Multi-channel optical module

Abstract

The present invention suppresses crosstalk between adjacent channels when optical output power is monitored. A multichannel optical module for multiplexing a plurality of wavelength channels for output, comprising: a plurality of light sources that have respective different wavelengths; a plurality of collimator lenses coupled to the respective outputs of the plurality of light sources; a beam splitter coupled to the output of each of the plurality of collimator lenses; a plurality of monitor PDs that monitor optical powers branched from the beam splitter; and a plurality of wavelength filters that are inserted between the beam splitter and the respective ones of the plurality of monitor PDs and that pass therethrough only the respective wavelengths of the light sources coupled by the beam splitter.

Description

[Technical field]

[0001] The present invention relates to a multi-channel optical module, and more particularly to a multi-channel optical module that serves as an optical transmitter in an optical communication system that uses a wavelength division multiplexing optical transmission method. [Background technology]

[0002] Conventionally, wavelength-division multiplexing optical transmission methods have been used to increase the transmission capacity in optical communication systems in response to an increase in communication traffic. To perform wavelength-division multiplexing optical transmission, a light source is prepared for each wavelength channel, and the output light from the multiple light sources is multiplexed by an optical multiplexer and output to an optical fiber. In optical communication systems, it is required to keep the optical intensity of optical transmission signals constant, and in wavelength-division multiplexing optical transmission methods, it is also necessary to keep the optical intensity of each wavelength channel constant. Therefore, a part of the optical transmission signal is branched off to monitor the optical intensity, and the light source is controlled so that the monitored optical intensity is constant.

[0003] 1 shows an example of a conventional multi-channel optical module, an optical transmitter that multiplexes four wavelengths. The output light from light source chips 11a-11d mounted on the light sources for each wavelength channel is input to an optical multiplexer 20 via collimator lenses 31a-31d and multiplexed. The output of the optical multiplexer 20 is multiplexed as wavelength-multiplexed light via a condenser lens 32, with all wavelength channels multiplexed, and is coupled to an optical fiber 41.

[0004] 2 shows an example of a light source for a conventional multi-channel optical module. In the light source, a light source chip 11 including a modulated light source section 16 and an optical amplifier section 15 is mounted on a subcarrier 12, and a monitor PD 13 for monitoring a part of the output light from the modulated light source section 16 is mounted on the rear end of the light source chip 11. The monitor PD 13 detects the optical output power of each wavelength channel as a current value, and a control circuit 14 adjusts the amount of current supplied to the light source chip 11 so that the detected current value becomes constant. Such an optical output control (APC) circuit makes it possible to always keep the optical output power from each light source chip 11 constant (for example, see Non-Patent Documents 2 and 3).

[0005] In this way, the configuration in which the monitor PD 13 is disposed at the rear end of the light source chip 11 makes it possible to monitor the optical output power proportional to the output light from the light source chip 11. However, it is not possible to accurately monitor the optical output power for each wavelength channel when the optical output is output as wavelength multiplexed light.

[0006] Fig. 3 shows another example of a conventional multi-channel optical module. Fig. 3(a) shows the configuration of the multiplexer as viewed from the plane of the substrate, and Fig. 3(b) shows the configuration as viewed from the side of the substrate. Output light from light source chips 11a-11d mounted on the light sources for each wavelength channel is input to optical multiplexer 20 via collimator lenses 31a-31d and beam splitter 51 and multiplexed. The output of optical multiplexer 20 is multiplexed as wavelength-multiplexed light via condenser lens 32, with all wavelength channels multiplexed, and is coupled to optical fiber 41 (see, for example, Non-Patent Document 1).

[0007] A portion of the output light from light source chips 11a-11d is split by beam splitter 51 and monitored by monitor PDs 53a-53d. The outputs of monitor PDs 53a-53d are input to light source control circuit 14, which adjusts the amount of current supplied to light source chip 11 so that the detected current value becomes constant. In this manner, the configuration in which monitor PD 53 is disposed on the output side of light source chip 11 can accurately monitor the output from optical amplifier 15 of the light source, but optical loss occurs by the amount of passage loss of beam splitter 51.

[0008] In addition, the output beam from the light source chip 11 has a large spread, and as shown by the thin line in Fig. 3(a), a light component that becomes a collimated light and is input to the multiplexer is output, and as shown by the dashed line, a stray light component that does not contribute to the collimated light is output. In this way, there was a problem that the stray light component that exceeds the effective diameter of the collimator lens 31 is coupled to the monitor PD 13 of the adjacent channel, causing crosstalk. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] K. Tsuzuki et.al., “Full C-Band Tunable DFB Laser Array Copackaged With InP Mach-Zehnder Modulator for DWDM Optical Communication Systems,” Journal of selected topics in quantum electronics, vol. 15, no. 3, pp. 521-527, 2009 [Non-Patent Document 2] LB Anronson et. al., “Transmitter Optical Subassembly for XFP Applications,” ECTC2005, DOI: 10.1109ECTC.2005.1441402 [Non-Patent Document 3] Tadashi Murao et al, "Integrated Spatial Optical System for Compact 28-Gb / s×4-lane Transmitter Optical Subassemblies", IEEE PHOTONICS TECHNOLOGY LETTERS, P. 2275 VOL. 26, NO. 22, NOVEMBER 15, 2014 Summary of the Invention

[0010] An object of the present invention is to provide a multi-channel optical module that suppresses crosstalk between adjacent channels when monitoring optical output power.

[0011] In order to achieve this object, one embodiment of the present invention is a multi-channel optical module that multiplexes and outputs a plurality of wavelength channels, comprising a plurality of light sources each having a different wavelength, a plurality of collimator lenses coupled to the output of each of the plurality of light sources, a beam splitter coupled to the output of each of the plurality of collimator lenses, a plurality of monitor PDs that monitor the optical power branched from the beam splitter, and a plurality of wavelength filters inserted between the beam splitter and each of the plurality of monitor PDs, each of which transmits only the wavelength of the light source coupled by the beam splitter. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an example of a conventional multi-channel optical module. [Diagram 2] FIG. 2 is a diagram showing an example of a light source of a conventional multi-channel optical module. [Diagram 3] FIG. 3 is a diagram showing another example of a conventional multi-channel optical module. [Figure 4] FIG. 4 is a diagram showing a multi-channel optical module according to a first embodiment of the present invention; [Diagram 5] FIG. 5 is a diagram illustrating a multi-channel optical module according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In this embodiment, a multi-channel optical module that multiplexes and outputs four wavelengths will be described, but the number of wavelengths to be multiplexed is not limited. EXAMPLES

[0014] FIG. 4 shows an example of an optical transmitter that multiplexes four different wavelengths, which is a multi-channel optical module according to the first embodiment of the present invention. FIG. 4(a) shows the configuration of the multiplexer as viewed from the plane of the substrate, and FIG. 4(b) shows the configuration of the multiplexer as viewed from the side of the substrate. Output light from light source chips 111a-111d mounted on the light sources for each wavelength channel is input to the optical multiplexer 120 via collimator lenses 131a-131d and beam splitter 151 and multiplexed. The output of the optical multiplexer 120 is multiplexed as wavelength-multiplexed light via a condenser lens 132, and is coupled to an optical fiber 141.

[0015] The output light from the light source chips 111a-111d is partially split by the beam splitter 151, and the optical power of each output light is monitored by the monitor PDs 153a-153d via the wavelength filters 152a-152d. The outputs of the monitor PDs 153a-153d are input to the light source control circuit, which adjusts the amount of current supplied to the light source chip 111 so that the detected current value is constant, that is, so that the optical power of each output light is constant.

[0016] The beam splitter 151 may be, for example, a cube-type in which the inclined surfaces of two right-angle prisms are joined with an optical thin film between them. In the first embodiment, the beam splitter 151 has an integrated structure capable of splitting four channels collectively. Wavelength filters 152a-152d made of an optical thin film are inserted between the beam splitter 151 and each of the monitor PDs 153a-153d. Each of the wavelength filters 152a-152d is an optical filter that transmits only the wavelengths of the light sources 111a-111d that are joined by the beam splitter 151, and transmits light in a specific wavelength range for each wavelength channel.

[0017] For example, as shown by the thin line in FIG. 4(a), the output light from the light source chip 111a passes through the collimator lens 131a to become collimated light, and is input to the optical multiplexer 120 via the beam splitter 151. On the other hand, as shown by the dashed line, a stray light component exceeding the effective diameter of the collimator lens 131a reaches an adjacent channel via the beam splitter 151. However, this stray light component cannot pass through the wavelength filter 152b of the adjacent channel, and therefore is not coupled to the monitor PD 153b of the adjacent channel. Therefore, crosstalk between adjacent channels when monitoring the optical output power can be suppressed.

[0018] After assembling the multi-channel optical module of Example 1 as an optical transmitter, the output of the light source chip 111 for each wavelength channel was set to +4 dBm, and the current value detected by the monitor PD 153 when only a single wavelength channel was operated was measured. The current values ​​for each of the wavelength channels 1 to 4 were 104, 101, 101, and 100 μA, respectively. Next, the current values ​​detected by the monitor PD 153 when the four channels were operated simultaneously were measured, and 104, 101, 101, and 100 μA were obtained, respectively.

[0019] For comparison, a similar measurement was also performed on the conventional optical transmitter shown in Figure 2. The output of the light source chip 11 for each wavelength channel was set to +4 dBm, and the current values ​​of the monitor PD 53 when only a single wavelength channel was operated were 105, 103, 101, and 99 μA, respectively. Next, the current values ​​detected by the monitor PD 53 when four channels were operated simultaneously were measured, and the results were 115, 113, 112, and 110 μA, respectively.

[0020] In the conventional example, the current value is larger when four channels are operated simultaneously than when a single wavelength channel is operated, indicating the influence of crosstalk. On the other hand, according to the first embodiment, there is no change in the current value when a single wavelength channel is operated and when four channels are operated simultaneously, indicating that crosstalk between adjacent channels is suppressed. EXAMPLES

[0021] FIG. 5 shows an example of an optical transmitter that multiplexes four different wavelengths, which is a multi-channel optical module according to the second embodiment of the present invention. FIG. 5(a) shows the configuration of the multiplexer as viewed from the plane of the substrate, and FIG. 5(b) shows the configuration of the multiplexer as viewed from the side of the substrate. Output light from light source chips 111a-111d mounted on the light sources for each wavelength channel is input to the optical multiplexer 120 via collimator lenses 131a-131d and beam splitter 251 and multiplexed. The output of the optical multiplexer 120 is multiplexed as wavelength-multiplexed light via a condenser lens 132, and is coupled to an optical fiber 141.

[0022] The output light from the light source chips 111a-111d is partially split by the beam splitter 251, and the optical power of each output light is monitored by the monitor PDs 253a-253d. The outputs of the monitor PDs 253a-253d are input to the light source control circuit, which adjusts the amount of current supplied to the light source chip 111 so that the detected current value is constant, that is, so that the optical power of each output light is constant.

[0023] The beam splitter 251 may be, for example, a cube type in which the slant surfaces of two right-angle prisms are joined with an optical thin film sandwiched therebetween. The difference from the beam splitter 151 of the first embodiment is that the optical thin film 252 formed on the slant surface is designed to split only the wavelengths of the light sources 111a-111d joined via the collimator lenses 131a-131d. That is, the two right-angle prisms have a four-channel integrated structure, but different optical thin films 252 are formed for each wavelength channel. As in the first embodiment, the stray light components from the light source chip 111a are not split by the optical thin film 252 of the adjacent channel, and therefore are not coupled to the monitor PD 253b of the adjacent channel. Therefore, crosstalk between adjacent channels when monitoring the optical output power can be suppressed.

[0024] After assembling the multi-channel optical module of Example 2 as an optical transmitter, the output of the light source chip 111 for each wavelength channel was set to +5 dBm, and the current value detected by the monitor PD 253 when only a single wavelength channel was operated was measured. The current values ​​for each of the wavelength channels 1 to 4 were 124, 121, 121, and 121 μA, respectively. Next, the current values ​​detected by the monitor PD 253 when the four channels were operated simultaneously were measured, and 124, 122, 122, and 121 μA were obtained, respectively.

[0025] For comparison, a similar measurement was also performed on the conventional optical transmitter shown in Figure 2. The output of the light source chip 11 for each wavelength channel was set to +5 dBm, and the current values ​​of the monitor PD 53 when only a single wavelength channel was operated were 125, 123, 121, and 119 μA, respectively. Next, the current values ​​detected by the monitor PD 53 when four channels were operated simultaneously were measured, and the results were 136, 133, 132, and 130 μA, respectively.

[0026] In the conventional example, the current value is larger when four channels are operated simultaneously than when a single wavelength channel is operated, indicating the influence of crosstalk. On the other hand, according to the second embodiment, there is no change in the current value when a single wavelength channel is operated and when four channels are operated simultaneously, indicating that crosstalk between adjacent channels is suppressed.

Claims

[Claim 1] A multi-channel optical module that multiplexes and outputs a plurality of wavelength channels, A plurality of light sources, each of which has a different wavelength; a plurality of collimator lenses coupled to the output of each of the plurality of light sources; a beam splitter coupled to each output of the plurality of collimator lenses, the beam splitter including a plurality of optical thin films each splitting off only the wavelength of the light source coupled through each collimator lens; a plurality of monitor PDs for monitoring the optical power split from the beam splitter; A multi-channel optical module comprising:

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