JPS63136589A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser device, in which the increase of oscillation line width is reduced even on modulation at high speed, by forming a laser resonator by a phase conjugate mirror and a diffraction grating. CONSTITUTION:A phase conjugate mirror 17 is constituted of a nonlinear type optical medium 101 consisting of a BaTiO3 single crystal, a DFB semiconductor laser 102 generating excitation beams, a reflecting mirror 103 and a convex lens 104. Beams from another end surface 13 of a semiconductor laser 11 are changed into parallel beams by a convex lens 18, a wavelength is selected by a diffraction grating 19 and the beams are returned to the semiconductor laser 11. The phase conjugate mirror 17 and the diffraction grating 19 shape a resonator, interposing a semiconductor laser as an amplifying medium for laser oscillation. The time delay required for feedback up to the semiconductor laser 11 from the phase conjugate mirror 17 is 67ps and response is enabled up to the modulation of approximately several Gb/s.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser device used in optical communications and the like.

(Prior Art) In optical transmission, there is a demand for a semiconductor laser whose line width does not increase even during modulation. Conventionally, the DFB laser, which is a semiconductor laser that oscillates at a single wavelength, has not been able to fully meet this requirement; for example, Fujita et al. 3-76 (+983) As reported on page 37 and at the 983 National Conference of the Communication Society in 1983, an optical feedback half-kiss body laser with an external cavity was used to suppress linewidth increase. ing.

FIG. 4 is a diagram showing the construction of an external cavity type semiconductor laser device. In this device, one end surface of the semiconductor laser 41 is covered with a dielectric film 42.
This reduces the reflectance. The emitted light from the end face 41a of the semiconductor laser 41, which has a low reflectance, passes through the dielectric film 42 to the convex lens 43, where it becomes parallel light, and the etalon 45 selects the external resonance 2 mode. The process then proceeds to the diffraction grating 46, where the oscillation wavelength is selected. A resonator is formed between this diffraction grating 46 and the end face 41b of the semiconductor laser 41 on the side where the reflectance is not lowered. The output light 47 is an end face 41b that is not made to have a low reflectance.
The light is extracted from the convex lens 44 as a beam of light.

(Problem to be Solved by the Invention) Even with the structure described above, if the injection current of the semiconductor laser is modulated, the refractive index of the semiconductor laser active layer will change as the optical power changes. Change. Therefore, the oscillated light is modulated not only in intensity but also in phase.

The line width of the oscillated light increases due to phase modulation, and the faster the modulation becomes, the more remarkable the increase in line width becomes. Therefore, the conventional configuration has the drawback that the modulation speed cannot be increased in order to be used in such a narrow range of oscillation linewidth.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a semiconductor laser device in which the oscillation line width increases less even during high-speed modulation.

(Means for Solving the Problems) The semiconductor laser device of the present invention is characterized in that a phase conjugate mirror and a diffraction grating form a laser resonator. (Operation) A phase conjugate mirror is schematically shown in FIG. Two excitation lights 2 with the same wavelength propagating in opposite directions to the nonlinear optical medium 21
When the reference beam 24 of the same wavelength is incident on the excitation beams 22 and 23 at a small angle while the reference beam 2.23 is being incident, new light that propagates the reference beam 24 in the opposite direction is generated.

This light becomes a phase co-projected light 25, and the spatial part becomes the reference light 24.
There is a complex conjugate relationship with Therefore, as shown in FIG. 3, for example, even if the phase of the emitted light 301 emitted from the light a31 is disturbed by the medium 32, the light 302 reflected by the phase conjugate mirror 33 returns through the medium 32 completely. The phase of the reflected light 302 that undergoes a reverse phase change and eventually returns to the light source 31 becomes the same as the phase of the light that initially exited the light source 31, and
The phase disturbance caused by 2 is canceled out.

When a resonator is configured with a diffraction grating and a phase conjugate mirror as in the present invention, even if the light selected by the diffraction grating is phase modulated by the semiconductor laser medium, it is reflected by the phase conjugate mirror and passes through the semiconductor laser medium again to the diffraction grating. By returning to , the effect of phase modulation is completely canceled out, and light with the same phase always returns to the diffraction grating. Therefore, even if the semiconductor laser is modulated, the line width will not increase.

(Example) FIG. 1 is a block diagram showing an embodiment of the present invention.

Light emitted from one end face 12 of the semiconductor laser 11 whose both end faces have a low reflectance of 1 to 2% by dielectric films 14 and 15 is turned into parallel light by the convex lens 16 and enters the phase conjugate mirror 17. The 6-phase conjugate mirror 17 is B.

'l"i 0. Nonlinear optical medium 10 made of il crystal
1, a DFB semiconductor laser 102 that generates excitation light,
It is composed of a reflecting mirror 103 and a convex lens 104. The light from the other end face 13 of the semiconductor laser 11 is converted into parallel light by a convex lens 18, and then returns to the semiconductor laser 11 after its wavelength is selected by a diffraction grating 19. The oscillation wavelength in this embodiment is made to be the same as the oscillation wavelength of the DFB semiconductor laser 102. Phase conjugate mirror 1 from end face 12 of semiconductor laser 11
The distance from the end face 12 to the diffraction grating 19 was 10 mm, and the distance from the end face 12 to the diffraction grating 19 was 200 mm. Phase conjugate mirror 17 and diffraction grating 1
A resonator 9 is formed by sandwiching a semiconductor laser which is an amplification medium for laser oscillation. The time delay required for return from the phase conjugate mirror 17 to the semiconductor laser 11 is 67p.
s, and the response is 6 functions up to 5 rotations of about several Gb/s. Further, the output J light 20 is extracted by a semi-transparent mirror 21.

(Effects of the Invention) As detailed above, according to the present invention, it is possible to obtain a semiconductor laser device that is capable of high-speed modulation and has a small oscillation linewidth.

4, [Cylinder-shaped explanation of ff1 side FIG. 1 is a block diagram showing an embodiment of the present invention.

In the figure, 11 is a semiconductor laser, 12.13 is an end face, 14.
15 is a dielectric film, 16 and 18 are convex lenses, 17 is a phase conjugate mirror, 19 is a diffraction grating, 20 is an output light, 21 is a semi-transparent mirror,
101 is a nonlinear optical medium, 102 is 1) an FB semiconductor laser, and 103 is a reflecting mirror.

FIG. 2 is a schematic diagram showing the concept of a phase conjugate mirror.

In the figure, 22 and 23 are excitation lights, 24 are reference lights, and 25 are phase co-projection lights.

FIG. 3 is a schematic diagram illustrating the function of a phase conjugate mirror. 3
1 is a light source, 32 is a medium, 33 is a phase co-projection light, and 30
1 represents emitted light, and 302 represents reflected light.

FIG. 4 is a block diagram of a conventional external cavity semiconductor laser. In the figure, 41 is a semiconductor laser, 42 is a dielectric film, 43.
44 is a convex lens, 45 is an etalon, 46 is a diffraction grating, 4
7 is output light.

Agent: Patent Attorney Shinsuke Honsho Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] A semiconductor laser device characterized in that a laser resonator consists of a phase conjugate mirror and a diffraction grating.