JPS5961984A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To restrict the noise caused by reflected feedback incident light by a method wherein an optical system is provided so that polarizing direction of the emitting light outputted from a laser element and the reflected feedback light thereof may intersect almost perpendicularly with each other. CONSTITUTION:The outgoing light outputted from a laser element 1 is radiated after being converted into parallel light by a collimator lens 2 passing through a beam splitter 3 and a quater wave length plate 4. The polarizing direction of the emitting light from the laser element 1 is set up to be perpendicular to the emitting direction as shown by the arrows. The linear polarization of the emitting light becomes circular polarization after passing the quater wavelength plate 4. The light reflected from a disc become the linear polarization again after reading the emitting channel reversely and passing the quater wavelength plate 4 but the polarizing direction will be perpendicular to that of the emitting lights from the laser element 1. The light is partially become perpendicular but after passing the beam splitter 3, proceed to an optical system for reading to feedback the remaining light to the laser 1. The feedback light to the laser element 1 may become equivalent to natural light for the laser element 1 since the emitting light from the laser element 1 is perpendicular to the polarizing direction.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a semiconductor laser device, and more particularly to a technique for improving the noise characteristics of a semiconductor laser device that confines light using a refractive index waveguide mechanism.

<Prior Art> In addition to optical communication systems, semiconductor laser devices have recently come to be used as light sources for pick amplifier systems, particularly in video disk devices and audio disk devices. However, when a semiconductor laser device is used as a light source for a pickup system, when the reflected light of the laser beam reflected on the disk surface becomes gI return light and enters the semiconductor laser device, the semiconductor laser device t/CN, This results in a reduction in the quality of the image reproduced from the video disc or abnormal sound in the sound reproduced from the audio disc, posing a serious problem in practice.

This is because it is known that multi-mode elements generate less noise due to the incidence of reflected feedback light and are more stable than single longitudinal mode elements. In addition, even if it is a single-longitudinal mode Rade element, an element with a large longitudinal mode spectral width and a temporal coherence length shorter than the distance between the laser element and the disk surface will generate less noise than an element with a longer temporal coherence length. , is known to be stable.

It is easier to obtain a laser element with a single longitudinal mode by confining light with a refractive index waveguide mechanism, and it is easier to obtain a laser element with multiple longitudinal modes by confining light with a gain waveguide mechanism. However, the transverse mode of a laser element that confines light using a gain waveguide mechanism is unstable, and due to changes in the injected current, the transverse oscillation mode ( When using a pickup system as a light source, the optical axis changes and it cannot be put to practical use.
′、Conductor-゛! The device used is one that confines light using a refractive index waveguide mechanism.In order to further suppress the generation of sound, the laser element is designed to have multiple longitudinal modes. Even if the laser element is configured in a single longitudinal mode, it is necessary to configure the laser element so that the temporal coheret length is shorter than the distance between the laser element P and the disk surface.

As is well known, the 1111 refractive index waveguide mechanism confines the active layer at the heterojunction interface, gives the active layer a difference in the refractive index of light, and focuses the light onto a striped micro region. I can get it. However, in this structure, the flux of light is high and the longitudinal mode is generally a stable single mode.

In general, the vertical mode F + Iv is small, and the coherent length is generally shorter than the distance between the laser element and the disk surface.

<Object of the Invention> The present invention confines light with a refractive index waveguide mechanism, or multiplies longitudinal modes by making full use of technical means in a laser element in which a single longitudinal mode is set, or r: 11
- Expanding the spectral width of the longitudinal mode even in
It is an object of the present invention to provide a new and useful semiconductor laser device in which the generation of noise in anti-4.1 feedback light is suppressed by making the coherence length shorter than the distance between the laser element and the disk surface.

<Summary of the Invention> The number of oscillation longitudinal modes and the spectral width of a semiconductor laser depend on the spontaneous emission coefficient. According to the theoretical results, the ratio between the output Qp of the dragon mode and the output Qm of the resonant spontaneous emission light is Qm/Q.
p, αth is the threshold gain of the main mode, αm is Qm
gain, ■ is the laser drive current, Ith is the threshold current,
If C is the spontaneous emission coefficient, then Qrrv'Qp=CCI
/I th-1) (1-am/at I]) ]'
・ ・ ・(1) Become. The spectral width △f of each shunted mode is MC(1/
1th-1-2)/(I/Ith+1),,(2)
/ゝf″″ 2yr, τp(I Ith-1)
'. As is clear from equation (1), as the spontaneous emission coefficient increases, the output of the spontaneous emission Qm becomes Ql.
), the ratio increases by 411, so it becomes a multi-mode. From equation (2), it can be seen that as the spontaneous emission coefficient increases, the spectral width increases, and therefore the coherence length decreases. As described above, it is effective to increase the spontaneous emission coefficient in order to create multiple longitudinal modes and shorten the coherent length.

1. In the conductor laser device of the present invention, the spontaneous emission coefficient can be effectively increased without changing the structure of the laser element. This will be explained in detail with reference.

GaAlAs-G that confines light with a refractive index waveguide mechanism
FIG. 1 shows the emission spectrum of a laser device made of a compound semiconductor of . This spectrum shows that there is a single longitudinal mode6.Furthermore, FIG. 2 shows an embodiment of the present invention 1' and a schematic configuration of a conductor laser device.

A laser element (11
The emitted light becomes parallel light through the collimator lens (2), and then passes through the beam block (3) and the quarter-wave plate (4).
is emitted through the The polarization direction of the emitted light from the laser element (1) is set to be perpendicular to the emitted direction as shown by the arrow in the figure. After passing through the quarter-wave plate (4), the linearly polarized light of the emitted light becomes circularly polarized light. For example, the emitted light is irradiated onto an optical disk, and information is read out and output.The light reflected from the disk travels in the opposite direction along the emitted path.
When the light passes through the quarter-wave plate (4), it becomes linearly polarized light again, but the polarization direction is different by 906 points from the polarization direction of the light emitted from the laser element (1). This light is beam splitter (3)
After passing through -), it is bent by 90 degrees, and the remaining light is returned to the laser element (1). The light that returns to the laser element (1) is the laser element f'-(], )
Since the emitted light and the polarization direction are different by 90 degrees, the laser element J'(1) has the same polarization direction as the spontaneously emitted light. Therefore, 1', the effective (spontaneous emission) of the radar element (1) in the conductor laser device has increased, and therefore tL, the spontaneous emission coefficient becomes insignificant. 3, the spontaneous emission coefficient By increasing , the medium longitudinal mode is multiplied, and even if -f/ζ is a 1゛11-mode, the spectrum width becomes wider. If the longitudinal mode becomes a multi-mode or a single-mode mode and the moss vector width becomes wide, noise will occur even if the signal light from the output light disk plate etc. is input for 1'1.1 hours as described above. This will result in stable information detection and DJ performance.

<Effects of the Invention> As explained in detail above, the present invention is capable of achieving multiple longitudinal modes in a semiconductor laser device that confines light by using an Ig4 refractive index waveguide mechanism to stabilize the semicircular mode. The spectral width has been expanded, which suppresses the noise that occurs when the feedback light from the disk is incident on the laser element, making it possible to obtain stable operation.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the oscillation spectrum of a laser bulb in which light is confined by a refractive index waveguide mechanism. FIG. 2 is a schematic diagram of a 1' conductor laser device showing an example of the I-JM of the present invention. 1 tracer, 2 collimating lens, 3...
Heems Burisoku, 4...1/4 wave A board.

Claims (1)

[Claims] 1. Optical control so that the polarization directions of the emitted light output from a single-longitudinal mode semiconductor laser device having a refractive index waveguide mechanism and the reflected feedback light of the emitted light are at an angle of approximately 9 degrees with respect to each other. A semiconductor laser device characterized by having a system installed therein.