JP2832017B2 - Optical information processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information processing apparatus, and more particularly, to an optical information processing apparatus using a prism optical system suitable for converting the shape of a light beam emitted from a semiconductor laser. is there.

[Conventional technology]

2. Description of the Related Art Conventionally, in an optical information processing apparatus that records and reproduces information on an optical information recording medium by using an optical head, a semiconductor laser is widely used as a monochromatic light source for forming a spot of about 1 μm on the medium. .

A light beam from a semiconductor laser generally has an elliptical cross-sectional shape with an aspect ratio of about 1: 2. In particular, an optical head for recording / reproducing requires a high output at the time of recording, so that it is necessary to effectively use a light beam from a laser.

For this purpose, it has been conventionally known to arrange a triangular prism between lenses for condensing spots from a semiconductor laser and to shape the beam shape (Japanese Patent Application Laid-Open No. Sho 56-41). This will be described with reference to FIG. In FIG. 8, reference numeral 10 denotes a semiconductor laser, 11 denotes a collimator lens for collimating a light beam from the semiconductor laser, and 18 denotes a beam shaping prism. The beam shaping prism 18 shapes the light beam having an elliptical shape (section BB ') as shown in (B) into a substantially circular light beam (section CC') as shown in (C).

Incidentally, the semiconductor laser has a problem that the oscillation wavelength depends on the temperature and the output. For example, in a general semiconductor laser, when the temperature rises by 10 ° C., the wavelength moves to the longer side by about 3 nm, and when the output is increased from 3 mW to 30 mW, the wavelength also increases.
〜4 nm wavelength moves to longer.

The problem will be described with reference to FIG. In FIG. 9, 18 is a beam shaping prism, 12 is an objective lens, and 13 is an optical disk as an optical information recording medium. For example, it is assumed that a light beam from a semiconductor laser having a wavelength of λ ₀ at the time of information reproduction is accurately formed on the information track of the disk 13 by the objective lens 12 after being beam-shaped by the beam shaping prism 18 (solid line in the drawing). Here, when the output of the laser is switched during recording, the wavelength changes to λ ₀ + Δλ ₀ nm (Δλ ₀ = _{3 to 4} nm). Therefore, the refraction angle changes due to the dispersion of the glass of the beam shaping prism 18 and the information track on the disc is changed. Is 0.3 to 0.4 μm, which is shifted in the disk radial direction. Since this wavelength change occurs on the order of nanoseconds, tracking servo tracking cannot be performed, which seriously hinders recording and reproduction of information. Further, even if the wavelength changes due to a temperature change, an offset is generated in the servo signal, which similarly affects the recording and reproduction of information. In order to solve this problem, it is conventionally known that the beam shaping prism 18 is a cemented prism made of two kinds of glass having different dispersions (Japanese Patent Laid-Open No. 60-234247). FIG. 10 shows the configuration of an optical information processing apparatus using the cemented prism. Tenth
In the figure, a material LaSF-16 is used for the triangular prism 19, a right-angled isosceles triangle of material SF11 is used for the triangular prism 20, and a vapor deposition layer having a function as a half mirror is formed on the oblique side 21 of the prism 20. ing.

By affixing these two prisms 19 and 20 made of different materials, an achromatic prism can be obtained, and
After converting the light beam from the semiconductor laser 10 having an elliptical intensity distribution into parallel light by the collimator lens 11, the prism
It can be converted into a light flux having a substantially circular intensity distribution by incident at a predetermined angle theta ₀ to 19. The light beam condensed as a minute light spot on the optical information recording medium 13 by the objective lens 12 is reflected by the medium 13, passes through the objective lens 12 again, is reflected by the half mirror surface 21 of the prism 20, and travels to the detection optical system. . Reference numeral 14 denotes a lens for condensing a light beam on the photodetector 15, and reference numeral 16 denotes an amplifier for amplifying the output of the photodetector 15, which obtains a desired signal (RF signal or servo signal) 17. Fig. 10 shows prism
For example, when the magnification of the incoming / outgoing light beam is set to 2 by the combination of 19 and 20, the apex angle of the prism 19 is α = 76.167 °,
Assuming that the incident light angle on the prism 19 is θ ₀ = 63.315 °,
Even if the oscillation wavelength λ = 830 nm of the semiconductor laser changes by 3 to 4 nm, the deviation of the light emitted from the prism 20 can be suppressed to about 0.4 seconds. This is 0.01 μm or less in terms of the displacement of the light spot focused on the optical information recording medium 13 by the objective lens 12, and has little effect on the recording and reproduction of information.

However, when such prisms of different materials are bonded together, and a vapor deposition layer that functions as a half mirror or a polarizing beam splitter is formed on the bonding surface, when a temperature change occurs, the two glasses are bonded due to a difference in expansion coefficient between the two glasses. The surface is distorted, and an aberration occurs in the wavefront of a light beam transmitted or reflected on the surface. Due to this wavefront aberration, the spot shape on the recording medium changes and the quality of the RF signal is degraded, or the spot shape on the photodetector 15 changes, causing an offset in the servo signal.・ It will hinder regeneration. The effect of the distortion of the bonding surface on the wavefront aberration is much greater when the light beam reflects on that surface (evaporated layer) than when it is transmitted. Therefore, in the example of FIG. 10, aberration occurs in the wavefront reflected by the half mirror surface 21, and the spot shape on the photodetector changes with the temperature change, thereby causing an offset in the servo signal.

In order to solve the above problem, it is only necessary to select different glass materials having the same expansion coefficient. However, in practice, glass having a dispersion that reduces the angular deviation of the light emitted from the prism is selected and their expansion coefficients are selected. It is very difficult to make

Further, since the prism 20 cannot always be formed as a right-angled isosceles triangle, the degree of freedom of the configuration of the optical head detecting optical system is limited in that case.

[Summary of the Invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the above-described problems in a conventional prism optical system or an apparatus using the same, and to provide an optical system capable of controlling a change in wavelength of a light beam and a change in temperature. It is an object of the present invention to provide an optical information processing apparatus using a prism optical system whose characteristic does not change.

The object of the present invention is to provide a semiconductor laser, a collimator lens that converts a light beam from the semiconductor laser into a parallel light beam, and a beam splitter that corrects the shape of the parallel light beam and extracts a reflected light beam from an optical information recording medium. Optical information processing system comprising: a functioning prism optical system; an objective lens for focusing a light beam from the prism optical system on the optical information recording medium; and a photodetector for receiving the reflected light beam extracted by the prism optical system. In the apparatus, the prism optical system is configured by bonding a first prism and a second prism made of different glass materials, and bonding the second prism and a third prism made of the same glass material, wherein the first prism is An incident surface on which the parallel light beam enters, and an exit surface from which the light beam refracted by the first prism exits, wherein the incident surface is the semiconductor laser. The second prism and the third prism are arranged so as to be parallel to a direction perpendicular to the polarization direction of the light beams, and the emission surface is not perpendicular to the light beam refracted by the first prism. A reference wavelength λ incident on the first prism at an incident angle θ ₀ , which is configured to be bonded via a half mirror or a vapor deposition film functioning as a polarizing beam splitter.
The parallel light beam is the relationship between the angle α of said entrance surface and said exit surface of the angle theta ₁₁ is refracted the first prism forms with the incident surface of ₁ is Arufashita _11, wherein said first prism The refractive indices at the reference wavelength λ ₁ and the changed wavelength λ ₂ (λ ₁ ≠ λ ₂ ) are respectively n ₁₁ and n _12, and the reference wavelength λ ₁ of the second prism and the changed wavelength λ
_{When the} refractive index at ₂ (λ ₁を 満 た す λ ₂ ) is n ₂₁ and n ₂₂ respectively, the condition of Δn ₁ = n ₁₁ −n ₁₂ Δn ₂ = n ₂₁ −n ₂₂ Δn ₁ / Δn ₂ > 1.5 is satisfied. Achieved by:

[Example] Hereinafter, the present invention will be described based on an illustrated example.

FIG. 1 shows a first embodiment of the prism optical system of the present invention. In FIG. 1, 1 is a first prism, 2 is a second prism, and 3 is a third prism. Reference numeral 4 denotes a light beam from a semiconductor laser (not shown) as a light source, which is converted into a parallel light beam by a collimator lens (not shown) as a light beam collimating optical system. Reference numeral 5 denotes a joint surface between the second prism and the third prism, on which an evaporation layer having a function of a half mirror or a polarizing beam splitter is provided. The first prism and the second prism are made of different glass materials. The first and second prisms shape the elliptical light beam from the semiconductor laser into a circular light beam at a beam shaping ratio of about 2 (cross section BB ′).
→ CC ′) and an objective lens (not shown) which is a light beam focusing optical system from the third prism when the wavelength of the semiconductor laser changes.
The angle deviation of the emitted light beam to the lens is substantially zero. The third prism is made of the same glass material as the second prism, and the surface of the joining surface 5 of the second and third prisms is hardly subjected to distortion or the like due to a temperature change. Here, the polarization plane of the semiconductor laser (not shown) is parallel to the paper surface (P polarization direction).

When the prism optical system shown in FIG. 1 is used in an optical information processing apparatus using a semiconductor laser as a light source, the configuration is as follows.

A semiconductor laser, a lens for collimating a light beam from the laser, a prism optical system for correcting the shape of the collimated light beam, and functioning as a beam splitter for extracting a reflected light beam from the optical information recording medium; An optical information processing apparatus comprising: an objective lens that focuses a light beam output from a prism optical system on an optical information recording medium; and a photodetector that receives the reflected light beam extracted by the prism optical system. Is formed by bonding first and second prisms made of different glass materials and bonding second and third prisms made of the same glass material, and the first prism receives the collimated light beam. Having an exit surface from which a light beam refracted by the prism exits, the incident surface being parallel to a direction perpendicular to the polarization direction of the light beam from the laser, and Is disposed so as exit plane is not perpendicular to the light beam refracted by the prism, the second and third
Are bonded together via a vapor deposition film functioning as a half mirror or a polarizing beam splitter.

FIG. 1 will be described in more detail. The incident angle of the light beam with respect to the prism 1 is θ ₀ , the apex angle of the prism 1 (the angle between the incident surface and the exit surface of the first prism) is α, and the wavelength of the semiconductor laser as the light source is λ. When λ = λ ₁ (reference wavelength), the refractive index of the glass material of the prism 1 is n ₁₁ , the refractive index of the glass material of the prism 2 is n ₂₁ (the first subscript is the prism number, and the subsequent subscript is the wavelength number). Are respectively θ ₁₁ , θ ₂₁ , and θ ₃₁ (the first suffix is the number of the refraction angle, and the last suffix is the wavelength number). Similarly, when the wavelength of the semiconductor laser changes to λ = λ ₂ (λ ₁ ≠ λ ₂ ), the refractive index of the glass material of the prism 1 is n ₁₂ , the refractive index of the glass material of the prism 2 is n ₂₂ , and each surface of the prism Angle of refraction at θ ₁₂ ,
θ ₂₂ and θ ₃₂ .

First, in the case of lambda = lambda _1, in each surface according to Snell's law, in a similar manner in the case of _{sinθ 0 = n 11 sinθ 11 ......} n 11 sinθ 21 = n 21 sinθ 31 ...... λ = λ 2, sinθ 0 = N ₁₂ sin θ ₁₂ ... n ₁₂ sin θ ₂₂ = n ₂₂ sin θ ₃₂ ... On the other hand, from the geometrical relationship, θ ₂₁ -θ ₁₁ = θ ₂₂ -θ ₁₂ = α ... Here, the emitted light flux from the prism due to the wavelength change In order to set the angle shift to 0, it is sufficient to set θ ₃₁ = θ ₃₂ ..., And by using, n ₁₁ sin (α + θ ₁₁ ) = n ₂₁ sin θ ₃₁ ... N ₁₂ sin (α + θ ₁₂ ) = Using n ₂₂ sinθ ₃₂ …, and ,Using Organize, What is necessary is just to select a glass material having a refractive index that satisfies the formula, the vertex angle α of the prism 1, and the incident angle θ ₀ of the light beam with respect to the prism 1.

When the magnification of beam shaping is β, the following expression is obtained using the refractive index of each surface.

If the magnification of the beam shaping is selected and satisfied, a beam shaping prism is obtained in which the angular deviation of the light beam emitted from the prism is substantially zero in the wavelength change of λ ₁ → λ ₂ . Hereinafter, two examples of the glass material of the prism in the first embodiment will be described. 2 (a) and 2 (b) show schematic diagrams of specific examples.

(Example 1) The glass material of the prism 1 is SF11 ｛n (λ = 835 nm) = 1.762.
81, n (λ = 820 nm) = 1.76359, n (λ = 850 nm) = 1.620
6 °, apex angle = 18.66 °, glass material of 2 prism is SK15 ｛n
(Λ = 835 nm) = 1.61439, n (λ = 820 nm) = 1.61474, n
(Λ = 850 nm) = 1.61406 °, and the incident angle θ ₀ of the light beam to the prism 1 is 69.0 °. The third prism is the same glass material as the second prism.

In Example 1, θ ₁₁ = 31.98 °, λ ₁ = 835 nm,
When λ ₂ = 820 nm, Δn ₁ / Δn ₂ = 2.23, and λ ₁ = 83
When 5 nm and λ ₂ = 850 nm, Δn ₁ / Δn ₂ = 2.27.

(Example 2) The glass material of the prism 1 is SFS1 ｛n (λ = 835 nm) = 1.891
96, n (λ = 820 nm) = 1.89304, n (λ = 850 nm) = 1.8909
4｝, apex angle = 10.48 ゜, 2 prism material is BK7 ｛n
(Λ = 835 nm) = 1.50965, n (λ = 820 nm) = 1.50993, n
(Λ = 850 nm) = 1.50938 °, and the incident angle θ ₀ of the light beam on the prism 1 is 70.6 °. The third prism is the same glass material as the second prism.

In Example 2, θ ₁₁ = 29.90 °, λ ₁ = 835 nm,
When λ ₂ = 820 nm, Δn ₁ / Δn ₂ = 3.86, and λ ₁ = 83
When 5 nm and λ ₂ = 850 nm, Δn ₁ / Δn ₂ = 3.78.

In the embodiment described above, the beam expansion rate β =
2. Assuming that the wavelength of the semiconductor laser is λ = 835 nm, even if a wavelength variation of ± 15 nm occurs, the angular deviation of the light beam emitted from the prism is almost zero.

FIG. 3 shows an example in which the embodiment of the prism optical system shown in FIG. 1 is developed. FIG. 3 shows a right angle prism after the prism 3
7 and 8 are joined, and mirror 9 is vapor-deposited on the 7, 8 joint surface to
90 ° bent. This is to make the entire optical head thin. Further, by integrating the five prisms 1, 2, 3, 7, 8 into one, the process of assembling the optical head can be significantly reduced.

FIG. 4 is a diagram showing a configuration of an optical head of an optical information processing apparatus using the prism optical system of FIG. Semiconductor laser 10
Is converted into a parallel light beam by the collimator lens 11. The light beam 4 from the collimator lens 11 having an elliptical intensity distribution is converted by the beam shaping prisms 1 and 2 into a light beam having a substantially circular intensity distribution. Of course prism 1,
Reference numeral 2 denotes a different glass material as shown in the above-described embodiment, an appropriate apex angle, and an incident angle of a light beam. No change in the exit angle occurs. Prism 2,
The joint surface 3 is provided with a vapor deposition film 5 such as a half mirror or a polarizing beam splitter. Since the prisms 2 and 3 are made of the same glass material, generation of wavefront aberration due to surface distortion due to a temperature change or the like is reduced. doing. The light beam that has passed through the prism 3 is bent at a right angle by the mirror 9 on the joining surface of the prisms 7 and 8 and enters the objective lens 12.
The light beam condensed as a small spot on the optical information recording medium 13 by the objective lens 12 obtains RF information and servo information (focus, tracking) from the medium, is reflected, and enters the objective lens 12 again. This luminous flux travels in the opposite direction to the outward path,
It is folded in the direction of the detection system by the deposition film 5 provided on the joint surface between the prisms 2 and 3. At this time, since the prisms 2 and 3 are made of the same glass material, the reflected light flux from the vapor-deposited film 5 is hardly affected by wavefront aberration caused by surface distortion due to temperature change or the like. Light is collected stably. Further, although not shown, an RF signal detection system and a servo signal detection system (focus, tracking) corresponding to a known optical information recording medium are added to FIG. The photoelectrically converted signal from the photodetector 15 is amplified by the amplifier 16 and extracted as the desired signal 17 described above.

FIG. 5 shows another reference example of the prism optical system of the present invention. As in the above-described reference example, the configuration is such that the enlargement ratio of beam shaping is selected and satisfied. Hereinafter, two examples of the glass material of the prism in the reference example shown in FIG. 5 will be described. 6 (a) and 6 (b) are schematic diagrams of specific examples.

(Example 3) The glass material of the prism 1 is FK5 ｛n (λ = 835 nm) = 1.4816
7, n (λ = 820 nm) = 1.41892, n (λ = 850 nm) = 1.4814
3｝, apex angle α = 83.41 ゜, glass material of 2 prism is F16 ｛n
(Λ = 835 nm) = 1.58016, n (λ = 820 nm) = 1.58063, n
(Λ = 850 nm) = 1.57971 °, and the incident angle θ ₀ of the light beam on the prism 1 is 65.2 °. The third prism is the same glass material as the second prism.

In Example 3, θ ₁₁ = 37.78 °, λ ₁ = 835 nm,
When λ ₂ = 820 nm, Δn ₁ / Δn ₂ = 0.53, and λ ₁ = 83
In the case of 5 nm and λ ₂ = 850 nm, Δn ₁ / Δn ₂ = 0.53.

(Example 4) The glass material of the prism 1 is FK01 ｛n (λ = 835 nm) = 1.492.
05, n (λ = 820 nm) = 1.49225, n (λ = 850 nm) = 1.4918
5｝, apex angle α = 70.84 ゜, glass material of 2 prism is F16 ｛n
(Λ = 835 nm) = 1.58016, n (λ = 820 nm) = 1.58063, n
(Λ = 850 nm) = 1.57971 °, and the incident angle θ ₀ of the light beam with respect to the prism 1 is 67.0 °. The third prism is the same glass material as the second prism.

In Example 4, θ ₁₁ = 39.28 °, λ ₁ = 835 nm,
When λ ₂ = 820 nm, Δn ₁ / Δn ₂ = 0.43, and λ ₁ = 83
In the case of 5 nm and λ ₂ = 850 nm, Δn ₁ / Δn ₂ = 0.44. In the reference example described above, the beam expansion rate β = 2, the wavelength of the semiconductor laser is λ = 835 nm, and even if a wavelength variation of ± 15 nm occurs, the angular deviation of the light beam emitted from the prism is almost zero. .

In the reference example shown in FIG. 5, the incident direction of the light beam from the semiconductor laser to the prism and the direction of the light beam to the detector are opposite to those in the embodiment shown in FIG. You can choose the one that is more compact.

In the reference example shown in FIG. 5, right prisms 7 and 8 are joined after the prism 3, and a mirror 9 is vapor-deposited on the joining surface of the prisms 8 and the light beam can be bent by 90 °. Also,
A thin optical head as shown in FIG. 4 can be formed.

FIGS. 7A and 7B are diagrams comparing the size of the prism optical system of the present invention (Example 1) with the size of a conventional beam shaping prism (JP-A-60-234247). . It can be seen that the size is almost the same despite the increase of one prism.

The configuration necessary for integrating the prism optical system of the present invention into a compact shape as in the above-described embodiment and reference example will be described below.

First, consider the case where the reference wavelength lambda = lambda ₁ of the light beam incident at an incident angle theta ₀ in the first prism is refracted at an angle of theta ₁₁ at the first surface. The above equation holds according to Snell's law.
When the case analysis using the first apex angle α and theta ₁₁ that the above-described prism, in the case of Arufashita ₁₁ becomes the structure shown in FIG. 1, in the case of Arufashita ₁₁ the configuration shown in Figure 5.

For Arufashita ₁₁ if (first configuration shown in FIG.) alpha Decrease It can be seen that a compact shape. Assuming that the changed wavelength is λ = λ ₂ (λ ₂ > λ ₁ ), the refractive indexes of the glass of the prism 1 at each wavelength are n ₁₁ and n, respectively.
₁₂ , the refractive index at each wavelength of the glass of the prism 2
Assuming n ₂₁ and n ₂₂ , in order to make α smaller than the formula, It is good. That is, Δn ₁ > Δn ₂ may be satisfied. That is, the prism 1 has a glass with a large dispersion, for example, SF, F, L
It is sufficient to select aSF, LaF, BaSF, or the like, and to select a glass having a small dispersion, such as FK, BK, K, BaK, SK, or LaK, for the prism 2. This is shown in FIGS. 2 (a) and 2 (b).
It is clear that it is more compact.

In more detail, it is more preferable that the following condition is satisfied.

For Arufashita ₁₁ if (fifth configuration shown in FIG.) also reduced α understood to be a compact shape. In order to reduce α by the formula, It is good. That is, Δn ₁ <Δn ₂ may be satisfied. That is, the prism 1 has small dispersion glass such as SF, F, LaSF,
LaF, BaSF, or the like may be selected, and a glass having a large dispersion, such as FK, BK, K, BaK, SK, or LaK, may be selected for the prism 2.
This is also apparent from the fact that Example 4 is more compact than Example 3 with reference to FIGS. 6 (a) and 6 (b).

In more detail, it is more preferable that the following condition is satisfied.

[Effects of the Invention] As described above, according to the present invention, a prism optical system is formed by bonding a first prism and a second prism made of different glass materials, and the second prism and the third prism made of the same glass material. And by satisfying the conditions set forth in the claims, it is possible to provide (1) a prism optical system whose optical properties do not change with respect to a change in wavelength or a change in temperature. It is possible to provide a prism optical system having a beam splitter function of a wavefront that is stable against temperature changes. (3) An achromatic beam shaping prism (first and second prisms) and a beam splitter (second and second prisms) (3) Prism) and the function of optical head can be increased. (4) Compact as same as conventional achromatized beam shaping beam splitter prism Those having the effect of, or the like can Rukoto. Further, when the prism optical system is applied to an optical information processing device, it is possible to provide a device that is not affected by a large change in the wavelength of the light source or a large change in the temperature of the device. .

[Brief description of the drawings]

FIG. 1 is a view showing a first embodiment of the prism optical system of the present invention, FIGS. 2 (a) and 2 (b) are views showing specific examples of the first embodiment, and FIG. 3 is a view showing the first embodiment. The figure which shows the developed example, 4th
FIG. 5 is a diagram showing an optical information processing apparatus using the prism optical system of FIG. 3, FIG. 5 is a diagram showing another reference example of the prism optical system of the present invention, and FIGS. 6 (a) and 6 (b) are FIG. 5 shows a specific example of the reference example of FIG. 5, FIGS. 7 (a) and 7 (b) are diagrams for comparing the sizes of the prism optical system of the present invention and a conventional beam shaping prism, and FIG. FIG. 9 illustrates a prism.
The figure is a diagram for explaining the angular deviation of the light beam emitted from the prism,
FIG. 10 is a diagram showing a conventional optical information processing apparatus. 1 ... first prism 2 ... second prism 3 ... third prism

Claims (1)

(57) [Claims] 1. A semiconductor laser, a collimator lens for converting a light beam from the semiconductor laser into a parallel light beam, and functioning as a beam splitter for correcting the shape of the parallel light beam and extracting a reflected light beam from an optical information recording medium. An optical information processing apparatus including a prism optical system, an objective lens that focuses a light beam from the prism optical system on the optical information recording medium, and a photodetector that receives the reflected light beam extracted by the prism optical system The prism optical system is configured to bond a first prism and a second prism made of different glass materials, and
A prism and a third prism are attached to each other, wherein the first prism has an incident surface on which the parallel light beam enters and an emission surface from which the light beam refracted by the first prism exits, and the incident surface is The second prism and the third prism are disposed so as to be parallel to a direction perpendicular to the polarization direction of the light beam from the semiconductor laser, and so that the emission surface is not perpendicular to the light beam refracted by the first prism. The prism is
A reference wavelength λ ₁ , which is formed by bonding together via a vapor deposition film functioning as a half mirror or a polarizing beam splitter, and is incident on the first prism at an incident angle θ _0.
The relationship between the angle θ _{11 at} which the parallel light beam is refracted at the incident surface and the angle α formed between the incident surface and the exit surface of the first prism is αθ ₁₁ , and the reference of the first prism is The wavelength λ ₁ and the changed wavelength λ
₂ (λ ₁ ≠ λ ₂ ), the refractive indexes are n ₁₁ and n ₁₂ , respectively.
The reference wavelength λ ₁ of the second prism and the changed wavelength λ
_{When the} refractive index at ₂ (λ ₁ ≠ λ ₂ ) is n ₂₁ and n ₂₂ respectively, the condition of Δn ₁ = n ₁₁ −n ₁₂ Δn ₂ = n ₂₁ −n ₂₂ Δn ₁ / Δn ₂ > 1.5 is satisfied. An optical information processing apparatus, characterized by the following.