JPS6136985A - Laser device - Google Patents

Abstract

PURPOSE:To take out the light output of two modes from one semiconductor laser with stability by arranging a 1/4 wavelength plate in an external resonator of semiconductor laser. CONSTITUTION:When the light of TE1 mode of straight polarization (TE wave) is emitted from a back part 7b of a laser diode 7 and it enters into a 1/4 wavelength plate 9, the projected light from the plate 9 becomes circularly polarized light CF1 and is reflected by a rear mirror to become polarized light CF2. Then the light enters into the plate 9 again from the back and is projected by the crossing component with the TE wave, i.e., TM wave. The light passes through the diode 7 and the plate 9 to become circularly polarized light CF3. The light CF3 reflected by the mirror 10 enters into the plate 9 to become TE2 wave and passes the diode 7 and is emitted from the mirror 11. Namely, TE wave projected from the diode 7 reciprocates to the plate 9 and becomes TM wave. It becomes a laser of one period by two reciprocation. And by one reciprocation, the light becomes the polarized light state which crossing each other.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a laser device, and more particularly to a laser device in which a semiconductor laser is guided to a polarization changing member to perform bistable operation.

(2) Technology background Recently, laser devices, especially semiconductor lasers, have been increasing their output.

Its application has become more common due to its improved performance such as lifespan.

It is used in laser printers, optical discs, etc. Unlike gas lasers, semiconductor lasers have an asymmetric far-field pattern.

The emission angle in the direction perpendicular to the active layer (planar) direction of the laser semiconductor may be 20 to 40 degrees, and correction using a collimating lens or the like is performed to obtain light with good directivity. Further, the transverse mode has a half-value angle of the far field pattern of the semiconductor laser, which is 8 to 20 degrees in the direction parallel to the planar junction surface. Currently, most semiconductor lasers have such an asymmetric far-field pattern. Furthermore, considering the polarization characteristics, the polarization direction is limited to one, and in most cases it is linearly polarized (hereinafter referred to as TE wave) parallel to the planar junction surface (active layer) of the semiconductor laser. When the output of the semiconductor laser is 3 to 5 mW, T
The light intensity ratio of the orthogonal component to the E wave (hereinafter referred to as TM wave) is 50
: 1 to 100 : Value of 1.

(3) Prior art and problems Semiconductor lasers with the above-mentioned asymmetric far-field pattern can be used in optical video disks and PCM (
When used for an audio disc (pulse code modulation), an optical pink amplifier is constructed as shown in FIG. That is, in FIG. 5, 1 is a semiconductor laser, and 2 is a semiconductor laser.
is a two-wavelength plate, 3 is a polarizing beam mirror, 4 is a lens for collimating the light from the semiconductor laser, and 5 is for condensing the laser light onto a spot about the wavelength of the light on the surface of the optical disk 6. The lens 6 is an optical disk that has information in the form of a focus on its surface, and the light from the semiconductor laser is
Polarizing beam splitter 3 and × corrugated plate 2 and lenses 4 and 5
A spot is focused on the optical disk 6 through the light beam. The light reflected by the optical disc 6 is reflected by the lens 5, 4 and the polarizing beam splitter 3, and is applied to the detector 16 through the cylindrical lens 15 to detect the presence or absence of bits on the optical disc 6. The present invention aims to provide a laser device in which a noise wavelength plate is provided in an external resonator of a semiconductor laser so that two bistable output lights (M) are generated from the output light of the semiconductor laser. Although it is similar to the one shown in FIG. 5 in that it uses a wave plate, its purpose is different.

(4) Purpose of the Invention As stated above, the purpose of the present invention is to obtain a laser device that can obtain bistable output by changing the longitudinal mode etc. of the light emitted from a semiconductor laser so that it becomes two different polarized outputs. It is something to do.

(5) Structure of the Invention According to the present invention, the above object is characterized in that a polarization changing member for changing the polarization state is disposed in front of one reflecting member of a semiconductor laser having an external resonator. This can be achieved by providing a laser device that achieves this goal.

(6) Embodiment of the Invention An embodiment of the present invention will be described in detail below with reference to FIGS. 1 to 4.

Figure 1 is an optical configuration diagram for obtaining bistable optical output of the laser device of the present invention, Figure 2 is a state diagram for explaining the polarization state of Figure 1, and Figure 3 is the laser device of the present invention. FIG. 3 is a polarization state diagram showing the output light polarization state of .

FIG. 4 is an optical configuration diagram showing another embodiment of the present invention. In FIG. 1, 7 is a gain medium such as a laser diode, which applies a bias to the pn junction, injects electrons, increases the current, causes stimulated emission, recombines electrons and holes, and amplifies them. 10.11. A reflecting mirror made of a half mirror or the like reflects at least 90% of the laser beam from the laser diode. 9 is a polarization changing member such as an A wavelength plate or a 45° Faraday rotator, and 8 is an external resonator, which is usually composed of a laser diode 7 and two reflecting mirrors. 12 is a polarization separation element.

In the present invention, a polarization changing member 9 is disposed within the external resonator 8 between the light emitted from the rear part 7b of the laser diode 7 and the rear half mirror 10, as shown in FIG. Further, as shown in FIG. 4, an A wavelength plate or a 45° Farade single rotator, which is a polarization changing member, is placed between the light emitted from all 7f of the laser diode 7 and the front half mirror 11, and the arrangement direction is The main axis of the two-wavelength plate is arranged at an angle of 45° with respect to the active layer of the laser diode.

The operations in the above configuration are shown in Figures 1 to 31! This will be explained using l. The oscillation mode from laser diode 7 is TE
or 7M mode, but 1 For example, from the rear part 7b of the laser diode in Fig. 1, as shown in Fig. 2 < T E +
When the light of the mode is emitted and enters the % wavelength plate 9, the light emitted from the A wavelength plate becomes circularly polarized light CF+ and the rear mirror 10
The circularly polarized light CF2 reflected by the A wavelength plate 8 enters the A wavelength plate 8 from the rear again and is emitted as a TMR wave, and then passes through the laser diode 7.
TMl reflected by the front half mirror 11
The wave passes through the laser diode 7 again, passes through the A wavelength plate 8, and becomes 1 circularly polarized light CF3.The CF3 reflected by the rear reflecting mirror 10 enters the 2nd wavelength plate 8 again, and becomes the TE2 wave, passing through the laser diode 7. and is emitted from the mirror 11 in front. That is, when the TE wave emitted from the laser diode goes back and forth through the A wavelength plate 9 six times, it becomes a TM wave, which becomes a laser with one cycle in two round trips, and becomes polarized in mutually orthogonal states in one round trip.

Now, if we look at the TE and TM waves from the front mirror 11 in Figure 1, there are two modes, TE and TM, and the phase relationship between the TE and TM waves at that time is if the TM waves and TE waves are in phase. , the optical output is 13 for positive 45° square linearly polarized light as shown in Figure 3+a+.

If the phase is reversed, the optical output 14 is linearly polarized light in the negative 45° direction, as shown in FIG. 3(b). i.e. light output 13.1
4 is a combination of TE wave and TM wave. This coincides with the intrinsic polarization state of this optical resonator. By changing one of various parameters such as the laser current of the laser device, the light intensity at the time of light injection, and the external resonator length, for example, the mirror 10
Alternatively, when the position of 11 is changed, since there is hysteresis in the hopping of the longitudinal mode of the optical output, the TE wave, which was stabilized in the TE mode, becomes stabilized in the 7M mode.

For this reason, if the output of either mode is given to the polarization separation element 12 such as a polarizer, it becomes possible to stably extract either the optical output 13 or 14. .

(7) Effects of the Invention Since the present invention is constructed as described above, it is possible to extract optical outputs of two modes more stably than a single semiconductor laser by simply inserting a polarization changing member such as an A-wave plate into an external resonator. There is one laser device that can be used for various optical circuits.
given.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing the optical system and resonator of the laser device of the present invention, Fig. 2 is a state diagram for explaining the polarization state of Fig. 1, and Fig. 3 is the output light of the laser device of the present invention. A polarization state diagram showing the polarization state, FIG. 4 is an optical configuration diagram showing another embodiment for obtaining bistable optical output of the present invention, and FIG. 5 is a diagram showing the conventional A.
FIG. 2 is a schematic diagram of an optical system using a wave plate. 1... Semiconductor laser, 2.8... 2 wavelength plate,
3...Polarizing beam splitter. 6... Optical disk, 7... Laser diode. 8...External resonator, 10.11...Mirror, 12...Polarization separation element. 13.14...Light output, 15...Cylindrical lens, 16...Detector. Figure 3 Figure 5

Claims (4)

[Claims] (1) A laser device characterized in that a polarization changing member for changing the polarization state is disposed in front of one reflecting member of a semiconductor laser having an external resonator. (2) The laser device according to claim 1, wherein the polarization changing member is a quarter wavelength plate. (3) The laser device according to claim 1, wherein the polarization changing member is a 45-degree Faraday rotator. (4) The laser device according to claim 2, wherein the main axis of the quarter-wave plate of the polarization changing member forms an angle of 45° with the active layer of the semiconductor laser.