JPH0372688A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To realize an optical disk pickup excellent in vibration resistance characteristics wherein a simple optical system and signal processing system are equipped, and each error signal of superior S/N ratio is obtained, by a method wherein two light emitting points are arranged along the optical axis of laser light, so as to be mutually shifted in the opposite direction. CONSTITUTION:Laser chips 1a, 1c which radiate respectively two beams of laser light 4a, 4b at both ends are fixed on a submount for a heat sink use, together with a laser chip 1b, in the manner in which the optical axes are set in the same direction. The light emitting points 6a and 6c of the chips 1a and 1c are arranged so as to be shifted reversely by a same distance in the direction of the optical axis of laser beam from a reference, i.e., the light emitting point 6b of the laser chip 1b. Laser light 2 converged on a recording signal track is used for reading an HF signal; laser lights 3a, 3b are used for reading a tracking error signal; the laser lights 4a, 4b whose positions of light emitting points are shifted from those of the above three laser lights are used for reading a focus error signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a semiconductor laser device, and is particularly suitable as a light source for an optical disk pickup or a light source for a sensor that detects the displacement of an object.

(b) Prior Art Currently, as a method for detecting information signals from an optical disc, a method is used in which reflected light from the optical disc is separated by a beam splitter and then detected by a light receiving element. Further, an astigmatism method using a cylindrical lens is used to detect a focus error of a laser beam with respect to an optical disk.

On the other hand, with the aim of reducing the number of optical components such as beam splitters and cylindrical lenses used in the above-mentioned detection method, Oyo Physics, Vol. 51, No. 4 (198
2), an optical disk pickup has been proposed that detects signals by utilizing changes in the oscillation state due to the return light of a laser beam, as disclosed in pages 450-453.

FIG. 8 shows an optical disk pickup employing such a signal detection method, which is described, for example, in US Pat. No. 4,190.775 and the drawings.

In the figure, the light emitted from the semiconductor laser chip (1) (
11) is an optical disk (1
The light is focused on the signal recording surface (13') of 3), obtains recorded information, and is reflected. The reflected light follows the above-mentioned reverse process and returns to the laser chip (1) again (hereinafter, the reflected light that returns to the laser chip (1) is referred to as return light).
. The influence of this returned light causes a change in the oscillation characteristics such as the backward emitted light output of the laser chip (1).

As shown in FIG. 9, this change, for example, the change in the voltage between the terminals of the laser chip, monotonically decreases in a certain region due to an increase in the return power factor (the ratio of the return light output to the output light output of the semiconductor laser).

Therefore, by measuring the voltage between the terminals of the laser chip, it is possible to detect a change in the reflectance of the reflective surface of the optical disk, that is, the presence or absence of pits.

FIG. 10 schematically represents the signal S due to the change in the voltage between the terminals of the laser chip shown in FIG. In the figure, the horizontal axis is a time axis corresponding to the rotation direction of the optical disc.

For example, as shown by A in the figure, when the focus of the semiconductor laser light is on a pit, the reflectance is low and the return power factor is also low, so the value of the signal S becomes sh (high potential). Further, when the focal point is on a reflective surface other than the pit, as shown in Note B, the reflectance becomes high, so the value of the signal S becomes S2 (low potential). In this way, depending on the presence or absence of pits, the 10th
A pulse-like signal as shown in the figure is obtained, and these sh, sI
! , becomes the HF signal which is pit information.

Next, a method of detecting a tracking error signal in such an apparatus will be explained.

When the focal spot of the semiconductor laser beam deviates from the track, the amount of back reflection within the spot increases, so that the maximum value of the signal S shown in FIG. 10 becomes smaller than sh. Therefore, the tracking error signal can be detected by detecting the amount of decrease. Furthermore, when detecting a focus error signal, if the focal position of the semiconductor laser beam deviates from the optical disk reflective surface, the returned light does not converge on the laser chip light emitting point (laser emission point on the laser resonator end face) and becomes blurred, causing the laser resonator to This is done by detecting the amount of increase, taking advantage of the fact that the minimum value of the signal S shown in Fig. 10 becomes larger than S, since the ratio of light optically coupled to the be exposed.

Also, when the return power factor is high, the influence of the return light causes the first
A return light induced signal is generated as shown in B in Figure 0, but the frequency of this return light induced signal changes monotonically depending on the distance from the semiconductor laser emission point to the external reflection surface, so by detecting the frequency, A method of obtaining a focus error signal is also being considered.

As described above, the HF signal, tracking signal, and seven-occurrence error signal in such an apparatus are obtained from the signal S in which these signals are mixed. After the HF signal is processed by a subsequent circuit, it is converted into sound in the case of an audio disc. The tracking error signal and the seven-occurrence error signal separated from the signal S are sent to the optical system drive unit (27) shown in FIG. According to the signal, the optical system drive unit (27) servo drives the entire optical system cartridge (25) and cartridge holder (26>) so that the focal spot of the laser beam scans the track.

(c) Problems to be Solved by the Invention However, in the above-mentioned conventional optical pickup, each error signal is set to the reference value of the maximum value and minimum value of the pulse of the signal S (the value when the focus and tracking are present).
However, with this method, it is not possible to determine which side of the reference position the track deviation or focus deviation is.

In addition, when using the method of reading the frequency of return light-induced vibration as a focus error signal detection method, it is necessary to keep the reference frequency constant and the distance from the semiconductor laser light emitting point to the focal point constant, so it is necessary to use a servo mechanism. As shown in FIG. 8, the structure must be such that the entire optical system including the semiconductor laser chip (1) and the rod lens (21) is driven. On the other hand, since the cartridge (25) serving as the frame of the optical system plays a role in dissipating heat generated from the semiconductor laser chip (1), most of the material must be made of metal. Therefore, such a device has disadvantages in that the weight of the movable parts is large and the vibration resistance of the optical pickup is poor. Furthermore, since the return light-induced vibration is a weak signal, the S/N ratio is poor, and in order to continuously detect the frequency of this vibration, it is necessary to add a large-scale signal processing system such as a spectrum analyzer.

Furthermore, in the case of conventional technology, all signals are read with a single beam, so track deviation and defocus affect each other's signals, deteriorating the S/N ratio of each error signal, and A problem arises in that the S/N ratio of the HF signal also deteriorates.

Therefore, the present invention has a simple optical system and a signal processing system, and the S
It is an object of the present invention to provide a semiconductor laser device which can obtain error signals with a good /N ratio and can realize an optical disk pickup with good vibration resistance characteristics.

(d) Means for Solving the Problems The present invention is a semiconductor laser device having a plurality of light emitting points and emitting laser light in the same direction from each light emitting point,
In order to solve the above problem, two of the light emitting points are arranged offset in opposite directions along the optical axis of the laser light.

(E) Effect The present invention provides a case where two light emitting points are shifted in opposite directions along the optical axis direction, and the laser light emitted from these two light emitting points is used for detecting a focus error signal. The direction and amount of defocus can be detected, and when used as a displacement signal, the direction and amount of displacement of an object can be detected.

(f) Embodiment FIG. 1(a) shows an embodiment of the present invention. In this example, five laser beams (2) (3a) (3
b) Among (4a) and (4b), the central three laser beams (
2) Laser resonator (5) that emits (3a) (3b)
)(5)(5) is monolithically formed on one laser chip (1b). Such a laser resonator (5) (5) (
5) has resonator end faces on the same plane, and electrodes (7) formed separately for each laser resonator (5).
・They are each driven independently. In addition, the laser chip (lb) (IC) that emits two laser beams (4a) and (4b) at both ends, respectively, and the laser chip (1b) are mounted on a heat sink submount (not shown) with their optical axes in the same direction. The light emitting point (6a) (
6c) are shifted by the same distance in opposite directions with respect to the optical axis of the laser beam with the light emitting point (6b) of the laser chip (1b) as a reference. In the semiconductor laser device having such a configuration, five laser beams are focused on the disk surface as shown in FIG. Of these, the laser beam (2) focused on the recording signal track (18) is used for reading the HF signal, and the laser beams (3a) and (3b) are used for reading the tracking error signal. The laser beams (4a) (4b) whose light emitting points are shifted from the laser beams are used for reading the focus error signal.

Next, a method of reading each signal in the device of this embodiment will be explained.

First, the HF signal is transferred to the recording signal track (
Since the return light weight of the laser beam (2) changes depending on the presence or absence of pits in the laser beam (18), the change in the voltage between the terminals of the laser resonator (5) that emits the laser beam (2) or the output of the light emitted from the rear of the laser chip This is done by reading changes.

The tracking error signal is generated when the laser beam (2) for reading the HF signal deviates from the center of the recording signal track (18>), the other laser beams also deviate at the same time, and the laser beams (3a) (3b)
), the laser light in the opposite direction to the shifted direction is applied to the recording signal track (18) to a large extent, so the amount of returned light becomes small and the voltage between the terminals of the laser resonator increases. Conversely, since the amount of the other laser beam applied to the recording signal track (18) decreases, the voltage across the terminals of that laser resonator decreases. Therefore, the direction and amount of tracking deviation are detected by taking the difference between the voltage between the terminals of the other laser resonator.

The detection direction of the focus error signal in the apparatus of this embodiment will be explained with reference to FIGS. 3 and 4. Figure 3 (a
) shows a normal state in which the focus of the laser beam (2) for reading the HF signal is on the signal recording surface (13') of the disk.

At this time, the laser beam (
The focal points of 4a and 4b do not coincide with the signal recording surface (13'), and the substantial divergence starting points of the reflected light exist at the positions of points (19) and (20). FIG. 4(a) shows how the laser light returns to each laser chip (1a), (1b), and (1c) in such a state. That is, laser light (2
) coincides with its emission point (6b), but the convergence point of laser beams (4a) (4b) coincides with its emission point (6a) (6b).
c). However, this laser chip (
Amount of deviation from the convergence point of the laser beam (4a) returning to 1a) to the emission point (6a) and an amount of deviation from the convergence point of the laser beam (4b) returning to the laser chip (1C) to the emission point (6C) are equal, so each laser chip (la) (l
The optical densities of the laser beams (4a) and (4b) that return to the laser beams (4a) and (4b) that return to the laser beams (4a) and (4b), that is, the actual return destination cars, are also equal, and therefore the voltages between the terminals of each laser chip (]a) and (1c) are also equal.

FIG. 3(b) shows a focus error state in which the focus of the HF signal reading laser beam (2) is closer to the signal recording surface (13'). At this time, as shown in the figure, the divergence point (19) of the laser beam (4a) is closer to the signal recording surface (13') than in the normal state shown in (a), and the laser beam (4a)
The divergence origin (20) in b) moves further away. FIG. 4(b) shows the state of the laser light returning to each laser chip (1a), (1b), and (1c) in such a state. That is, since the convergence point of the laser beam (4a) approaches its light emitting point (6a), the optical density increases, that is, the substantial amount of returned light increases, and the voltage across the terminals of the laser chip (1a) decreases. On the other hand, since the convergence point of the laser beam (4b) is further shifted from its light emitting point (6C), the voltage between the terminals of the laser chip (1C) increases.

FIG. 3(c) shows a focus error state in which the focal point of the laser beam (2) for reading the HF signal is located at a position far from the signal recording surface (13'). At this time, the divergence starting point (19) of the laser beam (4a) is farther away from the signal recording surface (13') than in the normal state shown in FIG. FIG. 4(C) shows the state of the laser light returning to each laser chip (1b, 1c) in such a state.

That is, the convergence point of the laser beam (4a) is its emission point (6a).
As the voltage between the terminals of the laser chip (1a) increases, the convergence point of the laser beam (4b) approaches its light emitting point (6C), and the voltage between the terminals of the laser chip (1C) increases. Decrease.

From the above, in the device of this embodiment, the laser chip (1a
) By taking the difference between the terminal voltage of the laser chip (IC) and the terminal voltage of the laser chip (IC), the direction of the defocus can be detected from the sign thereof. Further, focus adjustment may be performed so that the value of the voltage difference becomes O.

FIG. 5 shows an example of an optical disk pickup using the device of this embodiment. Laser chip (la) (1b) (lc)
is sealed in a package (10), and the package (10) is fixed to a frame (17), and emits each laser beam upward in the plane of the paper. (For convenience, five laser beams are illustrated as one laser beam (11)). Laser light (
11) passes through a condensing lens (12) fixed to a lens holder (14) to generate a signal recording surface (11) of an optical disc (13).
13'). Such a condensing lens (12) is a lightweight aspherical plastic lens with small spherical aberration ("Easy to Understand Optical Disc" published by Optronics, 72~
See page 84/jα) is used. Signal recording surface (13')
The laser light reflected by the laser beam is fed back into each semiconductor laser resonator. By performing simple calculations on the changes in each terminal voltage due to this as shown in the figure, the HF
signal (HF), tracking error signal (TE and)
Orcus error signals (EF) are obtained independently. The driving method for the tracking servo and focus servo is to simply drive the condenser lens (12). The combination can be adopted as is.

Other embodiments of the present invention are shown in FIGS. 1(b) and 1(c), respectively. Components that are the same as those in FIG. 3A are given the same numbers.

In the embodiment shown in FIG. 1(b), five laser resonators (
5) Apply monolithically to one laser chip (1d), and connect one of the resonator end faces to the light emitting points (6b) of the three central laser resonators (5). The light emitting points (6a) (6C) of the laser resonators (5) (5) at both ends are etched so as to be shifted in opposite directions along the optical axis direction of the laser beam. This end face formation by etching may be performed on the entire laser chip (1d), but may also be performed on only a shallow layer including the active layer of each laser resonator (5). Further, in this embodiment, although the resonator lengths of the laser resonators (5) are different from each other, each detection signal does not change due to this.

Next, in the embodiment shown in FIG. 1(c), five laser resonators (5)... are monolithically formed on one laser chip (1e), and each laser resonator (5)... Transparent plates (8) with different thicknesses are arranged on the optical axis of the right end, center (three), and left end laser resonators. The spread width of the laser light transmitted through the transparent plate (8) varies depending on the thickness of the transparent plate (8).
)..., the actual positions of the light emitting points (9a), (9b), and (9c) in the optical axis direction are different.

In this example, a monolithic structure was adopted in which five laser resonators (5) were integrated into one laser chip (1e), but in the configuration of this example, five laser resonators were integrated into a hybrid. Of course, the same effect can be obtained by using the same.

Further, the transparent plate (8) is not limited to the integral one as in this embodiment, and separate transparent plates with different thicknesses may be arranged for each laser resonator.

In each of the above embodiments, each signal is transmitted to each laser resonator (
5) Although the case where reading is performed by converting the voltage between the terminals of... is shown, the laser light directed to the rear of each laser resonator (5)... Each signal may be detected by receiving the light with a light receiving element (not shown) and reading the change in its output. However, in this case, in order to prevent crosstalk between the laser beams incident on each light receiving element, it is necessary to provide an optical isolator between the laser resonator and the light receiving element to separate each laser beam.

Although the above embodiment shows the case where the present invention is used for picking up an optical disk, the principle of focusing in this embodiment can be used to realize a sensor that detects minute displacement of an object. That is, for example, in the apparatus shown in FIG. 1(a), the seven-occasion error signals obtained from the laser chips 56 (Ia) (Ic) are used as they are as displacement signals, and are used to calculate the displacement of the object along the laser optical axis. Direction and displacement can be detected.

A semiconductor laser device used as a sensor for detecting only the displacement of an object is the semiconductor laser device shown in FIG. 1(a) with the laser chip (1b) omitted, that is, the laser chip (1a) as shown in FIG. (lc) may be used. In this case, the direction and amount of displacement of the object are determined by the respective light emitting points (6a) (
The intermediate position of 6C) is set as the reference position, and the deviation from this reference position is obtained.

Further, FIG. 7 shows a sensor for detecting displacement of an object using such a semiconductor laser device. The laser chip (l) shown in Figure 6
a) (lc) is sealed within the package (10) and the package (10) is fixed to the frame (17). Since such a sensor only needs to detect the displacement of the object (28), there is no need to move the focus of the laser beam (11) as in the pickup shown in FIG. is fixed to the frame (17).

(G) Effects of the Invention According to the present invention, the positions of two of the at least three light emitting points are moved in the optical axis direction of the laser beam, and the positions of the two light emitting points are opposite to each other with respect to at least one other light emitting point. By shifting in the direction, it is possible to realize an optical pickup that requires fewer optical components and can obtain the polarity of the focus error signal and the tracking error signal. Furthermore, in the device of the present invention, since the only movable part for focus servo is the condensing lens, it is light and has excellent anti-vibration characteristics.

Furthermore, according to the present invention, by shifting the two light emitting points in the optical axis direction of the laser beam, a sensor that detects minute displacements of an object can be realized.

[Brief explanation of drawings]

1(a) to 1(c) are plan views of main parts showing embodiments of the device of the present invention, FIG. 2 is a schematic diagram showing the arrangement of each laser beam on an optical disk in the device of the present invention, and FIG. 3 and 4 are enlarged views of essential parts for explaining the focus error detection method in the device of this embodiment, and FIG. 5 is a schematic diagram showing an example of when the device of the present invention is used to pick up an optical disc. 6 is a plan view showing another embodiment of the present invention;
The figure is a schematic diagram showing a displacement detection sensor using the embodiment device shown in Figure 6, Figure 8 is a schematic diagram showing a conventional device, and Figure 9 is a characteristic showing the change in voltage across the terminals of the laser chip due to returned light. 10 are characteristic diagrams showing changes in signals obtained depending on the presence or absence of pits on the optical disc.

Claims (1)

[Claims] (1) In a semiconductor laser device that has a plurality of light emitting points and emits laser light in the same direction from each light emitting point, two of the light emitting points are arranged in opposite directions along the optical axis of the laser light. A semiconductor laser device characterized by being arranged in a staggered manner.