JPH03175685A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser device excellent in stability to humidity change by completely sealing a Fabry-Perot resonator airtightly, and constituting a resonator such that it is not influenced by humidity. CONSTITUTION:A device including a Fabry-Perot resonator 19 is stored in a package 22 at large and is completely sealed airtightly. And, highly pure inert gas free of moisture or nitrogen is charged therein. Accordingly, since the humidity to the Fabry-Perot resonator 19 becomes constant, the refractive indexes of reflecting mirrors 191 and 192 also become constant, and it follows that the oscillating wavelength of a semiconductor laser 11 can be detected with high accuracy, whereby a radiated beam stable in wavelength can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a semiconductor laser device that is used, for example, as a light source for optical communications and stabilizes the wavelength of light emitted from a semiconductor laser.

(Conventional technology) Conventionally, the third type of semiconductor laser device used for optical communication has been
There is one shown in the figure. In FIG. 3, 11 is a semiconductor laser whose oscillation wavelength (oscillation frequency) can be controlled. Light S1 emitted from the left side of the semiconductor laser 11 in the drawing is focused on the input end of the communication optical fiber 14 via a lens 12.13. Furthermore, the light S2 emitted from the right side in the figure of the semiconductor laser 11 is converted into parallel light by the lens 15, and then converted into parallel light by the beam splitter 16.
branched in the direction. One of the branched lights S3 is sent to lens 1
The light is focused on a photodiode 18 via a photodiode 7 . The other light S4 is incident on the Fabry-Perot resonator 19.

This Fabry-Perot resonator 19 includes a pair of reflecting mirrors 191.
192 facing each other on the optical axis and separated by a certain distance, and the light transmitted through the vibrator 19 is
The free spectral spacing λ2/2nL (
λ: wavelength, n: refractive index in one Fabry-Perot cavity)
The light has a characteristic of repeating as a period, and is focused on the photodiode 21 via the lens 20.

Therefore, the light reception signal of the photodiode 21 changes according to the frequency change received by the light transmitted through one resonator. Therefore, the oscillation wavelength λ of the semiconductor laser 11 can be determined by measuring the ratio of the received light outputs of the photodiodes 18 and 21. Generally, in order to control the oscillation wavelength of the semiconductor laser 11, the oscillation wavelength of the semiconductor laser 11 is detected from the ratio of the output values of the photodiodes 18 and 21, and the temperature of the semiconductor laser 11 or the injection current is changed. , control to the desired wavelength.

Incidentally, the reflecting mirror of a conventional Fabry-Perot resonator used in such a device is formed of a dielectric multilayer film. Although it is known that the wavelength characteristics of this dielectric multilayer film shift depending on the humidity in the air, it is conventionally considered to be sufficient as a reflecting mirror for use in a Fabry-Perot resonator for the following reasons.

■The characteristics of the Fabry bellows resonator are given by a-4πnLeosθ/λ F-πJR/ (1-R). Here, α is the phase difference, θ is the angle of incidence of light into the Fabry-Perot resonator, F is the finesse of the Fabry-Perot resonator, and R is the reflectance of the reflecting mirror.

From this, the wavelength axis of the characteristics is affected! The amount you can get is nL
It is only eO8θ and does not depend on the wavelength shift of the multilayer film.

■The reflectance characteristics of the dielectric multilayer film used in Fabry-Perot resonators are characteristics that change gradually with wavelength. Therefore, even if a wavelength shift of the multilayer film occurs due to a change in humidity, the change in the reversal rate is extremely small and does not pose a problem.

However, when we confirmed the above opinion through highly accurate experiments, we found that the refractive index of the dielectric multilayer film that forms the reflecting mirror actually changes by 5 to 6% due to the influence of humidity. This changed the phase of the reflected wave and shifted the wavelength characteristics of the resonator. If the wavelength characteristics of the Fabry-Perot resonator shift in this way, the oscillation wavelength of the semiconductor laser that uses the resonator as a wavelength reference will also shift, making it impossible to obtain stable operation against humidity. Generally, humidity is also related to temperature, so devices with poor humidity stability tend to have poor temperature stability as well.

(Problems to be Solved by the Invention) As described above, in conventional semiconductor laser devices, the refractive index of the dielectric multilayer film used for the reflecting mirror of the Fabry-Perot cavity changes with changes in humidity, and the phase of the reflected wave changes. changes,
Because the wavelength characteristics of the resonator were shifted, stable operation against humidity could not be obtained.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a semiconductor laser device that has good stability against changes in humidity.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a Fabry-Perot system which is constructed by combining a reflection mirror made of a dielectric multilayer film to reflect a part of the light emitted from a semiconductor laser. In a semiconductor laser device, gl:c! The Soft Liperot resonator is completely hermetically sealed and is equipped with humidity compensation means to prevent the resonator from being affected by humidity.

Particularly, the humidity compensating means is characterized in that the Fabry-Perot resonator is completely hermetically sealed by being housed in a package having a window member disposed near the emission end thereof.

In addition, in the semiconductor laser device having the above structure, the Fabry-Perot resonator is completely hermetically sealed, so that a high-purity inert gas or nitrogen gas is sealed in the package. This eliminates the refractive index change due to humidity in the polygonal jφ film, suppresses the phase change of the reflected wave, and thereby suppresses the wavelength characteristic shift of the Fabry-Perot resonator.

In particular, if the Fabry-Perot resonator is completely hermetically sealed by being housed in a package with a window member placed near its emission end, interference with the outside will be eliminated and the influence of temperature will be further reduced.

Further, if a high purity gas is sealed in the package, moisture in the package is eliminated, and the influence of humidity can be completely eliminated.

(Example) Hereinafter, an example of the present invention will be described with reference to FIGS. 1 and 2. However, in FIGS. 1 and 2, the same parts as in FIG. 3 are designated by the same reference numerals, and the different parts will be mainly explained here.

FIG. 1 shows a first embodiment, in which reflecting mirrors 19+, 1
9□ is formed of a dielectric multilayer film.

Therefore, as described above, the phase of the reflected light changes under the influence of humidity, and as a result, the wavelength characteristics of the Fabry-Perot resonator 19 shift. Therefore, in order to completely hermetically seal the Fabry-Perot resonator 19, the entire device is housed in a package 22.

According to such a configuration, moisture does not enter or exit, and the humidity relative to the Fabry-Perot resonator 19 becomes constant. That is, since a semiconductor laser device normally performs temperature control using a Peltier element or the like, if the moisture content and temperature are constant, the humidity within the package 22 will be at a constant value. If the temperature is not controlled, even if the moisture content is constant, the humidity will not be constant.
Fill with moisture-free, high-purity inert gas or nitrogen.

Therefore, in the semiconductor laser device having the above configuration, since the humidity relative to the Fabry-Perot cavity 19 is constant,
The refractive index of the reflecting mirrors 19+ and 19□ also becomes constant, making it possible to detect the oscillation wavelength of the semiconductor laser 11 with high precision, thereby making it possible to obtain emitted light with a stable wavelength.

FIG. 2 shows a second embodiment. In this example, the Fabry-Perot resonator 30 is constructed by forming reflective mirrors 302 and 303 on the front surface of a parallel plate 30. This Fabry-Perot resonator 30 is housed in a package 31 consisting of a lid 313 and a casing 314 having window members 311 and 312 in order to be completely hermetically sealed, so that it is not affected by humidity. The window members 311 and 312 may be made of glass, sapphire, or the like.

The features of this configuration are as follows. That is, in the first embodiment, when the package 22 is filled with high-purity gas, the wavelength characteristics shift to a different one from that at the time of assembly.
In the second embodiment, the Fabry-Perot vibrator 30 is housed in the package 31 in advance and then attached to the laser device. The wavelength characteristics can be determined by adjusting the incident angle. Therefore, according to the configuration of the second embodiment, high-purity gas can be easily filled.

Note that the application of the present invention is not limited to the wavelength detection system as shown in the second embodiment; for example, the resonator length of a Fabry-Perot resonator is modulated with an alternating current signal to The present invention can also be applied to a device that obtains a wavelength error signal by receiving transmitted light and synchronously detecting the received light signal and the AC signal.

[Effects of the Invention] As described above, according to the present invention, since the Fabry-Perot resonator is completely hermetically sealed, it is stabilized against humidity, and since humidity is also related to temperature, the temperature of the environment is It is possible to provide a semiconductor laser device that is stabilized against changes and can also be expected to have improved general reliability.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the structure of a first embodiment of the semiconductor laser device according to the present invention, FIG. 2 is a perspective view showing the structure of another embodiment of the semiconductor laser device according to the present invention, and FIG. The figure is a perspective view showing the general configuration of a conventional semiconductor laser device.
FIG. 4 is a characteristic diagram showing the wavelength characteristics of the Fabry-Perot resonator used in the semiconductor laser device. 11... Semiconductor laser, 12, 13, 15° 17.2
0...Lens, 14...Optical fiber for communication, 16.
...Beam splitter, 18.21...Photodiode, 19.30...Fabry-Perot resonator, 191
．． 192,302.30*...Reflector, 22°31.
...Package, 23,311.31□...Window member,
30. ...parallel plate, 313...lid, 314...casing.

Claims (3)

[Claims] (1) A part of the light emitted from the semiconductor laser is received by a light receiving element through a Fabry-Perot resonator composed of a combination of reflecting mirrors made of a dielectric multilayer film, and based on this light reception signal, the light emitted from the semiconductor laser is A semiconductor laser device that controls oscillation and stabilizes the wavelength of emitted light, comprising a humidity compensation means for completely hermetically sealing the Fabry-Perot resonator so that the resonator is not affected by humidity. Semiconductor laser equipment. (2) The semiconductor according to claim (1), wherein the humidity compensation means completely hermetically seals the Fabry-Perot resonator by housing it in a package in which a window member is arranged near the light input/output end. laser equipment. (3) The semiconductor laser device according to claim 2, wherein a high purity inert gas or nitrogen gas is sealed in the package.