JPS62173401A - Method for fitting and adjusting refractive index distribution lens - Google Patents

Abstract

PURPOSE:To obtain an optical head of desired numerical aperture and working distance at all times by setting an interval between a lens contact surface and an object side end face of a lens frame, and a diameter of a diaphragm accordingly, even if an optical characteristic of a refractive index distribution lens to be fitted is varied. CONSTITUTION:In accordance with a focal distance f', a working distance WD', a center wall thickness (d) and a radius of curvature R, of a refractive index distribution lens 1 to be fitted, desired numerical aperture NA and working distance WD are obtained from equations I, II. Values of (a) and (l) are derived, respectively, a diaphragm 5 is worked so that these (a) and (l) are obtained, and thereafter, the refractive index distribution lens 1 is fitted by making its curved surface 1a abut on a lens contact surface 5a. In this way, when (a) and (l) of a lens frame 2 are set in accordance with an optical characteristic of the refractive index distribution lens 1 to be fitted, an optical head of desired numerical aperture NA and working distance WD can be obtained without being influenced by a variation of its optical characteristic.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides a lens frame having a lens contact surface and an aperture diaphragm, which is mounted so as to be displaceable with respect to an object, and a gradient index lens mounted on one surface of the lens frame. The mounting of the gradient index lens in manufacturing an optical head by mounting the gradient index lens in contact with the lens contact surface relates to an adjustment method.

[Conventional technology]

For example, as an optical pickup used to reproduce information recorded on an optical recording disk or to record information on such a disk, an objective lens for projecting a light spot onto the disk is configured with a gradient index lens. have been proposed previously.

[Problem that the invention seeks to solve]

However, in order to obtain such a gradient index lens, it is difficult to control the refractive index distribution constantly during the manufacturing process, and variations in the refractive index distribution occur between lenses. The lens design, ie, the radius of curvature of the lens surface and the center wall thickness, must be changed accordingly so that the aberrations are minimized.

On the other hand, in an optical pickup, in order to project the beam formed by the objective lens onto the disk in a focused state, an optical head consisting of an objective lens and a lens frame that holds it is placed against the disk. The lens is held movable in the optical axis direction, and is driven by a focusing drive mechanism based on a focusing error signal to perform focusing servo. In such an optical pickup, in order to obtain desired characteristics, it is necessary to set the numerical aperture of the optical head and the working distance to the disk to predetermined values.

However, when trying to use a gradient index lens like the one described above as an objective lens, its radius of curvature and center wall thickness differ between lofts, and therefore the numerical aperture and working distance of the lens itself differ. If the optical head is always mounted at a predetermined position, the numerical aperture and working distance of the optical head will change accordingly, resulting in a problem that the resolution and accuracy of the focusing servo by the focusing drive mechanism will deteriorate.

This invention has been made with attention to these problems, and it proposes an adjustment method for mounting a gradient index lens that allows an optical head with desired characteristics to be obtained even if the optical properties of the gradient index lens change. The purpose is to provide.

[Means and effects for solving the problem] In order to achieve the above object, in this invention, the distance from the object-side end surface of a lens frame having a lens contact surface and a diaphragm to the lens contact surface and the diameter of the diaphragm are Adjust the working distance and numerical aperture of the lens according to the optical characteristics of the gradient index lens to be attached, so that the working distance and numerical aperture of the lens are set to predetermined values, and then bring one surface of the gradient index lens into contact with the lens contact surface. and attach it to the mirror frame.

〔Example〕

FIG. 1 shows a first embodiment of the invention. In this embodiment, an optical head for an optical pink amplifier is manufactured, and a gradient index lens 1 is made of a plano-convex lens.A lens frame 2 to which this lens is attached is attached to an optical pickup so as to be displaceable in its axial direction. The drive mechanism drives the light beam 3 to focus it on the disk 4.

In this embodiment, a diaphragm 5 that also serves as a support for the gradient index lens 1 is provided on the lens frame 2, and the curved surface 1a of the gradient index lens l is brought into contact with one surface (lens contact surface) 5a of the diaphragm 5. Then, store this inside the lens frame 2 and attach it.

Hereinafter, a method for adjusting the attachment of this gradient index lens 1 will be explained.

The working distance WD in the optical head shown in FIG. 1 is the distance between the end surface (object side end surface) 2a of the four disks of the lens frame 2 and the surface (object surface) 4a of the disk 4, and the distance between the gradient index lens l When considered as a single lens, the working path 4WD' is the distance between the plane 1b of the gradient index lens 1 and the object surface 4a. In this example, a gradient index lens l consisting of a plano-convex lens with a center wall thickness d and a radius of curvature R is constructed such that its curved surface is aligned with the lens contact surface so that the working distance WD of the optical head and the aperture DNA are respectively desired values. 5a and install it inside the lens frame 2.

Here, if the focal length of the gradient index lens 1 to be attached is f', and the diameter of the aperture 5 of the lens frame 2 is a, then the numerical aperture N^ of the optical head is as follows. Therefore, in order to obtain the desired aperture fiNA, a = to 2f'
・・・・・・(2) will suffice. Further, if the distance between the object-side end surface 2a of the lens frame 2 and the lens contact surface 5a is l, the working distance of the optical head is as follows: WD=WD' -Ce -(d-R(1-cos θ)
)]・・・・・・・・・(3) However, sin θ−1R. Therefore, to obtain the desired working distance WD, ff=WD"-, d-1? (1-cos θ)-
WD −・−・−・(4+ will suffice.

Therefore, in this embodiment, the desired aperture is determined from equations (2) and (4) above according to the focal length f', working distance WD', center wall thickness d, and radius of curvature R of the gradient index lens 1 to be attached. The number NA and working distance WD are obtained. a and! After determining the values of a and β, the aperture 5 is processed so that these values a and β can be obtained, and then the gradient index lens 1 is mounted with its curved surface 1a in contact with the lens contact surface 5a.

In this way, if a and 2 of the lens frame 2 are set according to the optical characteristics of the gradient index lens l to be attached, the desired numerical aperture NA can be achieved without being affected by changes in the optical characteristics.
An optical head having a working distance of WD and a working distance of WD can be obtained.

Furthermore, since the aperture 5 is processed to set a and 12 so as to obtain the desired NA and WD, the inclination of the optical axis due to manufacturing errors of the gradient index lens 1 can also be corrected by this processing. can.

FIG. 2 shows a second embodiment of the invention. In this embodiment, the aperture 5 also serves as a receiver for the gradient index lens l.
is formed continuously on the end surface 2a at the object side end of the lens frame 2, and the surface of the diaphragm 5 opposite to the object side end surface 2a is used as a lens contact surface 5a, and a plano-convex lens is formed on this lens contact surface 5a. The gradient index lens 1 is mounted in the lens frame 2 by bringing the flat surface 1b of the gradient index lens 1 into contact with the lens.

Here, as in the first embodiment, the focal length of the gradient index lens 1 to be attached is f', the working distance is WD', the diameter of the aperture 5 is a, and the distance between the object side end surface 2a of the lens frame 2 and the aperture 5 is When the distance from the lens contact surface 5a, that is, the thickness of the aperture 5 is t, the numerical aperture NA and working distance of the optical head are as follows: WD = WD' - t (
6). Therefore, in order to obtain the desired numerical aperture NA and working distance -D, a γN8 ・2f'...
...(7) t = WD' - WD ・
・・・・・・・・・(8) will suffice.

Therefore, in this embodiment, the desired numerical aperture NA and working distance WD can be obtained from equations (7) and (8) above, depending on the focal length f' and working distance WD' of the gradient index lens l to be attached. Find the values of a and t, respectively,
After processing the aperture 5 so that these a and t are obtained, the gradient index lens 1 is attached so that its plane 1b is the lens contact surface 5.
Install it in contact with a.

In this way, as in the first embodiment, it is possible to obtain an optical head with a desired numerical aperture NA and working distance WD without being affected by changes in the optical characteristics of the gradient index lens 1 to be attached. By processing the diaphragm 5, it is also possible to correct the inclination of the optical axis due to manufacturing errors of the gradient index lens l. Further, in this embodiment, the lens contact surface 5a
Since the plane 1b of the gradient index lens 1 is brought into contact with the lens 1, there is an advantage that centering and positioning thereof can be easily performed.

Although the lens contact surface 5a is formed on the diaphragm 5 in the embodiment described above, these may be formed separately.

Further, the present invention is not limited to optical heads for optical pickups, but can be effectively applied to manufacturing optical heads for other optical instruments such as microscopes.

〔Effect of the invention〕

As described above, according to the present invention, even if the optical characteristics of the gradient index lens to be attached change, the distance between the lens contact surface and the object-side end surface of the lens frame and the diameter of the diaphragm can be set accordingly. Therefore, an optical head with a desired numerical aperture and working distance can always be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention, and FIG. 2 is a diagram showing a second embodiment.

Claims (1)

[Claims] 1. An optical head is manufactured by attaching a gradient index lens to a lens frame that has a lens contact surface and an aperture and is displaceably mounted relative to an object, with one surface of the lens in contact with the lens contact surface. In this process, the distance of the lens contact surface from the object-side end surface of the lens frame and the diameter of the diaphragm of the gradient index lens to be attached are adjusted so that the working distance and numerical aperture of the optical head are respectively desired values. A method for attaching and adjusting a gradient index lens, comprising: mounting the gradient index lens on the lens frame after adjusting the gradient index lens according to its optical characteristics.