Method of coupling external light into an optical waveguide and a guided wave from an optical waveguide and optical pickup employing an optical waveguide

• US 5,081,615 A
• Filed: 12/18/1989
• Issued: 01/14/1992
• Est. Priority Date: 12/16/1988
• Status: Expired due to Term

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Film Co Limited (Fujifilm Holdings Corporation)
• Inventors: Sunagawa, Hiroshi
• Primary Examiner(s): Envall, Jr., Roy N.
• Assistant Examiner(s): Dang, Hung
• Application Number:
  US07/451,677
• Time in Patent Office: 757 Days
• Field of Search: 369/44.12, 369/44.37, 369/44.38, 369/109, 369/112, 350/96.11, 350/96.14, 350/162.11, 350/96.12, 350/96.13, 350/96.15, 350/96.16, 360/114
• US Class Current: 369/44.12
• CPC Class Codes: G02B 6/34 utilising prism or grating G02B6/293 takes precedence
• CPC Class Codes: G11B 11/10543 using optical beam of radiation
• CPC Class Codes: G11B 7/124 the integrated head arrangements including waveguides
• 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

Abstract

A guided wave is coupled from an optical waveguide through a grating coupler, or an external light beam is coupled into an optical waveguide through a grating coupler. The grating coupler is disposed on a surface of the optical waveguide. The external light beam is diffracted by a wavelength-fluctuation-correcting grating in a direction opposite to the direction of diffraction by the grating coupler on the surface of the optical waveguide, while satisfying the Bragg condition or a predetermined equation. Alternatively, the external light beam is passed through an end surface of the substrate of the optical waveguide so that the light is refracted in the same direction as the direction of diffraction by the grating coupler on the surface of the optical waveguide, the end surface being inclined with respect to the optical waveguide at a certain angle. Optical pickups employing an optical waveguide are also disclosed.

Claims

1. A method of coupling external light to an optical waveguide or a guided wave from an optical waveguide through a grating coupler disposed on a surface of the optical waveguide, comprising the step of:

diffracting the external light with a wavelength-fluctuation-correcting grating in a direction opposite to the direction of diffraction by the grating coupler on the surface of the optical waveguide, while satisfying the Bragg condition defining the Bragg angle θ

_B as;

##EQU33## where λ

is the wavelength of the light, Λ

_GC is the period of the grating coupler on the surface of the optical waveguide, Φ

is the angle of incidence of the external light upon or the angle of exit of the external light from the grating coupler on the surface of the optical waveguide, nc is the refractive index of a medium on which the wavelength-fluctuation-correcting grating is disposed, and q is the coupling order number (=±

1, ±

2, ±

3, . . . ) of the grating coupler on the surface of the optical waveguide.

2. A method of coupling external light to an optical waveguide or a guided wave from an optical waveguide through a grating coupler disposed on a surface of the optical waveguide, comprising the step of:

diffracting the external light with a wavelength-fluctuation-correcting grating in a direction opposite to the direction of diffraction by the grating coupler on the surface of the optical waveguide, while satisfying the following equation;

##EQU34## when Λ and

θ

d are the period of and the angle of diffraction by the wavelength-fluctuation-correcting grating, m and q are the coupling order numbers (=±

1, ±

2, ±

3, . . . ) of the wavelength-fluctuation-correcting grating and the grating coupler on the surface of the optical waveguide, respectively, Λ

_GC is the period of the grating coupler on the surface of the optical waveguide, and Φ

is the angle of incidence of the external light upon or the angle of exit of the external light from the grating coupler on the surface of the optical waveguide.

3. A method of coupling external light to an optical waveguide or a guided wave from an optical waveguide through a grating coupler disposed on the surface of the optical waveguide, comprising the step of:

passing the external light through an end surface of the substrate of the optical waveguide so that the light is refracted in the same direction as the direction of diffraction by the grating coupler on the surface of the optical waveguide, said end surface being inclined with respect to the optical waveguide at an angle α

defined by;

##EQU35## where δ

is the ratio of the effective refractive index N of the optical waveguide to the refractive index n of the substrate at a desired temperature t_o, and Φ

is the angle of incidence of the external light upon or the angle of exit of the external light from the grating coupler at the temperature t_o.

4. An optical pickup for reading recorded information from an optical or magnetooptic recording medium, comprising:

i) means for applying a light beam to the recording medium;

ii) an optical waveguide;

iii) a light-introducing grating coupler mounted on said optical waveguide for diffracting a light beam reflected from the recording medium and introducing the diffracted light beam into said optical waveguide;

iv) light detecting means for detecting the light beam, which is converged in said optical waveguide so that the recorded information can be read and tracking and focusing errors can be detected therewith; and

v) a wavelength-fluctuation-correcting grating for diffracting the reflected light beam, before it is applied to said light-introducing grating coupler, in a direction opposite to the direction of diffraction by the light-introducing grating coupler, said wavelength-fluctuation-correcting grating being arranged such that it diffracts the reflected light beam while satisfying the Bragg condition defining the Bragg angle θ

B as;

##EQU36## where λ

is the wavelength of the light, Λ

_GC is the period of the light-introducing grating coupler, Φ

is the angle of incidence of the external light upon the light-introducing grating coupler, nc is the refractive index of a medium on which the wavelength-fluctuation-correcting grating is disposed, and q is the coupling order number (=±

1, ±

2, ±

3, . . . ) of the light-introducing grating coupler.

5. An optical pickup for reading recorded information from an optical or magnetooptic recording medium, comprising:

i) means for applying a light beam to the recording medium;

ii) an optical waveguide;

iii) a light-introducing grating coupler mounted on said optical waveguide for diffracting a light beam reflected from the recording medium and introducing the diffracted light beam into said optical waveguide;

iv) a plurality of light detectors for detecting the light beam, which is converged in said optical waveguide so that the recorded information can be read and tracking and focusing errors can be detected therewith; and

v) a wavelength-fluctuation-correcting grating for diffracting the reflected light beam, before it is applied to said light-introducing grating coupler, in a direction opposite to the direction of diffraction by the light-introducing grating coupler, said wavelength-fluctuation-correcting grating being arranged such that it diffracts the reflected light beam while satisfying the following equation;

##EQU37## where Λ and

θ

d are the period of and the angle of diffraction by the wavelength-fluctuation-correcting grating, m and q are the coupling order numbers (=±

1, ±

2, ±

3, . . . ) of the wavelength-fluctuation-correcting grating and the light-introducing grating coupler, respectively, Λ

_GC is the period of the light-introducing grating coupler, and Φ

is the angle of incidence of the reflected light beam upon the light-introducing grating coupler.