JP2014089336A - Methods for manufacturing multimode interference device, mach-zehnder interferometer, and light guide device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multimode interference device such that a wavelength band satisfying desired wavelength loss characteristics can be widen against processing variance of manufacturing processes.SOLUTION: A multimode interference device 11 has a 11th waveguide 15 and a 12th waveguide 17 optically coupled to a multimode waveguide 13, defined by a first side face 23a and a second side face 23b, a first end face 25a, and a second end face 25b, on the first end face 25a, and also has a 21st waveguide 19 and a 22nd waveguide 21 optically coupled on the second end face 25b. A first reference surface Ref1 is not parallel with a second reference surface Ref2, so an offset is provided so that the path length from one of the 11th waveguide 15 and the 12th waveguide 17 to one of the 21st waveguide 19 and the 22nd waveguide 21 is different from the path length from the other of the 11th waveguide 15 and the 12th waveguide 17 to the other of the 21st waveguide 19 and the 22nd waveguide 21.

Description

  The present invention relates to multimode interference devices, Mach-Zehnder interferometers, and methods of making optical waveguide devices.

  Non-Patent Document 1 discloses an outline of an integrated device based on multimode interference. The principle of self-imaging in a multimode waveguide is explained.

“Optical Multi- Mode Interference Devices Based on Self-Imaging: Principles and Applications,” JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL.13, NO.4, pp615-627, APRIL 1995

  Non-Patent Document 1 discloses design guidelines for multimode interference devices. Multimode interference devices such as multimode interferometers generate optical losses due to variations in processing dimensions in the fabrication process. For example, in a multimode interferometer, an exit port is provided at the focal position of light incident from the entrance port. According to the inventor's knowledge, the variation in the width dimension of the multimode interferometer causes another loss in addition to the branching loss.

  Also, wavelength multiplexing for optical communication requires low loss over a wide wavelength band. However, if the width of the multimode interferometer deviates from a desired value due to the limit of processing accuracy of the manufacturing process, the wavelength loss characteristic of the multimode interferometer shifts. As a result, a desired wavelength loss characteristic cannot be obtained in a desired wavelength band.

  The present invention has been made in view of such circumstances, and provides a multimode interference device capable of expanding a wavelength band that satisfies a desired wavelength loss characteristic against processing variations in a manufacturing process. It is an object of the present invention to provide a method of manufacturing an optical waveguide device including the multimode interference device, and to provide a Mach-Zehnder interferometer including the optical waveguide device.

  A multimode interference device according to the present invention includes: (a) a first side surface and a second side surface extending in the direction of a first axis; and a first end surface extending along a first reference plane intersecting the first axis. And a multimode waveguide including a second end face extending along a second reference plane intersecting the first axis, and (b) a multimode waveguide for multimode interference at the first end face. An eleventh optically coupled waveguide; (c) a twelfth waveguide optically coupled to the multimode waveguide at the first end surface; and (d) a multiplicity of the multiple waveguides at the second end surface. A first waveguide optically coupled to the mode waveguide; and (e) a twenty-second waveguide optically coupled to the multimode waveguide at the second end face, the first reference. The surface is not parallel to the second reference surface.

  According to this multimode interference device, the eleventh waveguide and the twelfth waveguide are optically connected to the multimode waveguide defined by the first side surface, the second side surface, the first end surface, and the second end surface. And the twenty-first and twenty-second waveguides are optically coupled at the second end face. Since the first reference plane is not parallel to the second reference plane, the path length from one of the eleventh waveguide and the twelfth waveguide to one of the twenty-first waveguide and the twenty-second waveguide is The path length is different from the other of the 11th waveguide and the 12th waveguide to the other of the 21st waveguide and the 22nd waveguide. Therefore, it is possible to provide a multimode interference device that can achieve a desired wavelength loss characteristic in a wider wavelength band against processing variations in the manufacturing process.

  In the multimode interference device according to the present invention, the center line of the eleventh waveguide intersects the first reference plane at the first position, and the center line of the twenty-first waveguide is the second reference plane at the second position. The first position and the second position are located on a second axis, the center line of the twelfth waveguide intersects the first reference plane at a third position, and A center line may intersect the second reference plane at a fourth position, and the third position and the fourth position may be located on a third axis.

  According to the multimode interference device, the eleventh waveguide and the twenty-first waveguide are coupled to the multimode waveguide so that the first position and the second position are located on the second axis, and the third position The twelfth waveguide and the twenty-second waveguide are coupled to the multimode waveguide so that the fourth position is located on the third axis. This structure of the multimode interference device makes it easy to achieve wavelength loss characteristics in a desired wavelength band against processing variations in the manufacturing process.

  In the multimode interference device according to the present invention, a distance between the first position and the second position on the first axis is different from a distance between the third position and the fourth position on the second axis. be able to.

  According to the multimode interference device, in the structure of the multimode interference device, the distance between the first position and the second position on the first axis is different from the distance between the third position and the fourth position on the second axis. It is easy to design to satisfy the wavelength loss characteristic in a desired wavelength band against processing variations in the manufacturing process.

  In the multimode interference device according to the present invention, the first end surface includes a connection surface that connects an inner side surface of the eleventh waveguide and an inner side surface of the twelfth waveguide, and the second end surface includes the first end surface. Another connection surface connecting the inner side surface of the 21st waveguide and the inner side surface of the 22nd waveguide may be included.

  According to this multimode interference device, the connection surface of the first end surface extends along the first reference plane and connects the inner side surface of the eleventh waveguide to the inner side surface of the twelfth waveguide. In addition, another connection surface of the second end surface extends along the second reference surface and connects the inner side surface of the twenty-first waveguide to the inner side surface of the twenty-second waveguide. In this multimode interference device, the eleventh waveguide and the twelfth waveguide are adjacent at the first end face, and the twenty-first waveguide and the twenty-second waveguide are adjacent at the second end face.

  In the multimode interference device according to the present invention, the eleventh waveguide, the twelfth waveguide, the twenty-first waveguide, the twenty-second waveguide, and the multimode waveguide have a waveguide structure. The waveguide structure includes a first InP clad layer, an AlGaInAs / AlInAs quantum well structure, and a second InP clad layer. The first InP clad layer, the AlGaInAs / AlInAs quantum well structure, and the second InP clad layer It is preferable that they are arranged in order.

  The multimode interference device according to the present invention preferably has a 2 × 2 structure.

  A Mach-Zehnder interferometer according to the present invention includes (a) a first branching waveguide, (b) a second branching waveguide, (c) the first branching waveguide, and the second branching waveguide. A first arm waveguide connecting the first branch waveguide and (d) a second arm waveguide connecting the first branch waveguide and the second branch waveguide, wherein the first branch waveguide is , Including any of the multimode interference devices described above.

  According to the Mach-Zehnder interferometer, desired wavelength loss characteristics can be achieved in a wide wavelength band against processing variations in the manufacturing process.

  In the Mach-Zehnder interferometer according to the present invention, the second branch waveguide may include any of the multimode interference devices described above.

  A method of manufacturing an optical waveguide device according to the present invention includes: (a) a process of manufacturing an optical waveguide device including the multimode interference device described in any of the above; and (b) From one of the eleventh waveguide and the twelfth waveguide of the multimode interference device to each of the twenty-first waveguide and the twenty-second waveguide via the multimode waveguide of the multimode interference device. Measuring the characteristics of the optical waveguide device in an individual form that allows light to pass; and (c) the multimode guide of the multimode interference device from one of the eleventh waveguide and the twelfth waveguide. Measuring the characteristics of the optical waveguide device in an individual form in which light passes through each of the twenty-first waveguide and the twenty-second waveguide through a waveguide; and (d Based on the results of the measurement, and a step of determining whether to apply any of the forms on the optical waveguide device.

  According to the method of manufacturing an optical waveguide device (hereinafter referred to as “manufacturing method”), any of these forms is applied to the use of the optical waveguide device based on a comparison of individual characteristics corresponding to several types of use. Therefore, it is possible to manufacture an optical waveguide device that can achieve desired wavelength loss characteristics in a wide wavelength band, against processing variations in the manufacturing process.

  In the manufacturing method according to the present invention, the optical waveguide device may include a Mach-Zehnder interferometer. According to this method, it is possible to provide a Mach-Zehnder interferometer that can achieve a desired wavelength loss characteristic in a wide wavelength band, to an optical waveguide device, against processing variations in the manufacturing process.

  As described above, according to the present invention, there is provided a multimode interference device that makes it possible to expand a wavelength band that satisfies a desired wavelength loss characteristic against processing variations in a manufacturing process. In addition, according to the present invention, a method for manufacturing an optical waveguide device including the multimode interference device is provided. Furthermore, according to the present invention, a Mach-Zehnder interferometer including this optical waveguide device is provided.

FIG. 1 is a drawing showing the structure of an optical waveguide device. FIG. 2 is a drawing showing a multimode interference device having a structure different from that of the multimode interference device according to the present embodiment. FIG. 3 is a diagram illustrating excess loss characteristics of a multimode interference device having a symmetrical structure and design dimensions. FIG. 4 is a diagram illustrating excess loss characteristics of a multimode interference device processed with some processing variation. FIG. 5 is a diagram showing excess loss characteristics of a multimode interference device processed with some processing variation. FIG. 6 is a diagram illustrating excess loss characteristics of a multimode interference device having an asymmetric structure and design dimensions. FIG. 7 is a drawing showing excess loss characteristics of a multimode interference device including processing variations imparted due to processing. FIG. 8 is a drawing showing excess loss characteristics of a multimode interference device including processing variations imparted due to processing. FIG. 9 is a drawing showing excess loss characteristics of a multimode interference device including processing variations imparted due to processing. FIG. 10 is a diagram illustrating excess loss characteristics of a multimode interference device including processing variations imparted due to processing. FIG. 11 is a drawing showing an example of a waveguide device according to the present embodiment. FIG. 12 is a diagram illustrating a Mach-Zehnder interferometer according to an embodiment. FIG. 13 is a diagram showing loss characteristics in the MZI circuit. FIG. 14 is a drawing showing an example of a method for designing an optical waveguide device according to the present embodiment. FIG. 15 is a drawing showing main steps in the method of manufacturing the optical waveguide device according to the present embodiment.

  Subsequently, embodiments of a method for manufacturing a multimode interference device, a Mach-Zehnder interferometer, and an optical waveguide device of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

  FIG. 1 is a drawing showing the structure of an optical waveguide device. In this example, a multimode interference device will be described as an example of an optical waveguide device.

  Referring to FIG. 1A as a top view, the multimode interference (MMI) device 11 includes a multimode waveguide 13, an eleventh waveguide 15, a twelfth waveguide 17, a twenty-first waveguide 19, and A twenty-second waveguide 21 is provided. The multimode waveguide 13 includes a first side surface 23a, a second side surface 23b, a first end surface 25a, and a second end surface 25b. The eleventh waveguide 15 is optically coupled to the multimode waveguide 13 for multimode interference (MMI) at the first end face 25a. The first side surface 23a and the second side surface 23b extend in the direction of the first axis Ax. The twelfth waveguide 17 is optically coupled to the multimode waveguide 13 at the first end face 25a. The twenty-first waveguide 19 is optically coupled to the multimode waveguide 13 at the second end face 25b. The twenty-second waveguide 21 is optically coupled to the multimode waveguide 13 at the second end face 25b. The first end face 25a extends along the first reference plane Ref1 that intersects the first axis Ax. The second end face 25b extends along the second reference plane Ref2 that intersects the first axis Ax. The first reference plane Ref1 is not parallel to the second reference plane Ref2. Therefore, an offset is provided in the positional relationship of the ports according to the present embodiment, and the asymmetric structure is provided.

  According to the multimode interference device 11, the multimode waveguide 13 defined by the first side surface 23a, the second side surface 23b, the first end surface 25a, and the second end surface 25b is changed to the eleventh waveguide 15 at the first end surface 25a. And the twelfth waveguide 17 are optically coupled, and the twenty-first waveguide 19 and the twenty-second waveguide 21 are optically coupled at the second end face 25b. Since the first reference plane Ref1 is not parallel to the second reference plane Ref2, from one of the eleventh waveguide 15 and the twelfth waveguide 17 to one of the twenty-first waveguide 19 and the twenty-second waveguide 21. Unlike the path length from the other of the eleventh waveguide 15 and the twelfth waveguide 17 to the other of the twenty-first waveguide 19 and the twenty-second waveguide 21, an offset is provided. Therefore, it is possible to provide a multimode interference device that can achieve desired wavelength loss characteristics in a wider wavelength band against processing variations in the manufacturing process.

  In the present embodiment, the eleventh waveguide 15 and the twelfth waveguide 17 can be used as the input ports INPUT1 and INPUT2, respectively, and the twenty-first waveguide 19 and the twenty-second waveguide 21 are respectively output. It can be used as ports OUTPUT and OUTPUTTB.

  In order to fabricate such a structure, a plurality of III-V compound semiconductor layers providing the above-described epi structure are grown on a substrate to form a semiconductor stack. Next, a mask that defines the shapes of the waveguide and the multimode waveguide is formed. Using this mask, the semiconductor stack is etched by dry etching to produce an optical waveguide device having an MMI structure. This waveguide structure can be embedded with resin. Further, the resin is processed to form an opening reaching the upper surface of the waveguide structure. An electrode is formed on the opening.

An example multimode interference device 11 has the following structure.
Waveguide width (waveguides 15, 17, 19, 21): 2.4 μm.
Waveguide spacing G: 2 μm.
Multimode waveguide width (MMI width) W: 6.8 μm.
Multimode waveguide length (MMI length) L: 199 μm.
(Length at the center of the multimode waveguide width W).
Offset amount OF: 6 μm.
n-type clad semiconductor layer (Si-doped InP layer): thickness 1 μm.
Core semiconductor layer (AlGaInAs / AlInAs multiple quantum well structure): thickness 0.6 μm.
p-type cladding semiconductor layer (Zn-doped InP layer): thickness 1 μm.
Inclination angle TH between the first reference surface Ref1 and the second reference surface Ref2 (reference surface Ref0): 70 degrees. The reference surface Ref0 is parallel to the second reference surface Ref2. Further, the pair of side surfaces of the multimode waveguide are parallel to each other.

  In one embodiment of the multimode interference device 11, in the production of the multimode interference device, in the epi growth process, an n-type cladding semiconductor layer (Si-doped InP layer), a core semiconductor layer (AlGaInAs / AlInAs multiple quantum well structure), and A p-type clad semiconductor layer (Zn-doped InP layer) is epitaxially grown on a semi-insulating InP substrate to produce a semiconductor stack. Thereafter, in the processing step, a high mesa waveguide structure is formed by processing using reactive ion etching of the semiconductor stack. In the embedding process, the high mesa waveguide structure is embedded with BCB resin. During this processing, the processing dimensions of the high mesa waveguide structure vary.

  FIG. 2 is a drawing showing a multimode interference device 31 having a symmetrical structure different from that of the multimode interference device according to the present embodiment. Referring to FIG. 2 shown as a top view, a multimode interference (MMI) device 31 includes a multimode waveguide 33, an eleventh waveguide 35, a twelfth waveguide 37, a twenty-first waveguide 39, and a twenty-second waveguide. A waveguide 41 is provided. The multimode waveguide 33 includes a first side surface 43a, a second side surface 43b, a first end surface 45a, and a second end surface 45b. The eleventh waveguide 35 is optically coupled to the multimode waveguide 33 for multimode interference (MMI) at the first end face 45a. The first side surface 43a and the second side surface 43b extend in the direction of the second axis Bx. The twelfth waveguide 37 is optically coupled to the multimode waveguide 33 at the first end face 45a. The twenty-first waveguide 39 is optically coupled to the multimode waveguide 33 at the second end face 45b. The twenty-second waveguide 41 is optically coupled to the multimode waveguide 33 at the second end face 45b. The first end face 45a extends along the third reference plane Ref3 that intersects the second axis Ax. The second end face 45b extends along the fourth reference plane Ref4 that intersects the second axis Bx. The third reference plane Ref3 is parallel to the fourth reference plane Ref4.

  FIG. 3 is a diagram illustrating excess loss characteristics of a correctly processed multimode interference device. In FIG. 3, a symbol dW indicates a processing variation when a multimode interference device is manufactured by processing, and dW = 0 indicates that the processing variation of the multimode interference device is zero. The horizontal axis in FIG. 3 indicates the optical wavelength in the wavelength band used for transmission, and 1510 nm, 1530 nm, 1550 nm, 1570 nm, and 1590 nm are described as wavelengths. Note that, in the excess loss characteristic in the present embodiment, a loss (3 dB) essential to the branching of light in the multimode interference device is excluded.

  Referring to FIG. 3, the excess loss characteristic of the multimode interference device 31 is shown. A multi-mode interferometer (MMI) manufactured according to design dimensional accuracy has a very low loss characteristic (for example, 0.2 dB or less) in the wavelength range of 1530 to 1570 nm.

  4 and 5 are diagrams showing excess loss characteristics of MMI processed with some processing variation.

  Part (a) of FIG. 4 shows excess loss characteristics of the multimode interference device 31 having a processing variation dW = −0.10 μm (0.10 μm narrower than the design dimension). In the MMI manufactured with this dimensional variation, the excess loss characteristics of the output ports A and B do not exceed 1 dB in the wavelength range of 1530 to 1570 nm.

  Part (b) of FIG. 4 shows the excess loss characteristic of the multimode interference device 31 having a processing variation dW = −0.15 μm (0.15 μm narrower than the design dimension). In the MMI manufactured with this dimensional variation, the output ports A and B have excess loss characteristics of about 1 dB or 1 dB or more in the wavelength range of 1530 to 1570 nm.

  Part (a) of FIG. 5 shows the excess loss characteristic of the multimode interference device 31 having a processing variation dW = + 0.15 μm (0.15 μm thick with respect to the design dimension). In the MMI manufactured with this dimensional variation, the excess loss characteristics of the output ports A and B do not exceed 1 dB in the wavelength range of 1530 to 1570 nm.

  5B shows excess loss characteristics of the multimode interference device 31 having a processing variation dW = + 0.20 μm (0.20 μm thick with respect to the design dimension). In the MMI manufactured with this dimensional variation, the output ports A and B have excess loss characteristics of about 1 dB or 1 dB or more in the wavelength range of 1530 to 1570 nm.

  As shown in FIG. 3, the multimode interference device 31 manufactured according to the design dimensional accuracy exhibits very low loss branching characteristics in the wavelength range of 1530 to 1570 nm. However, when the MMI width W deviates from the design target value in the multimode interference device 31, the imaging distance changes for each wavelength, so that the maximum loss in a predetermined wavelength range increases. According to the excess loss characteristics in FIGS. 3, 4, and 5, in order to make the MMI excess loss due to branching within the wavelength band 1530 to 1570 nm in quality of 1 dB or less, the dimensional processing accuracy of the manufacturing process is −0.1 μm. A range of about +0.15 μm is required.

  In order to alleviate the demand for this processing dimension, the multimode interference device 11 according to the present embodiment has an arrangement of output ports provided on one end face and an arrangement of input ports provided on the other end face. The coupling position of the input port is changed in the direction of the MMI length so that the distance between the corresponding output port and the input port is different from each other. With this structure, a suitable input port can be selected according to the amount of MMI width deviation due to variations caused by processing. By making this selection possible, it is possible to suppress MMI excess loss. Therefore, the dimensional processing accuracy required for the manufacturing process can be relaxed.

  Referring to FIG. 6A, the excess loss characteristic of the multimode interference device 11 is shown. This characteristic corresponds to the usage pattern in which light is input from the input waveguide INPUT1. The excess loss characteristic of the multimode interference device 11 manufactured according to the designed dimensional accuracy is, for example, 0.5 dB or less at a wavelength of 1530 to 1570 nm. 6B, the excess loss characteristic of the multimode interference device 11 corresponds to a usage pattern in which light is input from the input waveguide INPUT2. The excess loss characteristic of the multimode interference device 11 manufactured according to the designed dimensional accuracy is, for example, 0.65 dB or less at a wavelength of 1530 to 1570 nm. The distance between the two input / output ports is 4.4 μm. The inclination angle of the end face is 70 degrees.

  7 to 10 are diagrams showing excess loss characteristics of the multimode interference device 11 including processing variations given due to processing.

  FIG. 7A shows an excess loss when light is input from the input waveguide INPUT 1 to the multimode interference device 11 having a processing variation dW = −0.10 μm (0.10 μm narrower than the design dimension). Show properties. In the multimode interference device 11 manufactured with this dimensional variation, the excess loss characteristics at the output OUTPUT and the output OUTPUT TB exceed 1 dB at wavelengths of 1530 to 1570 nm.

  Moreover, the (b) part of FIG. 7 shows the excess loss characteristic of the multimode interference device 11 having a processing variation dW = −0.05 μm (0.05 μm narrower than the design dimension). In the multimode interference device 11 manufactured with this dimensional variation, the excess loss characteristics at the output OUTPUT and the output OUTPUT TB are 1 dB or less at wavelengths of 1530 to 1570 nm.

  Part (a) of FIG. 8 shows excess loss characteristics of the multimode interference device 11 having a processing variation dW = + 0.25 μm (a thickness of 0.25 μm with respect to the design dimension). In the multimode interference device 11 manufactured with this dimensional variation, the excess loss characteristics at the outputs OUTPUT and OUTPUTTB are 1 dB or less at wavelengths of 1530 to 1570 nm.

  8B shows the excess loss characteristic of the multimode interference device 11 having a processing variation dW = + 0.30 μm (thickness of 0.30 μm with respect to the design dimension). In the multimode interference device 11 manufactured with this dimensional variation, the excess loss characteristic at the output OUTPUT is about 1 dB at a wavelength of 1530 to 1570 nm, but the excess loss characteristic at the output OUTPUT TB exceeds 1 dB.

  Part (a) of FIG. 9 shows the excess loss characteristics of the multimode interference device 11 having a processing variation dW = −0.25 μm (0.25 μm narrower than the design dimension). In the multimode interference device 11 manufactured with this dimensional variation, the excess loss characteristics at the output OUTPUT and the output OUTPUT TB exceed 1 dB at wavelengths of 1530 to 1570 nm.

  FIG. 9B shows the excess loss characteristics of the multimode interference device 11 having a processing variation dW = −0.20 μm (0.20 μm narrower than the design dimension). In the multimode interference device 11 manufactured with this dimensional variation, the excess loss characteristics at the output OUTPUT and the output OUTPUT TB are 1 dB or less at wavelengths of 1530 to 1570 nm.

  Part (a) of FIG. 10 shows excess loss characteristics of the multimode interference device 11 having a processing variation dW = + 0.05 μm (thickness of 0.05 μm with respect to the design dimension). In the multimode interference device 11 manufactured with this dimensional variation, the excess loss characteristics at the output OUTPUT and the output OUTPUT TB are 1 dB or less at wavelengths of 1530 to 1570 nm.

  Moreover, the (b) part of FIG. 10 shows the excess loss characteristic of the multimode interference device 11 having the processing variation dW = + 0.10 μm (thickness of 0.10 μm with respect to the design dimension). In the multimode interference device 11 manufactured with this dimensional variation, the excess loss characteristics at the output OUTPUT and the output OUTPUT TB are 1 dB or more at wavelengths of 1530 to 1570 nm.

  As understood from the loss characteristics of FIGS. 7 and 8, in the form in which optical input is performed from the input port INPUT 1, the excess loss characteristic with a loss of 1 dB or less in the wavelength range of 1530 to 1570 nm has an MMI width of −0.05 μm to +0. In the range of 25 μm. As understood from the loss characteristics shown in FIGS. 9 and 10, in the form in which optical input is performed from the input port INPUT 2, the excess loss characteristic with a loss of 1 dB or less in the wavelength range of 1530 to 1570 nm has an MMI width of −0.20 μm to +0. In the range of .05 μm. These results indicate that the dimensional processing accuracy of the manufacturing process can be relaxed to −0.20 μm to +0.25 μm by selecting the input port according to the MMI width deviation amount.

  The multi-mode interference device 11 will be described with reference to FIG. 1 again. In the multimode interference device 11, the center line C1 of the eleventh waveguide 15 intersects the first reference plane Ref1 at the first position P1, and the center line C2 of the twenty-first waveguide 19 is the second reference plane at the second position P2. Crosses Ref2. The first position P1 and the second position P2 are located on the second axis Ax2. The center line C3 of the twelfth waveguide 17 intersects the first reference plane Ref1 at the third position P3, and the center line C4 of the twenty-second waveguide 21 intersects the second reference plane Ref2 at the fourth position P4. The third position P3 and the fourth position P4 are located on the third axis Ax3. The axes Ax, Ax2, Ax3 do not intersect each other. In the present embodiment, the second axis Ax2 is parallel to the third axis Ax3.

  According to the multimode interference device 11, the eleventh waveguide 15 and the twenty-first waveguide 19 are coupled to the multimode waveguide 13 so that the first position P1 and the second position P2 are located on the second axis Ax2. In addition, the twelfth waveguide 17 and the twenty-second waveguide 21 are coupled to the multimode waveguide 13 so that the third position P3 and the fourth position P4 are located on the third axis Ax3. This structure of the multimode interference device 11 makes it easy to achieve wavelength loss characteristics in a desired wavelength band against processing variations in the manufacturing process.

  A distance L2 between the first position P1 and the second position P2 on the second axis Ax2 is different from the MMI length L. A distance L3 between the third position P3 and the fourth position P4 on the third axis Ax3 is different from the MMI length L. The distance L2 is different from the distance L3. Center lines C1 and C3 are smoothly connected to axis Ax2 at points P1 and P3, respectively. Center lines C2 and C4 are smoothly connected to axis Ax3 at points P2 and P4, respectively.

  According to the multimode interference device 11, in the structure of the multimode interference device in which the distance L2 is different from the distance L3, it is easy to design the wavelength loss characteristic to satisfy a desired wavelength band against the processing variation of the manufacturing process.

  Further, the outer side surface 15a of the eleventh waveguide 15 is continuously connected to the first side surface 23a, and the outer side surface 19a of the twenty-first waveguide 19 is continuously connected to the first side surface 23a. Further, the outer side surface 17a of the twelfth waveguide 17 is continuously connected to the second side surface 23b, and the outer side surface 21a of the twenty-second waveguide 21 is continuously connected to the second side surface 23b.

  The outer side surface 15a of the eleventh waveguide 15 and the outer side surface 19a of the twenty-first waveguide 19 are continuously connected to the first side surface 23a, and the outer side surface 17a of the twelfth waveguide 17 and the outer side surface 21a of the twenty-second waveguide 21 are connected. In the structure continuously connected to the first side surface 23b, the side surface of the multimode waveguide 13 and the side surface of the waveguide are continuously connected to each other. Design that fills the bandwidth is easy.

  In the present embodiment, the first end surface 25 a is a connection surface that connects the inner side surface 15 b of the eleventh waveguide 15 and the inner side surface 17 b of the twelfth waveguide 17. The second end surface 25 b is another connection surface that connects the inner side surface 19 b of the twenty-first waveguide 19 and the inner side surface 21 b of the twenty-second waveguide 21. According to this multimode interference device, the connection surface of the first end face 25a extends along the first reference plane Ref1, and the inner side surface 15b of the eleventh waveguide 15 becomes the inner side surface 17b of the twelfth waveguide 17. Connect. The connection surface of the second end face 25 b extends along the second reference plane Ref 2 and connects the inner side surface 19 b of the twenty-first waveguide 19 to the inner side surface 21 b of the twenty-second waveguide 21. In the multimode interference device 11, the eleventh waveguide 15 and the twelfth waveguide 17 are adjacent to each other at the first end face 25a, and the twenty-first waveguide 19 and the twenty-second waveguide 21 are adjacent to each other at the second end face 25a. This structure facilitates a design in which the wavelength loss characteristic satisfies a desired wavelength band against the processing variation of the manufacturing process.

  As shown in FIG. 1A, in this embodiment, the second reference plane Ref2 is orthogonal to the axis Ax, and the first reference plane Ref1 is inclined with respect to the axis Ax.

  As already described, in the multimode interference device 11, the multimode waveguide 13, the eleventh waveguide 15, the twelfth waveguide 17, the twenty-first waveguide 19, and the twenty-second waveguide 21 are formed as shown in FIG. As shown in the figure), it has a waveguide structure 6 including two cladding layers 2a and 2b and a core layer 4 sandwiched between the cladding layers 2a and 2b. The waveguide structure 6 is provided on the substrate 8 and is embedded in the embedded region 10.

In one example, the waveguide structure can include a first InP cladding layer, an AlGaInAs / AlInAs quantum well structure, and a second InP cladding layer. The first InP cladding layer, the AlGaInAs / AlInAs quantum well structure, and the second InP cladding layer are sequentially arranged on the semi-insulating InP substrate. As a material to which the structure of the multimode interference device 11 can be applied, Si waveguide, SiO ₂ waveguide, or the like can be used in addition to InGaAsP.

  The multimode interference device 11 is preferably applied to a 2 × 2 structure as shown in FIG. According to the 2 × 2 structure, it is possible to create a Mach-Zehnder interferometer that satisfies desired wavelength loss characteristics in a wide wavelength band, against processing variations in the manufacturing process.

  FIG. 11 shows a Mach-Zehnder interferometer. The Mach-Zehnder interferometer 51 includes a first branch waveguide 53, a second branch waveguide 55, a first arm waveguide 57, and a second arm waveguide 59. The first arm waveguide 57 connects the first branch waveguide 53 and the second branch waveguide 55. The second arm waveguide 59 connects the first branch waveguide 53 and the second branch waveguide 55. The first branching waveguide 53 can include the multimode interference device 11. According to the Mach-Zehnder interferometer 51, desired wavelength loss characteristics can be achieved in a wide wavelength band against processing variations in the manufacturing process. Two first waveguides 61a and 61b are connected to the two input ports of the multimode interference device in the first branching waveguide 53, respectively. A first arm waveguide 57 and a second arm waveguide 59 are connected to the two output ports of the multimode interference device 11, respectively. Each of the first arm waveguide 57 and the second arm waveguide 59 is provided with a phase control electrode. Two second waveguides 63a and 63b are connected to the two output ports of the multimode interference device in the second branch waveguide 55, respectively. A first arm waveguide 57 and a second arm waveguide 59 are connected to the two input ports of the multimode interference device, respectively.

  Further, in the Mach-Zehnder interferometer 51, the second branch waveguide 55 can include the multimode interference device 11. Only the first branch waveguide 53 can include the multimode interference device 11, and only the second branch waveguide 55 can include the multimode interference device 11.

  The two second waveguides 63a and 63b are provided with first and second optical monitors 65a and 65b, respectively. These optical monitors 65 (65a, 65b) are used as optical output level monitors.

  An optical Mach-Zehnder interferometer (MZ1) can be configured using the multimode interference device 11. This Mach-Zehnder interferometer includes an MMI that splits incident light into two branches, two arm waveguides that adjust the phase of the light, and an MMI that combines light from these arms. In the example of the Mach-Zehnder interferometer 51 shown in FIG. 11, two-input / two-output MMI is used for optical multiplexing / demultiplexing, and the refractive index change of the waveguide is changed by applying a voltage to the phase control electrode provided in each arm. To adjust the phase of the light.

  FIG. 12 is a diagram illustrating a Mach-Zehnder interferometer according to an embodiment. The MMI on the input side of the Mach-Zehnder modulator preferably has the same structure as the MMI on the output side, and is incorporated in the Mach-Zehnder modulator so that the input port of the MMI on the input side is connected as the output port in the MMI on the output side. Thus, an MZI circuit is provided in which the output side MMI inverts the 2 × 2 input / output with respect to the input side MMI. In this MZI circuit, when the MMI width shifts, the input / output ports can be configured by combining ports with small focus shifts, and the increase in loss can be suppressed by the MZI circuit. According to this, loss can be suppressed even when an MMI width shift caused by process accuracy occurs.

  In the MZI circuit, the pair of arm waveguides are coupled to the optical waveguides 19 and 21 connected to the second end face 25b, respectively. Optical waveguides used for optical input and optical output are coupled to optical waveguides 15 and 17 connected to the first end face 25a. As shown in FIG. 1A, in this embodiment, the second reference surface Ref2 related to the second end surface 25b is orthogonal to the axis Ax, and the first reference surface Ref1 related to the first end surface 25a is the axis. Tilt with respect to Ax.

FIG. 13 is a diagram showing loss characteristics in the MZI circuit. As shown in part (a) of FIG. 13, the allowable range of width deviation in the MZI circuit using the MMI shown in FIG. 2 is from the input port INPUT1 to the output port OUTOUT2 in the MZI circuit shown in FIG. The value is −0.10 μm to +0.15 μm under the condition that the loss characteristic is 2 dB or less. On the other hand, by switching the input port and the output port to the MZI circuit according to the MMI width shift, the allowable range of the width shift in the MZI circuit using the MMI shown in FIG. 1 is shown in FIG. As shown in the graph, the loss characteristic is −0.20 μm to +0.25 μm under the condition of 2 dB or less. By this switching, a path with a small loss can be used among the following four paths.
A path from the input port INPUT1 to the output port OUTOUT2.
A path from the input port INPUT1 to the output port OUTOUT1.
A path from the input port INPUT2 to the output port OUTOUT2.
A path from the input port INPUT2 to the output port OUTOUT1.

  In the present embodiment, in an MMI having N input ports and M output ports, the distance between the output end face to which the output port is physically connected and each input port end face may be different from each other. When the MMI width deviates from the design value due to processing variations, the MMI can have an input port with a small defocus at the output port. It is possible to suppress loss due to MMI width deviation due to process accuracy. Preferably, the MMI can have a 2 × 2 structure. These MMIs can be applied to a waveguide type optical device such as a Mach-Zehnder modulator.

  FIG. 14 is a drawing showing an example of a method for designing an optical waveguide device according to the present embodiment. In step S101, the waveguide width W1 of the MMI is determined. At this time, it should be noted that the waveguide having the waveguide width W1 is a single mode waveguide without generating a higher-order mode, and that no loss occurs in the bending waveguide portion. In step S102, the port interval G is determined. Since the port gap G is related to the process accuracy of photolithography and reactive ion etching, the process window is considered. In step S103, the MMI width WM is determined. The determined MMI width WM is represented by (2 × W1 + G), for example. In step S104, an equivalent width We of the MMI is calculated. In step S105, beat lengths Lπ for the 0th order mode and the 1st order mode in MMI are calculated. In step S106, the MMI length L is determined as the power branching distance. The power equal branching distance L is, for example, 3 × Lπ / 2, and can be an integral multiple of this value. In step S107, an offset amount in the MMI is determined. In step S108, an MMI structure with offset and an MMI structure without offset are simulated. This simulation can be performed, for example, by a beam propagation method (BPM). Thereby, the MMI excess loss can be estimated. In step S109, the MMI is produced based on the design value of the MMI.

  FIG. 15 is a drawing showing main steps in the method of manufacturing the optical waveguide device according to the present embodiment. In step S201, an optical waveguide device including the multimode interference device according to the present embodiment is formed by processing. In step S202, the twenty-first waveguide and the twenty-second waveguide are routed from one of the eleventh waveguide and the twelfth waveguide of the multimode interference device of the optical waveguide device through the multimode waveguide of the multimode interference device. The characteristics are obtained by measuring the characteristics of the optical waveguide device in the first and second modes in which light is individually transmitted. In step S203, the third and second waveguides allow light to individually pass through either the eleventh waveguide or the twelfth waveguide through the multimode waveguide of the multimode interference device. The second characteristic is obtained by measuring the characteristics of the optical waveguide device in four forms. In step S204, based on the comparison between the first characteristic and the second characteristic, it is determined which of these forms is applied to the optical waveguide device. In step S205, the optical waveguide device is marked according to this determination. This marking indicates an available port. Thereby, the optical waveguide device whose use port is determined is manufactured.

  According to this fabrication method, when deciding which of several forms to apply to the use of an optical waveguide device based on a comparison of a plurality of characteristics, a desired wavelength band is countered against processing variations in the manufacturing process. Thus, an optical waveguide device capable of achieving a desired wavelength loss characteristic can be manufactured. The optical waveguide device can also include a Mach-Zehnder interferometer. A Mach-Zehnder interferometer capable of achieving a desired wavelength loss characteristic in a wide wavelength band can be provided to the optical waveguide device against the processing variation of the manufacturing process.

  The present invention is not limited to the specific configuration disclosed in the present embodiment.

DESCRIPTION OF SYMBOLS 11 ... Multimode interference device (MMI), 13 ... Multimode waveguide, 15 ... 11th waveguide, 17 ... 12th waveguide, 19 ... 21st waveguide, 21 ... 22nd waveguide, 23a ... 1st side surface , 23b ... second side surface, 25a ... first end face, 25b ... second end face, Ax, Ax2, Ax3 ... axis, Ref1, Ref2, Ref0 ... reference plane, W1 ... waveguide width, G ... waveguide spacing, W ... Multimode waveguide width, L ... multimode waveguide length, 2a, 2b ... cladding layer, 4 ... core layer, 6 ... waveguide structure, 8 ... substrate, 10 ... embedded region.

Claims (10)

A multi-mode interference device,
First and second side surfaces extending in the direction of the first axis, a first end surface extending along a first reference surface intersecting the first axis, and a second reference surface intersecting the first axis A multimode waveguide for multimode interference comprising a second end face extending along
An eleventh waveguide optically coupled to the multimode waveguide at the first end face;
A twelfth waveguide optically coupled to the multimode waveguide at the first end face;
A twenty-first waveguide optically coupled to the multimode waveguide at the second end face;
A twenty-second waveguide optically coupled to the multimode waveguide at the second end face;
With
The multi-mode interference device, wherein the first reference plane is inclined with respect to another reference plane parallel to the second reference plane. The center line of the eleventh waveguide intersects the first reference plane at a first position,
A center line of the twenty-first waveguide intersects the second reference plane at a second position;
The first position and the second position are located on a second axis;
A center line of the twelfth waveguide intersects the first reference plane at a third position;
The center line of the 22nd waveguide intersects the second reference plane at the fourth position,
The multi-mode interference device according to claim 1, wherein the third position and the fourth position are located on a third axis.   The multimode according to claim 2, wherein a distance between the first position and the second position on the first axis is different from a distance between the third position and the fourth position on the second axis. Interfering device. The first end surface includes a connection surface that connects an inner side surface of the eleventh waveguide and an inner side surface of the twelfth waveguide;
The said 2nd end surface was described in any one of Claims 1-3 including another connection surface which connects the inner side surface of the said 21st waveguide, and the inner side surface of the said 22nd waveguide. Multimode interference device. The eleventh waveguide, the twelfth waveguide, the twenty-first waveguide, the twenty-second waveguide, and the multimode waveguide have a waveguide structure;
The waveguide structure includes a first InP cladding layer, an AlGaInAs / AlInAs quantum well structure, and a second InP cladding layer,
5. The multimode interference according to claim 1, wherein the first InP cladding layer, the AlGaInAs / AlInAs quantum well structure, and the second InP cladding layer are sequentially arranged on a substrate. device.   The multimode interference device according to claim 1, wherein the multimode interference device has a 2 × 2 structure. A Mach-Zehnder interferometer,
A first branching waveguide;
A second branching waveguide;
A first arm waveguide connecting the first branch waveguide and the second branch waveguide;
A second arm waveguide connecting the first branching waveguide and the second branching waveguide;
With
The first branching waveguide is a Mach-Zehnder interferometer including the multimode interference device according to any one of claims 1 to 6.   The Mach-Zehnder interferometer according to claim 7, wherein the second branching waveguide includes the multimode interference device according to any one of claims 1 to 6. A method for producing an optical waveguide device, comprising:
Forming an optical waveguide device including the multimode interference device according to any one of claims 1 to 6 by processing;
The twenty-first waveguide and the twenty-second waveguide from either the eleventh waveguide or the twelfth waveguide of the multimode interference device of the optical waveguide device through the multimode waveguide of the multimode interference device. Measuring the characteristics of the optical waveguide device in an individual form that allows light to pass through each of the waveguides;
Individual light passing from the other of the eleventh waveguide and the twelfth waveguide to each of the twenty-first waveguide and the twenty-second waveguide through the multimode waveguide of the multimode interference device. Measuring the characteristics of the optical waveguide device in the form;
Determining which of the forms to apply to the optical waveguide device based on the measurement results;
A method of fabricating an optical waveguide device.   The method of making an optical waveguide device according to claim 9, wherein the optical waveguide device comprises a Mach-Zehnder interferometer.