JP3298184B2 - Optical head and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for an optical recording apparatus, and more particularly, to a method for easily aligning optical components, reducing the thickness and weight, reducing the cost, and reducing the wavelength fluctuation of a semiconductor laser. The present invention relates to an optical head that can be operated stably and hardly occurs.

[0002]

2. Description of the Related Art An optical head is an important component for reading signals from an optical recording element such as a compact disk (CD), an optical disk, and an optical card memory. The optical head needs to have not only a signal detection function but also a control mechanism such as a focus servo and a track servo in order to extract a signal from the optical recording element.

FIG. 7 shows a conventional optical head (Japanese Patent Application No. 2-189053). Light emitted from the semiconductor laser 1 in an oblique direction becomes a propagating light 8,
The light enters the reflective collimator lens 3 ′ and is reflected and collimated. The collimated light propagates in a zigzag shape, and is transmitted by a transmission type objective lens 4 a provided on the light propagation path 13.
The light is output in an oblique direction and becomes the condensed light 9 on the optical disk 7.
The light 10 reflected from the optical disk 7 is incident on the second transmission type objective lens 4b provided on the light propagation path 13 and is collimated to become propagation light 8 ', which propagates in a zigzag manner.
A signal detection element (focus /
Track error signal detecting means) reflection twin lens 5 '
Incident on. The propagating light 8 ′ is split into two by the lens 5 and propagates in a zigzag manner.
The light is focused on the divided photodetector 6. A reproduction signal and a focus error signal and a track error signal, which are position signals, are read out from the signal detected by the photodetector 6.

[0004]

In the conventional optical head shown in FIG. 7, when the temperature around the semiconductor laser 1 changes, the oscillation wavelength changes (about 2 nm / 10 ° C.). Transmission type objective lens 4a with a large number NA
In the aberration is significantly generated, it becomes impossible satisfactorily condensing on the optical disk 7, there is problem that an error in the read signal occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a small size, light weight, and an inexpensive optical system that can operate stably without changing the oscillation wavelength even when the ambient temperature of the semiconductor laser changes. A head is provided.

[0006]

An optical head according to the present invention comprises:
A substrate provided with a light propagation path through which light propagates in a zigzag shape; a diffractive light condensing element formed on the light propagation path; and a reflective and diffractive position signal formed on the light propagation path. a detecting optical element, the wavelength selection element and the diffraction type a reflective formed on the optical propagation path, a semiconductor laser, is composed of a light detector, the oscillation light from above Symbol semiconductor laser, the optical Guided to a propagation path as propagation light, at least a part of the propagation light is made incident on the wavelength selection element, and the diffracted light whose wavelength is selected by the wavelength selection element is made incident on a front emission end of the semiconductor laser, at least a portion of the propagating light outputted to the optical disk and condensed by the optical focusing elements, the reflected light from the optical disk, and input to the light collector elements, led to the position signal detecting optical element, said position signal detecting optical element La of the output light is configured to direct to the photodetector.

[0007]

According to the present invention, a wavelength selection element is provided on the same substrate (propagation path) on which other optical elements are provided, and a part of the oscillation light of the semiconductor laser is diffracted by the wavelength selection element to diffract a selected wavelength. By irradiating the light to the front emission end of the semiconductor laser, the oscillation wavelength is fixed at the selected wavelength irrespective of the temperature, and a stable operation can be realized even for a diffractive optical element. In addition, by providing the wavelength selection element on the same substrate (propagation path) on which other optical elements are provided, the production and alignment of all optical elements including the wavelength selection element can be easily and accurately performed using a known planar technology. (Because positioning can be performed simultaneously with production,
There is no need to assemble after fabrication), and the structure is small and stable, and all optical elements except the semiconductor laser and the photodetector are manufactured and duplicated at the same time by making a mold containing them, and their relative positions It can be manufactured at once while maintaining the relationship.

[0008]

1 and 2 are a side view and a plan view, respectively, showing the basic structure of an optical head according to a first embodiment of the present invention and how light is propagated and collected. An optical head according to a first embodiment of the present invention will be described in detail with reference to FIGS.

In FIG. 1, a substrate 1 has a thickness (size in the z direction) of 3 mm and a width (size in the x direction) of 10 m, for example.
Reflection layers 11a and 11b which are a metal layer of, for example, Ag, Al, Au or the like or a dielectric multilayer film are formed on the front and back surfaces of the substrate 2 using glass having a length of 20 mm in the y direction (size in the y direction). . The substrate 1 itself serves as a light propagation path 13 through which light propagates in a zigzag manner using reflection on the front surface and the back surface. The substrate 1 only needs to be transparent to the wavelength used. In particular, a glass substrate of quartz or the like is stable in temperature. As shown in FIG. 1, the substrate 2 is cut at the lower left portion in an oblique direction at an angle of, for example, 20 ° from the y direction, and the semiconductor laser 1 and the four-divided photodetector 6 are installed on the cut end surface. ing. At this time, if the semiconductor laser 1 and the four-divided photodetector 6 are modularized into one optical component,
Positioning becomes easier.

For example, light emitted from the surface emitting end of the semiconductor laser 1 having a wavelength of 0.78 μm in a direction in which the optical axis is inclined at an angle of, for example, 20 ° from the z-axis becomes a propagating light 8 and a light propagating path 1.
For example, the light enters a wavelength selection lens 12 which is a reflection-type and diffraction-type wavelength selection element having a focal length of 1.7 mm and an aperture of 1 mm provided on the lens 3. The wavelength selection lens 12, toward the y-direction, gradually period becomes smaller cross section consists parabolic grating rectangular, wavelength selective element
The incident light to the element 12 is reflected and diffracted at a diffraction efficiency of, for example, 20%, and the diffracted light whose wavelength is selected (for example, 0.78)
Only 0 .mu.m) is incident is condensed on the surface emission end of the semiconductor laser 1. Other wavelengths (for example, 0.77 to 0.79 μ)
The first-order diffracted light of m) is blurred on the surface emitting end, and the incident light quantity decreases as the distance from the selected wavelength increases. Although the amount of incident light depends on the reflectance of the front emission end, in the present embodiment, the incident light amount is, for example, 5% to 20% of the total oscillation light amount. If the rate is set to 5% or more (for example, 5%), the laser oscillation wavelength is dragged to the selected wavelength, and there is an effect that the wavelength fluctuation is suppressed to about 0.2 nm. In the present embodiment, the first-order diffracted light is used as the reflected diffracted light, but other-order diffracted light such as the second-order light may be used.

The transmitted light (zero-order diffracted light) of the wavelength selection lens 12 propagates in a zigzag manner in the light propagation path 13, and is provided on the light propagation path 13, for example, with a focal length of 8.5 mm and a diameter of 2 mm.
Incident on the reflective collimator lens 3, which is a collimator element, and the angle of the optical axis (propagation angle θ) remains unchanged (for example, 20).
Reflected and collimated in ゜). The reflective collimator lens 3 is formed of an elliptical grating having a sawtooth-shaped cross section whose period becomes smaller as it goes toward the outer periphery. The center position of the elliptical grating gradually shifts in the y direction toward the outer periphery.
By using a collimator lens with such a shape,
Coma and astigmatism, which normally occur due to the effects of oblique incidence, were eliminated, and good collimation was achieved.

For example, a collimated light having a width of 2 mm is
Propagates in a zigzag manner, also anti provided on the optical propagation path 13
Projection and diffraction type optical element for position signal detection (Focus
The transmitted light passes through a reflective twin lens 5 which is a scanning / track error signal detecting element), and the transmitted light is a light condensing element, for example, a transmission type objective lens 4 having a diameter of 2 mm and a focal length of 2 mm.
Is output in the vertical direction, and condensed light 9 on the optical disk 7
Becomes The light 10 reflected from the optical disk 7 is also incident on the transmission type objective lens 4 and is collimated to become a propagating light 8 ′, which propagates in a zigzag manner and has a reflection layer 11 b and is formed on the light propagation path 13. Optical element for signal detection
In it, for example, x-direction size 2 mm, y-direction size 2m
m, and enters the reflective twin lens 5 having a focal length of 10 mm. The reflection type twin lens 5 is a reflection type lens 5a having the same specification and composed of a parabolic grating,
5b having a structure in which two 5b are arranged in an array.
The first-order diffracted light is split into two by the lens 5, propagates in a zigzag manner at an optical axis propagation angle of, for example, 30 °, and is collected on the photodetector 6.

The reflective collimator lens 3 is, for example, an in-line reflective diffractive optical lens with a maximum groove depth of 0.28 μm, and the transmission objective lens 4 is, for example, an off-axis type with a maximum groove depth of 1.3 μm. With a transmission type diffractive optical lens,
The wavelength selection lens and the reflection type twin lens 5 are of an off-axis type having a maximum groove depth of, for example, 0.12 μm, and all four optical elements are diffractive optical elements for condensing light using a light diffraction phenomenon. In the present invention, the in-line type diffractive optical lens is a lens in which the angle of the optical axis of the incident light coincides with the angle of the optical axis of the outgoing light, and the off-axis type diffractive optical lens is the angle of the optical axis of the incident light. And a lens in which the angle of the optical axis of the emitted light is different. By using the diffractive optical element, the film thickness is at most several μm and the light propagation path 1
On the other hand, accurate alignment and integration are possible by using a known planar technology, and small, light and stable.

These diffractive optical elements 3, 4, 5, 12
For example, an electron beam resist such as PMMA or CMS is coated on a substrate, an electron beam drawing method is performed to control an irradiation amount according to a film thickness of an element to be manufactured, and a developing process is performed to perform the resist processing. Was formed by changing From the optical element (master) formed in this way, this mold is produced by, for example, nickel electroforming,
The same lenses 3, 4, 5, and 12 as the master were duplicated on the light propagation path 13 by using a cured resin. According to this method, four diffractive optical lenses 3, 4, 5, and 12 can be easily formed on the light propagation path 13 with good positional accuracy at the same time.
In the reflection type diffractive optical lenses 3, 5, and 12, after replication, a metal layer of, for example, Ag, Al, or Au was deposited thereon as the reflection layer 11b.

A metal layer such as Cu or Cr, a synthetic resin such as a UV curable resin or a lacquer paint,
When a dielectric multilayer film, SiO, SiO ₂ , MgF ₂ , SiC, graphite, diamond or the like is deposited, for example, from 1000 to several μm, the surface of the reflective layer is hardly damaged, and at the same time, the oxidation of the reflective layer is prevented, and environmental resistance is improved. Could be improved. In particular, when Ag was used as the reflective layer, the effect of the present invention was great because it was easily oxidized.

The signal recorded on the optical disk 7 can be reproduced from the sum (6a + 6b + 6c + 6d) of the outputs of the split photodetectors 6.

The focus error signal and the track error signal can be detected by using the position signal detecting optical element 5. The focus error signal is detected using a known Foucault method. That is, when the optical disk 7 is in the just focus position, the propagation light divided by the reflection twin lens 5 into two light detectors,
The light is condensed at the centers of a and 6b and 6c and 6d. The focus error signal is obtained from the output of the photodetector 6a.
The difference between the outputs of b (6a-6b) or 6d from the output of 6d
The difference between the outputs of c is (6d-6c). When the optical disc 7 is at the just focus position, the focus error signal is 0. Next, when the optical disk 7 moves away from the just focus position in the -z-axis direction, the propagation light 8 '
Becomes a converging spherical wave from parallel light, and the two divided propagation lights move closer to each other, so that the focus error signal becomes negative. Conversely, when the optical disc 7 moves so as to approach the z-axis direction from the just-focused position, the propagating light 8 ′ becomes a divergent spherical wave, so that the propagating lights divided into two move away from each other. Therefore, the focus error signal becomes positive, so that focus control can be performed by the focus error signal.

The track error signal can be detected by a known push-pull method by calculating the difference between the optical powers of the two divided propagation lights, that is, the output (6a + 6b-6c-6d) of the photodetector. When this calculation is 0, it is just tracking, and when it has a value, tracking is out of alignment, and track control can be performed based on this signal.

The focus control and the track control were performed by moving the entire substrate 1 provided with each optical element to an optimum position by an actuator based on each detected error signal.

In the optical head of the present invention, the light propagation path 13 has a width and a thickness on the order of, for example, about 500 times or more the wavelength, and this is based on the size of the optical elements 3, 4, 5, and 12. In other words, geometrical optics can be used to propagate light as light rays in a zigzag manner.

FIGS. 3 and 4 are a side view and a plan view, respectively, showing the basic structure of an optical head according to a second embodiment of the present invention, and how light is propagated and collected. The optical head according to the second embodiment of the present invention will be described only with respect to differences from the optical head according to the first embodiment. The difference is that the wavelength selection lens 14 is formed in a donut shape around the reflection type collimator lens as a wavelength selection element. By doing so, the light quantity of the oscillating light in the central part is not reduced, and the peripheral part of the oscillating light is not intentionally used in many cases conventionally because of beam shaping. The optical head has an effect of effectively utilizing this light. Since the oscillating light from the semiconductor laser 1 is usually not a circle but an elongated ellipse, the wavelength selection lens 3 may be partially formed at both ends of the donut shape so as to match the major axis direction of the ellipse.

FIGS. 4 and 5 show the basic structure of an optical head according to a third embodiment of the present invention and how light is propagated and collected.
They are a side view and a plan view, respectively. The optical head according to the third embodiment of the present invention is different from the optical head according to the first embodiment in that the wavelength selecting element is a linear grating 1 having a uniform period.
5, the light emitted from the collimator lens 3 is made incident on this wavelength selection element, and the 0th-order diffracted light emitted by the wavelength selection element is made incident on the light condensing element. Light is reflected by a reflective collimator lens 3
Through the surface of the semiconductor laser 1 through the surface emitting end. With such a configuration, the wavelength selection element may be a linear uniform-period grating, which facilitates fabrication.

The embodiments of the optical head of the present invention have been described above. In addition to the optical heads of these embodiments, optical heads obtained by combining the configurations of the respective optical heads can also be configured, and the same effects can be obtained. Needless to say, we have. The objective lens and the collimator lens used in the description of the first to third embodiments are named for convenience, and are the same as commonly used lenses. In this description, the optical disk device has been described, but it goes without saying that the same effect can be obtained with other optical recording devices using an optical head.

[0024]

According to the present invention, it is possible to realize an optical head which can easily align optical components, is thin and lightweight, can be manufactured at a low cost, and can operate stably with almost no wavelength fluctuation of a semiconductor laser. .

[Brief description of the drawings]

FIG. 1 is a side view showing a basic configuration of an optical head according to a first embodiment of the present invention, and how light is propagated and collected.

FIG. 2 is a plan view showing a basic configuration of the optical head according to the first embodiment of the present invention, and how light is propagated and collected.

FIG. 3 is a side view showing a basic configuration of an optical head according to a second embodiment of the present invention and how light is propagated and collected.

FIG. 4 is a plan view showing a basic configuration of an optical head according to a second embodiment of the present invention, and how light is propagated and collected.

FIG. 5 is a side view showing a basic configuration of an optical head according to a third embodiment of the present invention and how light is propagated and collected.

FIG. 6 is a plan view showing a basic configuration of an optical head according to a third embodiment of the present invention and how light is propagated and collected.

FIG. 7 is a configuration diagram of a conventional optical head.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Substrate 3 Reflection type collimator lens (collimator element) 4 Transmission type objective lens (light condensing element) 5 Reflection type twin lens ( optical element for position signal detection) 6 Photodetector 7 Optical disk 8 Propagation light 9 Emission light REFERENCE SIGNS LIST 10 reflected light 11 reflective layer 12 wavelength selection lens (wavelength selection element) 13 light propagation path 14 wavelength selection lens (wavelength selection element) 15 wavelength selection grating (wavelength selection element)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-282756 (JP, A) JP-A-1-298537 (JP, A) JP-A-3-233401 (JP, A) JP-A-63-1988 117337 (JP, A) JP-A-63-96982 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B ^7/ 12-7/22

Claims (9)

(57) [Claims] A substrate provided with a light propagation path through which light propagates in a zigzag shape; a diffractive light condensing element formed on the light propagation path; and a reflection type light condensing element formed on the light propagation path; An optical element for detecting a position signal of a diffraction type, a wavelength selection element of a reflection type and a diffraction type formed on the light propagation path, a semiconductor laser, and a photodetector, and oscillating light from the semiconductor laser. Is guided to the light propagation path as propagation light, at least a part of the propagation light is incident on the wavelength selection element, and the diffracted light whose wavelength is selected by the wavelength selection element is emitted from the oscillation light. Making the light incident on the front emission end of the semiconductor laser, condensing at least a part of the propagating light with the light condensing element and outputting the condensed light to the optical disc, and inputting the reflected light from the optical disc to the light condensing element; For the position signal detecting optical element Come, the optical head is characterized in that leads to the photodetector output light from said position signal detecting optical element. 2. The light propagation path of a substrate, wherein a reflection layer is provided on a front surface or a back surface of the light propagation path.
An optical head according to item 1. 3. The optical head according to claim 1, wherein a collimator element is provided on the light propagation path, and the propagating light from the semiconductor laser is collimated by the collimator element and then guided to the light condensing element. 4. The optical head according to claim 1, wherein at least one of the photodetector and the semiconductor laser is provided on or in the light propagation path. 5. A wavelength selecting element, a light condensing element, and a position signal detecting optical element are provided on an optical disk side (front side) on a light propagation path, and a semiconductor laser and a photodetector are provided on a back side of the light propagation path. The optical head according to claim 1, wherein: 6. The optical head according to claim 3, wherein the wavelength selection element is formed around the collimator element. 7. The apparatus according to claim 1, wherein the zero-order diffracted light emitted from the wavelength selection element is made incident on the light condensing element.
An optical head according to item 1. 8. The wavelength selection element is a linear grating having a uniform period, and outputs light emitted from the collimator element.
4. The optical device according to claim 3, wherein the light is incident on the wavelength selection element, and the zero-order diffracted light emitted by the wavelength selection element is incident on a light focusing element. 9. A method for manufacturing an optical head according to claim 1, wherein a mold including at least a light condensing element, a position signal detecting optical element and a wavelength selecting element at the same time is produced, and said mold is formed. A method for manufacturing an optical head, wherein the light condensing element, the position signal detecting optical element, and the wavelength selection element are simultaneously duplicated.