JPH02260480A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To stabilize negative feedback of a wind band even if frequency of a semiconductor laser and temperature of an etalon are varied by so negative feeding back to sweeping means of a sweep type Fabry-Perot etalon that the output signal of a photodetector attains a special value. CONSTITUTION:A semiconductor laser 3 outputs a light having an oscillating frequency set by a sweep signal 1, and a light reflected by a beam splitter 4 enters a sweep type Fabry-Perot etalon 5. Since the micro voltage output of an oscillator 8 is applied to the etalon 5 and swept by frequency fm at the Miller interval of the etalon 5, its resonance characteristic laterally moves in frequency fm at the transmission peak. The transmitted light of the etalon 5 is detected by a photodetector 6, its output electric signal is synchronously detected with frequency 2fm by a controller 7 to become a quadratic differentiation waveform signal, and the controller 7 drives sweeping means 52 to attain a zero point of this waveform. Thus, even if the oscillation frequency of the laser 3 and the temperature of the etalon 5 are varied, a wide band negative feedback becomes stable to reduce a spectral width.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to improving the characteristics of a device for stabilizing the wavelength of a semiconductor laser.

<Conventional technology> Narrowing the spectrum of semiconductor lasers is an important issue in coherent optical communication and cohesin l-optical measuring instruments. 6 For example, the method of narrowing the spectrum by passing the output light of a semiconductor laser through a Fabry-Perot etalon, converting phase fluctuations (frequency fluctuations) into amplitude fluctuations and feeding them back over a wide band, has already been proposed. (Furutashima, Otsu: Narrowing the oscillation linewidth of a 1,5.czm171 GaAgp laser by injection current control, Confucian Technical Report 0QE84-130).

<Problems to be Solved by the Invention> In a semiconductor laser device having the above configuration, in order to apply wideband negative feedback, the oscillation wavelength of the semiconductor laser is set in advance to the highest gain when converting phase fluctuation into amplitude fluctuation. It is necessary to set this to the part of the Fapry-Perot etalon resonance characteristic. However, in general, the wavelength of a semiconductor laser is not constant, and when used as a variable wavelength light source, the frequency is swept, so it is unclear where the operating point will be in the characteristics of the etalon. Furthermore, even if the laser frequency is stabilized, the etalon's discrimination sensitivity will change due to etalon temperature drift, laser power fluctuations, etc. This makes broadband negative feedback unstable, making it possible to achieve a sufficiently narrow spectral width. Can not. Furthermore, if the etalon were placed in a constant temperature bath to prevent drift or to sweep the frequency with temperature, the structure would be large and complicated.

The present invention has been made to solve these problems, and aims to realize a semiconductor laser device with a narrow spectrum width and stable negative feedback over a wide band even when the frequency of the semiconductor laser or the temperature of the etalon changes. With the goal.

Means for Solving the Problems> A semiconductor laser device according to the present invention includes a semiconductor laser, a swept Fabry-Bello etalon into which a part of the output light of the semiconductor laser is incident, and the swept Fabry-Bello etalon.
a light-receiving element for detecting light transmitted through the etalon; a first control circuit for providing negative feedback to the sweeping means of the swept Fabry-Bello etalon so that the output signal of the light-receiving element becomes a specific value; Reduce the fluctuation component of the element output! and a broadband second control circuit that controls the injection current of the semiconductor laser so as to control the injection current of the semiconductor laser.

Effect> Fabrication is performed so that the output signal of the light receiving element becomes a predetermined value.
Since the mirror spacing of the bellows etalon is controlled and the Fabry-bellows etalon can always obtain a predetermined discrimination sensitivity, negative feedback can be stably applied.

<Example> The present invention will be explained in detail below using the drawings.

FIG. 1 is a block diagram showing an embodiment of a semiconductor laser according to the present invention. 1 is an input terminal for a laser frequency sweep signal, 2 is an inductance for wide-range cutting through which the sweep signal passes, 3 is a semiconductor laser whose oscillation frequency is set by the sweep signal via the inductance 2, and 4 is an input terminal of the semiconductor laser 3. A beam splitter that separates the output light into two directions; 5 is a PZ that receives the reflected light from the beam splitter 4;
In the etalon 5, which is a Till pull type fab type Fabry etalon (hereinafter referred to as etalon), 51 is an opposing mirror, and 52 is a p z 'r constituting a sweeping means for changing the interval between the mirrors 51. 6 is a light receiving element that detects the light transmitted through the etalon 5; 7 is a first control circuit that negatively feeds back the output electrical signal of the light receiving element 6 to the P Z 'r'' 52 of 5; 8 is an oscillator; 9 is an oscillator 8 an adder circuit that adds the output of the control circuit 7 with the output of the control circuit 7 and applies the result to the PzT 52;
10 is a multiplier circuit which generates a frequency signal twice the output frequency of the oscillator 8 and serves as a reference signal input to the control circuit 7; 11;
amplifies the output of the light-receiving element 6 in a wide band and transmits it to the semiconductor laser 3.
A wideband amplifier 12 constitutes a second control circuit that provides negative feedback to the injected current. Reference numeral 12 is a low-frequency cut capacitor to which the output of the wideband amplifier 11 is added. The first control circuit 7 includes a detection circuit such as a lock-in amplifier and a PI connected to the detection circuit.
It consists of a D controller, etc.

The operation of the semiconductor laser device configured as described above will be explained next. The semiconductor laser 3 outputs light at an oscillation frequency set by the sweep signal input to the terminal 1. Figure 2 (A)
This light, whose frequency spectrum is shown in , passes through the beam splitter 4 and becomes output light to the outside. The light reflected by the beam splitter 4 enters the etalon 5. The mirror spacing of the etalon 5 is determined by the minute voltage output of the oscillator 8.
'! ” 5 and the frequency f,,'t-swept, its resonance characteristic shown in Fig. 2(B) is as follows:
is moving left and right at frequency f. The transmitted light of the etalon 5 is detected by the light receiving element 6, and the output electric signal modulated at the frequency f is synchronously detected at the frequency 2f in the control circuit 7, and the quadratic differential as shown in FIG. 2(D) is obtained. It becomes a waveform signal. The control circuit 7 is connected to the zero point of this waveform as shown in Fig. 2 (D).
The PZT 52 is driven so as to reach point A). By applying negative feedback to the etalon 5 as described above, the etalon 5 always has a peak of the first-order differential waveform shown in FIG. It is controlled to reach the point of maximum slope in the figure (,B). As a result, even if the frequency of the semiconductor laser 3 is swept, the etalon follows while being locked to the point A. In this state, as shown in FIG. 3, in the output of the light receiving probe 6, a signal appears in which the phase fluctuation b based on the width of the laser spectrum a is converted into an amplitude fluctuation d by the resonance characteristic C of the etalon 5. As mentioned above, the etalon 5 is controlled to be at the point of maximum slope of the resonance characteristic of the etalon 5 at the oscillation frequency of the semiconductor laser 3, and this point is also the point where the detection sensitivity is maximum. The detected amplitude fluctuation signal is sent to a wideband amplifier 11. Negative feedback is stably provided to the semiconductor laser via the capacitor 12, narrowing the oscillation spectrum width.

According to the semiconductor laser device having such a configuration, even if the oscillation frequency of the semiconductor laser changes or the temperature of the etalon changes, the etalon always follows and locks at the point of maximum detection sensitivity. Broadband negative feedback stabilizes the spectrum, making it possible to narrow the spectrum width.

Further, since there is no need to place the etalon in a constant temperature bath, miniaturization is easy.

In the above embodiment, if a semiconductor laser whose wavelength is stabilized by locking it to the absorption line of Rb or the like or the resonance characteristics of a Fabry-Bérot etalon is used as the semiconductor laser, a highly stable light source with a narrow spectrum can be obtained.

In addition, the mirror 51 of the etalon 5 may be composed of two semi-transparent concave mirrors arranged so that the focal point of each is on the mirror surface of the other, or one in which a semi-transparent concave mirror is opposed to a plane mirror. By using , it is possible to further reduce the size.

Alternatively, instead of detecting the transmitted light of the etalon 5, the resonance characteristics of the reflected light may be used.The zero reflected light has the minimum power when it resonates, so the phase is opposite, but it can be used in the same way.

FIG. 4 is a block diagram showing another embodiment of the semiconductor laser according to the present invention. The same parts as in FIG. 1 are given the same symbols and the explanation is omitted. The difference from FIG. 1 is that the etalon 5 is not phase-modulated and synchronously detected at twice the frequency, but is locked at the maximum slope point by applying a bias voltage. In order to avoid shifting from the locked point even if the power of the semiconductor laser 3 varies, a part of the output light of the semiconductor laser 3 is reflected by the beam splitter 13 and detected by the light receiving element 14, and the output light of the light receiving element 6 and the output light of the light receiving element 6 are detected. The subtractor 15 calculates the difference between the two.

The first control circuit 17 controls the etalon 5 so that its output becomes equal to a predetermined bias voltage V of the voltage source 17. By setting the voltage V to the maximum slope point, the same effect as in the case of FIG. 1 can be obtained.

<Effects of the Invention> As described above, according to the present invention, a semiconductor laser device with a narrow spectrum width, in which wide-band negative feedback is stably applied even when the frequency of the semiconductor laser or the temperature of the etalon changes, can be easily constructed. It can be realized.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of the semiconductor laser device according to the present invention, FIG. 2 is a characteristic curve diagram for explaining the operation of the device shown in FIG. 1, and FIG. 3 is an operation of the device shown in FIG. 1. FIG. 4 is a block diagram showing a second embodiment of the semiconductor laser device according to the present invention. 3... Semiconductor laser, 5... Swept type Fabry-Bello etalon, 6... Photodetector, 7.17... First
control circuit, 11... second control circuit.

Claims (1)

[Claims] A semiconductor laser, a swept Fabry-Perot etalon into which part of the output light of the semiconductor laser is incident, a light receiving element that detects the transmitted light of the swept Fabry-Perot etalon, and an output signal of this light receiving element. a first control circuit that provides negative feedback to the sweeping means of the swept Fabry-Perot etalon so that it reaches a predetermined value; and a first control circuit that controls the injection current of the semiconductor laser so as to reduce a fluctuation component of the output of the light receiving element. 1. A semiconductor laser device comprising: a broadband second control circuit.