Optical Transmitter / Receiver

Abstract

To provide an optical transceiver that can reduce a time required for controlling a wavelength.SOLUTION: An optical transceiver includes: a plurality of light sources 11 and 31 having ring resonators 19, 21, 39, and 41; a reception antenna 51 for receiving light; and a wavelength separating filter 52 for separating, from the light received by the reception antenna 51, light of the same wavelength as the light output from the light source 11. The wavelength separating filter 52 is composed of the ring resonator 19 of the light source 11. Since the wavelength separating filter 52 is composed of the ring resonator 19 of the light source 11, controlling a wavelength of output light allows controlling a transmission wavelength of the wavelength separating filter 52. Therefore, there is no need to control the transmission wavelength of the wavelength separating filter 52 separately, and a time required for controlling the wavelength can be reduced.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical transmitter / receiver. [Background technology]

[0002] An optical deflection device disclosed in Patent Document 1 has been proposed as a beam deflection system. This optical deflection device is configured to simultaneously scan multiple scanning ranges using multiple tunable laser light sources. Because the wavelength tuning range of the tunable laser light source limits the ability to cover a wide scanning range with a single laser beam, this optical deflection device uses multiple laser light sources to share the entire scanning range. Specifically, laser beams output from multiple laser light sources with different wavelengths are introduced into a beam deflector, and an emitter is configured to emit beams at an emission angle corresponding to each wavelength, enabling simultaneous scanning of multiple scanning ranges. A wavelength-discriminating filter is provided to process the received light, and the transmission characteristics of the wavelength-discriminating filter are controlled to track the wavelength of the laser light source, thereby separating and detecting received light of different wavelengths. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 003852 Summary of the Invention [Problem to be solved by the invention]

[0004] In the optical deflection device described in Patent Document 1, the laser light source and the wavelength discrimination filter are separate devices. Therefore, it is necessary to control the transmission wavelength of the wavelength discrimination filter separately from controlling the wavelength of the laser light source, and it takes a long time to control the wavelength of the optical deflection device as a whole.

[0005] SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide an optical transmitter / receiver that can reduce the time required for wavelength control. [Means for solving the problem]

[0006] In order to achieve the above object, the invention of claim 1 provides an optical transmitting and receiving device, comprising: a plurality of light sources (11, 31, 61) each having a ring resonator (19, 21, 39, 41, 69, 71); a receiving antenna (51) for receiving light; and a wavelength discrimination filter (52) for discriminating light having the same wavelength as light output from some of the plurality of light sources from the light received by the receiving antenna, wherein the wavelength discrimination filter is configured by the ring resonator of the some of the light sources. The light received by the receiving antenna is connected to a waveguide (20, 40, 57) extending from the receiving antenna, and the remaining light, after being separated by a wavelength separation filter into light having the same wavelength as the light output from the part of the light source, is detected at the end of the waveguide. do.

[0007] In this case, since the wavelength discrimination filter is configured with a ring resonator included in the light source, the transmission wavelength of the wavelength discrimination filter is also controlled by controlling the wavelength of the output light. Therefore, there is no need to separately control the transmission wavelength of the wavelength discrimination filter, and the time required for wavelength control can be reduced.

[0008] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating a schematic configuration of an optical transmitting and receiving device according to a first embodiment. [Figure 2] FIG. 2 is an explanatory diagram of dimensions of each part such as a waveguide and a ring resonator. [Figure 3] FIG. 1 is a cross-sectional view of a ring resonator. [Figure 4] FIG. 2 is a diagram illustrating a configuration of a semi-reflective mirror. [Figure 5] 1 is a transmission spectrum of a ring resonator. [Figure 6] 1 is a transmission spectrum of a ring resonator. [Figure 7]FIG. 10 is a diagram showing a schematic configuration of a comparative example. [Figure 8] FIG. 10 is a diagram illustrating a schematic configuration of an optical transmitting and receiving device according to a second embodiment. [Figure 9] 1 is a transmission spectrum of a ring resonator. [Figure 10] 1 is a transmission spectrum of a ring resonator. [Figure 11] 1 is a transmission spectrum of a ring resonator. [Figure 12] FIG. 10 is a diagram illustrating a schematic configuration of an optical transmitting and receiving device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following embodiments, identical or equivalent parts will be denoted by the same reference numerals.

[0011] (First embodiment) A first embodiment will be described below. The optical transmission / reception device of this embodiment is applied to, for example, a laser radar or an FMCW (Frequency Modulated Continuous Wave) LiDAR (Light Detection And Ranging).

[0012] As shown in Fig. 1, the optical transceiver includes a transmitter 1 that transmits light to the outside and a receiver 2 that receives light from the outside. The optical transceiver includes multiple transmitters 1. In this embodiment, a case will be described in which the optical transceiver includes two transmitters 1. The two transmitters 1 are referred to as transmitter 1a and transmitter 1b.

[0013] The transmitter 1a includes an external resonance laser 11 as a light source, a wavelength monitor 12, and a transmitting antenna 13. The external resonance laser 11 includes an SOA (Semiconductor Optical Amplifier) 14 and an external resonator 15. The wavelength monitor 12, the transmitting antenna 13, and the external resonator 15 are formed by performing a semiconductor process on a semiconductor substrate 100, and the SOA 14 is connected to the semiconductor substrate 100. The external resonance laser 11 is configured to emit internally emitted light from the SOA 14 to the external resonator 15, extract the light as strong light that is resonated in the external resonator 15 and the SOA 14, and output it as externally emitted light.

[0014] The SOA 14 amplifies and outputs light, and is configured, for example, with a III-V group semiconductor structure. One surface 14a of the SOA 14 is attached to an end surface 100a of the semiconductor substrate 100, thereby connecting and integrating with the external resonator 15. The SOA 14 is connected to the end surface 100a at this surface 14a via matching oil, ultraviolet curing resin, or the like (not shown) so as to be optically coupled to a waveguide 18 (described later).

[0015] The other surface 14b of the SOA 14 is provided with a total reflection mirror 16. The total reflection mirror 16 serves to reflect the light emitted from the SOA 14 back to the external resonator 15. The SOA 14 is provided with electrodes (not shown) and the like, so that the optical output can be changed based on the current injected from the electrodes.

[0016] The external resonator 15 includes an SSC (Spot Size Converter) 17, a waveguide 18, a ring resonator 19, a waveguide 20, a ring resonator 21, a waveguide 22, a frequency modulator 23, a semi-reflective mirror 24, and a waveguide 25 formed on a semiconductor substrate 100.

[0017] The SSC 17 is used to match the mode diameters of the SOA 14 and the waveguide 18. One end of the SSC 17 is exposed from the end face 100a of the semiconductor substrate 100, and the other end is connected to the waveguide 18. For example, the mode diameter of the SSC 17 gradually increases from the waveguide 18 toward the SOA 14. Furthermore, the other end of the SSC 17, which is on the waveguide 18 side, is inclined by a predetermined angle with respect to the longitudinal direction of the waveguide 18 to prevent reflection.

[0018] The waveguide 18 propagates the internally emitted light transmitted from the SSC 17 to the ring resonator 19 and propagates the internally emitted light returning from the ring resonator 19 toward the SOA 14, and is configured in a linear shape with one longitudinal direction. The end of the waveguide 18 connected to the SSC 17 extends in a direction inclined at a predetermined angle with respect to the longitudinal direction of the waveguide 18. This end is connected to the SSC 17, which includes a tapered waveguide 18a, thereby suppressing reflection and allowing light to propagate efficiently toward the SSC 17. The end of the waveguide 18 opposite the SSC 17 is connected to a waveguide 53, which will be described later. The waveguide 20 is configured in a linear shape parallel to the waveguide 18, and the ring resonator 19 is disposed between the waveguide 18 and the waveguide 20.

[0019] The ring resonator 19 is a resonator that generates a transmission spectrum with a predetermined FSR (free spectral range) when light is input to it. The ring resonator 19 is located at a position a predetermined distance away from the waveguide 18 and the waveguide 20, but is optically coupled to them. Therefore, when the internal output light propagates from the waveguide 18, the internal output light propagates into the ring resonator 19, and the light propagated into the ring resonator 19 propagates into the waveguide 20.

[0020] The waveguide 20 propagates the internally output light transmitted from the ring resonator 19 to the ring resonator 21, and propagates the internally output light returning from the ring resonator 21 to the ring resonator 19. One end of the waveguide 20 extends to an end face 100a of the semiconductor substrate 100, and the other end is connected to a receiving antenna 51 (described later). The ring resonators 19 and 21 are arranged so that the ring resonator 19 is closer to the receiving antenna 51. The waveguide 22 is configured in a line shape parallel to the waveguides 18 and 20, and the ring resonator 21 is arranged between the waveguide 20 and the waveguide 22. Note that it is not essential that the waveguides 18, 20, and 22 are parallel to each other; for example, the waveguides 20 and 22 may be inclined with respect to the waveguide 18.

[0021] Ring resonator 21 is a resonator that generates a transmission spectrum with a predetermined FSR when light is input to it. Ring resonator 21 is located at a position a predetermined distance away from waveguide 20 and waveguide 22, but is optically coupled to them. Therefore, when internally output light propagates from waveguide 20, the internally output light propagates into ring resonator 21, and the light propagated into ring resonator 21 propagates to waveguide 22.

[0022] The transmission spectrum of ring resonator 21 has a different FSR than ring resonator 19, but at a predetermined wavelength, both ring resonators 19 and 21 have peaks in their transmission spectra. This wavelength is designated λ1. At this wavelength λ1, the transmission spectra generated by ring resonators 19 and 21 overlap, and the combined spectrum of these two peaks in the double-ring transmission spectrum. This peak selects the longitudinal mode of the Fabry-Perot resonator formed between total reflection mirror 16 and partial reflection mirror 24, causing laser oscillation and resulting in intense light, which is then output. Note that ring resonators 19 and 21 are configured to block light of wavelength λ2 (described below), specifically, to have a transmittance of light of wavelength λ2 below a predetermined value.

[0023] The ring resonators 19 and 21 are provided with heaters 19a and 21a, respectively, and the FSR of the transmission spectrum can be intentionally changed by heating with the heaters 19a and 21a. In this way, the ring resonator 19, the waveguide 20, and the ring resonator 21 form a wavelength-tunable filter 26.

[0024] 2 and 3, details of each part of the waveguide 18, ring resonator 19, and waveguide 20 will be described. Note that, here, an example of dimensions of each part will be described for the ring resonator 19 and the waveguides 18 and 20 arranged on both sides thereof, but the same applies to the ring resonator 21 and the waveguides 20 and 22 arranged on both sides thereof, with some exceptions.

[0025] As shown in FIG. 2 , the waveguides 18 and 20 both have the same width Wt. Here, the width Wt is 0.45 μm. The ring resonator 19 is formed by quadrant-shaped rectangular shapes, and its width Wr is also 0.45 μm, the same as the width Wt. The linear portions of the ring resonator 19 facing the waveguides 18 and 20 are primarily optically coupled to the waveguides 18 and 20, and the length of the opposing portions is the coupling length Lc. The portion of the ring resonator 19 perpendicular to the linear portions facing the waveguides 18 and 20 has a length Ld. The radius of curvature R of the quadrant is, for example, 20 μm. The peripheral length Lring of the ring resonator 19 is 2×Lc + 2×Ld + 2πR, and is set by adjusting the coupling length Lc and the length Ld.

[0026] The coupling length Lc is set in consideration of the coupling efficiency κ between the waveguide 18 and the waveguide 20. That is, the coupling efficiency κ is determined by the coupling length Lc and the inter-waveguide gap W, which is the distance between the ring resonator 19 and the waveguide 18 or 20. GAPThe coupling efficiency κ can be set differently between the ring resonator 19 and the waveguide 18 and between the ring resonator 19 and the waveguide 20, or the coupling efficiency κ can be set the same. In this example, the widths Wt of the waveguides 18 and 20 are set equal, and the gap W between the waveguides is set equal. GAP is also set equal to 0.3 μm.

[0027] The ring resonators 19 and 21 have different perimeter lengths, and generate transmission spectra with different FSRs. The ring perimeter lengths Lring of the ring resonators 19 and 21 are 149.6 μm and 159.3 μm, respectively. The coupling efficiency κ between the ring resonators 19 and 21 and the waveguide 18, etc. is 0.13, and the coupling length Lc is 9 μm.

[0028] As shown in FIG. 3, the ring resonator 19 is configured by laminating a support substrate 101, an undercladding layer 102, a core layer 103, an overcladding layer 104, and a heater 19a.

[0029] The support substrate 101 is made of a silicon substrate or the like and has a thickness of 725 μm. The undercladding layer 102 is made of an insulating film such as silicon oxide (SiO2) and is deposited on the support substrate 101 to a thickness of 2 μm. The core layer 103 is a portion that constitutes the waveguide of the ring resonator 19, is made of silicon or the like, and is patterned so that its upper surface shape conforms to the shape of the ring resonator 19. The width of the core layer 103 corresponds to the width Wr of the ring resonator 19 and is set to 0.45 μm, and the thickness of the core layer 103 is set to 0.22 μm. The overcladding layer 104 is made of an insulating film such as SiO2 and is formed to a thickness of 3 μm so as to cover the core layer 103. The heater 19a is formed on the overcladding layer 104 at a position corresponding to the core layer 103 and to a thickness of 0.12 μm. The heater 19a is made of a heat-generating material, such as Ta, TiN, or TaN, that can heat the core layer 103 when energized.

[0030] Although the cross-sectional structure of ring resonator 19 has been described here, ring resonator 21 also has a similar structure. Waveguides 18, 20, and 22 also basically have the cross-sectional structure shown in Fig. 3, with heater 19a removed. An SOI (abbreviation for Silicon On Insulator) substrate is used as support substrate 101, undercladding layer 102, and core layer 103, and core layer 103 is formed by patterning an active layer in the SOI substrate.

[0031] The waveguide 22 propagates the internally emitted light propagated from the ring resonator 21 and reflected by the semi-reflective mirror 24 back to the ring resonator 21. As shown in FIG. 1 , one end of the waveguide 22 is connected to the semi-reflective mirror 24, and the other end is provided with a terminator 22a. The terminator 22a emits unwanted light propagated from the waveguide 22 to the outside of the waveguide 22. The terminator 22a extends in a direction inclined at a predetermined angle with respect to the longitudinal direction of the waveguide 22 and has a tapered shape so as to prevent the unwanted light from being reflected and propagated back into the waveguide. A frequency modulator 23 is disposed between the portion of the waveguide 22 connected to the ring resonator 21 and the end on the semi-reflective mirror 24 side.

[0032] The frequency modulator 23 modulates the frequency of the light passing through the waveguide 22. The frequency modulator 23 is configured with a phase modulator that utilizes, for example, the thermo-optic effect, the carrier plasma effect, or the electro-optic effect, and modulates the frequency by modulating the phase of the light.

[0033] The semi-reflective mirror 24 reflects a portion of the light propagating from the waveguide 22 and propagates it back into the waveguide 22, while outputting the remainder to the outside of the external cavity laser 11. The semi-reflective mirror 24 is configured as a directional coupler, for example, as shown in FIG. 1. Alternatively, the semi-reflective mirror 24 may be configured as a DBR (Distributed Bragg Reflector), as shown in FIG. 4. The reflectance of the semi-reflective mirror 24 is, for example, about 1 to 10%. The semi-reflective mirror 24 is connected to the wavelength monitor 12 and the transmitting antenna 13 by a linear waveguide 25 parallel to the waveguide 22, etc., and the light output from the external cavity laser 11 propagates to the wavelength monitor 12 and the transmitting antenna 13.

[0034] Wavelength monitor 12 detects the wavelength of the light output by external cavity laser 11 in order to perform feedback control of the wavelength of the light. Wavelength monitor 12 is composed of a filter, such as an etalon filter, that has peaks at certain wavelength intervals, and a photodiode. The monitoring results from wavelength monitor 12 are input to a control circuit (not shown), and the temperatures of heaters 19a and 21a provided in ring resonators 19 and 21 are adjusted based on these monitoring results.

[0035] The transmitting antenna 13 transmits the light output from the external resonator laser 11 to the outside of the optical transceiver. The transmitting antenna 13 is composed of a grating coupler, and outputs the light propagated from the semi-reflecting mirror 24 as a laser beam with a scanning range according to the wavelength.

[0036] As described above, light propagates in the transmitter 1a as indicated by the arrow A1 in FIG. 1 and is emitted to the outside of the optical transmitter / receiver. The wavelength of the light input to the transmitter antenna 13 is changed by adjusting the temperature of the ring resonator 19 and the heater 19a and heater 21a of the tunable filter 26, respectively, thereby changing the light emission angle θ1 from the transmitter antenna 13 and scanning the light. When the optical transmitter / receiver is used as an FMCW-type LiDAR, the frequency of the transmitted light is modulated into a triangular wave, and beat light is generated by combining the reference light demultiplexed from the transmitted light with the received light. Ranging is performed based on this beat light. In this case, the tunable filter 26 modulates the transmitted light for scanning, while the frequency modulator 23 simultaneously modulates the frequency for FMCW-type ranging into a triangular wave. However, the modulation for FMCW-type ranging is weaker than the modulation for scanning, and therefore has little effect on scanning accuracy.

[0037] The transmitter 1b includes an external cavity laser 31 as a light source, a wavelength monitor 32, and a transmitting antenna 33. The external cavity laser 31 includes an SOA 34 and an external resonator 35. The wavelength monitor 32, the transmitting antenna 33, and the external resonator 35 are formed by performing semiconductor processes on the same semiconductor substrate 100 as the external resonator 15, etc., and the SOA 34 is connected to the semiconductor substrate 100. The wavelength monitor 32 and the transmitting antenna 33 have the same configurations as the wavelength monitor 12 and the transmitting antenna 13 of the transmitter 1a. The external cavity laser 31 is configured to emit internally emitted light from the SOA 34 to the external resonator 35, extract the light as strong light that is resonated in the external resonator 35 and the SOA 34, and output it as externally emitted light. In the transmitter 1b, light propagates as indicated by arrow A2 and is emitted to the outside of the optical transceiver device.

[0038] The SOA 34 has a similar configuration to the SOA 14, and is provided with a total reflection mirror 36 on the end face opposite to the end face connected to the semiconductor substrate 100. The external resonator 35 includes an SSC 37, a waveguide 38, a ring resonator 39, a waveguide 40, a ring resonator 41, a waveguide 42, a frequency modulator 43, a semi-reflection mirror 44, and a waveguide 45. The SSC 37 to the waveguide 45 have almost the same configuration as the SSC 17 to the waveguide 25 of the external resonator 15, but differ in the following respects.

[0039] The waveguide 38 is provided with a terminator 38a at the end opposite the SSC 37, which, like the terminator 22a of the waveguide 22, allows unwanted light to be emitted to the outside. The waveguide 40 is provided with terminators 40a and 40b at both ends, allowing unwanted light to be emitted to the outside. The ring resonators 39 and 41 are configured so that their transmission spectra overlap and form the highest first peak at wavelength λ2, which is different from λ1. The ring resonators 39 and 41 are provided with heaters 39a and 41a, respectively, and heating by these heaters 39a and 41a allows the FSR of the transmission spectrum to be intentionally changed. In this way, the ring resonator 39, the waveguide 40, and the ring resonator 41 form a wavelength-tunable filter 46.

[0040] The ring perimeter lengths Lring of the ring resonators 39 and 41 are 153.1 μm and 163.1 μm, respectively. The coupling efficiency κ between the ring resonators 39 and 41 and the waveguide 38 etc. is 0.13, and the coupling length Lc is 9 μm.

[0041] In this embodiment, λ1 = 1540 nm and λ2 = 1560 nm. For example, if the emission angles from the transmitting antennas 13 and 33 are configured to change by 0.15 degrees when the wavelength changes by 1 nm, the emission angles of the light from the transmitters 1a and 1b will differ by approximately 3 degrees.

[0042] In Fig. 5, the solid line and dashed line show the transmission spectra of the ring resonators 19 and 21, respectively. In Fig. 6, the solid line and dashed line show the transmission spectra of the ring resonators 39 and 41, respectively. As shown in Fig. 5, in both the ring resonators 19 and 21, the transmittance peaks at wavelength λ1 and decreases at wavelength λ2. Furthermore, as shown in Fig. 6, in both the ring resonators 39 and 41, the transmittance peaks at wavelength λ2.

[0043] The tunable filter 46 changes the wavelength of the output light so that the light transmitted from the transmitting antenna 33 scans a range different from that of the light transmitted from the transmitting antenna 13. That is, in the tunable filter 46, the wavelength λ2 is set so that the emission angle θ2 at the transmitting antenna 33 changes in a range different from the emission angle θ1. In this way, laser beams of multiple wavelengths are simultaneously emitted from the optical transmitting and receiving device, so that laser beams can be simultaneously emitted to multiple scanning ranges.

[0044] The receiving unit 2 receives light from outside the optical transceiver, separates the received light by wavelength, and outputs the separated light. As shown in Fig. 1, the receiving unit 2 includes a receiving antenna 51, a wavelength separation filter 52, and a waveguide 53. The receiving antenna 51 receives light from outside and is configured with a grating coupler.

[0045] The wavelength discrimination filter 52 discriminates light having the same wavelength as light output from some of the light sources among the plurality of light sources provided in the optical transceiver, from the light received by the receiving antenna 51, and is configured with ring resonators included in the some of the light sources. In this embodiment, the wavelength discrimination filter 52 is configured with the ring resonator 19 included in the external resonance laser 11, and discriminates light having the same wavelength λ1 as light output from the external resonance laser 11 from the light received by the receiving antenna 51.

[0046] Specifically, as described above, receiving antenna 51 is connected to waveguide 20, and light received by receiving antenna 51 propagates through waveguide 20. The light received by receiving antenna 51 includes reflected light of light transmitted from transmitter 1a and transmitter 1b. That is, the received light includes light of wavelength λ1 and light of wavelength λ2.

[0047] A ring resonator 19 is connected to the waveguide 20, and the transmission spectrum of the ring resonator 19 is configured to transmit light of wavelength λ1 and block light of wavelength λ2. Therefore, of the light propagated to the waveguide 20, light of wavelength λ1 passes through the ring resonator 19 and is separated from the waveguide 20. The light of wavelength λ1 that has passed through the ring resonator 19 propagates to the waveguide 18 connected to the ring resonator 19.

[0048] The end of waveguide 18 opposite to SSC 17 is connected to waveguide 53. Waveguide 53 is configured in a line shape parallel to waveguide 18, and the connection portion between waveguide 18 and waveguide 53 is bent in a U shape. The end of waveguide 53 opposite to waveguide 18 extends to end face 100a of semiconductor substrate 100, and the received light of wavelength λ1 that has propagated through waveguide 18 propagates through waveguide 53 and is emitted from end face 100a. That is, the received light of wavelength λ1 propagates as shown by arrow A3 and is emitted from the optical transceiver.

[0049] On the other hand, the light of wavelength λ2 is blocked by ring resonator 19 and propagates through waveguide 20. Although ring resonator 21 is also connected to waveguide 20, the transmission spectrum of waveguide 20 is configured to block light of wavelength λ2, so the received light of wavelength λ2 continues to propagate through waveguide 20 and is emitted from end face 100a. In other words, the received light of wavelength λ2 propagates as shown by arrow A4 and is emitted from the optical transceiver.

[0050] In this way, the light of wavelengths λ1 and λ2 is separated by ring resonator 19 that constitutes wavelength separation filter 52 and output to the outside of the optical transceiver. A light detection unit (not shown) is provided outside the optical transceiver, and distance measurement and the like are performed based on the reception results of the light of wavelengths λ1 and λ2.

[0051] A comparative example will now be described. In the comparative example shown in Fig. 7, the external cavity laser 11 and the wavelength discrimination filter 52 are configured separately. Specifically, terminators 18a, 20a, and 20b are provided at the end of the waveguide 18 opposite the SSC 17 and at both ends of the waveguide 20. The receiving unit 2 includes a receiving antenna 51, a wavelength discrimination filter 52, a waveguide 53, as well as a waveguide 54, a waveguide 55, and a wavelength monitor 56.

[0052] Waveguide 54 is configured in a line shape parallel to waveguide 53. One end of waveguide 54 is connected to receiving antenna 51, and the other end extends to end surface 100a of semiconductor substrate 100. Waveguide 55 is configured in a line shape parallel to waveguide 54. Wavelength discrimination filter 52 is configured with a ring resonator disposed between waveguides 54 and 55, and is optically coupled to them. Wavelength discrimination filter 52 is equipped with a heater like ring resonator 19, and its transmission spectrum is adjusted so as to transmit light of wavelength λ1 and block light of wavelength λ2.

[0053] A terminator 55a is provided at one end of the waveguide 55, and the other end is connected to the waveguide 53. The end of the waveguide 53 opposite to the waveguide 55 is extended to an end face 100a of the semiconductor substrate 100. A wavelength monitor 56 is connected to the waveguide 53, and the wavelength monitor 56 detects the wavelength of light propagating through the waveguide 53. The temperature of the heater of the wavelength discrimination filter 52 is set based on the monitoring result by the wavelength monitor 56, and the transmission spectrum of the wavelength discrimination filter 52 is adjusted.

[0054] In this comparative example with such a configuration, the monitoring result from wavelength monitor 12 is used to control the wavelength of light output from external cavity laser 11, and the monitoring result from wavelength monitor 32 is used to control the wavelength of light output from external cavity laser 31. Furthermore, the monitoring result from wavelength monitor 56 is used to control the wavelength of light transmitted through wavelength discrimination filter 52. Then, by setting the transmission wavelength of wavelength discrimination filter 52 to λ1, the light of wavelength λ1 contained in the received light is discriminated by wavelength discrimination filter 52. This makes it possible to separately detect the reflected light of wavelength λ1 transmitted from transmitter 1a and the reflected light of wavelength λ2 transmitted from transmitter 1b.

[0055] In this way, in an optical transmitter / receiver in which the external cavity laser 11 and the wavelength discrimination filter 52 are configured separately, it is necessary to control the transmission wavelength of the wavelength discrimination filter 52 in addition to controlling the wavelength of the external cavity laser 11, which increases the time required for wavelength control.

[0056] In contrast to this, in this embodiment, the wavelength discrimination filter 52 is configured by the ring resonator 19 of the external resonance laser 11, and therefore the transmission wavelength of the wavelength discrimination filter 52 is controlled by controlling the wavelength of the output light of the external resonance laser 11. Therefore, there is no need to separately control the transmission wavelength of the wavelength discrimination filter 52, and the time required for wavelength control can be reduced.

[0057] Furthermore, if the external cavity laser 11 and the wavelength discrimination filter 52 are constructed separately, an electrical circuit for controlling the wavelength discrimination filter 52 is required in addition to the electrical circuit for controlling the ring resonator of the external cavity laser 11, which increases the number of required components and increases costs.

[0058] In contrast to this, in this embodiment, the wavelength discrimination filter 52 is configured by the ring resonator 19 of the external resonance laser 11, and the transmission wavelength of the wavelength discrimination filter 52 can be controlled by the same electrical circuit as that for the wavelength of the output light. Therefore, there is no need to separately prepare an electrical circuit for controlling the wavelength discrimination filter 52, which allows for cost reduction.

[0059] (Second embodiment) The second embodiment will be described. This embodiment is the same as the first embodiment except that a transmitter 1 is added, and therefore only the differences from the first embodiment will be described.

[0060] As shown in FIG. 8 , the optical transceiver of this embodiment includes a transmitter 1c in addition to transmitters 1a and 1b. The transmitter 1c includes an external resonance laser 61 as a light source, a wavelength monitor 62, and a transmitting antenna 63. The external resonance laser 61 includes an SOA 64 and an external resonator 65. The wavelength monitor 62, the transmitting antenna 63, and the external resonator 65 are formed by performing semiconductor processes on the same semiconductor substrate 100 as the external resonator 15, etc., and the SOA 64 is connected to the semiconductor substrate 100. The wavelength monitor 62 and the transmitting antenna 63 have the same configurations as the wavelength monitor 12 and the transmitting antenna 13 of the transmitter 1a. The external resonance laser 61 is configured to emit internally emitted light from the SOA 64 to the external resonator 65, extract the light as strong light resonating in the external resonator 65 and SOA 64, and output it as externally emitted light. In the transmitter 1c, light propagates as indicated by arrow A5 and is emitted to the outside of the optical transceiver.

[0061] The SOA 64 has a similar configuration to the SOA 14, and is provided with a total reflection mirror 66 on the end face opposite to the end face connected to the semiconductor substrate 100. The external resonator 65 includes an SSC 67, a waveguide 68, a ring resonator 69, a waveguide 70, a ring resonator 71, a waveguide 72, a frequency modulator 73, a semi-reflection mirror 74, and a waveguide 75. The SSC 67 to the waveguide 75 have substantially the same configuration as the SSC 37 to the waveguide 45 of the first embodiment, but differ in the following respects.

[0062] The ring resonators 69 and 71 are configured so that their transmission spectra overlap and have the highest first peak at a wavelength λ3, which is different from λ1 and λ2. The ring resonators 69 and 71 are equipped with heaters 69a and 71a, respectively, and the FSR of the transmission spectra can be intentionally changed by heating with the heaters 69a and 71a. Thus, the ring resonator 69, waveguide 70, and ring resonator 71 form a wavelength-tunable filter 76. In this embodiment, the ring perimeters Lring of the ring resonators 19, 21, 39, 41, 69, and 71 are 149.6 μm, 160.0 μm, 153.1 μm, 163.8 μm, 156.7 μm, and 167.6 μm, respectively. The ring coupling efficiency κ of the ring resonators 19, 21, 39, 41, 69, and 71 is set to 0.13, the coupling length Lc is set to 9 μm, and λ3 is set to 1580 nm.

[0063] In FIG. 9, the solid and dashed lines indicate the transmission spectra of the ring resonators 19 and 21, respectively. In FIG. 10, the solid and dashed lines indicate the transmission spectra of the ring resonators 39 and 41, respectively. In FIG. 11, the solid and dashed lines indicate the transmission spectra of the ring resonators 69 and 71, respectively. As shown in FIG. 9, in both the ring resonators 19 and 21, the transmittance peaks at wavelength λ1 and decreases at wavelengths λ2 and λ3. As shown in FIG. 10, in both the ring resonators 39 and 41, the transmittance peaks at wavelength λ2 and decreases at wavelength λ3. As shown in FIG. 11, in both the ring resonators 69 and 71, the transmittance peaks at wavelength λ3.

[0064] The tunable filter 76 changes the wavelength of the output light so that the light transmitted from the transmitting antenna 63 scans a range different from that of the light transmitted from the transmitting antennas 13 and 33. That is, in the tunable filter 76, the wavelength λ3 is set so that the emission angle θ3 at the transmitting antenna 63 varies in a range different from that of the emission angles θ1 and θ2.

[0065] The end of the waveguide 20 opposite to the receiving antenna 51 is connected to the end of the waveguide 40 via a meandering waveguide 57. The waveguide 57 passes between the terminator 22a and the end face 100a of the semiconductor substrate 100, and further passes between the waveguide 22 and a waveguide 58 (described later), passing on the side opposite to the end face 100a with respect to the junction of the waveguide 58 and the waveguide 38, and is connected to the end of the waveguide 40. The end of the waveguide 40 opposite to the side connected to the waveguide 57 is extended to the end face 100a.

[0066] In this way, the ring resonators 19, 21, 39, and 41 are connected to the waveguide extending from the receiving antenna 51 in order of proximity to the receiving antenna 51. The end of the waveguide 38 opposite the SSC 37 is connected to the waveguide 58. The waveguide 58 is configured in a line shape parallel to the waveguide 38, and the end opposite the end connected to the waveguide 38 extends to the end face 100a.

[0067] The wavelength discrimination filter 52 of this embodiment is composed of a ring resonator 19 and a ring resonator 39. Specifically, when light beams of wavelengths λ1, λ2, and λ3 are received by the receiving antenna 51, the light beam of wavelength λ1 of the received light is separated from the waveguide 20 by the ring resonator 19 constituting the wavelength discrimination filter 52, propagates through the waveguide 53, and is emitted from the end face 100a of the semiconductor substrate 100. The remaining light beams of wavelengths λ2 and λ3 are blocked by the ring resonator 21, propagate from the waveguide 20 through the waveguide 57, and are transmitted to the waveguide 40. Of the light beams propagating through the waveguide 40, the light beam of wavelength λ2 is separated from the waveguide 40 by the ring resonator 39 constituting the wavelength discrimination filter 52, propagates through the waveguide 58, and is emitted from the end face 100a. The remaining light beam of wavelength λ3 is blocked by the ring resonator 41, propagates through the waveguide 40, and is emitted from the end face 100a. In this way, the ring resonators 19 and 39 that make up the wavelength separation filter 52 separate the light into wavelengths λ1, λ2, and λ3, which propagate as shown by arrows A3, A4, and A6 and are output to the outside of the optical transceiver.

[0068] In this embodiment, the wavelength discrimination filter 52 is configured by the ring resonator 19 of the external resonance laser 11 and the ring resonator 39 of the external resonance laser 31. Therefore, by controlling the wavelengths of the output lights of the external resonance lasers 11 and 31, the transmission wavelength of the wavelength discrimination filter 52 is also controlled.

[0069] This embodiment has the same configuration and operation as the first embodiment, and can therefore obtain the same effects as the first embodiment.

[0070] (Third embodiment) A third embodiment will be described. This embodiment is the same as the second embodiment except that a blocking section is added, and therefore only the differences from the second embodiment will be described.

[0071] 12, in this embodiment, a blocking unit 59 that blocks light received by the receiving antenna 51 is disposed between the receiving antenna 51 and the wavelength discrimination filter 52. The blocking unit 59 is configured by, for example, an MZI (Mach-Zehnder Interferometer) type optical switch, a VOA (variable optical attenuator), or the like.

[0072] 12 illustrates a case where the cutoff unit 59 is configured as an MZI optical switch. In the cutoff unit 59 configured in this way, the received light is split into two paths for propagation, and the optical path length of each path is adjusted using a heater. By reversing the phase of the light propagating through one path from the phase of the light propagating through the other path, the intensity of the light after multiplexing becomes zero. This makes it possible to prevent the received light from entering the external resonator 15.

[0073] When the blocking unit 59 is configured with a VOA, the received light can be significantly attenuated, thereby preventing the received light from entering the external resonator 15.

[0074] This embodiment has the same configuration and operation as the first and second embodiments, and can therefore obtain the same effects as the first and second embodiments.

[0075] Furthermore, according to the above embodiment, the following effects can be obtained.

[0076] (1) A blocking unit 59 that blocks light received by the receiving antenna 51 is disposed between the receiving antenna 51 and the wavelength discrimination filter 52. By blocking the received light with the blocking unit 59 during wavelength control of the external resonance laser 11, it is possible to prevent unnecessary light from entering the ring resonator 19 and perform stable wavelength control.

[0077] (Other embodiments) The present invention is not limited to the above-described embodiments and can be modified as appropriate within the scope of the claims. Furthermore, the above-described embodiments are not unrelated to each other and can be combined as appropriate unless the combination is clearly impossible. It goes without saying that the elements constituting the embodiments are not necessarily essential unless specifically stated as essential or clearly considered essential in principle. Furthermore, when the numbers, values, amounts, ranges, etc. of the components of the embodiments are mentioned in the above-described embodiments, they are not limited to the specific numbers unless specifically stated as essential or clearly limited to a specific number in principle. Furthermore, when the shapes, positional relationships, etc. of the components are mentioned in the above-described embodiments, they are not limited to the shapes, positional relationships, etc., unless specifically stated or clearly limited to a specific shape, positional relationship, etc. in principle.

[0078] (1) In the first embodiment, the blocking section 59 may be disposed between the receiving antenna 51 and the wavelength discrimination filter 52.

[0079] (2) In the second and third embodiments, the semi-reflective mirrors 24, 44, and 74 may be configured as DBRs.

[0080] (3) Light of four or more wavelengths may be transmitted from the optical transmitting / receiving device. If the number of external cavity lasers serving as light sources is M, the wavelength discrimination filter 52 is configured as follows.

[0081] Let K be an integer between 1 and M inclusive, the wavelength of light output by the Kth light source among the multiple light sources be λK, N be an integer between 1 and M-1 inclusive, and L be an integer between N+1 and M inclusive. The Nth light source among the multiple light sources has two ring resonators that transmit light of wavelength λN, and wavelength discrimination filter 52 discriminates the light of wavelength λN using one of the two ring resonators that the Nth light source has.

[0082] The two ring resonators of the Nth light source are connected in sequence to a waveguide extending from the receiving antenna 51. Of the two ring resonators of the Nth light source, one closer to the receiving antenna 51 is configured so that when light of wavelength λN is input, the light passes through the ring resonator and is separated from the waveguide. The other ring resonator is configured so that when light of wavelength λL is input, the light is blocked from the ring resonator and propagates through the waveguide.

[0083] (4) The optical transceiver described in the first to third embodiments is an example in which one optical transceiver is provided on one semiconductor substrate 100, but it is also possible to provide a plurality of sets of optical transceivers, each set consisting of the components of the optical transceiver described in each embodiment, on one semiconductor substrate 100. In this case, any combination is acceptable, and for example, a plurality of sets of the optical transceivers described in the first embodiment may be provided, or the optical transceivers described in the first and second embodiments may be mixed. [Explanation of symbols]

[0084] 11, 31, 61 External cavity laser 19, 21, 39, 41, 69, 71 Ring resonators 51 Receiving antenna 52 Wavelength discrimination filter

Claims

1. An optical transceiver, a plurality of light sources (11, 31, 61) each having a ring resonator (19, 21, 39, 41, 69, 71); a receiving antenna (51) for receiving light; a wavelength discrimination filter (52) that discriminates light having the same wavelength as light output from some of the plurality of light sources from the light received by the receiving antenna, the wavelength discrimination filter is configured by the ring resonator included in the part of the light sources, and is connected to a waveguide (20, 40, 57) extending from the receiving antenna; An optical transmitting and receiving device in which, of the light received by the receiving antenna, light of the same wavelength as the light output by the part of the light source is separated by the wavelength separation filter, and the remaining light is detected at the end of the waveguide.

2. The number of the plurality of light sources is M, K is an integer between 1 and M, The wavelength of light output from the K-th light source among the plurality of light sources is denoted by λK, N is an integer between 1 and M-1, an N-th light source among the plurality of light sources has two of the ring resonators that transmit light of wavelength λN; 2. The optical transmitting and receiving device according to claim 1, wherein the wavelength discrimination filter discriminates light of wavelength λN using one of the two ring resonators included in the Nth light source.

3. Let L be an integer between N+1 and M, inclusive. The two ring resonators of the Nth light source are connected in sequence to a waveguide (20, 40, 57) extending from the receiving antenna, one of the two ring resonators included in the N-th light source, which is closer to the receiving antenna, is configured so that when light having a wavelength λN is input, the light passes through the ring resonator and is separated from the waveguide; 3. The optical transmitting and receiving device according to claim 2, wherein the other ring resonator is configured such that when light of wavelength λL is input, the light is blocked from the ring resonator and propagates through the waveguide.

4. An optical transceiver, A plurality of light sources (11, 3) having ring resonators (19, 21, 39, 41, 69, 71) 1, 61) and a receiving antenna (51) for receiving light; The light received by the receiving antenna is converted into light output from some of the plurality of light sources. a wavelength discrimination filter (52) for discriminating light of the same wavelength; the wavelength discrimination filter is formed by the ring resonator included in the part of the light sources, The number of the plurality of light sources is M, K is an integer between 1 and M, The wavelength of light output from the K-th light source among the plurality of light sources is denoted by λK, N is an integer between 1 and M-1, an N-th light source among the plurality of light sources has two of the ring resonators that transmit light of wavelength λN; the wavelength discrimination filter discriminates light of wavelength λN using one of the two ring resonators included in the Nth light source; Let L be an integer between N+1 and M, inclusive. The two ring resonators of the Nth light source are connected in sequence to a waveguide (20, 40, 57) extending from the receiving antenna, one of the two ring resonators included in the N-th light source, which is closer to the receiving antenna, is configured so that when light having a wavelength λN is input, the light passes through the ring resonator and is separated from the waveguide; the two ring resonators included in the N-th light source are configured such that, when light having a wavelength λ is input, the light is blocked from the two ring resonators and propagates through the waveguide; the ring resonator of the Lth light source is connected to the waveguide, the ring resonator of the Nth light source is connected to a portion of the waveguide between a portion connected to the receiving antenna and a portion connected to the ring resonator of the Lth light source, An optical transceiver in which light of wavelength λL passes through the ring resonator of the Lth light source and is separated from the waveguide.

5. 5. The optical transmitter-receiver according to claim 1, further comprising a blocking section (59) disposed between the receiving antenna and the wavelength discrimination filter for blocking the light received by the receiving antenna.

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