JPH01260642A - Optical head - Google Patents

Abstract

PURPOSE:To obtain the stable output of a beam of high power density and a longer life by using a laser having an InGaAsP layer strong to light damage as a light source and using the same in proximity to an optical memory medium. CONSTITUTION:The optical head 1 is mounted to a slider 3 attached to a load spring 4 of an arm 5 which moves at a high speed in the radial direction of the optical memory medium 2. The distance (proximate quantity) between the optical head 1 and the memory medium 2 is maintained at the specified value determined by the load of the spring 4, the shape and weight of the slider 3 and the traveling speed of the memory medium 2. The semiconductor laser having the InGaAsP as the active layer 7 is used as the light source, then writing and reading are executed while the width of the exit end of the beam is approximate nearly to 1mum from the memory medium 2 by having a waveguide 6 narrower than the width of the central part. The stable output by the high light power at the end face of the laser and the longer life are thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical storage device, and more particularly to an optical head using a semiconductor laser as a light source for writing and reading.

[Prior Art] Conventionally, optical heads that have been put into practical use pass light emitted from a semiconductor laser 47 through a lens 46 , as shown in FIG. Beam splitter 45, prism 44. The light is focused on the recording medium 40 by an optical system consisting of an objective lens 41,
The reflected light is passed through the objective lens 41. Prism 44. The beam was configured to enter the photodetector 42 through the beam splitter 45 and lens 43 to reproduce information on the recording medium 40.

The storage density of the recording medium 40 by this optical head is basically determined by the spot diameter W of the light beam, and its value depends on the numerical aperture NA of the objective lens 41 and the oscillation wavelength λ of the semiconductor laser 47, and is expressed by the following equation.

W = λ / N A where, - proportionality constant Therefore, in order to increase the storage density, it is necessary to use a laser with a short wavelength λ, and in conventional optical heads, the active layer is 0 μGa to s. , a semiconductor laser that oscillates at a wavelength of 78 to 0.85 μm is used. As a result, the spot diameter W is 1μ
It is about m.

However, since a laser using AλGa8S as a hemilayer contains AJ2 which is easily oxidized, deterioration due to oxidation of the end face is unavoidable. In particular, in order to perform high-speed recording, sudden deterioration (optical damage) that occurs when the optical power density increases
Or, it may be difficult to reduce long-term lifespan. In addition, in order to extend the lifespan, it must be used in an inert gas, etc.
There are restrictions on usage conditions.

On the other hand, the present inventor has disclosed the patent application No. 4
As shown in the figure, we proposed a ``optical head that levitates close to the optical storage medium.'' This optical head does not use an optical system such as an objective lens, and directly emits a beam by bringing the emission end of the semiconductor laser 18 close to the optical storage medium 19 at a distance of about 1 μm, and returns the reflected light directly to the semiconductor laser 18. A change in the reflectance of the optical recording medium 19 is detected by the photodetector 17 as a change in the optical output 20 due to the complex resonance effect, and information is reproduced. In this optical head, the storage density is determined only by the electric field intensity distribution at the emission end of the semiconductor laser, and since there is no optical system, less power is required.

[Problems to be Solved by the Invention] In this optical storage medium floating type optical head, the resonator length of the laser is determined by the proximity of the optical head to the optical storage medium, and the laser resonator length λ/ Since the optical output changes due to fluctuations in the period of 2, in order to obtain a stable output, it is necessary to reduce the fluctuation in the proximity of the optical head in proportion to the laser wavelength. Although the power consumption is reduced to a certain extent, when 8fL GaAs is used for the active layer, there is a drawback that optical damage and shortened life due to the high optical power of the laser end face are unavoidable.

[Means for Solving the Problems] The optical head of the present invention is an InG optical head that writes and reads from and to an optical storage medium at a distance of approximately 1 μm.
A semiconductor laser with aAsP as an active layer is used as a light source.

The optical head of the present invention has a waveguide in which the width of the beam emitting end is narrower than the width of the central part, and the optical head is an InGa waveguide that performs writing and reading while being close to the optical storage medium at a distance of approximately one length.
A semiconductor laser with AsP as an active layer is used as a light source.

[Function] 8. In a semiconductor laser having QGaAs in the active layer, the optical power density at which optical damage occurs is I x 106W/Cl11
It is about 2, considering the margin against surge current etc.
The maximum rating is usually 1/2 to 1/3 of this or less. Considering the lifespan, etc., the operating condition becomes an even lower optical power density. On the other hand, semiconductor lasers with InGaAsP as the active layer are less prone to optical damage and are suitable for communication light sources.
Even when operated at an optical power density of about X 106 W/cm2, a lifetime equivalent to that of a semiconductor laser having an active layer of Al1GaAs under normal conditions can be achieved.

Figure 6(a) shows a laser with an active layer of 8uGaAs that oscillates at 0.85 μm and an InGa laser that oscillates at 1.5 μm.
This is a diagram of the configuration of a rib-type waveguide assuming the emission end of a laser with AsP as the active layer, when both sides f are air layers. Figure 6(b) shows the full width at half maximum of the electric field intensity distribution of the transverse fundamental mode. (
FIG. 4 is a diagram showing a graph of calculation results of beam diameter).

As shown here, when InGaAsP is used for the active layer, the full width at half maximum is larger when the active layer is made of InGaAsP with the same rib width, but it is sufficient to make the rib width slightly narrower than when the active layer is made of Aj2GaAs. Since the same amount of light can be focused, the beam diameter can be reduced to 1 μm by keeping the width of the waveguide at the beam exit end to 2 or less.

Note that when InGaAsP is used for the active layer, the optical power density can be increased, so the output end width can be made much narrower than when 8R, GaAs is used for the active layer, and the beam diameter can also be reduced accordingly. It becomes possible to make it thinner.

Furthermore, since the wavelength is 1.3 to 1.9 times longer than that of conventional Al or GaAs, the margin for cavity length variation due to variation in proximity can be increased by 1.3 to 1.9 times. Stable output can be obtained.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing a part of an optical recording apparatus having an embodiment of the optical head of the present invention.

This optical head 1 is attached to a slider 3 attached to a load spring 4 of an arm 5 that moves at high speed in the radial direction of the optical storage medium 2, and the distance between the optical head 1 and the optical storage medium 2 is l! ! (Proximity amount) h (Fig. 4) is the load of the load spring 4,
It is maintained at a constant value determined by the shape and weight of the slider 3 and the traveling speed of the optical storage medium 2, and this proximity measurement is approximately 1-.

FIG. 2 is an enlarged perspective view of the semiconductor laser of the optical head 1. FIG.

This semiconductor laser is the light source of the optical head 1, and is an n-type 1nP laser diode.
n-type 1nP crat layer 9°p-type 1nGaA on substrate 15
sP (λ-1,3gn+) active layer7. A stripe structure formed by etching a double heterostructure consisting of a p-type InP cladding layer 8 and a p-type InP current blocking layer 14. n
The buried layer of the InP type current block layer 13 and the p-type 1nG
It is formed from an aAsP electrode layer 12 and Au electrodes II and 16, and is further formed by an insulating separation groove 10 to form a waveguide 6.
Since the horizontal direction of the beam is air, the width of the beam exit end is set to be 2μ according to the graph of FIG. 6(b). With this configuration of the output end, the lateral beam at the output end of the beam is focused to approximately 1 μm. This laser emits light stably in the atmosphere even with an optical output of 10 mW without an end face coating.

This light output is about 20% higher than that of a conventional optical head using an optical system.
m1? The light output is comparable to that of a laser.

FIG. 3 is an enlarged perspective view of another example of the semiconductor laser of the optical head 1. FIG.

This semiconductor laser has an n-type 1nP cladding layer 29 on an n-type InP substrate 35, similar to the example shown in FIG. p-type InGaAs
A stripe structure is formed by etching a double heterostructure consisting of a P active layer 27, a p-type InP cladding layer 28, and a p-type 1nP current blocking layer 34. Buried layer of n-type InP current block layer 33, p-type 1nGaAsP electrode layer 32. Au
Although it is formed from electrode layers 31 and 36, there is no insulating isolation groove, and the width of the output end of the waveguide 26 is realized by narrowing the stripe width during etching. Therefore, although the lateral refractive index difference of the striped waveguide 26 is small, the width of the stripe near the beam exit end is narrowed to 1 μm, so the width of the lateral beam at the beam exit end is approximately 1 μm. The light is focused on. This laser emits light stably in the atmosphere even with an optical output of 15 mW. This optical output is comparable to that of a laser with an optical output of about 30 mW in a conventional optical head using an optical system.

At this time, the allowable variation amount of the proximity meter that can maintain the optical output at 90% or more of the maximum value with constant current driving is 0.184a.
Eight f1. wavelength of 0.83gm. When using a GaAs diameter laser, the permissible variation in proximity weighing is 0.1 compared to 1.8.
The amount allowed will be doubled.

[Effects of the Invention] As explained above, the present invention provides InGaA that is resistant to optical damage.
By using a laser having an active layer of sP as a light source and using it in close proximity to an optical storage medium, the following effects can be obtained.

(1) Deterioration due to oxidation is significantly reduced, there is no restriction that the device must be used in an inert gas, and the mounting method can be simplified. Further, when used in an inert gas, the life can be further extended.

(2) The permissible width of the proximity amount is increased, and a beam with a high power density on the order of I x 106 W/cm2 can be stably output with a micro spot with a diameter of about 1 μm.

(3) The recording surface density of optical storage media can be increased.

(4) Writing speed can be increased.

(5) Design of the head structure becomes easier.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a part of an optical recording/reproducing apparatus having an embodiment of the optical head of the present invention, and FIGS. 2 and 3 are enlarged perspective views of the semiconductor laser of the optical head 1 of FIG. FIG. 4 is a diagram showing the positional relationship between an optical storage medium and a semiconductor laser in a floating optical head near an optical storage medium, FIG. 5 is a perspective view of a conventional example of an optical head having an optical system, and FIG. 6(a), (b) is 0.85
Configuration of a semiconductor laser with an air layer on both sides of a rib-type waveguide having a narrow emission end and an active layer of AlI and Ga that oscillates at 1.5 μm and an active layer of InGaAsP that oscillates at 1.5 μm. and a graph showing the calculation result of the full width at half maximum (beam diameter) of the electric field intensity distribution of the transverse fundamental mode. 1... Optical head, 2... Optical storage medium, 3...
・Slider, 4... Load spring, 5... Arm, 6... Waveguide, 7.27-p type InG
aAsP active layer, 8, 28-p-type 1nP cladding, 9.29... n-type TnP cladding, 10... insulation isolation groove, II, 3], 16.36- Au electrode, 12, 3
2-p-type InGaAsP electrode layer, 13, 33.15.3
5-n-type 1nP current blocking layer; 14, 34...p-type 1nP current blocking layer; Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. A semiconductor laser is used as a light source, and approximately 1
An optical head that performs writing and reading at close distances of μm, characterized in that the semiconductor laser is a semiconductor laser having an active layer of InGaAsP. 2. The optical head according to claim 1, wherein the optical head has a waveguide in which the width of the beam emitting end is narrower than the width of the central portion.