JP2002329925A - Semiconductor laser module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser module in which a change in an optical output does not occur since an exciting laser beam to be outputted is always set to a multi-mode. SOLUTION: The semiconductor laser module comprises a semiconductor laser element 3, an optical coupling means 4 and an optical fiber 7 disposed at the same optical axis, and an optical feedback unit A1 for reflecting the laser beam having a specific wavelength in such a manner that a reflecting spectral shape of the feedback unit A1 has a substantially rectangular shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser module, and more particularly, to a semiconductor laser module that outputs a laser beam for excitation having a specific wavelength in a stable state.

[0002]

2. Description of the Related Art Wavelength division multiplexing
ltiplexing (WDM) communication system has been developed as an optical communication system for transmitting a plurality of signal lights. In this system, for example, an Er-doped optical fiber amplifier (EDFA) is arranged at a predetermined position in an optical line, and a plurality of laser modules each having a semiconductor laser element incorporated as a light source are connected to the laser module. The laser light for use is incident on the EDFA, and the signal light transmitted from the signal light source is optically amplified, so that the optically amplified signal light is transmitted to the downstream side.

A laser module that outputs a laser beam for excitation has, for example, a structure as shown in FIG.
That is, a plurality of pairs of Peltier modules 2 are arranged in a package 1, and a substrate 6 on which a laser element 3, a thermistor 4, and a lens 5 serving as an optical coupling means are fixed, and the package 6 is fixed. An optical fiber 7 having a fiber grating 7a functioning as an optical feedback section is formed in a through-hole 1b formed in the side wall 1a of the optical fiber.
Are fixedly arranged.

In this laser module, the oscillating laser light emitted from the emission end face (front end face) of the laser element 3 is condensed by the lens 5 and enters the end face 7 b of the optical fiber 7. Then, of the laser light incident on the optical fiber 7,
Only the laser light of a specific wavelength located near the center wavelength of the reflection bandwidth of the fiber grating 7a returns to the laser element 3, and the wavelength of the oscillation laser light from the laser element 3 is fixed to the specific wavelength. As a result, the laser module outputs an excitation laser beam having the specific wavelength.

In the case of the laser module shown in FIG. 1, when the laser element 3 generates heat due to the drive current injected into the laser element 3 and the element temperature rises, the wavelength and light intensity of the oscillating laser light fluctuate. The light output of the excitation laser light from the laser module becomes unstable. In order to prevent such a situation from occurring, the temperature of the laser element is measured by the thermistor 4, and an external control circuit (not shown) is operated using the measured value to adjust the operating current of the Peltier module 2. Cooling the laser element 3 to stabilize the wavelength of the oscillating laser light from the laser element 3.

However, when the laser element 3 incorporated in the laser module is, for example, a GaAs-based laser element that oscillates in a 980 nm wavelength range, if a light feedback section such as the fiber grating 7a is formed, the resulting pumping is achieved. There is a case where the optical output of the laser light for use largely fluctuates with time and exhibits an unstable optical output state.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to provide 98 objects.
Resolves the above-mentioned problems in laser modules that incorporate a laser element that oscillates in the 0 nm wavelength range and have an optical feedback section such as a fiber grating, and suppresses temporal fluctuations in the optical output of the excitation laser light. And a semiconductor laser module capable of realizing the stabilization.

[0008]

In order to achieve the above object, the present invention provides a semiconductor laser device, an optical fiber, and an optical coupling for causing laser light emitted from the semiconductor laser device to enter the optical fiber. Means and a light feedback section for reflecting laser light of a specific wavelength, wherein the reflection spectrum of the light feedback section is substantially rectangular. A semiconductor laser element; an optical fiber; an optical coupling unit that causes the laser light emitted from the semiconductor laser element to enter the optical fiber; and a light feedback unit that reflects a laser light having a specific wavelength. A semiconductor laser module is provided, wherein the reflection spectrum shape of the feedback section is a shape having a peak and a valley at a top portion.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor relates to an excitation laser beam output from a laser module having the configuration shown in FIG.
The spectrum was observed. And the following findings were obtained. (1) In the case of an excitation laser beam whose optical output is unstable, its spectrum curve shows a single mode oscillation mode in which only one longitudinal mode oscillates and a plurality of longitudinal mode oscillations. The multi-mode oscillation mode appears alternately.

[0010] (2) The light output of the excitation laser light, which is always in a multi-mode oscillation mode over time, is stabilized. The present inventor has confirmed the necessity of constantly oscillating the laser light for excitation in a multimode in order to stabilize the optical output of the laser light for excitation based on the above findings. The present inventor examined the relationship between the characteristics of the optical feedback unit and the multi-mode of the excitation laser light, and when an optical feedback unit described later was formed, the excitation laser light output from the laser module was always multi-mode. And found that the light output was stabilized.

Based on such knowledge, the above-described semiconductor laser module of the present invention has been developed. One example of the main components of the laser module of the present invention is schematically shown in FIG. In this laser module, a laser element 3, an optical coupling means (lens) 5, and an optical fiber 7 are optically coupled in this order with their optical axes C aligned with each other. The entire optical coupling system is shown in FIG. As described above, it is enclosed in the package 1. The laser element 3 has an oscillation wavelength of 940 to 1100 nm.

A chirped grating A ₁ is formed in the optical fiber 7. This functions as an optical feedback unit. The incident end face 7c of the optical fiber 7 is orthogonal to the optical axis. In this laser module, the oscillation laser light from the laser element 3 is condensed by the lens 5 and is incident on the end face 7c of the optical fiber 7. And
Chirped grating A out of the incident laser light
Only the laser light of a specific wavelength within the _first reflection bandwidth is reflected in the chirped grating A _1, lens 5 again
And returns to the laser element 3 via. By repeating such a behavior, the laser beam emitted from the laser element 3 is fixed to the wavelengths near the center wavelength of the reflection band width of the chirped grating A _1, then the optical fiber 7 as excitation laser beam Output.

Chirped grating (optical feedback section) A
_When the reflection spectrum of ₁ is drawn, the reflection characteristic has a shape approximate to a rectangle as shown in FIG. Therefore, the chirped grating (optical feedback unit) A ₁ can return light in a wide wavelength band to the laser element 3. Therefore, the threshold value of the carrier density required for oscillating the laser element 3 can be reduced in a wide wavelength band. Therefore, it becomes possible to oscillate also in the longitudinal mode located in the wavelength band where the threshold value of the carrier density of the laser element 3 is lowered, and as a result, the oscillation laser light from the laser element 3 becomes multi-mode. .

The multimode laser light is output from the optical fiber 7 as excitation laser light, so that the optical output of the excitation laser light is stabilized. A reflection spectrum for realizing the above-described reflection characteristics will be described below. Now, it is assumed that the drawn reflection spectrum has a shape as shown in FIG.

First, the wavelengths (λ ₈₀ , λ ′ ₈₀ ) at which the reflectance (R ₈₀ ) corresponding to 80% of the peak reflectance (Rmax) in the reflection spectrum is obtained are determined. (Λ ′ ₈₀ −λ ₈₀ ) value is calculated. At the same time, the wavelength (λ ₇₀ , λ ′ ₇₀ ) at which the reflectance (R ₇₀ ) corresponding to 70% of the peak reflectance (Rmax) is obtained, and the wavelength bandwidth: (λ ′ ₇₀ −λ ₇₀ ) value Is calculated.

At this time, according to the present invention, (λ ′ ₈₀ −λ ₈₀ )
The reflection spectrum in a state where the value is 0.85 times or more the value of (λ ′ ₇₀ −λ ₇₀ ) is preferable. Since the shape of the reflection spectrum in this state is almost rectangular, as is clear from FIG. 4, light in a wide wavelength band can be fed back by the chirped grating.
In a laser device, the threshold value of the carrier density is reduced in a wide wavelength band. Therefore, it is effective for making the oscillation laser light from the laser element multimode.

The reflection spectrum may have a shape as shown in FIG. 5 depending on conditions such as a phase mask used for forming the grating or a profile of a laser beam for writing the grating.
That is, the spectrum has a plurality of peaks and troughs at the top of the reflection spectrum. Even in the case of a chirped grating (optical feedback section) exhibiting such a reflection spectrum, if the value of (λ ′ ₈₀ −λ ₈₀ ) is 0.85 times the value of (λ ′ ₇₀ −λ ₇₀ ), The light output of the excitation laser light from the laser module is stabilized.

It is preferable that the wavelength bandwidth represented by the value (λ ′ ₈₀ −λ ₈₀ ) is at least three times the longitudinal mode interval in the oscillation laser light of the laser element. In this case, since at least three longitudinal modes are included in the value of the oscillation bandwidth: (λ ′ ₈₀ −λ ₈₀ ), the light output of the obtained excitation laser light is stabilized. It is.

[0019] In chirped grating (light feedback portion) A ₁ to form the laser module described above, when the reflectance is too small, the energy of the reflected laser beam returned to the laser element is small. Therefore, when the oscillation wavelength of the laser element alone is separated from the wavelength of the optical feedback unit, a problem occurs that the wavelength cannot be fixed to the optical feedback unit. Conversely, if the reflectance is too large, The problem is that the light output at the end of the optical fiber is reduced due to the reflection of the optical feedback section. For this reason, the reflectance of the chirped grating should be 1 to 20%, preferably 2 to 10%.

If the reflection bandwidth of the chirped grating (optical feedback section) A ₁ is too narrow, it becomes difficult to lower the threshold value of the carrier density in a sufficiently wide wavelength band. There is a problem that mode oscillation cannot be obtained. On the other hand, if the width is too wide, a problem arises that fluctuation of the oscillation wavelength due to the injection current becomes large. Therefore, the reflection bandwidth should be 0.1 to 4.0 nm, preferably 0.2 to 1.5 nm.

The above-mentioned reflection bandwidth is suitable when a strict wavelength setting is required. In general, the oscillation wavelength of a laser device fluctuates depending on the injection current, the temperature of the laser device, and the like. When the laser element and the optical feedback section are combined, the oscillation wavelength of the laser light emitted from the laser element is fixed at the wavelength of the laser beam reflected from the optical feedback section, and the above-described wavelength fluctuation can be suppressed.

In the present embodiment, as shown in FIG. 1, a Peltier module is disposed inside the laser module, and the temperature of the laser element is controlled to be constant, so that even if the temperature outside the laser module changes. Since the temperature of the laser element does not change, the wavelength fluctuation of the laser light from the laser element alone can be suppressed. Then, the laser module can oscillate at the wavelength of the reflected laser light from the optical feedback section regardless of the external temperature change.

However, Peltier modules are relatively expensive. For this reason, there are cases where inconvenience is caused when an inexpensive laser module is manufactured. Therefore, a configuration that does not use a Peltier module is also practically important. In this case, if an optical feedback section having a wide reflection bandwidth and a laser element are combined as in the present embodiment, the oscillation wavelength of the laser light from the laser element and the wavelength of the reflected laser light from the optical feedback section are temporarily different. Even if it does, the laser module is preferable because it easily oscillates at the wavelength of the reflected laser light from the optical feedback section.

When the Peltier module is not used, the oscillation wavelength variation of the laser module when the injection current to the laser element or the external temperature changes is larger than that when the Peltier module is used. However,
In the case where a large amplification factor is not required in the amplifier, the above laser module does not require strict wavelength setting, and thus can function as an inexpensive laser module having appropriate wavelength accuracy without a Peltier module. .

Usually, a so-called uniform grating having a constant grating pitch is used as the optical feedback section. For example, a chirped grating having a change in the grating pitch is used as in the present embodiment. You can also. Thereby, when an optical feedback unit is formed such that the spectrum of the reflected light draws a shape approximate to a rectangle, the reflection bandwidth is increased by 10 to 25.
It can be as large as nm.

From the above, when it is not necessary to set a strict wavelength, the reflection bandwidth of the optical feedback unit is set to 4 to 4.
Preferably it is 25 nm. FIG. 6 shows another laser module of the present invention. This laser module includes a laser element 3 having an optical axis aligned, a lens (optical coupling means) 5,
The arrangement of the optical fiber 7 is the same as that of the laser module of FIG. However, a lens (optical coupling means) 5
A bandpass filter 8 and a reflector 9 such as a ferrule are arranged between the optical fiber 7 and the optical fiber 7 in a state of being inclined by an angle θ with respect to the optical axis C. The light feedback unit A ₂ is formed by the reflector 9 and the band pass filter 8.

Here, the band-pass filter 8 transmits only laser light in a specific wavelength band and does not transmit laser light in other wavelength bands. Specifically, it has the reflection characteristics shown in FIG. The end surface 9a of the reflector 9 is a flat surface orthogonal to the optical axis C and has a wavelength-independent reflection characteristic. Specifically, it has the reflection characteristics as shown in FIG.

In the case of this laser module, the oscillated laser light from the laser element 3 is condensed by a lens (optical coupling means) 5 and reaches a bandpass filter 8. At this time, of the oscillation laser light, only the laser light in the transmission wavelength band shown in FIG. 7 can be transmitted and incident on the end face 9a of the reflector 9, and the laser light in other wavelength bands has a reflection angle θ. Dissipates outside the system.

At the end face 9a of the reflector 9, reflection of the transmitted laser light occurs. At this time, the reflection spectrum of the reflected laser light is, as shown in FIG. Band and reflector 9 shown in FIG.
And a rectangular shape having the following reflectance. Then, the reflected laser light returns to the laser element 3 via the bandpass filter 8 and the lens (optical coupling means) 5. By repeating this operation, laser light for excitation is output from this laser module. Therefore, the excitation laser light has a rectangular reflection spectrum shown in FIG. 9 and is multi-mode, and its light output is stabilized.

The above-mentioned band-pass filter preferably has a transmittance of 100% in a specific wavelength band and 0% in other wavelength bands. Further, in the laser module of FIG. 6, the optical fiber 7 may be directly disposed without disposing the reflector 9. In this case, the end surface of the optical fiber is used as a reflection surface. The reflectance at that time may be about 3%.

[0031]

[Embodiment 1] Production of Laser Element The laser element shown in FIG. 10 was produced as follows. On a substrate 1 made of n-GaAs, n-AlGa
4 μm thick lower cladding layer 2 made of As, 30 nm thick lower GRIN-S made of undoped AlGaAs
A CH layer 3a is formed, and undoped GaAs is further formed thereon.
a 10 nm thick barrier layer made of sP and undoped InG
An active layer 4 having a two-layer structure composed of a 7 nm-thick well layer made of aAs, an upper GRIN-SCH layer 3 b composed of undoped AlGaAs having a thickness of 30 nm, an upper cladding layer 5 composed of p-AlGaAs having a thickness of 2 μm, and p-GaAs. A cap layer 6 having a thickness of 0.5 μm was laminated in this order.

On the upper surface of the formed layer structure, a ridge waveguide having a width of 4 μm and a height of 1.2 μm is formed by applying photolithography technology and etching technology, and then a protective film 7 made of SiN is formed thereon. did. Next, the lower surface of the substrate is polished to form a lower electrode 8 made of AuGeNi / Au, and a part of the protective film 7 on the upper surface of the cap layer is removed. Was formed.

Then, the substrate is cleaved to form a bar having a cavity length (L) of 1200 μm.
A front end face is formed by forming a low reflection film made of N and having a reflectivity of 2%, and a reflectivity 92 made of SiO ₂ / Si is formed on the other end face.
% Of a highly reflective film was formed to form a rear end face. Finally, the bar was processed to produce a laser element as a chip.

2. Assembly of laser module A chirped grating and a uniform grating were prepared as light feedback sections in the examples and comparative examples, respectively. These reflection characteristics are as follows. Chirped grating (Example): peak reflectance (Rmax) 7%, half width 1.5 nm, center wavelength 980 nm. λ ′ ₈₀ −λ ₈₀ = 1.22 nm, λ ′ ₇₀ −λ ₇₀ = 1.34 nm. Therefore, (λ ′ ₈₀ −λ ₈₀ ) / (λ ′ ₇₀ −λ ₇₀ ) ≒
0.9. Uniform grating (comparative example): peak reflectance (Rmax) 7%, half width 1.5 nm, center wavelength 980 nm. λ ′ ₈₀ −λ ₈₀ = 0.885 nm, λ ′ ₇₀ −λ ₇₀ = 1.125
nm. Therefore, (λ ′ ₈₀ −λ ₈₀ ) / (λ ′ ₇₀ −λ ₇₀ ) ≒
0.8. The laser module shown in FIG. 2 was assembled using these chirped gratings.

3. Excitation Laser Light from Laser Module In the laser modules of Examples and Comparative Examples, a laser beam having a wavelength of 980 nm was oscillated by injecting a current of 100 mA into a laser element. Then, the fluctuation amount of the excitation laser light obtained from the optical fiber 7 was measured. The results are shown in FIG. As is clear from FIG. 11, when the laser module of the embodiment is used, the light output of the excitation laser light is ± 0.1.
%, And hardly fluctuates. On the contrary, when the laser module of the comparative example is used,
Light output fluctuates violently.

Embodiment 2 Resonator length: 1200 μm, longitudinal mode interval: about 0.11 nm
Using a semiconductor laser element having the following characteristics, a laser module having the same components as those of the first embodiment except for the optical feedback unit was assembled. As the optical feedback section, two types of chirped gratings having the following reflection characteristics having different reflection bandwidths were used. Light feedback part a: center wavelength 979.8 nm, peak reflectance 7
%, Half-width 1.5 nm (λ _'80 -λ ₈₀ ) / (λ' ₇₀ -λ ₇₀ ) ≒ 0.9. Light feedback part b: center wavelength 979.1 nm, peak reflectance 7
%, Half-width 0.9 nm (λ _'80 -λ ₈₀ ) / (λ' ₇₀ -λ ₇₀ ) ≒ 0.9.

With respect to these two laser modules, it was examined how the peak wavelength in the oscillation spectrum changes depending on the reflection bandwidth of the optical feedback section. That is, the oscillation spectrum of the laser light output from the optical fiber was observed with an optical spectrum analyzer, and the peak wavelength of the oscillation spectrum was measured while changing the injection current to the laser element. FIG. 12 shows the result.

As is apparent from FIG. 12, the fluctuation of the peak wavelength due to the injection current is smaller in the laser module using the optical feedback section b having a narrow reflection bandwidth. As described above, it is preferable that the reflection band width of the optical feedback unit is narrow because the fluctuation of the peak wavelength with respect to the injection current of the laser light from the laser module becomes small and the current dependency of the peak wavelength becomes small.

In general, the wavelength range of 980 nm is 940 in the present invention.
The excitation light source having a wavelength range of 1 to 1100 nm is required to have a wavelength accuracy of ± 0.5 nm to ± 1.0 nm with respect to a set wavelength.
Therefore, in consideration of the wavelength fluctuation due to the change of the environmental temperature, the fluctuation of the wavelength of the reflected laser light in the optical feedback section, and the like, it is preferable that the wavelength fluctuation due to the injection current be kept within about 0.8 nm.

For this reason, the chirped grating used in the laser module of the present invention has a reflection bandwidth of 0.1 to 4.0 nm, preferably 0.1 nm.
The usefulness of setting the wavelength to 2 to 1.5 nm is apparent.

[0041]

As is apparent from the above description, the laser module of the present invention has a pumping laser beam of 940 output.
It is in the wavelength band of １1100 nm and is multi-mode, and its light output is stabilized. This is because the reflection spectrum of the reflected light at the optical feedback section formed in the laser module becomes substantially rectangular, and the longitudinal mode of the oscillation laser light from the laser element included in the wavelength band increases.

The laser module of the present invention can return light in a wide wavelength band to the laser element by using a chirped grating, and can reduce the threshold level required for oscillation of the laser element in a wide wavelength band. Lower,
Longitudinal mode oscillation that exists in the wavelength band where the threshold level of the laser element has been reduced becomes possible. As a result, the oscillation laser light from the laser element becomes multimode.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one example of a laser module.

FIG. 2 is a schematic view showing a basic configuration example of a laser module according to the present invention.

FIG. 3 is a reflection spectrum diagram of reflected laser light in a light feedback section of the laser module of the present invention.

FIG. 4 is an explanatory diagram for describing a shape of a reflection spectrum.

FIG. 5 is a reflection spectrum diagram of another shape.

FIG. 6 is a schematic diagram showing a basic configuration example of another laser module of the present invention.

FIG. 7 is a characteristic diagram showing reflection characteristics of a bandpass filter.

FIG. 8 is a characteristic diagram showing reflection characteristics of a reflector.

FIG. 9 is a characteristic diagram showing a reflection characteristic of reflected light returning from the reflector of FIG. 5;

FIG. 10 is a perspective view showing one example of a layer structure of a laser element in the embodiment.

FIG. 11 is a graph showing the variation of the optical output of the excitation laser light from the laser module.

FIG. 12 is a graph showing a relationship between an injection current and a peak wavelength in an oscillation spectrum.

[Explanation of symbols]

1 housing 3 laser element 5 lens (optical coupling means) 7 optical fibers 7a fiber grating (light feedback portion) 7b, the end faces A ₁ chirped grating facet 8 bandpass filter 9 reflector 9a reflector 9 7c optical fiber 7 ( Optical feedback section) A ₂ Optical feedback section C Optical axis

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H037 AA01 BA03 CA05 CA33 DA03 DA38 5F073 AA13 AA46 AA72 AB25 AB27 AB28 AB29 BA03 CA07 EA01 EA15

Claims (14)

[Claims] 1. A semiconductor laser device comprising: a semiconductor laser device; an optical fiber; an optical coupling unit that causes laser light emitted from the semiconductor laser device to enter the optical fiber; and a light feedback unit that reflects laser light of a specific wavelength. A semiconductor laser module, wherein the reflection spectrum shape of the light feedback section is substantially rectangular. 2. A reflection bandwidth in the reflection spectrum which shows a reflectance equivalent to 80% with respect to a peak reflectance,
2. The semiconductor laser module according to claim 1, wherein the reflectance is equal to or more than 0.85 times the reflection bandwidth in the reflection spectrum, the reflectance being equivalent to 70% with respect to the peak reflectance. 3. The semiconductor laser module according to claim 1, wherein a wavelength of the laser light emitted from said semiconductor laser element is in a range of 940 to 1100 nm. 4. A wavelength bandwidth in the reflection spectrum, which shows a reflectance equivalent to 80% with respect to a peak reflectance,
2. The semiconductor laser module according to claim 1, wherein the value is at least three times the longitudinal mode interval of the laser light emitted from the semiconductor laser element. 5. The semiconductor laser module according to claim 1, wherein said optical feedback section is a chirped grating formed on said optical fiber. 6. The bandpass filter according to claim 1, wherein the optical feedback unit is disposed obliquely with respect to an optical axis and transmits only laser light of a specific wavelength, and a wavelength disposed on an emission side of the bandpass filter. 2. The semiconductor laser module according to claim 1, wherein said semiconductor laser module is formed of a reflector having independent reflection characteristics. 7. The semiconductor laser module according to claim 6, wherein said reflector is an end face of said optical fiber on which laser light is incident. 8. A semiconductor laser device, comprising: an optical fiber; an optical coupling unit that causes laser light emitted from the semiconductor laser device to enter the optical fiber; and an optical feedback unit that reflects laser light of a specific wavelength. A semiconductor laser module, wherein a reflection spectrum shape of the light feedback section is a shape having a peak and a valley at a top portion. 9. A reflection bandwidth in the reflection spectrum which shows a reflectance equivalent to 80% with respect to a peak reflectance,
9. The semiconductor laser module according to claim 8, wherein the semiconductor laser module exhibits a reflectance equivalent to 70% with respect to the peak reflectance, and has a value equal to or more than 0.85 times the reflection bandwidth in the reflection spectrum. 10. The semiconductor laser module according to claim 8, wherein a wavelength of the laser light emitted from said semiconductor laser element is in a range of 940 to 1100 nm. 11. A wavelength bandwidth in the reflection spectrum, which shows a reflectance equivalent to 80% with respect to a peak reflectance, is a value that is three times or more a longitudinal mode interval of laser light emitted from the semiconductor laser device. The semiconductor laser module according to claim 8. 12. The semiconductor laser module according to claim 8, wherein said optical feedback section is a chirped grating formed on said optical fiber. 13. The optical feedback unit according to claim 1, wherein the optical feedback unit includes a band-pass filter that is arranged to be inclined with respect to an optical axis and transmits only a laser beam of a specific wavelength, and a wavelength that is arranged on an emission side of the band-pass filter. 9. The semiconductor laser module according to claim 8, wherein said semiconductor laser module is formed of a reflector having independent reflection characteristics. 14. The reflector receives a laser beam,
9. The semiconductor laser module according to claim 8, which is an end face of said optical fiber.