Optical waveguide module, optical transmission module, and manufacturing method of optical waveguide module

Abstract

To provide a compact and inexpensive optical transmitter.SOLUTION: An optical waveguide module is provided, comprising a wavelength control unit configured to control wavelength of output light generated by a light source, and a wavelength locker configured to receive the output light and output an electrical signal indicative of a relationship between an output light wavelength and a target wavelength, where the wavelength control unit and the wavelength locker are formed as a semiconductor optical waveguide on a single semiconductor substrate.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical waveguide module and the like.

Background Art

[0002] In an optical transmitter used in an optical wavelength division multiplexing transmission system, in order to set the wavelength of an optical signal to a light source according to the specifications of the system, a wavelength tunable laser is generally used. The wavelength tunable laser includes a light source that generates laser light and a wavelength tunable unit that controls the wavelength of the light source.

[0003] As a technique for accurately setting the wavelength of a wavelength tunable laser, a wavelength locker is known. The light output from the wavelength tunable laser is input to the wavelength locker. The wavelength locker outputs a signal indicating the relationship between the wavelength of the input light and a desired wavelength. The desired wavelength is the wavelength defined in the system. Then, the wavelength of the wavelength tunable light source is controlled so that the signal output from the wavelength locker indicates that the wavelength tunable laser is emitting light at the desired wavelength. By such control, the wavelength of the optical signal can be accurately set. In relation to the present invention, techniques related to wavelength tunable light sources are described in Patent Documents 1-4.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a typical optical transmitter equipped with a wavelength rocker, the wavelength rocker and the tunable section were provided as separate optical components. Furthermore, to monitor the wavelength of the light output by the tunable laser using the wavelength rocker, it was necessary to use additional optical components such as beam splitters to create an optical circuit that inputs the light output from the tunable section to the wavelength rocker. However, in such optical transmitters where the tunable section and wavelength rocker are provided separately, the number of optical components increases, and the optical axis adjustment required to optically couple the tunable section and the wavelength rocker becomes time-consuming. As a result, a challenge in reducing the cost of a typical optical transmitter equipped with a wavelength rocker was that it was difficult. Additionally, because a typical optical transmitter equipped with a wavelength rocker requires the placement of numerous optical components one by one, reducing the mounting area was also a challenge.

[0006] (Purpose of the invention) The optical waveguide module of the present invention aims to provide technology for realizing a small and low-cost optical transmitter. [Means for solving the problem]

[0007] The optical waveguide module of the present invention comprises a wavelength control means for controlling the wavelength of output light output by a light source, and a wavelength rocker that receives the output light and outputs an electrical signal indicating the relationship between the wavelength of the output light and a target wavelength, wherein the wavelength control means and the wavelength rocker are formed as a semiconductor optical waveguide on the same semiconductor substrate.

[0008] The present invention provides a method for manufacturing an optical waveguide module, comprising the steps of forming a wavelength control means on a semiconductor substrate for controlling the wavelength of output light emitted by a light source, and forming a wavelength rocker on the semiconductor substrate that outputs an electrical signal indicating the relationship between the wavelength of the output light and a target wavelength. [Effects of the Invention]

[0009] The optical waveguide module of the present invention provides technology for realizing a small and low-cost optical transmitter. [Brief explanation of the drawing]

[0010] [Figure 1] This is a block diagram showing an example configuration of an optical waveguide module according to the first embodiment. [Figure 2] This is a block diagram showing an example configuration of a wavelength rocker according to the first embodiment. [Figure 3] This figure shows an example of the characteristics of a wavelength rocker. [Figure 4] This block diagram shows an example configuration of an optical waveguide module according to the second embodiment. [Figure 5] This block diagram shows an example configuration of an optical waveguide module according to the third embodiment. [Figure 6] This is a block diagram showing an example configuration of an optical waveguide module according to the fourth embodiment. [Figure 7] This block diagram shows an example configuration of an optical transmission module according to the fifth embodiment. [Figure 8] This block diagram shows an example configuration of an optical transmission module according to the sixth embodiment. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described below. In the embodiments and drawings, the same names and reference numerals will be used for elements that have already been shown, and redundant explanations will be omitted in each embodiment.

[0012] (First embodiment) Figure 1 is a block diagram showing an example configuration of an optical waveguide module 10 according to the first embodiment. The optical waveguide module 10 includes a wavelength control unit 110 and a wavelength rocker 120. The wavelength control unit 110 receives light (output light) output from a light source. However, the light source is not shown in Figure 1. The wavelength control unit 110 has a function to control the wavelength of the light source. For example, the wavelength control unit 110 may control the wavelength of the output light by configuring a resonator for the light source. The wavelength control unit 110 is one form of wavelength control means.

[0013] The wavelength locker 120 is formed of a silicon optical waveguide. The configuration of the wavelength locker 120 will be described with reference to FIG. 2. Output light whose wavelength is controlled by the wavelength control unit 110 is input to the wavelength locker 120. Then, the wavelength locker 120 generates and outputs a signal indicating the relationship between the wavelength of the output light and the target wavelength. Here, the target wavelength is the wavelength required for the light output from the optical waveguide module 10.

[0014] The wavelength control unit 110 and the wavelength locker 120 are formed as silicon optical waveguides on the same silicon substrate 100. Also, the optical transmission path between the wavelength control unit 110 and the wavelength locker 120 is formed as a silicon optical waveguide. Note that the materials of the substrate and the optical waveguide are not limited to silicon.

[0015] The optical waveguide module 10 having such a configuration can realize a small and low-cost optical transmitter. The reason is that since the wavelength control unit 110 and the wavelength locker 120 are formed on the same silicon substrate, manufacturing is easier compared to a configuration in which these are individually mounted as optical elements, and optical axis adjustment between them is also unnecessary.

[0016] FIG. 2 is a block diagram showing a configuration example of the wavelength locker 120. The wavelength locker 120 includes optical waveguides 121 - 124, a ring optical waveguide 125, a heater 126, a ring resonator 127, optical couplers 128 - 129, photodetectors 130 - 131, and terminals 132 - 133.

[0017] The optical waveguides 121 - 124, the ring optical waveguide 125, the ring resonator 127, and the optical couplers 128 - 129 are silicon optical waveguides. The ring optical waveguide 125 is optically coupled with the optical waveguides 123 and 124 and together with them constitutes the ring resonator 127. The heater 126 is a thin film heater formed on at least one of the upper and lower portions of the ring optical waveguide 125. FIG. 2 is an example of a top view of the transmission of the wavelength locker 120, and the heater 126 is illustrated as the region between two dashed circular shapes. The heater 126 may be formed so as to cover the ring optical waveguide 125. The heater 126 controls the temperature of the ring optical waveguide 125 by power supply from the outside. By forming the heater 126 only in the vicinity of the ring optical waveguide 125, the resonance wavelength of the ring resonator 127 can be controlled with less power as compared with the case where the entire wavelength locker 120 is heated by a larger heater. The power of the heater 126 is supplied from an electric circuit outside the wavelength locker 120. However, in FIG. 2, the description of the wiring regarding the power supply of the heater 126 is omitted.

[0018] The light output from the wavelength control unit 110 is input to the optical coupler 128. The optical coupler 128 branches the input light. One of the branched lights is output to the photo detector (PD) 130, and the other branched light is output to the optical coupler 129. The photo detector 130 is, for example, a photodiode and outputs a photocurrent proportional to the intensity of the light input to the optical coupler 128. The output current of the photo detector 130 is output from the terminal 132 to an external electric circuit via the electrical wiring on the silicon optical waveguide.

[0019] One portion of the light output from optical coupler 128 is input to optical coupler 129. Optical coupler 129 splits the input light. One portion of the light split by optical coupler 129 is output to the outside of wavelength rocker 120 via optical waveguide 121. The other portion of the light split by optical coupler 129 is output to ring resonator 127. A photodetector 131 is connected to one end of optical waveguide 124 contained in ring resonator 127. The photodetector 131 is, for example, a photodiode. The output current of the photodetector 131 is output to an external electrical circuit from terminal 133 via electrical wiring on the silicon optical waveguide.

[0020] Figure 3 shows an example of the characteristics of wavelength rocker 120. The horizontal axis of Figure 3 represents the power applied to heater 126, and the vertical axis represents the light-receiving power P1 of photodetector 130 and the light-receiving power P2 of photodetector 131. As the power applied to heater 126 increases, the temperature of heater 126 rises, and the characteristics of P2 change. Also, the position of the peak of P2 differs for each wavelength.

[0021] For example, characteristic data for the wavelength rocker 120 is prepared for each different wavelength, corresponding to each wavelength. Then, characteristic data for the wavelength required for the light source (target wavelength) is selected from the characteristic data for each wavelength. Furthermore, the control targets for P1 and P2, as well as the temperature of the heater 126 at that time, are determined from the selected characteristic data. Figure 3 shows P1=P1a, P2=P2a, and T=Ta as examples of control targets. Then, the wavelength of the light source is controlled using the wavelength control unit 110 so that P1 and P2 become the target values ​​P1a and P2a while maintaining the heater temperature T at Ta. The control of the wavelength control unit 110 and the temperature control of the heater 126 based on P1 and P2 are performed by an electrical circuit outside the wavelength rocker 120. Alternatively, P2 / P1, which is P2 normalized by P1, may be used as the target value. In this way, the electrical circuit controls the wavelength control unit 110 so that P1 and P2 become specific values ​​that indicate the relationship between the wavelength of the output light and the target wavelength. It should be noted that configurations for monitoring the wavelength of a tunable laser using a wavelength rocker are known. For example, Patent Document 1 describes a general procedure for monitoring the wavelength of a light source.

[0022] Conventional wavelength rockers required the individual preparation of components such as etalons and beam splitters, and the optical coupling between these optical components. Therefore, compared to the wavelength rocker 120 explained in Figure 2, conventional wavelength rockers required a large number of optical components, and the time required for optical axis alignment between these components made it difficult to control costs and miniaturize them. Furthermore, in conventional wavelength rockers, the entire substrate on which the wavelength rocker, consisting of multiple optical elements, was mounted on a large heater for temperature control. Therefore, conventional wavelength rockers had the problem of high power consumption.

[0023] However, the wavelength rocker 120 shown in Figure 2 does not require etalons or beam splitters, which are separate components in typical wavelength rockers. Instead, a silicon optical waveguide that incorporates these functions forms the wavelength rocker 120 as a single unit. This makes it possible to miniaturize and reduce the cost of the wavelength rocker 120. Furthermore, the wavelength rocker 120 can also achieve low power consumption through the heater 126 provided near the ring optical waveguide 125.

[0024] (Second embodiment) Figure 4 is a block diagram showing an example configuration of the optical waveguide module 11 according to the second embodiment. The optical waveguide module 11 differs from the optical waveguide module 10 in Figure 1 in that it includes a control circuit 200. The control circuit 200 is an electrical circuit connected to the wavelength rocker 120 and the wavelength control unit 110, as described in the first embodiment. Specifically, the control circuit 200 is connected to the heater 126 and terminals 132 and 133 by electrical wiring. The control circuit 200 is also connected to the wavelength control unit 110 by electrical wiring.

[0025] The control circuit 200 uses the photocurrent output from the wavelength rocker 120 (i.e., the light-receiving power of the photodetectors 130 and 131) to control the wavelength of the light source input to the wavelength control unit 110. In other words, the control circuit 200 controls the wavelength control unit 110 so that the amplitude of the electrical signal output by the wavelength rocker 120 reaches a target value. In Figure 4, the control circuit 200 is located outside the silicon substrate 100. However, the control circuit 200 may also be located on the silicon substrate 100.

[0026] An optical waveguide module 11 having such a configuration can be provided as an integrated module comprising a wavelength control unit 110, a wavelength rocker 120, and a functional module that provides control functions for these.

[0027] (Third embodiment) Figure 5 is a block diagram showing an example configuration of an optical waveguide module 12 according to the third embodiment. The optical waveguide module 12 differs from the optical waveguide module 10 in Figure 1 in that it includes an optical modulator 140. In the optical waveguide module 12, in addition to the wavelength control unit 110 and the wavelength rocker 120, the optical modulator 140 is formed as a silicon optical waveguide on the same silicon substrate 100. Furthermore, the optical transmission path between the wavelength rocker 120 and the optical modulator 140 may also be formed as a silicon optical waveguide integrated with the wavelength rocker 120 and the optical modulator 140.

[0028] The optical modulator 140 modulates the light output from the wavelength rocker 120 with a data signal and outputs the modulated light to the outside of the optical waveguide module 12. The data signal is, for example, user data transmitted in the optical transmission system in which the optical waveguide module 12 is used, or data for managing the optical transmission system.

[0029] An optical waveguide module 12 with this configuration can realize a small and low-cost optical transmitter. This is because the wavelength control unit 110, wavelength rocker 120, and optical modulator 140 are formed on the same silicon substrate, making manufacturing easier compared to a configuration in which these are individually mounted as optical elements, and eliminating the need for optical axis adjustment between them.

[0030] (Fourth embodiment) Figure 6 is a block diagram showing an example configuration of an optical waveguide module 13 according to the fourth embodiment. The optical waveguide module 13 adds the control circuit 200 found in the optical waveguide module 11 of Figure 4 to the optical waveguide module 12 of Figure 5, which is equipped with an optical modulator 140. An optical waveguide module 13 with this configuration achieves the effects of both optical waveguide modules 11 and 12.

[0031] (Fifth embodiment) Figure 7 is a block diagram showing an example configuration of the optical transmission module 20 according to the fifth embodiment. The optical transmission module 20 comprises the optical waveguide module 13 described in Figure 6 and a light source 300. In the first to fourth embodiments, the light source 300 is a light source that generates light input to the wavelength control unit 110, and the wavelength of the light source 300 is controlled by the wavelength control unit 110. That is, the light source 300 and the wavelength control unit 110 constitute a single tunable light source. The control circuit 200 controls the wavelength control unit 110 so that the photocurrents of the photodetectors 130 and 131 of the wavelength rocker 120 become predetermined values ​​(i.e., the wavelength of the light source 300 becomes the target wavelength). The light source 300 may be formed on a silicon substrate 100 together with the wavelength control unit 110, the wavelength rocker 120 and the optical modulator 140.

[0032] An optical transmission module 20 with this configuration can be applied to the optical transmitter of an optical transceiver. Furthermore, because the optical transmission module 20 includes an optical waveguide module 13, it is possible to realize a compact and low-cost optical transmitter and optical transceiver.

[0033] (Sixth embodiment) Figure 8 is a block diagram showing an example configuration of an optical transmission module 21 according to the sixth embodiment. The optical transmission module 21 comprises the optical transmission module 20 described in Figure 7 and an optical amplifier 400. The optical amplifier 400 is, for example, a silicon optical amplifier. The optical amplifier is an example of an optical amplification means that amplifies the light output from the optical modulator 140. The optical amplifier 400 may be formed on the silicon substrate 100 together with the wavelength control unit 110, the wavelength rocker 120, and the optical modulator 140. The optical amplifier 400 is also called a booster amplifier.

[0034] An optical transmission module 21 with this configuration can be applied to the optical transmitter of an optical transceiver. Furthermore, the optical transmission module 21 can realize a small and low-cost optical transmitter and optical transceiver, and can extend the propagation distance of light modulated by the optical modulator 140.

[0035] The embodiments of the present invention may also be described as follows, but are not limited thereto.

[0036] (Note 1) Wavelength control means for controlling the wavelength of output light emitted by a light source, The system includes a wavelength rocker that receives the output light and outputs an electrical signal indicating the relationship between the wavelength of the output light and the target wavelength, The wavelength control means and the wavelength rocker are formed as a semiconductor optical waveguide on the same semiconductor substrate. Optical waveguide module.

[0037] (Note 2) The optical waveguide module described in Appendix 1, wherein the wavelength rocker comprises a ring optical waveguide, and the characteristics of the wavelength rocker are set by a heater that controls the temperature of the ring optical waveguide.

[0038] (Note 3) The optical waveguide module described in Appendix 2, wherein the heater is a thin-film heater formed on at least one of the upper and lower parts of the ring optical waveguide.

[0039] (Note 4) An optical waveguide module according to any one of the appendices 1 to 3, further comprising a control circuit for controlling the wavelength control means such that the amplitude of the electrical signal becomes a specific value indicating the relationship between the wavelength of the output light and the target wavelength.

[0040] (Note 5) An optical waveguide module as described in any one of the appendices 1 to 4, wherein the semiconductor substrate is a silicon substrate and the semiconductor optical waveguide is a silicon optical waveguide.

[0041] (Note 6) An optical waveguide module according to any one of the appendices 1 to 5, further comprising an optical modulator formed on the semiconductor substrate for modulating the output light.

[0042] (Note 7) The aforementioned light source, The optical waveguide module described in Appendix 6, An optical transmission module equipped with the following features.

[0043] (Note 8) An optical transmission module as described in Appendix 7, comprising optical amplification means for amplifying the light output from the optical modulator.

[0044] (Note 9) A wavelength control means for controlling the wavelength of the output light emitted by the light source is formed on a semiconductor substrate. A wavelength rocker is formed on the semiconductor substrate to output an electrical signal indicating the relationship between the wavelength of the output light and the target wavelength. A method for manufacturing optical waveguide modules.

[0045] (Note 10) A method for manufacturing an optical waveguide module as described in Appendix 9, further comprising forming a heater for controlling the temperature of the ring optical waveguide provided in the wavelength rocker.

[0046] (Note 11) A method for manufacturing an optical waveguide module as described in Appendix 10, wherein a thin-film heater is formed as the heater on at least one of the upper and lower parts of the ring optical waveguide.

[0047] Although the present invention has been described above with reference to embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the configuration and details of the present invention that will be understood by those skilled in the art within the scope of the present invention. For example, in the above embodiments, the case in which the wavelength control unit 110, wavelength rocker 120, etc., are formed on a silicon substrate 100 was described as an example. However, the material of the substrate and optical waveguide is not limited to silicon. For these materials, semiconductor substrates and semiconductor optical waveguides of any material applicable to the optical transmitter can be used.

[0048] Furthermore, the configurations described in each embodiment are not necessarily mutually exclusive. The operation and effects of the present invention may be achieved by a configuration that combines all or part of the above-described embodiments.

[0049] Some or all of the functions and procedures described in each of the above embodiments may be implemented by a central processing unit (CPU) in the control circuit 200 executing a program. The program is recorded on a fixed, non-temporary recording medium in a format readable by the CPU. The recording medium may be, but is not limited to, semiconductor memory or fixed magnetic disk devices. [Explanation of Symbols]

[0050] 10-13 Optical waveguide module 20-21 Optical Transmitter Module 100 silicon substrates 110 Wavelength control unit 120 wavelength rocker 121-124 Optical waveguide 125 Ring Optical Waveguide 126 Heater 127 Ring resonator 128-129 Optical coupler 130-131 Photodetector Terminals 132-133 140 Optical modulators 200 Control circuits 300 light source 400 Optical Amplifier

Claims

1. Wavelength control means for controlling the wavelength of output light emitted by a light source, The system includes an optical coupler that splits the output light input from the wavelength control means into a first light, a second light, and a third light, a first photodiode and a second photodiode, and a ring optical waveguide, and a wavelength rocker that outputs an electrical signal indicating the relationship between the wavelength of the output light and the target wavelength, The first light is output to the outside of the wavelength rocker, The second light is input to the first photodiode, The third light is input to the second photodiode via the ring optical waveguide. The wavelength control means and the wavelength rocker are formed as a semiconductor optical waveguide on the same semiconductor substrate. Optical waveguide module.

2. The optical waveguide module according to claim 1, wherein the electrical signal indicating the relationship between the wavelength of the output light and the target wavelength includes a first electrical signal output from the first photodiode and a second electrical signal output from the second photodiode.

3. The optical waveguide module according to claim 1 or 2, wherein the characteristics of the wavelength rocker are set by a heater that controls the temperature of the ring optical waveguide.

4. The optical waveguide module according to claim 3, wherein the heater is a thin-film heater formed on at least one of the upper and lower parts of the ring optical waveguide.

5. An optical waveguide module according to any one of claims 1 to 4, further comprising a control circuit for controlling the wavelength control means such that the amplitude of the electrical signal becomes a specific value indicating the relationship between the wavelength of the output light and the target wavelength.

6. The optical waveguide module according to any one of claims 1 to 5, wherein the semiconductor substrate is a silicon substrate and the semiconductor optical waveguide is a silicon optical waveguide.

7. An optical waveguide module according to any one of claims 1 to 6, further comprising an optical modulator formed on the semiconductor substrate for modulating the output light.

8. The aforementioned light source, The optical waveguide module described in claim 7, An optical transmission module equipped with the following features.

9. A wavelength control means for controlling the wavelength of the output light emitted by the light source is formed on a semiconductor substrate. A wavelength rocker is formed on the semiconductor substrate to output an electrical signal indicating the relationship between the wavelength of the output light and the target wavelength. A method for manufacturing an optical waveguide module, The aforementioned wavelength rocker is The system includes an optical coupler that splits the output light input from the wavelength control means into a first light, a second light, and a third light, a first photodiode and a second photodiode, and a ring optical waveguide. In the aforementioned wavelength rocker, The first light is output to the outside of the wavelength rocker, The second light is input to the first photodiode, The third light is input to the second photodiode via the ring optical waveguide. A method for manufacturing optical waveguide modules.

10. The electrical signal indicating the relationship between the wavelength of the output light and the target wavelength includes a first electrical signal output from the first photodiode and a second electrical signal output from the second photodiode. A method for manufacturing an optical waveguide module as described in claim 9.

Images