JPS63233585A - Laser light source - Google Patents

Abstract

PURPOSE:To facilitate control of the width of a spectral line, by providing a reflection type filter, which feeds back rear emitting light of a laser to the laser, at a distance that is integer times the wavelength to be selected among laser light rays, and forming an external cavity. CONSTITUTION:Any of laser light rays having a plurality of wavelengths from a laser device 2 is selectively reflected by a reflection type filter 8. For example, the distance between the laser device 2 and the reflection type filter 8 is set at the length integer times the central wavelength of the laser light rays, and the light ray is reflected. With respect to only this reflecting component, the phase of the laser light, which is inputted into the laser device 2 from an external cavity 13 formed with the laser device 2 and the reflection type filter 8, is optimized, and oscillation occurs. Said component is made to be the laser light, which is outputted from the laser device 2. Namely, the laser light having the single wavelength is obtained. The width of the spectral line of the laser light having the single wavelength can be made narrow by the extension of the distance. When the setting conditions are misaligned, the conditions are recovered with an optical pathlength adjusting means 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The external resonator of a laser that generates laser beams of a plurality of wavelengths is configured to be selectively set to one of the laser beams.

[Industrial application field]

The present invention relates to a laser light source, and more particularly, to a laser light source with an improved laser light resonance system.

Laser light sources are used for optical coherent communication, length measurement, etc., but the laser light sources used in these application fields have a single oscillation wavelength, a narrow spectral linewidth, and excellent high frequency stability. required to be present. This is due to the use of the wave nature of laser light in the above-mentioned general fields.

[Conventional technology]

An example of a conventional semiconductor laser light source is shown in FIG.

In this figure, the laser beam output from the laser diode 52 is transmitted to the optical input section 53. Beam splitter 54. The light is divided into two optical fiber type ring resonators 60 and 40 by a directional coupler 58 via a Faraday isolator 56.

The optical fiber ring resonator 60 is composed of a directional coupler 64, a phase modulator 66, and an oscillator 68, and is centered at a predetermined spectral linewidth with respect to the spectral linewidth of the input laser beam. It is configured to be adjusted so that it exhibits sharp characteristics.

Therefore, the photodetector 70 detects a light output determined according to the degree to which the spectral linewidth of the input laser beam deviates from the spectral linewidth set in the optical fiber ring resonator 60. The detection signal is sent to the inverting amplifier 72. Peak value holding circuit 74. The PZT plate 8 is used to change the position of the mirror 82 that constitutes the external resonator of the semiconductor laser 52 via the differential amplifier 76, the integrator 78, and the buffer amplifier 80.
The spectral line width of the laser beam is controlled by a feedback control system such as that applied to the laser beam.

On the other hand, the light branched to the optical fiber ring resonator 40 is used to stabilize the oscillation frequency of the laser light in the following manner. That is, the output optical signal of the optical fiber type ring resonator 40 is transmitted to the photodetector 421, the inverter 44. Differential amplifier 46.
It is used to control the current supplied from the current source 51 to the semiconductor laser 52 via the filter 48 and the buffer amplifier 50, and acts to stabilize the oscillation frequency of the semiconductor laser 52.

[Problem that the invention seeks to solve]

In the light source configured as described above, since the peak value of the optical fiber ring resonator 60 is used to control the spectral linewidth of the laser beam, optical output fluctuations caused by fluctuations in the optical output of the semiconductor laser and deviations in the optical system due to vibrations, etc. Therefore, the configuration is such that the control of the spectral linewidth is easily affected by this, and the linewidth control is not easy.

Furthermore, control of the driving current of the semiconductor laser 52 in response to the output signal of the optical fiber ring resonator 40 is used to stabilize the frequency of the laser beam. The optical fiber ring resonator 40 is a semiconductor laser 5 capable of oscillating at multiple frequencies.
It is possible to output sharp transmitted light, which is a signal component for frequency control, to light having any of the two oscillation frequencies. Therefore, although the oscillation frequency of the laser 52 can be stabilized by the frequency control loop described above, it is uncertain which of the plurality of oscillation frequencies the stabilized oscillation frequency is. If you want to know this, you must make that determination using known measuring means.

This is inconvenient in the field of communication, where it is desired to use laser light with a specific single oscillation frequency.

The present invention was created in view of these problems, and aims to narrow the spectral linewidth of the generated laser beam with a single oscillation wavelength, strengthen high frequency stability, and select frequencies while making the configuration more compact. The purpose is to provide a laser light source that can be realized in the following manner.

[Means for solving problems]

FIG. 1 shows a block diagram of the principle of the present invention. In this figure, 2 is a laser that can generate laser beams of multiple wavelengths. In order to be able to select one of the wavelengths of the laser light on the backward emitted light side of the laser 2, a reflective filter 8 is provided at a position that is an integral multiple of the wavelength to form an external resonator 13. The laser light source of the present invention has features. In addition, in order to adjust the distance between the laser 2 and the reflective filter 8 to an integral multiple of the center wavelength of the laser beam, an adjustment device is optically coupled to the external resonator 13 via a half mirror 4. Means 10 are provided.

[For production]

A reflective filter 8 selectively reflects one of the plurality of wavelengths of laser light from the laser 2 . For example, the distance between the laser 2 and the reflective filter 8 is set to an integral multiple of the center wavelength of the laser beam, and the laser beam is reflected. Only this reflected component is oscillated in an external resonator formed by the laser 2 and the reflective filter 8 by optimizing the phase of the laser light incident on the laser 2, and that component is output from the laser 2. It is considered to be a laser beam. In other words, laser light of a single wavelength can be obtained. This single wavelength laser beam remains constant as long as there is no change in the conditions set in the external resonator. By extending the distance described above, it is also possible to narrow the spectral linewidth of a single wavelength laser beam. Note that if the setting conditions are disrupted, the adjustment means 10 restores them to their original state.

〔Example〕

FIG. 2 shows an embodiment of the invention. In the figure, 2 is a laser capable of generating laser beams of a plurality of wavelengths, 12 is an etalon, 4 is a half mirror, 16 is a confocal mirror (confocal interferometer), and 8 is a grating. The half mirror 4 and the confocal mirror 6 constitute a circulating optical system 9. The etalon 2, the circulating optical system 9, and the grating 8 are set so as to optimize the phase of the laser beam returning to the laser 2. For example, the distance between the laser 2 and the grating (reflection filter) 8 is an integral multiple of the center wavelength of the laser beam, and is adjustable. Adjustment means 10 is provided for returning to the setting conditions when the above-mentioned setting conditions are disrupted. Finesse adjustment mechanism 12A1 of etalon 12; PZT6A for displacing the confocal mirror 6; PZT8A for displacing the grating 8; A light receiving element 20 that receives transmitted light and a control system 11 constitute an adjusting means 10 for the entire configuration described above. Note that 22 and 24 are the oscillation spectrum linewidth control loop 22 and the frequency control loop 24 that constitute the control system 11, and as will be clear from what will be described later, these loops 22 and 24 are used to oscillate the external resonator of the present invention. Since it has frequency selectivity, it is not an essential element of the present invention. It is sufficient that these loops 22 and 24 can generate the signals intended to be achieved by the corresponding corresponding loops shown in FIG.

The finesse of the confocal mirror 6 is adjusted so that the resonance point of the confocal mirror 6 in the laser light source configured as described above becomes one of the resonance points (vertical line segments in the figure) shown in FIG. 3(A). Set. Also, the resonance point of the etalon 12 is shown in FIG. 3 (B
) The finesse of the etalon I2 is set so as to reach one of the resonance points (vertical line segments in the figure) shown in FIG. The semiconductor laser 2, which provides a system laser beam that can be phased and set as described above, can oscillate at several oscillation wavelengths (vertical line segments in the figure) as shown in FIG. 3(C). It has become. In addition, the grating 8 serves to complete the oscillation wavelength selectivity at intervals wider than the interval at which the semiconductor laser 2 can oscillate, that is, to complete the resonant system for the laser 2 for the laser light component at its oscillation center wavelength. . Therefore, the oscillation laser beam component having a single oscillation wavelength selected by this resonant system is used as the output of the laser light source (see (E) in FIG. 3).

As is clear from the above, the wavelength (frequency) of the output laser light is determined by the geometrical structure of the resonant system, and as long as the semiconductor laser 2 is stable, no adjustment is necessary. This resonant system itself has a structure that facilitates frequency stabilization. Further, the spectral linewidth of the laser beam having a single oscillation wavelength changes depending on the angle-corresponding loss set in the etalon 12, and is controlled by changing the amount of light passing therethrough. The loss of the etalon 12 can be easily varied from 0 to infinity, and its dynamic range is large. These make it easier to increase speed and stability. Therefore, spectral linewidth control becomes easy.

Furthermore, since the semiconductor laser 2 has the property that its oscillation frequency changes due to changes in the drive current, etc., the above-mentioned frequency control loop 24 may be operated in order to compensate for such changes. Similarly, the above-mentioned oscillation spectral linewidth control loop 22 may be operated for changes in the spectral linewidth. As is clear from the above, simple loops are sufficient.

The present invention may be configured as shown in FIG. 4 without an etalon. Since its constituent elements are the same as those in the embodiment shown in FIG. 2, they will be given the same reference numerals and their explanation will be omitted.

In the above embodiment, the selectivity of the oscillation wavelength of the external resonator may be a wavelength selectivity of two wavelengths or the like.

[Effects of the Invention] As described above, according to the present invention, as long as the oscillation of a laser capable of generating laser beams with multiple wavelengths is stable, a laser beam with a predetermined single oscillation wavelength is output. In addition to this, the spectral linewidth can be easily controlled and the light source can be made smaller.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle configuration of the present invention, Fig. 2 is a diagram showing an embodiment of the present invention, Fig. 3 is a development diagram of the operable frequencies of each part of the embodiment of the present invention, and Fig. 4 is a diagram showing the operable frequencies of each part of the embodiment of the present invention. FIG. 5, which is a diagram showing another embodiment, is a diagram showing an example of a conventional semiconductor laser light source. 1, 2, and 4, 2 is a laser, 4 is a half mirror 1, 6 is a confocal mirror, 6R is a reflective surface, and 6A and 8A are PZT. 8 is a grating, 9 is a circulating optical system, 10 is an adjustment means, and 12 is an etalon. , starting El River's 厥 V beans 7° ゛ Tips 7 Figure 1 Figure 2 (D) (E) 寥-z [￥ll ita'' each not pf 7 + p production possible 1b long figure 3゛Figure ζ￥mon Mei begging's actual destination first J Figure 4 Conventional,! n Nagisa - ° guide 44 mi - "gu' ° ° Me Tomoe n blowing,
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Claims (4)

[Claims] (1) A reflective filter (which returns back-emitted light from the laser (2) that generates laser light of multiple wavelengths to the laser (2)
8) is provided at a distance that is an integral multiple of the wavelength to be selected of the laser light, thereby forming an external resonator (13) with an optical path length of the backward emitted light. (2) The laser light source according to claim 1, wherein a part of the optical path of the external resonator (13) formed using the reflective filter is constituted by a circulating optical system. (3) A reflective filter (which returns back-emitted light from the laser (2) that generates laser light of multiple wavelengths to the laser (2)).
8) at a distance that is an integral multiple of the wavelength to be selected of the laser beam, an external resonator (13) is formed by the optical path length of the backward emitted light, and a A laser light source characterized by being provided with an adjusting means (10) for changing the optical path length. (4) A reflective filter (which returns back-emitted light from the laser (2), which generates laser light of multiple wavelengths, to the laser (2)).
8), and a circulating optical system (9) is provided in the optical path between the reflective filter (8) and the laser (2) to form an external resonator (13), and the optical path length of the external resonator is equal to that of the laser. 4. A laser light source according to claim 3, further comprising means for adjusting the distance within the circulating optical system (9) so that the distance is an integral multiple of the wavelength to be selected of the light.