JPS6245614B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is used in a signal reproducing device, etc. that reproduces and demodulates a signal contained in a high-density signal recording medium such as a video disk using a beam of light or the like without contacting the signal recording medium. This invention relates to an optical system suitable for.

As is already known, video discs that record TV signals, etc., have a signal track pitch of approximately several microns, and a method of detecting signals by scanning this narrow signal track non-contact using a beam or the like is difficult. In order to reproduce and demodulate the correct signal, some kind of correction means must be provided. A conventional example of an optical system of a signal reproducing device provided with such means is shown in FIG. Here, a parallel light beam 1 emitted from a laser or the like passes through a rectangular mask 2, passes through a polarizing beam splitter 3, a λ/4 plate 4, and is reflected by a driving mirror 5, and a rectangular mask 2 is formed on the focal plane of a reproduction lens 6. Create a diffraction image of. The recording medium 7 is placed on the focal plane of the reproducing lens and constitutes a cat's eye optical system together with the reproducing lens 6, and reflects the light beam, and the reflected light beam passes through the reproducing lens again toward the driving mirror 5. The light reflected by the drive mirror 5 is reflected in the same direction as when it was incident, passes through the λ/4 plate again, changes the polarization angle by 90 degrees from the time when it was incident, and is reflected by the polarizing beam splitter 3 to the right in the figure. This light beam forms an image of the illuminated portion of the recording medium 10 on its focal plane by the lens 10. That is, the focal plane of the lens 10 and the recording medium 7 are in a conjugate relationship (in an imaging relationship).

Further, the light flux passing through the lens 10 is divided into two by a beam splitter 11, and a signal detector (light receiving element) 8 and a tracking correction signal detector ( (light receiving elements) 9a and 9b are placed. Here, by driving the driving mirror 5 in accordance with the tracking signals obtained by the light receiving elements 9a and 9b, the focal point of the light beam on the recording medium 7 can be moved and tracking can be performed. In FIG. 1, the optical path when the driving mirror is rotated is shown by a broken line. When the recording medium 7 and the focal plane of the lens 10 on which the light receiving elements 9a and 9b are placed are in an imaging relationship as in this example, Even if the drive mirror 5 is rotated, the position where the image of the recording medium 7 is formed on the focal plane of the lens 10 does not change.

On the other hand, as another optical system for a signal reproducing device, the first
A tracking signal is obtained by directly receiving the parallel light beam reflected from the recording medium by a light receiving element without using the lens 10 as shown in the figure, without forming an image, and by detecting the diffraction pattern information of the reflected light. Conceivable. Since such a system can omit the imaging lens and shorten the optical path length, it is advantageous for downsizing and cost reduction of the signal reproducing device.

However, when using the conventional optical system as shown in FIG.
When rotated, it is translated in parallel as shown by the dashed line. Therefore, if a conventional optical system attempts to detect the reflected light beam without forming an image, the positional relationship between the reflected light beam and the light-receiving element will be distorted each time the driving mirror is rotated to perform tracking, making it difficult to perform accurate signal detection and tracking. The inconvenience of not having one occurred.

In view of the above facts, an object of the present invention is to provide a beam scanning optical system in which, when scanning a beam, the reflected beam from an object irradiated with the beam does not undergo parallel movement due to scanning.

The present invention comprises a driving mirror and an objective lens that focuses the parallel light beam reflected by the driving mirror onto an irradiated object, and rotates the driving mirror to move a focal point on the irradiated object. In the beam scanning optical system, the center of rotation of the driving mirror is set at a position on the reflective surface of the driving mirror that coincides with the optical axis of the objective lens, and the distance between the center of rotation and the center of the objective lens is determined by the distance between the center of rotation and the center of the objective lens. The above objective is achieved by making the focal length equal to the focal length of the lens.

The present invention will be explained in detail below using the drawings.

FIG. 2 shows an optical system to which the present invention can be applied. In Fig. 2, 12 is the irradiated object, 13
14 indicates an objective lens, 14 indicates a driving mirror, and 15 indicates a center of rotation of the mirror. The driving mirror 14 is initially placed at an angle of approximately 45° with the object 12 to be irradiated. Further, 20 is the center of the lens. It is now assumed that the beam 16 is reflected at the rotation center of the mirror 14. Furthermore, it is assumed that the rotation center 15 and the optical axis of the lens center 20 coincide. After being reflected by the mirror 14, the beam 16 passes through the center of the lens and impinges on the illuminated object 12. Since the beam passing through the center of the lens is not refracted, the beam 16 is directed toward the illuminated object 12.
is incident perpendicularly to . Beam 16 at irradiated object 12
is reflected and passes through the center of the lens 13 again, following the same path as when it was incident. Also, the beam 17 next to the beam 16 is reflected by the mirror 14 and then reflected by the lens 1.
3 and is refracted by the irradiated object 12, the irradiated object 1
The light is reflected at an angle equal to the angle at which it enters the lens 13, passes through the lens 13 again, faces the mirror 14 at the same angle as the angle it makes with the optical axis when it enters the lens 13, and is reflected by the mirror 14, facing the same direction as when it entered. It takes a path symmetrical to beam 16, resulting in the beam shown as 18 in FIG. That is, beam 16 and beam 1
When the distance of 7 is d, the beam 17 undergoes a parallel movement of 2d after being reflected by the object to be irradiated. Conversely, if beam 18 is the incident beam, beam 17 will be generated after reflection.
It is reflected along the path of That is, assuming that a beam beam having a width of 2d is incident, when it is reflected by the object to be irradiated and then reflected by the mirror 14 through the lens again, the incident beam beam and the reflected beam beam completely match. Such a system is called a cat's eye optical system. In such a system, when mirror 14 is rotated by θ (mirror comes to position 14'), beam 16
has an angle of 2θ with the optical axis after being reflected by the mirror 14. Here, if θ is small enough, by rotating the mirror by θ, △
The focal point can be moved by x=2θ.

Considering the reflected light from the irradiated object 12 in FIG. 2, if the drive mirror 14 is rotated by θ, it will follow the path shown by the broken line and return from the beam 16 as a beam 19 translated by D. come. Further, the amount of parallel movement D can be determined from simple geometric considerations as follows: D≒2(z/-1)△x (1). Here, z is the distance between the lens 13 and the rotation center 53 of the mirror, as shown in the figure.

Here, the optical system shown in Fig. 2 is used as a signal reproducing device,
The irradiated object 12 is used as a recording medium, and the driving mirror 14
Considering the case where tracking is performed by rotating the recording medium and the light receiving element receives and detects the reflected light from the recording medium, the parallel movement of the reflected light as described above is very inconvenient. This is because when the light receiving element is installed at the position of the beam 16, the mirror 1 is
4 is rotated by θ, the reflected light causes a positional shift between the light receiving element and D, as in the case of beam 19, and accurate signal detection cannot be performed.

In the present invention, the distance z in FIG. 2 is set equal to the focal length of the lens. In the present invention, considering the case where the beam 16 is reflected by the driving mirror 14 at an angle of 2θ with respect to the optical axis, this beam is reflected by the lens 13 parallel to the optical axis since z is the focal length of the lens 13. deflected in the direction.
That is, the beam is perpendicularly incident on the irradiated object 12 and is reflected at the position of the beam 16 following the same optical path as the incident optical path.

This can be easily understood from the above equation (1). That is,
In equation (1), by setting z=, D becomes zero, which indicates that no parallel movement of the reflected beam with respect to the incident beam occurs.

Also, as in the previous case, beam 17
is at the position of beam 18, and beam 18 is at the position of beam 17.
It will return to the position of Therefore, in the present invention, when a light beam whose optical axis passes through the rotation center of the drive mirror is incident,
Regardless of the beam scanning by the driving mirror, the incident beam and the reflected beam always match.

As explained above, the present invention has an effect that the reflected light beam from the irradiated object always returns to a fixed position in the conventional light beam scanning optical system, and the present invention has the effect that the light beam reflected from the irradiated object always returns to a fixed position, and the light beam is suitable for use in signal reproducing devices. This is a scanning optical system.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of an optical system of a conventional signal reproducing device, and FIG. 2 is a schematic diagram illustrating the optical system of the present invention. 12...Irradiated object, 13...Objective lens, 1
4... Drive mirror, 15... Center of rotation, 16,1
7, 18, 19...Light beam, 20...Lens center.

Claims (1)

[Claims] 1. A light source, a driving mirror that deflects the light beam emitted from the light source, and a light beam deflected by the driving mirror,
an objective lens for focusing a light beam on a track provided on the surface of an object to be irradiated, which is made of a light-reflecting plane arranged at right angles to the optical axis; A beam scanning optical system comprising means for receiving light via a driving mirror and detecting a tracking signal, and means for rotating the driving mirror in accordance with the detected tracking signal to track the track of the irradiated object, The center of rotation of the driving mirror is located at a position on the reflective surface of the driving mirror that coincides with the optical axis of the objective lens, and the distance between the center of rotation and the center of the objective lens is equal to the focal length of the objective lens. A beam scanning optical system featuring: