JPS62112234A - Rotating optical system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a rotating optical system, and particularly to a rotating optical system suitable for stabilizing the output of an optical rotating head that reads and writes information on an optical storage medium.

[Background of the invention]

Generally, optical disk devices utilize polarized light to efficiently extract the amount of reflected light. For example, if linearly polarized light is incident on a quarter-wave plate under certain conditions, it becomes circularly polarized light, and this circularly polarized light is then 1/4
When the light enters the four-wavelength plate, it becomes linearly polarized light that is orthogonal to the original polarization plane. Further, the polarizing beam splitter transmits P-polarized light with a polarization component parallel to the plane of incidence, and reflects S-polarized light with a polarization component perpendicular to the plane of incidence. Taking advantage of these properties, optical disk devices use a 174-wave plate and a polarizing beam splitter as means for extracting reflected light. On the other hand, when light is transmitted or reflected by an anisotropic optical component with a different refractive index within the component, a phase difference occurs in the light separated in each axial direction, and when the anisotropic optical component rotates, the plane of polarization changes. The optical system of the conventional optical rotary head was developed in U.S. Pat.
As described in Japanese Patent No. 5515, the optical system is divided into a static optical system and a rotating optical system, and reflected light is extracted by a polarizing beam splitter. However, no consideration was given to the influence of polarization due to rotation of the rotating optical system. As a prior art for changing the polarization of a stationary optical system, there is Japanese Patent Application Laid-Open No. 59-44020, which describes how linearly polarized light can be changed by combining a 1/2 wavelength plate and a birefringent crystal. A directional phase shifter that gives different phase differences to light depending on its traveling direction is described. [Object of the Invention] The present invention has been made in view of the actual state of the prior art described above, and in order to suppress the increase or decrease in the amount of reflected light extracted by the polarizing beam splitter, the plane of polarization does not change due to rotation of the anisotropic optical component. Its purpose is to provide a rotating optical system. [Summary of the Invention] The configuration of the rotating optical system according to the present invention is such that, in the rotating optical system in which light is transmitted or reflected by a rotating anisotropic optical component, the rotational optical system has a structure in which the optical axis of the surface anisotropic optical component is rotated. A wavelength plate having a phase difference equal to that of the anisotropic optical component is provided, and a slow axis of the anisotropic optical component having a large refractive index and a fast axis of the anisotropic optical component having a small refraction of the wavelength are positioned in parallel. Additionally, in the present invention, by installing a wave plate having the same phase difference as the anisotropic optical component, the amount of delay between the slow axis and the fast axis of the anisotropic optical component including the wavelength plate becomes equal. . Therefore, since the rotating anisotropic optical component can be regarded as an isotropic optical component, the plane of polarization does not change due to rotation. [Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 1 to 6. First, FIG. 1 is a configuration diagram of an optical rotary head according to an embodiment of the present invention. In FIG. 1, 1 is an objective lens, and 2 is a mirror. Reference numeral 3 denotes a rotating body to which the objective lens 1 and mirror 2 are mounted, and 4 a motor for driving the rotating body 3. These constitute a condensing section for the incident light 21. 6 is an optical tape related to an optical storage medium, and this optical tape 6 is wound diagonally around a glass circle [5, and is supported and fed by an air bearing. The rotating body 3 of the light condensing section rotates at high speed to scan the optical spot 20 on the optical tape 6 at high speed, thereby reading and writing information. That is, the optical tape 6
Information is written on the surface as holes called pits, and the information written in the pits is read from the reflected light 22. 7.8 is a lens for controlling the focus of the light spot 20. A light spot 20 forms incident light 21- generated from the laser transmitter 13 on the surface of the optical tape 6 using the lens 7.8 and the objective lens 1. The optical spot 20 is configured to move in the optical axis direction of the objective lens 1 by driving the lens 8 in the direction of the arrow. Reference numeral 9 denotes image raw data that rotates at half the angular velocity of the rotating body 3 of the condensing unit, and 1.0 denotes a swinging galvano mirror whose optical axis angle can be adjusted. The optical spot 20 is moved in the track direction (rotation direction of the rotating body 3) by the galvanometer mirror 10 and its position is controlled. The mirror 2 and the image raw data 9 installed on the rotating body 3 of the condensing section have different refractive indexes within the parts, and are called anisotropic optical parts. 11 is a polarizing beam splitter that separates P-polarized light and S-polarized light, and 12 is a quarter-wave plate that converts linearly polarized light into circularly polarized light. ．． This is provided to separate the reflected light 22 from the reflected light 22. 13 is a laser oscillator constituting a light source section;
Generates linearly polarized light. 4 is an information detecting section which extracts the reflected light 22 reflected from the optical tape 6 through the polarizing beam splitter 11. This information detecting section 14 includes a lens 15 and a detector 16, and detects a focus error signal, a tracking error signal, and a data signal, and uses the focus error signal and track error signal as feedback information to control the lens 8 for focus control and the galvanometer mirror 10 for track direction control. ] 8 is a wavelength plate provided on the rotating optical axis of the image raw data 9 related to anisotropic optical components, and this wavelength plate 18 is
It has a phase difference equal to that of the image raw data 9, and specifically, it is attached to the rotating part of the image raw data 9 and is located between the image rotary take 9 and the lens 8. Reference numeral 19 denotes a wavelength plate provided on the rotating optical axis of the mirror 2, which is an anisotropic optical component.
Specifically, it is mounted on the rotating body 3 and located between the lens 7 and the mirror 2. Next, the functions and effects of the optical rotary head constructed as described above will be explained with reference to FIGS. 2 to 6 in conjunction with FIG. 1 above. Fig. 2 is an explanatory diagram showing the polarization state from the laser oscillator to the quarter-wave plate, Fig. 3 is an amplitude diagram showing the phase relationship between the X' axis and the y' axis, and Fig. 4 is , a diagram showing the relationship between the delay angle and the rate of reflected light, FIG. 5 is an explanatory diagram showing the polarization state of a conventional optical rotary head, and FIG. 6 is a diagram showing the image low-take and wave plate of this embodiment. It is an explanatory view showing the installation relationship with. In the following description, an axis with a small refractive index in an anisotropic optical component having a different refractive index within the component will be referred to as a fast axis, and an axis with a large refractive index will be referred to as a slow axis. Generally, the optical path length is (refractive index)×(distance 1lJl), so the optical path lengths are different between the fast axis and the slow axis, and a phase difference occurs. First, the principle behind the return of the reflected light 22 will be explained using FIGS. 2 and 3. The polarizing beam splitter 11 is installed so as to transmit waves having a vibration plane parallel to ylltl and reflect waves having a vibration plane parallel to the X axis. From the laser oscillator 13,
A wave 24 with a vibration plane parallel to the y-axis is transmitted to the polarization splitter 1
1 and becomes wave 25. The x-y coordinates were transmitted 45 degrees / , / wave 2 at the / coordinates
5, the waves 25 have the same phase and amplitude. The slow axis of the quarter-wave plate 12 and the X' axis coincide. Wave 25 passes through quarter-wave plate 12 and becomes wave 26. wave 2
6 is a wave 31.6 with a phase difference of 90 degrees at the x'-y' coordinates shown in FIG. , 29, resulting in circularly polarized light. The wave 26 is reflected by the optical tape 6 and passes through the quarter-wave plate 12 again.
becomes a wave 27. The wave 27 has the relationship of a wave 32.29 with a phase difference of 180 degrees in the x'-y' coordinate, and becomes linearly polarized light with a vibration plane parallel to x#I6. Therefore, the wave 27 is polarized by the polarizing beam splitter 11. It is reflected and becomes a wave 28, which is taken into the information detection section 14. Now, in the conventional optical rotary head, when the wave 26 reciprocates between the quarter-wave plate 12 and the optical tape 6, the delay is different in the X'-axis direction and the y'-axis direction. If wave 32 is used as a reference in FIG. 3, wave 29 is delayed like wave 33 shown by a broken line, and a phase difference, that is, a delay angle φ occurs, and the amount of reflected light decreases as shown in FIG. In Figure 4, the horizontal axis shows the delay angle φ (degrees), and the vertical axis shows the reflected light amount rate G.
It shows the change in the amount of reflected light. This reflected light quantity rate G is given by: However, φ=360×n (degrees) (n=o, ±1°±2・
), G=100%. Mirror 2 and image low take 9 are anisotropic optical components
Since the delay angle φ changes with the rotation of the polarizing beam splitter 11, the amount of reflected light taken out to the information detecting section 14 increases or decreases. Here, the polarization state of the conventional optical rotary head will be explained using FIG. In FIG. 5, the same reference numerals as in FIG. 2 indicate equivalent parts. Assume that a wave 25 having an amplitude parallel to the y-axis is transmitted through the polarizing beam splitter 11. Here, ω represents the maximum amplitude, ω represents the angular frequency, and t represents the time. If wave 25 is expressed in x'-y' coordinates, it becomes. ], the slow axis of the /4 wave plate 12 coincides with the X' axis. Since the wave 26 that has passed through the quarter-wave plate 12 is delayed by 90 degrees from the wave that coincides with the X'-axis direction, it is converted into x-y coordinates again and transmitted through the delay element 34 corresponding to the image rotator 9. However, the phase difference between the fast axis and the slow axis of the image rotator 9 is α, and the slow axis is at an angle of 0 from the X-y coordinate system.
It coincides with the X' axis of the rotated X'-y' coordinate system. Also, the fast axis coincides with the y' axis. Next, when the delay element 35 corresponding to the rotating mirror 2 is reciprocated, the following is obtained. However, the phase difference between the slow axis and the fast axis of mirror 2 is β
and the slow axis is x rotated by 20 degrees from the x-y coordinate system.
1'-y'''' coordinates coincide with the # axis. Also, the fast axis coincides with the y'' axis. When it is converted again to x#-y# coordinates and passed through the delay element; 34, it becomes as follows. Next, it is converted to x-y coordinates and then to x'-y' coordinates. If the light is further transmitted through the 174-wavelength plate 12, it becomes. When converted to x-yJg5 standard, it becomes. IXIII is the amount of reflected light extracted by the polarizing beam splitter 11. If we rearrange equations (2) or 9), l xtxl=l-((sincl+t+5in(ωt
−2a −2β)) cos” 0+(sin(ωt−2
α)+5in(ωt-2β))sin” o ) 1・
...(lO). In contrast to the prior art described above, in the optical rotary head of this embodiment, the phase difference α between the fast axis and the slow axis. The respective wavelength plates 18 and 19 of β are provided on the image rotator 9 and the mirror 2 to equalize the delay between the linked axes and the linked axes. In other words, image raw data 9. The wavelength having a phase difference equal to the phase difference of an anisotropic optical component such as the mirror 2 is configured such that the slow axis of the anisotropic optical component and the fast axis of the wave plate are located parallel to each other. FIG. 6 shows the installation relationship between the image rotator 9 and the wave plate 18. Long axis 39 of wave plate 18. Fast@38 corresponds to the fast axis 37. of the image rotator 9, respectively. Coincident with slow axis 36. Therefore, the phase difference becomes zero. Therefore, image raw data 9. Waves 40 and 41 before and after passing through the wave plate 18 have the same phase and the same amplitude. In the case of mirror 2, the wavelength plate 19 is
is installed. If the phase difference of the image rotator 9 including the delay of the wave plate 18 is A, and the position difference of the mirror 20 including the delay of the wave plate 19 is B, then Equation (10) becomes! xxtl=l [(
sinωt+gin(ωt-2A-2B)) cos”f
? +(sin(ωt-2A)-1-8in(ωt(-2
B)) sinze ) l...(11) It becomes. According to this embodiment, since A=O and B=O, 1x1zl=lI ・sin (ωt)1, and regardless of the rotation angle O, the amount of reflected light is the same as that of the polarizing beam splitter 1.
It can be taken out in 1. According to this embodiment, image raw data 9. Phase compensation is achieved by providing one wavelength plate 18, 19 on each of the mirrors 2, and the plane of polarization to be transmitted is determined by these image raw data 9. Since the amount of reflected light taken out by the polarizing beam splitter 11 does not change due to the rotation of the anisotropic optical component such as the mirror 2, it is possible to realize an optical rotary head in which the amount of reflected light taken out by the polarizing beam splitter 11 does not change due to the rotation of the anisotropic optical component. In the above embodiment, the phase differences A and B between the image rotator section including the wave plate and the mirror 2 were set to zero, but as is clear from Equation 1 (11), it is possible to set either one to zero. However, regardless of the rotation angle of 0, a constant amount of reflection can be extracted using a polarizing beam splitter. [Effects of the Invention] As described above, according to the present invention, it is possible to provide a rotating optical system in which increase or decrease in the amount of reflected light extracted by a polarizing beam splitter is suppressed and the plane of polarization does not change due to rotation of anisotropic optical components. can.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an optical rotary head according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the polarization state from the laser oscillator to the quarter-wave plate, and FIG. 3 is the X Figure 4 is an amplitude diagram showing the phase relationship between the '' and y' axes, Figure 4 is a line showing the relationship between the delay angle and the rate of reflected light, and Figure 5 is the polarization state of a conventional optical rotary head. FIG. 6 is an explanatory diagram showing the installation relationship between the image rotator and the wave plate of this embodiment. 2... Mirror, 3... Rotating body, 6... Optical tape,
9... Image rotator, 11... Polarizing beam splitter, 13... Laser oscillator, 14... Information detection section, 20... Light spot, 21... Incident light, 22
...Reflected light, 18°! Z Figure 103 Figure J Publication [Creation Z 5 Figure Otsu Figure

Claims (1)

[Claims] 1. In a rotating optical system in which light is transmitted or reflected by a rotating anisotropic optical component, a wavelength having a phase difference equal to the phase difference of the anisotropic optical component is placed on the rotating optical axis of the anisotropic optical component. A rotating optical system characterized in that a plate is provided, and a slow axis of the anisotropic optical component having a large refractive index and a fast axis of the wavelength plate having a small refractive index are positioned parallel to each other.