JPS61118708A - Lens for optical disk - Google Patents

Abstract

PURPOSE:To reduce the size and weight of a device by setting NA to >=0.1 at a semiconductor laser side and to >=0.4 at a disk side, and satisfying a specific conditional equation. CONSTITUTION:Light from a semiconductor laser 1 is converted on a disk pit surface through an aspherical lens 3 and cover glass 3 and its reflected light is made incident on a detector 5. The distance X from the optical axis of a lens for this optical disk to a contact plane at the peak of the aspherical surface at height H is as shown by the equation I, and specific conditional inequalities II hold, where K is a conic coefficient K, 10 is the distance from the laser 1 to the pit surface, and (r) is the radius of curvature. An equality (1) is for the size reduction of the device and the compensation of sine condition, an inequality (2) is for the compensation of sine condition and a spherical aberration, and inequalities (3) and (4) are for the balancing of the spherical aberrations of the 3rd surface r3 and the 4th surface r4. In this case, H is the height from the optical axis, (f) the focal length of the lens for the disk, n3 the refractive index of a single lens, and D, E, F, and G coefficients of terms proportional to the incidence height raised to the 4th power, the 6th power, the 8th power, and the 10th power. Consequently, the device is reduced in size and weight.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention uses an optical disc lens, specifically a semiconductor laser, as a light source, and a beam splitter or scoop type information reproduction system between the light source and the disc objective lens. The device relates to an optical disc lens in which a transparent flat plate is arranged.

(Prior Art) In a lens system for an optical disc, laser light from a semiconductor laser passes through the lens system and converges on the bit surface on the disc, which is an information recording medium.

After the reflected light passes through the lens system again and a part of the returned light is deflected by the beam splitter, it enters the de (chictor) and obtains the 1st fish signal and the 1st to 8th rucks. A scoop type device is known in which the reflected light from the disk is returned to the semiconductor laser as a light source through a lens and a flat plate, and changes in the output light of the semiconductor laser are detected by a detector. ing.

(Problems to be Solved by the Invention) In an optical disc lens system, the semiconductor laser and objective lens work together during focusing and tracking operations, so in order to improve responsiveness to control signals, It is desirable that the components of an optical disc lens system be made as small and lightweight as possible. Also,
Generally, the lens system of this system uses a collimating lens to convert the laser beam from the light source into a parallel beam, and then uses an objective lens to correct aberrations so that the parallel beam falls within the diffraction limit. The system generally includes a collimating lens and an objective lens.

A plurality of other adjustment parts are required, which tends to cause deterioration in system performance and increases costs. Furthermore, lenses for optical discs require a resolution of at least 1 μm in order to read signals on discs recorded at high density.

It is important to correct the sine condition in order to correct the optical characteristics within the necessary range considering variations due to m adjustment, and it is also required to increase the working distance to prevent contact between the lens system and the disk. .

(Means for Solving the Problems) The present invention provides an aspherical lens that has the functions of a collimating lens and an objective lens, and solves the above-mentioned problems.

The optical disc lens of the present invention is an aspherical lens in which both the third and fourth surfaces in FIG. The NA on the semiconductor laser side should be 0.1 or more, and the NA on the optical disk side should be O.
o·1 or more and satisfies the condition of first order.

(1) 0.1<<0.251.0 (2) -1,0<K3<0 (4) K/l<-1,0 However, X: At the height of H from the optical axis Distance of aspherical apex from tangent plane H: Height from optical axis C: Curvature of aspherical apex (1/R) K: Conic coefficient f: Focal length of disk lens 1.0: Conductor laser oscillation surface distance from to the bit surface of the disk r3: radius of curvature near the light source side apex of the single lens n3: refractive index of the single lens, E, F, G: 4th power, 6th power of each incident height,
Vertex coefficients proportional to the 8th power and the 0th power FIG. 1 shows an example of an optical disc lens system using the optical disc lens of the present invention. Beam splitter 2. An optical disc lens 3 and a detector cover glass are shown. Light from light source 1 is transmitted to beam splitter 2. It passes through the lens 3 and the cover glass 4 and converges on the bit surface on the disk,
A part of the reflected light is deflected by the beam splitter 2 and enters the detector 5.

Figure 2 is a two-dimensional representation of the emission radiation pattern and energy intensity distribution of a semiconductor laser, and a three-dimensional diagram of the energy intensity distribution corresponding to NA on one emission axis of the semiconductor laser radiation pattern is 0.15. As can be inferred from Figure 3, in order to obtain the maximum efficiency without causing distortion in the energy distribution from the emission pattern of the semiconductor laser, the NA on the semiconductor laser side should be 0.1 to 0.2.
The NA on the laser side in the present invention is preferably set to approximately 0.15, which is an ideal value.

In this type of optical system, the collimating lens system and the objective lens system generally perform their own corrections. Therefore,
The condition for the light flux entering the objective lens is usually 1.0 = (V)
Therefore, it is treated as aberration-free light. On the other hand, in the case of the objective lens of the present invention, in the case of a beam splitter or scoop method, since a transparent flat plate is present, there is a large aberration in the incident light beam, and it is necessary to perform aberration correction including this aberration. . The above condition (1) particularly indicates correction of the size of the device and the sine condition, and is also a condition for keeping the working distance VD large.

Each of the above conditions (1) to (4) will be explained below.

(1) 0.1<f/1.0<0.25 Among these conditions, if f/1.0 exceeds the lower limit of 0.1, the device becomes large and the intended purpose cannot be achieved. Moreover, when the upper limit of 0.2 is exceeded, it becomes difficult to correct the sine condition within the necessary good image range, and the working distance VD becomes small.

(2) -1<K3<0 This condition defines the shape of the third surface, and 3 is the upper limit of 0.
If it exceeds the lower limit -0, 1, it becomes difficult to correct the sine condition within the necessary range, and if the lower limit -0,1 is exceeded, the spherical aberration increases, making it difficult to correct the central part.

This condition depends on the lens shape, and if the power applied to the third surface is exceeded, spherical aberration and off-axis aberration become unbalanced, and astigmatism also increases. If the lower limit of 0.5 is exceeded, it becomes difficult to correct five-spherical aberration.

(4) K4<-1,0 This condition defines the shape of the fourth surface and also relates to the balance of residual aberrations. If this condition is exceeded, the sine condition increases, and off-axis comatic aberration increases, making it impossible to maintain balance with one-spherical aberration.

(Example) Focal length f = 4.0 + am, 1.0 = 24.15 ma
+, working distance = 3.0mm, wavelength used = 780 stops, NA on the disk side = 0. /15. Laser side NA=0.1
5 (Effects) According to the present invention, it is possible to reduce the size and weight of an optical disc lens system without deteriorating its performance.
Various conventional problems can be solved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of an optical disc lens system using the lens of the present invention, and FIG. Figure 3 is an intensity distribution diagram that two-dimensionally displays the emission radiation pattern and energy intensity distribution of a semiconductor laser. A three-dimensional diagram of the energy intensity distribution corresponding to NA=0.15 on the emission axis, and FIG. 4 is an aberration curve diagram of the example. 1... Semiconductor laser, 2... Beam splitter 13... Aspherical lens, r3... Third surface,
r4...Fourth side. 734 shakun A -41 agency 11//'IIL -afpn
n a//ml-ring @ aberration
Fish Harvest - = JE Ko 4 + - Procedural Amendment

Claims (1)

[Claims] A beam splitter (where the first and second surfaces are mutually parallel planes) is provided between the semiconductor laser and the aspherical lens whose third and fourth surfaces both have positive refractive power. In the scoop method, it is an optical disk lens configured by arranging a transparent flat plate, and is an aspherical surface including at least a term proportional to the 10th power of the incident height as shown in the formula below, and N on the semiconductor laser side.
A lens for an optical disc, which is configured such that A is 0.1 or more and NA on the disc side is 0.4 or more, and satisfies the following conditions (1) to (4). X=(CH^2)/[1+1-(k+1)C^2H^2
]+DH^4+EH^6+FH^8+GH^1+...
(1) 0.1<f/(L0)<0.25 (2)-1.0<K3<0 (3)0.5<(n3-1)/(r3)・f<1.0(
4) K4<-1.0 However, /R) K: Conic coefficient f: Focal length of the disk lens L0: Distance from the semiconductor laser oscillation surface to the bit surface of the disk r3: Radius of curvature near the light source side vertex of the single lens n3: Refractive index of the single lens D, E, F, G: 4th power, 6th power, 8th power for each incident height
Coefficient of the term proportional to the 10th power