JP2016149529A - Wavelength-tunable light source and wavelength-tunable light source module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength variable light source that can be made low in power consumption and can stably operate.SOLUTION: A wavelength-tunable light source comprises; an optical coupling circuit which outputs light input from an input waveguide to two output waveguides; a semiconductor laser connected to an input end of the input waveguide; first and second optical amplifiers connected to corresponding output ends of the two output waveguides; and first and second output portions respectively outputting the light passing through the first optical amplifier and the second optical amplifier. A first arm portion and a second arm portion have an arrangement distance therebetween greater than a distance between the input ends of the two output waveguides and greater than a distance between an output end of the first output portion and an output end of the second output portion, the first arm portion forming a traveling path of light from one of the two output waveguides to the first output portion through the first optical amplifier, the second arm portion forming a traveling path of light from another one of the two output waveguides to the second output portion through the second optical amplifier, and the first optical amplifier and the second optical amplifier have curved portions in which the first output portion and the second output portion are curved in a direction toward each other, and the first optical amplifier and the second optical amplifier respectively output light from the output end of the first output portion and the output end of the second output portion.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wavelength tunable light source using a semiconductor laser.

  2. Description of the Related Art In recent years, with a dramatic increase in communication demand, a wavelength division multiplexing communication system has been realized that enables large-capacity transmission with a single optical fiber by multiplexing a plurality of signal lights having different wavelengths.

  As a light source used in the wavelength division multiplex communication system, a single mode LD (Laser Diode) (hereinafter referred to as a single diode) capable of obtaining a high side mode suppression ratio (SMSR) of at least 30 to 40 dB or more. (Referred to as mode LD). The single mode LD includes, for example, a distributed feedback laser diode (hereinafter referred to as DFB-LD), a distributed Bragg reflector laser diode (hereinafter referred to as DBR-LD), and the like. Is mentioned.

  In order to realize a wavelength division multiplexing communication system, a low-cost tunable light source that covers the entire wavelength band is required. As the wavelength tunable light source, an LD light source monolithically integrated on the same substrate has attracted attention.

  In general, the above-described wavelength tunable light source is used in combination with an external modulator module that generates a data signal. In addition, an electroabsorption (EA) type optical modulator or a Mach Zehnder (MZ) type is used. Research is also underway to monolithically integrate optical modulators on the same substrate.

  Conventionally, output sides of a plurality of DFB-LDs are connected to an input waveguide of a multi-mode interference (Multi Mode Interference) type optical multiplexing circuit (hereinafter referred to as MMI), and the light multiplexed by the MMI is a semiconductor optical amplifier ( For example, Patent Document 1 discloses a variable wavelength light source configured to output from an output waveguide after being amplified by a semiconductor optical amplifier (hereinafter referred to as SOA).

  For example, in Patent Document 2, the output sides of a plurality of LDs are connected to N × 2-MMI (N is a natural number of 3 or more), and two output waveguides of MMI are connected to two arms of a Mach-Zehnder modulator. A connected tunable light source is disclosed. According to Patent Document 2, it is possible to improve the optical loss as compared with the case of using N × 1-MMI.

  Also, for example, in Patent Document 3, the output sides of a plurality of DFB-LDs are connected to an MMI, phase adjustment is performed in each of the two output waveguides of the MMI, and then one output is output via the other MMI. A tunable light source configured to output light from a waveguide is disclosed. According to Patent Document 3, it is possible to increase the output and improve the SN ratio (Signal to Noise Ratio).

  Further, for example, in Patent Document 4, in a Mach-Zehnder interferometer having two arm waveguides, when only one arm waveguide is heated by a heater, the influence of heat on the other arm waveguide is prevented. In order to achieve this, a configuration in which the arm waveguide interval is increased is disclosed.

  For example, in Patent Document 5, in a Mach-Zehnder interferometer having two arm waveguides, when only one arm waveguide is heated by a heater, the other arm waveguide is prevented from being affected by heat. In order to achieve this, a configuration in which the arm waveguide interval is widened and grooves are provided between the arm waveguides is disclosed.

JP 2003-258368 A JP 2007-65357 A JP 2011-44581 A JP 2003-215369 A JP 2005-156855 A

  In a wavelength division multiplexing communication system having a transmission rate of 40 Gbps or higher in a trunk line system, digital coherent communication using optical phase modulation has recently been put into practical use. In a wavelength division multiplex communication system employing digital coherent communication, a narrow linewidth variable wavelength light source having a laser oscillation line width of 1 MHz or less, more preferably 500 kHz or less is used as a light source for transmission and reception.

  In wavelength division multiplex communication employing the above digital coherent communication, if the wavelengths of optical signals used for transmission and reception are different, separate wavelength variable light sources are required for transmission and reception. The power consumption of the entire transmission / reception device including the light source increases.

  On the other hand, in the wavelength division multiplex communication employing the above-mentioned digital coherent communication, there are many cases where the wavelengths of optical signals used for transmission and reception are the same, which is generally required for transmission and reception. The light output of the line width variable wavelength light source is different. In such a case, it is desirable to use one tunable light source as a light source for transmission and reception from the viewpoint of reducing power consumption of the entire transmission and reception device and reducing the mounting area.

  For example, in the case where the wavelength tunable light source disclosed in Patent Documents 1 to 3 is also used as a light source for transmission and reception, the wavelength tunable light source disclosed in Patent Documents 1 to 3 needs to have two outputs by a polarization maintaining coupler. However, in such a configuration, a branching loss occurs in the polarization maintaining coupler. Therefore, in order to compensate for the branching loss, the drive current density of the SOA provided on the output side of the wavelength tunable light source is increased to increase the branch current from the wavelength tunable light source. Although it is necessary to increase the optical output, there is a problem that it causes an increase in power consumption and laser oscillation line width. In addition, the Mach-Zehnder interferometers of Patent Documents 4 and 5 control the phase by changing the refractive index of the waveguide by heating only one of the arm waveguides, and actively incorporating the action of heat. Therefore, heat may propagate to the other arm portion, which may affect the refractive index of the waveguide.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a wavelength tunable light source capable of reducing power consumption and capable of stable operation.

  In the wavelength tunable light source according to the present invention, the output end of at least one input waveguide is connected to the input section, and the input ends of the two output waveguides are connected to the output section, and input from the at least one input waveguide. An optical coupling circuit for outputting the light to the two output waveguides, a semiconductor laser connected to the input end of the at least one input waveguide, and a first connected to the output ends of the two output waveguides, respectively. 1 and a second optical amplifier, and first and second output units to which light passing through the first and second optical amplifiers is output, respectively, from one of the two output waveguides A first arm that forms a traveling path of light reaching the first output through the first optical amplifier, and the second optical amplifier from the other of the two output waveguides through the second optical amplifier. Path of light reaching the output The second arm portion to be configured has an arrangement interval wider than the interval between the input ends of the two output waveguides and the interval between the output ends of the first and second output portions. The second optical amplifier has bent portions that curve in directions in which the first and second output sections approach each other, and outputs light from the output ends of the first and second output sections, respectively. .

  According to the wavelength tunable light source of the present invention, thermal crosstalk between optical amplifiers can be suppressed, power consumption can be reduced, and stable operation is possible.

It is a top view which shows the structure of the wavelength variable light source of Embodiment 1 which concerns on this invention. It is a top view which shows the other structure of the wavelength variable light source of Embodiment 1 which concerns on this invention. It is a figure explaining the structure which performs temperature control of a wavelength variable light source. It is a top view which shows the structure which mounted the wavelength variable light source of Embodiment 1 in the Peltier device. It is a top view which shows the structure of the wavelength variable light source of Embodiment 2 which concerns on this invention. It is a top view which shows the structure of the wavelength variable light source of the modification 1 of Embodiment 2 which concerns on this invention. It is a top view which shows the structure of the wavelength tunable light source of the modification 2 of Embodiment 2 which concerns on this invention. It is a top view which shows the structure of the wavelength tunable light source of the modification 2 of Embodiment 2 which concerns on this invention. It is a top view explaining the control method of the wavelength variable light source of Embodiment 2 which concerns on this invention. It is a top view explaining the control method of the wavelength variable light source of Embodiment 2 which concerns on this invention. It is a top view explaining the control method of the wavelength variable light source of Embodiment 3 which concerns on this invention. It is a figure which shows the fluctuation characteristic of the wavelength of the output for transmission when the output for reception is made into an ON state. It is a figure which shows the output fluctuation characteristic of the output for transmission when the output for reception is made into an ON state. It is a top view which shows the structure of the wavelength variable light source of Embodiment 4 which concerns on this invention. It is sectional drawing which shows the structure of the wavelength variable light source of Embodiment 4 which concerns on this invention. It is a top view which shows the structure of the wavelength variable light source of the modification 1 of Embodiment 4 which concerns on this invention. It is sectional drawing which shows the structure of the wavelength variable light source of the modification 1 of Embodiment 4 which concerns on this invention. It is a top view which shows the structure of the wavelength tunable light source of the modification 2 of Embodiment 4 which concerns on this invention. It is sectional drawing which shows the structure of the wavelength variable light source of the modification 2 of Embodiment 4 which concerns on this invention. It is a top view which shows the structure of the wavelength variable light source of the modification 3 of Embodiment 4 which concerns on this invention. It is sectional drawing which shows the structure of the wavelength variable light source of the modification 3 of Embodiment 4 which concerns on this invention. It is a top view which shows the structure of the wavelength variable light source of Embodiment 5 which concerns on this invention. It is a top view which shows the structure of the wavelength variable light source of Embodiment 5 which concerns on this invention. It is a figure which shows the structure of the wavelength variable light source module which applied the wavelength variable light source which concerns on this invention as a light source. It is a figure which shows the structure which applied the wavelength variable light source module which has a wavelength variable light source which concerns on this invention as a light source module in a transmission / reception apparatus. It is a top view which shows the structure of the wavelength variable light source of the premise technique of this invention. It is sectional drawing which shows the structure of the MMI input waveguide in the wavelength variable light source of the premise technique of this invention. It is sectional drawing which shows the structure of SOA in the wavelength variable light source of the premise technique of this invention. It is a figure which shows the structure of the transmitter / receiver of the premise technique of this invention. It is a figure which shows the structure of the wavelength variable light source module of the premise technique of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In the following, the same or similar components in each drawing are denoted by the same reference numerals or the same names, and their functions are also the same, and redundant description is omitted.

  In addition, the dimensions, materials, shapes, and relative arrangements of the constituent elements exemplified in each embodiment are appropriately changed depending on the configuration of the apparatus to which the present invention is applied and various conditions. The present invention is not limited to these examples.

<Prerequisite technology>
First, the prerequisite technology of the present invention will be described with reference to FIGS. FIG. 26 is a plan view showing an example of the configuration of the wavelength tunable light source 15 according to the base technology, and shows the configuration of a wavelength tunable light source using a plurality of single mode LDs having different oscillation wavelengths.

  As shown in FIG. 26, the wavelength tunable light source 15 according to the base technology includes a DFB-LD array 2 configured by integrating N (N is a natural number of 2 or more) DFB-LD1, and has N inputs and 1 N × 1-MMI3 (N is a natural number of 3 or more) MMI input waveguides 4 having one output. That is, each of the N DFB-LDs 1 is connected to the N MMI input waveguides 4, and the light combined by N × 1-MMI 3 is transmitted through the SOA 6 connected to the MMI output waveguide 5. The credit light output 7 is output to the outside.

  In the above configuration, when any one DFB-LD1 in the DFB-LD array 2 is laser-oscillated, the output of light output from one DFB-LD1 (hereinafter referred to as LD output light) is output. 1 / N is coupled to the MMI output waveguide 5, and the remaining (N−1) / N output is radiated out of the MMI output waveguide 5. Compensation for branch loss, coupling loss, and the like is performed by injecting current into the SOA 6, and a high transmission optical output 7 is output from the SOA 6.

  FIG. 27 is a diagram showing a cross-section in the direction of the arrow along line FF in FIG. 26, and shows an example of the configuration of the MMI input waveguide 4. As shown in FIG. 27, an InP lower cladding layer 41, an InP current blocking layer 44, and an InP upper cladding layer 43 are sequentially stacked on an InP substrate 40 containing indium (In) and phosphorus (P), which are semiconductor substrates. In the film (semiconductor laminated film), the InGaAsP waveguide layer 42 containing In, gallium (Ga), arsenic (As), and P selectively formed on the InP lower cladding layer 41 functions as the MMI input waveguide 4. To do.

  The InGaAsP waveguide layer 42 is made of an InGaAsP-based material that does not absorb LD output light. The InGaAsP waveguide layer 42 may be composed of a bulk epitaxial layer or a multiple quantum well (MQW) layer.

  27 shows the cross-sectional configuration of the MMI input waveguide 4, the cross-sectional configuration of the MMI output waveguide 5 is the same, and the InGaAsP waveguide layer 42 functions as the MMI output waveguide 5. In this case, there is only one InGaAsP waveguide layer 42.

  Further, N × 1-MMI3 has a large length in the arrangement direction of the MMI input waveguides 4 so that N MMI input waveguides 4 can be connected, and this wide portion becomes a multimode region. ing. The multimode region is made of the same InGaAsP as the InGaAsP waveguide layer 42 shown in FIG. 27, and the width of the InGaAsP waveguide layer 42 (the length in the left-right direction toward the plane of FIG. 27) is wide as described above. It is just a configuration. Of course, this multi-mode region is surrounded by the InP lower cladding layer 41, the InP current blocking layer 44, and the InP upper cladding layer 43.

  FIG. 28 is a diagram showing a cross-section in the direction of the arrow along the line GG in FIG. 26, and shows an example of the configuration of the SOA 6. As shown in FIG. 28, in a laminated film (semiconductor laminated film) in which an InP lower clad layer 41, an InP current blocking layer 44, an InP upper clad layer 43, an InGaAsP contact layer 46, and an electrode 47 are laminated in this order on an InP substrate 40. The InGaAsP active layer 45 selectively formed on the InP lower cladding layer 41 functions as the SOA 6.

  For the InGaAsP active layer 45, an InGaAsP-based material having a gain with respect to light passing through the MMI output waveguide 5 (hereinafter referred to as guided light) is used. The InGaAsP active layer 45 may be a bulk epitaxial layer or an MQW layer.

  28 shows the cross-sectional configuration of the SOA 6, the configuration of the DFB-LD 1 is the same. However, the electrodes 47 are separated between adjacent DFB-LDs 1, and current is independently injected into each DFB-LD1. In the DFB-LD 1 and the SOA 6, when current is injected through the electrode 47 provided on the InGaAsP contact layer 46, a gain is generated in the InGaAsP active layer 45 and spontaneous emission light is generated. In the DFB-LD1, spontaneous emission light having a specific wavelength reflected by the diffraction grating becomes stimulated emission seed light, and laser oscillation occurs when a predetermined threshold current is exceeded. On the other hand, the SOA 6 functions as an amplifier for the LD output light, but is designed so as not to oscillate alone.

  The oscillation wavelength of the DFB-LD1 changes at a rate of about 0.1 nm / ° C. according to the temperature of the DFB-LD1 (hereinafter referred to as element temperature). Therefore, when the element temperature is changed within a predetermined range (for example, 10 to 50 ° C.), the oscillation wavelength of any DFB-LD 1 in the DFB-LD array 2 (for example, N = 10 to 16) is The interval of the oscillation wavelength of each DFB-LD1 is designed so as to coincide with the oscillation wavelength of another adjacent DFB-LD1. In this case, the combination of the selection of the DFB-LD1 and the element temperature adjustment allows the DFB-LD array 2 formed in one chip to use the entire wavelength band (about 30 to about C band (Conventional band) or L band (Long band)). 40 nm).

  FIG. 29 is a block diagram showing an example of the configuration of the transmission / reception device 8 using the wavelength tunable light source 15 according to the base technology described above, and shows the configuration of the transmission / reception device 8 for a digital coherent communication system.

  The transmission optical output 7 output from the wavelength tunable light source module 9 (including the wavelength tunable light source 15) is modulated by the modulator module 10 and then output to the outside as a transmission signal 11.

  The reception signal 12 received from the outside is input to the reception module 14 together with the reception light output 13 output from the wavelength variable light source module 9, and is restored after the signal processing.

  In the transmitter / receiver 8 shown in FIG. 29, an insertion loss occurs in the modulator module 10. Therefore, the transmission optical output 7 generally requires a high output, but the reception optical output 13 has a relatively low output. May be.

  However, as described above, when the wavelengths of optical signals used for transmission and reception are the same, one wavelength variable light source module is used for transmission / reception from the viewpoint of reducing the power consumption of the entire transmission / reception device 8 and the mounting area. It is desirable to also use as a light source.

  FIG. 30 is a block diagram showing an example of the configuration of the wavelength tunable light source module 9 including the wavelength tunable light source according to the base technology, and the wavelength of the optical signal used for transmission and reception is the same, and one wavelength tunable light source The configuration when the module is also used as a light source for transmission and reception is shown.

  The wavelength tunable light source module 9 includes a wavelength tunable light source 15, a coupling optical system 16, a beam splitter 18 incorporated in the coupling optical system 16, and a monitor 19 that monitors light separated by the beam splitter 18. . An optical fiber 17 and a polarization maintaining coupler 20 are connected to the LD output side of the wavelength tunable light source module 9.

  The variable wavelength light source 15 emits single mode LD output light, and the emitted LD output light is coupled to an optical fiber 17 via a coupling optical system 16 including a lens, an optical isolator (not shown), and the like. The LD output light coupled to the optical fiber 17 is branched at a predetermined ratio by the polarization maintaining coupler 20, and each of the branched LD output lights is output as a transmission light output 7 and a reception light output 13.

  Part of the LD output light that passes through the coupling optical system 16 is separated by the beam splitter 18, and the wavelength and output level of the LD output light are detected by the monitor 19 including a wavelength filter, a photodiode, and the like (not shown). Is done.

  In the above configuration, since the wavelength tunable light source 15 has one output, it has two outputs by the polarization maintaining coupler. However, in such a configuration, a branching loss occurs in the polarization maintaining coupler. Therefore, in order to compensate for the branching loss, the drive current density of the SOA (not shown) provided on the output side of the wavelength tunable light source is increased. Although it is necessary to increase the output of LD output light from the wavelength tunable light source 15, this causes an increase in power consumption and laser oscillation line width. Further, since the polarization maintaining coupler is used, the mounting area is also increased.

<Embodiment 1>
<Device configuration>
FIG. 1 is a plan view showing an example of the configuration of a wavelength tunable light source 100 according to Embodiment 1 of the present invention. As shown in FIG. 1, a wavelength tunable light source 100 includes a DFB-LD array 2 configured by integrating 12 DFB-LD1s (semiconductor lasers), 12 × 2 having 12 inputs and 2 outputs. -It is connected to the MMI input waveguide 4 of the MMI 21 (optical coupling circuit). That is, each of the 12 DFB-LDs 1 is connected to the input ends of the 12 MMI input waveguides 4. The twelve DFB-LDs 1 can perform single mode oscillation at different wavelengths.

  The 12 × 2-MMI 21 has 12 input portions IP and 2 output portions OP, and the output ends of 12 MMI input waveguides 4 are connected to the 12 input portions IP, respectively. The input ends of the two MMI output waveguides 5 are connected to each of the output parts OP of each of the optical output units OP, and the LD output light input from each MMI input waveguide 4 is combined, and the combined LD output light is guided to the MMI output guide. Output to the waveguide 5.

  The output ends of the two MMI output waveguides 5 are connected to the input ends of the same waveguide-type SOAs 22 and 23 (optical amplifiers), respectively, and the optical outputs 251 (first output) from the output ends of the SOAs 22 and 23, respectively. Optical output) and optical output 252 (second optical output) are output to the outside. A current can be individually applied to each of the SOAs 22 and 23. This will be described later.

  Here, the output ends of the SOAs 22 and 23 can be referred to as the output ends of the first and second output units of the wavelength tunable light source 100, and the first and second outputs from the input ends of the two MMI output waveguides 5. The traveling paths of light to the output end of the unit are referred to as first and second arm units, respectively.

  The two MMI output waveguides 5 expand in a direction away from each other so that the interval between the output ends is wider than the interval between the input ends connected to the two output units OP of 12 × 2-MMI 21. It is provided to have a shape. The input ends of the SOAs 22 and 23 are connected to the output ends of the two MMI output waveguides 5, so that the interval SD (arrangement interval) between the SOAs is equal to that of the two MMI output waveguides 5. It is wider than the input end interval MD. This can be said in other words that the first and second arm portions have an interval wider than the input end interval MD of the two MMI output waveguides 5. In FIG. 1, the input end interval MD of the two MMI output waveguides 5 is shown as the distance between the inner outer edges, but may be the distance between the outer outer edges or the center of each. It may be the distance between. The same applies to the interval SD between SOAs. In FIG. 1, the output end interval d of the SOAs 22 and 23 is shown as the distance between the inner outer edges, but may be the distance between the outer outer edges or the distance between the centers. good.

  The SOAs 22 and 23 are configured to have a straight line portion that maintains the distance SD and a bent portion that curves in a direction in which the first and second output portions approach each other. Note that the shape of the bent portion is not limited as long as the first and second output portions bend in a direction in which the first and second output portions approach each other.

  Further, for example, the SOA 22 and the SOA 23 may have different lengths, such as changing the position of the input end of the SOA 22 to shorten the SOA length. In this way, the SOAs 22 and 23 are provided so as to have a bent portion that curves in a direction in which the first and second output portions approach each other, and therefore the output end interval d of the SOAs 22 and 23 is set to the SOA. It can be narrower than the interval SD.

  By adopting such a configuration, even when the interval between the SOAs is widened, the output end interval d of the SOAs 22 and 23 can be reduced, and the light coupling efficiency to the lens can be improved. it can. This will be described later.

  Further, the SOA may have a curved shape having no straight portion, like the SOAs 22A and 23A of the wavelength tunable light source 100A shown in FIG. 2, and the MMI output waveguide 5A may have a curved shape corresponding thereto. In this case, the curved SOAs 22A and 23A are arranged so that the peaks of the respective curves face outward, and the peak interval is defined as the interval SD between the SOAs. In FIG. 4, the SOA interval SD is shown as the distance between the inner outer edges of the SOAs 22A and 23A, but may be the distance between the outer outer edges of the SOAs 22A and 23A, or the SOAs 22A and 23A. It is good also as the distance between each center.

  Next, a method for forming the SOAs 22 and 23 will be described. First, the two MMI output waveguides 5 are formed so as to reach the edge of the InP substrate 40 on the light output side. At this stage, the portion where the SOAs 22 and 23 are formed is also the MMI output waveguide 5.

  Thereafter, a predetermined portion of the MMI output waveguide 5, that is, a portion where the SOAs 22 and 23 are formed is removed by etching until reaching the InP substrate 40, and then the InP lower cladding layer 41, by a regrowth technique called butt joint growth. An InP current blocking layer 44, an InGaAsP active layer 45, an InP upper cladding layer 43, and an InGaAsP contact layer 46 are formed, and a cross section of the MMI output waveguide 5 (that is, a cross section of the InGaAsP waveguide layer 42) and a cross section of the SOAs 22 and 23 (that is, The cross section of the InGaAsP active layer 45 is directly bonded. Thereafter, an electrode 47 is formed on the InGaAsP contact layer 46. Here, the butt joint growth is a technique for forming a structure called a butt joint in which different layers such as a waveguide layer and an active layer are joined together.

  In order to suppress the generation of reflected return light at the output ends of the SOAs 22 and 23, the output end faces of the SOAs 22 and 23 are provided with a non-reflective coating (not shown), thereby suppressing the generation of reflected return light. By doing so, an increase in the laser oscillation line width can be suppressed.

  The configurations of the MMI input waveguide 4 and the MMI output waveguide 5 are the same as those shown in FIG. 27, and the configurations of the DFB-LD 1 and the SOAs 22 and 23 are the same as those shown in FIG. Is omitted.

<Operation>
Next, the operation of the wavelength tunable light source 100 will be described. When an arbitrary one DFB-LD1 is selected and current injection equal to or greater than the threshold current is performed, laser oscillation occurs in the selected DFB-LD1. The LD output light output from the DFB-LD 1 is input to the multi-mode region of 12 × 2-MMI 21 via the MMI input waveguide 4.

  If the 12 × 2-MMI 21 is appropriately designed, 1/12 of the LD output light output from the DFB-LD 1 is coupled to each of the two MMI output waveguides 5 over the entire wavelength band. Become. Note that when a plurality of DFB-LD1s are selected and each of them is injected with a current exceeding the threshold current, laser oscillation occurs in each selected DFB-LD1, and the LD output light outputted from each DFB-LD1 is Then, it is input to the multi-mode region of 12 × 2-MMI 21 through the MMI input waveguide 4 and is combined, and the combined LD output light is output to the MMI output waveguide 5. In this case, if the number of selected DFB-LDs is N, N / 12 of the LD output light is coupled to the two MMI output waveguides 5 respectively.

  Therefore, even if two MMI output waveguides 5 are provided, it is not necessary to increase the drive current density compared to the DFB-LD 1 according to the base technology. In other words, the driving current density of the DFB-LD1 is almost the same as that of the base technology.

  When current injection is performed on the SOAs 22 and 23, the LD output light traveling through each MMI output waveguide 5 is amplified, and when the current value is increased, the amplification factor in the SOAs 22 and 23 also increases. The amplification factor is expressed by logarithmically expressing the output light intensity based on the input light, but generally exhibits a nonlinear characteristic. That is, when the input light is weak (low output), the amplification factor is substantially constant, but when the input light is strong (high output), the amplification factor decreases, so the maximum output tends to saturate as the input light intensity increases. .

  The saturation output per unit length of the SOAs 22 and 23 is determined by the optical confinement coefficient and current density of the active layers of the SOAs 22 and 23 (corresponding to the InGaAsP active layer 45 in FIG. 28). Therefore, if the optical confinement coefficients and current densities of the active layers of the SOAs 22 and 23 are the same, the maximum outputs of the SOAs 22 and 23 are determined by the lengths of the SOAs 22 and 23.

  The optical outputs 251 and 252 output from the respective output ends of the SOAs 22 and 23 are coupled to a two-core fiber (not shown) through a lens system (not shown), but as shown in FIG. The output end interval d must be close to several tens of μm. That is, the lens constituting the lens system described above has spherical aberration, and the focal position is slightly different between light passing near the center of the lens and light passing through a position away from the center, and the coupling efficiency deteriorates due to spherical aberration. For this reason, the output end interval d is close to several tens of μm. If the coupling efficiency is poor, it is necessary to increase the drive current density of the LD or SOA in order to obtain a desired light output, resulting in an increase in power consumption.

  Therefore, as shown in FIG. 1, the SOAs 22 and 23 have a bent portion, and each output portion is bent in a direction approaching each other. Further, the two MMI output waveguides 5 move away from each other so that the intervals between the output ends are wider than the intervals between the input ends connected to the two output portions OP of 12 × 2-MMI 21. It is provided so as to have a shape that spreads out. As a result, the distance between the input ends MD of the two MMI output waveguides 5 and the distance SD between the SOAs 22 and 23 are wider than the distance between the SOAs SD, and a good coupling efficiency is obtained. Thermal crosstalk between SOAs can be suppressed.

  For example, in a Mach-Zehnder interferometer, a pair of arm portions having a relatively wide interval is narrowed to a few μm by a curved waveguide and multiplexed by MMI or the like to output light. In the present invention, the output end interval d is several tens of μm, whereas the Mach-Zehnder interferometer is close to several μm in order to cause light to interfere with MMI or the like. Further, in the Mach-Zehnder interferometer, the light output is turned on / off by the effect of light interference by controlling the phase of the light passing through the arm portion with a heater or the like, whereas the present invention does not cause light interference, Like the optical outputs 251 and 252, the light output from each arm unit is directly used, which is different from the Mach-Zehnder interferometer.

  In the Mach-Zehnder interferometer, the phase is controlled by changing the refractive index of light in one arm part by heating the heater, and the action of heat is actively taken in, so the other arm part is also heated. Propagates and affects the characteristics. In the present invention, attention is paid to the possibility that heat is generated when a current is applied to the SOA to amplify the light, and the heat interferes with the SOA of the adjacent arm portion, and a configuration that can reduce the heat interference is adopted. Yes.

  That is, if the interval SD between the SOAs is set to the same level as the output end interval d, the interval SD between the SOAs becomes relatively narrow, and thermal crosstalk occurs between the SOAs. The amplification factor of the SOA has temperature dependence, and the amplification factor decreases as the temperature increases.

  When both transmitting and receiving light is required in the wavelength division multiplexing communication system, it is necessary to apply current to both the SOAs 22 and 23. However, due to thermal crosstalk at that time, the transmitting side and the receiving side are required. Both may reduce the light output. When thermal crosstalk occurs, the power consumption increases if the drive current density of the LD or SOA is increased in order to suppress a decrease in light output.

  However, by adopting a configuration in which the interval SD between the SOAs 22 and 23 is larger than the input end interval MD of the two MMI output waveguides 5 and the output end interval d of the SOAs 22 and 23 as in the present embodiment, The interval SD becomes relatively wide, thermal crosstalk between SOAs can be suppressed, and power consumption can be reduced.

  Further, in order to keep the temperature of the wavelength tunable light source constant, temperature control is usually performed by a Peltier element or the like. That is, as shown in FIG. 3, temperature control is performed by adopting a configuration in which the wavelength tunable light source 100 is mounted on a heat conductor 61 such as a metal plate or a submount, and the heat conductor 61 is mounted on a Peltier element 62. . FIG. 4 is a plan view of a configuration in which the wavelength tunable light source 100 is mounted on the Peltier element 62 as viewed from the wavelength tunable light source 100 side. FIG. 3 corresponds to a cross section taken along the line AA in FIG.

  As described above, when the temperature is controlled from the lower side of the InP substrate 40, the lower surface of the InP substrate 40 has a substantially constant temperature. However, for example, heat generated from the SOA 23 and diffused in the horizontal direction of the InP substrate 40 reaches the SOA 22 to generate thermal crosstalk. On the other hand, the heat diffused in the vertical direction reaches the lower surface of the InP substrate 40 and is absorbed by temperature control.

  Therefore, with respect to the heat diffused in the horizontal direction of the InP substrate 40, the thermal crosstalk is reduced as the distance SD between the SOAs is increased, and the heat diffused in the vertical direction of the InP substrate 40 is reduced. As the substrate thickness h is reduced, the effect of heat absorption by temperature control is increased, and thermal crosstalk is reduced.

  When the relationship between the spacing SD between the SOAs and the substrate thickness h is SD = h, for example, the amount of heat generated from the SOA 23 and diffused in the horizontal direction of the InP substrate 40 to reach the SOA 22, and the amount of heat generated from the SOA 23 and the InP substrate 40 The amount of heat that diffuses vertically and reaches the lower surface of the substrate is at the same level.

  Here, under the condition of SD> h, the effect of heat absorption by temperature control is increased, so that thermal crosstalk is suppressed. Therefore, it is desirable to configure so that the condition of SD> h is satisfied. For example, when the substrate thickness h is 100 μm, it is desirable that the interval SD between the SOAs exceeds 100 μm.

  As described above, according to the wavelength tunable light source 100 of the first embodiment, the thermal crosstalk between the SOAs can be suppressed and the power consumption can be reduced.

<Embodiment 2>
In the wavelength tunable light source 100 of the first embodiment described above, the interval SD between the SOAs is made larger than the input end interval MD of the two MMI output waveguides 5 and the output end interval d of the SOAs 22 and 23. By adopting this, thermal crosstalk between SOAs was suppressed. However, in the wavelength tunable light source 100 of the second embodiment, the SOA has a multi-stage configuration, and the SOA including the output unit reduces thermal crosstalk by reducing the drive current density. Further suppress.

<Device configuration>
FIG. 5 is a plan view showing an example of the configuration of the wavelength tunable light source 200 according to Embodiment 2 of the present invention. The difference from the wavelength tunable light source 100 of the first embodiment is that the SOA is a two-stage type.

  The output ends of the two MMI output waveguides 5 are connected to the input ends of the same waveguide type SOAs 221 and 231, respectively. The SOAs 221 and 231 are connected in series to the SOAs 222 and 232 via the SOA connection waveguide 24, respectively. The optical outputs 251 and 252 are output from the output ends of the SOAs 222 and 232, respectively.

  Here, the output ends of the SOAs 222 and 232 can be referred to as the output ends of the first and second output units of the wavelength tunable light source 200, and the first and second outputs from the input ends of the two MMI output waveguides 5. The traveling paths of light to the output end of the unit are referred to as first and second arm units, respectively.

  The SOAs 221, 222, 231, and 232 are each provided with a configuration in which the electrodes 47 shown in FIG. That is, the SOAs 221 and 222 have the same cross-sectional structure, but the SOA connection waveguide 24 at the boundary between the SOAs 221 and 222 has no electrodes, and the respective electrodes of the SOAs 221 and 222 are electrically separated. Independent current control is possible. Similarly, the SOA connection waveguide 24 at the boundary between the SOAs 231 and 232 does not have electrodes, and the electrodes of the SOAs 231 and 232 are electrically separated so that independent current control is possible. . The length of the SOA connection waveguide 24 is about several μm.

  The SOA connection waveguide 24 may have a configuration in which the electrode 47 is omitted from the same configuration as the LD or SOA (see FIG. 28), or the same configuration as the MMI input waveguide 4 or the MMI output waveguide 5 (see FIG. 27). Also good. The former is desirable in order to suppress the reflected return light from the connecting portion. When the current is not injected into the SOA connection waveguide 24 in the former configuration, if the length of the SOA connection waveguide 24 is several hundred μm, a transmission loss of several dB or more occurs. However, as described above, it is about several μm. In this case, almost no transmission loss occurs and it can be used without any problem.

  When the SOA connection waveguide 24 is configured as shown in FIG. 27, a predetermined portion of the MMI output waveguide 5, that is, a portion where the SOAs 221, 222, 231 and 232 other than the portion where the SOA connection waveguide 24 is formed is formed. The InP lower clad layer 41, the InP current blocking layer 44, the InGaAsP active layer 45, the InP upper clad layer 43, and the InGaAsP contact layer 46 are formed by butt joint growth, and are removed by etching until reaching the InP substrate 40. The cross section of the waveguide 5 (ie, the cross section of the InGaAsP waveguide layer 42) and the cross sections of the SOAs 221, 222, 231 and 232 (ie, the cross section of the InGaAsP active layer 45) are directly joined.

  As a result, the MMI output waveguide 5 and the SOAs 221 and 231 are butt jointed, the SOAs 221 and 231 and the SOA connection waveguide 24 are butt jointed, and the SOAs 222 and 232 and the SOA connection waveguide 24 are butt jointed. .

  When the SOA connection waveguide 24 is configured by omitting the electrodes from the configuration of FIG. 28, the SOA 221 and 222 including a predetermined portion of the MMI output waveguide 5, that is, a portion where the SOA connection waveguide 24 is formed. After the portions where 231 and 232 are formed are removed by etching until reaching the InP substrate 40, the InP lower cladding layer 41, the InP current blocking layer 44, the InGaAsP active layer 45, the InP upper cladding layer 43, the InGaAsP are grown by butt joint growth. A contact layer 46 is formed, and the cross section of the MMI output waveguide 5 (ie, the cross section of the InGaAsP waveguide layer 42) and the cross sections of the SOAs 221, 222, 231 and 232 (ie, the cross section of the InGaAsP active layer 45) are directly joined. . Thereafter, when the electrode 47 is formed on the InGaAsP contact layer 46, the electrode 47 may not be formed on the SOA connection waveguide 24.

  Further, in order to suppress the generation of reflected return light at the output ends of the SOAs 222 and 232, a non-reflective coating (not shown) is applied to the output end surfaces of the SOAs 222 and 232 to suppress the generation of reflected return light. By doing so, an increase in the laser oscillation line width can be suppressed.

  The configurations of the MMI input waveguide 4 and the MMI output waveguide 5 are the same as those shown in FIG. 27, and the configurations of the DFB-LD1, the SOAs 221, 222, 231 and 232 are the same as those shown in FIG. The overlapping description is omitted.

<Operation>
Next, the operation of the wavelength tunable light source 200 will be described. When current is injected into the SOAs 221 and 222, the LD output light traveling through the MMI output waveguide 5 is first amplified in the SOA 221, and the light amplified in the SOA 221 is further amplified in the subsequent SOA 222 and output as the optical output 251. The

  Further, when current is injected into the SOAs 231 and 232, the LD output light traveling through the MMI output waveguide 5 is first amplified in the SOA 231 and the light amplified in the SOA 231 is further amplified in the subsequent SOA 232 as an optical output 252. Is output.

  Here, if the drive current density applied to each SOA is the same as the current density of the SOA in the first embodiment, thermal crosstalk between the SOAs occurs in the vicinity of the output ends of the SOAs 222 and 232, resulting in power consumption. May increase.

  Therefore, in controlling the wavelength tunable light source 200, the SOA 222 and 232 have a drive current density smaller than that of the SOAs 221 and 231, thereby suppressing thermal crosstalk near the output end and suppressing an increase in power consumption. It becomes. In FIG. 5, the SOA having a large drive current density is provided with dark hatching, and the SOA having a low drive current density is provided with thin hatching.

  In the above description, the current density of both the SOAs 222 and 232 is reduced. However, the current density of only the SOA including the output part in one arm part, for example, the SOA 222 may be reduced. When such control is performed, the optical output 251 is smaller than the optical output 252, but there is no problem if the optical output 251 is used for reception and the optical output 252 is used for transmission.

<Modification 1>
Further, the number of stages of the SOA is not limited to two, but may be a three-stage type as in the wavelength tunable light source 200A shown in FIG.

  That is, the output ends of the two MMI output waveguides 5 are respectively connected to the input ends of SOAs 223 and 233 which are the same waveguide type first stage optical amplifiers, and the SOAs 223 and 233 are respectively connected via the SOA connection waveguide 24. The SOAs 221 and 231 are connected in series. Further, the SOAs 221 and 231 are connected in series with the SOAs 222 and 232 via the SOA connection waveguide 24, respectively, and the optical outputs 251 and 252 are output from the output ends of the SOAs 222 and 232, respectively. ing.

  The SOAs 221, 222, 223, 231, 232, and 233 are each provided with a configuration in which the electrodes 47 shown in FIG. 28 are electrically separated from each other and can be controlled independently. That is, the SOAs 221, 222, and 223 have the same cross-sectional structure, but the SOA connection waveguide 24 has no electrodes, and the electrodes of the SOAs 221, 222, and 223 are electrically separated and independent. The current control is possible. Similarly, the respective electrodes of the SOAs 231, 232 and 233 are electrically separated so that independent current control is possible.

  The two MMI output waveguides 5 have the same length of several μm as the SOA connection waveguide 24, and have the same distance between the input end and the output end. However, the SOAs 223 and 233 have the same input end. And the input ends of the SOAs 221 and 231 are connected to the respective output ends, so that the interval SD between the SOAs is the input end of the two MMI output waveguides 5. It is wider than the interval. This can be said in other words that the first and second arm portions have an interval wider than the input end interval MD of the two MMI output waveguides 5.

  In the case of adopting such a configuration, in the control of the wavelength tunable light source 200A, the current density of the SOAs 222, 223, 232 and 233 is made smaller than that of the SOAs 221 and 231, so Thermal crosstalk is suppressed, and an increase in power consumption can be suppressed. In FIG. 5, the SOA having a large drive current density is provided with dark hatching, and the SOA having a low drive current density is provided with thin hatching.

  In addition, compared with the tunable light source 200 using the two-stage SOA, the total SOA length is increased and the optical output is increased by replacing most of the MMI output waveguide 5 with the SOAs 223 and 233. It becomes possible.

  In the above description, the example in which the current density of the SOAs 222, 232, 223, and 233 is reduced has been described. However, as shown in FIG. 7, for example, only the SOAs 222 and 223 reduce the current density, and the SOAs 232 and 233 reduce the current density. You can make it as big as. In FIG. 7, the SOA having a large drive current density is darkly hatched, and the SOA having a small drive current density is thinly hatched.

  When such control is performed, the optical output 251 is smaller than the optical output 252, but there is no problem if the optical output 251 is used for reception and the optical output 252 is used for transmission.

  Further, when the current densities of the SOAs 222 and 233 are reduced and the current densities of the other SOAs are increased, the optical outputs 251 and 252 are approximately the same.

<Modification 2>
Further, as a second modification of the second embodiment, as in the wavelength tunable light source 200B shown in FIG. 8, the SOA of one arm may be a single-stage type, and the SOA of the other arm may be a two-stage type.

  That is, as shown in FIG. 8, the output ends of the two MMI output waveguides 5 are respectively connected to the input ends of the same waveguide type SOAs 221 and 23, and the SOA 221 is connected to the SOA 222 via the SOA connection waveguide 24. Are connected in series, and the optical output 251 is output to the outside from the output end of the SOA 222. However, since the SOA 23 is a single-stage type, the optical output 252 is output to the outside from the output end of the SOA 23. ing.

  Here, the output ends of the SOAs 222 and 23 can be referred to as the output ends of the first and second output portions of the wavelength tunable light source 200B, and the first and second outputs from the input ends of the two MMI output waveguides 5 can be said. The traveling paths of light to the output end of the unit are referred to as first and second arm units, respectively.

  In the case of adopting such a configuration, in the control of the wavelength tunable light source 200B, if the current density of the SOA 222 is made smaller than the SOAs 221 and 23, the optical output 251 becomes smaller than the optical output 252 but the optical output 251 is received. If the optical output 252 is used for transmission, there is no problem.

  Hereinafter, the control of the wavelength tunable light source 200 according to the second embodiment will be further described. For example, the current density of each SOA can be controlled by using a current controller 70 as shown in FIG. That is, by applying different currents from the current controller 70 via the wirings W221 and W222 electrically connected to the respective electrodes 47 (FIG. 28) of the SOAs 221 and 222, the current density of the SOA is controlled. Light can be amplified. Similarly, the current controller 70 controls the current density of the SOA by applying different currents from the current controller 70 via the wirings W231 and W232 electrically connected to the respective electrodes 47 (FIG. 28) of the SOAs 231 and 232. Thus, light can be amplified. Such a wavelength tunable light source 200 and the current controller 70 constitute a part of the wavelength tunable light source module.

  Further, the control of the wavelength tunable light source 200A according to the first modification of the second embodiment will be described. For example, by using a current controller 71 as shown in FIG. 10, the current density of each SOA can be controlled. . That is, by applying different currents from the current controller 71 via the wirings W223, W221 and W222 electrically connected to the respective electrodes 47 (FIG. 28) of the SOAs 223, 221 and 222, the current of the SOA Light can be amplified by controlling the density.

  Similarly, by applying different currents from the current controller 71 via the wirings W233, W231 and W232 electrically connected to the respective electrodes 47 (FIG. 28) of the SOAs 233, 231 and 232, Light can be amplified by controlling the current density. Moreover, the control demonstrated using FIG. 7 is also possible by using the current controller 71 shown in FIG. The tunable light source 200A and the current controller 71 constitute a part of the tunable light source module.

  Note that the control of the wavelength tunable light source 200B of the second modification of the second embodiment can also be controlled by using the current controller 70 shown in FIG. 9, and each of the SOAs 221 and 222 is controlled from the current controller 70. By applying different currents through the wirings W221 and W222 electrically connected to the electrode 47 (FIG. 28), the current density of the SOA can be controlled to amplify the light. ) Electrode 47 (FIG. 28), for example, by applying a current from the current controller 70 via the wiring W231, the current density of the SOA can be controlled to amplify the light.

  As described above, according to the wavelength tunable light source 200 of the second embodiment and the wavelength tunable light sources 200A and 200B of the modifications 1 and 2, the thermal crosstalk between the SOAs is further suppressed, and the power consumption is further reduced. It becomes possible.

<Embodiment 3>
In the wavelength tunable light source 200 according to Embodiment 2 described above, the configuration in which the SOA is further configured to further suppress the thermal crosstalk has been described. However, the SOA in the multi-stage configuration turns on the optical output by the SOA in the subsequent stage. It is possible to turn it off.

  That is, as described with reference to FIG. 5, when current is injected into the SOA 221 and the SOA 222, the LD output light traveling through the MMI output waveguide 5 is amplified in the SOA 221 and the LD output light amplified in the SOA 221 is amplified in the SOA 222. Further amplified and output as an optical output 251. The same applies to the arm portion on one side having the SOAs 231 and 232.

  Here, when current is injected into the SOA 221, but current is not injected into the SOA 222, the LD output light is absorbed in the SOA 222 and the optical output 251 is not output.

  As described above, the SOA 222 as the latter stage (final stage) has a function (shutter function) for turning on and off the light output in addition to the function for amplifying the LD output light. The same applies to the SOA 232 in the arm portion on one side, and the light output from the MMI output waveguide 5 can be turned on and off by the SOA that is the subsequent stage (final stage).

  In such a configuration, when one arm part performs ON / OFF control that repeats on and off, and the other arm part is always used in an on state, heat fluctuation due to the ON / OFF control occurs in one arm part. When this occurs and reaches the other arm part, not only the optical output of the other arm part fluctuates, but also the oscillation wavelength may fluctuate due to the heat reaching the DFB-LD.

  Therefore, as shown in FIG. 11, as a control method of the wavelength tunable light source 200 according to the present invention, the SOAs 221 and 231 at the previous stage always inject current regardless of whether the optical output is ON / OFF controlled. When the ON state is turned on and ON / OFF control is performed, the SOA 222 and 232, which are the subsequent stages, are turned on and off to suppress heat fluctuations and to suppress fluctuations in optical output and oscillation wavelength.

  FIG. 12 is a diagram showing the wavelength variation characteristics of the transmission output when the reception output is turned on. The horizontal axis represents the time axis, and the vertical axis represents the wavelength variation of the transmission output. In FIG. 12, the characteristics of the one-stage SOA shown in FIG. 1 are indicated by broken lines, and the characteristics of the two-stage SOA shown in FIG. 11 are indicated by solid lines.

  As shown in FIG. 12, the wavelength of the transmission output starts to change by turning on the reception output. However, by monitoring the wavelength and controlling the temperature of the DFB-LD, the wavelength fluctuation is zero with time. Become. Compared with the case of the one-stage SOA shown in FIG. 1, in the configuration of the two-stage SOA shown in FIG. 11, the front-stage SOA is always in an on state by injecting current and is turned on / off by the rear-stage SOA. It can be seen that the wavelength variation of the transmission output is suppressed by performing the OFF control.

  FIG. 13 is a diagram showing the fluctuation characteristics of the output intensity of the transmission output when the reception output is turned on. The horizontal axis represents the time axis and the vertical axis represents the fluctuation of the output intensity of the transmission output. Show. In FIG. 13, the characteristics of the one-stage SOA shown in FIG. 1 are indicated by broken lines, and the characteristics of the two-stage SOA shown in FIG. 11 are indicated by solid lines.

  As shown in FIG. 13, when the reception output is turned on, the output intensity of the transmission output starts to fluctuate. However, by monitoring the wavelength and controlling the temperature of the DFB-LD, the output fluctuation is zero with time. It becomes. Compared with the case of the one-stage SOA shown in FIG. 1, in the configuration of the two-stage SOA shown in FIG. 11, the front-stage SOA is always in an on state by injecting current and is turned on / off by the rear-stage SOA. It can be seen that the output fluctuation of the output for transmission is suppressed by performing the OFF control.

  The control method of the third embodiment will be further described. For example, by using a current controller 70 as shown in FIG. 9, the current density of each SOA can be individually controlled.

  That is, when the optical output is continuously performed, current is applied to all of the SOAs 221, 222, 231, and 232 from the current controller 70 via the wirings W 221, W 222, W 231, and W 232 to turn them on. The light is amplified by controlling the density. When switching on / off the optical output, switching can be performed by applying or blocking current from the current controller 70 to the subsequent SOAs 222 and 232 via the wirings W222 and W232, respectively. .

  The light output can be switched on and off in a predetermined cycle (msec or μsec order) at a timing that does not hinder reception / transmission, and during reception and transmission, It is also possible to perform ON / OFF control only for the arm portion used for the person who is not executing. Also, when the output wavelength fluctuation and output intensity fluctuation are suppressed (when stabilized) as shown in FIG. 12 and FIG. 13 by switching the optical output on and off, the ON / OFF control is canceled and the output is always on. It is also possible to control the state.

<Embodiment 4>
FIG. 14 is a plan view showing a configuration of a wavelength tunable light source 100C according to Embodiment 4 of the present invention. As shown in FIG. 14, in the wavelength tunable light source 100C, each of the first arm portion (configured by the MMI output waveguide 5 and the SOA 22) and the second arm portion (configured by the MMI output waveguide 5 and the SOA 23) are provided. Thus, the absorption layer 80 is provided.

  Absorbing layer 80 is provided in a region between the first and second arm portions, and emits light in a planar direction (a direction parallel to the main surface of substrate 40) from the first and second arm portions. It is the structure which absorbs.

  When radiated light is generated from the first and second arm portions and propagates through the wavelength tunable light source 100C, the light returns to the DFB-LD array 2 and the laser oscillation line width, which is an indicator of phase stability, deteriorates. End up.

  As described above, in a wavelength division multiplexing communication system employing digital coherent communication, a narrow linewidth wavelength tunable light source is used as a light source for transmission and reception, and it is not desirable that the laser oscillation linewidth deteriorate (expand), Although it is required to suppress generation of radiated light from the arm portion, by providing the absorption layer 80, in the wavelength tunable light source 100C, the laser oscillation line width can be reduced from 600 kHz to 500 kHz.

  In FIG. 15, the arrow direction cross section in the BB line in FIG. 14 is shown. As shown in FIG. 15, the absorption layer 80 is provided on the InP lower cladding layer 41 in parallel with the InGaAsP active layer 45, and emits light emitted from the InGaAsP active layer 45 (schematically indicated by an arrow). Can be absorbed. The absorption layer 80 is provided in parallel with the InGaAsP waveguide layer 42 (FIG. 27) in a portion along the MMI output waveguide 5.

  The absorption layer 80 is composed of the same process and the same material (InGaAsP) as the InGaAsP active layer 45 and the InGaAsP waveguide layer 42 (FIG. 27). However, since no current is applied to the absorption layer 80, it is shown in FIG. As described above, the InGaAsP contact layer 46 and the electrode 47 are not provided above the absorption layer 80.

  14 shows a configuration in which the absorption layer 80 is provided in a region between the first and second arm portions, the absorption layer 80 is provided in a region outside the first and second arm portions. Alternatively, it may be provided in both the region between the first and second arm portions and the outer region. Moreover, it is good also as a structure which provided the absorption layer 80 along only one of the 1st and 2nd arm parts.

<Modification 1>
In the wavelength tunable light source 100C of the fifth embodiment described above, the absorption layer 80 is provided along each of the first and second arm portions. However, the absorption layer of the wavelength tunable light source 100D shown in FIG. Like 81, you may provide linearly so that it may extend over the whole extension area | region of the 1st and 2nd arm part in the intermediate part between the 1st and 2nd arm part. Also in this case, the emitted light in the planar direction from the first and second arm portions can be absorbed.

  In FIG. 17, the arrow direction cross section in CC line in FIG. 16 is shown. As shown in FIG. 17, the InGaAsP contact layer 46 and the electrode 47 are not provided above the absorption layer 81.

  The width of the absorption layer 81 may be increased to such a size that it does not contact the SOAs 22 and 23, that is, the same size as the interval SD between the SOAs.

<Modification 2>
In the wavelength tunable light source 100C of the fifth embodiment, the absorption layer 80 is provided along each of the first and second arm portions, but the wavelength tunable light source 100E shown in FIG. A groove TR may be provided as shown in FIG.

  As shown in FIG. 18, the wavelength tunable light source 100E has a configuration in which a groove TR is provided along each of the first and second arm portions.

  The trench TR is provided in a region between the first and second arm portions, and emits light emitted from the first and second arm portions in a plane direction (a direction parallel to the main surface of the substrate 40). It is configured to reflect and radiate outside the wavelength variable light source 100D. By providing the groove TR, the laser oscillation line width can be reduced from 600 kHz to 400 kHz.

  FIG. 19 shows a cross section taken along the line DD in FIG. As shown in FIG. 19, the trench TR passes through the electrode 47, the InGaAsP contact layer 46, the InP upper cladding layer 43, the InP current blocking layer 44, and the InP lower cladding layer 41, and exposes the main surface of the InP substrate 40. The radiated light from the InGaAsP active layer 45 (schematically indicated by arrows) can be reflected. The trench TR is provided in parallel with the InGaAsP waveguide layer 42 (FIG. 27) in a portion along the MMI output waveguide 5.

  Note that the trench TR can be formed by etching using an arbitrary mask pattern.

  FIG. 19 shows the configuration in which the groove TR is provided in the region between the first and second arm portions. However, the groove TR may be provided in the region outside the first and second arm portions. Alternatively, it may be provided in both the region between the first and second arm portions and the outer region. Moreover, it is good also as a structure which provided groove | channel TR along only one of the 1st and 2nd arm parts.

<Modification 3>
The wavelength tunable light source 100E of Modification 2 employs a configuration in which the groove TR is provided along each of the first and second arm portions. However, like the groove TR1 of the wavelength tunable light source 100F shown in FIG. You may provide linearly in the intermediate part between 1 and 2nd arm parts so that the whole extension area | region of 1st and 2nd arm parts may be covered. Also in this case, the emitted light from the first and second arm portions in the planar direction can be reflected.

  In FIG. 21, the arrow direction cross section in the EE line in FIG. 20 is shown. As shown in FIG. 21, the trench TR penetrates the electrode 47, the InGaAsP contact layer 46, the InP upper cladding layer 43, the InP current blocking layer 44, and the InP lower cladding layer 41, and exposes the main surface of the InP substrate 40. It is provided as follows.

  Note that the width of the trench TR1 may be increased to such a size that it does not contact the SOAs 22 and 23, that is, the same size as the interval SD between the SOAs.

<Embodiment 5>
In Embodiments 1 to 4 described above, an example in which a wavelength tunable light source is configured using DFB-LD is shown, but a wavelength tunable light source may be configured using DBR-LD. In the case of using DFB-LD, a plurality of DFB-LDs having different oscillation wavelengths are combined and temperature control is performed, but in the case of using DBR-LD, in the case of using DBR-LD, a single DBR-LD is used. On the other hand, by adjusting the current injection amount and controlling the equivalent refractive index of the DBR reflector, the wavelength can be varied.

  FIG. 22 is a plan view showing an example of the configuration of the wavelength tunable light source 300 according to Embodiment 5 of the present invention. The difference from the wavelength tunable light source 100 of the first embodiment is that the DFB-LD array 2 is DBR-LD51 and the 12 × 2 MMI 21 is 1 × 2 MMI 52. The other components that are the same as those in FIG. The description which overlaps is abbreviate | omitted.

  In the wavelength tunable light source 300, the light output from the DBR-LD 51 is branched into two by the 1 × 2 MMI 52, amplified by the SOA, and output.

  Similarly to the wavelength tunable light source 100, the wavelength tunable light source 300 employs a configuration in which the distance SD between the SOAs 22 and 23 is larger than the input end distance MD between the two MMI output waveguides 5 and the output end distance d between the SOAs 22 and 23. As a result, the interval SD between the SOAs becomes relatively wide, thermal crosstalk between the SOAs can be suppressed, and power consumption can be reduced.

<Modification 1>
Further, like the wavelength tunable light source 200 of the second embodiment, the SOA may be a two-stage type. FIG. 23 is a plan view showing an example of the configuration of a wavelength tunable light source 400 having a two-stage SOA. As shown in FIG. 23, the SOA is a two-stage type, and the SOA including the output section can further suppress thermal crosstalk by reducing the drive current density, thereby reducing power consumption and reducing power consumption.

<Modification 2>
Further, the number of stages of the SOA is not limited to two, but by adopting a three-stage type like the wavelength tunable light source 200A shown in FIG. 6, the SOA is near the output end and near the MMI output waveguide 5. Thermal crosstalk is suppressed, and an increase in power consumption can be suppressed.

<Application example to tunable light source module>
FIG. 24 shows a configuration in which the variable wavelength light source 100 according to Embodiment 1 shown in FIG. 1 is applied as a variable wavelength light source in the variable wavelength light source module 35. Other configurations and operations of the wavelength tunable light source module 35 are the same as those of the wavelength tunable light source module 9 described with reference to FIG. 30, and the same components are denoted by the same reference numerals and redundant description is omitted.

  As shown in FIG. 24, the wavelength tunable light source module 35 includes two optical fibers 17 as output ports. The optical outputs 251 and 252 (FIG. 1) emitted from the wavelength tunable light source 100 are coupled to the two optical fibers 17 via the coupling optical system 16 and are used as the transmission optical output 7 and the reception optical output 13, respectively. be able to.

  24 shows an example in which two optical fibers are applied to the output port, a two-core fiber having two cores in one optical fiber may be applied. By doing so, only one optical fiber is required to adjust the core position, and the assembly time can be reduced. The tip of the two-core fiber is branched into two without loss and taken out as a transmission light output and a reception light output.

  In the above description, the example in which the wavelength tunable light source 100 of FIG. 1 is applied as the wavelength tunable light source has been shown. However, as the wavelength tunable light source, FIGS. 2, 5 to 8, 14, 16, 18, 20. , 22 and 23 may be applied.

  According to the wavelength tunable light source module 35 described above, since two optical outputs are emitted from the wavelength tunable light source 100 and coupled to the output port, a polarization maintaining coupler having a branching loss is not required, and the drive current density of the SOA The power consumption can be reduced and the space can be saved as compared with the case where the polarization maintaining coupler is provided.

<Application example to transmitter / receiver>
FIG. 25 shows a configuration in which the variable wavelength light source module 35 shown in FIG. 24 is applied as a light source module in the transmission / reception device 37.

  As shown in FIG. 25, the transmission / reception device 37 is configured such that the transmission optical output 7 output from the wavelength tunable light source module 35 is modulated based on the transmission data TD in the modulator module 10 and then transmitted to the outside as the transmission signal 11. Is output.

  The reception signal 12 received from the outside is input to the reception module 14 together with the reception light output 13 output from the wavelength variable light source module 35, demodulated after signal processing, and output from the reception module 14 as reception data RD. .

  As described above, the wavelength tunable light source module 35 can be used as a light source module for transmission and reception, and a polarization maintaining coupler is not required. Therefore, power consumption is reduced as compared with a transmission and reception apparatus using two wavelength tunable light source modules. In addition, space can be saved.

  It should be noted that the present invention can be freely combined with each other within the scope of the invention, and each embodiment can be appropriately modified or omitted.

  1 DFB-LD, 2 DFB-LD array, 21 12 × 2-MMI, 22, 23, 221, 222, 223, 231, 232, 233, 24 SOA connection waveguide, 251, 252 Optical output, 60, 61 Absorption Layer, TR, TR1 groove.

Claims (13)

An output end of at least one input waveguide is connected to the input section, an input end of two output waveguides is connected to the output section, and light input from the at least one input waveguide is transmitted to the two output waveguides. An optical coupling circuit that outputs to
A semiconductor laser connected to an input end of the at least one input waveguide;
First and second optical amplifiers respectively connected to output ends of the two output waveguides;
A first and a second output unit for outputting light via the first and second optical amplifiers, respectively,
A first arm portion constituting a traveling path of light reaching one of the two output waveguides from the one of the two output waveguides via the first optical amplifier and the other of the two output waveguides. A second arm part that constitutes a traveling path of light reaching the second output part via two optical amplifiers, the distance between the input ends of the two output waveguides and the first and second output parts Having an arrangement interval wider than the output end interval of
Each of the first and second optical amplifiers has a bent portion that curves in a direction in which the first and second output portions approach each other, and each of the first and second optical amplifiers has an output end from the output ends of the first and second output portions. A tunable light source that outputs light.   The tunable light source according to claim 1, wherein at least one of the first and second optical amplifiers has a multistage configuration in which a plurality of individually controllable optical amplifiers are connected in series. The two output waveguides are provided such that the output end interval is wider than the input end interval,
Of the first and second optical amplifiers, one final-stage optical amplifier having the multi-stage configuration and the other optical amplifier of the first and second optical amplifiers are the first and second optical amplifiers. The wavelength tunable light source according to claim 2, wherein each of the output portions has a bent portion that curves in a direction approaching each other. The two output waveguides are provided such that the input end interval and the output end interval are the same,
The first and second optical amplifiers have the multistage configuration,
3. The variable wavelength light source according to claim 2, wherein the first-stage optical amplifiers of the first and second optical amplifiers are provided so that an output end interval is wider than an input end interval thereof. The wavelength tunable light source is formed on a semiconductor substrate,
The wavelength tunable light source according to claim 1, wherein the arrangement interval is set wider than the thickness of the semiconductor substrate. The wavelength tunable light source is
Formed in a semiconductor laminated film laminated on a semiconductor substrate,
An absorption layer that is provided along at least one of the first and second arm portions and absorbs light emitted from the first and second arm portions;
The variable wavelength light source according to claim 1, wherein the absorption layer is made of the same material and in the same layer as the first and second arm portions. The wavelength tunable light source is
Formed in a semiconductor laminated film laminated on a semiconductor substrate,
An intermediate portion between the first and second arm portions is linearly provided so as to extend over the entire extension region of the first and second arm portions, and from the first and second arm portions. Further comprising an absorption layer for absorbing radiation,
The variable wavelength light source according to claim 1, wherein the absorption layer is made of the same material and in the same layer as the first and second arm portions. The wavelength tunable light source is
Formed in a semiconductor laminated film laminated on a semiconductor substrate,
The wavelength tunable light source according to claim 1, further comprising a groove provided so as to reach the semiconductor substrate through the semiconductor multilayer film along at least one of the first and second arm portions. The wavelength tunable light source is
Formed in a semiconductor laminated film laminated on a semiconductor substrate,
An intermediate portion between the first and second arm portions is linearly provided so as to extend over the entire extension region of the first and second arm portions, and penetrates the semiconductor multilayer film to form the semiconductor. The wavelength tunable light source according to claim 1, further comprising a groove reaching the substrate. The tunable light source according to claim 2,
An optical amplifier current controller;
The first and second optical amplifiers have the multistage configuration,
The current controller is
In the first and second optical amplifiers, in the set of optical amplifiers in which the distance between the optical amplifiers is narrower than the arrangement interval, the drive current density is smaller than in the set of optical amplifiers that maintain the arrangement interval. A tunable light source module that controls the current. The tunable light source according to claim 2,
An optical amplifier current controller;
The first and second optical amplifiers have the multistage configuration,
The current controller is
In the first and second optical amplifiers, in a set of optical amplifiers in which the distance between the optical amplifiers is narrower than the arrangement interval, the drive current density of one of the optical amplifiers is an optical amplifier that maintains the arrangement interval. A wavelength tunable light source module that controls the current to be smaller than the driving current density of the set. The tunable light source according to claim 2,
An optical amplifier current controller;
At least one of the first and second optical amplifiers has the multistage configuration,
The current controller is
Of the first and second optical amplifiers, current control is performed to determine whether or not to inject current into the optical amplifier of the final stage having the multi-stage configuration. A tunable light source module that controls on / off of optical output. The tunable light source according to claim 1,
The first and second light outputs respectively output from the output terminals of the first and second output units are coupled to an optical fiber via a coupling optical system, and the first light output is transmitted to the transmission light. A wavelength tunable light source module having the output, the second optical output, and the receiving optical output.

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