JPS60129941A - Optical head - Google Patents

Abstract

PURPOSE:To obtain a miniature and simple optics head with low cost by using a focusing rod lens of a large caliber which turns the beams given from a light source into parallel ones to form a collimator lens system. CONSTITUTION:For a collimator lens system, the beams radiated from a laser light source 201 are turned into parallel beams 206 through a focusing rod lens 203 of a large coliber which has a microfocus surface and a short focus with about 10mm. length. Therefore an optical path of about 10mm. suffices with the lens system. This can solve a problem where the size of an optical head is increased owing to the size of the collimator lens system. Furthermore both manufacturing processes, the material cost, etc. can be reduced since the production is not needed for plural microlenses. In addition, the lens 203 can be unified with the source 201 or a polarizing prism 207. This can omit additional parts such as a spacer, a lens holder, etc. As a result, the constitution of an optical head is simplified.

Description

[Detailed Description of the Invention] [Technical Field] The present invention involves converting light from a light source into parallel light using a collimating lens system, then turning the parallel light into a light spot, and following the light spot with a track on a recording medium. The present invention relates to an optical head that emits light and detects reflected light of the light spot from the recording medium.

[Prior art]

In this type of optical head, in order to correctly reproduce information, it is necessary to make the beam from the laser light source into a sufficiently small spot. Therefore.

The collimating lens system must have as little aberration as possible and must have a predetermined beam diameter.

Conventionally, collimating lens systems were designed using the ray tracing method6.
It is generally made up of a combination of lenses.

However, this six-course combination lens contained several problems. First, the optical gutter becomes larger. That is, a semiconductor laser is generally used as a laser light source in order to downsize the optical device, and a 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.

Even if the lens diameter is made as small as possible, it is only 5 to 6 degrees at most, and cannot be made extremely small.

Therefore, at present, as shown in Figure 1, the lens diameter is approximately 6W.
Single lens of Un] Focal length 15-2 with 6 01 lenses combined
A 0rtun collimating lens is used.

Therefore, this combination lens requires an optical path length of 15 to 2 degrees, and even if a semiconductor laser is used to make it compact, the collimator lens becomes troublesome and it is not possible to construct a compact optical path.

The second problem is that it increases costs. Namely.

To create a lens that is small and has a large aperture ratio.

It is very difficult to polish and center three individual lenses with a diameter of 5 to 6 wn.

It is an extremely difficult task. Unfortunately, in order to increase the collimation efficiency of the lens, each lens must be coated with anti-reflective coating on both sides. Therefore, the number of man-hours and material costs increase, resulting in an expensive collimating lens.

The third problem is that additional parts such as spacers and lens holders are required, making the configuration complicated. Namely.

If the combined lens system is constructed using a bonding method using Canadian balsam, etc. like a normal optical system, a high-quality beam pattern cannot be obtained due to diffraction of the laser beam at the bonded portion, so spacers are required. 102 must be used to discretely arrange the individual lenses 101. Further, in order to keep the optical axis within a predetermined tolerance range, the lens holder 103. The spacer 102 is threaded with a very small pitch. Therefore, additional items such as spacers and lens holders are required, resulting in a complicated configuration.

The problems with the collimating lens system based on the conventional combination method have been explained above, but in any case, the conventional method is too small and expensive. Problems such as the structure being too complicated have arisen, and it has been desired to realize an optical head that can improve these problems.

OBJECTS OF THE INVENTION Accordingly, an object of the present invention is to provide an optical head having a collimating lens system that eliminates the above-mentioned drawbacks.

[Structure of the invention]

According to the present invention, light from a light source is made into parallel light by a collimating lens system, and then the parallel light is combined into a light spot.
irradiating the light spot by following the track of the recording medium;
In an optical head that detects the reflected light of the light spot from the recording medium, the collimating lens system converts the beam from the light source into parallel light. An optical head is obtained which is characterized in that it consists of a large-diameter converging rod lens with a flat entrance end or a convex entrance end forming a part of a spherical surface of a predetermined radius.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a diagram showing an optical head according to an embodiment of the present invention. In the figure, linearly polarized light 202 emitted from a laser light source 201 has both an input end face and an output end face made flat, or an input end face that is a convex surface that forms part of a spherical surface with a predetermined radius, and an output end face that is flat. Large diameter (i.e.
by a focusing rod lens 203 with a diameter of 2 mm or more.

It becomes parallel light 206. The parallel light 206 passes through the polarizing prism 2
After passing through the 1/4 wavelength plate 208. Total reflection prism 2
09 and is focused by a focus lens 210. The converged light spot 211 is reflected by a track 213 on the rotating recording medium 212, and the two reflected lights pass through the focus lens 210, 174 and wavelength plate 208 again, and then return to the polarizing prism 207. Since the reflected light travels back and forth through the quarter-wave plate 208, it becomes linearly polarized light with a plane of polarization perpendicular to that at the time of incidence, and therefore travels only in the direction of the half mirror 215. The diffraction pattern that has passed through the half mirror 215 is detected by a track detector 216. The focus detector 217 is irradiated with trunk signals 218 . Focus signal 2
19 further includes a track signal 218° focus signal 2
At least recorded information is detected from either one of 19.

FIG. 3 shows the collimating lens system of FIG. In FIG. 6, linearly polarized light in a horizontal transverse mode and a vertical transverse mode, each of which has a length of several μm or 0.2 μm, is emitted from a laser light source 201 and enters a large-diameter focusing rod lens 203 via a cover glass 301. do. The focusing rod lens 203 is made by an ion exchange method or the like.
It is approximately alomm long, has a diameter of 4 to 5 mrn, and has an NA of 0.4 to 0.6. Focusing rod lens 20
No. 3 has a parabolic distribution in which the refractive index decreases from the central axis toward the outer circumferential surface, and the refractive index distribution is such that the fourth-order and sixth-order terms of aberration are reduced as much as possible.

A focusing rod lens 203 has a laser light source 201 on its focal plane.
206, parallel light 206 is emitted at the output end.

As is clear from the above figures 2 and 6.

In this example, in a collimating lens system.

The beam emitted from the laser light source 2 is converted into parallel light 206 by a large-diameter converging rod lens 203 having a short focus having a minute focal plane and having a length of about 10 lenses. Therefore, the optical path length of the collimating lens system is only about 10 degrees, and the problem that the optical head becomes large due to the collimating lens system can be alleviated. Furthermore, since it is not necessary to produce a plurality of microlenses, the number of man-hours and material costs can be reduced. Further, the focusing rod lens 203 can be integrated with the laser light source 201 or the polarizing prism 207, and has the advantage that additional objects such as spacers or lens holders are not required, making the configuration simple.

The embodiments of the present invention have been described above.

Each component has been modified as long as the basic operating principle 9 of the present invention is characterized by its operation, effect, etc. It is clear that the present invention can be applied to any optical head. For example, the large-diameter focusing rod lens 203 refers to a lens with a diameter of 2 mm or more, which has not been made conventionally.

〔Effect of the invention〕

As explained above, according to the present invention, an optical head having a small size, low cost, and a simple structure can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing a typical conventional collimating lens system, Fig. 2 is a configuration diagram of an optical head according to an embodiment of the present invention, and Fig. 6 is a sectional view showing the collimating lens system of Fig. 2. It is a diagram. 201...Laser light source, 202...Linearly polarized light. 203...Large diameter focusing rod lens. 206... Parallel light, 207... Polarizing prism, 20
8...1/4 wavelength plate, 209...Total reflection prism,
210... Focus lens, 211... Light spot, 212... Recording medium, 213... Track, 2
15... Half mirror 9216... Trunk detector, 217... Focus detector. 218...Track signal, 219...Focus signal. Agent (7127) B1 Rido Goto Yosuke Figure 1 Figure 2 Figure 3 Figure 3

Claims (1)

[Claims] 1. Light from a light source is made into parallel light by a collimating lens system, and then the parallel light is made into a light spot. irradiating the light spot while following the trunk of the recording medium;
In an optical node that detects the reflected light of the light spot from the recording medium, the collimating lens system converts the beam from the light source into parallel light. An optical head comprising a large-diameter focusing rod lens having a flat entrance end or a convex end forming a part of a spherical surface of a predetermined radius.