JPH09211460A - Light modulator and optical head device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light modulator which has high utilization efficiency of light, can be manufactured at a low cast and has a double-focus lens effect and also to provide an optical head device using the modulator. SOLUTION: Manufacture of this modulator comprises: forming a concentric- circular transparent electrode 6 on the surface of each of a pair of glass substrates 4; further forming a polyimide film 5 on the surface of the transparent electrode 6; then, subjecting the polyimide film 5 to rubbing treatment in a prescribed direction; laminating and sticking together the resulting pair of glass substrates 4 so that the two transparent electrodes 6 are opposite to each other and the rubbing directions of the two polyimide films are consistent with each other; and thereafter, filling the space between the pair of glass substrates 4 with a liquid crystal 7 under vacuum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device for writing and reading optical information on an optical disk such as a CD (compact disk), a CD-ROM, a video disk and a magneto-optical disk. , And an optical modulator suitable for an optical head device.

[0002]

2. Description of the Related Art Conventionally, in an optical head device for writing optical information on an optical disc or for reading the optical information, like an CD, a CD-ROM and a DVD disc,
It is often necessary to read and write signals with one optical head device for optical recording media having different thicknesses.

In order to realize the optical head device for such a purpose, conventionally, for example, a lens element having a Fresnel lens type blazed hologram formed on the surface of the lens has been used. Of the light incident on the lens element from the semiconductor laser, for example, about half of the light is diffracted by the blaze hologram in the direction in which the beam expands, and the other half is transmitted as it is. Then, by converging each of them by the lens element main body, light having two focal points has been generated by one optical head device.

Further, it has been attempted that the lens has the same shape as the conventional one and a Fresnel lens hologram plate having a blazed hologram formed on the plate is separately installed.

However, a major drawback of these methods is that the blazed hologram reduces the amount of light in half by a single passage of light. Therefore, the amount of light is 1/4 in two passes in the forward direction (the direction from the light source side toward the optical recording medium side) and the backward direction (the direction from the optical recording medium side toward the light source side and the photodetector side). There is a problem that it becomes. Therefore, in the case of an optical head device using a red semiconductor laser, which is particularly difficult to obtain a large output, the load on the light source increases in order to obtain a large output, resulting in an increase in cost and a decrease in reliability. become.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, improves the light utilization efficiency, and can be manufactured at low cost.
An object of the present invention is to provide an optical modulator and an optical head device having a double focus lens effect.

[0007]

According to the present invention, there are provided two transparent substrates which are substantially parallel to each other and a liquid crystal sandwiched between the transparent substrates. The liquid crystal has a plurality of concentrically distributed regions, and each of the regions has a plurality of regions. Corresponding electrodes are formed, the liquid crystal is aligned substantially parallel to the transparent substrate when a non-electric field is applied and aligned in a predetermined direction as a whole, and when an electric field is applied, the alignment direction is from the central region to the peripheral region. Provided is a light modulation element characterized by being set to change periodically.

A preferred aspect of the present invention is that the orientation direction in one cycle is asymmetrical in the direction from the central region to the peripheral region. With such a configuration, it is possible to easily form the Fresnel lens hologram structure by the distribution of the alignment direction of the liquid crystal by the electric field.

Another preferred aspect of the present invention is that the length of one cycle becomes smaller from the central region toward the peripheral region. With such a configuration, the Fresnel lens hologram structure can be easily formed by the electric field, and when the electric field is applied, the Fresnel lens hologram structure can be shifted from the focus of the lens to a near focus or a far focus.

In another preferred embodiment of the present invention, the liquid crystal alignment direction during one period when an electric field is applied is substantially parallel to the transparent substrate, substantially perpendicular to the transparent substrate, or substantially parallel to and substantially perpendicular to the transparent substrate. It is to include those in the intermediate state. With such a configuration, a light modulation element equivalent to the Fresnel lens hologram structure can be obtained. In particular, it is preferable to set the vertical state, the intermediate state, and the substantially parallel state from the central region to the peripheral region, which is equivalent to the far focus Fresnel lens hologram structure. In the case of a near focus, it is set so as to be in a substantially parallel state, an intermediate state, and a substantially vertical state from the central region toward the peripheral region.

Another preferred embodiment of the present invention is that the voltages applied to the individual electrodes during one period when an electric field is applied are different from each other. With such a configuration, the alignment direction of the liquid crystal is controlled only by controlling the voltage applied to the electrodes,
The Fresnel lens hologram structure can be easily formed.

The present invention is also an optical head device for reading information and / or writing information by irradiating an optical recording medium with light from a light source through a diffraction element, wherein the diffraction element is the light modulation element. An optical head device is provided.

According to the present invention, the aspherical lens is separated from
It is possible to switch between the two focal points by providing a Fresnel lens hologram plate made of liquid crystal and applying an electric field to the electrodes provided on the Fresnel lens hologram plate. Therefore, it is possible to realize an optical modulator and an optical head device that have high light utilization efficiency and can switch between two focal points.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION When the light modulation element of the present invention is viewed from above, the alignment direction of liquid crystal is as shown in FIG. That is, it faces a certain direction regardless of the area. However, in FIG. 2, only two cycles of the central region are drawn, and the peripheral side is omitted. The straight line in the concentric circle indicates the alignment direction of the liquid crystal, and in this case, three layers (three regions) have one cycle. Although one period may be four or more regions, it is preferable that the alignment direction of the liquid crystal is asymmetrical in the direction from the central region to the peripheral region within one period.

It is preferable to provide at least three regions in one period, and the larger the number of regions into which one period is divided, the finer the change in the alignment direction between adjacent regions becomes, and the more equivalent the Fresnel lens hologram structure becomes. preferable. However, it is difficult to provide a large number of regions within one cycle of several tens of μm to several hundreds of μm, and about 10 regions is the upper limit. Therefore, it is preferable that the change in the orientation direction between the adjacent regions is small, and it is preferably 45 ° or less when the horizontal state is 0 ° and the vertical state is 90 °.

In the case of FIG. 3, the orientation direction is from the central region to the peripheral region, and one cycle is 90 ° (region 1) and 45 °.
(Region 2) and 0 ° (region 3) are repeated, and 90
The distribution in the orientation direction in one cycle of °, 45 ° and 0 ° is asymmetric. However, for example, 0 °, 30 °, 60
When repeated at 0, 30 and 0 degrees, the symmetry is centered around the 60 degree region. In this case, it is not equivalent to a so-called blazed diffraction grating or pseudo blazed diffraction grating, and is not equivalent to a Fresnel lens hologram structure.

Within one cycle, for example, 0 ° and 90 °
As described above, it is preferable that there are two regions having different orientation direction angles of 90 °. In this case, the optical anisotropy (refractive index anisotropy) of liquid crystal is a Since it is the largest in the (short axis direction), a diffraction grating having a high diffraction efficiency can be obtained. Furthermore, it is preferable to match the polarization direction of the incident light to either the minor axis direction or the major axis direction because the diffraction efficiency can be maximized.

Further, a side sectional view taken along line A1-A2 passing through the central region is as shown in FIG. Upper and lower electrodes are provided in each region so that different electric fields can be applied. The part without electrodes corresponds to 0V.

In this case, when a non-electric field is applied, the liquid crystal looks optically uniform and does not form a diffraction grating, so that light is transmitted as it is regardless of the polarization direction. In this case, the light reflected from the optical disk also passes as it is.

The liquid crystal is vertically aligned when an electric field is applied, and is vertically aligned at an angle corresponding to the value of the electric field. A side sectional view when an electric field is applied is shown in FIG. An electric field is applied to, for example, the electrode A part by 5
When V and 2.5 V are applied to the electrode B portion, the liquid crystal portion functions as a pseudo-blaze (saw) type diffraction grating for polarized light parallel to the paper surface in FIG. The light beam spreads as it is diffracted, and the light beam is focused on a position farther from the optical disk surface. The reflected light returns through the same optical path, and 60% of the reflected light returns to the original optical path.

An example in which such an optical modulator is used in an optical head device is shown in FIG. When a non-electric field is applied, almost all of the incident light (incident from below in FIG. 4) is directly transmitted,
Focus on the recording surface on the optical disk 10. The reflected light returns through the same optical path and passes through almost 100%. When an electric field is applied, most of the light that has passed through the central Fresnel lens hologram portion is diffracted and spread, and then is converged by the lens 12 at a slightly distant place. The reflected light also passes through the same path, and most of it is also diffracted by the liquid crystal hologram portion and returns to the original optical path. At this time, the incident light is assumed to be polarized in the A1-A2 direction.

The alignment direction of the liquid crystal can be controlled by forming an alignment film such as a polyimide film on the surface of the transparent substrate and rubbing it. In the case of the present invention, it is sufficient that all liquid crystals are parallel to the transparent substrate and aligned in a predetermined direction when a non-electric field is applied. Therefore, the alignment film may be coated with a solid and rubbed in a predetermined direction. That is, one rubbing process is enough. It is also possible to provide relatively shallow grid-shaped grooves on the surface of the transparent substrate and align the liquid crystal by the alignment force of the grid-shaped recesses.

The light source of the present invention is a semiconductor laser or YA.
Various solid and gas lasers such as solid-state lasers such as G lasers and gas lasers such as He-Ne can be used, and semiconductor lasers are preferable in terms of downsizing and weight reduction, continuous oscillation, maintenance and inspection. Further, by using a harmonic generator (SHG) in which a semiconductor laser or the like and a non-linear optical element are incorporated in the light source unit and a short wavelength laser such as a blue laser is used, high density optical recording and reading can be performed.

The optical recording medium of the present invention is a medium capable of recording and / or reading information by light. Examples are CDs (compact discs) and CD-ROs.
Optical discs such as M, video discs, DVDs (digital video discs), magneto-optical discs, and phase change optical discs can be used.

[0025]

EXAMPLES Examples of the present invention will be described below with reference to FIGS. IT is concentrically formed on the surface of the glass substrate 4 having a thickness of 0.5 mm, a size of 10 mm × 10 mm, and a refractive index of 1.52.
The transparent electrode 6 made of an O film was formed. A polyimide film 5 was formed on the transparent electrode 6, and a rubbing process was performed in a predetermined direction. Similarly, another glass substrate 4 on which the transparent electrode 6 and the polyimide film 5 were formed was prepared, and the two glass substrates 4 were laminated and adhered so that the transparent electrodes 6 face each other and the rubbing directions coincided with each other. The adhesion was performed by printing an epoxy resin (seal portion 8) on the peripheral portion and overlapping the cells so that the cell gap was about 1 μm.

A liquid crystal (nematic liquid crystal, product name PL-008 manufactured by Merck & Co., Inc., ordinary refractive index =) between two glass substrates 4.
1.525 and extraordinary light refractive index = 1.771) 7 were vacuum-injected. After that, the injection port was sealed with an epoxy resin to manufacture a light modulation element. Here, the Fresnel lens hologram structure made of liquid crystal was formed on a circular portion having a diameter of 2.5 mm at the center of the 10 mm × 10 mm transparent substrate.

At this time, one cycle in the central region is 285 μ.
m, one cycle in the most peripheral region is 33 μm, and electrode A (6
A), the electrode B (6B), and the electrodeless portion (6C) each have a width of 1/3 of one cycle. Electrode A 5V, Electrode B 2.0
When V was applied, the forward diffraction efficiency was about 60%, the backward diffraction efficiency was about 60%, and the reciprocating diffraction efficiency was about 36% for the semiconductor laser light having the wavelength of 780 nm. On the other hand, when no voltage is applied, the forward light transmittance is about 90%, and the backward light transmittance is about 90%.
The light transmittance of was obtained.

As shown in FIG. 4, the light modulation element, a semiconductor laser (not shown, and located below in the figure),
An optical head device was manufactured using the lens 12 and the optical disk 10. In this case, two focal points were obtained by one light modulation element, and two types of optical disks 10 having different thicknesses could be used at the same time.

[0029]

According to the present invention, a light modulation element having a dual focus lens effect which has high light utilization efficiency and can be manufactured at low cost, and an optical head device using the same are obtained. CD and CD-ROM by having a double focus lens effect
One optical head device can read and write signals with respect to optical disks having different thicknesses such as a DVD disk and a DVD disk.

[Brief description of drawings]

FIG. 1 is a side sectional view of a light modulation element taken along line A1-A2 of FIG. 2 showing an embodiment of the present invention.

FIG. 2 is a plan view of a central portion of the light modulation element according to the embodiment of the present invention.

FIG. 3 is a partial side cross-sectional view of a light modulation element illustrating an alignment state of liquid crystal when an electric field is applied according to an embodiment of the present invention.

FIG. 4 is a side view of the optical head device according to the embodiment of the present invention.

[Explanation of symbols]

 1: region 2: region 3: region 4: glass substrate 5: polyimide film 6: transparent electrode 6A: electrode A 6B: electrode B 6C: electrodeless part 7: liquid crystal 8: seal part 10: optical disk 11: Fresnel lens hologram structure

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G11B 7/135 G11B 7/135 Z 19/12 501 501/12 12 501E

Claims (6)

[Claims] 1. A transparent substrate having two substantially parallel transparent substrates and a liquid crystal sandwiched between the transparent substrates, the liquid crystal having a plurality of regions concentrically distributed, and electrodes formed corresponding to the respective regions.
The liquid crystal is set so that the alignment direction is substantially parallel to the transparent substrate when a non-electric field is applied and aligned in a predetermined direction as a whole, and the alignment direction periodically changes from the central region to the peripheral region when an electric field is applied. An optical modulation element characterized in that 2. The light modulation element according to claim 1, wherein the alignment direction in one cycle is asymmetrical in the direction from the central region to the peripheral region. 3. The optical modulator according to claim 1, wherein the length of one cycle becomes smaller from the central region toward the peripheral region. 4. An alignment direction of liquid crystal in one cycle when an electric field is applied includes one in a state substantially parallel to the transparent substrate, one in a state substantially vertical to the transparent substrate, and one in an intermediate state between substantially parallel and substantially vertical. Item 2. The light modulation element of 2 or 3. 5. The light modulation element according to claim 2, wherein the voltages applied to the individual electrodes in one cycle when an electric field is applied are different from each other. 6. An optical head device for reading information and / or writing information by irradiating an optical recording medium with light from a light source through the diffraction element, wherein the diffraction element is an optical modulator. An optical head device characterized by being an element.