JPH02118927A - Method and device for driving semiconductor laser - Google Patents

Abstract

PURPOSE:To reduce noise in any mode of erasure, recording and reproduction by injecting a current including an AC component whose phase is almost inverted in nearly the same frequency to each of at least two current areas. CONSTITUTION:Plural current injection areas 23-25 are formed to a stripe in an active layer applying laser oscillation in a built-in type semiconductor laser 2. A signal representing the information to be recorded or reproduction is recognized by a microprocessor 35 via an interface 34, modulated by a modulation circuit 33 and a signal current is injected to the area 23 via a drive circuit 31. On the other hand, an AC current to reduce induced noise is obtained by an oscillation circuit 38 and an AC current whose phase is deviated by 180 deg. by an inverse circuit 39 is obtained. The AC current is superimposed onto a DC current via a capacitor 41 obtained from a DC bias circuit 37 via a coil 40 and a current including the AC component whose phase is deviated by 180 deg. is injected to the areas 24, 25 respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for driving a semiconductor laser, and in particular, to a method for driving a semiconductor laser. 'V- reduction.

[Prior Art] Conventionally, when a semiconductor laser is used as a light source in an information playback device that optically reproduces information from an optical video disk, etc., the return light from the optical disk is converted into the output light of the semiconductor laser. It is known that induced noise interferes with the reproduction of ↑hm.

As a countermeasure, as shown in Japanese Patent Publication No. 59-9086, it has been proposed to reduce noise by superimposing a high frequency current on a direct current so that a semiconductor laser oscillates in multiple longitudinal modes.

In addition, in the field of optical communications, speckle e occurs due to differences in propagation constants between modes at the receiving end of a multimode fiber.
To reduce pattern noise, Special Publication No. 61-24837
As shown in the issue, the electrode of a semiconductor laser is divided into multiple parts, and a high-frequency voltage is applied to some of them.
A method of causing a semiconductor laser to oscillate in multiple longitudinal modes has been proposed.

[Problems to be Solved by the Invention] By the way, as shown in Japanese Patent Publication No. 59-9086, the noise reduction effect is achieved when a high frequency current lowers the oscillation threshold of a semiconductor laser to a depth <! , IJ, a sufficient effect is obtained when the high frequency '+W current amplitude is increased and pulsed light is emitted.

Therefore, in the case of a reproduction-only device like the one disclosed in Japanese Patent Publication No. 59-9086, there is no problem because the optical power is low, but in a device that requires high optical power for erasing and recording information, There are the following problems. In other words, even when the laser output is high, in order to apply a high-frequency current that increases the threshold value to a depth of <9J, conversely, due to the constraint that the peak optical output due to the high-frequency current does not exceed the maximum rating of the laser, The level of the current component of the erasing/recording signal modulated according to the information must be below the midpoint between the threshold current and the maximum rated current, and the optical output necessary for erasing and recording must be fl
There is a problem that it cannot be played.

Therefore, Japanese Unexamined Patent Publication No. 119743/1983, Utility Model Application No. 62-
As shown in Japanese Patent Application No. 142721, a method has been proposed in which superimposition of high-frequency current is stopped and a high optical output level is ensured at the optical output level for erasing or recording. However, for that.

There was a problem with reliability because the return light induced noise during erasing and recording was not sufficiently reduced. In particular, if the recording medium is one in which the energy or power of light changes slowly, such as a color density medium, and the threshold value 1 is not constant, the quality of the erased or recorded bits may be poor. Naru 6 again. If the medium is 7E, such as an optical card or optical tape, and the relative speed between the optical head and the medium is small, the servo band for autofocus and autotracking/king and the information signal band are very close to each other or overlap, so erasing, There is a problem in that the crosstalk of the information signal to the servo signal due to the modulation of the optical output during recording is large, and therefore the noise at the high output level during erasing and recording becomes noise not only in the information signal but also in the servo signal. are doing.

Also, in the method shown in the above-mentioned Japanese Patent Publication No. 61-24837 for optical communication, the electrodes of a semiconductor laser are separated.
However, even if only a certain amount of light is applied, a decrease in the optical output in the information signal band due to the high frequency current cannot be avoided, making it difficult to apply the method to optical information recording and reproducing devices.

Furthermore, in the past, there was not only the problem of a reduction in the optical output for pulsed emission of a half-four-body laser as shown in the above example, but also the problem of a reduction in optical output due to the problem of overlapping intersections. There was a problem because there was a restriction on the lower limit of the frequency of the i-current.

This is based on the lower limit of the frequency for the laser to always oscillate in multiple longitudinal modes while emitting light, and the so-called sampling theorem, which requires a frequency that is at least twice the maximum frequency of information, and in practice a frequency that is at least 10 times higher. There is a limit of 40
It is common to superimpose a high frequency current of 0 to 800 MHz. In this high frequency range, it is difficult to implement a high frequency superimposition circuit on a normal laser drive circuit, so a hybrid circuit built on a ceramic substrate or a G
The method used is to put a circuit constructed using aAs IC into a shield case and connect it directly to the laser pin. For this reason, the present situation is that it is not only an obstacle to the heat dissipation of the laser and the miniaturization and weight reduction of the optical head, but also increases the process and difficulty of assembly and adjustment, leading to an increase in cost.

[Object of the Invention] In view of the above-mentioned conventional problems, the present invention is capable of suppressing a decrease in optical output, achieving good erasure recording and transmission of information, and achieving a sufficient noise reduction effect. The purpose of this invention is to provide a stable, highly reliable, and inexpensive method for driving a semiconductor laser by improving the heat dissipation of the laser, making the optical head smaller and lighter, and making assembly and adjustment easier.

[N Essentials of the Invention] The above purpose is to enable a semiconductor laser as a light source to
having a plurality of current injection regions, each of the at least two injection regions having approximately the same frequency for noise reduction;
This is achieved by a semiconductor laser driving method that injects a current containing an alternating current component whose phase is almost reversed.

Further, a semiconductor laser driving device that implements such a method includes a semiconductor laser having a plurality of current injection regions, and a driving circuit that drives the semiconductor laser according to a signal from a modulation circuit that modulates information to be recorded. , has a DC bias circuit, an oscillation circuit that generates an AC current, and an inversion circuit that obtains an AC current with a waveform phase shifted by about 180 degrees from the oscillation circuit, and the DC 'IE current from the DC bias circuit is Further, a semiconductor laser driving device can be considered in which the two alternating currents are superimposed on each other and the currents are injected into a plurality of '1 wave injection regions corresponding to the driving circuit.

According to the method of driving a semiconductor laser as described in L, one pulse is applied to each of at least two implantation regions at approximately the same frequency.
By injecting a current containing an alternating current component whose phase is almost reversed, Hn is reduced and the laser light output is kept almost constant, making it possible to cope with high output levels during erasing and recording. .

[Examples] Examples of the semiconductor laser driving method and device of the present invention will be described below in detail with reference to the drawings.

FIG. 8 is an explanatory diagram of the configuration of the optical part of the optical information recording/reproducing apparatus, and is an example of information reproduction of an optical cart. The outline of the configuration will be described below with reference to FIG. 8, but portions known to those skilled in the art will only be briefly described.

The elliptical diverging light from the semiconductor laser 2 having a plurality of current injection regions according to the present invention is converted into parallel light by the collimator lens 3, and has a light intensity distribution that is almost symmetrical with respect to the optical axis by the beam shaping prism 4. , the light is shaped into approximately circular parallel light.

The light is divided into three parallel beams by the diffraction grating 5, and transmitted through the non-polarizing beam splitter 6. The light is bent approximately orthogonally by the bending mirror 7, and is then directed to the tracking track 9 of the optical card 17 by the objective lens 8. Spots Sl, S2 . Image S3. The optical card 1 is moved back and forth in the direction of the arrow R at a constant velocity 'yj' by a driving means (not shown), and the spot is scanned on the tracking track. Each sport, ToSl, S2. The reflected light S3 passes through the objective lens 8 again, and the component reflected by the non-polarizing beam splitter 6 is reflected by the astigmatic condensing lens system 10 including, for example, a cylindrical surface.
The light is focused on photodetectors 11, 12, and 13, respectively. Autofocus is performed using a well-known aberration method to control the objective lens 8 in the F direction to obtain a minute spot. Auto trunking uses a known 3-beam system to control the objective lens 8 in the T direction, thereby making it possible to reliably control the spot.

The recording surface of the optical card 1 is protected by a protective layer (not shown), and the light from the laser 2 passes through this protective layer 17 to obtain information from the recording surface (1).Reducing the price of the optical card Therefore, a polycarbonate cap is used as a protective layer, but birefringence occurs due to factors such as card manufacturing, usage conditions, stress during recording, and residual stress. Therefore, it combines effective use of light and an isolator. In the combination of a polarizing beam splinter and a quarter-wave plate, the F- of the light reflected to the photodetector side and the impurity of the light transmitted to the laser 2 side vary depending on the degree of birefringence. The light on the detector side is small,
When the signal pair 3t Fx ratio is small, the most light returns to the laser 2 side, the return light induced 2I sound is generated, and the signal pair 24 [
There is the problem of further deteriorating the 1" f ratio. Therefore, in this embodiment, a non-polarizing beam splitter that does not depend on polarization in the wavelength range of laser 2 is used, and the light φ on the photodetector and the laser 2.Specifically, the transmittance is 60~7096, anti'!#
+30 to 40% is a reasonable range, but since the return light 1 to the laser 2 reaches several percent, a DC signal is superimposed on the laser 2 to reduce the intensity of sweat induced by the return light. At that time, since the non-polarized beam splinter 6 is used, the transmittance from the laser 2 to the card L is reduced, so a high-power laser must be used.However, as mentioned in Problem 5 of the conventional example, As mentioned above, when recording, a high level is required,
According to the present invention, it is actually impossible to apply a normal high frequency hair length, but it is possible to sufficiently reduce 317T even at high output.

FIG. 1 is a schematic enlarged view of the chip structure of the laser 2. FIG.

Laser 2 is a so-called embedded semiconductor laser.
For the stripe 21 in the active layer that performs laser oscillation, a plurality of P-type 'It poles form a plurality of 'current injection regions 23 and 24 in pairs with the n-type electrode 22.

25 is formed. For injection region 23, 24.25
Since the region is small, the laser 2 can oscillate only with the injection region 23, but one oscillation is controlled by the positive/negative and magnitude of the current (carrier) injected into the regions 24 and 25.

A photodiode 26 is monolithically attached behind the laser 2, and it is possible to apply a reverse bias and extract a current according to the output of the laser 2. According to those skilled in the art, this type of semiconductor laser can be manufactured using well-known techniques, for example, by a wire bond growth method and a reactive ion etching method. omitted. In addition, in order to increase the output of laser 2, the reflectance of the front end face of laser 2 was lowered to 5 to 30%, and the reflectance of the rear end face was reduced to 70 to 90%.
It is also easy to raise the

FIG. 2 is a schematic block diagram of a semiconductor laser driving device for driving the semiconductor laser 2 according to the present invention.

In the figure, 2 is a semiconductor laser according to the present invention,
23, 24, and 25 are the current injection regions, respectively.

34 is an interface that connects recording information to the modulation circuit 33 and MPU 35. If necessary, the modulation circuit 33 modulates the signal No. 111 from the interface 34 into a predetermined modulation method, and inputs it to the current injection region 23 via the drive circuit 31.

32 is an APC circuit that detects the optical output of the laser 2 obtained by the photodiode 26 and performs APC control on the drive circuit 31. 37 is a bias circuit that generates a W current, 38 is an oscillation circuit that generates an alternating current, 3
9 is an inversion circuit that inverts the alternating current; 36 is an MPU
This is a switching circuit that can switch between the oscillation circuit 38 and the bias circuit 37 according to the command 35.

What information should be recorded or what signal should be played?

Through the interface 34, the microprocessor-M
The signal current is recognized by the PU 35 and modulated by the modulation circuit 33 according to a predetermined modulation method during recording, converted into the recording format of the optical card t, and sent to the injection region 23 via the drive circuit 31. inject. During playback, a DC bias current is selected and injected.

On the other hand, an alternating current for reducing return light induced noise is obtained by the oscillation circuit 38, and an alternating current, rL current, whose phase is roughly shifted by 180 degrees, is obtained by the inversion circuit 39. These alternating currents are superimposed on the direct current from the direct current bias circuit 37 via the coil coil 40 via the capacitor 41, and the alternating current components with a phase shift of 180° are superimposed on the -1tt current injection region 24.25. A current containing is injected.

FIG. 3 shows an example of each injection*a waveform 42, 43. 1th shown in FIG. 3 indicates the effective oscillation threshold controlled by the injection region 24.25. By injecting the inverted AC signal, the noise is reduced by the same effect as shown in the above-mentioned Japanese Patent Publication No. 59-9086, and the effective component is increased, so the optical output of the laser 2 is kept almost constant. It is also capable of handling high output levels during recording. Furthermore, according to the present invention,
Since the optical output of the laser is kept almost constant regardless of the frequency of the AC component, there is no longer a frequency restriction due to the sampling theorem, which was a problem in the past, so it is possible to set the optimal frequency for the noise reduction effect. . Therefore, the frequency does not need to be as high as several 100 MHz as in the prior art, and as long as the desired noise reduction effect is ensured, it is possible to select a frequency that overlaps with the signal band or is lower than that. Furthermore, it is effective not only for reducing laser intensity noise, but also for reducing noise caused by changes in the diffraction pattern and interference fringe pattern on the detector due to wavelength changes. In other words, this kind of 31 sound mainly appears as unnecessary undulations and discontinuities of the erroneous signal in the servo band and becomes a problem, but the interference h: 4! The brightness contrast of S decreased, and 3
It is known to have the effect of reducing sound. In addition to this effect, the present invention moves and changes the interference i/4'9 on the photodetector by modulating a relatively low frequency earlier than the servo band, and in the servo band, a low-pass filter is used. As a result, it is possible to achieve a noise reduction effect in which the optical power is equalized.

In addition, since the frequency is not limited to high frequencies, there is no need to put a special circuit in a shield case and combine it with the laser as in the past. This makes it possible to improve the heat dissipation of lasers, reduce the size of optical heads,
Light weight and ease of assembly and adjustment are realized, making it possible to reduce costs. Furthermore, in No. 21A, '1lt1 is injected into the injection area 24.25 in response to a plurality of output levels such as a plurality of output levels during recording and a reproduction level.
The frequency, amplitude, and DC bias level of the i-waveform are determined by the MPU.
35, it becomes easy to optimally switch through the switching circuit 36 17, and more stable recording and reproducing operations are possible.

Although not shown, the frequency of the oscillation circuit due to temperature, etc.
In order to compensate for changes in amplitude, a detection circuit known to those skilled in the art is used to detect deviations from a reference value, and the oscillation circuit 38. By feeding back to the bias circuit 37, it is possible to modify the tree embodiment to stabilize the current waveforms 42-43. Also, although not shown,
The noise level is detected from the output of the photodiode 26 monitoring the output of the laser 2 or the output of the photodetectors 11, 12, 13, and the noise is reduced to a desired level accordingly. 'It is also the driving part that controls the upstream waveforms 42 and 43.

For example, if 8I pups are sufficiently tolerated under certain conditions, the oscillation circuit 38 may be stopped and only the DC bias 37 may be injected into the injection regions 24 and 25, or nothing may be injected. .

In addition, since the injection regions 24 and 25 are small, they can be driven with less power than modulating the entire stripe region as in the conventional method, which reduces power consumption and reduces the amount of leakage electromagnetic radiation. It will be reduced.

Furthermore, the capacitance of the implanted region is small and smooth, making it possible to drive up to higher frequencies, thereby expanding the selection of one frequency.

Hereinafter, a plurality of other embodiments of the present invention will be described.

FIG. 4 is a cross-sectional view of the semiconductor laser taken along the stripe direction, and is an example showing an embodiment in which a plurality of frequencies are used.

In the figure, there are nine injection areas, five of which are injection areas jL for normal erasing and recording r+f generation.
4, a current containing an AC component having a fundamental frequency f1 and a phase shift of 180' is injected into the injection regions 45 and 48, and an AC component having a fundamental frequency f2 and a phase shift of 1800' is injected into the injection regions 46 and 47. 'Inject current. With this configuration, two i? For each region, each optimal ′[l! By setting the current waveform frequency fl, f2 amplitude, and DC bias, and using them in combination with l and Ml as necessary, stable operation at a lower value of 11 is achieved as a device. .

Figure 5 is a diagram showing another embodiment of a conductor laser.
a, 49b, and AC component injection regions 50 and 51 divided in the width direction of the stripe 21 were provided. In this configuration, since the phase-shifted AC component is injected in the width direction of the drive, it also affects the laser beam Ja moat, resulting in a larger multi-mode longitudinal mode oscillation effect. Compared to the embodiment, since the injection area in the active layer is smaller, it can be driven with a smaller gravity, and since the container is smaller, it can be driven up to a higher frequency.

FIG. 6 shows a modification of the embodiment shown in FIG.
Injection areas 53 and 54 are added on both sides of the injection area 52 by the normal electrode above. In this embodiment, in order to further facilitate multi-longitudinal mode oscillation, the width of the embedded stripe is widened by a portion 55 corresponding to the injection regions 53 and 54 to further increase the ':# resonance with respect to the transverse mode.

FIG. 7 shows that in another embodiment, TJS (TranSvevSe Junc
t+onStripe) structure AC component injection region 57.
58 are provided. The TJS structure is a structure well known to those skilled in the art. For example, by selectively diffusing zinc into the regions 59 and 60 shaded by broken lines in FIG. ) can be injected. With this configuration, it can be erased.

Injection area 56 for recording and reproduction, and AC component injection area 57
．． Since it is possible to reduce the wolf talk between 58 and 58, a more reliable 3m￥f reduction effect can be achieved.

Although the optical information recording and reproducing device was explained using an optical card system as an example, the present invention is not limited to this, and the present invention is not limited to this. It can also be applied to tapes, etc.

In addition, although we have only explained the effect of reducing laser return light-induced noise, there are also reductions in mode hopping noise that occurs due to changes in excitation level and temperature, intensity noise reduction, interference fringes due to wavelength skipping, etc. Needless to say, the technical idea of the present invention is also effective in reducing noise related to speckle patterns transmitted by optical communications and optical meters JIH. .

Furthermore, in the embodiment, the superimposition of rectangular wave-like alternating current signals has been described, but the present invention C is not limited to this, and may be a sine wave or a triangular wave (however, in this case, the optical output may be modulated to some extent). ), and the frequency, phase, and amplitude may be modulated in some way. In short, it is sufficient to inject current into multiple injection regions so that fluctuations in optical output are small and almost constant, so it is not necessary to pair two injection regions as explained in the example, but instead to pair three injection regions. The above configuration may be used. Further, even if the sizes of the implanted regions or the gains and losses are not uniform due to manufacturing accuracy, the present invention can be implemented by independently controlling the amplitude of the alternating current with one phase inverted.

Furthermore, it is also possible to keep the optical output substantially constant by a combination of multiple frequencies, multiple phase shifts, etc., or by a combination of random signals. In addition, in the example, the injection region was set only on one side, and one electrode was always used in common, but it goes without saying that crosstalk between the injection regions can be reduced by setting the injection region from both sides. Nor.

[Effects of the Invention] As explained above, according to the unfired+JJ semiconductor laser driving method and semiconductor laser driving device, a semiconductor laser having a plurality of current injection regions is used as a light source, and at least two injection regions are By injecting and driving a current containing a G-wave component with almost the same frequency and almost inverted phase, it reduces noise during erasing, recording, and playback, making it stable and reliable. An optical information recording/reproducing device can be provided.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram regarding the configuration of a semiconductor laser used in the present invention. FIG. 2 is an explanatory diagram regarding the configuration of a semiconductor laser driving device used in the present invention. FIG. 3 is a diagram for explaining the current waveform injected into the semiconductor laser. FIGS. 4 to 7 are explanatory diagrams regarding the configurations of other embodiments of the semiconductor laser according to the present invention, respectively. FIG. 8 is an explanatory diagram of the configuration of the optical heald section of the optical information recording/reproducing apparatus of the present invention. 1... Optical card, 2... Semiconductor laser 2
3.24.25... Current injection desired area 42.43... Injection current waveform.

Claims (3)

[Claims] (1) In a semiconductor laser driving method in which the output of the semiconductor laser is modulated according to information, the semiconductor laser has a plurality of current injection regions, and a current is applied to each of at least two injection regions at approximately the same frequency. A method for driving a semiconductor laser, characterized by injecting a current containing an alternating current component whose phase is almost reversed. (2) A driving device for a semiconductor laser used in an optical information recording/reproducing device that records at least information, comprising a semiconductor laser having multiple current injection regions and a signal from a modulation circuit that modulates information, etc. to be recorded. a drive circuit for driving the semiconductor laser according to the invention, a direct current bias circuit, an oscillation circuit for generating an alternating current, and an inverting circuit for obtaining an alternating current with a waveform phase shifted by about 180 degrees from the oscillation circuit; A driving device for a semiconductor laser, characterized in that the two alternating currents are superimposed on the direct current from the direct current bias circuit, and the currents are injected into a plurality of current injection regions each corresponding to the driving circuit. (3) Control means for controlling the frequency and amplitude of the current waveform injected into the injection region, the DC bias level of the DC bias circuit, etc. in response to a plurality of output levels such as a plurality of output levels during recording and a reproduction level. 3. The semiconductor laser driving device according to claim 2, further comprising: