JPS60103529A - Optical signal processing unit - Google Patents

Abstract

PURPOSE:To decrease noise without producing radiation by monitoring a laser light of a laser element in an optical pickup device of an optical video disc device so as to apply negative feedback to an applied current of the laser element. CONSTITUTION:A laser light 2 irradiated from a semiconductor laser element 1 is separated into three laser lights by a diffraction grating 4 and made incident to a half mirror 5. The laser light 12 reflected on an optical disc 11 is collected into three points on a 3-spot photodetector 16, where the light is converted into an information signal for a video signal or a sound signal or the like, a focusing signal and a track signal. An electric signal proportional to the luminous amount of the laser light 6 incident to a photodiode 8 is fed back to the applied current of the laser element 1 via an inverse amplifier 9 and a capacitor C so as to keep the luminous amount of the laser light 6 to a constant value thereby decreasing an SCOOP noise.

Description

Detailed Description of the Invention [Technical Field] The present invention provides a technique that is particularly effective when applied to a semiconductor laser device and a semiconductor laser device that oscillates in a single longitudinal mode, such as an optical video disc device. Optical pickup device (optical signal processing bag fFi')
Concerning effective techniques that can be used.

[Background technology]

Semiconductor laser elements are being put into practical use as signal pickup light sources for optical video discs, optical digital audio discs, and the like.

However, in the semiconductor laser device N that oscillates in a single longitudinal mode, mesh mode hopping (MH) noise due to changes in device temperature and applied current, and output laser light reflected outside the semiconductor laser device are generated in the semiconductor laser device. Self-Coupled Optical Pi
ck-up noise (abbreviated as 5cOOP noise)) This causes a problem in that the laser output fluctuates.

In order to avoid the above-mentioned mode hopping noise and 5-coop noise, there are methods to superimpose a high frequency on the applied current to make the longitudinal mode a stable multi-mode, and to make the mode fluctuations smooth, and a method to structurally prevent multi-mode oscillation. A method using a so-called narrow stripe laser diode, which is easy to perform, has been developed.

However, the former method poses problems such as having to comply with strict regulations in the United States and other countries to prevent unnecessary electromagnetic wave radiation from the oscillator from adversely affecting other devices such as televisions.

In addition, in the latter method, the transverse mode of a narrow stripe laser element tends to have bimodality, and when fc is focused on an optical disk by an objective lens in an optical pickup device, the spot is separated into two. The applicant has found that a problem arises in that the information on the optical disk cannot be obtained sufficiently.

[Purpose of the invention]

The present invention solves the above-mentioned problems, and its purpose is F! The object of the present invention is to provide a light emitting device technology that reduces noise without causing radiation and is well coupled with an optical system.

The above and other objects and novel features of the present invention include:
It will become clear from the description of this specification and the attached drawings. - [Summary of the Invention] A brief summary of typical inventions disclosed in this application is as follows.

That is, the forward emitted light of the light emitting element is guided to a half mirror, a part of the light is taken into the light receiving element, the electrical signal from the light receiving element is inverted and amplified, and the current applied to the light emitting element is subjected to negative feedback. , No. 48 generated from the light-receiving element is made constant, thereby reducing noise and achieving the above object.

〔Example〕

FIG. 1 is a schematic diagram of an optical pickup device according to the present invention.

The optical pickup device ut/i in the figure has the following features. That is, the laser light 2Fi emitted from the semiconductor laser device 1, which is a light emitting device, becomes a parallel light beam by the coupling lens 3. Next, the laser beam is separated into three laser beams by the diffraction grating 4 and enters the half mirror 5. At this time, the laser beam 2 is divided and reflected within the half mirror to become the laser beam 6. The laser beam 6 is then focused by a convex lens 7 onto a photodiode 8, which is a light receiving element. Next, the electrical signal from the photodiode 8 applies negative feedback to the current applied to the semiconductor laser probe 1 via an inverting amplifier 9 serving as an amplifier and a capacitor C.

As described above, even if the return light from the external optical system enters the semiconductor laser element and the optical output fluctuates, the electric signal from the photodiode 8 is kept constant.

The operation of the optical pickup cylinder will be explained with reference to the same figure.

A forward emitted laser beam 2 from the semiconductor laser element 1 passes through a coupling lens 3 to become parallel light, passes through a diffraction grating 4 and a half mirror 5, and is focused onto an optical disk 11 by an objective lens 10. At this time, it passes through the diffraction grating 4 (5
Therefore, although not shown in the figure, there are 3
Focus the light on a point.

Next, the laser beam 12 reflected on the optical disk has information on the presence or absence of a hole (pit) 13 arranged on the optical disk 11. Thereafter, the reflected laser beam 12 passes through the objective lens 10, and a portion of the scene is reflected by the half mirror 5, which is reflected by the tongue cylindrical lens 14. convex lens 15
After that, the light is focused on three points on the three-spot light receiving element 16. 1. Focusing light on three points on the three-spot light receiving element 16; out of a light spot.

One spot is opened on the optical disc 11 as described above.
'It also has information on the presence or absence of the hole 13 and focusing information, which is converted into an electrical signal by a portion of the 3-spot light receiving element 16, and is converted into an electrical signal by a first electrical circuit (not shown), such as an information signal such as a video signal or an audio signal. It can be converted into a focusing signal. The other two spots are for detecting track No. 4J, and are converted into electrical signals by the 3-spot light receiving element 16, and error signals are differentially obtained by a servo circuit (not shown) to prevent tracking errors. There is.

By the way, half of the laser beam 2 emitted forward from the semiconductor laser probe 1 is passed through the convex mirror 5 by the half mirror 5.
The light passes through and is irradiated onto the photodiode 8. The photodiode 8Fi emits an fcs signal in proportion to the sight of the incident laser beam 6. The phase of the electrical signal is then inverted by the inverting amplifier 9, and the alternating current component is fed back to the current applied to the semiconductor laser element 1 by the capacitor CK. Thereby, the amount of laser light 6 incident on photodiode 8 is kept constant. For example, when 5COOP noise occurs and fc, the laser beam 2 fluctuates due to 5C00P noise, and the amount of laser beam 6 decreases or increases. Therefore, the light intensity of laser beam 6 should be kept constant, and 5co
This is to reduce OP noise.

Incidentally, the semiconductor laser element 1 emits laser light 17 not only forward but also backward. This laser beam 17 is received by a light receiving element 18 incorporated in the same package as the semiconductor laser element 1, and this laser beam 17
It is conceivable to apply negative feedback to the current applied to the semiconductor element 1 so as to keep the amount of light constant. However, this method generally cannot reduce the 5COOP noise. Therefore, the spatial distribution of the forward-emitting laser beam 2 and the backward-emitting laser beam 17 of the semiconductor laser device 1 does not change over time in a completely symmetrical state, and the rear-emitting laser beam 17
This is because even if the light amount of the forward laser beam 2 is constant, the light amount of the forward laser beam 2 is not constant. However, this rear-emitting laser 5' (, 17) is monitored by a light receiving element 18 disposed in the same package, and the amount of light changes slowly due to changes in the element temperature of the #-conductor laser element 1. In other words, slow fluctuations in light intensity are converted into electrical signals by the light receiving element 18, and the automatic power controller (AP
Abbreviated as C. ) 19 applies slow negative feedback to the current applied to the semiconductor laser element 1.

As described above, by monitoring the forward emitting laser beam 27 and applying fast negative feedback to the applied current to the semiconductor laser element 1, and by monitoring the backward emitting laser beam 17 and applying slow negative feedback to the applied current, feedback is achieved. 5c, which occurs when stimulated emission of carriers in the semiconductor laser device 1 is promoted by light.
It is possible to reduce oop noise and mode popping noise caused by changes in the temperature of the semiconductor laser element 1 and changes in the applied current. image quality can be improved.

〔Effect of the invention〕

(1) In order to reduce the noise associated with mode hopping or mode instability of a longitudinal single mode laser device by monitoring the laser light of the laser device and applying negative feedback to the first current of the laser device, the laser light It is possible to provide a light-emitting device that does not require a high-frequency superimposition circuit required for multimode, does not generate unnecessary radiation such as electromagnetic waves, or does not cause deterioration of optical characteristics due to the use of a multimode element. This effect can be obtained.

(2) By monitoring the laser light and applying negative feedback to the current applied to the laser element, mode hopping noise and 5coop noise can be reduced, improving the sound quality of digital audio discs (DAD) and video discs. The effect is that the image quality of the player is improved.

Based on the above invention made by the present inventor@
Although the present invention has been specifically described, it goes without saying that the present invention is not limited to the above embodiments and can be modified in various ways without departing from the spirit thereof. Bukoe uses a prism beam splitter and a quarter-wave plate instead of a half mirror as optical components for optical branching and optical 1i'1Mff history, and the optical axis of the laser beam of the quarter-wave plate is By adjusting the rotation angle of the surroundings, it may be possible to monitor one group of forward emitted laser beams. Also, half mirror
2 does not have to perform one-to-one branching of the amount of light for one incident light component, but may have an arbitrary branching ratio. In addition, a circuit that performs high-speed negative feedback for noise reduction and a circuit that performs slow negative feedback to electrify slow changes in light intensity due to temperature changes are separately provided, but the amplifier 12 is sufficiently fast and If the output is high, the APC 19 and the built-in light receiving element 18Fi will be uncomfortable. In other words, all of the 5-coop noise, the 7-de-hopping noise, and the slow changes in the scene due to temperature changes in the LD are monitored only by the light receiving element 8, and a single high-speed, high-output amplifier applies negative feedback to the applied current. It is something. In this case, by reducing mode hopping noise by monitoring only the forward emitted laser beam, mode hopping noise can be reduced to a higher F#& compared to mode hopping noise reduction by monitoring the rear emitted laser beam. 6 Also,
By reducing the number of parts required for the optical pickup device, it is possible to produce it at a lower cost.

[Application field]

Although the above explanation has mainly been about the case where the invention made by the present inventor is applied to the optical pickup device technology that is the background thereof, the present invention is not limited thereto, and can be applied to, for example, optical communication device technology. The present invention can be applied to optical system M using at least LD under conditions where mode hopping or 5coop noise occurs.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of an optical pickup device showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Ox conductor laser element, 2... Front emitting laser beam, 3... Coupling lens, 4... Diffraction grating, 5...
-7 mirror, 6... branched laser beam, 7... convex lens, 8... photodiode, 9... amplifier (
(inverting amplifier), 10... Objective lens, 11... Optical disk, 12... Reflected laser beam, 13... Hole (pit), 14... Cylindrical lens, 15...
Convex lens, 16...3 spot light receiving element, 17...
Rear emitting laser beam, 18... Light receiving element (photodiode), 19... Automatic 9 power controller (APC), C... Capacitor, L... Reactance.

Claims (1)

[Claims] 1. A light emitting means, a signal recording medium for recording a signal read out or written using the light emitted from the light emitting means, and a light beam for reading out the signal recorded on the No. N recording medium. means for converting the optical output of the light output into an electrical signal; and a light output detection means for detecting the light output of the light emitted from the light output means and used for signal processing; a feed having a function of applying feedback to the light emitting means according to the amount of variation in the output of the light emitted from the light emitting means to keep the light output of the light emitted from the light emitting means at a constant value; An optical signal processing device comprising a fist back means.