JPH03135088A - Semiconductor laser beam width constriction apparatus - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser beam width constriction apparatus which is stably operated with a simple structure by so injecting part of a laser output light to a semiconductor laser as not to interfere with the laser output light through a resonance absorption medium. CONSTITUTION:A semiconductor laser 1, a resonance absorption medium (adsorption cell) 5, and light feedback means (collimating lens 3, the cell 5, an optical attenuator 11, a lambda/4 plate 10, and a reflecting mirror 9) are provided. Part of the output light of the laser 1 is incident to the cell 5, and the passed light is so injected to the laser 1 as not to interfere with the output light of the laser 1 by the feedback means. With this structure, if the laser 1 is oscillated, when a frequency (f) becomes high, the transmitted light intensity P of the cell 5 is increased. As a result, the carrier density of the active layer of the laser 1 is reduced, and its refractive index is decreased to reduce the frequency (f). If the frequency (f) is, on the contrary, decreased, the frequency (f) is increased. That is, a negative feedback control for suppressing the variation in the frequency is conducted by a light feedback system. Thus, the beam width constriction is stabilized.

Description

[Detailed description of the invention] "Industrial application field" The present invention relates to a semiconductor laser linewidth narrowing device.

"Conventional Technology J Since the cavity of a semiconductor laser is very small, the number of stimulated emission photons stored in the cavity is far smaller than that of gas lasers. Therefore, spontaneous emission photons can easily mix into the oscillation mode. The phase is disturbed,
The oscillation frequency changes and the line width widens. When using a semiconductor laser for light wave communication, optical measurement, optical bombing of an atomic oscillator, etc., it is necessary to sufficiently narrow the line width of the semiconductor laser. Several techniques are used for this purpose.

FIG. 2 is a diagram showing an example of a semiconductor laser line width narrowing device configured by an electrical device.

In the figure, ■ is a semiconductor laser, 2 is a current source, 3 is a collimating lens, 4 is an optical isolator, 5 is an absorption cell,
6 is an avalanche photodiode, and 7 is an injection current control circuit.

A part of the output light of the semiconductor laser I is collimated by the collimating lens 3 and enters the absorption cell 5.

This absorption cell 5 has a semiconductor laser! Atoms and molecules having a resonance absorption spectrum near the oscillation frequency are enclosed, and there is a relationship between the frequency r of the semiconductor laser l and the transmitted light intensity P of the absorption cell 5 as shown in FIG. The transmitted light of the absorption cell 5 is detected by the avalanche photodiode 6, and a detection signal corresponding to the transmitted light intensity P is input to the injection current control circuit 7, and the injection signal is supplied from the current source 2 to the semiconductor laser l. The current is adjusted. That is, when the semiconductor laser 1 is oscillated at point A in FIG. 3, as r increases, P increases, and as f decreases, P increases.
decreases. Therefore, when P decreases, f increases, and when P increases, f decreases.
Frequency fluctuations can be compensated by controlling the injection current with the injection current control circuit 7.

FIG. 4 is a diagram showing the configuration of a semiconductor laser line width narrowing device using an optical method. In this device, an anti-reflection film 8 is provided on one end face of a semiconductor laser 1 operated by an injected current from a current source 2, and the output light from this end face is collimated by a collimating lens 3.
The light is returned to the semiconductor laser l through the reflecting mirror 9j. Here, a cavity is formed by the opposite end face of the semiconductor laser l and the reflecting mirror 9. In this case, since the effective cavity becomes large, the influence of phase fluctuation due to spontaneous emission light becomes relatively small, and the line width is narrowed.

[Problem to be solved by the invention] The semiconductor laser linewidth narrowing device shown in FIG. , frequency reproducibility and long-term stability are also excellent. However, in order to narrow the linewidth, it is necessary to suppress fluctuations in high Fourier frequency components, and for this purpose, the injection current control circuit 7 must have a bandwidth wider than the linewidth of the semiconductor laser I in the free-running state. There is a need for a wideband electronic circuit with negative feedback over the entire band. If this condition is not satisfied, there is a problem in that the shape of the spectrum is distorted. Further, in the semiconductor laser linewidth narrowing device shown in FIG. 4, since the optical feedback system itself has broadband characteristics, a broadband electronic circuit is not required, and the configuration is simplified. However, there is a problem in that the operation becomes unstable if the phase of the reflected light is disturbed due to external vibrations or the like.

This invention was made in view of the above circumstances,
It is an object of the present invention to provide a semiconductor laser line width narrowing device that has a simple configuration and can provide stable operation.

"Means for Solving the Problems" The present invention includes a semiconductor laser, a resonant absorption medium, and an optical feedback means, and makes a part of the output light of the semiconductor laser enter the resonant absorption medium, and transmits the transmitted light. The light is injected into the semiconductor laser by the optical feedback means so as not to interfere with the output light of the semiconductor laser.

"Operation" A part of the output light of the semiconductor laser is injected into the semiconductor laser through the resonant absorption medium so as not to interfere with the output light of the semiconductor laser, and the line width of the output light of the semiconductor laser is narrowed. That is, since the present invention performs negative feedback control using optical means having broadband properties, stable line width narrowing can be performed with a simpler configuration.

"Example" Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a semiconductor laser line width narrowing device according to an embodiment of the present invention.

In this device, an antireflection film 8 is provided on one end face of a semiconductor laser I, and a collimating lens 3, an absorption cell 5, and an optical attenuator are placed on the optical path of the output light of the semiconductor laser 1 output from this end face. 11, a λ/4 tentative 10 and a reflecting mirror 9 are arranged.

Laser light output from the semiconductor laser 1 via the anti-reflection film 8 is collimated by the collimating lens 3 and enters the absorption cell 5, and the transmitted light is transmitted through the optical attenuator 11 and the λ/·1 plate! The light enters the reflecting mirror 8 through 0, is reflected by the reflecting mirror 8, and is again injected into the semiconductor laser via the λ/4 plate, the optical abtenuator 11, the absorption cell 5, and the collimating lens 3.

Here, since the reflected light passes through the λ/4 plate 10 twice, its plane of polarization is orthogonal to the plane of polarization of the output light of the semiconductor laser, and they do not interfere with each other. Further, the optical attenuator II adjusts the intensity of the light that is fed back to the semiconductor laser as the injected light.

When the injection current from the current source 2 is adjusted so that the semiconductor laser 1 oscillates at point A in FIG. 3, as the frequency r increases, the transmitted light intensity P of the absorption cell 5 increases,
As a result, the carrier density in the active layer of the semiconductor laser I decreases and the refractive index increases, so the frequency f decreases.

Conversely, when the frequency r decreases, the refractive index of the active layer decreases due to a decrease in the amount of injected light, and the frequency f increases.

That is, negative feedback is applied to suppress changes in frequency f. In this method, since the optical feedback system itself has broadband characteristics, the configuration is simple without requiring a broadband electronic circuit, and the operation is stable because of negative feedback control. In addition, since the absorption spectra of atoms and molecules are used, frequency reproducibility and
It also has excellent long-term stability. Therefore, light wave communication, optical measurement,
It can be used as a light source for optical bombing of atomic oscillators, etc.

"Effects of the Invention" As explained above, the present invention includes a semiconductor laser, a resonant absorption medium, and an optical feedback means, and makes a part of the output light of the semiconductor laser incident on the resonant absorption medium, so that the output light is transmitted through the resonant absorption medium. Since light is injected into the semiconductor laser by the optical feedback means so as not to interfere with the output light of the semiconductor laser, there is an effect that line width narrowing can be performed with a simple configuration and stable operation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a semiconductor laser linewidth narrowing device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a semiconductor laser linewidth narrowing device realized by a conventional electrical device. 3 is a diagram showing the relationship between the frequency r of the output light of the semiconductor laser l and the transmitted light intensity P of the absorption cell 5 in the device shown in FIG. 2, and FIG. FIG. 2 is a block diagram showing the configuration of a laser line width narrowing device. 1... Semiconductor laser, 2... Current source,
3... Collimating lens, 4...
・Optical isolator, 5...Absorption cell (resonant absorption medium), 8...Antireflection film, 9...Reflector, lO...λ/4 Board, 1! ...Optical attenuator. Figure 1

Claims (1)

[Scope of Claims] A semiconductor laser, a resonant absorption medium, and an optical feedback means, a part of the output light of the semiconductor laser is made incident on the resonant absorption medium, and the transmitted light is transmitted to the resonant absorption medium by the optical feedback means. A semiconductor laser linewidth narrowing device characterized by injecting into the semiconductor laser so as not to interfere with the output light of the semiconductor laser.