JP2002270941A - Semiconductor laser optical device - Google Patents

Abstract

(57) Abstract: In an optical device using a semiconductor laser without a built-in photodetector, a monitor photodetector monitors the optical output without greatly reducing the laser light output used in the optical device, and is stable. And a semiconductor laser optical device capable of performing various operations. A semiconductor laser that emits light in an elliptical shape detects light at an edge of laser light emitted by a semiconductor laser with a photodetector and detects light intensity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor laser optical device using a semiconductor laser without a built-in photodetector.

[0002]

2. Description of the Related Art The light output of a laser beam emitted from a semiconductor laser (hereinafter referred to as an LD) is constant if the driving current is constant.
It fluctuates greatly due to environmental temperature changes. Therefore, in order to keep the light output of the laser light constant, it is essential to detect the light output of the laser light and feed it back to the laser drive current. The LD is often supplied in a package as shown in FIG. The LD chip 1 is adhered to the heat block 3, and a laser beam is emitted from the end face of the LD chip through the window 5 by an electric signal supplied from the terminal 4. The laser light is also emitted from the back surface of the LD chip 1, and its light output is detected by the built-in light detector 2 and output from the terminal 4 as an electric signal. The light detection signal detected by the built-in light detector is input to the LD drive circuit, and is used as a feedback signal for keeping the light output of the LD constant. By the way, in order to increase the output of an LD, an LD from which laser light is emitted
The coating is used to reduce the reflectivity of the window-side end surface of the chip, that is, to improve the transmittance and reduce the transmittance of the back-side end surface. For this reason, the light intensity detected by the built-in photodetector in a high-power LD is extremely small,
A sufficient light detection signal cannot be obtained. For this reason, some high-power LDs do not have a built-in photodetector.

[0003]

In such a case, conventionally, as shown in FIG. 2, the light from the LD 6 is split by the beam splitter 10 and guided to the monitor light detector 8, and the light of the monitor light detector 8 is changed. Feedback of a detection signal to an LD drive circuit has been performed. However, in this conventional method,
If a sufficient light intensity for the light detection of the monitor light detector 8 is secured, the light intensity of the laser beam 11 input to the optical device becomes small, and there is a limit to the optical device realizing sufficient performance.

Accordingly, an object of the present invention is to provide an optical device using an LD without a built-in photodetector, wherein the monitor photodetector monitors the optical output without greatly reducing the laser beam output used in the optical device, An object of the present invention is to realize an optical device capable of performing a stable operation.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to detect at least the light in the major axis direction of an ellipse among the light at the edge of the laser light of a semiconductor laser which emits the laser light in an elliptical shape. This is achieved by detecting the light intensity of the semiconductor laser.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Light emitted from an LD generally has an elliptical distribution. However, many optical devices require a circular light spot. For example, consider a case where a beam from the LD 6 is guided to the optical fiber 18 by the lens 16 as shown in FIG. The cross section of the optical fiber comprises a clad portion 12 and a core portion 13 as shown in FIG. The cladding diameter is usually 125 μm, and the core diameter is 640 wavelength.
The diameter of a single mode optical fiber of nm is about 4 μm. Laser light propagates through this core. Since the light spot illuminating the core portion has a circular core shape, a circular light spot having a predetermined size is guided into the optical fiber with high light efficiency.

When reading information on an optical disk, it is desirable that the light spot has a circular shape. That is, as shown in FIG. 5, information is recorded along the tracks on the optical disc in the form of pits 14. It is desirable that the light spot 15 has a circular shape so as not to erroneously read an adjacent track and to accurately read pits.

In order to allow the light 17 emitted from the LD 6 that emits in an elliptical shape to pass through the optical system with high light use efficiency, it is better to use a lens having a large aperture ratio (given by sin θ). However, since a lens with a large aperture ratio is expensive and requires a high optical system arrangement accuracy, and the narrowed optical spot has an elliptical shape, it is necessary to obtain a circular spot with a simple optical system. Is the aperture ratio (si
It is widely used to use a lens 16 having a small value (given by nθ). In other words, a circular spot 15 is obtained by using the central portion of the light emitted in an elliptical shape. In this case, light outside the lens aperture will not be used. The present invention is characterized in that the light outside the elliptical light emitted from the LD is detected by a photodetector and the light intensity of the semiconductor laser is monitored. With the above configuration, the light intensity can be monitored without wasting the laser light.

Hereinafter, embodiments of the present invention will be described. FIG. 7 is for explaining one embodiment of the present invention. A lens 1 having a large aperture ratio is formed by using a laser beam emitted from the LD 6 in an elliptical shape.
When the aperture is narrowed down at 6, the narrowed light spot also has an elliptical shape. However, in the optical disk device, the narrowed light spot 15 needs to be circular. Also, when the light spot is guided to the optical fiber, the light propagating through the optical fiber has a circular cross-sectional light intensity distribution, so that a circular spot is preferable. From the above, it is not necessary to use a lens having a large aperture ratio, which is expensive and requires high precision in the arrangement of the optical system. Therefore, as shown in FIG. 7, the lens 16 has an aperture ratio of 0.3.
By using the following small one, only the light near the center of the light emitted from the LD is narrowed down by the lens 16. For this reason, the total light intensity of the outside light protruding from the lens 6 is LD
From the light intensity toward the lens. The light outside the lens 6 is detected by the photodetector 19 to detect the light intensity. The detected light detection signal is fed back to a circuit that drives the LD, and is used to make the light intensity of the emitted laser light constant.

It is best to detect all the light protruding from the lens 16 with a photodetector, but as shown in FIG.
Even if a part of the light emitted in the major axis direction of the light emitted in an elliptical shape is detected, a sufficient light detection signal can be obtained.

FIG. 8 shows an optical device of the present invention for guiding a light spot formed by the optical system of FIG. Light that does not enter the lens 16 and protrudes is detected by a photodetector 19 disposed outside the lens.

FIG. 9 shows an optical device of the present invention for guiding a light spot formed by the optical system of FIG. The optical disk is rotated by a motor 26. Here L
The light emitted from D is converted into parallel light by a lens 23 and is focused on an optical disk by a lens 24. The laser beam protruding outside the lens 23 is detected by the photodetector 19 adhered to the LD package.

[0013]

According to the present invention, the light intensity can be monitored by the light of the portion of the light from the semiconductor laser that is off the optical device, so that the light intensity can be used effectively.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a packaged semiconductor laser.

FIG. 2 is a configuration diagram of a conventional semiconductor laser optical device for monitoring light intensity.

FIG. 3 is an explanatory view of a semiconductor laser optical device for guiding an optical fiber.

FIG. 4 is a sectional view of an optical fiber.

FIG. 5 is an explanatory diagram showing a situation in which information on an optical disc is read by a light spot.

FIG. 6 is a diagram illustrating the principle of a semiconductor laser optical device according to the present invention.

FIG. 7 is a diagram illustrating the principle of a semiconductor laser optical device according to the present invention.

FIG. 8 is an explanatory view of a semiconductor laser optical device for introducing light into an optical fiber according to the present invention.

FIG. 9 is an explanatory diagram of a semiconductor laser optical device for recording and reproducing the optical disc of the present invention.

[Explanation of symbols]

1) a semiconductor laser chip, 2 a built-in photodetector, 3 a heat block, 5 a window, 6 a semiconductor laser, 7 a lens, 8 a monitor photodetector, 10 a beam splitter, 12 a clad, 13 Is the core, 14 is the pit, 1
5 is a light spot, 16 is a lens, 17 is light emitted from the semiconductor laser in an elliptical shape, 18 is an optical fiber, 19 is a photodetector, 23 and 24 are lenses, 25 is an optical disk, and 26 is a motor.

Claims (3)

[Claims] 1. An optical detector for detecting at least the light in the major axis direction of an ellipse of a laser beam emitted from a semiconductor laser that emits the laser beam in an elliptical shape, thereby detecting the light intensity of the semiconductor laser. A semiconductor laser optical device, characterized in that: 2. The semiconductor laser optical device according to claim 1, wherein light emitted from said semiconductor laser is guided to an optical fiber. 3. The semiconductor laser optical device according to claim 1, wherein recording or reproduction on an optical disk is performed using light emitted from said semiconductor laser.