JP3157898B2 - Optical semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device having a light receiving element for monitoring the light output of a semiconductor laser.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 4, in a semiconductor laser device, a rear surface output light 3 from a laser element 1 is detected by a photodiode 5, and its output fluctuation (signal change) is detected by a laser constant output driving circuit ( APC circuit: Auto Power
Controller), and feedback is performed so that the laser output is always constant. In a device using a semiconductor laser, it is desired to reduce the oscillation threshold current Ith and the drive current Iop in order to reduce power consumption. Therefore, the rear surface of the semiconductor laser device is multi-coated (MC), and Ith is reduced and internal differential efficiency η is increased to increase the efficiency of using light output.

[0003]

The prior art has the following problems.

[0004] i) Since the light output of the laser is divided into front light and rear light, utilization efficiency of the light output as a laser element is poor.

Ii) When the rear surface is multi-coated as described above, the monitor current Im becomes small, and the design of the constant output drive circuit (APC circuit) becomes difficult.

Generally, the oscillation threshold current Ith is given by the following equation.

[0007]

[Formula 1]

[0008] L is the length of the resonator, W is the stripe width of the current path, η _SP is the internal quantum efficiency, Jo and β are constants, Г is the confinement coefficient, αi is the internal loss, and Rf is the reflection of the front laser light extraction surface. The ratio, Rr, is the reflectivity of the rear surface.

Therefore, it is desirable that the product of Rf and Rr, that is, RfRr, be large from the equation (1).
Increases the light density inside the laser element, the light extraction efficiency η decreases, and the driving current Iop increases. Therefore, in general, in a semiconductor laser, I
In order to suppress the increase in th and efficiently take out the light output, R
Rr is set higher than f.

However, when a semiconductor laser is actually used as a light source, the light emitted from the rear surface is monitored by a photodiode or the like, and feedback is performed so that the output of the light source is always constant. Is high, the light output of the monitor emission light is reduced, and the output current (Im) of the photodiode for monitoring is reduced. As a result, feedback becomes difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a monitoring light receiving element is disposed in front of a laser element so that most light is reflected on a desired surface of the light receiving element.

[0012]

A semiconductor laser device and a light receiving device for controlling the light output of a semiconductor laser disposed in front of the light output surface of the semiconductor laser device. Characterized in that a diffraction grating for diffracting is formed.

[0013]

By providing, for example, a grating on the surface of the light receiving element, a three-beam light source for an optical pickup can be obtained, and the reflectance on the rear side of the laser element can be increased (multi-coating). A low threshold value and low drive current of the laser can be realized, and the characteristics can be improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a block diagram showing one embodiment, in which a laser light output is monitored by a photodiode 13 having a light diffraction function using front output light from a semiconductor laser element 1 on a submount 4. Like that. The rear surface of the laser element 1 is multi-coated to increase the reflectance. The glass 14 on which the diffraction grating 14a is engraved is incorporated into the surface of the photodiode 13. In addition,
Since the inclination angle θ of the photodiode 13 on the stem 6 can be set arbitrarily, the direction of the diffracted light from the photodiode 13 can be set freely.

FIG. 2 shows an example in which a submount 9 in which the submount 4 and the photodiode 13 of FIG. 1 are integrated is used. Also in this case, the inclination angle θ can be freely set in the figure.

Reference numerals 10 and 11 in FIGS. 1 and 2 denote first-order diffracted light by the diffraction grating. Using these diffracted light beams 10 and 11, it is possible to perform tracking servo for reading and writing on the disk. Reference numeral 12 denotes a zeroth-order light beam, which can be used as a main light beam for reading and writing data on a disk.

FIG. 3 shows an embodiment in which a photodiode 13 incorporating a diffraction grating glass 14 is used as a mirror of an external optical system circuit of a laser unit 16. In addition, 1
5 is a lens.

[0019]

As described above, according to the present invention, it is possible to install a power monitoring light receiving element of a semiconductor laser in front of the semiconductor laser element, and to set a high reflectance on the rear surface side of the semiconductor laser element. Even when the oscillation threshold current is kept low, the output current of the light output control light receiving element can be sufficiently ensured.

Further, a diffraction grating is imprinted on the light receiving element surface,
By providing the function of diffracting laser light, it is possible to reduce the number of components of an optical device using the optical semiconductor device.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a second embodiment.

FIG. 3 is a configuration diagram showing a third embodiment.

FIG. 4 is a configuration diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 13 Photodetector 14 Glass with diffraction grating

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Hayashi 22-22, Nagaikecho, Abeno-ku, Osaka, Osaka Inside Sharp Corporation (72) Inventor Yoshiaki Ueda 22-22 Nagaikecho, Abeno-ku, Osaka, Osaka Sharp shares In-company (72) Inventor Masaru Ogawa 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Keisuke Miyazaki 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) Reference Document JP-A-1-270382 (JP, A) JP-A-2-252131 (JP, A) JP-A-61-243963 (JP, A) JP-A-3-106091 (JP, A) JP-A-3-302 212828 (JP, A) JP-A-4-349687 (JP, A) JP-A-4-89638 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5 / 00-5 / 50 G11B 7/125

Claims (2)

(57) [Claims] 1. A semiconductor laser device comprising : a semiconductor laser device;
The semiconductor laser disposed in front of the optical output of the semiconductor laser device.
The light receiving element for controlling the optical output of the element is fixed on the stem
The diffraction grating is integrated into the light receiving surface of the light receiving element.
An optical semiconductor device characterized by being rare . 2. The method according to claim 1, wherein said first-order diffracted light by said diffraction grating is dis- played.
0th order diffracted light for tracking servo
2. The optical semiconductor device according to claim 1, wherein the optical semiconductor device is used as main light for reading and writing data from / to a disk .