JPS62112241A - Semiconductor laser for optical head - Google Patents

Abstract

PURPOSE:To suppress the output change and to stabilize the recording action by forming the optical recording media side output edge surface by inclining in to the light axis and forming the reflecting edge surface of the semiconductor laser opposite to the output edge surface vertically to the light axis. CONSTITUTION:For the formation of the edge surface of the semiconductor laser, to constitute the laser resonator, a light axis 31 of the semiconductor laser arranges a reflecting edge surface 33 at an angle B diagonal to the reflecting surface of optical recording media 21 and the light axis 31 is made vertical to the optical recording media 21 and the reflecting edge surface 33. Namely, the light axis is inclined in the thickness direction of a semiconductor laser 14. In case of the semiconductor laser 14 provided on a heat sink 34, at an output edge surface 32, the laser light is almost refracted, comes out into an air 35 and reflected on the optical recording media surface, and thereafter, a light R1 to return into the activated layer is specially minimized. Thus, the modulating degree of the light strength due to the interference with a reflecting light R2 from the optical recording media 21 is significantly reduced.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to improvements in semiconductor lasers for optical heads used for non-contact recording or reproducing recorded information on optical recording media such as optical disks. .

<Prior art> As shown in FIG. 6, an optical head is attached to an arm 2 that rotates by the drive of a position control motor 1, and a light beam emitted from the optical head is emitted onto an optical recording medium surface 4 to record or record information. used for playback. A conventional optical head of this type includes a semiconductor laser 6 housed in a case 5, as shown in FIG.
A light beam emitted from a light source, such as The structure was such that the information was detected by a photodetector 9 via a mirror 7 and reproduced.

However, in the optical head with the above structure, the light source 6, semi-transparent mirror 7, and light focusing lens 8 are assembled in such a way that they have an organic relationship. Therefore, in order to smoothly move such an optical head relative to an optical recording medium, the drive device had to be made large.

Therefore, the inventors of the present invention proposed a patent application filed in 1983 to develop such an optical head as a compact and highly reliable optical head.
No. 86406, as shown in FIG. 8, a rad layer 1 is formed on a semiconductor substrate 10 by liquid phase or vapor phase growth.
1. Grow the active layer 12, upper cladding layer 13, etc., and form the PN
A semiconductor laser section 14 is located in the center of a semiconductor woofer having a bonding layer, and photodetectors 16a are arranged on both sides of the semiconductor laser section 14 across an insulating groove 15 formed from the surface of the wafer to a depth extending beyond the active layer.
, 16b was proposed.

In addition to the above-mentioned components, the optical head 17 with this structure includes an upper electrode 18 and a photodetector 116a on the top surface of one semiconductor laser.
, 16b upper surface (?O′ photodetector electrode 18a, ],
8b, and a common electrode 19 is provided on the surface of the substrate 10r opposite to these electrodes. Near M of semiconductor laser 17
8'Gg should be biased in the forward direction, and the upper and lower photodetector electrodes should be biased in the opposite direction.

When this optical head 17 is used for recording on or reproducing from an optical recording medium, as shown in FIG. , the arm 22J, which can move statically at a speed of A in the radial direction of the optical disc 21, is attached to a slider 24 that can fly close to the surface of the optical disc by means of a gimbal spring 23.

In the optical head 17 described above, the laser beam 25 emitted from the semiconductor laser 14 is oriented in a direction parallel to the active layer 12, and the reflected diffracted beam 26 is emitted from the track guide groove (not shown) of the optical disk 21.
a, 26 b are respectively photodetectors 16 a, 16
b, and the track error equal sign can be obtained from the difference signal between the two, and the data signal can be obtained from the sum signal.

<Problems to be Solved by the Invention> However, in the semiconductor laser for an optical head having the above structure, a part of the light that is reflected and diffracted from the optical recording medium returns to the semiconductor laser, and some of the light is reflected from the output end face of the semiconductor laser. It has the disadvantage that it interferes with light and fluctuates the output of the semiconductor laser.

More specifically, if the distance (flying height) between the output end face of the semiconductor laser for an optical head and the optical recording medium is half a wavelength (
This causes an output fluctuation with a period of λ/2), lowering the signal-to-noise ratio of the signal.

This invention was made to eliminate these drawbacks of semiconductor lasers for optical heads, and suppresses output fluctuations caused by changes in the distance (flying height) between the output end face of the semiconductor laser and the optical recording medium. However, it is an object of the present invention to provide a semiconductor laser for an optical head that can perform recording and reproduction with a stable recording operation and a high signal-to-noise ratio of reproduced signals.

In order to achieve the above object, the present invention forms a semiconductor laser for an optical head with its output end face on the optical recording medium side inclined to the optical axis. It is characterized in that the reflective end face of the semiconductor laser facing the output end face is formed perpendicular to the optical axis and forms a laser resonator together with the reflective face of the optical recording medium.

Furthermore, in the above-mentioned semiconductor laser for an optical head, a preferable LN inclination angle θ of the output end face on the optical recording medium side is 56≦θ≦166 with respect to one stone perpendicular to the active layer of the semiconductor laser.

In addition, in forming the end face of the semiconductor laser, the optical axis 31 of the semiconductor laser is formed on the reflective end face 3 in order to form a laser resonator.
3 is placed at a diagonal angle β to the reflective surface of the optical recording medium 21, and the optical axis 31 is perpendicular to the optical recording medium 21 and the reflective end surface 33.

That is, the first method is to tilt the semiconductor laser 14 in the thickness direction as shown in FIG. This is a method in which the end of the stripe (width S) is inclined with respect to the optical axis within the plane.

Since the structure is as described above, when the semiconductor laser 14 is installed on the heat sink 34 of FIG. 1 (al is a cross-sectional view in the thickness direction), the output end face ( At the inclined end face) 32, most of the laser light is refracted and emitted into the atmosphere 35, and after being reflected on the optical recording medium surface, the light beam returning into the active layer is much more dramatic than in the case of a conventional vertical end face. Therefore, the degree of modulation of the light intensity due to interference with the reflected light from the optical recording medium 21 is significantly reduced.

Furthermore, in the case of the configuration shown in FIG. 1(b), considering the two beams 31a and 31b in the active layer of the semiconductor laser 14, the reflected light from the optical recording medium produces an optical path difference Δl, which suppresses the interference effect. can.

Note that Δl is calculated as follows. That is, if the inclination angle of the output end face 31 is α, and the alignment angle for mutually forming a laser resonator between the optical recording medium 21 and the reflecting surface (vertical end face) 33 of the semiconductor laser is β, then the refractive index of the active layer is 3.6, set the inclination angle α of the output end face to 10° ((7=10°
), then β=28.7, so light 31a.

If 31b interval (stripe width) S = 2 houses, Δl-= l -1= sm(a+β) -n stt
mao becomes 23 (tiles).

In the case of wavelength ^ = 0.87Jn, considering that peaks and valleys of light intensity occur every Δl = 0.2 cape, optical path differences occur between the light rays in the resonator, and these are collectively As a result, the interference effect decreases as a whole, and the distance g between the optical recording medium and the output end face of the semiconductor laser decreases! Fluctuations in semiconductor laser output due to changes in flying height can be suppressed.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples. However, among the examples described below, Examples 1 and 2 correspond to the configuration shown in FIG. 1(al), and Examples 3 and 4 correspond to the configuration shown in FIG. 1(b). .

Embodiment 1 FIG. 2 is a perspective view of a semiconductor laser 14 for an optical head according to an embodiment of the invention of B, and corresponds to the semiconductor laser 14 in the center of the optical head of the conventional structure shown in FIG. . The output end surface 32 on the optical recording medium side is at an angle α with a plane perpendicular to the active layer 12.
It is formed by tilting only. α is a condition for reducing the amount of reflected light returning to the active layer at the end face 32 of the semiconductor laser 14
56≦a≦1 under the condition that the configuration angle β of the laser resonator with respect to the optical recording medium 21 does not exceed 90″.
It should be set at 6@. The reflective end face facing the main power end face of the semiconductor laser is a vertical image 33. The current flows in and out through the stripes 41 of the upper electrode 18 and the lower electrode 19. The stripe 41 is an insulating layer 42 under the lower electrode.
(Si, N,) is formed to have a width of about two doors, and the current density is increased to generate laser oscillation. The optical head semiconductor laser 14 is formed by sequentially forming a lower cladding A 11 (n-GaAlAs) and an active layer 12 on a substrate 10 (n-GaAs) by M-phase or vapor phase eviaxial growth.
(GaAlAs), upper cladding layer 13 (P-GaA
LAs), a cap layer 43 (P-GaAq) was created, and the insulating layer 42 (Si
,,N,) , upper electrode 18. The lower electrode 19 is now formed. The inclined output end face of this embodiment is processed, for example, by polishing using a bromomethyl solution.

Further Example 2 FIG. 3 (f) This is another embodiment of the semiconductor laser 14 for an optical head according to the present invention.The difference from FIG. 2 is that the shape of the output end face 32 on the optical recording medium side is In this embodiment, the inclined surface 32 is formed by reactive ion beam etching from the upper electrode 18 to a depth exceeding the active layer 12 (for example, 3 capes).From the bottom 51 of the processing groove to the lower electrode 19 (for example, xoOm ) is the vertical end face formed by cleavage.

Reactive ion beam etching: First, T, 02. After forming a thin film of S, q, etc. and spin-coding a photoresist, an inclined end face 32 is formed by reactive ion beam etching. Next, align this semiconductor laser with α
The slit pattern is transferred by etching to a depth exceeding the active layer by reactive ion beam etching using C12 as a reactive gas. In the ion beam sputtering method, the ion beam flows approximately parallel to the ion axis. Furthermore, when C12 gas is used, the etching rate ratio of GaAs, which is the substrate of the semiconductor laser, and T.
Even if 1jO etching is performed, the T and 02 masks will hardly become thinner. Therefore, the semiconductor laser is placed in a plane perpendicular to the ion axis.

By etching at an angle, it is possible to form an inclined end face 32 which is inclined by α° with respect to the vertical plane of the semiconductor laser. In the ion beam sputtering method, the ion beam acceleration voltage can be controlled over a wide range and can be operated at an acceleration voltage of several tens of volts. Therefore, machining damage caused by ion bombardment can be significantly reduced compared to reactive ion etching and machining methods. In this embodiment, since the output end face can be formed at an angle of inclination with less processing distortion than in the first embodiment, the oscillation characteristics of the semiconductor laser are improved.

Embodiment 3 FIG. 4 shows a semiconductor laser section 1 of an optical head according to the present invention.
4 and has a configuration corresponding to FIG. 1 (bl).The end face 52 of the semiconductor laser on the optical recording medium side
On the other hand, the output end face 32 is inclined, is perpendicular to the active layer 12 and forms an angle α with the end face 52, and extends from the upper electrode 18 to the active layer 12.
has reached an extremely deep level. Such an inclined end face is formed by reactive ion beam etching as in the second embodiment. The outline is almost the same as that described in Example 2 (Fig. 3), but the slit pattern is tilted by α with respect to the end face of the semiconductor laser, and reactive ion beam etching (ζ There are 9 ions of ions against the semiconductor laser end facet.
A semiconductor laser is arranged so that it is incident at an angle of 0°.

In the semiconductor laser having the structure of this embodiment, the output end face on the optical recording medium side is an etched mirror surface having an inclined angle, and the other reflective end face is a cleavage face perpendicular to the active layer 12.

The reflective end face of the semiconductor laser for the present optical head is arranged with a cleavage plane 61 perpendicular to the active layer 12 at an angle β so as to form a laser resonator with the reflective surface of the optical recording medium.

This angle β is β-
=28.7°.

Embodiment 4 FIG. 5 shows a semiconductor laser for an optical head according to the embodiment of FIG. 4.

In this embodiment, a semiconductor laser 14 for an optical recording medium is used.
In order to make the alignment angle of the reflective end face 0 degrees, it is perpendicular to the active layer 12 and forms an angle β (for example, 28.7°) with the cleavage face 61 on the side opposite to the output end face; A reflective end face 71 extending from the upper electrode 18 to the depth of the active layer 12 is formed. Note that the optical axis is perpendicular to the reflective end surface 71.

In this embodiment, since both of the output end faces of the laser are optical mirrors, there are drawbacks such as an increase in the oscillation threshold, but the arrangement of the semiconductor laser and the optical head relative to the optical recording medium is facilitated.

When the semiconductor laser of the above embodiment is used as a light source, it is usually used with photodetectors arranged on both sides of the semiconductor laser. The track difference signal is detected by differential detection. However, for example, if the wobbling method is used to detect rank errors 1 to 3, it is not necessary to place the photodetector on both sides of the semiconductor laser, but on the side of the reflective end face opposite to the output end face of the semiconductor laser. It is also possible to arrange

The output end face having the inclined structure of the present invention is also effective for the optical head 7 having such a structure.

<Effects of the Invention> As is clear from the above description, in the semiconductor laser for an optical head of the present invention, the output end face on the optical recording medium side is within the resonant word formed by the optical recording medium and the reflective end face of the semiconductor laser. Since it is tilted with respect to the optical axis, (1) the amount of reflected light from the inclined end face that returns into the active layer is extremely small; (2) the optical distance to the optical recording medium varies depending on the position of the optical path within the active layer;

As a result, there is almost no interference between the reflected light from the output end face and the reflected light from the optical recording medium. Since there is no fluctuation, the recording characteristics are uniform in signal recording, and the signal-to-noise ratio is improved in signal reproduction.

[Brief explanation of drawings]

FIGS. 1(a) fb) are explanatory diagrams of the construction principle of a semiconductor laser for an optical head according to the present invention, and FIGS. 2 to 5 show a schematic construction of an embodiment of the semiconductor laser for an optical head according to the present invention. FIG. 6 is a perspective view showing the configuration of a conventional optical head, FIG. 7 is a perspective view showing the state of use of the optical head in FIG. 9 is a state diagram of the optical head shown in FIG. 8. In the drawings, 14... Semiconductor laser, 16a, J6b --- Photodetecting section, 10. Substrate, 11... Upper cladding. Layer, 12... Active layer, 13... Lower cladding layer, 18... Upper #I electrode, 21... Optical recording medium, 32... Inclined end surface, 33 Vertical end surface, 41... Stripe, 42 ...Insulating layer, 43...Cap layer. Patent applicant: Agent of Nippon Telegraph and Telephone Corporation

Claims (2)

[Claims] (1) The output end face of the semiconductor laser on the optical recording medium side is formed to be inclined to the optical axis, and the reflective end face of the semiconductor laser facing the output end face is formed perpendicular to the optical axis of the semiconductor laser, and optical recording is performed. A semiconductor laser for an optical head, characterized in that a laser resonator is formed together with a reflecting surface of a medium. (2) The inclination angle θ of the output end face on the optical recording medium side of the semiconductor laser is formed such that 5°≦θ≦16° with respect to a plane perpendicular to the active layer of the semiconductor laser. The semiconductor laser for an optical head according to item 1.