JP5665728B2 - Optical device - Google Patents

Description

  The present invention relates to an optical device including a multimode optical waveguide having, for example, an MMI (Multi Mode Interference) structure.

  A multi-mode interference optical waveguide (MMI optical waveguide, hereinafter referred to as “MMI”) is widely used to connect a plurality of semiconductor lasers and an optical waveguide or to construct an MZ interferometer. As a background to this, with the dramatic increase in communication demand in recent years, wavelength division multiplex communication that enables large-capacity data transmission over a single optical fiber by multiplexing a plurality of signal lights having different wavelengths. System development is underway. In order to realize a wavelength division multiplexing communication system, a wavelength tunable light source capable of covering the entire wavelength band is necessary, and it is preferable that the cost be low. Therefore, an optical semiconductor device that can be monolithically integrated attracts attention. Yes.

  In such a wavelength tunable light source in the optical semiconductor device, an LD array in which a plurality of LDs (Laser Diodes) each emitting light of different wavelengths are arranged, and an MMI that couples the light to one optical waveguide. And are applied. In addition to the LD array, a configuration in which an intensity modulator for generating a data signal and an optical amplifier (Semiconductor Optical Amplifier: SOA) are integrated in one optical semiconductor device (element) is also realized.

  However, in the conventional MMI, not all of the light from each LD is coupled to the desired output optical waveguide, but some light is emitted from the MMI as unwanted stray light. Therefore, when stray light emitted from the MMI and reflected within the substrate is incident on the optical waveguide and recombined, there is a possibility of adversely affecting the characteristics (for example, communication characteristics) of the elements of the optical waveguide. . Further, since MMI is applied to the MZ type interferometer used as the intensity modulator for branching and multiplexing light, the MZ type is similar to the MMI for coupling the LD arrays described above. Stray light is generated in the interferometer. As a result, the MZ interferometer may be adversely affected such as deterioration of extinction ratio.

  Therefore, various techniques have been proposed in order to solve such a problem of MMI radiation (stray light). For example, Patent Document 1 discloses a technique for suppressing deterioration of element characteristics by arranging an absorption layer on the side surface of an MMI and absorbing stray light.

JP 2007-94336 A

  According to the technique disclosed in Patent Document 1, stray light transmitted through the surface of the light reaching the output side surface of the MMI can be removed by the absorption layer. However, among the light that has reached the output side of the MMI, the amount of light that is internally reflected on the output side of the MMI is still large. As a result, the light reflected on the output side surface of the MMI may become the return light to the LD (input port), and in this case, there is a problem that the operation of the LD becomes unstable.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of suppressing the return light to the input port.

An optical device according to the present invention includes an input port configured by a single mode optical waveguide, an input side surface to which the input port is connected, an output side surface facing the input side surface, a single mode optical waveguide, An output port configured by a single-mode optical waveguide and connected to the output side surface, and an absorption layer provided in the vicinity of the output side surface of the multimode optical waveguide. At least one of said input ports及beauty before SL output port are provided a plurality of. The output side surface of the multimode optical waveguide includes a surface that is convex from the end side to the center side of the output side surface and is inclined with respect to the direction perpendicular to the optical axis of the multimode optical waveguide. A surface of the absorption layer opposite to the multimode optical waveguide side is inclined with respect to the vertical direction.

  According to the present invention, the surface included in the output side surface is inclined with respect to the vertical direction of the optical axis, and the angle formed by them is greater than 0 degrees. Therefore, the reflectance of light at the output side surface can be reduced, and return light to the input port can be suppressed. Therefore, the operation of the optical element provided at the input port such as an LD can be stabilized. Moreover, since the absorption layer is provided in the vicinity of the output side surface, it is possible to suppress the influence on the characteristic deterioration due to the light emitted from the output side surface.

1 is a plan view showing a configuration of an optical waveguide device according to a first embodiment. 1 is a cross-sectional view illustrating a configuration of an optical waveguide device according to a first embodiment. 1 is a cross-sectional view illustrating a configuration of an optical waveguide device according to a first embodiment. It is a figure which shows the relationship between angle (theta) t and a reflectance. 5 is a cross-sectional view showing the method of manufacturing the optical waveguide device according to Embodiment 1. FIG. FIG. 6 is a plan view showing the method for manufacturing the optical waveguide device according to the first embodiment. FIG. 6 is a plan view showing the method for manufacturing the optical waveguide device according to the first embodiment. 5 is a cross-sectional view showing the method of manufacturing the optical waveguide device according to Embodiment 1. FIG. 1 is a plan view showing a configuration of an optical waveguide device according to a first embodiment. 6 is a plan view showing a configuration of an optical waveguide device according to a second embodiment. FIG. 6 is a plan view showing a configuration of an optical waveguide device according to a second embodiment. FIG. 6 is a plan view showing a configuration of an optical waveguide device according to a second embodiment. FIG. It is a figure which shows the relationship between angle (theta) t and a reflectance. 6 is a plan view showing a configuration of an optical waveguide device according to a third embodiment. FIG. 6 is a plan view showing a configuration of an optical waveguide device according to a third embodiment. FIG. FIG. 10 is a plan view showing a configuration of an optical waveguide device according to a fourth embodiment. FIG. 6 is a cross-sectional view illustrating a configuration of an optical waveguide device according to a fourth embodiment. FIG. 6 is a cross-sectional view illustrating a configuration of an optical waveguide device according to a fourth embodiment. FIG. 6 is a cross-sectional view illustrating a configuration of an optical waveguide device according to a fourth embodiment. FIG. 6 is a cross-sectional view illustrating a configuration of an optical waveguide device according to a fourth embodiment. FIG. 6 is a cross-sectional view illustrating a configuration of an optical waveguide device according to a fourth embodiment. FIG. 10 is a plan view showing a method for manufacturing an optical waveguide device according to a fourth embodiment. FIG. 10 is a plan view showing a method for manufacturing an optical waveguide device according to a fourth embodiment.

<Embodiment 1>
FIG. 1 is a plan view showing a configuration of an optical waveguide device that is an optical device according to Embodiment 1 of the present invention.

  As shown in FIG. 1, an optical waveguide device 1 includes an input port 2 configured by a single mode optical waveguide, a multimode optical waveguide 5 having an input side surface 3 and an output side surface 4 facing each other, and a single mode optical signal. An output port 6 constituted by a waveguide and an absorption layer 7 are provided.

  A plurality of input ports 2 and / or output ports 6 are provided. The input port 2 is connected to the input side surface 3 that is wider than that, and the output port 6 is connected to the output side surface 4 that is wider than that. In the example shown in FIG. 1, nine input ports 2 and one output port 6 are provided, and these are connected to the multimode optical waveguide 5 to form a 9 × 1 MMI.

  The absorption layer 7 is provided in the vicinity of the output side surface 4 of the multimode optical waveguide 5 and absorbs light emitted from the output side surface 4 as described later. In the present embodiment, the absorption layer 7 is provided adjacent to the output side surface 4 of the multimode optical waveguide 5. That is, the output side surface 4 of the multimode optical waveguide 5 and the surface 7a of the absorption layer 7 on the multimode optical waveguide 5 side (hereinafter referred to as “absorption layer incident surface 7a”) are provided in contact with each other. In the present embodiment, the surface 7 b of the absorption layer 7 opposite to the multimode optical waveguide 5 side (hereinafter referred to as “absorption layer reflection surface 7 b”) is orthogonal to the optical axis 5 a of the multimode optical waveguide 5. ing.

  As shown in FIG. 1, the output side surface 4 of the multimode optical waveguide 5 protrudes from the end side of the output side surface 4 toward the center side so as to be perpendicular to the optical axis 5 a of the multimode optical waveguide 5. (Hereinafter referred to as “optical axis vertical direction 5b”) and two inclined surfaces 4a and 4b which are inclined with respect to each other. That is, if the angle formed between the inclined surfaces 4a and 4b and the optical axis vertical direction 5b of the multimode optical waveguide 5 is θt, θt> 0 degrees.

  2 and 3 are cross-sectional views of the optical waveguide device 1 according to the present embodiment. 2 is a cross-sectional view taken along a cutting line A-A ′ shown in FIG. 1, and FIG. 3 is a cross-sectional view taken along a cutting line B-B ′ shown in FIG. 1.

  As shown in FIGS. 2 and 3, the optical waveguide device 1 according to the present embodiment is formed with a buried structure. Specifically, the optical waveguide device 1 is formed on an InP substrate 11 having a pedestal on its surface, a multimode optical waveguide 5 made of InGaAsP bulk formed on the pedestal, and the multimode optical waveguide 5. And an InP layer 13 surrounding the pedestal, the multimode optical waveguide 5 and the upper cladding layer 12, and an InP layer 14 formed on the upper cladding layer 12 and the InP layer 13. Yes. Between the pedestal, the multimode optical waveguide 5, the upper cladding layer 12, and the InP layer 13, an absorption layer 7 having an InGaAsP quantum well structure is selectively provided.

  Next, the basic operation of the MMI will be described. The MMI has a function of outputting light from the output port 6 when light is input from any input port 2. Therefore, for example, by connecting a plurality of LDs (not shown here) each emitting light of a different wavelength to the plurality of input ports 2 and emitting only the LD of light of a desired wavelength, Light of a desired wavelength can be output from the output port 6. That is, according to the MMI, it is possible to realize a broadband wavelength tunable light source by selectively causing the LD to emit light. If each LD is provided with a temperature adjustment mechanism, etc., and configured to have a fine adjustment function of the wavelength of each LD, the wavelength of the light can be complemented, and a tunable light source that covers a wide band without gaps is realized. can do.

  As described above, the light input from any one of the input ports 2 propagates through the multimode optical waveguide 5 and is then coupled to the output port 6. Here, for example, when there are twelve input ports 2, only 1/12 light is coupled in principle, and the remaining 11/12 light is not coupled to the output port 6, but the output side surface 4. Radiated from. The light (stray light) radiated from the output side surface 4 is not only lost, but also reflected by an external element or the like and recombined with the multimode optical waveguide 5, causing deterioration of the element characteristics. Yeah.

  Therefore, in the technique disclosed in Patent Document 1, an absorption layer is disposed in contact with the output side surface of the MMI, thereby absorbing light emitted from the output side surface and suppressing characteristic deterioration. However, since the boundary surface between the output side surface of the MMI and the absorption layer is parallel to the optical axis vertical direction (that is, θt = 0 degrees), a relatively large amount of light from the input port is output. Reflected on the side. As a result, the light reflected on the output side surface becomes the return light to the LD, which causes problems such as unstable operation of the LD.

  Therefore, as described above, in the present embodiment, the output side surface 4 is not parallel to the optical axis vertical direction 5b, but is inclined with respect to the optical axis vertical direction 5b (θt> 0 degrees). 4b is included. Thereby, the return light to the input port 2 can be suppressed. This will be described below.

  FIG. 4 shows the result of calculating the reflectance with respect to the angle θt formed by the output side surface 4 (inclined surfaces 4a and 4b) and the optical axis vertical direction 5b. The refractive index of MMI was n = 3.4 (InGaAsP bulk), and the refractive index of the absorption layer 7 was n = 3.5 (InGaAsP quantum well structure). As shown in the calculation result, compared to the case where the angle θt is 0 degree as in Patent Document 1, the reflectance is reduced when the angle θt is about 10 degrees to 55 degrees, and the degree is 40 degrees to 50 degrees. It can be seen that the reflectance is particularly reduced between the following levels. When the angle θt is 45 degrees, the reflectance is almost zero.

  Here, when the reflectance is lowered, the return light to the input port 2 (return light to the LD) is suppressed, and the operation of the LD is stabilized. On the other hand, when the reflectivity is low, the radiation (stray light) from the output side surface 4 of the multimode optical waveguide 5 increases somewhat, but the radiation (stray light) is absorbed by the absorption layer 7. The characteristic deterioration by it is suppressed.

  Further, according to the configuration in which the angle θt is set to about 45 degrees as shown in FIG. 1, even if the reflected light is generated at the output side surface 4, the return light to the input port 2 (return to the LD) In order to become (light), it is necessary to reflect a plurality of times (for example, twice) on the output side surface 4 as indicated by the broken line arrow in FIG. Therefore, since the reflected light at the output side surface 4 is difficult to return to the input port 2 (LD), the return light to the input port 2 (return light to the LD) can be further suppressed from this viewpoint.

  In particular, the light from the input port 2 actually has a divergence angle of about 5 to 10 degrees, and the light intensity is small at the outer portion where the divergence angle is large, and the light intensity is at the center where the divergence angle is small. The light intensity distribution is the largest. Therefore, when it is desired to reduce the return light to the input port 2 due to the light intensity component at the center, the angle θt is set to about 45 degrees so that the return light to the input port 2 can be reliably suppressed. It is desirable to have a configured configuration.

  5 to 8 are views in the manufacturing process of the optical waveguide device 1 according to the present embodiment. Next, a manufacturing method of the optical waveguide device 1 will be described with reference to FIGS.

  First, as shown in FIG. 5, after forming an active layer 16 having an InGaAsP / InGaAsP quantum well structure to be an absorption layer 7 on the InP substrate 11 by using MOCVD (Metal Organic Chemical Vapor Deposition) method or the like, A part of the upper cladding layer 12 made of InP is formed thereon.

  Thereafter, using a photolithography technique, as shown in FIG. 6, a mask 17 such as silicon oxide is formed in a region where the absorption layer 7 is formed, and the other regions are removed by wet etching or dry etching. Thereafter, an InGaAsP bulk core layer serving as an MMI (input port 2, multimode optical waveguide 5 and output port 6) and a layer serving as an upper cladding layer 12 made of InP are sequentially stacked by a selective growth method.

  Then, as shown in FIG. 7, a mask 18 such as silicon oxide is further formed in the region where the MMI is to be formed, and the region where the masks 17 and 18 are not formed is removed by etching. FIG. 8 is a cross-sectional view of the configuration taken along the section line C-C ′ shown in FIG. 7 among the configurations formed at that time. However, the masks 17 and 18 are not shown in FIG.

  Thereafter, the InP layer 13 surrounding the MMI, the absorption layer 7 and the upper cladding layer 12 is grown by a selective growth method. In this state, the masks 17 and 18 are all removed with hydrofluoric acid or the like, and then the uppermost InP layer 14 is formed. Thus, the optical waveguide device 1 according to the present embodiment shown in FIGS. 1 to 3 is formed.

  As described above, in the optical waveguide device 1 according to the present embodiment, the angle θt formed by the inclined surfaces 4a and 4b and the optical axis vertical direction 5b is greater than 0 degrees. Therefore, the reflectance of light at the output side surface 4 can be reduced, and the return light to the input port 2 can be suppressed. Therefore, the operation of the LD can be stabilized. Moreover, since the absorption layer 7 is provided in the vicinity of the output side surface 4, it is possible to suppress the influence on the characteristic deterioration due to the light emitted from the output side surface 4.

  Further, according to the present embodiment, the absorption layer 7 is provided adjacent to the output side surface 4 of the multimode optical waveguide 5. Therefore, the light emitted from the output side surface 4 can be absorbed before diffusing. It can also be expected to reduce the size of the optical waveguide device 1. When the absorption layer 7 is provided adjacent to the output side surface 4 and the angle θt is 10 degrees or more and 55 degrees or less, as shown in FIG. Therefore, the LD operation can be reliably stabilized.

  In the above, as shown in FIG. 1, the absorption layer 7 is formed only in the vicinity of the inclined surfaces 4a and 4b, but this is not restrictive. For example, as illustrated in FIG. 9, the absorption layer 7 may be configured to be elongated along the output port 6. With such a configuration, the distance that the stray light incident on the absorption layer 7 propagates in the absorption layer 7 becomes long, so that the stray light can be sufficiently attenuated in the absorption layer 7. 7 can be reliably absorbed. Unlike the configuration shown in FIG. 9, the absorption layer 7 may be provided in contact with the output port 6, but in order not to attenuate light propagating through the output port 6, as shown in FIG. 9, the absorption layer 7 7 and the output port 6 are desirably provided, and an InP layer (for example, InP layer 13) is preferably formed in the gap.

<Embodiment 2>
10 to 12 are plan views showing the configuration of the optical waveguide device 1 according to the second embodiment of the present invention. In the present embodiment, the shape of the absorption layer 7 in plan view is different from that of the first embodiment. Therefore, in the optical waveguide device 1 according to the present embodiment, the same or similar components as those described in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the configuration of the optical waveguide device 1 according to the first embodiment described above, the light emitted from the output side surface 4 of the MMI is absorbed by the absorption layer 7. However, as shown in FIG. 1, in the configuration in which the absorbing layer reflecting surface 7b is parallel to the optical axis vertical direction 5b, it is assumed that strong light is transmitted from the MMI output side surface 4 to the absorbing layer 7 (absorbing layer incident surface). 7a), the light may be incident / reflected at an incident angle / reflection angle of 0 degree on the absorbing layer reflecting surface 7b to be returned to the input port 2 (LD). is there. As a configuration for solving this, a configuration in which the absorption layer 7 is elongated as shown in FIG. 9 is also conceivable, but it is considered that the configuration cannot be adopted when there is not enough space due to the layout. .

  Therefore, in the optical waveguide device 1 shown in FIG. 10, the absorbing layer reflecting surface 7b is inclined with respect to the optical axis vertical direction 5b. According to such a configuration, the light reflected by the absorbing layer reflecting surface 7b can be prevented from going to the input port 2 side. Therefore, even if there is not enough space, the absorbing layer 7 The incident light can be reliably absorbed in the absorption layer 7.

  In addition, when there is room in the space, as shown in FIG. 11, in the configuration shown in FIG. 10, the absorption layer 7 may be elongated along the output port 6. According to such a configuration, the light incident on the absorption layer 7 can be more reliably absorbed in the absorption layer 7. In this configuration, the absorption layer 7 may be provided in contact with the output port 6, but in order not to attenuate the light propagating through the output port 6, the absorption layer 7 and the output port as shown in FIG. It is desirable to provide a gap between 6 and form an InP layer (for example, InP layer 13) in the gap.

  In the configuration shown in FIG. 12, the absorption layer 7 is provided apart from the output side surface 4 of the multimode optical waveguide 5, unlike the conventional configuration. The absorption layer incident surface 7 a is inclined with respect to the optical axis vertical direction 5 b so as not to face the multimode optical waveguide 5. According to such a configuration, the ratio at which stray light emitted from the output side surface 4 is reflected so as not to return to the multimode optical waveguide 5 at the absorption layer incident surface 7a (here, toward the optical axis vertical direction 5b). On the other hand, it is possible to reduce the rate of transmission from the absorption layer incident surface 7a into the absorption layer 7. Therefore, since the return light from the absorption layer 7 to the input port 2 can be suppressed, the operation of the LD can be stabilized.

  FIG. 13 shows the result of calculating the reflectance with respect to the angle θt formed by the output side surface 4 (inclined surfaces 4a and 4b) and the optical axis vertical direction 5b in the configuration shown in FIG. The refractive index of MMI was n = 3.4 (InGaAsP bulk), and the refractive index of the medium outside the MMI was n = 3.17 (InP). As shown in the calculation results, the reflectance is almost zero when the angle θt is about 40 to 45 degrees as compared to the case where the angle θt is 0 degrees as in Patent Document 1 described above.

  Further, as described in the first embodiment, according to the configuration in which the angle θt is set to about 45 degrees, even if the reflected light is generated on the output side surface 4, the return light (LD) to the input port 2 To return to the light output side 4), the output side surface 4 needs to be reflected a plurality of times (for example, twice). Therefore, since the reflected light at the output side surface 4 is difficult to return to the input port 2 (LD), the return light to the input port 2 (return light to the LD) can be further suppressed from this viewpoint.

  As shown in FIG. 12, the absorption layer 7 may be provided in contact with the output port 6. However, in order not to attenuate the light propagating through the output port 6, it is desirable to provide a gap between the absorption layer 7 and the output port 6, and to form an InP layer (for example, InP layer 13) in the gap. In the configuration shown in FIG. 12, the absorption layer 7 may be elongated along the output port 6 in order to completely absorb the light propagating through the absorption layer 7. In the configuration shown in FIG. 12, the absorbing layer reflecting surface 7b may be provided inclined with respect to the optical axis vertical direction 5b. Even in these cases, since the return light to the input port 2 can be suppressed, the operation of the LD can be stabilized.

<Embodiment 3>
14 and 15 are plan views showing the configuration of the optical waveguide device 1 according to Embodiment 2 of the present invention. In the optical waveguide device 1 according to the present embodiment, the same or similar components as those described in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the optical waveguide device 1 shown in FIG. 14, one input port 2 and two output ports 6 are provided, and a 1 × 2 MMI is configured. In this MMI, light incident from one input port 2 is branched into two, and is output from two output ports 6 in principle with little loss. However, there are some components emitted from the output side surface 4 due to production errors and the like. Here, in the present embodiment, since the absorption layer 7 is provided adjacent to the output side surface 4, it is possible to absorb light emitted from the output side surface 4.

  Note that in the 1 × 2 MMI shown in FIG. 14, the proportion of light emitted from the output side surface 4 is considered to be high between the two output ports 6. In addition, since the emitted light from the output side surface 4 travels substantially parallel to the longitudinal direction of the element, there is a relatively high possibility that it will be recombined at other MMI or at the coupling portion between the element and the fiber. In FIG. 14, the light that travels between the two output ports 6 that is considered to have the most adverse effect on the characteristics of the element is indicated by an arrow.

  Here, as shown in FIG. 14, in the configuration in which the angle θt is set to 45 degrees, the light traveling between the two output ports 6 has an incident angle of approximately 45 degrees on the output side surface 4. In order to be incident / reflected at the reflection angle and return light to the input port 2 (return light to the LD), it is necessary to reflect the output side surface 4 a plurality of times (for example, twice). Therefore, since the reflected light at the output side surface 4 is less likely to return to the input port 2 (LD), the return light to the input port 2 (return light to the LD) can be further suppressed.

  In the configuration shown in FIG. 14, the absorption layer 7 is provided adjacent to the output port 6. However, in order not to attenuate the light propagating through the output port 6, the absorption layer 7 is provided between the absorption layer 7 and the output port 6. It is desirable to provide a gap in the substrate and to form an InP layer (for example, InP layer 13) in the gap.

  In the optical waveguide device 1 shown in FIG. 15, two input ports 2 and one output port 6 are provided, and a 2 × 1 MMI is configured. In this MMI, if the light incident from the two input ports 2 is in phase, the light is output from the output port 6. However, if the phase of light incident from the two input ports 2 is shifted by, for example, π, the light is extinguished, and ideally no light is output from the output port 6.

  Actually, there are some components radiated from the output side surface 4 due to creation errors or the like, regardless of whether the phase of light is in phase or shifted by π. Here, in the present embodiment, since the absorption layer 7 is provided adjacent to the output side surface 4, it is possible to absorb light emitted from the output side surface 4.

  Further, as shown in FIG. 15, in the configuration in which the angle θt is set to 45 degrees, the reflected light on the output side surface 4 is similar to the configuration described with reference to FIG. Since it becomes difficult to return to the input port 2 (LD), the return light to the input port 2 (return light to the LD) can be further suppressed.

<Embodiment 4>
FIG. 16 is a plan view showing the configuration of the optical waveguide device according to the fourth embodiment of the present invention. As shown in FIG. 16, the optical waveguide device according to the present embodiment has nine LDs 31 each emitting light of a different wavelength and the same configuration as the optical waveguide device 1 of the first embodiment. A 9 × 1 MMI 41 and an MZ (Mach-Zehnder) type modulator 51 are provided. The MZ modulator 51 includes a modulation electrode 52, a 1 × 2 MMI 53 having a configuration similar to the configuration shown in FIG. 14, and a 2 × 1 MMI 54 having a configuration similar to the configuration shown in FIG. .

  Nine LDs 31 are respectively connected to nine input ports 2 of 9 × 1 MMI 41, and one output port 6 of 9 × 1 MMI 41 is connected to one input port 2 of 1 × 2 MMI 53. One of the two output ports 6 of the 1 × 2 MMI 53 is connected to one of the two input ports 2 of the 2 × 1 MMI 54, and the other of the two output ports 6 of the 1 × 2 MMI 53 is connected to the 2 × 1 MMI 54. The other of the two input ports 2 is connected via the modulation electrode 52.

  In the above configuration, when one desired LD 31 emits light, light having a desired wavelength is output from the output port 6 of the 9 × 1 MMI 41. At this time, in principle, 1/9 light is output from the output port 6 of the 9 × 1 MMI 41, but the remaining 8/9 light cannot be coupled to the output port 6 and is emitted from the output side surface of the 9 × 1 MMI 41. Is done. However, in the present embodiment, since the absorption layer 7 is provided adjacent to the output side surface, light emitted from the absorption layer 7 is absorbed. Therefore, the adverse effect of the light on the modulation signal of the subsequent MZ type modulator 51 can be suppressed. Further, since the output side surface of the 9 × 1 MMI 41 is inclined at 45 degrees with respect to the optical axis vertical direction 5b, the return light to the LD 31 side can be made extremely small as described in the first embodiment and the like. And the characteristics of the LD 31 can be stabilized.

  Next, components of the MZ type modulator 51 located at the subsequent stage of the 9 × 1 MMI 41 will be described.

  In the 1 × 2 MMI 53 connected to the output port 6 of the 9 × 1 MMI 41, the light incident from one input port 2 is branched into two, and in principle, the two output ports 6 receive almost no loss. Is output from. However, there are some components radiated from the output side of the 1 × 2 MMI 53 due to creation errors and the like. Here, in the present embodiment, since the absorption layer 7 is provided adjacent to the output side surface, light emitted from the absorption layer 7 is absorbed. Accordingly, adverse effects of the light on the subsequent element can be suppressed. Further, since the output side surface of the 1 × 2 MMI 53 is inclined at 45 degrees with respect to the optical axis vertical direction 5b, the return light to the LD 31 side can be made extremely small as described in the first embodiment. And the characteristics of the LD 31 can be stabilized.

  The above-described modulation electrode 52 is provided on an intermediate arm portion between the 1 × 2 MMI 53 and the 2 × 1 MMI 54. By applying a voltage to the modulation electrode 52, the refractive index of the arm portion (optical waveguide) provided with the modulation electrode 52 changes, and the phase of light changes. As a result, the optical output of the MZ type modulator 51 can be switched ON / OFF depending on the magnitude of the applied voltage. For example, when the phases of the light transmitted through the two arms are the same, the light is output, and when the phases are shifted by π, the lights cancel each other and are not output. Therefore, by applying an electric RZ (Return to Zero) signal to the modulation electrode 52 using the signal voltage applying means 55 for applying a voltage (signal), an optical RZ signal can be obtained.

  Actually, the light transmitted through the arm is radiated from the output side surface of the 2 × 1 MMI 54 regardless of whether the phase of the light transmitted through the arm is in phase or π is shifted due to a creation error or the like. There is some light. If this radiated light is mixed from the coupling portion of the fiber through which the signal light passes, problems such as deterioration of the extinction ratio of the modulation signal occur. On the other hand, in the present embodiment, since the absorption layer 7 is provided adjacent to the output side surface, it is possible to absorb light emitted from the output side surface. Problems can be prevented from occurring. Further, since the output side surface of the 2 × 1 MMI 54 is inclined at 45 degrees with respect to the optical axis vertical direction 5b, the return light to the LD 31 side can be made extremely small as described in the first embodiment. And the characteristics of the LD 31 can be stabilized.

  17 to 21 are sectional views taken along cutting lines A-A ', B-B', C-C ', D-D', and E-E 'shown in FIG. 16, respectively.

  As shown in FIG. 17, the LD 31 is provided in the InP substrate 11, the layer 22 having an InGaAsP quantum well structure formed thereon, the upper cladding layer 12, the InP layer 14, and the upper cladding layer 12. The diffraction grating 21 is provided. On the side surface of the layer 22, an optical waveguide 23 made of an InGaAsP bulk connecting the layer 22 and the input port 2 of the 9 × 1 MMI 41 is provided.

  The configuration shown in FIGS. 18 and 19 is almost the same as the configuration shown in FIGS. 2 and 3, and the configuration shown in FIGS. 20 and 21 is the same as that shown in FIG. 20 except for the difference between the embedded structure and the high mesa structure. 2 and the configuration shown in FIG. Here, the 9 × 1 MMI 41 is formed with a buried structure (FIGS. 18 and 19) and the 1 × 2 MMI 54 is formed with a high mesa structure (FIGS. 20 and 21), but this is not restrictive. All of these may be formed with a buried structure.

  Next, a method for producing an optical waveguide device according to the present embodiment will be described.

  First, an active layer 16 having an InGaAsP / InGaAsP quantum well structure to be the LD 31 and the absorption layer 7 is formed on the InP substrate 11 by MOCVD or the like, and then the upper cladding layer 12 made of InP is formed thereon. Forming part. At this time, in order to construct a DFB laser by obtaining wavelength selectivity, a diffraction grating 21 is formed on the quantum well structure region constituting the LD 31 as shown in FIG.

  Thereafter, using a photolithography technique, as shown in FIG. 22, a mask 26 made of silicon oxide or the like is formed in a region where the LD 31 and the absorption layer 7 are formed, and other regions are removed by wet etching or dry etching. . Thereafter, an InGaAsP bulk core layer serving as an MMI (input port 2, multimode optical waveguide 5 and output port 6) and a layer serving as an upper cladding layer 12 made of InP are sequentially stacked by a selective growth method.

  Then, as shown in FIG. 23, MMI 41, 53, 54, an optical waveguide for coupling LD31 and MMI41, an optical waveguide for coupling MMI41 and MMI53, and an optical waveguide for coupling MMI53 and MMI54 A mask 27 made of silicon oxide or the like is further formed in a region where the film is to be formed. Then, the regions where the masks 26 and 27 are not formed are removed by etching.

  Thereafter, the InP layer 13 surrounding the LD 31, the MMI 41, 53, and 54, the above-described optical waveguide, the absorption layer 7 and the upper cladding layer 12 is grown by a selective growth method. From this state, the masks 26 and 27 are all removed with hydrofluoric acid or the like, and then the uppermost InP layer 14 is formed. Thus, the optical waveguide device according to the present embodiment shown in FIGS. 16 to 21 is formed.

  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.

  DESCRIPTION OF SYMBOLS 1 Optical waveguide type device, 2 input port, 3 input side surface, 4 output side surface, 5 multimode optical waveguide, 5b optical axis perpendicular direction, 6 output port, 7 absorption layer, 7a absorption layer incident surface, 7b absorption layer reflective surface.

Claims (4)

An input port composed of a single mode optical waveguide;
A multimode optical waveguide having an input side to which the input port is connected, and an output side facing the input side;
An output port configured by a single mode optical waveguide and connected to the output side surface;
An absorption layer provided in the vicinity of the output side surface of the multimode optical waveguide,
At least one of said input ports及beauty before SL output port are provided a plurality of,
The output side of the multimode optical waveguide is:
In a convex shape toward the central side from the end side of the output side, seen including a surface which is inclined with respect to the vertical direction of the optical axis of the multimode optical waveguide,
An optical device , wherein a surface opposite to the multimode optical waveguide side of the absorption layer is inclined with respect to the vertical direction . The optical device according to claim 1,
The optical device, wherein the absorption layer is provided adjacent to the output side surface of the multimode optical waveguide . An optical device according to 請 Motomeko 2,
Wherein said inclined to have plane vertical and the angle of the multimode optical waveguide, Ru der least 10 degrees 55 degrees or less, the optical device. The optical device according to claim 1 ,
The absorption layer is provided apart from the output side surface of the multimode optical waveguide,
The surface of the multimode optical waveguide side of the absorbent layer, it is inclined to the vertical direction so as not suitable for the multi-mode optical waveguide, the optical device.

Images