JP2010091900A - Optical circuit element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the influence of reflected and returned light on the element characteristic of an optical circuit element. <P>SOLUTION: The optical circuit element 1 includes: a 2×2 MMI coupler 30; a 2×2 MMI coupler 31; an optical waveguide 303; and an optical waveguide 304, wherein the 2×2 MMI coupler 30 has a port 32 and a port 33 on one end face and a port 34 and a port 35 on the other end face, the 2×2 MMI coupler 31 has a port 36 and a port 37 on one end face and a port 38 and a port 39 on the other end face, the port 34 and the port 36 are connected via the optical waveguide 303, the port 35 and the port 37 are connected via the optical waveguide 304, a light absorption region 20 is connected to the port 33, a light absorption region 21 is connected to the port 38, and a reflection boundary 22 exists between the port 34 and the port 36, and between the port 35 and the port 37. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical circuit element.

  The demand for miniaturization and high functionality of optical component packages is increasing year by year, and the integration of optical devices is progressing accordingly. For that purpose, it is necessary to examine the integration method of optical devices, selected materials, and element structures.

  First, in the case where different function elements such as a wavelength tunable filter and a modulator are integrated in a light emitting element such as a laser, it is desirable that the material of each function element is made of an optimum material according to each feature. Materials used for optical devices include compound semiconductor systems, silicon systems, and quartz systems.

  For functional elements that use compound semiconductors for some or all regions as materials, the structure of each functional element is configured according to the characteristics of each element in terms of element size, high-speed response, reliability, etc. It is desirable to do. The structure includes a core structure and a waveguide structure.

  First, the core structure will be described. The core structure can be divided into an active region having a layer having a small band gap energy and a passive region having a layer having a large band gap energy in order to obtain an optical gain at a target wavelength. The band gap can be adjusted by the layer thickness, the crystal composition ratio, and the crystal strain resulting from the crystal composition ratio. The active region is used for lasers, LEDs (Light Emitting Diodes), optical amplifiers, photodetectors, and the like. The passive region is used for a modulator, an optical filter, and the like. In addition, physical properties can be made different by changing the type of atomic material constituting each active region and passive region, and atoms such as Al, Ga, In, N, P, As, and Sb are often used for optical devices. Used.

  Next, the waveguide structure will be described with reference to FIG. Waveguide structures are classified into a plurality of types depending on the shape and the number of waveguide modes. In terms of shape, there are three types of waveguide structures that are often used in optical devices: a high-mesa waveguide structure, a rib waveguide structure, and a buried waveguide structure.

  FIG. 8A is a schematic diagram showing an example of a high mesa waveguide structure. As shown in FIG. 8A, a mesa-shaped laminate including a clad 11 and a core 12 sandwiched between the clads 11 is formed on the substrate 10. The high mesa waveguide structure has a shape in which the side part of the waveguide is replaced with a low refractive index material such as air or dielectric over the top and bottom of the core 12, so that the refractive index contrast between the semiconductor and the low refractive index material is large. . Therefore, even if the waveguide is sharply bent, the radiation loss is not easily increased. Therefore, the high mesa waveguide structure is used for forming a device that uses a bent waveguide in a small size. Further, by filling both sides of the high mesa waveguide with a material having a low refractive index, that is, a low dielectric constant, the electric capacity can be reduced. At this time, since the charging time of the capacity portion at the time of signal modulation is short, it is also used for a device that requires high-speed operation.

  FIG. 8B is a schematic diagram illustrating an example of a rib waveguide structure. As shown in FIG. 8B, a laminate composed of a clad 11 and a core 12 sandwiched between the clads 11 is formed on the substrate 10, and the clad 11 formed on the core 12 is formed in a mesa shape. ing. The rib waveguide structure has a shape in which the clad 11 above the core 12 is replaced with a low refractive index material such as air or dielectric. In this structure, since the core 12 is not processed for forming the waveguide, lattice defects are hardly generated. As a result, even if a local temperature rise due to current injection occurs, an increase in lattice defects that leads to device deterioration is unlikely to occur, and the reliability is good. Therefore, the rib waveguide structure is often used for gain elements such as lasers, LEDs, and optical amplifiers that involve current injection.

  FIG. 8C is a schematic diagram illustrating an example of a buried waveguide structure. As shown in FIG. 8C, a clad 11 and a core 12 embedded in the clad 11 are formed on the substrate 10. The buried waveguide structure has a shape in which a portion on the side of the waveguide is replaced with a semiconductor material having a refractive index smaller than that of the core 12. In this structure, since the damage caused by the processing for forming the waveguide is recovered by crystal regrowth, lattice defects are hardly generated. As a result, as with the rib waveguide shown in FIG. 8B, even if a local temperature rise due to current injection occurs, an increase in lattice defects that leads to device deterioration is unlikely to occur, and the reliability is good. is there. Therefore, the buried waveguide structure is often used for gain elements such as lasers, LEDs, and optical amplifiers with current injection. The buried waveguide structure has a drawback that the process is complicated, but carrier confinement is better than the rib waveguide structure shown in FIG. 8B, and is exposed like the high mesa waveguide structure shown in FIG. Therefore, when applied to a laser, the threshold value can be lowered and the device can be operated with high efficiency.

  Regarding the number of waveguide modes, there are two types of waveguide structures that are often used in optical devices: multi-mode waveguides that guide a plurality of modes and single-mode waveguides that guide a single mode. Yes (not shown).

  A multi-mode waveguide is a waveguide that guides a plurality of mode lights. Since it guides multiple mode lights, it is not suitable as a waveguide for optical communication devices, but it can add functions such as optical multiplexing / demultiplexing by skillfully utilizing interference of multiple mode lights. . This property is called multimode interference (MMI).

  The single mode waveguide is a waveguide that guides only fundamental mode light, and is often used as a waveguide of an optical communication device. The width of the waveguide is narrower than that of the multimode waveguide.

  There is no waveguide structure or core structure that is optimal for any device. Therefore, in order to improve the performance of the integrated device as a whole, it is important to use a waveguide structure or a core structure suitable for each device.

  As one of the monolithic integration methods of two types of core structures, a part of the core structure is processed by dry etching or the like, and another core structure is newly obtained by using the Metal-Organic Vapor Phase Epitaxy (MOVPE) method or the Chemical Beam Epitaxy. There is a known butt joint (BJ) technique formed by crystal growth such as the (CBE) method.

Since the waveguide structures have greatly different cross-sectional shapes, the electric field distribution of the waveguide mode is also different. When directly connected, part of the mismatched component of the electric field distribution of the waveguide mode becomes reflected return light. . The reflected return light causes laser noise, and changes in characteristics occur even if the relative amount of return light is as small as about 10 ⁻⁶ . Specifically, the optical output, the number of oscillation modes, the oscillation spectrum, the noise intensity, and the response output waveform during modulation change. As a related technique, the waveguide width of the boundary portion (reflection boundary 22) between the high mesa waveguide structure 72 and the embedded waveguide structure 71 is adjusted so that the electric field distributions of the waveguide modes match each other as much as possible. A method has been developed in which the shape of the waveguide is gradually changed to a tapered shape to suppress a steep change in the waveguide mode and suppress reflected reflected light (FIG. 9).
Japanese Patent Laid-Open No. 11-87844 "Spotsize Converter With Improved Design for InP-Based Deep-Ridge Waveform Structure", Masaki Kotoku et al., J. MoI. Lightwave Technology, 23 (12), pp. 4207-4214, 2005.

  However, the optical circuit elements disclosed in Non-Patent Document 1 and Patent Document 1 have the following problems.

  First, regarding the connection between different waveguide structures, practically sufficient reflectance reduction has not been achieved. This is because the high-mesa waveguide structure, rib waveguide structure, and buried waveguide structure have different cross-sectional structures, and it is difficult to perfectly align the electric field distribution of the waveguide mode of each waveguide. . In addition, since each waveguide structure is often formed in a separate process, the waveguide at the boundary portion is displaced due to a positional shift such as exposure, which may cause reflected return light.

  Secondly, the BJ technology for connecting different core structures has not achieved a practically sufficient reflectivity reduction. This is because the shape control is difficult because high-precision etching and crystal regrowth techniques are required. Therefore, reflected return light is formed at the BJ.

  The present invention has been made in view of the above circumstances, and provides a technique capable of suppressing the influence of the generated reflected return light on the element characteristics in an optical circuit element having a reflection boundary where the reflected return light is formed. The purpose is to do.

According to the present invention, a first multimode interference coupler;
A second multimode interference coupler facing the first multimode interference coupler;
First and second optical waveguides respectively connecting between the first multimode interference coupler and the second multimode interference coupler;
Have
The first multimode interference coupler is:
A first port and a second port on one side;
Have a third port and a fourth port on the other side,
The second multimode interference coupler is:
Has a fifth port and a sixth port on one side,
It has a seventh port and an eighth port on the other side,
The third port and the fifth port are connected via the first optical waveguide;
The fourth port and the sixth port are connected via the second optical waveguide;
A first light absorbing portion is connected to the second port,
A second light absorbing portion is connected to the seventh port,
The first multimode interference coupler or the second multimode interference coupler is propagated either between the third port and the fifth port or between the fourth port and the sixth port. An optical circuit element is provided in which a reflection boundary for reflecting light is interposed.

  According to the present invention, the influence of the reflected return light on the semiconductor laser can be suppressed by guiding the reflected return light generated at the reflection boundary to the light absorbing portion. As a result, it is possible to realize an optical integrated device in which an optimum material, waveguide structure, and core structure are arranged in each region while suppressing residual reflection.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

(First embodiment)
FIG. 1 is a plan view of an optical circuit element 1 according to the present embodiment. The optical circuit element 1 includes a 2 × 2 MMI coupler (first multimode interference coupler) 30, a 2 × 2 MMI coupler (second multimode interference coupler) 31 facing the 2 × 2 MMI coupler 30, and 2 × An optical waveguide 303 (first optical waveguide) and an optical waveguide 304 (second optical waveguide) are connected between the 2MMI coupler 30 and the 2 × 2 MMI coupler 31, respectively. The 2 × 2 MMI coupler 30 has a port 32 (first port) and a port 33 (second port) on one end face, and a port 34 (third port) and a port 35 (fourth port) on opposite end faces. ). The 2 × 2 MMI coupler 31 has a port 36 (fifth port) and a port 37 (sixth port) on one end face, and a port 38 (seventh port) and a port 39 (eighth port) on the opposite end face. ). The port 34 and the port 36 are connected via an optical waveguide 303, and the port 35 and the port 37 are connected via an optical waveguide 304. An optical waveguide 302 is joined to the port 33, and the port 33 and the light absorption region 20 (first light absorption portion) are connected via the optical waveguide 302. An optical waveguide 305 is joined to the port 38, and the port 38 and the light absorption region 21 (second light absorption portion) are connected via the optical waveguide 305. Between the port 34 and the port 36 and between the port 35 and the port 37, the reflection boundary 22 that reflects the light propagated through the 2 × 2 MMI coupler 30 or the 2 × 2 MMI coupler 31 is interposed.

  In other words, the configuration of the optical circuit element 1 of the present embodiment is as follows. A 2 × 2 MMI coupler 30 and a 2 × 2 MMI coupler 31 are provided, and two ports are connected to two opposite end faces of each 2 × 2 MMI coupler. Of the two end faces of the 2 × 2 MMI coupler 30, the ports connected to the end face far from the 2 × 2 MMI coupler 31 are the port 32 and the port 33, and the ports connected to the other end face are the port 34 and the port 35. It is. Of the two end faces of the 2 × 2 MMI coupler 31, the ports connected to the end face far from the 2 × 2 MMI coupler 30 are the port 38 and the port 39, and the ports connected to the other end face are the port 36, Port 37. The port 34 and the port 36 are connected to face each other, and the port 35 and the port 37 are connected to face each other. The port 33 is connected to the light absorption region 20, and the port 38 is connected to the light absorption region 21.

  The optical circuit element 1 includes a laser, an optical amplifier, a photodetector, an optical modulator, an optical deflector, an optical attenuator, an optical mode converter, an optical frequency converter, an optical isolator, a filter, an optical demultiplexer, and a beam splitter. , Beam expanders, optical delay circuits, polarizers, optical couplers and the like. The optical circuit element 1 is an element that gives various operations to light intensity, phase, frequency, polarization state, traveling direction, beam diameter, and the like.

  In the present embodiment, the reflection boundary 22 refers to a region where reflected return light is formed. FIG. 1 shows an example in which the reflection boundary 22 of the present embodiment is interposed in the optical waveguide 303 and the optical waveguide 304. However, the reflection boundary 22 is provided in any of the ports 34, 35, 36, and 37. Also good.

  In the present embodiment, the port refers to a light entrance / exit. In other words, the ports 32, 33, 34, and 35 are end faces that input / output light to / from the 2 × 2 MMI coupler 30, and the ports 36, 37, 38, and 39 input / output light to / from the 2 × 2 MMI coupler 31. This is the end face. An optical waveguide 301 is bonded to the port 32, and an optical waveguide 306 is bonded to the port 39. Light enters the 2 × 2 MMI couplers 30 and 31 from the outside via the optical waveguides 301 and 306, and light is emitted from the 2 × 2 MMI couplers 30 and 31 to the outside via the optical waveguides 301 and 306. The optical waveguides 301 and 306 can be connected to, for example, a laser, an LED, a modulator, and an optical switch.

  The light absorption regions 20 and 21 are regions that absorb the reflected return light formed at the reflection boundary 22. The light absorption regions 20 and 21 are provided with a layer having a large band gap energy. For example, the light absorption regions 20 and 21 can be provided with an optical receiver or an optical attenuator.

  Next, the operation of the optical circuit element 1 will be described with reference to FIG. The operation of the optical circuit element 1 includes a first mode in which light is incident on the port 32 from the outside and a second mode in which light is incident on the port 39 from the outside.

  FIG. 2A shows the operation of the optical circuit element 1 in the first mode. When light is incident on the port 32 from the outside, the light is divided into a plurality of propagation modes in the 2 × 2 MMI coupler 30, and the intensity is equally distributed to the ports 34 and 35 due to mutual interference effects. However, the light distributed to each port has a phase difference of 2 / π. On the other hand, the reflected return light from the reflection boundary 22 passes through the 2 × 2 MMI coupler 30 again. As a result, the phase relationship of the light reaching the positions of the ports 32 and 33 is more than that when entering from the outside. Also changes by π. As a result, the port to which the light is coupled is switched to the port 33 and is guided to the light absorption region 20 and absorbed.

  Further, the light transmitted through the reflection boundary 22 enters the 2 × 2 MMI coupler 31 through the port 36 and the port 37. Similar to the 2 × 2 MMI coupler 30, the 2 × 2 MMI coupler 31 is designed so that a phase difference of 2 / π is generated in the light at each port during input and output. Then, the light incident on the 2 × 2 MMI coupler 31 passes through the 2 × 2 MMI coupler twice in total, so that the phase relationship of the light reaching the positions of the ports 38 and 39 changes by π more than when incident from the outside. As a result, light is coupled to port 39. At this time, the transmitted light is hardly coupled to the port 38. Therefore, most of the light input from the ports 36 and 37 is output from the port 39.

  FIG. 2B shows the operation of the optical circuit element 1 in the second mode. When light is incident on the port 39 from the outside, the light is divided into a plurality of propagation modes in the 2 × 2 MMI coupler 31 and is equally distributed to the ports 36 and 37 due to the mutual interference effect. However, the light distributed to each port has a phase difference of 2 / π. On the other hand, the reflected return light from the reflection boundary 22 passes through the 2 × 2 MMI coupler 31 again. As a result, the phase relationship of the light reaching the positions of the ports 38 and 39 is more than that when entering from the outside. Also changes by π. As a result, the port to which the light is coupled is switched to the port 38 and is guided to the light absorption region 21 and absorbed.

  On the other hand, the light transmitted through the reflection boundary 22 enters the 2 × 2 MMI coupler 30 via the port 34 and the port 35. Then, the light incident on the 2 × 2 MMI coupler 30 passes through the 2 × 2 MMI coupler twice in total, so that the phase relationship of the light reaching the ports 32 and 33 changes by π more than when incident from the outside. As a result, light is coupled to port 32. At this time, the transmitted light is hardly coupled to the port 33. Therefore, most of the light input from the ports 34 and 35 is output from the port 32.

  In addition, the phase difference of the light at each port when the light is emitted from the 2 × 2 MMI coupler needs to be preserved when it is reflected at the reflection boundary through each port and enters the 2 × 2 MMI coupler again. is there. For this purpose, the distance from the 2 × 2 MMI coupler 30 to the reflection boundary 22 via the optical waveguides 303 and 304 and the distance from the 2 × 2 MMI coupler 31 to the reflection boundary 22 via the optical waveguides 303 and 304 are: It is preferable that they are almost the same.

  It continues and demonstrates the effect of the optical circuit element 1. FIG. In the optical circuit element 1, two 2 × 2 MMI couplers are arranged so as to face each other, and the light absorption regions 20 and 21 are connected to ports 33 and 38 provided on surfaces that are not opposed to each other, respectively. In this way, in the first mode in which light is incident through the port 32, the reflected return light is output to the port 33 to be absorbed by the light absorption region 20 and the transmitted light is output from the port 39. On the other hand, in the second mode in which light is incident through the port 39, the reflected return light is output to the port 38 to be absorbed by the light absorption region 21 and the transmitted light is output from the port 32. Therefore, the reflected return light in the element can be concentrated locally to prevent re-incident into the element.

The reflected return light adversely affects the stable operation of the semiconductor laser. Trans. IEICE, E73 (1), pp. FIG. 8 of 77-82, 1990 shows an analysis of the reflectance of reflected return light. From this figure, it can be seen that when about 10 ⁻⁶ times or more of the light emitted from the semiconductor laser re-enters as reflected return light, it can cause unstable operation.

For example, when different core structures are connected using the BJ technique, the etching depth control and the processing shape are good, and no step or the like occurs in the shape of crystal regrowth. Therefore, when no vacancies or the like are generated at the regrowth interface, the reflection is almost negligible. However, with the current etching and crystal regrowth techniques, the reflectivity is not reduced sufficiently for practical use, and reflection of about 10 ⁻³ times or more may occur.

  On the other hand, in the optical circuit element 1, the reflected return light generated at the reflection boundary 22 is guided to the light absorption regions 20 and 21, whereby re-incidence of the reflected return light can be prevented. Therefore, the semiconductor laser can be stably operated by introducing the optical circuit element 1.

(Second Embodiment)
FIG. 3 is a plan view showing the optical circuit element 2 of the present embodiment. In the optical circuit element 2, the 2 × 2 MMI coupler 30 and the 2 × 2 MMI coupler 31 are formed of different materials. Other configurations are the same as those of the first embodiment. In the optical circuit element 2, the reflection boundary 22 is provided on the joint surface between the material 41 and the material 42. In the present embodiment, the optical waveguide 303 and the optical waveguide 304 are made of two different materials. The reflective boundary 22 is provided on the joint surface 201 between the material 41 and the material 42 of the optical waveguide 303, and the reflective boundary 22 is provided on the joint surface 202 between the material 41 and the material 42 of the optical waveguide 304. The joint surfaces 201 and 202 become reflective surfaces that reflect light, respectively, and form reflected return light.

Examples of the materials 41 and 42 include quartz-based materials, Si-based materials, and InP-based materials. Specifically, InGaAsP, InGaAlAs, etc. are exemplified as the InP-based material. Moreover, Si, Ge, SiGe, SiC etc. are illustrated as Si type material. Further, examples of the quartz-based material include SiN, SiO ₂ , and SiON.

  Also in the optical circuit element 2, the reflected return light generated at the reflection boundary 22 is guided to the light absorption region 20 or the light absorption region 21 and absorbed by the same principle described in the first embodiment. Therefore, a material suitable for each element to be integrated can be used while suppressing the influence of the reflected return light on the semiconductor laser. Therefore, according to the optical circuit element 2, it is possible to improve the final performance of the integrated optical device.

(Third embodiment)
FIG. 4 is a plan view showing the optical circuit element 3 of the present embodiment. In the optical circuit element 3, a 2 × 2 MMI coupler 30 and a 2 × 2 MMI coupler 31 are formed with different waveguide structures. In the optical circuit element 3, the reflection boundary 22 is provided on the joint surface between the waveguide 61 and the waveguide 62. In the present embodiment, the optical waveguide 303 and the optical waveguide 304 are each composed of two different waveguide structures. The reflection boundary 22 is provided on the joint surface 201 between the waveguide structure 61 and the waveguide structure 62 of the optical waveguide 303, and the reflection boundary 22 is provided on the joint surface 202 between the waveguide structure 61 and the waveguide structure 62 of the optical waveguide 304. It has been. The joint surfaces 201 and 202 become reflective surfaces that reflect light, respectively, and form reflected return light. Other configurations are the same as those of the first embodiment.

  For example, the waveguide structure 61 can be a buried waveguide structure, and the waveguide structure 62 can be a rib waveguide structure.

  Further, the waveguide structure 61 may be a rib waveguide structure, and the waveguide structure 62 may be a high mesa waveguide structure.

  The waveguide structure 61 may be a buried waveguide structure, and the waveguide structure 62 may be a high mesa waveguide structure.

  Also in the optical circuit element 3, the reflected return light is guided to the light absorption region 20 or the light absorption region 21 and absorbed by the same principle described in the first embodiment. Therefore, it is possible to use a waveguide structure suitable for each element to be integrated while suppressing the influence of the reflected return light on the semiconductor laser. Therefore, according to the optical circuit element 3, it is possible to improve the final performance of the integrated optical device.

(Fourth embodiment)
FIG. 5 is a plan view showing the optical circuit element 4 of the present embodiment. In the optical circuit element 4, the core structure of the 2 × 2 MMI coupler 30 is configured by the active region 51, and the core structure of the 2 × 2 MMI coupler 31 is configured by the passive region 52. In the optical circuit element 4, the reflection boundary 22 is provided at the joint surface between the active region 51 and the passive region 52. In the present embodiment, the optical waveguide 303 and the optical waveguide 304 are configured from different core structures. The reflection boundary 22 is provided on the joint surface 201 between the active region 51 and the passive region 52 of the optical waveguide 303, and the reflection boundary 22 is provided on the joint surface 202 between the active region 51 and the passive region 52 of the optical waveguide 304. The joint surfaces 201 and 202 become reflective surfaces that reflect light, respectively, and form reflected return light. Other configurations are the same as those of the first embodiment.

  The core of the active region 51 is composed of a layer having a small band gap energy in order to obtain an optical gain at a target wavelength. On the other hand, the core of the passive region 52 is composed of a layer having a large band gap energy. The band gap can be adjusted by the layer thickness, the crystal composition ratio, and the crystal distortion caused by the crystal composition ratio. For example, the active region 51 is made of a material such as InGaAsP or InGaAlAs whose band gap wavelength conversion value is 1.47 to 1.63 μm. The passive region 52 can be made of a material such as InGaAsP or InGaAlAs having a band gap wavelength conversion value of 1.05 to 1.45 μm. The active region 51 can be a laser, LED, optical amplifier, photodetector, or the like. On the other hand, the passive region 52 can be a modulator, an optical filter, or the like.

  Thus, in the present embodiment, the 2 × 2 MMI coupler 30 and the 2 × 2 MMI coupler 31 are configured to use different core structures. Therefore, although the joint portion of the separate core structure can be the reflection boundary 22, as described in the first embodiment, when light is incident on the port 32 from the outside, the reflected return light is absorbed by the light absorption region 20. When light is incident on the port 39 from the outside, the reflected return light is absorbed by the light absorption region 21. Therefore, a material suitable for each element to be integrated can be used while suppressing the influence of the reflected return light on the semiconductor laser. Therefore, according to the optical circuit element 4, it is possible to improve the final performance of the integrated optical device.

(Fifth embodiment)
FIG. 6 is a plan view showing the optical circuit element 5 of the present embodiment. In the optical circuit element 5, the gain region 81 is connected to the port 32 through the optical waveguide 301, and the modulator 82 is connected to the port 39 through the optical waveguide 306. Other configurations are the same as those of the first embodiment.

  In the optical circuit element 5, like the optical circuit element 2, the 2 × 2 MMI coupler 30 and the 2 × 2 MMI coupler 31 may be formed of different materials. Examples of materials used include quartz-based materials, Si-based materials, and InP-based materials.

  In the optical circuit element 5, like the optical circuit element 3, the 2 × 2 MMI coupler 30 and the 2 × 2 MMI coupler 31 may be formed with different structures. For example, the 2 × 2 MMI coupler 30 can be a buried waveguide structure, and the 2 × 2 MMI coupler 31 can be a rib waveguide structure. Further, the 2 × 2 MMI coupler 30 may have a rib waveguide structure, and the 2 × 2 MMI coupler 31 may have a high mesa waveguide structure. Further, the 2 × 2 MMI coupler 30 may have a buried waveguide structure, and the 2 × 2 MMI coupler 31 may have a high mesa waveguide structure.

  In the optical circuit element 5, as in the optical circuit element 4, the 2 × 2 MMI coupler 30 and the 2 × 2 MMI coupler 31 may be formed with different core structures. That is, the core structure of the 2 × 2 MMI coupler 30 may be configured with an active region, and the core structure of the 2 × 2 MMI coupler 31 may be configured with a passive region.

  In this embodiment, the gain region 81 is connected to the port 32, and the modulator 82 is arranged to the port 39. By doing so, it becomes possible to reduce the reflected return light inside the resonator of the integrated laser composed of a plurality of elements. The reflected return light inside the laser also causes an unstable operation of the laser, similar to the reflected return light from the outside. Therefore, by reducing the reflected return light inside the laser, the laser oscillation operation is stabilized and the final performance of the integrated optical device is improved.

  In the present embodiment, a gain region (laser or SOA) that generates light is provided, and the generated light power may be constant or may change with time, and the wavelength of the generated light. Can be changed by design according to the purpose. Furthermore, in this embodiment, a modulator or a wavelength tunable filter is provided, and their extinction characteristics and reflectivity depend on the wavelength.

  In general, in an optical integrated device (modulator integrated laser) in which a gain region and a modulator are combined, the polarization state handled by the entire device is either TE mode light or TM mode light. Therefore, it is necessary for the two light absorption regions constituting the present embodiment to absorb at least one light having a common polarization state.

  On the other hand, in the optical circuit element 5 of the present embodiment, the light generated in the gain region 81 as a constituent element and the light incident from the outside of the optical circuit element receive the reflected return light formed at the reflection boundary 22 as the light absorption region 20 and 21 can be absorbed. Moreover, even if the polarization state handled by the optical circuit element 5 is either TE mode light or TM mode light, the light absorption regions 20 and 21 can absorb the light. Therefore, according to the optical circuit element 5, it is possible to reduce the reflected return light inside the element and stabilize the oscillation operation of the laser.

  In the present embodiment, a wavelength tunable filter may be connected instead of the modulator 82. By using an integrated laser including the gain region 81 and the wavelength tunable filter, the optical circuit element 5 can reduce reflected return light inside the laser. Therefore, the operation of the semiconductor laser can be stabilized.

(Sixth embodiment)
FIG. 7 is a plan view showing the optical circuit element 6 of the present embodiment. In this embodiment, the reflective boundaries 22 and 23 are provided on the adhesive layer 24 made of an adhesive.

  Specifically, as in the optical circuit element 2, the optical circuit element 6 is formed of different materials 41 and 42 in the 2 × 2 MMI coupler 30 and the 2 × 2 MMI coupler 31. And the adhesive agent is used for the junction part of the material 41 and the material 42, and the contact bonding layer 24 is formed by this. Further, the optical waveguide 303 and the optical waveguide 304 are made of different materials 41 and 42, respectively, and the adhesive layer 24 is formed at the connection portion between the material 41 and the material 42. The joint surfaces 201a and 202a between the optical waveguides 303 and 304 made of the material 41 and the adhesive layer 24 become reflecting surfaces that reflect the light propagated through the 2 × 2 MMI coupler 30, respectively, and the optical waveguides 303 and 304 made of the material 42 and the adhesive layer The bonding surfaces 201b and 202b with the light 24 are reflection surfaces that reflect the light propagated through the 2 × 2 MMI coupler 31, respectively. Therefore, the reflective boundary 22 is provided on the joint surfaces 201a and 202a, and the reflective boundary 23 is provided on the joint surfaces 201b and 202b. Other configurations are the same as those of the first embodiment.

  Examples of the materials 41 and 42 include quartz-based materials, Si-based materials, and InP-based materials.

  As an adhesive material for forming the adhesive layer 24, an adhesive material having an intermediate refractive index between the respective materials is used. In this way, when materials having greatly different refractive indexes are combined, reflected return light generated at the reflection boundary 22 and the reflection boundary 23 can be suppressed, and loss of the optical integrated device can be reduced.

  In the optical circuit element 6, as in the optical circuit element 3, the 2 × 2 MMI coupler 30 and the 2 × 2 MMI coupler 31 may be formed with different structures. At this time, the adhesive layer 24 is formed at the joint portion having a different structure. For example, the 2 × 2 MMI coupler 30 can be a buried waveguide structure, and the 2 × 2 MMI coupler 31 can be a rib waveguide structure. Further, the 2 × 2 MMI coupler 30 may have a rib waveguide structure, and the 2 × 2 MMI coupler 31 may have a high mesa waveguide structure. Further, the 2 × 2 MMI coupler 30 may have a buried waveguide structure, and the 2 × 2 MMI coupler 31 may have a high mesa waveguide structure.

  In the optical circuit element 5, as in the optical circuit element 4, the 2 × 2 MMI coupler 30 and the 2 × 2 MMI coupler 31 may be formed with different core structures. That is, the core structure of the 2 × 2 MMI coupler 30 may be configured with an active region, and the core structure of the 2 × 2 MMI coupler 31 may be configured with a passive region. At this time, the adhesive layer 24 is formed at the joint between the active region and the passive region.

  As described above, in the present invention, the 2 × 2 MMI coupler 30 is configured such that the light incident from the first incident port (port 32) of the 2 × 2 MMI coupler 30 is the first output port (port 34) of the 2 × 2 MMI coupler 30. ) And the second exit port (port 35). The reflected return light from the reflection boundary 22 passes through the 2 × 2 MMI coupler 30 twice, and is coupled to the second incident port (port 33) of the 2 × 2 MMI coupler 30 from the light coherence of the optical coupler. Then, it is guided to the light absorption region 21 and absorbed. As a result, the reflected return light through the first incident port (port 32) of the 2 × 2 MMI coupler 30 is suppressed, and the semiconductor laser can be stably operated. Thereby, it is possible to provide a novel element structure capable of realizing an optical integrated device in which an optimum waveguide structure and core structure are arranged in each region.

  As an application example of the present invention, there is a medium and long distance light source for wavelength multiplexing communication used for a trunk line system and an access system.

  As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable.

For example, the following aspects can also be applied to the present invention.
(1) In an optical circuit element that propagates light,
A first 2 × 2 multimode interference (MMI) coupler (hereinafter 2 × 2 MMI coupler) and a second 2 × 2 MMI coupler;
The first 2 × 2 MMI coupler has port 1 and port 2 on one side, port 3 and port 4 on the opposite side,
The second 2 × 2 MMI coupler has port 5 and port 6 on one side, port 7 and port 8 on the opposite side,
Port 3 and port 5 are connected face to face, port 4 and port 6 are connected face to face,
A light absorption region 1 is connected to the port 2, and a light absorption region 2 is connected to the port 7.
(2) In the optical circuit element according to (1), the optical circuit element has a reflection boundary at any position between the position of the port 3 and the port 4 and the position of the port 5 and the port 6;
The optical circuit element characterized in that the range includes the position of the base of each port.
(3) The optical circuit element according to (2), wherein the first 2 × 2 MMI coupler and the second 2 × 2 MMI coupler are formed of different materials.
(4) The optical circuit element described in (2), wherein the first 2 × 2 MMI coupler and the second 2 × 2 MMI coupler are formed in different structures.
(5) In the optical circuit elements described in (1) to (4), the first 2 × 2 MMI coupler and the second 2 × 2 MMI coupler are formed of different materials or different structures, and gain is provided at one end. An optical circuit element having a region connected and a modulator or a wavelength tunable filter connected to the other end.
(6) In the optical circuit element described in (1) to (5), the core structure of the first 2 × 2 MMI coupler is configured in the active region, and the core structure of the second 2 × 2 MMI coupler is configured in the passive region. An optical circuit element characterized by being made.
(7) In the optical circuit element described in (1) to (5), the first 2 × 2 MMI coupler is configured with a buried waveguide structure, and the second 2 × 2 MMI coupler is configured with a rib waveguide structure. An optical circuit element characterized by comprising:
(8) In the optical circuit device described in (1) to (5), the first 2 × 2 MMI coupler is configured with a rib waveguide structure, and the second 2 × 2 MMI coupler is configured with a high mesa waveguide structure. An optical circuit element characterized by comprising:
(9) In the optical circuit element described in (1) to (5), the first 2 × 2 MMI coupler is configured with a buried waveguide structure, and the second 2 × 2 MMI coupler is configured with a high mesa waveguide structure. An optical circuit element characterized by comprising:
(10) The optical circuit element according to any one of (1) to (9), wherein the reflective boundary uses an adhesive at the joint of the material boundary.

  Needless to say, the above-described embodiment and a plurality of modifications can be combined within a range in which the contents do not conflict with each other. Further, in the above-described embodiments and modifications, the structure of each part has been specifically described, but the structure and the like can be changed in various ways within the scope of the present invention.

It is a top view which shows the optical circuit element of 1st Embodiment. It is a figure which shows operation | movement of the optical circuit element of 1st Embodiment. It is a top view which shows the optical circuit element of 2nd Embodiment. It is a top view which shows the optical circuit element of 3rd Embodiment. It is a top view which shows the optical circuit element of 4th Embodiment. It is a top view which shows the optical circuit element of 5th Embodiment. It is a top view which shows the optical circuit element of 6th Embodiment. It is a schematic diagram which shows a waveguide structure. It is a schematic diagram which shows a related waveguide structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical circuit element 2 Optical circuit element 3 Optical circuit element 4 Optical circuit element 5 Optical circuit element 6 Optical circuit element 10 Substrate 11 Cladding 12 Core 20 Light absorption area 21 Light absorption area 22 Reflection boundary 23 Reflection boundary 24 Adhesive layer 30 2 × 2 MMI coupler 31 2 × 2 MMI coupler 32 Port 33 Port 34 Port 35 Port 36 Port 37 Port 38 Port 39 Port 41 Material 42 Material 51 Active region 52 Passive region 61 Waveguide structure 62 Waveguide structure 71 Embedded waveguide structure 72 High mesa conductor Waveguide structure 81 Gain region 82 Modulator 201 Joining surface 201a Joining surface 201b Joining surface 202 Joining surface 202a Joining surface 202b Joining surface 301 Optical waveguide 302 Optical waveguide 303 Optical waveguide 304 Optical waveguide 305 Optical waveguide 306 Optical waveguide

Claims (10)

A first multimode interference coupler;
A second multimode interference coupler facing the first multimode interference coupler;
First and second optical waveguides respectively connecting between the first multimode interference coupler and the second multimode interference coupler;
Have
The first multimode interference coupler is:
A first port and a second port on one side;
Have a third port and a fourth port on the other side,
The second multimode interference coupler is:
Has a fifth port and a sixth port on one side,
It has a seventh port and an eighth port on the other side,
The third port and the fifth port are connected via the first optical waveguide;
The fourth port and the sixth port are connected via the second optical waveguide;
A first light absorbing portion is connected to the second port,
A second light absorbing portion is connected to the seventh port,
The first multimode interference coupler or the second multimode interference coupler is propagated either between the third port and the fifth port or between the fourth port and the sixth port. An optical circuit element having a reflection boundary for reflecting light.   The optical circuit element according to claim 1, wherein the reflection boundary is interposed in either the first optical waveguide or the second optical waveguide.   The optical circuit element according to claim 1 or 2, wherein the first multimode interference coupler and the second multimode interference coupler are formed of different materials.   The optical circuit element according to claim 1, wherein the reflection boundary is provided in a layer made of an adhesive.   5. The optical circuit element according to claim 1, wherein the first multimode interference coupler and the second multimode interference coupler are formed with different structures.   6. The optical circuit element according to claim 5, wherein the first multimode interference coupler is configured with a buried waveguide structure, and the second multimode interference coupler is configured with a rib waveguide structure.   6. The optical circuit element according to claim 5, wherein the first multi-mode interference coupler is configured with a rib waveguide structure, and the second multi-mode interference coupler is configured with a high mesa waveguide structure.   The optical circuit element according to claim 5, wherein the first multimode interference coupler is configured with a buried waveguide structure, and the second multimode interference coupler is configured with a high mesa waveguide structure.   9. The optical circuit element according to claim 5, wherein the core structure of the first multimode interference coupler is configured in an active region, and the core structure of the second multimode interference coupler is configured in a passive region. .   The optical circuit element according to claim 5, wherein a gain region is connected to the first port, and a modulator or a wavelength tunable filter is connected to the eighth port.

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