JP2015094812A - Wavelength variable light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength variable light source capable of individually adjusting light power of two outputs and being small size.SOLUTION: The wavelength variable light source of the invention comprises: a wavelength variable light source part for outputting laser beam; an optic amplifier for amplifying the laser beam outputted from the wavelength variable light source part; and a branch part for branching into two branches the laser beam outputted after being amplified by the optic amplifier. The branch part is a Mach-Zehnder interferometer or a directional coupler, and to the branch part, an electrode for adjusting a branch ratio of the laser beam at the branch part is coupled.

Description

  The present invention relates to a wavelength tunable light source that is a component of a large-capacity optical communication network.

  With an increase in the speed of a long-distance communication network, a communication method using multilevel modulation has begun to be used. FIG. 1 shows an example of the configuration of a multi-level modulation transceiver as shown in Non-Patent Document 1. FIG. 1 shows a multilevel modulation transceiver 100 including an optical receiver 110, a digital signal processor 120, and an optical transmitter 130.

  The optical receiving unit 110 receives the transmitted light and demultiplexes it, a polarization demultiplexer PBS, a receiving variable wavelength light source LO that generates interference light in the optical receiving unit 110, and two 90 degree lights. A hybrid circuit 111 and eight light receivers 112 are provided. The digital signal processing unit 120 includes an analog / digital conversion unit ADC. The optical transmission unit 130 includes a transmission wavelength variable light source LD that generates light that is a source of modulated light, two modulators 131 that modulate light generated by the transmission wavelength variable light source LD, and a polarization multiplexer PBC.

  The received optical signal is demultiplexed by the polarization demultiplexer PBS, subjected to coherent detection that causes interference with the output light of the receiving wavelength variable light source LO, and then converted into an electric signal by the light receiver 112 for digital signal processing. Is output to the unit 120.

  The electric signal output to the digital signal processing unit 120 is input to the analog / digital conversion unit ADC and subjected to analog / digital conversion. The converted digital signal is subjected to chromatic dispersion (CD) and polarization mode dispersion ( PMD) is compensated and the like is output to the optical transmitter 130.

  In the optical transmission unit 130, the light output from the transmission wavelength variable light source LD is input to the two modulators 131, and the modulator 131 performs modulation based on the signal output from the digital signal processing unit 120, After being combined by the polarization multiplexer PBC, it is output as an optical transmission signal of quaternary modulation (QPSK: Quadrature Phase Shift Keying).

  What is important here is that the multilevel modulation transceiver 100 shown in FIG. 1 requires two wavelength variable light sources, ie, a transmission wavelength variable light source LD and a reception wavelength variable light source LO. Examples of the tunable light source used in the multi-level modulation transceiver include the tunable light sources disclosed in Non-Patent Documents 2 to 4. Hereinafter, a conventional wavelength tunable light source used in a multilevel modulation transceiver will be described with reference to FIGS.

  FIG. 2 shows a conventional wavelength tunable light source using a distributed reflection laser (hereinafter referred to as DBR laser). A tunable light source 200 shown in FIG. 2 is a laser using, for example, a super-periodic structure grating reflector (SSG-DBR) as a wavelength selector, and includes an optical amplification unit 210 and a tunable light source unit 220.

  The wavelength tunable light source unit 220 includes four regions: a front mirror unit 221, a rear mirror unit 222, a phase adjustment unit 223, and an optical gain unit 224 (active region). The front mirror unit 221 and the rear mirror unit 222 are each SSG-DBR, and a diffraction grating subjected to periodic phase modulation is formed on the front mirror unit 221 and the rear mirror unit 222. As a result, reflection characteristics are formed. A plurality of peaks are formed on the wavelength axis. Since the interval between the front and rear reflection peaks is different, laser oscillation occurs only at one point where the front and rear reflection peaks coincide. By changing the combination of reflection peaks by injecting current into the front mirror part 221 and the rear mirror part 222, a large wavelength change can be obtained. The current to the phase adjustment unit 223 is used for vertical mode control.

  The light output from the wavelength tunable light source unit 220 is amplified and output by the optical amplifying unit 210 installed in front of the wavelength tunable light source unit 220.

  FIG. 3 shows a conventional wavelength tunable light source using a semiconductor laser array. A wavelength tunable light source 300 shown in FIG. 3 uses a semiconductor laser array in which a plurality of distributed feedback lasers (hereinafter referred to as DFB lasers) 321 are arranged, and includes an optical amplification unit 310 and a wavelength tunable light source unit 320. The wavelength variable light source unit 320 includes five DFB lasers 321 and an optical multiplexer 322.

  In the wavelength tunable light source 300 shown in FIG. 3, the oscillation light frequency of the DFB laser 321 is determined by the period of the diffraction grating formed in the resonator. The oscillating light frequencies of the five DFB lasers 321 can be changed over a wide wavelength by forming the oscillating light frequency by gradually changing the period of the diffraction grating. Furthermore, since the oscillation light frequency of the DFB laser 321 changes at a rate of about 12 GHz per 1 ° C. of the chip temperature, current is passed through only one of the five DFB lasers 321 to oscillate, and further, the laser chip By adjusting the temperature, a desired optical frequency (wavelength) can be obtained.

  The light output from the wavelength tunable light source unit 320 is amplified and output by the optical amplification unit 310 installed in front of the wavelength tunable light source unit 320.

Suzuki Ota, et al., “Research and development of digital coherent signal processing technology for increasing capacity of optical communication networks”, IEICE Journal, 2012, Vol.95, No.12, p.1100-1116 Hiroyuki Ishii et al., “Expansion of wavelength tunable width by SSG-DBR laser”, Electronics Society Conference of IEICE, 1995, SC-2-8, p.355-356 Naoki Fujiwara et al., "Suppression of thermal wavelength drift in SSG-DBR laser with thermal drift compensation structure", Semiconductor Laser Conference, 2006, (ISLC 2006) Conference Digest. 2006 IEEE 20th International, p.31-32 Hiroyuki Ishii et al., “Highly functional tunable light source technology”, NTT Technical Journal, November 2007, p.66-69

  As described above, the multi-level modulation transceiver includes one tunable light source as described above for transmission and reception, that is, two in the transceiver. At this time, the light output from the two wavelength variable light sources needs to have the same wavelength. In the future, in order to reduce the size and power consumption of transceivers, it is necessary to use both a tunable light source for transmission and reception.

  However, in order to combine transmission and reception with a single wavelength tunable light source, a new optical branching unit that divides the output light of the wavelength tunable light source is required, but there is a problem that the structure becomes complicated. .

  FIG. 4 shows a first example of a conventional two-output wavelength tunable light source. FIG. 4 shows a two-output variable wavelength light source 400 including the variable wavelength light source 200, the lens 410, and the beam splitter 420 shown in FIG. A two-output wavelength tunable light source 400 shown in FIG. 4 inputs the laser light output from the wavelength tunable light source 200 shown in FIG. This is an example of branching.

  Similarly, FIG. 5 shows a second example of a conventional dual output wavelength variable light source. FIG. 5 shows a two-output variable wavelength light source 500 including the variable wavelength light source 300, the lens 410, and the beam splitter 420 shown in FIG. The two-output wavelength tunable light source 400 shown in FIG. 5 inputs the laser light output from the wavelength tunable light source 300 shown in FIG. 3 to the beam splitter 420 (light branching unit) through the lens 410, and the upper part and the left part thereof. This is an example of branching.

  However, the conventional two-output wavelength tunable light source as shown in FIGS. 4 and 5 has a problem that the beam splitter 420 branches the light only at a determined branching ratio, so that the branching ratio is fixed. It was. In general, since the light intensity required for transmission and the light intensity required for reception are different, it is necessary to branch to the optimal light intensity for each of transmission and reception. Therefore, it is difficult to control the branching ratio and transmit the optimum optical power for both transmission and reception. In addition, the conventional dual output wavelength variable light source as shown in FIGS. 4 and 5 uses a spatial optical system composed of a lens 410 and a beam splitter 420, which complicates the structure and increases the size of the apparatus. There was a problem.

  In order to solve the above-described problem, a wavelength tunable light source according to claim 1 includes a wavelength tunable light source unit that outputs laser light, an optical amplifying unit that amplifies the laser light output from the wavelength tunable light source unit, A first output waveguide and a second output waveguide, and the laser light amplified and output by the optical amplifying unit is branched into the first output waveguide and the second output waveguide. A branching unit, and the branching unit is a Mach-Zehnder interferometer or a directional coupler, and the branching unit adjusts a light branching ratio in the first output waveguide and the second output waveguide. It is characterized in that an electrode for connecting is connected.

  The wavelength tunable light source according to claim 2 includes a wavelength tunable light source unit that outputs laser light, a branching unit that divides the laser light output from the wavelength tunable light source unit into two, and a first output guide of the branching unit. A first optical amplification unit that amplifies the light output from the waveguide, and a second optical amplification unit that amplifies the light output from the second output waveguide of the branching unit, A Mach-Zehnder interferometer or a directional coupler, wherein the first output waveguide and the second output waveguide are adjusted by adjusting the degree of light amplification in the first optical amplifier and the second optical amplifier. It is possible to control the intensity of the light output from.

  The wavelength tunable light source according to claim 3 is the wavelength tunable light source according to claim 1 or 2, wherein a direction of light guided through the first output waveguide is the same as that of the second output waveguide. It differs from the direction of the guided light by 90 degrees or 180 degrees.

  A wavelength tunable light source according to claim 4 is the wavelength tunable light source according to any one of claims 1 to 3, wherein the wavelength tunable light source section is a distributed feedback semiconductor laser or a distributed reflection semiconductor laser. It is characterized by.

  The wavelength tunable light source according to claim 5 is the wavelength tunable light source according to any one of claims 1 to 3, wherein the wavelength tunable light source unit includes n semiconductor lasers (n is an integer of 2 or more). A semiconductor laser array arranged in an array; and an n-input 1-output multiplexing unit that multiplexes and outputs light output from the semiconductor laser array, and the semiconductor laser is a distributed feedback semiconductor laser or It is a distributed reflection type semiconductor laser.

  The wavelength tunable light source according to claim 6 is the wavelength tunable light source according to claim 5, wherein the demultiplexing unit and the multiplexing unit are integrated, and the demultiplexing unit and the multiplexing unit An n-input 2-output multiplexer / demultiplexer is configured.

  According to the two-output wavelength tunable light source according to the present invention, it is possible to realize a tunable light source that is small and capable of individually adjusting the optical power of two outputs.

It is a figure which shows an example of a structure of the transceiver for multi-value modulation. It is a figure which shows the conventional wavelength variable light source (DBR laser). It is a figure which shows the conventional wavelength variable light source (DFB laser array). It is a figure which shows the 1st example of the conventional 2 output wavelength variable light source. It is a figure which shows the 2nd example of the conventional 2 output wavelength variable light source. It is a figure which shows the wavelength variable light source (both ends SOA integrated DBR laser) which concerns on Example 1 of this invention. It is a figure which shows the structure of an MZ interference type | mold branching filter. It is a figure which shows the wavelength variable light source (both ends SOA integrated DFB laser array) which concerns on Example 2 of this invention.

  Hereinafter, a specific embodiment of the present invention will be described as an example. The following embodiment is an example showing the effect of the present invention, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

Example 1
FIG. 6A shows a two-output wavelength tunable light source according to the first embodiment of the present invention. 6A shows a two-output wavelength tunable light source 600 including an optical amplifying unit 610, a wavelength tunable light source unit 620, and a Mach-Zehnder interference type branching device (hereinafter referred to as an MZ interference type branching device) 630. Has been. In the dual-output wavelength tunable light source 600 according to the first embodiment of the present invention, a DBR laser is used as the wavelength tunable light source unit 620. The wavelength tunable light source unit 620 includes a front mirror unit 621, a rear mirror unit 622, and a phase adjustment unit. 623 and an optical gain unit 624 (active region).

  In the two-output wavelength tunable light source 600 according to the first embodiment, the MZ interference type branching device 630 is used as an optical branching unit. A branching ratio adjusting electrode 640 is connected to the MZ interference type branching device 630. As the optical amplifier 610, a semiconductor optical amplifier (SOA) can be used.

  FIG. 7 shows the configuration of the MZ interference type duplexer 630. The MZ interference type duplexer 630 shown in FIG. 7 is a 1-input 2-output duplexer, and includes an input waveguide 631, a first output waveguide 632, and a second output waveguide 633. A multi-mode interference type waveguide coupler (hereinafter referred to as an MMI coupler) 634 having one input and two outputs, an MMI coupler 635 having two inputs and two outputs, two arm waveguides 636 and 637, and a phase adjustment region 638. With.

  The MMI coupler 634 branches the light input to the input waveguide 631 into the two arm waveguides 636 and 637. The phase adjustment region 638 adjusts the phase of light propagating through the arm waveguide 637 in accordance with the applied voltage. By applying a voltage to the phase adjustment region 638 via the branching ratio adjustment electrode 640 connected to the MZ interference type demultiplexer 630, the light input to the input waveguide 631 is supplied to the two arm waveguides 636 and 637. Can branch at any branching ratio. The lights whose branching ratios are adjusted in the two arm waveguides 636 and 637 are output from the first output waveguide 632 and the second output waveguide 633 via the MMI coupler 635, respectively.

  In the two-output wavelength tunable light source 600 according to the first embodiment, by integrating the MZ interference type branching device 630, an optical branching unit is not required and a small two-output wavelength tunable light source can be realized. Further, the MZ interference type branching device 630 dynamically adjusts the light branching ratio by applying a voltage to the branching ratio adjusting electrode 640, so that the first output waveguide 632 and the second output waveguide 633 are adjusted. Can be output from.

  FIG. 6B shows another example of the dual output wavelength variable light source according to the first embodiment of the present invention. In the two-output wavelength tunable light source 600 shown in FIG. 6A, the output from the first output waveguide 632 of the MZ interference type branching device 630 is on the left, and the output from the second output waveguide 633 is on the right. The two output wavelength tunable light sources shown in FIG. 6B are shown in FIG. 6B, although the light guide directions of the first output waveguide 632 and the second output waveguide 633 differ by approximately 180 degrees. As shown in 601, the output from the first output waveguide 632 is output to the left, and the output from the second output waveguide 633 is output to the bottom, so that the first output waveguide 632 and the second output are output. The waveguide direction of light can be made to differ by about 90 degrees from the waveguide 633. By changing the output surface, the lens configuration of the spatial optical system becomes easy. In addition, when considering an optical system connected to, for example, a silica-based waveguide instead of a spatial optical system, the outputs of the first output waveguide 632 and the second output waveguide 633 may both be output to the left part. It is valid.

  FIG. 6C shows still another example of the dual output wavelength variable light source according to the first embodiment of the present invention. A two-output wavelength tunable light source 602 shown in FIG. 6C is different from the two-output wavelength tunable light sources 600 and 601 shown in FIGS. 6A and 6B, and the output of the wavelength tunable light source unit 620 is one input. After being branched into two by a two-output optical branching unit 650, two optical amplification units, a first optical amplification unit 611 and a second optical amplification unit 612, are passed.

  According to the two-output wavelength tunable light source 602 shown in FIG. 6C, by adjusting the light amplification degree in the first optical amplifying unit 611 and the second optical amplifying unit 612, FIG. The branching ratio can be adjusted more freely than the two-output wavelength variable light sources 600 and 601 shown in FIG. For example, the maximum output intensity of the two-output wavelength tunable light sources 600 and 601 shown in FIGS. 6A and 6B is a value obtained by subtracting the optical loss of the MZ interference type branching device 630 from the saturated output of the optical amplifying unit 610. However, the maximum output intensity of the two-output wavelength variable light source 602 shown in FIG. 6C is the saturated output itself of the first optical amplification unit 611, and the same light is output from the two-output wavelength variable light sources 600, 601 and 602. When the amplification unit is used, a stronger maximum output intensity can be obtained with the two-output wavelength variable light source 602 shown in FIG. 6C.

  In the two-output wavelength tunable light source 602 shown in FIG. 6C, even if the branching ratio of the optical branching unit 650 is fixed (for example, the Y branching waveguide uses an MMI coupler), A free branching ratio can be obtained by adjusting the degree of light amplification in the optical amplification unit 611 and the second optical amplification unit 612.

  In the MZ interference type branching device 630 shown in FIGS. 6A and 6B, a voltage is applied only to one of the arm waveguides via the branching ratio adjusting electrode 640 and the phase adjusting region 638. You may apply to. In the dual-output wavelength tunable light source shown in FIGS. 6A and 6B, an MZ interference type branching unit is used, but an optical directional coupler is used, and one or both waveguides of the directional coupler are used. A voltage may be applied to the capacitor.

  Although FIG. 6C outputs to the left part and the right part, the left part and the lower part, or both may be the left part. In addition, when the output light intensity of one of the two outputs may be weak (normally, the light intensity required for the reception light source LO is weaker than the light intensity required for the transmission light source LD) The element lengths of the optical amplifiers may not be the same, and one (weaker) element length may be shortened.

  A method for producing a two-output wavelength tunable light source according to Example 1 of the present invention will be described below.

  For the crystal growth of the semiconductor layer, a metal-organic vapor phase epitaxy (MOVPE) method was used to grow a crystal on the n-InP substrate. The active layer of the optical amplification unit 610 and the optical gain unit 624 is an InGaAsP multi-quantum well (MQW) layer with a band gap wavelength of 1.59 microns. Distorted. An n-InP clad layer is provided below the active layer of the optical amplifying unit 610 and the optical gain unit 624, and a p-InP clad layer is provided above the active layer, thereby forming a double hetero structure in which the active layer is sandwiched between the two clad layers. A p-InGaAsP contact layer was grown on the p-InP cladding layer.

The core layer of the front mirror unit 621, the rear mirror unit 622, the phase adjustment unit 623, and the MZ interference type branching device 630 is a non-doped InGaAsP core layer with a band gap wavelength of 1.3 microns, and an optical amplification unit 610 and an optical gain unit 624. And butt jointed. An n-InP clad layer was provided below the core layer, and a non-doped InP clad layer was provided above. The diffraction gratings of the front mirror part 621 and the rear mirror part 622 were formed in a non-doped InP clad layer. The depth of the diffraction grating was 40 nm. A p-InGaAs contact layer was grown on the non-doped InP cladding layer. The mesa width was 1.2 microns, and both sides of the mesa formed by Cl ₂ reactive ion etching (RIE) were buried by burying growth with a pn current blocking layer.

  The p-side electrode is AuZn / Au, and AuZn / Au is used to separate the optical amplification unit 610, the front mirror unit 621, the rear mirror unit 622, the phase adjustment unit 623, the optical gain unit 624, and the branching ratio adjustment electrode 640. The electrode and the p-InGaAsP contact layer were separated. The n-side electrode was AuGe / Au. After the device was cleaved, anti-reflecting (AR) coating was applied to both ends in order to reduce reflection at the end face. The reflectance of the AR coat was 0.5% or less.

  The lengths of the optical amplification unit 610, the front mirror unit 621, the rear mirror unit 622, the phase adjustment unit 623, and the optical gain unit 624 were 500 microns, 400 microns, 600 microns, 150 microns, and 350 microns, respectively. The length of the MZ interference type duplexer 630 was 2000 microns.

  The conventional two-output wavelength tunable light source 400 shown in FIG. 4 and the two-output wavelength tunable light source 600 according to Example 1 were compared in size. The two-output wavelength tunable light source 600 according to the first embodiment has a length of 3.0 mm and a width of 0.5 mm, whereas the conventional two-output wavelength tunable light source 400 has a length of 5.0 mm and a width of 1. mm. It was 5 mm. From this, it can be seen that the two-output wavelength tunable light source 600 according to Example 1 is more suitable for miniaturization than the conventional two-output wavelength tunable light source 400.

  Next, the optical output power was confirmed with the conventional two-output wavelength variable light source 400 and the two-output wavelength variable light source 600 according to Example 1. At this time, a bias current of 100 mA was applied to each optical gain section, and a bias current of 200 mA was applied to the optical amplification section. In the conventional dual-output wavelength tunable light source 400, the branched light is +13.1 dBm to the top and +12.9 dBm to the left, but the branching ratio is fixed, and the optical power cannot be adjusted.

  On the other hand, in the dual-output wavelength tunable light source 600 according to Example 1, it was +13.2 dBm to the left and +12.6 dBm to the right. Further, when a voltage of 1.0 V is applied to the MZ interference type branching device 630 via the branching ratio adjusting electrode 640 of the two-output wavelength variable light source 600 according to the first embodiment, the optical power is +10.2 dBm to the left side, +14.6 dBm. Further, when a voltage of −1.0 V was applied to the MZ interference type branching device 630 via the branching ratio adjusting electrode 640, the optical power became +13.2 dBm to the left and +12.7 dBm to the right. From this result, in the dual output wavelength tunable light source 600 according to the first embodiment, by adjusting the voltage applied by the branching ratio adjustment electrode 640, it is possible to arbitrarily set the optical power required for each of the reception side and the transmission side. It could be confirmed.

  From the above, it is apparent that a small wavelength variable light source capable of individually adjusting the optical power of two outputs can be realized.

  6A to 6C uses the wavelength tunable light source unit 220 shown in FIG. 2 as the wavelength tunable light source unit 620. However, the wavelength tunable light source unit 620 shown in FIG. Needless to say, the light source unit 320 may be used.

  Further, the wavelength variable light source unit 220 in FIG. 2 is a so-called “SSG-DBR” type having a “front mirror unit”, a “phase adjustment unit”, an “optical gain unit”, and a “rear mirror unit”. However, the wavelength tunable light source section has “DFB type optical gain section having sampled grating (SG)” and “mirror section slightly chirped by sampled grating (SG)” (“phase length adjusting section It may be of the so-called “SG-DBR” type.

  In order to adjust the “front mirror part”, “rear mirror part”, and “mirror part slightly chirped with the sampled grating (SG)”, current may be injected from the corresponding electrode, or a heater electrode is provided. Local heating may be used.

(Example 2)
FIG. 8A shows a two-output wavelength tunable light source according to the second embodiment of the present invention. FIG. 8A shows a two-output wavelength variable light source 800 including a first optical amplification unit 810, a second optical amplification unit 815, a wavelength variable light source unit 820, and an optical demultiplexer 830. Has been. In the two-output wavelength tunable light source 800 according to the second embodiment, the wavelength tunable light source unit 820 includes a plurality of DFB lasers 821 and an optical multiplexer 822.

  As shown in FIG. 8A, in the two-output wavelength tunable light source 800 according to the second embodiment, a DFB laser array is used as the wavelength tunable light source unit 820, and an MMI coupler with five inputs and one output is used as the optical multiplexer 822. The optical branching unit 830 uses a 1-input 2-output MMI coupler. In addition, the first optical amplifier 810 is connected to the first output waveguide 832 of the optical branching unit 830, and the second optical amplifier 815 is connected to the second output waveguide 833 of the optical branching unit 830. ing. The first optical amplification unit 810 and the second optical amplification unit 815 can be SOAs, and the SOA length is 1.2 mm.

  FIG. 8B shows another example of the dual output wavelength variable light source according to the second embodiment of the present invention. FIG. 8B shows a two-output variable wavelength light source 801 including a first optical amplification unit 810, a second optical amplification unit 815, and a variable wavelength light source unit 840. In the two-output wavelength variable light source 801, the wavelength variable light source unit 840 includes a plurality of DFB lasers 821 and an MMI coupler (optical multiplexing / demultiplexing unit) 841.

  In the two-output wavelength tunable light source 801 shown in FIG. 8B, the 5-input single-output MMI coupler (optical multiplexing unit) 822 in the two-output wavelength-tunable light source 800 shown in FIG. An MMI coupler (optical demultiplexing unit) 830 is integrated to form a 5-input 2-output MMI coupler 841.

  Here, in the two-output wavelength tunable light sources 800 and 801 shown in FIG. 8A and FIG. 8B, the left part and the lower part through the first output waveguide 832 and the second output waveguide 833. However, the light may be output from the left part and the right part. In addition, when considering an optical system connected to, for example, a silica-based waveguide instead of a spatial optical system, it is also effective to output both outputs of the branching portion to the left portion.

  Hereinafter, a method of creating the dual-output wavelength tunable light source 800 according to Example 2 of the present invention will be described.

  The crystal growth of the semiconductor layer was performed on the n-InP substrate using the MOVPE method. InGaAsP multiple quantum well (MQW) layers were used as active layers of the DFB laser 821, the first optical amplification unit 810, and the second optical amplification unit 815. An n-InP clad layer is provided below the active layer of the DFB laser 821, the first optical amplifying unit 810, and the second optical amplifying unit 815, and a p-InP clad layer is provided above the active layer. A double hetero structure sandwiching the active layer was formed. A p-InGaAsP contact layer was grown on the p-InP cladding layer.

  The core layer of the waveguide and the MMI coupler was a non-doped InGaAsP core layer having a thickness of 0.3 microns, and butt-jointed with the DFB laser 821, the first optical amplification unit 810, and the second optical amplification unit 815, respectively. An n-InP clad layer was provided below the core layer, and a non-doped InP clad layer was provided above.

The minimum radius of the curved waveguide is 250 microns, the resonance length of the DFB laser 821 is 450 microns, and the lengths of the first optical amplification unit 810 and the second optical amplification unit 815 are 1200 microns. The mesa width was 1.5 microns, and both sides of the mesa formed by Cl ₂ reactive ion etching (RIE) were buried by burying growth with a pn current blocking layer.

  The p-side electrode of the DFB laser 821, the first optical amplification unit 810, and the second optical amplification unit 815 was AuZn / Au, and the n-side electrode was AuGe / Au. After the device was cleaved, AS coating was applied to both ends in order to reduce reflection at the end face. The reflectance of the AR coat was 0.5% or less.

  The conventional two-output wavelength tunable light source 500 shown in FIG. 5 and the two-output wavelength tunable light source 800 according to Example 2 were compared in size. The two-output wavelength variable light source 800 according to the second embodiment has a length of 4.0 mm and a width of 1.3 mm, whereas the conventional two-output wavelength variable light source 500 has a length of 6.0 mm and a width of 1. mm. It was 5 mm. From this, it can be seen that the two-output wavelength tunable light source 800 according to the second embodiment is more suitable for miniaturization than the conventional two-output wavelength tunable light source 500.

  Next, the optical output power was confirmed with the conventional two-output wavelength tunable light source 500 shown in FIG. 5 and the two-output wavelength tunable light source 800 according to Example 2. At this time, a bias current of 100 mA is applied to the optical gain section of the DFB laser, a bias current of 200 mA is applied to the optical amplification section 310 in the conventional two-output wavelength variable light source 500, and the first in the two-output wavelength variable light source 800 according to the second embodiment. A bias current of 110 mA was applied to each of the optical amplifier 810 and the second optical amplifier 815. In the conventional dual-output wavelength tunable light source 500, the optical power of the branched light was +10.1 dBm to the left and +9.9 dBm to the upper part, but the branching ratio was fixed and the optical power could not be adjusted. .

  On the other hand, in the dual-output wavelength tunable light source 800 according to Example 2, the optical power was +9.8 dBm to the left and +10.2 dBm to the bottom. In addition, by setting the bias current of the first optical amplification unit 810 to 150 mA and the bias current of the second optical amplification unit 815 in the dual-output wavelength tunable light source 800 according to the second embodiment to 80 mA, the optical power is reduced to the left side. +13.0 dBm and +8.2 dBm at the bottom. Further, by setting the bias current of the first optical amplifier 810 to 80 mA and the bias current of the second optical amplifier 815 to 150 mA, the optical power is +8.1 dBm to the left and +13.3 dBm to the lower part. It became. From this result, it was confirmed that by adjusting the current values of the first optical amplifying unit 810 and the second optical amplifying unit 815, the power required for the receiving side and the transmitting side can be arbitrarily set, respectively. .

  From the above, it is apparent that a small wavelength variable light source capable of individually adjusting the optical power of two outputs can be realized.

  In the example shown in FIGS. 8A and 8B, the array of the DFB laser 821 has been described. However, a DBR laser array in which a plurality of wavelength variable light source units shown in FIG. Absent. 8A and 8B illustrate an example in which five DFB lasers 821 are used as the DFB laser array, the number of DFB lasers is not limited to five. Absent. The number of DFB lasers 821 may be 12, for example.

  In the second embodiment, an example of an MMI coupler is given as a multiplexer / demultiplexer. However, an MZ interference type, directional coupler type, Y-branch type multiplexer / demultiplexer may be used. In addition, these various types may be combined.

  In Examples 1 and 2, an example in which an InGaAsP system is used as the composition of the active layer and the core layer is shown, but an InGaAlAs system and an AlGaAs system may be used as the composition of the active layer and the core layer. Further, it may be a III-V group compound semiconductor composed of at least two kinds of elements among Si, Al, Ga, In, As, P, and Sb. Further, although the p-side electrode is AuZn / Au, for example, Ti / Pt / Au may be used. The n-side electrode is AuGe / Au, but it may be, for example, AuGeNi / Au, and any material can be used as long as an ohmic contact can be obtained.

Multilevel modulation transceiver 100
Optical receiver 110
90 degree optical hybrid circuit 111
Receiver 112
Digital signal processor 120
Optical transmitter 130
Modulator 131
Polarization demultiplexer PBS
Polarization multiplexer PBC
Tunable light source for reception LO
Variable wavelength light source for transmission LD
Analog to digital converter ADC
Wavelength variable light source 200, 300
Optical amplifier 210, 310, 610
Wavelength variable light source 220, 320, 620, 820, 840
Front mirror part 221, 621
Rear mirror 222, 622
Phase adjustment unit 223, 623
Optical gain unit 224, 624
DFB laser 321, 821
Optical multiplexer 322, 822
Dual output wavelength variable light source 400, 500, 600, 601, 602, 800, 801
Lens 410
Beam splitter 420
First optical amplifier 611, 810
Second optical amplification section 612, 815
MZ interference type duplexer 630
Input waveguide 631
First output waveguide 632, 832
Second output waveguide 633, 833
MMI coupler 634, 635
Arm waveguide 636, 637
Phase adjustment region 638
Branching ratio adjustment electrode 640
Optical branching unit 650, 830
Optical multiplexing / demultiplexing part 841

Claims (6)

A wavelength tunable light source that outputs laser light;
An optical amplifying unit for amplifying laser light output from the wavelength variable light source unit;
A first output waveguide and a second output waveguide are provided, and the laser light amplified and output by the optical amplification unit is branched into the first output waveguide and the second output waveguide. And a branching section
The branch is a Mach-Zehnder interferometer or a directional coupler,
An electrode for adjusting a branching ratio of light in the first output waveguide and the second output waveguide is connected to the branch portion. A wavelength tunable light source that outputs laser light;
A branching unit that splits the laser light output from the wavelength tunable light source unit into two;
A first optical amplifying unit for amplifying light output from the first output waveguide of the branching unit;
A second optical amplifying unit for amplifying light output from the second output waveguide of the branching unit,
The branch is a Mach-Zehnder interferometer or a directional coupler,
The intensity of light output from the first output waveguide and the second output waveguide can be controlled by adjusting the degree of light amplification in the first optical amplifier and the second optical amplifier. A wavelength tunable light source characterized by being.   The direction of light guided through the first output waveguide is 90 degrees or 180 degrees different from the direction of light guided through the second output waveguide. The wavelength tunable light source according to 2.   4. The wavelength tunable light source according to claim 1, wherein the wavelength tunable light source unit is a distributed feedback semiconductor laser or a distributed reflection semiconductor laser. The wavelength tunable light source unit is
a semiconductor laser array in which n (n is an integer of 2 or more) semiconductor lasers are arranged in an array;
An n-input 1-output combiner for combining and outputting the light output from the semiconductor laser array,
The wavelength tunable light source according to any one of claims 1 to 3, wherein the semiconductor laser is a distributed feedback semiconductor laser or a distributed reflection semiconductor laser.   6. The demultiplexing unit and the multiplexing unit are integrated, and the demultiplexing unit and the multiplexing unit constitute an n-input 2-output multiplexer / demultiplexer. Tunable light source.

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