CN100365442C - Optical pickup and its optical components - Google Patents

Abstract

The present invention discloses a miniaturized and easy-to-operate optical pickup for a reproducing device and its optical element, in which a diffraction grating pattern is formed outside a desired area provided near the center of a birefringent plate, and the diffraction grating pattern has a predetermined Width and length, and has a specified thickness in the direction of the incident optical axis, which is composed of a periodically formed ion exchange region and a dielectric film formed on the region, and passes through the normal light of the aforementioned birefringent plate The above-mentioned diffraction grating mode and the 0th order diffracted wave of the extraordinary light are blocked by the diffraction grating mode, so that the thickness of the above-mentioned ion exchange region and the film thickness of the above-mentioned medium can be set.

Description

Optical pickup and its optical components

Industrial Utilization Area

The present invention relates to an optical pick-up and its optical element, especially to an optical pick-up applicable to storage media of different thicknesses and two optical storage media having different distances from a predetermined position to the surface of the storage medium.

prior art

Since a digital video disc (DVD: digital·Video·disk) has a storage capacity 6 to 8 times that of a popular compact disc (CD) or laser disc (LD), it is a memory medium of a new era that attracts attention.

While improving the memory density on the disk, DVD ensures a large amount of memory capacity by increasing the number of openings (NA) of the objective lens on the playback device side. That is, increasing the number of openings NA makes use of the The spot diameter of the irradiated laser light is narrowed and concentrated, and the data recorded at high density on the disk surface can be read.

On the other hand, if the aperture number NA of the objective lens is increased, it is easy to accept the influence of aberration or birefringence due to the thickness of the disk, so the allowable value of the inclination angle from the perpendicular to the optical axis disk surface of the optical pickup becomes smaller. , and there is a problem that it becomes an unreproducible state due to the upside-down situation of the disk. The effect of tilt is represented by Ad(NA) ³ , where A is the coefficient and d is the thickness of the disk. Therefore, by thinning the thickness of the disk and shortening the distance for the laser to enter from the surface of the disk and reflect on the memory surface and come out again, DVD expands the allowable tilt angle, even if a larger opening number NA is used. Under certain circumstances, the allowable value of the required inclination angle can also be ensured. Therefore, the thickness of DVD is only 0.6mm, which is half of the thickness t=1.2mm of the previous CD, and the use of an objective lens with a large number of openings can reduce the spot diameter of the laser, so as to achieve stable data reading.

However, the disk-shaped memory medium, CD has been widely popularized in the market, and it is the same as DVD and CD (including VIDEO-CD) in terms of external dimensions and similar use forms, that is, it is expected to use DVD as a high-end From the perspective of sound quality CDs, it is required to provide DVD playback devices that have DVD playback functions and CD playback functions, and ensure compatibility.

In general optical systems, CDs and DVDs with different disk substrate thicknesses are reproduced on the same device. However, when reproducing thicker CDs, it is impossible to read the data after the spot diameter has been expanded. Therefore, it is proposed to adapt to the thickness of the disk. Various processing methods for different 2 optical memory media.

First, the first method: install an optical pickup for a disk (DVD) with a thickness of 0.6mm and an optical pickup for a disk (CD) with a thickness of 1.2mm in the reproduction device, and switch the optical pickup according to the type of disk to be reproduced. device.

However, the method of installing a plurality of optical pickups has a problem of increasing the size of the playback device and increasing the cost.

The second method is to install an objective lens for DVD and an objective lens for CD on the optical pickup, and switch the objective lens in response to reproducing the disk, but this method also has a problem of increasing the size of the reproducing device.

And the third method is a method of realizing two focal lengths in one optical pickup as disclosed in JP-A-7-311945. This is as shown in Figure 8, switching the power device of the light source 1, thereby showing the difference in the beam diameters emitted from the light source, and generating different focal distances 18a, 18b by the beams 17a, 17b with different diameters entering the objective lens beam method. Such an optical pickup contributes to the miniaturization of the device compared with the above-mentioned first and second methods.

However, the above-mentioned third method is very dependent on the light source, and there is a possibility that the required light cannot be obtained due to the deterioration of the light source over time. error, and there is a possibility of reading errors due to fluctuations in the diameter of the light spot irradiated on the disk.

The present invention is made in view of the above problems, and an object of the present invention is to provide an optical pickup and an optical element thereof that contribute to miniaturization of a playback device and are easy to handle.

disclosure of invention

In the optical element (birefringent thin plate) related to the present invention to achieve this purpose, a diffraction grating pattern is formed outside the required area near the center of the birefringent plate, and the diffraction grating pattern has a predetermined width and length. It has a thickness defined by the direction of the incident optical axis, and is composed of periodically formed ion exchange regions and a dielectric film formed on the ion exchange regions.

The normal light of the aforementioned birefringent plate passes through the aforementioned diffraction grating mode and the 0th order diffracted wave of the extraordinary light is blocked by the diffraction grating mode, so that the thickness of the above-mentioned ion exchange region and the aforementioned dielectric film can be set. The thickness is its characteristic.

In particular, the refractive index for ordinary light and the refractive index for extraordinary light of the aforementioned birefringent plate are various n ₁₀ and n _1e , and the refractive index for ordinary light and the refractive index for extraordinary light in the aforementioned ion exchange region are Ratio and thickness as various n ₂₀ , n _2e , d ₂ , and the refractive index and film thickness of the aforementioned dielectric film as various n ₃ , d ₃ , in order to satisfy the following formula:

(n ₁₀ -n ₂₀ )d ₂ +(1-n ₃ )d ₃ =0

(n _1e -n _2e )d ₂ +(1-n ₃ )d ₃ =λ/2

It is characterized by being able to set the thickness _d2 of the ion exchange region and the film thickness _d3 of the dielectric film.

It also relates to the optical element (birefringent sheet) of the present invention.

A diffraction grating pattern is formed outside the required area near the center of the birefringent plate. The diffraction grating pattern has a specified width and length and a specified thickness according to the direction of the incident optical axis. It is a birefringence formed periodically. Concave-convex made of a non-conductive material and an ion-exchange region having a predetermined thickness in the direction of the incident optical axis formed in the concavity.

The extraordinary light of the birefringent plate passes through the diffraction grating mode, and the 0th order diffracted wave of the normal light is blocked by the diffraction grating mode, so that the thickness of the protrusion and the ion exchange region can be set. The thickness is its characteristic.

In particular, n 10 , n 1e , and d 1 are various n ₁₀ , n _1e , and d ₁ for the refractive index for ordinary rays, the refractive index for extraordinary rays, and the thickness of the convex portion made of the above-mentioned birefringent material. When the refractive index of light, the refractive index and thickness of extraordinary light are used as various n ₂₀ , n _2e , d ₂ , it must satisfy the following formula:

(n ₁₀ -1)d ₁ +(n ₁₀ -n ₂₀ )d ₂ =λ/2

(n _1e -1)d ₁ +(n _1e -n _2e )d ₂ =0

It is characterized by being able to set the thickness _d1 of the protrusion and the thickness _d2 of the ion exchange region.

Furthermore, the predetermined area provided near the center of the birefringent plate is characterized by being a circular area.

Also have the optical pick-up that has used above-mentioned optical element relevant to the present invention, on the optical axis of the light emitted from the light source, non-polarized light beam splitter, aforementioned optical element, object lens and change polarization direction device are arranged, and borrow The device for changing the polarization direction is arranged between the aforementioned non-polarized beam splitter and the aforementioned optical element, so that the polarization direction of the linearly polarized light incident on the optical element can be changed, and the light beam emitted by the aforementioned optical element can be restricted. It is characterized by changing the focal length of the collected light according to the aforementioned objective lens.

A brief description of the graphics

FIG. 1 is a diagram showing the overall configuration of an optical pickup according to the present invention.

Fig. 2 is a perspective view illustrating the structure of a first embodiment of a birefringent thin plate according to the present invention.

Fig. 3 is an A-A sectional view of the birefringent sheet 5 of the present invention shown in Fig. 2 .

Fig. 4 is a perspective view illustrating the function of the first example of the birefringent thin plate of the present invention.

Fig. 5 is a diagram for explaining changing the focal length of the optical pickup according to the present invention.

Fig. 6 is a cross-sectional view illustrating a second example of the birefringent sheet of the present invention.

Fig. 7 is a perspective view for explaining the function of the second type example of the birefringent thin plate of the present invention.

Fig. 8 is a diagram showing the configuration of a conventional optical pickup.

Description of figure number

1 light source

2 objective lenses

3 beam splitters

4 1/2 wavelength plate

5 birefringent sheet

6 pairs of objective lenses

7 Optical memory media

8 Concentrating mirrors

9 cylindrical mirror

10 light detector

The best form for the implementation of the drawing

The implementation forms of the present invention will be described in detail below with reference to the drawings.

Fig. 1 shows the overall configuration diagram of the optical pickup of the present invention, 1 is a light source, 2 is a lens, 3 is a beam splitter, 4 is a 1/2 wavelength plate, 5 is a birefringent thin plate, 6 is an objective lens, 7 Is an optical memory medium, 8 is a narrow aperture, 9 is a cylindrical mirror, and 10 is a light detector.

The aforementioned 1 light source uses, for example, a laser diode, and emits a beam of constant power. Also, if the light beam from the light source is linearly polarized or requires a required optical element, such as using a polarizing beam splitter, etc., it will only contain a single linearly polarized component. at right angles.

The aforementioned lens 2 is an aiming lens that changes the beam from the 1 light source into a parallel beam. The aforementioned beam splitter in 3 is a non-polarized beam splitter (Non Poralized Beam Splitter), which is to guide the light beam reflected on the memory surface of the optical memory medium in 7 to the photodetector in 10.

The 1/2 wavelength plate, which is a means to change the polarization direction of the incident light incident on the optical memory medium, is made into a structure that can be installed on or detached from the optical axis according to needs, and the 1/2 wave plate The optical axis of the /2 wavelength plate 4 is installed so that the polarization direction of the incident linearly polarized light is inclined at 45°. Based on this, depending on whether the 1/2 wavelength plate 4 can be installed on the optical axis, the polarization direction of the incident linearly polarized light incident on the birefringent thin plate can be smoothly rotated by 90°.

The birefringent thin plate 5 is, as shown in FIG. 2, made of a rectangular flat plate (birefringent plate) 11 made of a transparent birefringent material such as _LiNiO3 . The area formed by the birefringence material of the diffraction grating mode forms an optical diffraction grating mode outside the circular portion 12 . To describe the structure of this diffraction grating mode in detail, Fig. 3 is a cross-sectional view of the birefringent sheet 5A-A shown in Fig. 2 , and the main surface of the birefringent sheet 11 is formed with a specified width and length and on the incident optical axis The ion exchange region 13 with thickness _d2 in the direction has a dielectric film with thickness _d3 formed thereon.

The transmittance I ₀ of the directly transmitted wave (zero-order diffracted wave) among the light passing through this mode can be expressed by the following formula:

I ₀ =COS ² (δ/2)

(However, δ: the phase difference of the light on the optical path a, b)

However, the aforementioned phase difference is different in the case of the polarized light component (ordinary ray) in which the optical axis of the aforementioned double refraction plate is at right angles to the polarized light component (abnormal ray) in parallel to the aforementioned optical axis. Difference δ. and the phase difference δ _e for the extraordinary ray are each as follows.

δ _o ＝2π/λ{(n ₁₀ -n ₂₀ )d ₂ +(1-n ₃ )d ₃ }

δ _e =2π/λ{(n _1e -n _2e )d ₂ +(1-n ₃ )d ₃ }

However, n ₁₀ : is the refractive index of ordinary ray with respect to the birefringent plate, n _1e : is the refractive index of extraordinary ray with respect to the birefringent plate, and n ₃ : is the refractive index of ordinary ray and extraordinary ray with respect to the dielectric film.

Here, by setting d ₂ and d ₃ to make (n ₁₀ -n ₂₀ )d ₂ +(1-n ₃ )d ₃ =0, and the transmittance to normal light I ₀₀ =1, it can pass through All 0th diffracted waves. Also by setting d ₂ and d ₃ to make (n _1e -n _2e )d ₂ +(1-n ₃ )d ₃ =λ/2, and the transmittance to the extraordinary light I _oe =0, then all The 0th diffracted wave.

Therefore, as shown in Figure 4(a), there is a light beam with a polarization direction at right angles to the optical axis of the birefringent plate 11, that is, the normal light completely passes through the birefringent thin plate, and as shown in Figure 4(b), the polarized light is parallel to the optical axis The light beam of the directional component, that is, the extraordinary light diffracted by the above-mentioned diffraction grating mode, transmits only the light beam irradiated on the circular part 12 with the same pupil diameter as the diameter of the circular part 12. of.

Table 1

sample                     Light transmittance of birefringent thin plate normal light Abnormal light 0 light +1 light -1 light 0 light +1 light -1 light 12345678910 94.494.393.794.393.794.194.294.193.293.7 0.00.00.00.00.00.00.00.00.00.0 0.00.00.00.00.00.00.00.00.00.0 1.50.81.80.91.50.81.70.81.30.8 35.335.434.735.434.935.135.135.534.935.4 35.235.334.635.334.834.934.935.434.635.1 average 94.0 0.0 0.0 1.2 35.2 35.0

Table 1 is a table showing the experimental results of measuring the transmittance of light incident on the diffraction grating mode of the birefringent plate, and the thickness _d2 of the ion exchange region 13 of the birefringent plate 5 in FIG. 3 is set to 9.5 μm , set the thickness d ₃ of the dielectric film 14 as 1.85 μm, set the pitch of the diffraction grating mode as 12 μm, and set the wavelength λ of the incident light beam as 636 nm, which means that each of the 10 samples incident to the normal The light transmittance of 0-order and ±1-order diffracted waves (0-order and ±1-order light components) for light rays and extraordinary rays.

As shown in the table, it can be seen that when ordinary light rays enter the birefringent sheet 5, the transmittance of the zero-order light passing through the birefringent sheet 5 is 94.0% on average, and the transmittance of ±1st-order light becomes 0.0%. , and almost the incident light can pass through without diffraction by the diffraction grating mode.

It can also be seen that once the extraordinary light is incident on the birefringent thin plate 5, the transmittance of the 0th order light passing through the birefringent thin plate 5 is 1.2% on average, the transmittance of the +1st order light is 35.2%, and -1 The transmittance of the secondary light is 35.0%, and the 0th-order light at the directly transmitted wave of the incident light is hardly obtained, and it appears as ±1-order light.

It is also clear from the above results that the normal light beams of the light beams traveling in the same direction as the incident optical axis are transmitted by the birefringent thin plate 5 and the abnormal light rays are blocked.

In addition, the objective lens 6 is used to concentrate the image points on the memory surface of the optical memory medium, and the aforementioned birefringent thin plate 5 and the objective lens 6 are fixed into one body by the holder 15 and made into a unit.

In the optical pickup of the above structure, at first, the 1/2 wavelength plate 4 is kept in a state not inserted on the optical axis, and the light beam emitted from the light source 1 becomes a parallel light beam by the collimator 2, and then or incident on the birefringent sheet 5 passing through the beam splitter 3 . At this time, the polarization direction of the incident light beam is at right angles to the optical axis of the birefringent thin plate 5 .

As mentioned above, the birefringent thin plate 5 forms a diffraction grating pattern outside the circular portion 12, so the diameter of the linearly polarized beam incident on the birefringent thin plate 5 and the beam emitted from the beam splitter 3 have the same diameter. through. On the other hand, once the 1/2 wavelength plate 4 is inserted on the optical axis, the polarization direction of the linearly polarized light incident on the birefringent thin plate 5 is rotated by 90 degrees, and because the birefringent thin plate 5 will become one of the extraordinary rays Therefore, the linearly polarized light incident on the birefringent thin plate 5 is diffracted at the diffraction grating mode, and only the light beam passing through the circular portion 12 has a pupil diameter equal to the circular shape of the circular portion 12 (No. 2 pupil diameter) through.

Therefore, as shown in FIG. 5 , the light beam passing through the birefringent thin plate 5 enters the objective lens 6 and is concentrated to the junction point to form a light spot on the memory surface of the optical memory medium as a focal point. At this time, because the focal distance of the objective lens 6 has the relationship that when the pupil diameter of the incident light beam is large, it is short and the pupil diameter is small, the focal distance is long, so the focal distance of the first pupil diameter is short, and the focal distance of the second pupil diameter will become shorter. long.

And the light beam reflected on the memory surface of the optical memory medium passes through the objective lens 6, the birefringent thin plate 5 and enters the beam splitter again, but its part is reflected, and enters the light beam through the reducing mirror 8 and the cylindrical mirror 9. on detector 10. Therefore, the recorded data on the optical storage medium can be read.

In the case of reproducing the optical memory medium (CD) of t=1.2mm on the above-mentioned optical pickup, by inserting the 1/2 wavelength plate 4 on the optical axis, the polarization direction of the linearly polarized light incident on the birefringent thin plate 5 The optical axis of the birefringent thin plate is parallel to the optical axis so that it can smoothly complete the rotation, and smoothly complete the diffraction of the light entering the diffraction grating mode. Utilize this to make the light beam passing through the birefringent thin plate 5 equal to the diameter of the circular area (the second pupil diameter) arranged at the central part of the birefringent thin plate 5, and form an image at a long focal distance as shown in FIG. The dots are connected to form light dots on the aforementioned optical memory medium.

Under the situation of desiring to reproduce the optical memory medium (DVD) of t=0.6mm again, utilize to pull down 1/2 wavelength plate 4 from the optical axis, the polarization direction of the linearly polarized light that just enters the birefringent thin plate 5 is in the same direction as the aforementioned optical axis. At right angles, since the light beam from the light source enters the objective lens 6 while maintaining the formed state (the first pupil diameter) through the cylindrical mirror 2, it is connected at the short focal distance junction point as shown in Figure 3, and in the aforementioned Light spots are formed on the optical memory medium.

In addition, in the above description, it has been explained that the 1/2 wavelength plate is inserted on the optical axis to obtain the first pupil diameter, and the 1/2 wavelength plate is removed from the optical axis to obtain the second pupil diameter. , but comparing the polarization direction of the light incident on the 1/2 wavelength plate with the above example, it can also be changed by moving the 1/2 wavelength plate on the optical axis by shifting 90°. The second pupil diameter can be obtained and the first pupil diameter can be obtained by removing the 1/2 wavelength plate from the optical axis.

FIG. 6 is a diagram showing an example of a second form of the birefringent sheet 5, and is a cross-sectional view of the birefringent sheet 5. As shown in FIG. In this figure, a concave-convex portion 16 is provided on the main surface of the birefringent thin plate 11, and the concave-convex portion 16 is composed of a convex portion having a predetermined width and length and a thickness _d1 in the direction of the incident optical axis. , and the bottom surface of the concave portion faces the direction of the incident optical axis to form an ion exchange region 14 with a thickness _d2 .

As mentioned above, the transmittance I _o of the directly transmitted wave (0th order diffracted wave) of the light passing through this mode is:

I _o ＝COS ² (δ/2)

It can be represented by δ: optical path a, b: phase difference of light, but the phase difference is polarized light parallel to the optical axis in the case of a polarized light component (ordinary light) at a right angle to the optical axis of the birefringent plate It is different in the case of the component (extraordinary ray), which has a phase difference δ for the ordinary ray and a phase difference δ _e for the extraordinary ray.

δ _o =2π/λ{(n ₁₀ -1)d ₁ +(n ₁₀ -n ₂₀ )d ₂ }

δ _e =2π/λ{(n _1e -1)d ₁ +(n ₁₀ -n _2e )d ₂ }

However, n ₁₀ : is the refractive index of ordinary rays with respect to the birefringent plate, n _1e : is the refractive index of extraordinary rays with respect to the birefringent plate, n ₂₀ : is the refractive index of ordinary rays with respect to the ion exchange region, and n _2e : is the refractive index for the extraordinary light in the ion exchange region.

Here, by setting d ₁ and d ₂ so that (n ₁₀ -1)d ₁ +(n ₁₀ -n ₂₀ )d ₂ =λ/2, and the transmittance for normal light I _oo =0, it can block All 0th diffracted waves. Furthermore, by setting d ₁ and d ₂ to make (n ₁₀ -1)d ₁ +(n ₁₀ -n ₂₀ )d ₂ = 0, and the transmittance I _OE = 1 for the extraordinary light can pass through All 0th diffracted waves.

Therefore, as Fig. 7 (a) has the light beam of the polarization direction that is at right angles to the optical axis of birefringent plate 11, that is to say normal light is diffracted on the aforementioned diffraction grating mode, and for only being irradiated on pattern portion 12 The light beam on the top is transmitted, so it is transmitted with a pupil diameter equal to the diameter of the circular part 12, and as shown in Figure 7, the light beam of the polarization direction component parallel to the optical axis, that is, the extraordinary light completely passes through the birefringence sheet.

The birefringent sheet 5 with the above-mentioned structure is opposite to the relationship between the birefringent sheet 5 shown in the first form example and the polarization direction of the incident light and the pupil diameter, and has the same function, so it can respond to the incident light. The direction of polarization changes the pupil diameter of the light beam and enables different focal distances to the optical memory medium.

In the above form example, the λ/2 wavelength plate is inserted into the optical path or removed to change the polarization direction of the light, but by using the so-called polarization beam splitter to rotate it by 90° around the optical axis, or to make it It is also possible to change the direction of the linearly polarized light incident on the birefringent sheet 5 by changing the voltage applied to the liquid crystal panel.

In addition, although the circular part 12 was used in each of the above-mentioned form examples, it is also possible to change the circular part into a polygonal structure.

As explained above, the optical pickup of the present invention deforms the pupil diameter of the light beam by switching the polarized light component of the light source. According to this, the focal distance matching the thickness of the optical memory medium disk is changed, so compared with the original Its structure is simple, and it has a remarkable effect in miniaturizing the playback device. Furthermore, since the focus distance does not change greatly due to the error in the output of the light source, it is also effective in achieving operational stability of the optical pickup.

Claims (8)

1. birefringence assembly, be possess birefringent plate, be positioned at this birefringent plate interarea central authorities flat site and be formed on the birefringence assembly of diffraction grating pattern of the exterior lateral area of this flat site, it is characterized by:

Aforementioned diffraction grating pattern is made of ion-exchange zone that is formed at aforementioned birefringent plate interarea and the top deielectric-coating that is formed at this ion-exchange zone,

The structure in aforementioned ion-exchange zone is, the thickness that has regulation in incident light axis direction with the interarea quadrature of birefringent plate, and possess periodic palisade pattern in a direction along interarea;

Aforementioned deielectric-coating is lamination on the palisade pattern that constitutes aforementioned ion-exchange zone;

The thickness in aforementioned ion-exchange zone and the thickness of aforementioned deielectric-coating are set to, and ordinary ray sees through the diffraction grating pattern, and 0 diffracted wave of extraordinary light is stopped by the diffraction grating pattern.

2. birefringence assembly as claimed in claim 1, wherein:

If be respectively n for the refractive index of the ordinary ray of aforementioned birefringent plate with for the refractive index of extraordinary light _1o, n _1e, and establish refractive index for the ordinary ray in aforementioned ion-exchange zone, the refractive index and the thickness of extraordinary light is respectively n _2o, n _2e, d ₂, refractive index and the thickness of establishing aforementioned deielectric-coating are respectively n ₃, d ₃The time, with aforementioned ion-exchange zone thickness d ₂Thickness d with deielectric-coating ₃Be set at and satisfy following formula:

(n _1o-n _2o)d ₂+(1-n ₃)d ₃＝0

(n _1e-n _2e)d ₂+(1-n ₃)d ₃＝λ/2。

3. birefringence assembly, be possess birefringent plate, be positioned at this birefringent plate interarea central authorities flat site and be formed on the birefringence assembly of diffraction grating pattern of the exterior lateral area of this flat site, it is characterized by:

Aforementioned diffraction grating pattern possesses the palisade jog that is formed at aforementioned birefringent plate interarea and is formed in each recess and has in the incident light axis direction with the interarea quadrature of birefringent plate the ion-exchange zone of specific thickness;

The thickness in the thickness of aforementioned protuberance and aforementioned ion-exchange zone is set to, and extraordinary light sees through the diffraction grating pattern, and 0 diffracted wave of ordinary ray is stopped by the diffraction grating pattern.

4. birefringence assembly as claimed in claim 3, wherein:

Setting is for the refractive index of the ordinary ray of the protuberance that is made of described birefringence material, be respectively n to the refractive index and the thickness of extraordinary light _1o, n _1e, d ₁, establish refractive index, the refractive index and the thickness of extraordinary light be respectively n for the ordinary ray in aforementioned ion-exchange zone _2o, n _2e, d ₂The time, with the thickness d of aforementioned protuberance ₁And the thickness d in ion-exchange zone ₂Be set at and satisfy following formula:

(n _1o-1)d ₁+(n _1o-n _2o)d ₂＝λ/2

(n _1e-1)d ₁+(n _1e-n _2e)d ₂＝0。

5. as each described birefringence assembly in the claim 1,2,3,4, wherein, the required zone that is located at the cardinal principle centre of aforesaid birefringent plate is made of the birefringence material.

6. as each described birefringence assembly in the claim 1,2,3,4, wherein, the required zone that is located at the cardinal principle centre of aforesaid birefringent plate is that the circular regions by birefringent material constitutes.

7. light picker is characterized by:

On the optical axis of the light that penetrates from light source, in turn possess;

Finder lens,

The beam splitter of no polarized light type,

1/2 wavelength plate,

The birefringence assembly, and

Object lens;

Wherein, described birefringence assembly be possess birefringent plate, be positioned at this birefringent plate interarea central authorities flat site and be formed on the birefringence assembly of diffraction grating pattern of the exterior lateral area of this flat site,

Aforementioned diffraction grating pattern is made of ion-exchange zone that is formed at aforementioned birefringent plate interarea and the top deielectric-coating that is formed at this ion-exchange zone,

The structure in aforementioned ion-exchange zone is, the thickness that has regulation in incident light axis direction with the interarea quadrature of birefringent plate, and possess periodic palisade pattern in a direction along interarea;

Aforementioned deielectric-coating is lamination on the palisade pattern that constitutes aforementioned ion-exchange zone;

The thickness in aforementioned ion-exchange zone and the thickness of aforementioned deielectric-coating are set to, and ordinary ray sees through the diffraction grating pattern, and 0 diffracted wave of extraordinary light is stopped by the diffraction grating pattern;

By above-mentioned 1/2 wavelength plate being disposed between aforementioned no polarized light type beam splitter and the aforementioned birefringence assembly, can change the polarization direction that incides the linear polarization on the aforementioned birefringence assembly, and from the beam diameter that aforementioned birefringence assembly penetrates, can change the focal length of the light of aforementioned object lens focusing by restriction.

8. light picker is characterized by:

On the optical axis of the light that penetrates from light source, in turn possess;

Finder lens,

The beam splitter of no polarized light type,

1/2 wavelength plate,

The birefringence assembly, and

Object lens,

Wherein, described birefringence assembly is the flat site that possesses birefringent plate, is positioned at the interarea central authorities of this birefringent plate.And be formed on the birefringence assembly of diffraction grating pattern of the exterior lateral area of this flat site,

Aforementioned diffraction grating pattern possesses the palisade jog that is formed at aforementioned birefringent plate interarea and is formed in each recess and has in the incident light axis direction with the interarea quadrature of birefringent plate the ion-exchange zone of specific thickness;

The thickness in the thickness of aforementioned protuberance and aforementioned ion-exchange zone is set to, and extraordinary light sees through the diffraction grating pattern, and 0 diffracted wave of ordinary ray is stopped by the diffraction grating pattern;

By above-mentioned 1/2 wavelength plate being disposed between aforementioned no polarized light type beam splitter and the aforementioned birefringence assembly, can change the polarization direction that incides the linear polarization on the aforementioned birefringence assembly, and from the beam diameter that aforementioned birefringence assembly penetrates, can change the focal length of the light of aforementioned object lens focusing by restriction.

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