JPH04349230A - Light pick-up - Google Patents

Abstract

PURPOSE:To prevent the performance deterioration due to the wavelength fluctuation by controlling constantly a waveguide light wavelength in an integrated pick-up. CONSTITUTION:The fluctuation of the wavelength of a waveguide light projected from a semiconductor laser part 3 to a waveguide layer 5 is detected through a grating 20 for detecting a wavelength by light receiving elements 22a and 22b. The signal obtained here and the signal obtained by a light receiving element 24 are inputted to a division circuit 32 and the signal corresponding to the regularized wavelength shifting quantity is outputted. The regularized output is compared with the reference voltage, the compared output is fed back to an electrode for controlling the wavelength of the semiconductor laser and the waveguide light wavelength is constantly controlled.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an optical information recording medium (
The present invention relates to an optical pickup for recording a signal on a (hereinafter abbreviated as an optical disk) or reproducing a recorded signal, and particularly relates to a small and lightweight optical pickup.

0002

2. Description of the Related Art Conventional optical disk reading devices are assembled using individual parts such as an objective lens, a prism, a semiconductor laser, and a photodetector. In this method, the lower limit of the size of each component is determined from the viewpoint of operability during assembly, positioning accuracy, etc., and a mechanism for mutual position adjustment is also required, making it difficult to reduce the size of the optical pickup too much. It is not possible. To overcome this drawback, optical integrated pickups using optical waveguides, grating couplers, etc. have been proposed.
986,5 Vol. J69-CNo. 5 P609
-P615 is known as an optical integrated pickup disclosed in US Pat.

The structure of a conventional optical integrated pickup will be briefly explained with reference to FIG. An optical waveguide 52 is formed on the silicon substrate 50. The light emitted from the semiconductor laser 53 is coupled to the optical waveguide 52 from the end face of the optical waveguide,
Emitted from the grating coupler 55, the optical disc 60
is irradiated. The light reflected from the optical disk 60 is guided into the optical waveguide again by the grating coupler 55 and detected by the photodetecting elements 62 and 63.

Furthermore, Japanese Patent Laid-Open No. 1-175784 discloses an optical integrated pickup in which a wavelength control electrode section is provided in a semiconductor laser section to perform wavelength control.

[0005]

[Problems to be Solved by the Invention] The model proposed in the above paper has many practical problems, and one of these problems is the difficulty in determining the device characteristics with respect to minute wavelength fluctuations of laser light. One point is that there is a large change in

[0006] In general, since grating elements utilize a diffraction phenomenon, their characteristics change sensitively depending on the wavelength of an incident wave. Normally, semiconductor lasers have a property that the wavelength fluctuates due to temperature changes, etc., but when such fluctuations occur, in this conventional configuration, a difference in power occurs in the light emitted from the grating coupler, and the optical disc The upper spot diameter increases and the S/N ratio of the reproduced signal decreases. For this reason, in the conventional technology, performance deterioration due to wavelength fluctuations of laser light could not be avoided.

Furthermore, the above-mentioned Japanese Patent Laid-Open No. 1-175784 discloses only wavelength control of a semiconductor laser, and does not disclose any means for detecting wavelength fluctuations and controlling the wavelength based on this. It has not been.

An object of the present invention is to provide an integrated optical pickup that prevents performance deterioration due to wavelength fluctuations by controlling the wavelength of guided light to be constant.

[0009]

[Means for Solving the Problems] In order to solve the above problems, an optical pickup of the present invention includes a semiconductor laser, a waveguide for guiding laser light emitted from the semiconductor laser, and a waveguide provided in the waveguide. It has a grating that focuses the laser light in the waveguide onto an optical recording medium outside the waveguide, and a light detection means that detects the reflected light from the optical recording medium, an optical pickup for recording and/or reproducing signals, comprising: detection means for detecting wavelength fluctuations of the laser light; means for stabilizing the wavelength of the laser light based on the signal detected from the detection means; It is characterized by having the following.

0010

[Operation] A grating and a light receiving element for detecting the wavelength of guided light are provided in the waveguide. When the laser light emitted from the semiconductor laser enters the grating, the diffracted light from the grating is detected by the light receiving element, and the wavelength variation is detected as a photocurrent variation. The semiconductor laser section is provided with a wavelength control electrode, and by injecting a current into the semiconductor laser according to the amount of fluctuation, the emission wavelength is kept constant.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a first embodiment of the invention. Ga
A semiconductor laser section 3 is mounted on the As substrate 10. This semiconductor laser section 3 is, for example, JP-A-1-17
The structure is similar to that of the semiconductor laser section disclosed in Japanese Patent No. 5784. That is, when a current is injected into the active layer part electrode and a current is injected into the wavelength control electrode, the wavelength of the emitted laser light is shifted to the shorter wavelength side as the current increases. The laser light emitted from here propagates through a waveguide layer 5 provided on the GaAs substrate 1.

A beam splitter 7 and a grating coupler 9 are formed at the rear end of the waveguide layer 5.
The laser light incident on the beam splitter 7 is focused by the grating coupler 9 and projects a light spot onto the optical disk 11. The information signal from the optical disc 11 is detected by light receiving elements 13 and 14, which are divided into two parts and formed on both sides of the center of the substrate 1, respectively.

A wavelength detection grating 20 for diffracting the laser beam emitted from the semiconductor laser section 3 is formed in the waveguide layer 5 . Two light receiving elements 22a and 2 are placed on the substrate 1 at positions where they can receive the leakage light of the first-order diffracted light from the grating 20.
2b is formed. Further, on the substrate 1, a light receiving element 24 is formed between the grating 20 and the semiconductor laser section 3 to receive leaked laser light.

An example of the arrangement of the wavelength detection grating 20 is shown in FIG. As an example, the laser wavelength is 0.78μm
, grating length L=95μm, pitch 0.43μm
m and the grating angle θg = 127.5 degrees, the angle θd of the diffracted light is 75 degrees with respect to the incident light, and the diffracted light rate is 3.6%. At this time, the diffraction efficiency is halved to about 1.8% for a wavelength shift of 0.1%, so a wavelength error of about several angstroms can be detected by detecting the diffracted light.

The photocurrents obtained by the light-receiving elements 22a, 22b, and 24 are transmitted to current-voltage conversion circuits 26 and 24, respectively.
The voltage is converted at 27 and 28. current voltage conversion circuit 26,
The outputs of 27 are respectively input to differential amplifiers 30, and the outputs from the differential amplifiers 30 are input to one end of a divider circuit 32. On the other hand, the output from the current-voltage conversion circuit 28 is input to the other end of the division circuit 32. Division circuit 32
The output of is input to a differential amplifier circuit 34, where it is compared with a reference voltage. Then, the output from the operational amplifier circuit 34 is converted into a current by a voltage-current conversion circuit 36, and is fed back to the wavelength control electrode of the semiconductor laser section 3.

Next, the control of wavelength fluctuation according to the present invention will be explained.

When wavelength fluctuation occurs, the diffraction light index and diffraction angle of the grating 20 change, so that the light receiving element 22a
, 22b changes, and the amount of light incident on the two-split element 2 changes.
An imbalance occurs in the amount of light received by 2a and 22b. The difference between the signals obtained by the light receiving element 22a and the light receiving element 22b becomes a signal corresponding to the amount of wavelength shift. However, in this case, even if there is a simple change in the amount of light that is not accompanied by a wavelength change, the amount of light incident on the light receiving elements 22a and 22b will change.
This variation is canceled. Therefore, after converting the photocurrents detected by the respective light receiving elements 22a and 22b into voltages by the voltage conversion circuits 26 and 27, the difference between the two is taken by the differential amplifier 30, and the output is inputted to one end of the dividing circuit 32. do. Then, the signal detected by the light receiving element 24 is voltage-converted and inputted to the other end of the division circuit 32, and the signal corresponding to the amount of wavelength shift is normalized. The normalized output of the division circuit 32 is compared with a reference voltage by a differential amplifier 34, and the error signal is converted into a current signal by a voltage-current conversion circuit 36, which is then fed back to the wavelength control electrode of the semiconductor laser. . By driving the semiconductor laser in a direction that reduces wavelength fluctuation using the feedback signal, the guided light wavelength is kept constant.

The present invention can also be modified as shown in FIG. 3, for example. In this figure, the same parts as in the previous embodiment are given the same reference numerals, and the explanation thereof will be omitted. In this modification, a beam splitter 40 is formed in the waveguide layer 5, and the laser beam emitted from the semiconductor laser section 3 is configured to be split. and,
The laser light branched here passes through the grating 20 for detecting wavelength variation and is detected by the light receiving elements 22a and 22b. The following operations are the same as in the embodiment described above.

[0020]

[Effects of the Invention] A pickup according to the present invention includes a detection means for detecting wavelength fluctuations of a laser beam, and a means for stabilizing the wavelength of the laser beam based on a signal detected from the detection means. It is characterized by Thereby, since the wavelength of the guided light is always kept constant, deterioration of the characteristics of the pickup due to wavelength fluctuations of the guided light can be prevented.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of a pickup according to the present invention.

FIG. 2 is a diagram showing an example of the arrangement of wavelength detection gratings 20 in the embodiment of FIG. 1;

FIG. 3 is a perspective view showing a modification of the pickup according to the present invention.

FIG. 4 is a perspective view showing the configuration of a conventional optical integrated pickup.

[Explanation of symbols]

3... Semiconductor laser section, 20... Grating for wavelength detection, 22a, 22b, 24 light receiving element, 40... Beam splitter.

Claims (1)

[Claims] 1. A semiconductor laser, a waveguide for guiding laser light emitted from the semiconductor laser, and a semiconductor laser provided in the waveguide to focus the laser light in the waveguide onto an optical recording medium outside the waveguide. an optical pickup for recording and/or reproducing a signal on the optical information recording medium, the optical pickup having a grating for detecting reflected light from the optical recording medium and a photodetecting means for detecting reflected light from the optical recording medium; An optical pickup comprising: a detection means for detecting fluctuation; and a means for stabilizing the wavelength of the laser beam based on a signal detected from the detection means.