JPH02192043A - Optical information processor - Google Patents

Abstract

PURPOSE:To cancel the phase dislocation generated according to the rotation of a swing arm by calculating and setting the apex angle and refraction index of a parallelogram prism by means of an optical theoretical expression so that the sum of the phase dislocation quantities of P polarized light and S polarized light at the time of total reflection may be the integer times of 180 deg.. CONSTITUTION:The linearly polarized light made incident on a parallelogram prism 21 is total-reflected for plural times in the parallelogram prism 21, and an apex angle alphaand the refraction index of the parallelogram prism 21 are set by the optical theoretical expression so that the sum of the phase dislocation quantities of the P polarized light and the S polarized light at the time of the total reflection may be integer times of 180 deg.. Consequently on the forward path of the optical system, the phase dislocation quantity from a time when light beams are made incident on the parallelogram prism 21 up to a time when the beams are emitted is made into 180 deg. X M (M is an integer), and the quantity taking the forward and backward path into consideration is 180 deg. XM X 2. Out of the phase dislocation quantity, since integer time of 360 deg. means no dislocation, by using such a parallelogram prism 21, the generation of the phase dislocation quantity due to the rotation of a swing arm 6 can be canceled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improved structure of an optical information processing device that records and reproduces information using light.

In recent years, as the amount of data handled by computers has increased enormously, there has been a need for high-speed, large-capacity file memory. Optical information processing devices, so-called optical disk devices, are advantageous in terms of large storage capacity and medium portability when compared to magnetic disk devices, but the weight of moving parts is unavoidable for boat fishing. Therefore, it has the disadvantage that access time is long. In order for optical disk devices to become a mainstay of file memory, it is necessary to overcome this shortcoming of slow access time.

[Conventional technology]

As one method for shortening access time in optical disk devices, a device using a swing arm system as a mechanism for accessing a target position with a light beam has been proposed.

Figure 4 is a perspective view of the main mechanism of the conventional swing arm system.
FIG. 5 is a perspective view showing the configuration of a conventional optical system, and in order to make the explanation of the configuration and operation easier to understand, the same parts will be given the same reference numerals throughout the figures and their repeated explanation will be omitted. .

In Figure 4, ■ is the medium on which information is recorded, 2 is medium 1
3 is an objective lens, and rough access of the objective lens 3 to the target trunk on the medium I is performed by a swing arm 6 driven by a swing arm actuator 12. 5 is a parallelogram prism attached to the swing arm 6, and a galvanometer mirror is arranged at a relative position on the light entrance surface at one end, and an objective lens 3 is arranged at a relative position at the exit surface at the other end. . A light beam from a semiconductor laser (not shown) reflected by the galvanomirror 7 is reflected twice by the parallelogram prism 5 and enters the objective lens 3, where it is focused into a beam spot having a diameter of about IIM. The focus actuator 4 drives the objective lens 3 so that the beam spot is always focused on the medium 1.

In FIG. 5, laser light emitted from a semiconductor laser 11 is converted into a perfectly circular parallel light (light beam) by a collimator lens 10 and a perfectly circular correction prism 9, and a beam splitter 8
The light is transmitted through the galvanometer mirror 7 and enters the parallelogram prism 5, and the output light is entered into the objective lens 3. The galvano mirror 7 also serves to provide precise access of the light beam to the target track. In this optical system, from the semiconductor laser 11 to the galvanometer mirror 7 is a fixed part,
The parallelogram prism 5 and the objective lens 3 are movable parts. Since the weight of the movable part is reduced, access time can be shortened. However, in this structure, rotational motion is applied in the middle of the optical path, that is, between the galvanometer mirror 7 and the parallelogram prism 5.

FIG. 6 shows an explanatory diagram of changes in the incident direction of linearly polarized light as seen from a parallelogram prism. In the figure, a semiconductor laser 11
When the parallelogram prism 5 is set at position b, the incident linearly polarized light (for example, in the direction of arrow X as shown) coincides with the direction of arrow P. In this case, light in the P direction (referred to as the P-polarized light component and a light component that vibrates in a plane parallel to the plane of incidence) and light in the direction of arrow S (referred to as the S-polarized light component and that vibrates in a plane perpendicular to the plane of incidence) There is no phase shift between the two light components. This is because only the P-polarized component exists.

However, when the parallelogram prism 5 is at position a or position C, the incident linearly polarized light appears to be rotating when viewed from the parallelogram prism 5. In other words, if the incident light now has a P component and an S component, and if the reflecting surface of the parallelogram prism 5 is just using total internal reflection, there will always be a phase difference between the P and S polarized light. (Refer to the theoretical formula ■ below) is generated.

[Problem to be solved by the invention]

In conventional swing arm type optical disk devices, when the arm rotates to access information on the medium, a phase difference is generated in the light, and when a phase difference occurs, the detection system in CD-ROM and WORM type optical disk devices There are also problems in that the amount of light that returns to the optical disk decreases, and in magneto-optical optical disk devices, the reproduced signal deteriorates.

The present invention has been made in view of the above conventional problems, and is a means for canceling the phase shift between P polarized light and S@ light that occurs when the swing arm rotates in a swing arm type optical disk device. The purpose is to provide.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention. In an optical information processing apparatus having an access mechanism of a swing arm 6 equipped with a parallelogram prism 21 for guiding a light beam to a target track on a medium 1 on which information is recorded, the light beam is incident on the parallelogram prism 21. The parallelogram prism 21 is configured such that the linearly polarized light is totally reflected within the parallelogram prism 21 multiple times, and the total amount of phase shift between the P polarized light and the S polarized light at each total reflection is an integral multiple of 180 degrees. The apex angle and the refractive index of the swing arm 6 are calculated and set using optical theoretical formulas, and the structure is configured so that the phase shift that occurs with the rotation of the swing arm 6 is canceled out.

[For production]

The linearly polarized light incident on the parallelogram prism 21 is totally reflected multiple times within the parallelogram prism 21, and the total amount of phase shift between the P polarized light and the S polarized light at each total reflection is 18.
By setting the apex angle and refractive index of the parallelogram prism 21 according to an optical theoretical formula so that the angle is an integral multiple of 0 degrees, the light beam passes through the parallelogram prism 2 on the outward path of the optical system.
The amount of phase shift from entering the 1 to exiting is 180 degrees XM (M is an integer), and considering the round trip, it is 180 degrees x
It becomes M×2. Since an integer multiple of 360 degrees in the amount of phase shift is the same as no shift, by using such a parallelogram prism 21, it is possible to cancel out the amount of phase shift caused by rotation of the swing arm 6. becomes.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram explaining the principle of the present invention. As shown in the figure, consider an optical system in which total reflection occurs multiple times within a parallelogram prism 21. The phase shift when a light beam is totally reflected in a medium is jan(δ/2 ) = (cosψ 5i
It is expressed as n2ψ-1/n2)/5in2ψ-■.

The angle of incidence at the first total reflection surface R1 is α1, and the amount of phase shift is δh
The angle of incidence at the second total reflection surface R2 is β2, and the amount of phase shift is 62
．． If the amount of phase shift at the total reflection surface Rk in the box below is δW, the angle of incidence at the total reflection surface Rk in terms of geometric optics is the total reflection surface R
1, and the angle of incidence on each total reflection surface R3 to Rk-1 is the same as the angle of incidence on total reflection surface R2. The total phase shift amount δto ta I is δto ta 1-δ, 10 δ2+...+δW-2δ,
+(n-2) δ2 ・ ・ ・ ・ ■ However, jan (δ+ /2 ) = (cosα 5in2α-
1/n”)/sin”αtan (δ2/2) =
(cosβ 5in2β-1/n")/5in2β. Here, M is a positive integer and δtotal = 1806XM...
δ1 in equation 0 so as to satisfy ■. Calculate the value of δ2+n.

Here, the light beam incident from A is incident perpendicularly to the third total reflection surface R3, so due to the relationship of a right triangle, the first
The angle of incidence α at the total reflection surface R1 of the parallelogram prism 21
is equal to the apex angle of

That is, the apex angle α and the refractive index n of the parallelogram prism 21 in FIG. 1 are calculated so as to satisfy Equation 0. Since the angle formed by the perpendicular lines drawn to the first reflective surface R1 and the second reflective surface R2 is equal to α, β=180'-
It is found by 2α.

FIG. 2 is a diagram showing one embodiment of the improved parallelogram prism of the present invention. As the material of the optical glass of the parallelogram prism 21, 785257-3FII (refractive index n = 1 at 837 nm, 76037) was used, and in the figure, the apex angle α = 57°17°, and 4 of C, D, E, and F were used.
It is designed for total reflection on surfaces. Here, the reflective surface C
In this case, the angle of incidence is 57°17°. By substituting this value into the equation 0, we obtain δ, =50'41°. In D, the incident angle is 65°26'' and δ2=39619'' is obtained. Since the incident angle at E is the same as D, and the incident angle at F is the same as C, the total amount of phase shift from when the light beam enters from A to when it exits to B is δtotal
= (50841'+39°19') X2=
The angle will be 180°. Considering the outbound and return trips, it is 180'
A phase shift of 3606 at x 2 =360' is the same as no phase shift.

FIG. 3 shows a layout diagram of the entire optical system of the present invention.

In the figure, the position of the parallelogram prism 21 corresponds to the parallelogram prism 5 of FIG. 5 in the improved arrangement described above, and the other parts are the same as in the conventional example.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, in a swing arm type optical disk device that aims to shorten the access time to a target trunk on a medium, the phase difference of the optical beam that occurs due to the rotation of the swing arm can be reduced. 3 on the round trip
Setting the angle to 60° has the effect of avoiding this effect and contributing to preventing deterioration of the reproduced signal.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the principle of the present invention, Fig. 2 is a diagram showing an embodiment of the improved parallelogram prism of the present invention, Fig. 3 is a layout diagram of the entire optical system of the present invention, and Fig. 4 is a conventional diagram. FIG. 5 is a perspective view showing the configuration of a conventional optical system, and FIG. 6 is an explanatory diagram of changes in the incident direction of linearly polarized light as seen from a parallelogram prism. In FIGS. 1 and 4, ■ indicates a medium, 6 indicates a swing arm, and 5 and 21 indicate parallelogram prisms. good

Claims (1)

[Claims] An optical information processing device having an access mechanism of a swing arm (6) equipped with a parallelogram prism (21) for guiding a light beam to a target track on a medium (1) on which information is recorded. In, the linearly polarized light incident on the parallelogram prism (21) is totally reflected multiple times within the parallelogram prism (21), and the total amount of phase shift between the P polarized light and the S polarized light at each total reflection is calculated. The apex angle and refractive index of the parallelogram prism (21) are calculated and set using optical theoretical formulas so that An optical information processing device characterized by canceling out.