JPS6052939A - Optical head - Google Patents

Abstract

PURPOSE:To attain an optical head with compact and simple constitution by providing a focusing rod lens with a large aperture having its both end surfaces made flat or turned into front sphere by an irradiating means of light spots and a collimator lens system having a circular aparture to cut off the peripheral beams at the output end of said rod lens. CONSTITUTION:The linear polarized light from a laser light source 201 is turned into parallel beams by a focusing rod lens 203 having a large aperture with its both ends made flat or turned into front sphere. While the peripheral beams are cut off by a collimator lens having a circular aperture 205. Thus parallel beams 206 having no disorder are made incident. These beams 206 are focused by a focusing lens 210 via a polarizing prism 207, 1/4 wavelength plate 208 and a total reflecting prism 209. A focused light spot 211 is sent back to the prims 207. Thus the linear polarized light having a plane of polarization orthogonal to that obtained in an incident mode is produced. This polarized light travels only toward a half mirror 215. Thus a track signal 218 corresponding to the track position is detected together with a focusing signal 219 which is turned into the focus position information.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical head that detects recorded information from an optical head.

In this type of optical head, in order to correctly reproduce information, it is necessary to make the beam from the V-the light source into a sufficiently small spot. Therefore, the collimating lens system must have as little aberration as possible and have a predetermined beam diameter.

Conventional collimating lens systems are generally composed of a combination of about three lenses designed using a ray tracing method.

Therefore, the first drawback of the conventional optical head is that it is large. In other words, even if a semiconductor laser is used as a small laser light source in an optical head, a galen lens with a large numerical aperture is required to collimate the wide-angle beam emitted from the semiconductor laser. However, there is a limit to the lens diameter that can be manufactured, and even if you make the lens diameter as small as possible, it will only be 5 to 6 m at most! It is. Therefore, at present, as shown in the cross-sectional view of the collimating lens system in Fig. 1, a single lens with a force and V lens diameter of approximately 611II11 is combined with a focal length of 15 to 15mm.
A 20-sieve collimating lens can be used with conventional optical heads (・
It is being Therefore, in the combination lens, the optical path length is 15 to 2
011111 is required. The first drawback of conventional optical heads is their high cost. That is, in order to create a collimating lens system with a compact size and a large aperture ratio, it is extremely difficult to polish and center a plurality of small lenses each having a diameter of 5 to 6 mm. Furthermore, in order to increase the collimation efficiency of the lens, each lens must be coated with anti-reflective coating on both sides. Therefore, man-hours and material costs increase. Second, the conventional optical head requires additions such as a spacer and a lens holder to the collimating lens system, resulting in a complicated configuration. In other words, constructing the combined lens system using Canadian balsam or other materials like a normal optical system (using the bonding method) is difficult to achieve a high-quality beam pattern due to diffraction at the bonded part in the case of a laser beam. Therefore, it is necessary to arrange the individual V lenses 101 discretely using spacers 102. Also, in order to keep the optical axis within a predetermined tolerance range, the lens holder 1
03, Sube 9J02 was cut with a very small pitch.

As described above, conventional optical heads cannot be made compact and tend to be expensive. The drawback is that the configuration is too complex (
·Ta.

Accordingly, an object of the present invention is to provide an optical head that is small in size, low in cost, and simple in construction.

The optical head of the present invention detects recorded information from the reflected light of a light spot that follows and irradiates a track on a recording medium.
a large-diameter focusing rod lens with flat or spherical end surfaces; and a focusing rod lens located at the output end of the focusing rod lens;
It is characterized by comprising a collimating lens system having a circular aperture that brightens the beam at the periphery.

Next, the present invention will be explained with reference to the drawings.

FIG. 2 is a configuration diagram showing an embodiment of the optical head of the present invention. Linearly polarized light 202 emitted from a laser light source 201 is converted into parallel light by a large-diameter focusing rod lens 203 with both end faces flat or spherical. A circular aperture 205 is provided near the output end of the converging rod lens 203 to obscure the beam at the periphery. The circular aperture 205 draws a sinusoidal or helical optical path within the convergent rod lens 203 (and the beam propagates through the convergent rod lens 203 due to non-uniformity of the refractive index distribution or reflection at the cleavage surface). The circular aperture 205 emits parallel light 206 that is as strong as the mode.The parallel light 206 is
After passing through the polarizing prism 207, the % wavelength plate 208. The total reflection prism 209 is focused by a trans-Cy orcus lens 210. The focused light spot 211 is reflected by the track 213 on the rotating recording medium 212, and the reflected light 214
Re-Hifu Orcus V's 210. After passing through the X wavelength plate 208, it returns to the polarizing prism 207. Since the reflected light 214 reciprocates through the wavelength plate 20B, it becomes linearly polarized light with a plane of polarization perpendicular to that at the time of incidence.
Proceed only in the direction of 215.

The diffracted turns that have passed through the half mirror 215 are detected by a track detector 216. The focus detector 217 is irradiated with
track signals 218, each corresponding to a track position;
．． The focus position information and the focus signal 219 are
Furthermore, the recorded information is detected from at least one side of the track signal 218° and the focus signal 219.
The linearly polarized light 202 in the vertical transverse mode is emitted from the V-the light source 201 and enters the large-diameter focusing rod lens 203 via the cover glass. The focusing rod lens 203 has a length of about 1o,
The diameter is 4-5I+a, and the numerical aperture NA of the lens is 0.4-0.
6. Regarding aberrations, the refractive index distribution reduces the fourth and sixth order terms as much as possible.
It is also possible to integrate it with

According to the present invention, it is possible to realize an optical head that is small in size, has a simple configuration, and can reduce manufacturing man-hours and material costs.

[Brief explanation of the drawing]

1 is a sectional view showing a conventional collimating lens system, and FIG. 2 is a configuration diagram showing an embodiment of the optical head of the present invention. 201...Laser light source, 202...Linearly polarized light, 203...Dog caliber focusing rod lens, 204...Light in a dirty mode, 205...
...Circular aperture, 206 ...Parallel light, 21
1... Light spot, 212... Recording medium, 213... Track, 214...
Reflected light, 215...Half mirror-1216...
...Track detector, 217...Focus detector, porridge flash

Claims (1)

[Claims] In an optical head that detects recorded information from the reflected light of a light spot irradiated following a track on a recording medium, the irradiation means of the light beams have a large-cut convergence type in which both end surfaces are flat or have a spherical tip. An optical head comprising a collimating lens system having a rod lens and a circular aperture located at an output end of the converging rod lens and for illuminating a beam in one peripheral portion.