JP2786352B2 - Variable focus optics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable focal length optical device for electrically changing a focal length.

[0002]

2. Description of the Related Art As a means for changing the focal length of an optical system, it is common to mechanically move a lens constituting the optical system or the optical system itself along the optical axis direction. On the other hand, as a method of electrically changing the focal length of an optical system, as disclosed in Japanese Patent Application Laid-Open No. 63-249125, a transmission type liquid crystal panel capable of electrically generating an image pattern and an optical lens are combined. Those are known. According to this method, a pattern of a Fresnel zone plate is generated in a transmission type liquid crystal panel, and a spatial frequency of the Fresnel zone plate is electrically controlled, so that a combined focal length of an optical system combining a transmission type liquid crystal panel and an optical lens. Is changing.

FIG. 6 is an explanatory view showing an example of a Fresnel zone plate in a conventional variable focus optical device, and FIG.
FIG. 8 is a configuration diagram showing a variable focal point optical device using the Fresnel zone plate of FIG. 6, and FIG. 8 is an explanatory diagram showing a liquid crystal panel constituting the Fresnel zone plate of FIG.

As shown in FIG. 6, the pattern of the Fresnel zone plate is a pattern in which transparent (white area in the figure) and opaque (black area in the figure) are alternately repeated. The spatial frequency, that is, the reciprocal of the spatial pitch, is proportional to the distance r from the center O. Therefore,
The Fresnel zone plate functions as a focusing lens having a certain focal length, like a normal optical lens.

The focal length of the Fresnel zone plate is inversely proportional to the spatial frequency of the concentric annular zone pattern, and decreases as the spatial frequency increases.

When a uniform parallel plane wave is applied to the Fresnel zone plate, the amplitude transmittance g (r) of the light wave of the Fresnel zone plate is expressed by the following equation (1).

[0007]

(Equation 1)

In the above equation, r ₀ is the distance from the center O of the ring shown in FIG. 6 to the center of the first ring, and n is an integer. The area from the center O of the orbicular zone where g (r) = 1 to the distance r is the transparent area shown in FIG. 6, and g (r)
An area up to a distance r where = 0 is an opaque area. In this case, the focal length f of the Fresnel zone plate expressed by Expression (1) is expressed by Expression (2).

[0009]

(Equation 2)

[0010] In (2), lambda is the wavelength of a light wave, r ₀ is consistent with Equation 1 r _0. Therefore, a lens having a desired focal length can be formed by electrically configuring a Fresnel zone plate having an appropriate spatial frequency on the liquid crystal panel. However, there is a limit to the spatial frequency that can be displayed by a liquid crystal panel. Therefore, usually, an optical system having a shorter focal length is configured by combining with an optical lens. Focal length f ₁ ,
When configuring the combination lens in close contact with two lenses of f _2, the combined focal length f is approximated by equation (3).

[0011]

(Equation 3)

As shown in FIG. 7, in an optical device using an optical lens 31 having a focal length f ₁ and a transmission type liquid crystal panel 30 having a focal length f ₂ , the transmission type liquid crystal panel 30 is used.
By controlling the spatial frequency of the upper Fresnel zone plate by the controller 32, the focal lengths f ₁ and f ₂
A variable focal length optical device having a shorter and variable composite focal length f can be configured.

The liquid crystal panel 30 may be a phase modulation type (amplitude modulation type) instead of a transmittance modulation type such as a liquid crystal television. In this case, in the Fresnel zone plate, only the refractive index of the white area and the black area shown in FIG. 6 changes, and the transmittance does not change. Therefore, the phase modulation type panel has higher light diffraction efficiency, that is, utilization efficiency. It is advantageous.

As the transmissive liquid crystal panel 30, not only a liquid crystal television or the like having pixels arranged in a matrix but also a transmissive modulation type pixel 33 formed concentrically as shown in FIG. May be used.

[0015]

However, the conventional variable focal length optical apparatus in which the focal length is changed by mechanical driving requires mechanical parts, so that the overall configuration becomes large and the structure becomes complicated. There is a problem that becomes.

On the other hand, in the above-mentioned conventional variable focal length optical device in which the focal length of the optical system is electrically changed, the above-mentioned problem can be solved. It must be formed for each pixel of the zone plate pattern.
Therefore, there is a limit in increasing the density of pixels and improving the spatial resolution, and the focal length f of the Fresnel zone plate is limited.
₂ cannot be shortened. That is, when f ₁ (focal length of the lens) << f ₂ (focal length of the Fresnel zone plate), as is apparent from the equation (3), the combined focal length f cannot be largely changed.

Accordingly, the present invention provides a variable focal length optical device having a wide variable focal length range.

[0018]

According to the present invention, a first spatial light modulating means including a plurality of light modulating elements and a light emitting surface of the first spatial light modulating means including a plurality of light modulating elements are provided. A second spatial light modulating means having an incident surface, and an optical lens , wherein the first and second spatial light modulating means and an optical lens are provided.
Are arranged in series along the optical axis direction, and the center of the exit surface of the light modulating element of the first spatial light modulating means and the center of the incident surface of the corresponding light modulating element of the second spatial light modulating means. Are arranged so as to be displaced from each other, and are configured so that a part of the light emitted from the light modulating element of the first spatial light modulating means enters the corresponding light modulating element of the second spatial light modulating means. An optical device is provided.

[0019]

According to the variable focus optical device of the present invention, the first
The center of the exit surface of the light modulating element of the spatial light modulating means and the center of the incident surface of the corresponding light modulating element of the second spatial light modulating means are arranged so as to be shifted from each other. Since a part of the light emitted from the light modulating element is configured to be incident on the corresponding light modulating element of the second spatial light modulating means, each of the light beams passing through the light modulating element of the first spatial light modulating means The light is split and incident on at least two light modulation elements corresponding to the second spatial light modulation means. Specifically, of the light incident on the first spatial light modulating means, the light flux incident on one light modulating element is modulated and transmitted or reflected by this light modulating element, and is adjacent to the second spatial light modulating means. The light enters the two light modulation elements separately. The light beams incident on the two light modulation elements are separately light-modulated. Therefore, the second
If the modulation amounts of two adjacent light modulating elements of the spatial light modulating means are different, the spatial resolution can be improved without reducing the size of each light modulating element of the spatial light modulating means. Becomes

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a variable focus optical device according to the present invention, FIG. 2 is an explanatory diagram showing pixels of the two electric address type spatial light modulators of FIG. 1, and FIG. FIG. 4 is an explanatory diagram showing a positional relationship between pixels of the two electric address type spatial light modulators.

As shown in FIG. 1, the variable focus optical device comprises:
Two electrically addressable spatial light modulators 10, 11 and an optical lens
12 and electrically addressable spatial light modulators 10, 11
Are both constituted by a phase modulation type liquid crystal panel.
The variable focus optics further comprises a controller 13, and the electrically addressed spatial light modulators 10, 11 are respectively connected to the controller 13 by connection lines 14. still,
The electric address type spatial light modulator corresponds to a spatial light modulator.

The electric address type spatial light modulator used in this embodiment is of a transmission type. As shown in FIG. 1, first and second electric address type spatial light modulators 10 and 11 and an optical lens 12 are provided.
Are arranged in series along the optical axis direction. That is, the first
The light that has entered the electrical address type spatial light modulator 10 is subjected to light modulation and transmitted therethrough, and then has a second electrical address having an incident surface parallel to the emission surface of the first electrical address type spatial light modulator 10. After entering the spatial light modulator 11 and further modulating and transmitting the light, the light enters the optical lens 12 and is condensed to a focal point.

Each electric address type spatial light modulator includes a plurality of light modulation elements. In a phase modulation type liquid crystal panel, the light modulation elements correspond to pixels. A voltage is applied to each pixel by the controller 13, which changes the refractive index of each pixel. At this time, the change in the refractive index is controlled to be different for each pixel. Therefore, the phase of the light incident on the electric address type spatial light modulator changes in each pixel, and the degree of modulation, that is, the modulation amount differs in each pixel.

As shown in FIG. 2, the pixels of the electric address type spatial light modulators 10 and 11 are formed concentrically, and the pixels of the first electric address type spatial light modulator 10 emit light. The center of the surface and the center of the incident surface of the pixel of the second electrically-addressable spatial light modulator 11 are arranged to be shifted in the radial direction by half the pixel pitch. That is, for example, the luminous flux transmitted through the pixel 15 of the first electric address type spatial light modulator 10 is split into the pixel 16 and the pixel 17 of the second electric address type spatial light modulator 11 so as to be incident. Each pixel of the electric address type spatial light modulators 10 and 11 is arranged.

Accordingly, the luminous flux split into the pixels 16 and 17 of the second electrically-addressed spatial light modulator 11 is further phase-modulated by the second electrically-addressed spatial light modulator 11, respectively. As shown in FIG. 3, the phase modulation amount of the region 18 is determined by the pixel 15 of the first electrically-addressed spatial light modulator 10 and the pixel 16 of the second electrically-addressed spatial light modulator 11 shown in FIG.
The phase modulation amount of the region 19 is the sum of the phase modulation amounts of the pixel 15 of the first electric address type spatial light modulator 10 and the second electric address type spatial light modulator 11. Pixel 17
Is the amount obtained by adding the phase modulation amounts of. Such addition is performed for other pixels.

As a result, the spatial resolution of one electrical address type spatial light modulator can be doubled, the spatial frequency of the Fresnel zone plate is doubled, and the shortest focal length is reduced to about 1/2. It is possible to do. Therefore, the variable range of the combined focal length f shown in the equation (3) can be extended about twice.

When the phase of the light is changed by 2π (360 °), the phase of the light coincides with that of the original light.
It is enough to perform in the range of. Furthermore, the phase is set to 2
Even if it is changed in the range of mπ (m is 0 or a positive integer), spatially the same phase modulation pattern is obtained. Therefore, even if it is configured by using three or more electric address type spatial light modulators, Although the phase of light changes by 2π or more as a whole, the same effect as described above can be obtained.

Next, a second embodiment will be described. FIG. 4 is an explanatory diagram showing pixels of two electric address type spatial light modulators 20 and 21 in a second embodiment of the variable focal length optical device according to the present invention, and FIG. 5 is a diagram showing two electric addresses of FIG. FIG. 3 is an explanatory diagram showing a positional relationship between pixels of the spatial light modulators 20 and 21.

As shown in FIG. 4, the pixels of the electric address type spatial light modulators 20 and 21 are formed in the same concentric circle, and are divided into four by 90 ° in the circumferential direction. The division is made such that the center of the emission surface of the pixel of the first electrically addressed spatial light modulator 20 and the center of the incidence surface of the pixel of the second electrically addressed spatial light modulator 21 are shifted by 45 °. . That is, for example, a first electrical address type spatial light modulator
The pixels of the electric address type spatial light modulators 20 and 21 are separated so that the light flux transmitted through the 20 pixels 22 is split into the pixels 23 and 24 of the second electric address type spatial light modulator 21 and enters. Are located. In this embodiment, the electric address type spatial light modulator also corresponds to a spatial light modulator.

Accordingly, the luminous flux split into the pixel 23 and the pixel 24 of the second electric address type spatial light modulator 21 is further phase-modulated by the second electric address type spatial light modulator 21, respectively. As shown in FIG. 5, the amount of phase modulation in the region 25 is determined by the pixel 22 of the first electric address type spatial light modulator 20 and the pixel 23 of the second electric address type spatial light modulator 21 shown in FIG.
The phase modulation amount of the region 26 is the sum of the phase modulation amounts of the pixel 22 of the first electric address type spatial light modulator 20 and the second electric address type spatial light modulator 21. Pixel 24
Is the amount obtained by adding the phase modulation amounts of. Such addition is performed for other pixels.

As described above, in the second embodiment, the resolution in the circumferential direction can be improved by using the two electric address type spatial light modulators configured as described above. The variable focus optical device thus configured is
This is effective when the focal point moves perpendicular to the optical axis,
The focal length can be largely moved in the vertical direction.

In the above embodiment, the pixel shape of the phase modulation type liquid crystal panel, which is an electric address type spatial light modulator, is concentric, but is not limited to this, and may be a matrix.

Although the transmission type electric address type spatial light modulator is used as the spatial light modulation means, a reflection type electric address type spatial light modulator may be used instead. Also,
Instead of an optical lens, a reflecting mirror such as an off-axis parabolic mirror may be used.

[0034]

As described above, according to the present invention,
Each of the light beams that have passed through the light modulating elements of the first spatial light modulating means is split and incident on at least two corresponding light modulating elements of the second spatial light modulating means. Specifically, a light beam incident on one light modulating element of the first spatial light modulating means is modulated and transmitted or reflected by this light modulating element, and the two adjacent light modulating elements of the second spatial light modulating means are modulated. The incident light is split into elements. The light beams incident on the two light modulation elements are separately light-modulated. Therefore, if the modulation amounts of two adjacent light modulation elements of the second spatial light modulation means are different, the spatial resolution can be improved without reducing the size of each light modulation element of the spatial light modulation means. It is possible to do.
Thereby, for example, it is possible to provide a variable focus optical device capable of greatly changing the combined focal length with the optical lens.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a variable focus optical device according to the present invention.

FIG. 2 is an explanatory diagram showing pixels of the two electric address type spatial light modulators of FIG. 1;

FIG. 3 is an explanatory diagram showing a positional relationship between pixels of the two electric address type spatial light modulators in FIG. 1;

FIG. 4 is an explanatory view showing pixels of two electrically-addressable spatial light modulators in a second embodiment of the variable focus optical device according to the present invention.

FIG. 5 is an explanatory diagram showing a positional relationship between pixels of the two electric address type spatial light modulators of FIG. 4;

FIG. 6 is an explanatory view showing a Fresnel zone plate.

7 is a configuration diagram showing a conventional variable focus optical device using the Fresnel zone plate of FIG. 6;

FIG. 8 is an explanatory diagram showing a liquid crystal panel constituting the Fresnel zone plate of FIG.

[Explanation of symbols]

 10, 11 Electrically-addressed spatial light modulator 12 Optical lens 13 Controller 15, 16, 17 pixels

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Terutaka Tokumaru 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/00 -1/335 G02B 27/46

Claims (1)

(57) [Claims] 1. A first spatial light modulating means including a plurality of light modulating elements, and a second space including a plurality of light modulating elements and having an incident surface parallel to an emission surface of the first spatial light modulating means. a light modulating means comprises an optical lens, said first and second
The spatial light modulator and the optical lens are arranged along the optical axis direction.
So that the center of the emission surface of the light modulation element of the first spatial light modulation means and the center of the incidence surface of the corresponding light modulation element of the second spatial light modulation means are shifted from each other. And a part of the light emitted from the light modulating element of the first spatial light modulating means is arranged to enter the corresponding light modulating element of the second spatial light modulating means. Variable focus optical device.