JP2000215506A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable simple switching of the number of openings of an optical system and to realize ultrahigh resolution by constituting the space modulation element of a part functioning as a diffraction type lens element and a part functioning as a rotary polarization optical element, and controlling functions of the diffraction type lens element and the rotary polarization optical element by an electrical signal. SOLUTION: When the function of a diffraction type lens element 105 is stopped and the function of the rotary polarization optical system 106 is made valid, since linearly polarized light passing through the optical rotating optical element 106 and linear polarization light passing through the diffraction type lens element 105 intersect orthogonally to each other, ultrahigh resolution is produced. The number of openings for an optical device is decided by a condenser lens 107, read and write of DVD are performed in this state. Next, when a function of the optical rotating optical element 106 is stopped and a function of the diffraction type lens element 105 is made valid, ultrahigh resolution will not be produced. The focal distance of an optical device is made a combined focal distance by the diffraction type optical element 106 and the condenser lens 107, it is assumed that the number of openings is varied as compared with that of the condenser lens 107 only, and reading of a CD is performed in this state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a variable aperture technique for effectively switching the numerical aperture of an optical system and an effect of effectively switching the theoretical resolution of an optical system determined by a diffraction limit and equivalently switching the wavelength of a light source. The present invention relates to an optical device to which a super-resolution optical technology having the above is applied. In particular, the effective numerical aperture of an optical pickup and the effective light source wavelength are switched in a recent optical disk device, and DVD (digital versatile disk), CD-ROM, CD-R (write-type CD) and CD-RW (rewritable-type) An optical device that provides an optical pickup that requires a condensing optical system having a different numerical aperture and a laser light source having a different oscillation wavelength, such as for a CD), using a kind of condensing lens and a kind of wavelength laser light source. About.

[0002]

2. Description of the Related Art To facilitate understanding of the prior art, the numerical aperture of an optical system will be briefly described. In an optical system designed with almost no aberration in geometrical optics, a point image is formed as an infinitely small spot. However, in reality, the spot has a finite spread due to diffraction due to the wave nature of light. At this time, assuming that the numerical aperture of the optical system contributing to image formation or light collection is NA, the physical definition of the spread of the spot is represented by k × λ ÷ NA. Here, λ is the wavelength of light, and k is a constant determined by the optical system and usually takes a value of about 1 to 2. NA is proportional to the ratio D / f between the effective entrance pupil diameter D of the optical system (generally, the diameter of the effective light beam) and the focal length f. The spread of the spot represented by this equation becomes the theoretical resolution limit and is called the diffraction limit.

[0003] As is apparent from the above equation, the theoretical resolution of an optical system largely depends on the numerical aperture. In general, in the case of an optical disc, the numerical aperture of the converging optical system (objective lens) of the optical pickup is about 0.45 for a CD or CD-ROM, and about 0.6 for a DVD that requires higher resolution. Also,
The thickness of the optical disc substrate is 1.2 mm for CD and 0 for DVD.
Since the focusing optical system is designed different from 6 mm and the aberration is optimized for each thickness, the focusing optical system having the same numerical aperture cannot be shared between CD and DVD. This means that a condenser lens for DVD having a higher numerical aperture cannot be used for CD as it is.

Further, CD-Rs (write-type CDs) and C
In the case of a D-RW (rewritable CD), there is a restriction that a laser having a wavelength of about 780 nm must be used due to the photosensitive characteristics of the disc.
It is impossible to use a laser of about 70 nm. In addition, since a DVD requires a higher resolution than a CD, a 780 nm laser light source for a CD cannot be used at present. Therefore, DVDs, CDs, and CDs that are becoming mainstream recently
In an optical disk device compatible with -R, it is necessary to prepare two different types of objective lenses and laser light sources of two different wavelengths.

[0005] In order to solve this problem, two types of optical pickups are installed in one device, or two laser light sources and two objective lenses are used in the device. A method has been used in which two laser light sources and a wavelength filter are provided, and the effective aperture of the objective lens for one of the light sources is changed by the wavelength filter.

Next, one of the conventional examples is shown in FIG. This is based on application to an optical disk. For the sake of simplicity, a sectional view is shown, and portions of the detection optical system which are not related to the essence of the present invention are omitted. First laser light source 70 having a wavelength of 670 nm
The first laser light 704 emitted from 1 and transmitted through the half mirror 702 and converted into a plane wave by the collimating lens 703 is transmitted through the wavelength filter 705 and condensed on the optical disk 707 by the condenser lens 706. The wavelength filter 705 has a rounded center portion and selectively transmits only light near a wavelength of 670 nm. In this state for DVD or DV
Functions as an optical system for D-ROM (RAM)

Next, a second laser light source 7 having a wavelength of 780 nm
08, reflected by the half mirror 702, and converted into a plane wave by the collimating lens 703.
Numeral 9 passes through only the cut-out portion of the wavelength filter 705 and is condensed on the optical disk 707 by the condensing optical system 706. At this time, as is clear from FIG. 7, the second laser light 709 has a light beam diameter smaller than that of the first laser light 704 and enters the condensing optical system 706. That is, the condensing optical system 7
06 is reduced in effective numerical aperture. In this state, it functions as a CD, CD-ROM, or CD-R (RW).

[0008]

However, in the conventional example, since two pickups are installed in one device, the structure of the device becomes complicated and the space is disadvantageous. In addition, installing two laser light sources and two objective lenses in one pickup, or installing two laser light sources and a wavelength filter complicates the alignment of the optical system configuration and optical axis, etc. In addition, since the optical axes from the two light sources are combined using a half mirror or the like, there is a problem that the light utilization rate is significantly reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical device which solves the above-mentioned problems and which can easily switch the numerical aperture of an optical system easily and can realize super-resolution easily and electrically. It is.

[0010]

An optical device according to the present invention comprises at least a spatial light modulator for modulating a laser beam and a condenser lens for condensing a light beam modulated by the spatial light modulator. The spatial light modulator is composed of at least a part functioning as a diffractive lens element and a part functioning as an optical rotation element, and the functions of the diffraction lens element and the optical rotation element are controlled by electric signals. And

Further, the portion functioning as the optical rotatory optical element is characterized in that it acts on a substantially circular region centered on the optical axis of the light beam condensed by the condenser lens.

Further, a linearly polarized laser light source is used as a laser light source, a liquid crystal spatial light modulator is used as a spatial light modulator, and a portion functioning as a diffractive lens element of the liquid crystal spatial light modulator is composed of a parallel alignment type liquid crystal element. The part functioning as an optical rotation optical element is composed of a 90-degree twisted nematic liquid crystal element, and the direction of the polarization axis of the linearly polarized laser light source is substantially the same as the direction of the liquid crystal molecule alignment axis on the side of the linearly polarized light incident side of the liquid crystal spatial light modulator. The feature is that they match.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) To facilitate understanding of an embodiment of the present invention, the function can be controlled by the super-resolution effect of an optical system using polarized light and electric signals. A general variable focus optical device using a liquid crystal Fresnel lens which is a diffraction lens element will be briefly described. First, the super-resolution effect of an optical system using polarized light will be briefly described with reference to FIG. FIG. 8 is a configuration example of a super-resolution optical device using polarized light. Although drawn in a cross-sectional view for simplicity, it is actually a rotationally symmetric shape with the optical axis 803 as a rotation axis. As shown in FIG. 8, a linearly polarized laser beam 802 having a wavelength λ is incident on a converging lens 801 whose aberration is well corrected, and the optical axis 8 of the converging lens 801 is changed.
A point image 804 is formed at a point P on 03. At this time, the point image 804 has a wave optical spread as described above, and the spread is represented by kλf / d. This is the theoretical limit determined by wave optics. Where k is a constant specific to the optical system, f
Is the distance from the condenser lens 801 to the point image 804, and d is the beam diameter of the linearly polarized laser light 802. However, d must be smaller than the effective diameter of the condenser lens 801. For simplicity, the linearly polarized laser light 802 is parallel light.

Here, the optical rotation optical element 805 is connected to the condenser lens 8.
Installed before 01. The function of the optical rotation optical element 805 is to make the polarization axes of the linearly polarized light passing through the central portion (hatched portion in FIG. 8) 806 and the linearly polarized light passing through other than the central portion orthogonal. Also, the optical rotation optical element 805 is usually installed symmetrically with respect to the optical axis 803. At this time, it is known that the super-resolution phenomenon occurs and the spread of the point image 804 is reduced. It is also known that the rate of decrease is proportional to the size of the central portion 806. However, if the size is too large, a large side band is generated in the point image 804, resulting in a three-mountain spot, which is inconvenient. Of course, the central part 80
6 becomes too large, and all the linearly polarized laser light 802 passes through the central portion 806, so that the super-resolution phenomenon does not occur. Normally, when the ratio (r / d in FIG. 3) of the central portion 806 to the beam diameter of the linearly polarized laser light 802 is about 20%, the point image 804 is about 15% smaller than the theoretical limit. That is, the same effect as when the wavelength of the laser light is shortened by 15% is obtained. If the optical rotatory optical element is controlled by an electric signal to lose optical rotation, super-resolution will not occur.

Next, a variable focus optical device using a liquid crystal Fresnel lens will be briefly described with reference to FIG. Although drawn in a cross-sectional view for simplicity, it is actually a rotationally symmetric shape with the optical axis 903 as a rotation axis. A transparent electrode having a pattern of a Fresnel lens functioning as a lens having a focal length f1 is formed on the liquid crystal Fresnel lens 901, and by applying an appropriate voltage to the transparent electrode, the liquid crystal Fresnel lens 901 functions as a lens. At this time, the focal length of this optical device is the combined focal length of the liquid crystal Fresnel lens 901 and the condenser lens 902, and the laser light 904 is focused on point P2. When no voltage is applied, the liquid crystal Fresnel lens 901 does not function as a lens, so that the focal length of this optical device is the focal length of the condenser lens 902 and the laser light 904
Focuses on point P1. Therefore, the liquid crystal Fresnel lens 901
This means that the focal length of the optical device, that is, the numerical aperture, is changed before and after the voltage is applied.

Next, an optical device according to a first embodiment of the present invention will be described with reference to FIG. The optical device according to the present embodiment is based on an optical device for an optical pickup capable of supporting all DVDs (RAMs), CDs, and CD-Rs (W). For simplicity, FIG. 1 is drawn by projecting onto a two-dimensional YZ plane. Actually, it has a rotationally symmetric shape with the optical axis 109 as the rotation axis. In addition, parts of the detection optical system that are not directly related to the present invention are omitted. As shown in FIG. 1, the optical device according to the present embodiment emits from a linearly polarized laser light source 101 having a wavelength of about 780 nm, and a linearly polarized laser beam 103 converted into a parallel plane wave by a collimating lens 102 enters a spatial light modulator 104. . The spatial light modulator 104 includes at least a portion functioning as a diffractive lens element 105 (shown with diagonally left lines) and a portion functioning as an optical rotation element 106 (showing diagonally right lines), and each function is controlled by an electric signal. . The part functioning as the diffractive lens element 105 functions as a lens having a focal length f1, and the part functioning as the optical rotation element 106 has a function of rotating the polarization axis of incident linearly polarized light by 90 degrees as compared with other parts. The portion functioning as the optical rotation optical element 106 acts on a substantially circular region 108 centered on the optical axis of the condenser lens 107.

First, the function of the diffractive lens element 105 is stopped, and the function of the optical rotation optical element 106 is made effective. At this time, the linearly polarized light that has passed through the optical rotatory optical element 106 and the linearly polarized light that has passed through the diffractive lens element 105 are orthogonal to each other, resulting in super-resolution. At this time, it is understood that the numerical aperture of the optical device is determined by the condenser lens 107. As described in the description of the super-resolution, if the super-resolution of about 15% is performed, the cross-sectional ratio of the optical rotation optical element 106 to the light beam of the linearly polarized laser beam 103 is about 20%. This state is used for reading and writing of the DVD.

Next, the function of the optical rotation optical element 106 stops,
The function of the diffractive lens element 105 is made effective. In this state, super-resolution does not occur. At this time, the focal length of this optical device is determined by the diffraction optical element 106 and the condenser lens 10.
The combined focal length is 7, which means that the numerical aperture has been changed as compared with the case where only the condenser lens 107 is used. This state is CD
Used for reading.

Strictly speaking, the central part of the diffractive lens element 105 is the optical rotatory optical element 106, so that it has almost no function as a lens. However, the focal length of the diffractive lens element required for switching the numerical aperture between DVD and CD is several tens of meters.
Since the distance is from m to several hundred mm, the vicinity of the center originally does not require much action as a lens. Further, as described above, when super-resolution of about 15% is performed, the optical rotation optical element 106 is used.
However, since the cross-sectional ratio that can be set near the center is about 20%, there is not much influence.

As is clear from the above description, the effective numerical aperture of the optical device is switched by controlling the function of the diffractive lens element 105 and the function of the optical rotation optical element 106, and the effective wavelength of the laser is switched. It becomes possible.

(Second Embodiment) Next, an optical device according to a second embodiment of the present invention will be described. Basically, it is the same as the first embodiment shown in FIG. 1, except that a parallel alignment type liquid crystal element and a 90-degree twisted nematic liquid crystal are used as a diffraction type lens element and an optical rotatory optical element which can be easily controlled by an electric signal. A liquid crystal spatial light modulator composed of elements is used. First, in order to facilitate understanding of the present embodiment, operations, diffraction phenomena, and the like of the parallel alignment type liquid crystal element and the 90-degree twisted nematic type liquid crystal element will be briefly described.

FIGS. 3 (a) and 3 (b) schematically show the structure and operation of a general electrically controllable parallel alignment type liquid crystal element and a 90 ° twist nematic type liquid crystal element. Liquid crystal molecules 302 are sandwiched between glass substrates 301 coated with transparent electrodes. The incident side glass substrate has the orientation axis 303 in the Y-axis direction and the exit side glass substrate has the orientation axis 3
In the direction 03, the upper half is the Y-axis direction and the lower half is the X-axis direction. As shown in FIG. 3A, the liquid crystal molecules 302 are aligned in a parallel or homogenous manner, as shown in FIG. 3A, from the property of aligning the major axis direction to the orientation axis direction and the property of behaving as a continuum. This is called alignment, and the liquid crystal molecules 302 in the lower half are twisted 90 degrees.
Degree of twist nematic orientation.

When linearly polarized light 304 is incident on the liquid crystal element, when the polarization axis is in the same direction as the alignment axis 303, the linearly polarized light 304 is kept linearly polarized due to the dielectric anisotropy of the liquid crystal molecule 302. It propagates along the long axis direction of 302. Therefore, in the 90-degree twisted nematic region, the output linearly polarized light rotates 90 degrees in the X-axis direction. In this case, assuming that the refractive index in the major axis direction of the liquid crystal molecules 302 is n1 and the thickness of the liquid crystal layer is L, the optical path length of the linearly polarized light 304 traveling in the liquid crystal layer is n1 × L
Becomes

Next, when an electric field in the Z-axis direction is applied to the liquid crystal molecules via the transparent electrode coated on the glass substrate 301, the major axis of the liquid crystal molecules 302 is the direction of the electric field as shown in FIG. Stand still in the Z-axis direction. This state is called homeotropic. In this case, linearly polarized light 3 traveling in the liquid crystal layer
04 also propagates while maintaining linearly polarized light. 9
Optical rotation in the 0 degree twisted nematic region is lost. At this time, assuming that the refractive index in the minor axis direction of the liquid crystal molecules 302 is n2, the optical path length of the linearly polarized light 304 traveling in the liquid crystal layer is n2 × L
It turns out that it becomes. That is, before and after the voltage is applied, the refractive index for the linearly polarized light 304 is changed from n1 to n2, and thus the optical path length is changed.
This means that (n1-n2) × L has been changed. It is also possible to create these intermediate states by controlling the applied voltage. It is also known that a small voltage immediately before the liquid crystal starts moving by an electric field should be applied to the liquid crystal layer in order to make the liquid crystal layer close to an ideal homogenous state.

FIG. 4 shows a light diffraction phenomenon by a general binary type approximately transparent phase type diffraction grating.
For simplicity, it is drawn in a sectional view projected on a plane. When a laser beam 402 is incident on a phase type diffraction grating 401 having a thickness d and having a different refractive index of n1 and n2 repeatedly at a pitch P,
The emitted laser light is diffracted by the diffraction effect. Here, for simplicity, the laser beam 402 is a phase type diffraction grating 401.
It is assumed that the light is perpendicularly incident on. At this time, usually, the zero-order light 403, which is light passing through as it is, and the first-order light 404 and the minus first-order light 4 diffracted in the θ direction and the −θ direction, respectively.
05 (higher-order diffracted light having a larger diffraction angle is also generated, but is ignored because the ratio is small). At this time, the diffraction angle θ is determined by sin (θ) = λ / P. Here, λ is the wavelength of the laser light 402.

At this time, n1 and n2 with respect to the laser beam 402
Are almost equal in area, and the optical path length difference (n1-n2) × L is λ
When it is / 2, this is called a Ronchi grating, and it is known that the zero-order light 403 disappears. Optical path length difference (n1-n2) x L
It is known that when the refractive index is repeatedly changed at λ and the pitch P to continuously and smoothly change the refractive index from n1 to n2, this is called a blazed grating and only primary light 404 is generated. Actually, it is also known that an ideal blazed grating can be obtained by changing stepwise from n1 to n2 in 16 steps or more, which is called a multilevel binary grating. In general, a phase type diffraction grating is advantageous in that it has higher light utilization efficiency than an amplitude type diffraction grating having an opaque portion. As is generally known, by continuously changing the pitch of the diffraction grating, various lens effects can be provided, and a typical one is a Fresnel lens.

FIGS. 5A and 5B illustrate the cross-sectional structure of a liquid crystal diffraction optical element 501 that can be electrically controlled. The liquid crystal molecules 502 are aligned in parallel so that the major axis direction coincides with the Y axis direction, and the refractive index in the major axis direction is n1 and the refractive index in the minor axis direction is n2. Further, on one side of the glass substrate, stripe-shaped transparent electrodes 503 are formed at a pitch P. A transparent electrode is coated on almost the entire surface of the other glass substrate. At this time, the linearly polarized laser light 504 in the Y-axis direction enters the liquid crystal diffraction optical element 501.

At this time, as shown in FIG. 5A, when no voltage is applied to the liquid crystal diffraction optical element 501, the refractive index for the linearly polarized light 504 becomes n1 uniformly. Therefore, no diffraction occurs, and the linearly polarized light 504 passes through to become the output light 508. Strictly speaking, slight diffraction is caused by the transparent electrode 503, but the refractive index of the transparent electrode 503 and the liquid crystal molecules 502
If the refractive index in the major axis direction is the same, diffraction by the transparent electrode 503 does not occur.

Next, as shown in FIG.
When a sufficient voltage is applied to the liquid crystal molecule 3 from the power supply, the liquid crystal molecules 502 in that portion are brought into a homeotropic state by an electric field in the Z-axis direction. As a result, the linearly polarized light 504 has a structure in which the refractive index repeats n1 and n2 at the pitch P. Therefore, it functions as a binary phase diffraction grating exactly equivalent to FIG.
Zero-order light 505, first-order light 506, and -1st-order light 507 are generated. At this time, if the condition of the Ronchi grating is satisfied, the zero-order light 505 is not generated. If the above-described condition of the multi-level binary grating is satisfied, only the primary light 506 is generated. However, for multi-leveling, the transparent electrode 5
03 needs to be chopped at a finer pitch, and the voltage must be changed in a stepwise manner.

Next, an optical device according to a second embodiment of the present invention will be described with reference to FIG. The optical device according to the second embodiment is based on an optical device for an optical pickup that can support all DVDs, CDs, and CD-Rs. For simplicity, FIG. 2 is drawn by projecting on a two-dimensional plane, which is a YZ plane. Actually, it becomes a rotation reference with the optical axis 209 as a rotation axis. In addition, parts of the detection optical system that are not directly related to the present invention are omitted.

The optical device according to the second embodiment emits light from a linearly polarized laser light source 201 having a wavelength of about 780 nm,
The linearly polarized laser light 203 converted into a parallel plane wave by the collimator lens 202 enters a liquid crystal spatial light modulator 204. The liquid crystal spatial light modulating element 204 has its liquid crystal molecule alignment axis substantially coincident with the direction of the polarization axis of the linearly polarized laser light source 201, and both directions are in the Y-axis direction. The liquid crystal spatial light modulating element 204 functions as a diffractive lens element 205 composed of at least a parallel alignment type liquid crystal element (shown by diagonal left) and 9.
It is composed of a portion (displayed with diagonal right) that is composed of a 0-degree twisted nematic liquid crystal and functions as the optical rotation optical element 206, and each function is controlled by an electric signal. The part functioning as the diffractive lens element 205 functions as a lens having a focal length f1, and the part functioning as the optical rotation element 206 has a function of rotating the polarization axis of incident linearly polarized light by 90 degrees as compared with other parts. The portion functioning as the optical rotation optical element 206 acts on a substantially circular region 208 centered on the optical axis of the condenser lens 207.

First, the function of the diffractive lens element 205 stops, and the function of the optical rotation element 206 is made effective. At this time, the linearly polarized light that has passed through the optical rotatory optical element 206 and the linearly polarized light that has passed through the diffractive lens element 205 are orthogonal to each other, resulting in super-resolution. At this time, it is understood that the numerical aperture of the optical device is determined by the condenser lens 207. As described in the description of the super-resolution, if the super-resolution of about 15% is performed, the cross-sectional ratio of the optical rotation optical element 206 to the light beam of the linearly polarized laser beam 203 is about 20%. This state is used for reading and writing of the DVD.

Next, the function of the optical rotation optical element 206 stops,
The function of the diffraction lens element 205 is made effective. In this state, super-resolution does not occur. At this time, the focal length of the optical device is the same as that of the diffractive optical element 206 and the condenser lens 20.
The composite focal length is 7, which means that the numerical aperture has been changed compared to the case where only the condenser lens 207 is used. In other words, it can be considered that the spherical aberration generated when reading the CD with the condenser lens 207 is corrected by the diffractive lens element. This state is used for reading a CD.

Strictly speaking, the central part of the diffractive lens element 205 is the optical rotatory optical element 206, so that it has almost no function as a lens. However, the focal length of the diffractive lens element required for switching the numerical aperture between DVD and CD is several tens of meters.
Since the distance is from m to several hundred mm, the vicinity of the center originally does not require much action as a lens. According to another interpretation, the spherical aberration generated at the time of reading a CD is proportional to the cube of the lens aperture, and has little effect near the center. Furthermore, as described above, when super-resolution of about 15% is performed, the cross-sectional ratio of the optical rotation optical element 206 near the center is about 20%, so that there is not much effect.

As is apparent from the above description, by controlling the function of the diffractive lens element 205 and the function of the optical rotation optical element 206, the effective numerical aperture of the optical device is switched, and the effective wavelength of the laser is switched. It becomes possible. It is also possible to set the operating state of the diffractive lens element 205 to the numerical aperture for reading and writing a DVD, but in this case, if writing to the DVD is necessary unless the efficiency of the diffractive lens element is increased, Insufficient power.

Next, the electrode shape of the liquid crystal spatial light modulator 204 will be described with reference to FIG. The electrode of the liquid crystal spatial light modulator has a circular region 601 in the center and a ring region 602 in which a plurality of concentric rings having the same center as the circular region 601 are arranged on the outer periphery thereof. Are connected to the terminal electrode 603. FIG. 6 shows the annular shape of the Fresnel zone plate. However, only four ring zones are illustrated because they are schematically illustrated, but there are actually several tens to several hundreds of annular zones. When an electric signal is applied through the terminal electrode 603, the annular zone 602 functions as a diffractive lens, and at the same time, the optical rotation of the circular zone 601 disappears.

Further, since the liquid crystal spatial light modulation element 204 is used as a phase type element which does not require a polarizing plate or the like, no light quantity loss occurs in principle. In the actual measurement, the light quantity loss was about 15%, but it can be reduced to 10% or less by applying a non-reflection coating to the liquid crystal glass substrate.

[0038]

As is clear from the above description, the optical device using the liquid crystal spatial light modulator according to the present invention has a simple configuration and can easily switch the numerical aperture easily without losing a large amount of light. The super resolution can be easily caused electrically and the wavelength of the light source can be equivalently shortened. This is particularly effective for an optical pickup having both reproduction and recording of CD and CD-R in an optical system of a DVD-RAM, that is, a writable or rewritable digital versatile disk. This is because increasing the light output of a semiconductor laser as a light source is a difficult problem, and a light source having a wavelength of about 780 nm is required to read a CD-R, and a light source for DVD having a wavelength of about 660 nm cannot be used.

The liquid crystal spatial light modulator according to the present invention is small in size and very simple in structure as compared with current liquid crystal display panels for personal computers having a complicated matrix pixel structure, so that it is easy to manufacture. In this embodiment, the liquid crystal spatial light modulator is used as the electrically controllable spatial light modulator. However, bismuth silicon oxide (BS
O) or solid crystals such as lithium niobate, or PL
Electro-optic ceramics such as ZT may be used. However, since these materials have an effective operating voltage of several hundred to several thousand volts, a liquid crystal having an effective operating voltage of several volts is advantageous because it can be directly driven by a CMOS LSI or the like.

[Brief description of the drawings]

FIG. 1 is a configuration example of an optical device according to a first embodiment of the present invention.

FIG. 2 is a configuration example of an optical device according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating an operation of an electrically controllable parallel alignment type liquid crystal element in a second embodiment of the present invention.

FIG. 4 is a diagram showing a light diffraction phenomenon by a general binary phase diffraction grating.

FIG. 5 is a diagram showing a basic cross-sectional structure of a liquid crystal diffractive optical element that can be electrically controlled in a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a shape of a transparent electrode of a liquid crystal spatial light modulator according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a configuration example of an optical device according to a conventional technique.

FIG. 8 is a configuration example of a super-resolution optical device using polarized light.

FIG. 9 is a diagram illustrating a configuration example of a variable focus optical device using a liquid crystal Fresnel lens.

[Explanation of symbols]

 101, 201, linearly polarized laser light sources 102, 202, 703, collimate lenses 103, 203, 504, 802, linearly polarized laser light 104, spatial light modulators 105, 205, diffractive lens elements 106, 206, 805, optical rotation Optical elements 107, 207, 706, 801, 902, condenser lenses 108, 208, circular areas 109, 209, 803, 903, optical axes 203, 504, linearly polarized laser light 204, liquid crystal spatial light modulator 301, glass substrate 302, 502, liquid crystal molecules 303, alignment axis 304, linearly polarized light 401, phase type diffraction gratings 402, 904, laser beams 403, 505, zero-order light 404, 506, first-order light 405, 507, minus first-order light 501, Liquid crystal diffraction optical element 503, transparent electrode 508, outgoing light 601, circular area 60 , Annular zone 603, terminal electrode 701, first laser light source 702, half mirror 704, first laser light 705, wavelength filter 707, optical disk 708, second laser light source 709, second laser light 804, point Image 806, central part 901, liquid crystal Fresnel lens

Claims (6)

[Claims] 1. An optical device comprising at least a spatial light modulator for modulating a laser beam and a condenser lens for condensing a light beam modulated by the spatial light modulator, wherein the spatial light modulator is at least diffractive. An optical device comprising a part functioning as a mold lens element and a part functioning as an optical rotation optical element, wherein the functions of the diffractive lens element and the optical rotation optical element are controlled by electric signals. 2. An optical device comprising at least a spatial light modulating element for modulating a laser beam and a condensing optical system for condensing a light beam modulated by the spatial light modulating element, wherein the spatial light modulating element is at least A part comprising a part functioning as a diffractive lens element and a part functioning as an optical rotation optical element, and the functions of the diffraction lens element and the optical rotation optical element being controlled by electric signals, and functioning as the optical rotation optical element An optical device characterized by acting on a substantially circular area centered on the optical axis of a light beam condensed by the condenser lens. 3. The optical device according to claim 1, wherein a liquid crystal spatial light modulator is used as the spatial light modulator. 4. The optical device according to claim 2, wherein a liquid crystal spatial light modulator is used as the spatial light modulator. 5. A linearly polarized laser beam as a laser beam and a liquid crystal spatial light modulator as a spatial light modulator,
The part functioning as a diffractive lens element is composed of a parallel alignment type liquid crystal element, and the part functioning as an optical rotation optical element is composed of a 90 degree twist nematic type liquid crystal element.
And a polarization axis direction of the linearly polarized laser light source substantially coincides with a direction of a liquid crystal molecule alignment axis on the side of the linearly polarized laser light source of the parallel alignment type liquid crystal element and the 90 ° twisted nematic type liquid crystal element. The optical device according to claim 1. 6. A liquid crystal spatial light modulating element using a linearly polarized laser light as a spatial light modulating element as a laser light, and a portion functioning as a diffractive lens element is constituted by a parallel alignment type liquid crystal element and functioning as an optical rotation optical element. The site is 90
The direction of the polarization axis of the linearly polarized laser light source is composed of the twisted nematic liquid crystal element, and the direction of the liquid crystal molecule alignment axis on the side of the linearly polarized laser light source of the parallel alignment type liquid crystal element and the 90 degree twisted nematic liquid crystal element. 3. The optical device according to claim 2, wherein the optical device substantially coincides with the following.