JPH08167755A - Multi-channel optical signal generator - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a multi-channel optical signal generation method for oscillating optical signals having the same wavelength and synchronized phases. The optical output end faces of a single driving semiconductor laser and a plurality of semiconductor lasers having mutually identical oscillation wavelengths are optically made to correspond to a plurality of input / output ends of a multi-branching branch coupler. With connection, the mirror is optically faced to the other input / output end of the multi-branch branch coupler, and at least the other optical output end face of the semiconductor laser and the mirror constitute a composite resonator laser, An optical signal is emitted from the other optical output end face of each semiconductor laser biased with a direct current by modulation control of the driving semiconductor laser, and the optical signal is sent to an optical fiber arranged corresponding to the semiconductor laser.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-channel optical signal generator for distributing and transmitting optical signals having the same wavelength and synchronized phases in a large number of channels in optical communication and the like.

[0002]

2. Description of the Related Art As a multi-channel optical signal generator,
When the existing components are combined, a configuration in which a single high-power semiconductor laser 1 and a 1 × N star coupler 2 are optically connected as shown in FIG. 5 and each semiconductor laser control as shown in FIG. A configuration in which a plurality of semiconductor lasers 7 that can be individually driven by the device 5 and the output-side optical fiber 4 are optically connected can be considered.

In the former multi-channel optical signal generator shown in FIG. 5, a set of signal generators 6 and a semiconductor laser control device 5 are combined, and the semiconductor laser control device 5 allows direct modulation at several GHz. The high output semiconductor laser 1 of 100 mW is controlled to send the optical output (optical signal) 8 emitted from the high output semiconductor laser 1 to the single input side optical fiber 3 of the star coupler 2 and the star coupler 2
Are output from a plurality (N, here N = 4) of output side optical fibers 4 and distributed to a large number of channels. A current pulse having a rise of several hundred psec and a peak current of several hundred mA (DC conversion) required for direct modulation is supplied by an integrated circuit (IC) which receives a high-speed voltage pulse and converts it into a current pulse. The distributed optical output (optical signal 8) is determined by the coupling efficiency between the high-power semiconductor laser 1 and the star coupler 2, the excess loss of the star coupler, the branch loss, and the like.

In the latter multi-channel optical signal generator shown in FIG. 6, the electric signal from the signal generator 6 is divided into a large number of channels, and each semiconductor laser 7 is individually divided by the divided signals. The semiconductor laser controller 5 drives the semiconductor laser 7 to send an optical signal 8 from each semiconductor laser 7 to the output side optical fiber 4 optically connected to each semiconductor laser 7.

[0005]

In the former structure using a high-power semiconductor laser and a star coupler (multi-branch branch coupler), the peak intensity of the signal light before division is very large, and therefore the star coupler is absorbed due to absorption or the like. May be destroyed. Further, if dust or the like adheres between the semiconductor laser and the star coupler, it may be oxidized or adhered by the signal light, and the coupling efficiency may be significantly deteriorated.

In the latter structure in which a plurality of semiconductor lasers are arranged in parallel, a driving circuit is required for each semiconductor laser, and therefore there is a limit to downsizing and cost reduction. In addition, the time from the injection of current to the semiconductor laser until the start of oscillation is
Since it depends on the element and the driving condition, when the isochronism of the optical signal is important, the signal delay must be adjusted for each channel. For example, FIG. 7 shows an experimental waveform of laser output by a CSP laser [Source: IEEE JOURNAL OF QUANTU
M ELECTRONICS, VOL.QE-14, NO.8, AUGUST 1978, P625]. In this case, the CSP laser is Type-II
And W = 6 μm and Jth = 1.83 kA / cm 2.
As can be seen from (a) to (d) of the waveform diagram, it can be seen that the smaller the forward current (12 mA, 14 mA, 16 mA, 19 mA), the greater the signal delay.

An object of the present invention is to provide a multi-channel optical signal generator that oscillates optical signals having the same wavelength and the same phase.

Another object of the present invention is to provide a highly reliable multi-channel optical signal generator which is free from damage due to a high output optical signal.

Another object of the present invention is to provide a multi-channel optical signal generator which is small in size and can be manufactured at a reduced cost.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0011]

The outline of the representative ones of the inventions disclosed in the present application will be briefly described as follows. That is, the multi-channel optical signal generator of the present invention comprises a multi-branch type branch coupler (star coupler) having a plurality of input / output terminals on one side and one input / output terminal on the other side, and the multi-branch type branch coupler. A plurality of Fabry-Perot type semiconductor lasers of the same structure, which are optically connected to one of the input / output ends of the coupler via one of the optical output end faces, and the other input / output end of the multi-branch branch coupler. And a mirror (external mirror) that is optically opposed to each other, and one of the semiconductor lasers is driven for modulation by receiving a modulation current pulse, and the remaining semiconductor lasers are driven by a direct current source. The current is biased below the oscillation threshold. Further, the reflectance of the light output end face on the side optically connected to the multi-branch type branch coupler of the semiconductor laser is lower than the reflectance of the light output end face on the opposite side, and the reflectance of each semiconductor laser The high light output facet and the mirror form a composite resonator laser.

Another multi-channel optical signal generator of the present invention is a multi-branch type branch coupler (star coupler) having a plurality of input / output terminals on one side and one input / output terminal on the other side,
A drive semiconductor laser optically connected to one of the input / output terminals of the multi-branch branch coupler via an optical isolator, and the remaining one of the input / output terminals of the multi-branch branch coupler. A plurality of Fabry-Perot type semiconductor lasers of the same structure which are optically connected through one light output end face and the other input / output end of the multi-branching branch coupler are arranged to face each other optically. A mirror (external mirror), the semiconductor laser is biased with a direct current, and the driving semiconductor laser is modulated and driven.
That is, the driving semiconductor laser is modulated and driven by inputting a modulation current pulse, and the remaining semiconductor lasers are biased with a direct current below the oscillation threshold by a direct current. Further, the reflectance of the light output end face on the side optically connected to the multi-branch type branch coupler of the semiconductor laser is lower than the reflectance of the light output end face on the opposite side, and the reflectance of each semiconductor laser The high light output facet and the mirror form a composite resonator laser.

[0013]

According to the above-mentioned means, the multi-channel optical signal generator of the present invention utilizes the external compound resonator formed by each semiconductor laser and the external mirror by modulating a single semiconductor laser. Since laser oscillation is performed, it is possible to simultaneously oscillate optical signals having the same wavelength and synchronized phases from the respective semiconductor lasers. That is, one modulated semiconductor laser optical signal excites a semiconductor laser biased below the other threshold value through the star coupler to cause laser oscillation.

The multi-channel optical signal generator of the present invention is a low-output semiconductor laser in which the semiconductor laser does not oscillate a high-output optical signal of several hundred mW and the optical signal does not reach 20 mW. Therefore, thermal damage to the star coupler due to a strong signal light will not occur, and oxidation adhesion and fusion due to dust adhesion between the semiconductor laser and the star coupler will not occur, preventing deterioration of coupling efficiency and reliability. Get higher

Further, since the multi-channel optical signal generator of the present invention uses one of the plurality of semiconductor lasers connected to the star coupler as a semiconductor laser for modulation (driving semiconductor laser), it is large for modulation. It is not necessary to prepare an output pulse drive source or a plurality of drive sources.

Another multi-channel optical signal generator of the present invention, that is, a multi-channel optical signal generator having a structure in which a driving semiconductor laser is joined to a star coupler via an optical isolator, is an optical signal oscillated from the driving semiconductor laser. Is sent to the compound resonator laser, it is possible to simultaneously oscillate optical signals having the same wavelength and the same phase from the semiconductor lasers constituting the compound resonator laser. That is, the modulated optical signal of the driving semiconductor laser excites the semiconductor laser biased below the other threshold value through the star coupler to cause laser oscillation.

Further, in another multi-channel optical signal generator of the present invention, the semiconductor laser does not oscillate a high output optical signal such as several hundred mW, and a low output semiconductor laser in which the optical signal does not reach 20 mW. Therefore, thermal damage to the star coupler due to the strong signal light will not occur, and oxidation adhesion and fusion due to dust adhesion between the semiconductor laser and the star coupler will not occur, preventing deterioration of coupling efficiency and reliability. Will be more likely.

In another multi-channel optical signal generator of the present invention, that is, in the structure in which the optical output of the driving semiconductor laser (master semiconductor laser) is sent to the star coupler through the optical isolator, the light from each semiconductor laser is driven. Since it does not return to the laser, accurate modulation can be performed.

Further, in another multi-channel optical signal generator of the present invention, that is, in the structure in which the optical output of the driving semiconductor laser (master semiconductor laser) is sent to the star coupler through the optical isolator, the oscillation of the light is emitted by the laser (laser). Since it is performed by sending (light) to the star coupler, it is not necessary to mount an electric circuit in the master semiconductor laser.

Embodiments of the present invention will be described in detail below with reference to the drawings. In all the drawings for describing the embodiments, components having the same function are denoted by the same reference numerals, and their repeated description will be omitted.

[0021]

【Example】

(Embodiment 1) FIG. 1 is a block diagram showing a schematic configuration of a multi-channel optical signal generator of Embodiment 1 according to the present invention, and FIG. 2 is a verification of generation of an optical signal in the multi-channel optical signal generator of Embodiment 1. FIG. 3 is a schematic diagram showing a schematic configuration of an optical signal generation verification device to perform, and FIG. 3 is a waveform diagram showing a spectrum according to an optical signal generation verification example.

As shown in FIG. 1, the multi-channel optical signal generator of the first embodiment includes a multi-branch type branch coupler (star coupler) 2 having an input / output terminal of 1 × N (N = 4). It has N (4) Fabry-Perot type semiconductor lasers 10 and mirrors (external mirrors) 11 having the same structure. That is, N Fabry-Perot type semiconductor lasers 10 are arranged in parallel on one side of the star coupler 2, that is, on the N port side, and one optical output end face of these semiconductor lasers 10 and one of the star couplers 2 are arranged. The N input / output ends are optically connected to each other via an optical fiber 12.
Output side optical fibers 4 are optically connected to the other optical output end faces of the respective semiconductor lasers 10. This output side optical fiber 4 has an optical signal (optical output)
8 is sent from the semiconductor laser 10.

The semiconductor laser 10 is, for example, GaAs.
System DH laser, the oscillation wavelength band is 0.8 μm.

On the other hand, an optical fiber 13 is optically connected to the other one input / output end of the star coupler 2, and a mirror (external mirror) 11 faces the tip of the optical fiber 13. It is arranged as follows.

Output side optical fiber 4 of each semiconductor laser 10
The other light output end face A facing the outer mirror 11 and the external mirror 11
The surface B becomes the cavity end, and the compound cavity laser is formed. That is, the reflectance of the light output end face on the side optically coupled to the star coupler 2 of the semiconductor laser 10 becomes lower than the reflectance of the light output end face A on the opposite side. The high optical output end face and the external mirror 11 constitute a composite resonator laser.

In order to form the composite resonator laser, one light output end face of the semiconductor laser 10 optically connected to the star coupler 2 is provided with an antireflection film 14 having a remarkably low reflectance. There is. The antireflection film 14 is formed of, for example, a SiON film and has a reflectance of 0.01.
% Or less. Further, the other optical output end face A facing the output side optical fiber 4 of the semiconductor laser 10 is formed with a high reflectance of several tens% in order to form a mirror of the laser resonator. The light output end face A is formed by a cleavage plane having a reflectance of 32%. In addition, the optical fiber 13
In order to increase the efficiency of feedback from the laser to the semiconductor laser 10,
The optical fiber 13 has a multimode of 50 μmR (50 G
I) It is a spherical fiber.

In the present configuration, due to the presence of the star coupler 2, the laser light emitted from one light output end face of each semiconductor laser 10 is mixed in the star coupler 2 and the external mirror 1
It reflects on the surface B of 1 and returns to each semiconductor laser 10, and the other optical output end face of the semiconductor laser 10 and the external mirror 11 form one compound resonator laser.

Each semiconductor laser 10 is DC biased below an oscillation threshold by a current source (not shown), and one of the plurality of semiconductor lasers 10 is used as a driving semiconductor laser 15 for modulation. The driving semiconductor laser 15 is drive-controlled by the semiconductor laser control device 5 and is modulated and driven by inputting a modulation current pulse. The drive control in the semiconductor laser control device 5 is based on the signal generator 6.

Each semiconductor laser 10 is brought into a state of emitting the spontaneous emission light spectrum by the bias by the direct current.

Since the Fabry-Perot type semiconductor laser emits laser light from both ends of the cavity end, the driving semiconductor laser 15 also emits laser light from both ends thereof. Therefore, when the driving semiconductor laser 15 is modulated, the laser light emitted from the optical output end face of the driving semiconductor laser 15 on the star coupler 2 side enters the star coupler 2. In the star coupler 2, the laser light emitted from the driving semiconductor laser 15 is integrated with the laser light emitted from the other semiconductor laser 10, and the composite resonator laser oscillates with a new wavelength. . That is, if the respective semiconductor lasers 10 are perfectly synchronized, single mode oscillation occurs in the entire compound resonator, resulting in single mode oscillation. That is,
Each semiconductor laser 10 emits an optical signal having the same wavelength and the same phase.

Similarly to the other semiconductor lasers 10, the driving semiconductor laser 15 emits the optical signal 8 from the other optical output end face A and outputs the optical signal to the output side optical fiber 4 optically connected to the driving semiconductor laser 15. It is configured to send the signal 8.

In the multi-channel optical signal generator according to the first embodiment, the semiconductor lasers 10 other than the driving semiconductor laser 15 are biased with a DC current below the oscillation threshold so as not to oscillate, and the driving is performed. The semiconductor laser 15 is modulated (ON, OFF). As a result, oscillation occurs in the composite resonator laser, and the optical output 8 is emitted from the other optical output end face A of all the semiconductor lasers 10 including the driving semiconductor lasers 15, and the optical output corresponding to each semiconductor laser 10 is performed. It is sent to the output side optical fiber 4 connected to.

Therefore, since the multi-channel optical signal generator of the first embodiment oscillates the optical signal 8 as the laser light from the composite resonator laser having a part in common, the wavelengths are the same for a plurality of channels. In addition, it is possible to send an optical signal (isochronous optical signal) whose phase is synchronized.

FIG. 2 is a schematic diagram showing an outline of an optical signal generation verification apparatus for verifying that the multi-channel optical signal generator of the first embodiment surely generates the optical signal 8 by modulation.

In the optical signal generation verification apparatus, two semiconductor lasers 1 are provided on the N port side of the 1 × N star coupler 2 (N = 4).
0 is optically connected via an optical fiber 12 (a 50 μmR multimode front spherical fiber), and the remaining 2
An optical spectrum analyzer 20 or an optical power meter 21 is connected to each of the two ports via an optical fiber 12.
Is connected.

One of the semiconductor lasers 10 is used as a driving semiconductor laser (LD # 1) 15, and the other semiconductor lasers (LD # 2) 10 are used for optical communication. The output side optical fiber 4 optically connected to the semiconductor laser (LD # 2) 10 is the optical spectrum analyzer 20.
Connected to.

In this optical signal generation verification apparatus, a bias current (I2 = 110 mA) below the oscillation threshold is applied to the semiconductor laser (LD # 2) 10 and the driving semiconductor laser (LD # 1) 15 is turned on. / OFF modulation. As a result, O of the driving semiconductor laser (LD # 1) 15
During N / OFF modulation, waveform diagrams as shown in FIGS. 3A and 3B were obtained. This waveform diagram shows the optical spectrum
This is due to the analyzer 20.

The driving semiconductor laser (LD # 1) 15 is OF
At F, the waveform diagram (spontaneous emission spectrum) appearing in the optical spectrum analyzer 20 is as shown in FIG. 3A, the spectrum is 0.80800 μm, and the optical output is 7.237 mW. On the other hand, when the driving semiconductor laser (LD # 1) 15 is turned on, the waveform diagram appearing in the optical spectrum analyzer 20 becomes a laser oscillation spectrum as shown in FIG. 3B, and the spectrum becomes 0.812800 μm. Its light output is 1
It becomes 5.32 mW. From this, it can be verified that the same signal as the optical signal due to the switching of the driving semiconductor laser 15 is generated from the other semiconductor lasers 10. Even if the number of semiconductor lasers arranged in parallel is further increased, optical signals having the same wavelength and the same phase can be simultaneously oscillated from the respective semiconductor lasers.

Further, the multi-channel optical signal generator of the first embodiment has a structure in which one of the plurality of semiconductor lasers connected to one of the star couplers (N port side) is used as a driving semiconductor laser. Therefore, it is not necessary to prepare a high output pulse drive source or a plurality of drive sources for modulation.

Since the multi-channel optical signal generator of the first embodiment does not use a high-power semiconductor laser, it is a highly reliable multi-channel optical signal generator that is not easily damaged.
That is, since a high-power semiconductor laser is not used, damage to the star coupler due to strong signal light cannot be prevented. Further, oxidation adhesion and fusion due to dust adhesion between the semiconductor laser and the star coupler due to the strong signal light do not occur, the coupling efficiency does not decrease, and the reliability becomes high.

The multi-channel optical signal generator of the first embodiment uses a plurality of semiconductor lasers, but only a single semiconductor laser (driving semiconductor laser) is controlled by the semiconductor laser control device, and all semiconductors are controlled. Compared to a multi-channel optical signal generator that individually drives and manufactures lasers, the number of parts can be reduced and the device can be downsized.

Although the multi-channel optical signal generator of the first embodiment uses a plurality of semiconductor lasers, only a single semiconductor laser (driving semiconductor laser) is controlled by the semiconductor laser control device, and all semiconductors are controlled. Compared with a multi-channel optical signal generator that individually drives and manufactures lasers, the number of parts can be reduced, and the manufacturing cost of the device can be reduced.

(Second Embodiment) FIG. 4 shows a second embodiment according to the present invention.
3 is a block diagram showing a schematic configuration of the multi-channel optical signal generator of FIG.

In the multi-channel optical signal generator of the second embodiment, the optical signal of the driving semiconductor laser (master semiconductor laser), which is directly and independently modulated from the outside, is input into the compound resonator laser and the semiconductor lasers in parallel are connected. The light output is controlled. That is, the multi-channel optical signal generator according to the second embodiment includes a 1 × N (N = 5) star coupler 2.
And a driving semiconductor laser which is optically connected to one of the input / output terminals of one side (N port side) of the star coupler 2 through an optical isolator 25 and which is directly modulated to send an optical output to the star coupler 2. (Master semiconductor laser)
15, a plurality of semiconductor lasers 10 for optically connecting one optical output end face to the remaining input / output end of one of the star couplers 2 (N port side), and the other of the star couplers 2 (1 port side). And an optical fiber (optical signal output port) (not shown) optically connected to the other optical output end face A of each of the semiconductor lasers 10 Having the semiconductor laser 1
0 is a direct current, which is biased below the oscillation threshold.

In the case of the second embodiment, the driving semiconductor laser (master semiconductor laser) 15 which is directly and independently modulated from the outside is used.
Is input to the compound resonator laser to control the optical output of the semiconductor lasers 10 in parallel. The second embodiment is similar to the first embodiment in that the semiconductor laser 1
The reflectance of the light output end face on the side optically connected to the star coupler 2 of 0 is formed lower than the reflectance of the light output end face A on the opposite side.

In the multi-channel optical signal generator of the second embodiment, the optical isolator 25 can suppress the return of the light from the compound resonator laser to the driving semiconductor laser (master semiconductor laser) 15, so that accurate modulation can be achieved. Is possible.

In addition to the effect of the multi-channel optical signal generator of the first embodiment, the multi-channel optical signal generator of the second embodiment drives the compound resonator laser with light, so that the driving in the driving semiconductor laser is performed. The effect that the mounting of the electric circuit for control becomes unnecessary is produced.

As described above, the invention made by the present inventor is
Although the present invention has been specifically described based on the above-mentioned embodiments, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the scope of the invention.

For example, in the above embodiment, the external mirror and the star coupler and the star coupler and the semiconductor laser are optically connected by an optical fiber. However, the optical fiber is not used and the spatial coupling is the same as in the above embodiment. Can be obtained.

Further, by using the present invention, it is possible to provide a multi-channel optical transmitter, an optical booster and the like which are small in size and low in cost and have the same oscillation wavelength with no signal delay.

[0051]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) According to the multi-channel optical signal generation technique of the present invention, by modulating one semiconductor laser, an external composite resonator formed by a plurality of remaining semiconductor lasers and an external mirror is utilized. Since laser oscillation can be performed, it is possible to simultaneously oscillate optical signals having the same wavelength and synchronized phases from the respective semiconductor lasers.

(2) Since the multi-channel optical signal generator of the present invention does not use a high-power semiconductor laser, it causes damage to the star coupler due to a strong signal light and dust adhesion between the semiconductor laser and the star coupler. Oxidation adhesion and fusion can be prevented, and reliability is improved.

(3) The multi-channel optical signal generator of the present invention uses a plurality of semiconductor lasers, but modulation can be performed only by a single semiconductor laser and does not require a large number of semiconductor laser control devices. Since the number of parts is reduced, downsizing of the device and reduction of manufacturing cost can be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a multi-channel optical signal generator according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing an outline of an optical signal generation / verification device for performing optical signal generation verification in the multi-channel optical signal generator of the first embodiment.

FIG. 3 is a waveform diagram showing a spectrum according to an optical signal generation verification example in the multi-channel optical signal generator of the first embodiment.

FIG. 4 is a block diagram showing a schematic configuration of a multi-channel optical signal generator according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing an example of a conventional multi-channel optical signal generator.

FIG. 6 is a block diagram showing another example of a conventional multi-channel optical signal generator.

FIG. 7 is a waveform diagram showing an experimental waveform of laser output by a CSP laser.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... High output semiconductor laser, 2 ... Multi-branch type branch coupler (star coupler), 3 ... Input side optical fiber, 4 ... Output side optical fiber, 5 ... Semiconductor laser control device, 6 ... Signal generator,
7 ... Semiconductor laser, 8 ... Optical signal (optical output), 10 ... Semiconductor laser, 11 ... Mirror (external mirror), 12, 13 ... Optical fiber, 14 ... Antireflection film, 15 ... Driving semiconductor laser (master semiconductor laser) , 20 ... Optical spectrum analyzer, 21 ... Optical power meter, 25 ... Optical isolator.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location H04B 10/02 (72) Inventor Yuji Uenishi 1-1-6 Uchiyuki-cho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp. (72) Inventor Shinji Nagaoka 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Japan Telegraph and Telephone Corp. (72) Inventor Akinori Watanabe 1-6, Uchiyuki-cho, Chiyoda-ku, Tokyo Japan Inside Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. A plurality of input / output terminals are provided on one side, and one is provided on the other side.
A multi-branch type branch coupler having one input / output terminal, and a plurality of Fabry-Perots of the same structure optically connected to one input / output terminal of one of the multi-branch type branch couplers via one optical output end face. -Shaped semiconductor laser and a mirror arranged to face the other input / output end of the multi-branch branch coupler optically facing each other, one of the semiconductor lasers being driven by modulation and the other A multi-channel optical signal generator characterized in that the semiconductor laser is biased with a direct current. 2. A plurality of input / output terminals are provided on one side, and one is provided on the other side.
A multi-branch branch coupler having one input / output terminal, a driving semiconductor laser optically connected to one of the input / output terminals of the multi-branch branch coupler via an optical isolator, and the multi-branch A plurality of Fabry-Perot type semiconductor lasers of the same structure which are optically connected to the remaining input / output ends of one of the multi-branch couplers, and the other of the multi-branch couplers. And a mirror disposed optically facing each other at the input and output ends of the multi-channel optical signal, wherein the semiconductor laser is biased with a direct current and the driving semiconductor laser is modulation-driven. Generator. 3. The reflectance of the light output end face on the side optically connected to the multi-branch branch coupler of the semiconductor laser is lower than the reflectance of the light output end face on the opposite side. The multi-channel optical signal generator according to claim 1 or 2.