. It is a figure which shows the wavelength dependence of the coupling efficiency of the optical demultiplexer by Embodiment 3 of this invention. It is a figure which shows an example of a structure of the conventional optical demultiplexer.

  Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1>
In the first embodiment of the present invention, a 1-input 2-output optical demultiplexer used in an optical integrated device including a single mode semiconductor laser in optical fiber communication will be described. Here, the 1-input 2-output optical demultiplexer refers to an optical demultiplexer including one input optical waveguide and two output optical waveguides.

  FIG. 16 is a diagram illustrating an example of a configuration of a conventional optical demultiplexer.

  As shown in FIG. 16, the optical demultiplexer includes one input optical waveguide 1a, two output optical waveguides 3a and 3b, and a rectangular MMI section 5. Such an optical demultiplexer including the MMI unit 5 is particularly referred to as an MMI type (multimode interference type) optical demultiplexer.

  FIG. 1 is a diagram illustrating an example of the configuration of the optical demultiplexer according to the first embodiment.

  As shown in FIG. 1, the optical demultiplexer according to the first embodiment is connected to the input end face of the MMI section 5 with the input optical waveguide 1a inclined as compared with the conventional optical demultiplexer shown in FIG. It is characterized by that. Other configurations are the same as those of the conventional optical demultiplexer shown in FIG.

  The input optical waveguide 1a is connected to the input end face by being inclined at an inclination angle θ so as to be away from the center line 6 passing through the center of the input end face and the output end face of the MMI portion 5.

  The rectangular MMI unit 5 is configured such that convergent light is obtained at two locations on the output end face of the MMI unit 5.

  That is, the optical demultiplexer according to the first embodiment has at least one input optical waveguide 1a connected to the input end face, and at least one input optical waveguide 1a connected to the output end face. At the same time, it is a multimode interference type optical demultiplexer (optical waveguide element) having an output optical waveguide 3a, 3b, which is not one, and having the function of optical demultiplexing, and the input optical waveguide 1a has an input end face It is located on the end side from the center, and is connected to the input end face so that the connection position with the input end face is inclined so as to escape further to the end side with respect to the center.

  FIG. 2 is a diagram illustrating an example of a cross section of the optical demultiplexer, and is a diagram illustrating an example of the AA cross section of FIG. 1. The optical demultiplexer according to the first embodiment is manufactured as part of an InGaAsP-based semiconductor optical circuit, for example.

  As shown in FIG. 2, on the InP substrate 11, an InGaAsP layer 12 (thickness 0.2 μm) having a composition with a photoluminescence wavelength of 1.30 μm, and an InP layer 13 (thickness 1.5 μm). Are epitaxially grown in order. Next, a mask layer for obtaining the shape shown in FIG. 3 is formed on the semiconductor wafer after the epitaxial growth by a known exposure process, and then etched by a depth of 4.0 μm by a known dry etching process. Thereafter, the mask layer is removed, and a dielectric layer 14 (thickness of 0.6 μm or more) such as SiO 2 covering the semiconductor portion is formed by a known method such as sputtering.

  Details of each component of the optical demultiplexer shown in FIG. 1 including the MMI unit 5 having the configuration of FIG. 2 are as follows. That is, the width of the input optical waveguide 1a and the output optical waveguides 3a and 3b is 1.8 μm. When the wavelength used (the wavelength of light used in optical fiber communication) is 1.55 μm, the width W of the input end face and the output end face of the MMI section 5 is 12 μm, and the length L of the MMI section 5 is 610 μm. Further, the input optical waveguide connection position 2 a and the output optical waveguide connection positions 4 a and 4 b are W / 4 of the input end face and the output end face of the MMI portion 5. Further, the inclination angle θ of the input optical waveguide 1 a is 2.87 ° toward the end of the MMI unit 5.

  Next, the operation of the optical demultiplexer according to the first embodiment will be described.

  FIG. 3 is a diagram showing a simulation calculation result of the light intensity distribution in the optical demultiplexer (FIG. 16) in which the input optical waveguide 1a is not inclined. FIG. 4 is a diagram showing a simulation calculation result of the light intensity distribution in the optical demultiplexer (FIG. 1) in which the input optical waveguide 1a is inclined. A rectangular solid line in FIGS. 3 and 4 indicates the outer shape of the MMI unit 5. 3 (b) and 4 (b) are enlarged views on the right side (near the output end face of the MMI unit 5) of FIGS. 3 (a) and 4 (a). 3 and 4, it is assumed that TE (Transverse Electric) polarized light having a wavelength of 1.55 μm is input.

  3 and 4, in order to see the intensity distribution of the convergent light in the vicinity of the output end face of the MMI section 5, the output end face of the MMI section 5 is not actually provided, and light propagates with the width of the MMI section 5 being constant. The result is shown.

  Moreover, the two white broken lines shown in FIGS. 3 and 4 indicate the start position and the end position of the region where the light intensity of the convergent light read from the intensity distribution is maintained. A range in which the start position and the end position are indicated by white double arrows is an area where the intensity distribution of the convergent light is flat. Actually, the vicinity of the center of the intensity distribution of the convergent light is set as the design value of the length of the MMI unit 5. 3 and 4, it is shown that the output light is converged at two locations in the vicinity of the output end face of the MMI unit 5.

  FIG. 5 is a diagram schematically showing the convergence state of the output light shown in FIG. FIG. 6 is a diagram schematically showing the convergence state of the output light shown in FIG. 5 and 6 show a case where the length of the MMI unit 5 is assumed to be sufficiently long.

  As shown in FIG. 5, a light convergence state (light convergence regions 15a and 15b) that is a mirror image of the input light appears near the output end face. The position of the output end face in the light propagation direction is such that the connection portion of the output optical waveguides 3a and 3b and the position B where the light intensity distribution is the highest near the center of the light convergence state coincide with each other. This position is the optimum position of the output end face (a position indicated by a broken line in the vertical direction of the paper passing through position B in FIG. 5).

  However, in practice, a deviation between the light convergence state and the position of the output end face may occur due to various variation factors. In FIG. 5, as the light convergence state decreases from B at the optimum position of the output end face as B or A or C, the light intensity distribution decreases, and the optical coupling to the output optical waveguides 3 a and 3 b decreases. . Details will be described later with reference to FIG.

  On the other hand, as shown in FIG. 6, since the input optical waveguide 1 a is inclined and connected to the input end face of the MMI section 5, the convergence state of light that is a mirror image of the input light that appears near the output end face is MMI section 5. It inclines toward the side surface side (outside) (between AB in FIG. 6). When such light propagates inside the MMI unit 5, the light intensity propagates in the order of A, B, and C as shown in FIG. 6, reflecting the contribution of light reflection from the side surface of the MMI unit 5. A small bend (curvature) occurs in the distribution. Similar to FIG. 5, the light intensity distribution becomes maximum at the position B and decreases at the positions A and C.

  The deviation between the position of the light intensity distribution in the width direction of the MMI section 5 and the position of the output optical waveguide is adjusted so that the position B is larger than the positions A and C, and the output optical waveguides 3a and 3b The optical coupling when connected to the output end face at the position B is smaller than the positions A and C. Accordingly, the dependence of optical coupling (or insertion loss) on the output optical waveguide connection positions 4a and 4b (or the length of the MMI portion 5) is flatter in the case of FIG. 6 than in the case of FIG.

  FIG. 7 is a diagram illustrating a result of the dependency of the transmission efficiency (coupling efficiency) on the length of the MMI unit 5 calculated under the same simulation conditions as those in FIGS. The MMI length on the horizontal axis indicates the length of the MMI unit 5, and the insertion loss on the vertical axis indicates the transmission efficiency.

  FIG. 7 shows the transmission efficiency of the two output optical waveguides. Further, the range of the length of the MMI portion 5 where the transmission efficiency is reduced by 0.3 dB from the condition that the transmission efficiency is maximized is indicated by rectangular hatching. This range is 9.5 μm for the optical demultiplexer shown in FIG. 1 in which the input optical waveguide 1a is inclined by 2.87 °, and 7.7 μm for the optical demultiplexer shown in FIG. 16 in which the input optical waveguide 1a is not inclined. Thus, it can be seen that the dependence of the transmission efficiency on the length of the MMI portion 5 is smaller in the optical demultiplexer shown in FIG. 1 in which the input optical waveguide 1a is inclined by 2.87 °. This result shows that the optical demultiplexer shown in FIG. 1 in which the input optical waveguide 1a is inclined by 2.87 ° is more resistant to structural variations (manufacturing variations) of the MMI section 5.

  Next, the optimum inclination angle of the input optical waveguide 1a will be described.

  In FIG. 8, the angle when the input optical waveguide 1a is inclined toward the outside of the MMI portion 5 is positive, the angle when the input optical waveguide 1a is inclined toward the inside is negative, and the inclination angle of the input optical waveguide 1a is −2 It is a figure which shows the dependence of the transmission efficiency in the optical demultiplexer changed in the range of .87 degrees-+5.74 degrees of the length of the MMI part 5. FIG. The MMI length on the horizontal axis indicates the length of the MMI unit 5, and the insertion loss on the vertical axis indicates the transmission efficiency.

  As shown in FIG. 8, the above-described flattening of the dependency of the transmission efficiency on the length of the MMI portion 5 occurs only when the transmission efficiency is inclined toward a positive angle, that is, toward the outside of the MMI portion 5. I understand. In addition, as the inclination angle of the input optical waveguide 1a increases, the dependency of the transmission efficiency on the length of the MMI portion 5 is flattened, but on the other hand, there is a trade-off relationship that the maximum value of the transmission efficiency decreases. is there. Therefore, when designing the optical demultiplexer, it is only necessary to determine the angle at which the input optical waveguide 1a is inclined toward the outside of the MMI unit 5 within a range that satisfies the target specification of transmission efficiency.

  FIG. 9 is a diagram showing the wavelength dependence of the transmission efficiency of the optical demultiplexer shown in FIGS. 16 and 1 when the length of the MMI unit 5 is fixed to 610 μm. The horizontal axis indicates the wavelength, and the insertion loss on the vertical axis indicates the transmission efficiency. The inclination angle of the input optical waveguide 1a shown in FIG. 1 is fixed at 2.87 °.

  As shown in FIG. 9, when the input optical waveguide 1a is inclined (FIG. 1), the wavelength range in which the decrease in transmission efficiency is within 0.3 dB from the maximum value of the transmission efficiency is 20 nm or more. It can be seen that the wavelength dependence of the transmission efficiency is flatter than that when 1a is not inclined (FIG. 16).

  From the above, according to the first embodiment, in the 1-input 2-output MMI type optical demultiplexer, the input optical waveguide 1 a is inclined toward the outside of the MMI unit 5, and the input end face of the MMI unit 5 By connecting to the optical demultiplexer, it is possible to obtain an optical demultiplexer having a flat transmission efficiency with respect to the structural variation of the MMI portion 5 and a small wavelength dependency. In other words, the wavelength range applicable to the optical demultiplexer according to the first embodiment can be made wider than that in the past.

  In the first embodiment, the case where there is one input optical waveguide that is inclined and connected to the MMI unit has been described, but the same effect can be obtained even when there are two input optical waveguides. That is, it is possible to obtain an optical demultiplexer in which the demultiplexing characteristics of input light from each input optical waveguide have a flat transmission efficiency with respect to manufacturing variations and have small wavelength dependence.

<Embodiment 2>
In the second embodiment of the present invention, a two-input one-output or two-input two-output optical multiplexer used in an optical integrated device including a single mode semiconductor laser in optical fiber communication will be described.

  10 and 11 are diagrams illustrating an example of the configuration of the optical multiplexer according to the second embodiment. FIG. 10 shows a 2-input 1-output optical multiplexer, and FIG. 11 shows a 2-input 2-output optical multiplexer. In the following, the optical multiplexer shown in FIG. 10 will be described in particular.

  As shown in FIG. 10, the optical multiplexer according to the second embodiment includes two input optical waveguides 1a and 1b, one output optical waveguide 3a, and a rectangular MMI unit 5.

  The input optical waveguides 1 a and 1 b are connected to the input end face of the MMI section 5 while being inclined at an inclination angle θ so as to be away from the center line 6 passing through the center of the input end face and the output end face of the MMI section 5.

  The rectangular MMI unit 5 is configured such that convergent light is obtained at two locations on the output end face of the MMI unit 5.

  That is, the optical multiplexer according to the second embodiment includes at least one or more input optical waveguides 1a and 1b connected to the input end face, and at least one input optical waveguide connected to the output end face. 1a, 1b and an output optical waveguide 3a that does not become one at the same time, and is a multimode interference type optical multiplexer (optical waveguide element) having an optical multiplexing function, and the input optical waveguides 1a, 1b are input end faces And the input end face is inclined so that the connection position with the input end face escapes further toward the end side with respect to the center.

  Details of each component of the optical multiplexer shown in FIG. 10 are as follows. That is, the width of the input optical waveguides 1a and 1b and the output optical waveguide 3a is 1.8 μm. When the wavelength used (the wavelength of light used in optical fiber communication) is 1.55 μm, the width W of the input end face and the output end face of the MMI section 5 is 12 μm, and the length L of the MMI section 5 is 610 μm. The input optical waveguide connection positions 2a and 2b and the output optical waveguide connection position 4a are W / 4 of the input end face and the output end face of the MMI section 5. Further, the inclination angle θ of the input optical waveguides 1 a and 1 b is 2.87 ° toward the outside of the MMI unit 5. The cross section (epitaxial structure) of the optical multiplexer according to the second embodiment is the same as that of the first embodiment (FIG. 2). The same applies to each component of the optical waveguide device shown in FIG.

  Next, the operation of the optical multiplexer (FIG. 10) according to the second embodiment will be described.

  The optical multiplexing characteristics of the optical multiplexer shown in FIG. 10 are similar to the optical demultiplexing characteristics of the optical demultiplexer (FIG. 1) according to the first embodiment.

  For example, the optical multiplexing characteristics of the optical multiplexer shown in FIG. 10 can be obtained from the transmission efficiency from the input optical waveguide 1a to the output optical waveguide 3a and the transmission efficiency from the input optical waveguide 1b to the output optical waveguide 3a. . This is because the transmission efficiency from the input optical waveguide 1b in FIG. 10 to the output optical waveguide 3a in FIG. 10 depends on the symmetry of the shapes of the optical multiplexer shown in FIG. 10 and the optical demultiplexer shown in FIG. The transmission efficiency from the waveguide 1a to the output optical waveguide 3b is the same. That is, in a structure including an input optical waveguide having a predetermined inclination angle, when used as an optical demultiplexer, an optical demultiplexer having a flat transmission efficiency with respect to structural variations of the MMI unit 5 can be obtained, and used as an optical multiplexer. Thus, an optical multiplexer having a flat transmission efficiency with respect to the structural variation of the MMI unit 5 can be obtained.

  In the above description, the two-input one-output optical multiplexer (FIG. 10) has been described. However, even if the two-input two-output optical multiplexer (FIG. 11) is used, two outputs having similar optical multiplexing characteristics are obtained. Therefore, there is almost no difference in the transmission efficiency characteristics of each output.

  From the above, according to the second embodiment, the two input optical waveguides 1a and 1b are inclined toward the outside of the MMI unit 5 in the two-input one-output or two-input two-output MMI type optical multiplexer. By connecting to the input end face of the MMI unit 5, it is possible to obtain an optical multiplexer that has a flat transmission efficiency with respect to structural variations of the MMI unit 5 and a small wavelength dependency. That is, the wavelength range applicable to the optical multiplexer according to the second embodiment can be made wider than that of the conventional one.

<Embodiment 3>
In a third embodiment of the present invention, a two-input one-output or two-input two-output optical multiplexer used in an optical integrated device including a single mode semiconductor laser in optical fiber communication will be described.

  12 and 13 are diagrams illustrating an example of the configuration of the optical multiplexer according to the third embodiment. 12 shows a two-input one-output optical multiplexer, and FIG. 13 shows a two-input two-output optical multiplexer. In the following, the optical multiplexer shown in FIG. 13 will be described in particular.

  As shown in FIG. 13, the optical multiplexer according to the third embodiment includes two input optical waveguides 1a and 1b, two output optical waveguides 3a and 3b, a rectangular MMI section 5, and an input optical waveguide 1b. And an extending portion 7 provided between the MMI portion 5 and the MMI portion 5.

  The input optical waveguides 1 a and 1 b are connected to the input end face of the MMI section 5 while being inclined at an inclination angle θ so as to be away from the center line 6 passing through the center of the input end face and the output end face of the MMI section 5.

  The rectangular MMI unit 5 is configured such that convergent light is obtained at two locations on the output end face of the MMI unit 5.

  That is, the optical multiplexer according to the third embodiment has at least one or more input optical waveguides 1a and 1b that are connected to the input end face and to which light having different frequencies are respectively input, and are connected to the output end face. Output optical waveguide 3a and an extending portion 7 connected between the input optical waveguides 1a and 1b to which light having the longest wavelength is input and the input end face, and has a function of optical multiplexing. It is a mode interference type optical multiplexer (optical waveguide element), and the extending portion 7 is wider than the input optical waveguides 1 a and 1 b connected to the extending portion 7 and connected to the extending portion 7. The input optical waveguides 1a and 1b have a length corresponding to the difference between the wavelength of the light input to the input optical waveguides 1a and 1b and the longest wavelength, and the input optical waveguides 1a and 1b are located on the end side from the center of the input end face. , And the connection position with the input end face or the extended portion 7 is centered. Further characterized by connecting the inclined to the input end face or drawing unit 7 to escape on the end side.

  The light of wavelength λ1 input to the input optical waveguide 1a and the light of wavelength λ2 input to the input optical waveguide 1b are included in different wavelength bands designed in advance, and the output end face of the MMI unit 5 The wavelength λ1 with a shorter propagation distance is made longer than the wavelength λ2.

The length ΔL of the extending portion 7 is determined according to the wavelength λ1 and the wavelength difference Δλ (= λ1-λ2), and is obtained from the following equation (1) with respect to the length L of the MMI portion 5.
ΔL = (Δλ / λ1) × L (1)
The width of the extending portion 7 may be selected so that the input light can propagate in multiple modes. For example, the width of the extending portion 7 is ½ of the input end face width of the MMI portion 5 as shown in FIG. By providing such an extending portion 7, the convergence positions in the propagation direction of the output light by the input light having different wavelengths are substantially matched in the vicinity of the output end face of the MMI portion 5.

  Details of each component of the optical multiplexer shown in FIG. 13 are as follows. That is, the width of the input optical waveguides 1a and 1b and the output optical waveguides 3a and 3b is 1.8 μm. When the wavelength used (the wavelength of light used in optical fiber communication) is 1.55 μm, the width W of the input end face and the output end face of the MMI section 5 is 12 μm, and the length L of the MMI section 5 is 610 μm. Further, the input optical waveguide connection positions 2 a and 2 b and the output optical waveguide connection positions 4 a and 4 b are W / 4 of the input end face and the output end face of the MMI unit 5. Further, the inclination angle θ of the input optical waveguides 1 a and 1 b is 2.87 ° toward the outside of the MMI unit 5. Further, the wavelength λ1 of the input light input to the input optical waveguide 1a is 1.55 μm, and the wavelength λ2 of the input light input to the input optical waveguide 1b is 1.53 μm. Further, the length of the stretched portion 7 is ΔL = 7.8 μm. The cross section (epitaxial structure) of the optical multiplexer according to the third embodiment is the same as that of the first embodiment (FIG. 2). The same applies to each component of the optical waveguide device shown in FIG.

  Next, the operation of the optical multiplexer (FIG. 13) according to the third embodiment will be described.

  FIG. 14 is a diagram illustrating a simulation calculation result of the wavelength dependence of the transmission efficiency of the optical multiplexer in which the input optical waveguides 1a and 1b are not inclined. FIG. 15 is a diagram showing a simulation calculation result of the wavelength dependence of the transmission efficiency of the optical multiplexer in which the input optical waveguides 1a and 1b are inclined. The horizontal axis indicates the wavelength, and the insertion loss on the vertical axis indicates the transmission efficiency.

  As shown in FIG. 14, the wavelength dependency is significantly smaller than that of the first embodiment (FIG. 9). This is because the wavelength dependency of the convergence position of the output light is corrected by providing the extending portion 7. It is.

  Further, when FIG. 14 is compared with FIG. 15, the wavelength dependency of the transmission efficiency is flatter in FIG. This is because the input optical waveguides 1a and 1b are inclined and connected to the MMI unit 5 in the same manner as in the first and second embodiments, so that the length that the output light convergence state is maintained near the output end face is increased. it is conceivable that.

  From the above, according to the third embodiment, the input optical waveguides 1a and 1b are inclined toward the outside of the MMI section 5 and connected to the input end face of the MMI section 5, and the input optical waveguide 1b and the MMI section 5 are connected. By providing the extending portion 7 between the two, it is possible to obtain an optical multiplexer that is particularly excellent in wavelength dependency of transmission efficiency with respect to input light of different wavelengths (small wavelength dependency of transmission efficiency). That is, the wavelength range applicable to the optical multiplexer according to the third embodiment can be made wider than that in the second embodiment.

  Although the optical multiplexer having the optical multiplexing function has been described in the third embodiment, the present invention can also be applied as an optical demultiplexer having the optical demultiplexing function.

  It should be noted that the present invention can be freely combined with each other within the scope of the invention, and each embodiment can be appropriately modified or omitted.

  1a, 1b Input optical waveguide, 2a, 2b Input optical waveguide connection position, 3a, 3b Output optical waveguide, 4a, 4b Output optical waveguide connection position, 5 MMI part, 6 Center line, 7 Extension part, 11 IP substrate, 12 InGaAsP Layer, 13 InP layer, 14 Dielectric layer, 15a, 15b Light converging region.

Claims (2)

At least one input optical waveguide connected to the input end face;
An output optical waveguide connected to the output end face, and at least one output optical waveguide that is not simultaneously with the input optical waveguide;
A multimode interference optical waveguide element having at least one function of optical multiplexing and demultiplexing,
The input optical waveguide is positioned closer to the end side than the center of the input end face, and is connected to the input end face with an inclination so that the connection position with the input end face escapes further toward the end side with respect to the center. And
Connection position between the input optical waveguide and the input end face, characterized by position der Rukoto said center of said input end face is not included in the input optical waveguide, optical waveguide elements. A plurality of input optical waveguides connected to the input end face and receiving light of different frequencies respectively;
At least one output optical waveguide connected to the output end face;
An extending portion provided connected between the input optical waveguide to which light that is not the longest wavelength is input and the input end face;
A multimode interference optical waveguide element having at least one function of optical multiplexing and demultiplexing,
The extending portion is wider than the input optical waveguide connected to the extending portion, and the difference between the wavelength of the light input to the input optical waveguide connected to the extending portion and the longest wavelength. According to the length,
Each of the input optical waveguides is positioned closer to the end side than the center of the input end surface, and is inclined so that the connection position with the input end surface or the extending portion escapes further toward the end side with respect to the center. Connect to the input end face or the extension part ,
Connecting position between each said input optical waveguide and the input end face, characterized by position der Rukoto said center of said input end face is not included in each of said input optical waveguide, optical waveguide elements.