JPH01230278A - Wavelength stabilizing device for semiconductor laser - Google Patents

Abstract

PURPOSE:To reduce the size and cost of a device, by controlling the wavelengths of semiconductor lasers with the outputs of a photoelectric receiving element measuring transmitted beam intensities. CONSTITUTION:A spectrum of a plurality of absorption lines at almost equal intervals is obtained by branching the output beams of semiconductor laser 101-10n with a branching device 11, inputting them into a light modulator 12, modulating them with the output of an oscillator 17, and making them strike an absorption cell 13. When the transmitted beams through the absorption cell 13 are inputted into a lock-in amplifier 15, and when they are so controlled that the outputs of the lock-in amplifier 15 may become zero, the wavelengths of the output beams can be locked at the peak wavelengths value of the absorption lines of the absorption spectrums. Accordingly, an output of a plurality of stabilized wavelengths at equal intervals can be produced with one absorption cell.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a device for stabilizing the wavelength of output light of a semiconductor laser, and in particular to a semiconductor laser capable of outputting light of a plurality of wavelengths that are approximately equally spaced. This invention relates to a wavelength stabilizing device.

<Prior art> Fig. 6 shows a wavelength stabilizing device for a semiconductor laser.
In the figure, output light from a semiconductor laser 1 is split into two by a beam splitter 2, and the other is reflected by a mirror 3 and taken out to the outside.

Further, the other branched light is incident on the absorption cell 4.

A standard substance that absorbs light of a specific wavelength, such as 87Rb, is sealed inside the absorption cell 4 . The light transmitted through the absorption cell 4 is incident on a photodetector 5, and its intensity is measured. The output of this photodetector 5 is the lock-in amplifier 6
The current is synchronously rectified and input to the current control circuit 7. The output of this current control circuit 7 and the output of an oscillator 8 that oscillates an output of frequency fm are added and fed back to the semiconductor laser, and the output of the 9 oscillator 8 whose drive current is controlled is also input to the lock-in amplifier 6. be done.

In such a configuration, only light of a specific wavelength is absorbed from the light transmitted through the absorption cell 4, and the intensity of the transmitted light becomes weak only at that wavelength. Therefore, by controlling the driving current of the semiconductor laser 1 by the current control circuit 7 so that the output of the photodetector 5 is constant, the wavelength of the output light can be made constant.

Note that the output light of the semiconductor laser 1 is modulated at the frequency fm by the output of the oscillator 8, and is synchronously rectified at the same frequency by the lock-in amplifier 6.
The wavelength of the output light can be precisely controlled to a constant value.

<Problems to be Solved by the Invention> However, such wavelength stabilizing devices for semiconductor lasers have the following problems. Frequency multiplex communication is one of the procedures for transmitting large-capacity data using optical communication. This involves transmitting a large number of lights with slightly different wavelengths through a single optical fiber, each of which is used as a medium for data transmission. To do this, many light sources with different wavelengths are required at equal intervals. . One wavelength stabilizing device for a semiconductor laser shown in Fig. 6 can output only one wavelength of light, so a large number of devices are required to perform such frequency multiplexing communication, making the configuration complicated. There was also the problem that it was expensive.

<Objective of the Invention> An object of the present invention is to provide a wavelength stabilizing device for a semiconductor laser, which is capable of outputting light of a plurality of substantially equally spaced wavelengths with one device.

Means for Solving the Problems> In order to solve the above problems, in the present invention, a part of the output light of at least three semiconductor lasers is incident on an absorption cell in which a standard substance having at least three absorption lines is enclosed. The intensity of transmitted light of the absorption cell is measured by a light receiving element arranged corresponding to the plurality of semiconductor lasers, and the wavelength of the semiconductor laser is controlled by the output of this light receiving element.

<Embodiment> FIG. 1 shows an embodiment of a wavelength stabilizing device for a semiconductor laser according to the present invention. In FIG. 1, 101 to Ion are semiconductor lasers, and their output lights are input to a splitter 11 and branched into two. 12 is an optical modulator;
Semiconductor laser 101~ton branched by splitter 11
One of the output lights is incident and modulates these lights. The optical modulator 12 uses an acousto-optic modulator or an electro-optic modulator. 13 is an absorption cell into which light modulated by the optical modulator 12 is incident. This absorption cell 13 contains an aK quasi-substance that absorbs light of a specific wavelength. 14 is a light receiver, which includes a plurality of light receiving elements. A row of individual photodiodes or a photodiode array is used. The light receiving element of the light receiver 14 includes an absorption cell 13.
transmitted light is incident. 15 is a lock-in amplifier, into which the output of the light receiver 14 is input. 16 is a control circuit to which the output of the lock-in amplifier 15 is input.

The output of this control circuit 16 is the semiconductor laser 101 to Io.
input to n. Reference numeral 17 denotes an oscillator which oscillates an output at a frequency fIl, the output of which is input to the optical modulator 12 and the lock-in amplifier 15. The optical modulator 12 is connected to this oscillator 1.
The input light is modulated by the output of the lock-in amplifier 15, and the lock-in amplifier 15 performs synchronous rectification using the same signal or a signal having a frequency that is an integral multiple thereof. 181 to 18n are optical modulators, into which the other of the output lights of the semiconductor lasers 101 to 10n branched by the splitter 11 is inputted. Optical modulators 181-18
n is modulated by the data to be transmitted by a modulating signal. Numeral 19 is a multiplexer into which the output lights of the optical modulators 181 to 18n are input, multiplexed, and output as an optical fiber or a spatial beam.

Next, one of the output lights of the semiconductor lasers 101 to 10n, which are split into two by a zero splitter 11, which will explain the operation of this embodiment, is input to an optical modulator 12.

The output of the oscillator 17 is also input to the optical modulator 12 . The optical modulator 12 modulates the incident light with the output of the oscillator 17. This modulated light is incident on the absorption cell 13. For example, acetylene is sealed in the absorption cell 13 as a standard substance. The absorption spectrum of molecules such as acetylene includes a spectrum due to electronic transition, a spectrum due to vibration, and a spectrum due to rotation. Usually, vibration and rotation are combined to form an equally spaced band structure as shown in Figure 2.
Therefore, if attention is focused only on a narrow portion, the spectrum will have a plurality of absorption lines at approximately equal intervals as shown in FIG. 3. The wavelengths of the output lights of the semiconductor lasers 101 to Ion are locked to different absorption lines, for example, those marked with O. That is, the individual absorption lines due to the standard material in the absorption cell 13 are expressed as shown in FIG. 4(A), and the transmitted light intensity changes depending on the wavelength.
When the wavelength of the output light of the semiconductor lasers 101 to 10n is modulated at the frequency fl by The differential value of the change in transmitted light intensity with respect to the change in wavelength can be obtained. Therefore, control circuit 1
6, performs PID control etc., and lock-in amplifier 1
Semiconductor lasers 101 to 1 so that the output of 5 becomes zero
By controlling the wavelength of the output light by changing the 0n drive current or the ambient temperature, it is possible to lock the wavelength of the output light to the peak wavelength of the absorption line of the absorption spectrum of the standard substance. As shown in FIG. 3, acetylene and the like have multiple absorption lines, so by locking the wavelength of the output light from the semiconductor lasers 101 to Ion to each absorption line,
It is possible to obtain light of multiple stable wavelengths at the same time. Note that when there is no need to modulate the multi-wavelength output light, the optical modulators 181 to 18n are unnecessary, and when multiplexing is not required, the multiplexer 19 is also unnecessary.

FIG. 5 shows an embodiment of the present invention. In this embodiment, the wavelength of the output light is modulated by controlling the driving flow of the semiconductor lasers 101 to LOn, and the modulation frequency is changed. . Note that the same elements as in FIG. 1 are given the same reference numerals and their explanations will be omitted. In FIG. 5, 20 is a multiplexer, into which the output lights of the semiconductor lasers 101 to Ion are input, and these lights are multiplexed. This multiplexed light is transmitted through the optical fiber 21. 22 is a demultiplexer, which demultiplexes the light multiplexed by the multiplexer 20 again. This demultiplexed light is incident on an absorption cell 13, and the light intensity of the light transmitted through the absorption cell 13 is converted into a current signal by a light receiver 14. 2
21 to 22n are lock-in amplifiers, into which the output of the light receiver 14 is input. This lock-in amplifier 221-22
n also has a frequency f from the oscillators 231 to 23n.
A signal is input to Noki 1. The lock-in amplifiers 221 to 22n synchronously rectify the input output of the photodetector 14 at a frequency f, 1 to f4 degrees. These outputs are input to the control circuit 16. 241 to 24n are adders, each of which is connected to the oscillator 2.
31 to 23n and the output of the control circuit 16, which corresponds to the output of the lock-in amplifiers 221 to 22n, are added. The drive currents of the semiconductor lasers 101-Ion are controlled by the outputs of the adders 241-24n. Since the operation is the same as that of the embodiment shown in FIG. 1, the explanation will be omitted.

Although this embodiment has the disadvantage that the wavelengths of the multi-wavelength output light are modulated, it has the advantage that it simplifies the configuration because no optical modulator is required, and that mutual interference is reduced because the modulation frequencies are different. be.

Note that in the embodiment shown in FIG. 1, semiconductor lasers 101 to Io
It is also possible to modulate by changing the driving current of n.

In addition, in the embodiments shown in FIGS. 1 and 5, a lock-in amplifier is used to place the semiconductor lasers 101 to 10n at the center of the absorption line.
Although the wavelength of the output light of the light receiver 14 is locked, it may be locked at the shoulder of the absorption line.In this case, a lock-in amplifier is not necessary, and the output of the light receiver 14 is kept constant. The control circuit 16 controls the semiconductor lasers 101 to Ion.
All you have to do is control it.

Further, an optical fiber converter or a beam splitter may be used for the splitter, demultiplexer, and multiplexer.

<Effects of the Invention> As explained above based on specific examples, in this invention, a part of the output light of a plurality of semiconductor lasers is encapsulated with a standard substance having a plurality of absorption lines at approximately equal intervals. The wavelength of the output light of the semiconductor laser is locked to each of a plurality of absorption lines by entering the absorption cell and returning the transmitted light to the semiconductor laser. Therefore, it is possible to output light of a plurality of stable wavelengths at approximately equal intervals with one absorption cell, and it is possible to realize an inexpensive and small wavelength stabilizing device that outputs light of a plurality of wavelengths.

[Brief explanation of the drawing]

1 [J is a configuration diagram showing an embodiment of the semiconductor laser wavelength stabilizing device according to the present invention, FIGS. 2 to 4 are characteristic curve diagrams for explaining the operation, and FIG. FIG. 6 is a block diagram showing another embodiment of the present invention, and FIG. 6 is a block diagram of a conventional wavelength stabilizing device for a semiconductor laser. DESCRIPTION OF SYMBOLS 11... Brancher, 12... Optical modulator, 13... Absorption cell, 14... Light receiver, 15,221-22n...
・Lock-in amplifier, 16... Control circuit, 20...
Multiplexer, 22...Demultiplexer, 101~Ion...Semiconductor laser, Figure 3, Figure 4 (A) Broken table (B), Figure 5, Figure 6] b

Claims (1)

[Claims] at least three semiconductor lasers, an absorption cell in which a part of the output light of these semiconductor lasers is input and a standard substance having at least three substantially equally spaced absorption lines is enclosed, and the absorption cell is arranged corresponding to the semiconductor laser. at least three light receiving elements into which the output light of the absorption cell is incident;
A wavelength stabilizing device for a semiconductor laser, comprising: a control section to which the output of the light receiving element is input and controls the wavelength of the output light of the semiconductor laser.