Light source unit and method of adjusting for maximizing focus and tracking errors thereby

• US 5,442,616 A
• Filed: 02/11/1993
• Issued: 08/15/1995
• Est. Priority Date: 02/13/1992
• Status: Expired due to Term

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Sato, Hideaki, Ogata, Nobuo
• Primary Examiner(s): Epps, Georgia Y.
• Assistant Examiner(s): CHU, KIM KWOK
• Application Number:
  US08/016,456
• Time in Patent Office: 915 Days
• Field of Search: 369/112, 369/109, 369/44.37, 369/44.14, 369/44.32, 369/44.23, 369/44.38, 369/122, 369/44.12, 369/44.41
• US Class Current: 369/44.23
• CPC Class Codes: G11B 7/123 Integrated head arrangements, e.g. with source and detectors mounted on the same substrate
• CPC Class Codes: G11B 7/1353 Diffractive elements, e.g. holograms or gratings diffraction gratings per se G02B5/18; holograms per se G02B5/32; grating systems G02B27/44
• CPC Class Codes: G11B 7/22 Apparatus or processes for the manufacture of optical heads, e.g. assembly

Abstract

A diffraction element is positionally adjusted on a substitute optical head arrangement while an objective lens is positionally adjusted so as to maximize a total signal calculated in a photodetector, whereby predetermined focusing error signal and tracking error signal are obtained. The thus adjusted diffraction element is adhesively secured on a package housing a light source and a photodetector to form a light source unit. The thus prepared light source unit is positioned on and assembled into an optical head by angularly adjusting the light source and an objective lens on the optical head individually so that both the optical axis of the light, emitted from the light source, and incident on a recording medium and the axis of the objective lens are aligned normal to the recording medium and by coinciding the optical axis of the objective lens with the center of intensity distribution of the incident light on the objective lens. This configuration eliminates the necessity of mechanical parts on the optical head for adjusting the diffraction element and the necessity of a space for the adjustment, so that it is possible to promote the optical head small and light-weighted. In addition, by effecting the optical adjustment when the light source unit is assembled into the optical head, error signals can be adjusted. Therefore, the adjustment step can be omitted.

Claims

1. A light source unit which is utilized together with;

a collimator lens and an objective lens;

means for producing a signal for focusing and tracking which is calculated by adding up all amounts of light received by respective light receiving areas of a light receiving element;

means for adjusting a position of the objective lens, so as to maximize the signal;

where said light source unit which is integrally constructed of a package comprising;

a light source of an optical head and the light receiving element housed therein with a diffraction element which is adhesively secured on said package wherein predetermined focusing error signal and tracking error signal are obtained.

2. A method for predetermining and obtaining focus and tracking error signals in an optical head that includes a light source unit which is utilized together with a collimator lens and an objective lens;

means for adjusting a position of the objective lens, so as to maximize a signal for focussing and tracking, which signal is calculated by adding up all amounts of light received by respective light receiving areas of a light receiving element;

where said light source unit which is integrally constructed of a package comprising;

a light source of an optical head and the light receiving element housed therein with a diffraction element which is adhesively secured on said package, the method comprising the steps of;

(a) angularly adjusting individually the light source and the objective lens so that both an optical axis of light from the light source which is incident to a recording medium, and an axis of the objective lens is aligned normal to the recording medium; and

(b) positioning the light source so that it coincides with the objective lens optical axis with the center of intensity distribution of incident light on the objective lens.

3. A method for obtaining a predetermined focus and tracking error signal in an optical head that includes

a light source;

a collimator lens converting light emitted from said light source into a parallel beam;

an objective lens which is supported for movement in a direction perpendicular to an optical axis for condensing the parallel beam on a recording medium and leading the light reflected on and from the recording medium to a diffraction element;

a light receiving element for detecting a focusing error signal and tracking error signal based on the reflected light, said light receiving element is divided into at least two light receiving areas; and

a diffraction element disposed at a point on the optical path between said light source and the recording medium for leading the reflected light from the recording medium to said light receiving element, the method comprising the steps of;

(a) providing an integrated luminous block containing said light source and said collimator lens,

(b) moving the luminous block and objective lens relative to each other, so that the objective lens is adjusted relative to the intensity distribution of light incident on the objective lens,

(c) moving the diffraction element while said luminous block and objective lens are moved relative to each other so as to maximize a signal for focussing and tracking which is calculated by adding up all the light amounts received by respective light receiving areas of said light receiving element; and

(d) further adjusting a position of the diffraction element precisely so as to obtain the predetermined focus error signal and tracking error signal.

4. The method of claim 3, wherein said relative movement is performed by moving the luminous block.

5. The method of claim 3, wherein said relative movement is performed by moving the objective lens.