JPS6331766B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) This invention uses an optical disk lens, more specifically a semiconductor laser as a light source, and a beam splitter or a transparent flat plate in a scoop type information reproducing device between the light source and the disk objective lens. This invention relates to an optical disk lens in which a (Prior art) As a lens system for an optical disk, laser light from a semiconductor laser passes through a lens system and converges on a pit surface on the disk, which is an information recording medium, and the reflected light passes through the lens system again and returns. After part of the light is deflected by a beam splitter,
The light that enters the detector and is configured to obtain a focusing signal or tracking signal, or the reflected light from the disk, is returned to the semiconductor laser that is the light source via a lens and a flat plate, and the output light of the semiconductor laser is changed. A scoop-type device configured to detect this with a detector is known. (Problems to be Solved by the Invention) In the optical disk 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 the optical disk lens system be made as small and lightweight as possible. Additionally, in general, the lens system of this system uses a collimating lens to collimate the laser beam from the light source, and then corrects aberrations using the objective lens to bring the parallel beam within the diffraction limit. A lens system generally requires a collimating lens, an objective lens, and a plurality of other adjustment parts, which tends to deteriorate the performance of the system and also causes high costs. Furthermore, lenses for optical discs are
A resolution of at least 1μ is required to read signals recorded on a disc with high density, and in addition, it is important to correct the sine condition in order to correct the optical characteristics within the necessary range, taking into account variations due to adjustments. In addition, it is 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 disk lens of this invention is An aspherical lens whose third and fourth surfaces in FIG. 1 both have positive refractive power, which is expressed by the formula:
It includes at least a term proportional to the 10th power of the incident height, is configured such that the NA on the semiconductor laser side is 0.1 or more, and the NA on the optical disk side is 0.4 or more,
It satisfies the following conditions. (1) 0.1<f/I.0<0.25 (2) −1.0<K3<0 (3) 0.5<(n3−1)/r3・f<1.0 (4) K4<−1.0 where X: from optical axis Distance of aspherical apex from tangent plane at height H: Height from optical axis C: Curvature of aspherical apex (1/R) K: Conic coefficient f: Focus of disk lens Distance I.0: Distance from the conductor laser oscillation surface to the pit 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: 4 for each incident height squared, 6
Vertex coefficient proportional to power, 8th power, and 10th power Figure 1 shows an example of an optical disk lens system using the optical disk lens of the present invention. 2. It is composed of an optical disc lens 3 and a disc 5. Note that the reference numeral 4 indicates a cover glass of the disk. Light from a light source 1 passes through a beam splitter 2, a lens 3, and a cover glass 4 and converges on the bit surface on the disk, and a part of the reflected light is deflected by the beam splitter 2 and enters a detector 5. . Figure 2 shows a two-dimensional display of the emission radiation pattern and energy intensity distribution of a semiconductor laser, and the emission pattern on the emission axis of the semiconductor laser.
As can be inferred from Figure 3, which is a three-dimensional diagram of the energy intensity distribution corresponding to NA=0.15, in order to obtain the maximum efficiency without causing distortion in the energy distribution from the emission pattern of the semiconductor laser, it is necessary to The side NA is preferably set to 0.1 to 0.2, and the laser side NA in the present invention is preferably set to 0.1 to 0.2.
The NA is configured to be 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, since the condition for the light beam incident on the objective lens is usually 1.0=∞, it is treated as aberration-free light. In contrast, with the objective lens of the present invention,
I.0 is finite, about 0.1<f/I.0<0.25, and at the same time, in the case of a beam splitter or scoop method, there is a transparent flat plate, so there is a large aberration in the incident light flux, and this It is necessary to perform aberration correction including aberrations. The above condition (1) particularly indicates the correction of the size of the device and the sine condition, and is also a condition for keeping the working distance WD 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/I.0 exceeds the lower limit of 0.1, the device becomes large and the intended purpose cannot be achieved. Furthermore, 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 WD becomes small. (2) −1<K3<0 This condition defines the shape of the third surface.
When K3 exceeds the upper limit of 0, it becomes difficult to correct the sine condition within the necessary range, and when K3 exceeds the lower limit of -0.1, the spherical aberration increases, making it difficult to correct the central part. (3) 0.5<(n3-1)/r3f<1.0 This condition defines the lens shape and the power applied to the third surface. If (n3-1)/r3・f exceeds the upper limit of 1.0, the lens becomes spherical. Aberrations and off-axis aberrations become unbalanced, and astigmatism also increases. If the lower limit of 0.5 is exceeded, it becomes difficult to correct spherical aberration. (4) K4<-1.0 This condition defines the shape of the fourth surface and also concerns the balance of residual aberrations. If this condition is exceeded, the sine condition increases, and off-axis coma aberration increases, making it impossible to balance it with spherical aberration. (Example)

[Table] (Effects of the Invention) According to the present invention, an optical disk lens system can be made smaller and lighter without deteriorating its performance, and various conventional problems can be solved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of an optical disk 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, 3... Aspherical lens, r3... Third surface, r4
...Fourth page.

Claims (1)

[Claims] 1. Between the semiconductor laser and the aspherical lens whose third and fourth surfaces both have positive refractive power,
It is an optical disk lens that is constructed by arranging a beam splitter (transparent flat plate in the scoop method) whose first and second surfaces are parallel planes, and the term is proportional to at least the 10th power of the incident height as shown in the following formula. The NA of the semiconductor laser side is 0.1.
An optical disk lens that is configured so that the NA on the disk side is 0.4 or more and satisfies the following conditions (1) to (4). (1) 0.1<f/I.0<0.25 (2) −1.0<K3<0 (3) 0.5<(n3−1)/r3. f<1.0 (4) K4<-1.0 where X: Distance from the tangential plane of the aspherical apex at a point H from the optical axis H: Height from the optical axis C: Curvature of the aspherical apex (1/R) K: Conic coefficient f: Focal length of the disk lens I.0: Distance from the semiconductor laser oscillation surface to the pit surface of the disk r3: Radius of curvature near the apex on the light source side of the single lens n3: Single lens refractive index D, E, F, G: 4th power, 6 for each incident height
Vertex coefficient proportional to power, 8th power, 10th power