JP2614855B2 - Light head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an ultra-small, low-cost optical head utilizing a combined resonance effect of a semiconductor laser and an optical recording medium.

<Prior art and its problems> Conventionally, an optical head of this type is described, for example, in Miyazawa et al .: “Semiconductor laser pickup for PCM deck”, Electronic Materials, p.
As shown in the February 2009 issue, the structure was as shown in FIG. That is, the emitted light of the semiconductor laser 1 is focused on the optical recording medium 4 via the coupling lens 2 and the condenser lens 3.
The light reflected by the optical recording medium 4 is fed back to the semiconductor laser 1 via an optical path opposite to the above. The light output in this case is detected by a light detector 5 provided at the rear end of the semiconductor laser 1. Reference numerals 6 and 7 denote wobbling elements for obtaining a focus error signal and a track error signal, for example, PZT elements. The oscillators 8 and 9 drive the PZT element 6 and the PZT element 7 to slightly vibrate in a direction perpendicular to the optical recording medium 4. The focus error signal and the track error signal are obtained by phase-detecting the above-mentioned feedback light by the phase shift detectors 10 and 11. In the drawing, 12 is a support spring, 13 is a focus control actuator, and 14 is a track control actuator.

As described above, in the conventional optical head, when reproducing information, the semiconductor laser is kept in a laser oscillation state at all times, and the focusing lens 3 is slightly vibrated to obtain a focus error signal, and the focus error signal is used to drive the focus control actuator. It was necessary to perform focus control. For this reason, the conventional optical head requires not only optical components such as the condenser lens 3 and the photodetector 5 but also mechanical components that are actuators for focus control, so that the optical head becomes large in size, low in cost, and high in reliability. There was a disadvantage that it was difficult.

<Object of the Invention> An object of the present invention is to mount an optical head on a slider and fly the slider close to an optical recording medium, thereby enabling the semiconductor laser to be automatically focused in a laser non-oscillation state. An object of the present invention is to provide a small, low-cost, and highly reliable optical head.

<Means for Solving the Problems> In order to achieve the above object, the present invention causes the optical head 21 to fly close to the optical recording medium 4 as shown in FIG. That is, the optical head 21 is used by being mounted on a slider 24 attached to a load spring 23 on an arm 22 that can move at a high speed in the radial direction of the optical recording medium 4.

As a result, the focus control of the optical head 21 is maintained at a constant spacing value determined by the load of the load spring 23, the shape and weight of the slider 24, and the traveling speed of the optical recording medium 4.

<Embodiment> FIGS. 1 (a), 1 (b) and 1 (c) show a first embodiment of the present invention. FIG. 1A is a diagram showing the use state of the optical head, FIG. 1B is a diagram showing the configuration of the optical head, and FIG. 1C is another diagram showing the configuration of the optical head. In FIG. 4B, the optical head 21 has a width and a substrate 31.
The semiconductor laser 1 and the photodetector 5 are separated by a separation groove 32 having a depth reaching several μm. 33 is an output end face, 34 is an active layer, 35 is an insulating layer, 36 is a semiconductor laser electrode, 37 is a photodetector electrode, 38 is a light receiving section, and 39 is a common electrode. The light beam 40 from the semiconductor laser 1 is reflected by the optical recording medium, the reflected light 41 returns to the semiconductor laser 1, and the light output (composite resonance signal output) 42 at that time is detected by the light receiving unit 38. FIG. 3C shows a state in which a waveguide lens unit 50 is disposed at the tip.
The light beam spot 51 above can be reduced, and the recording density can be improved. Reference numeral 52 denotes a buffer layer 53 (for example, SiO ₂ ) and a waveguide layer 54 (for example, glass 7059) for forming a waveguide lens portion 50 on an etched mirror surface formed by a fine processing technique.
Touch Reference numeral 55 denotes a Luneburg lens, which is made of a dielectric material (for example, Si-N) having a higher refractive index than the waveguide layer 54, and has a circular periphery and a semicircular surface. The operation is the same as (b).

As a result, the light output 42 changes (H, L) as shown in FIG. 2 (a) in accordance with the change in the reflectance of the optical recording medium 4 (presence or absence of information bits), and the data shown in FIG. Get the signal. FIGS. 3A and 3B show the relationship between the light output and the spacing (the distance between the output end face 33 and the optical recording medium 4) h.
(B) is an enlarged view of (a). From the figure, (1) the optical output P decreases rapidly with an increase in the spacing h.

(2) The optical output P has a period λ / 2 (λ
Is the wavelength, and the refractive index between the output end face 33 and the optical recording medium 4 is n =
It changes in 1).

You can see that.

Therefore, in order to detect a high-quality data signal, the semiconductor laser 1 and the optical recording medium 4 need to be held at a spacing h corresponding to the peak portion in FIG. The spacing h is the size, shape, weight, and load spring 23 of the slider 24.
Then, it depends on the traveling speed of the optical recording medium 4 and the like.

Embodiment 2 FIG. 4 shows an optical head according to a second embodiment of the present invention. In this optical head, a phase transformation type rewritable medium is assumed as an optical recording medium. 40-1 is an erasing beam, 40-2 is a recording light beam, and 40-3 is a reproducing light beam. The near-field image of the erasing light beam is an ellipse having an axial ratio of about 10: 1, and the near-field image of the recording light beam and the reproducing light beam has an axial ratio of about 1: 1.
Is a circle. Recording is performed with a middle circular light beam while erasing with a front elliptical light beam, and reproduction is performed with a rear circular light beam. As a result, overwriting of information and reading check of recorded information can be performed at the same time. By combining this optical head with a phase-change type rewritable medium, an extremely high-performance optical recording / reproducing apparatus can be realized.

Such a multi-beam is realized by condensing outgoing light of three semiconductor lasers 1 divided by insulating grooves 60 having a width and a depth of several μm by a waveguide lens 61, respectively. Further, three photodetectors 5 are formed by the insulating grooves 32. 36-1, 36-2, 36-3 are the electrodes of the semiconductor laser, 37-1,
37-2 and 37-3 are electrodes of the photodetector, and 39 is a common electrode.
Reference numerals 38-1, 38-2, and 38-3 denote light receiving units of the respective photodetectors. These insulating grooves 32 and 60 are formed on the semiconductor laser substrate by, for example, reactive ion beam etching. The semiconductor laser 1, the photodetector 5, the waveguide lens
61 may be individual components.

Embodiment 3 FIG. 5A shows another embodiment of the optical head according to the present invention. 1 (b), (c) and FIG. 4 is that an antireflection film 70 is formed on the output end face 33 of the optical head 21. Such an anti-reflection film 70 is realized by, for example, forming a transparent dielectric material with a thickness of λ / 4n (λ is a wavelength and n is a refractive index).

FIG. 5B shows a signal _{SPP depending} on the presence or absence of the antireflection film 70.
And the noise N _rms . The vertical axis is S _PP = P ^H -P ^L (second
_Nrms is an integral value of a noise component in a band of 30 kHz to 20 MHz. The horizontal axis represents the semiconductor laser drive current I and the threshold value ▲ I ^O when there is no optical feedback (no optical recording medium).
_th ▼ ratio. Spacing is 2.9μm, output end face 33
0.32 without anti-reflection coating 70, anti-reflection coating
If there is 70, it is 0.05. As shown in the figure, the formation of the anti-reflection film 70 sharply increases the signal _SPP , while the noise N
_It can be seen that _rms increases slightly. Therefore, it is understood that the application of the antireflection film significantly improves the SN ratio of the data signal.

<Effect of the Invention> As described above, in the optical head according to the present invention, the optical components including the semiconductor laser and the photodetector are integrated on the same substrate, mounted on the slider, and brought close to the optical recording medium by air lubrication. Since it is used by floating, it does not require various optical components and an actuator for focus control, so it is ultra-compact and low-cost. Since the flying height is set to a distance at which the signal component becomes large, and the signal is amplified by the antireflection film, there is an advantage that the signal quality at the time of information reproduction is high.

[Brief description of the drawings]

1 (a) is a perspective view showing an optical head moving close to and floating at high speed, FIGS. 1 (b) and 1 (c) are perspective views each showing an example of the structure of the optical head of the present invention, and FIG. (A) and (b) are the principle diagrams of signal detection by the composite resonance action, respectively, and FIG.
(B) is a graph showing the relationship between the optical output and the spacing of the optical head of the present invention, an enlarged view thereof, FIG. 4 is a perspective view showing another example of the structure of the optical head of the present invention, and FIG. a) is a perspective view showing still another example of the structure of the optical head of the present invention, and FIG.
FIG. 6B is a graph showing the relationship between signal components and noise, and FIG.
FIG. 1 is a configuration diagram of a conventional optical head using a composite resonance action. In the figure, 1 is a semiconductor laser, 4 is an optical recording medium, 5 is a photodetector, 31 is an optical head, 32 is an insulating groove, 33 is an output end face, 38 is a light receiving section, 40 is a light beam, 41 is reflected light, 42 is an optical output, 61 is a waveguide lens, 70 is an anti-reflection film, and h is spacing.

Claims (2)

(57) [Claims] An optical recording medium is arranged at one output end face of a semiconductor laser, and a photodetector is arranged at the other output end face, and reflected light of the optical recording medium is fed back to the semiconductor laser, and information is reflected by a composite resonance action. In an optical recording medium proximity floating type optical head for performing reproduction, an optical head in which a semiconductor laser and a photodetector are integrally formed on the same substrate, and the optical head is movable in a radial direction of the optical recording medium. A distance h between one output end face of the semiconductor laser and the optical recording medium, which is disposed on a slider mounted on a load spring on the arm;
Is maintained at a value substantially represented by the following equation. h = (N / 2n) λ where λ is the oscillation wavelength, n is the refractive index of the medium between the semiconductor laser and the optical recording medium, and N is a positive integer. 2. An optical head according to claim 1, wherein an antireflection film is formed on an output end face of said semiconductor laser on the optical recording medium side.