JPH1062654A - Semiconductor laser module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the oscillating wavelength to stabilize the gain of an optical fiber amplifier by setting the half-width of the reflectance spectrum of a fiber grating to a specified number times or more of the resonator mode interval of a semiconductor laser element. SOLUTION: This semiconductor laser module has a fiber grating whose half-width of reflectance spectrum is 2. 5 times or more of the resonator mode interval of a semiconductor laser element. The half-width Δλ of reflectance spectrum of the fiber grating is changed to set the wavelength skip probability to 2 % or less, preferably 1% or less. When the ratio of the half-width Δλof reflectance spectrum of the fiber grating to the resonator mode interval Δλm of the semiconductor laser element is 2.5 or more (Δλ/Δλm <=. 2.5), or at least 2.5 resonator internal modes, more preferably, 2. 8 resonator modes are present in the half-width Δλ of the reflectance spectrum, the wavelength skip probability is smaller than 2% and 1%, respectively, to stabilize the oscillating wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a semiconductor laser module using an optical fiber grating.

[0002]

2. Description of the Related Art As an excitation light source for amplification using an erbium-doped optical fiber in which erbium is added to the core of an optical fiber, those having a wavelength band of 1480 nm and a wavelength band of 980 nm are used. Of these, the excitation light source in the 1480 nm wavelength band has already been put to practical use and is being actively used. On the other hand, the pumping light source in the 980 nm wavelength band is currently in the development stage, and is expected to be put to practical use in the future in that it has lower noise and lower power consumption than those in the 1480 nm wavelength band. The width of the absorption band in the 980 nm wavelength band of this erbium-doped optical fiber is + centered around 980 nm.
/ −5 nm, and +/− 1 in the 1480 nm wavelength band.
Very narrow compared to 5 nm. Therefore, a semiconductor laser module serving as an excitation light source in a 980 nm wavelength band is required to have an oscillation wavelength within the wavelength range of about 10 nm.

It is known that the oscillation wavelength of a semiconductor laser device changes when the driving current and the operating temperature are changed. For example, the oscillation wavelength of an AlGaAs-based semiconductor laser device is 0.02 n
m / mA, and changes at a rate of 0.4 nm / K with respect to temperature. Therefore, if the driving current changes by 100 mA and the temperature changes by 10 ° C., the wavelength changes by 6 nm due to these factors. For this reason, when selecting a semiconductor laser element for a semiconductor laser module serving as an excitation light source, the oscillation wavelength must be within the required absorption band of the optical fiber within the range of the drive current and the operating temperature to be used. Must.

As a method for solving this problem, it is known to use a fiber grating for a semiconductor laser module. FIG. 1 shows an example of a 980 nm wavelength semiconductor laser module equipped with a fiber grating for such a purpose. In FIG. 1, 1 is a semiconductor laser device, 2 is a collimator lens, 3
Is a condenser lens, 4 is an optical fiber, 5 is a Peltier element for cooling, 6 is a copper base, 7 is a package, 8 is a fiber grating, and 9 is a reinforcing member. As can be seen from the reflectance spectrum shown in FIG. 2, the fiber grating 8 has a center wavelength of 980 nm and a peak reflectance of 4%.
And the half width is about 0.3 nm. In this semiconductor laser module, a laser beam emitted from a semiconductor laser element 1 is coupled to an optical fiber 4 by a collimator lens 2 and a condenser lens 3, and only a specific wavelength component is partially reflected by a fiber grating 8 so that the semiconductor laser It is returned to element 1. At this time, the oscillation wavelength of the semiconductor laser device 1 is drawn into the center wavelength of the fiber grating 8.

FIG. 3 shows this pull-in phenomenon.
Generally, when the temperature of the semiconductor laser element is changed, the oscillation wavelength changes as indicated by a broken line. However, when coupled to a fiber grating, the oscillation wavelength becomes almost constant regardless of the temperature of the semiconductor laser element, as indicated by the solid line. . This phenomenon is considered to be due to the fact that the loss in the composite resonator system of the fiber grating and the semiconductor laser element is reduced at the center wavelength of the grating, so that the resonator mode near the center wavelength of the grating is selectively excited.

[0006]

However, the present inventors have found that the semiconductor laser module equipped with the fiber grating as described above has the following problems. That is, as shown in FIG. 4, the oscillation wavelength changes over time between the reflection center wavelength of the fiber grating and the oscillation wavelength of the semiconductor laser device itself, and becomes unstable. If there is such an oscillation wavelength jump, when a semiconductor laser module is used for an optical fiber amplifier,
There is a disadvantage that the gain of the amplifier changes abruptly.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a semiconductor laser device which emits oscillating light in a desired wavelength band and a semiconductor laser device which emits a specific wavelength component in the wavelength band. In a semiconductor laser module having a fiber grating for reflecting light to a laser element, a half-width of a reflectance spectrum of the fiber grating is at least 2.5 times a cavity mode interval of the semiconductor laser element. .

[0008] The present invention is based on new experimental findings obtained as a result of intensive studies. That is, as shown in FIG. 5, for example, the half-width Δλ of the reflectance spectrum of the fiber grating is changed to obtain the wavelength jump probability. Here, the wavelength jump probability on the vertical axis is the total time of the oscillation time when the semiconductor laser device is continuously driven with a direct current for a certain time, and the oscillation wavelength is the oscillation wavelength when there is no fiber grating. Percentage.
This value is required to be 2% or less, more preferably 1% or less, in order to stabilize the gain of the optical fiber amplifier over time. The horizontal axis, and the half-width [Delta] [lambda] of the reflectivity spectrum of the fiber grating, the ratio of the resonator mode interval [Delta] [lambda] _m of the semiconductor laser element, is inside the resonator mode in the half-width [Delta] [lambda] of the reflectivity spectrum Indicates how many are included. As can be seen from FIG. 5, when at least 2.5 resonator modes exist in Δλ (Δλ / Δλ _m ≧ 2.5), more preferably, when 2.8 resonator modes exist. (Δλ / Δλ _m
≧ 2.8), it can be seen that the wavelength jump probabilities are smaller than 2% and 1%, respectively, and the oscillation wavelength is stabilized. Therefore, when a semiconductor laser module using a fiber grating whose Δλ satisfies this condition is used for an optical fiber amplifier, it can be expected that the operation of the amplifier will be stable.

The above experimental findings can be considered as follows. That is, the loss of the composite resonator system composed of the fiber grating and the semiconductor laser element decreases near the center wavelength of the fiber grating. Therefore, if the cavity mode of the semiconductor laser device exists within the half-width Δλ of the reflectance spectrum of the grating, oscillation is likely to occur in that mode. If [Delta] [lambda] is smaller than the cavity mode spacing [Delta] [lambda] _m of the semiconductor laser device, when the FIG. 6 (a), the like (b), for example, a semiconductor laser device in the vicinity of the central wavelength of the reflection spectrum of the fiber grating Is not always present, the operation of the resonator system becomes unstable,
Even if a wavelength pull-in occurs, pull-in may not occur due to a slight change in operating conditions such as an operating temperature and a drive current. However, as shown in FIG. 6C, if there are many resonator modes of the semiconductor laser element within Δλ, the resonator mode of the semiconductor laser element always exists within Δλ even if the operating conditions slightly change. Therefore, since the wavelength is always drawn, the oscillation wavelength of the composite resonator system including the fiber grating and the semiconductor laser element is stabilized. For this purpose, from the experimental results shown in FIG. 5, Δλ / Δλ _m ≧ 2.5, more preferably Δλ / Δm
It is sufficient that λ _m ≧ 2.8 or more.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a semiconductor laser module according to the present invention will be described in detail. The semiconductor laser module of the present embodiment uses, for example, an AlGaAs-based semiconductor laser element having a resonator length L = 700 μm and a relative refractive index n _r = 3.5 as a semiconductor laser element in the 980 nm band, and uses a wavelength as a fiber grating. 980 nm
And a half-width Δλ = 0.65 nm of the reflectance spectrum was used. The interval Δλ _m between the resonator modes of the semiconductor laser device can be calculated as follows. ^{_{That, Δλ m = λ 2 / 2n}} r L = 0.2nm ( where, lambda: band wavelength 980 nm) Thus, in the present embodiment, Δλ / Δλ _m = 3.2
It becomes 5. With respect to this semiconductor laser module, when the change over time of the oscillation wavelength was measured, as shown in FIG.
During the operation time of 200 seconds, no jump of the oscillation wavelength occurred. On the other hand, as a comparative example, a semiconductor laser module was constructed using the same semiconductor laser element and using a fiber grating having a Δλ of 0.35 nm. In this comparative example, Δλ / Δλ _m = 1.75. With respect to this semiconductor laser module, the change with time of the oscillation wavelength was measured, and as shown in FIG. 4, the oscillation wavelength jumped.

[0011]

As described above, the semiconductor laser module according to the present invention has an excellent effect that the oscillation wavelength is stabilized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a semiconductor laser module.

FIG. 2 is a diagram showing a reflectance spectrum of a fiber grating.

FIG. 3 is a diagram showing the relationship between the oscillation wavelength of a semiconductor laser device and temperature.

FIG. 4 is a diagram showing a time change of an oscillation wavelength of a semiconductor laser module.

FIG. 5 is a diagram showing the relationship between the jump probability and Δλ / Δλ _m of the oscillation wavelength.

6 (a) to 6 (c) show the jump probability of the oscillation wavelength and Δλ.
FIG. 4 is an explanatory diagram of a relationship of / Δλ _m .

FIG. 7 is a diagram showing a change over time of the oscillation wavelength of one embodiment of the semiconductor laser module according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser element 2 Collimator lens 3 Condensing lens 4 Optical fiber 5 Peltier element 6 Base 7 Package 8 Fiber grating 9 Reinforcement member

Claims (1)

[Claims] 1. A semiconductor laser module comprising: a semiconductor laser device that emits oscillation light in a desired wavelength band; and a fiber grating that reflects a specific wavelength component in the wavelength band to the semiconductor laser device. A semiconductor laser module, wherein a half value width of a rate spectrum is at least 2.5 times a cavity mode interval of the semiconductor laser device.