Optical waveguide device, coherent light source, integrated...

Details Optical waveguide device, coherent light source, integrated... Optical waveguide device, coherent light source, integrated...

2000-10-13

2002-12-31

Kim, Ellen E. (Department: 2874)

Optical waveguides

Integrated optical circuit

C385S130000, C385S037000

Reexamination Certificate

active

06501868

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical waveguide device and a coherent light source for use in a field such as optical information processing or optical communication. The present invention also relates to an integrated unit and an optical pickup device including the optical waveguide device or the coherent light source.
2. Description of the Related Art
In the optical information processing field, a small-sized light source for emitting light having a short wavelength is required for achieving high-density optical disks and high-definition displays. There are know techniques for generating light having a short wavelength. An example of such a technique is a second harmonic generation (hereinafter referred to as “SHG”) technique using a semiconductor device and an optical waveguide wavelength conversion (Yamamoto et al., Optics Letters Vol. 16, No. 15, 1156 (1991)) device using quasi phase matching (hereinafter referred to as “QPM”).
FIG. 20
is a diagram schematically showing a structure of a SHG blue laser
2000
using an optical waveguide type wavelength conversion device
83
. Herein, a tunable semiconductor laser
80
having a distribution Bragg reflection (hereinafter referred to as “DBR”: Distributed Bragg reflector) region is employed. A tunable semiconductor laser having a DBR region is hereinafter referred to as a tunable DBR semiconductor laser. The tunable DBR semiconductor laser
80
is an AlGaAs DBR semiconductor laser whose input is in a power range of around 100 mW and whose oscillated wavelength is in a band range of around 0.85 &mgr;m. The tunable DBR semiconductor laser
80
includes an active region
81
and a DBR region
82
. The oscillation wavelength of the semiconductor laser
80
can be adjusted by changing an amount of current injected into the DBR region
82
. The optical waveguide type wavelength conversion device
83
includes an optical waveguide
84
and a periodic polarization inversion region
85
on an X-plate MgO-doped LiNbO
3
substrate (the X axis of crystal is substantially perpendicular to the substrate). Laser light emitted from a facet of the tunable DBR semiconductor laser
80
is coupled with the optical waveguide
84
of the optical waveguide type wavelength conversion device
83
. With the configuration of
FIG. 20
, about 60 mW laser light out of about 100 mW laser output is coupled with the optical waveguide
84
. By controlling the amount of current injected into the DBR region
82
of the tunable DBR semiconductor laser
80
, the oscillation wavelength is fixed to fall within a wavelength allowance range of phase matching of the optical waveguide type wavelength conversion device
83
, resulting in about 10 mW blue light having a wavelength of about 425 nm.
Such as SHG blue laser may be used for an optical disk recording and reproduction apparatus. Referring to
FIG. 21
, an SHG blue laser
2000
is mounted in an optical pickup
2100
. A module (the SHG blue laser
2000
) emits blue light which is in turn collimated by a collimator lens
86
and transmitted through a polarizing beam splitter
87
(hereinafter referred to as “PBS”) and a quarter-wave plate
88
. Thereafter, the blue light is bent into a 90° angle (substantially perpendicular to the plane of the figure) by a raising mirror (not shown) and converged by an objective lens
89
onto an optical disk
95
. The light is reflected by the optical disk
95
and is bent into a 90° angle by the PBS
87
. The light is guided into a photodetector
91
(hereinafter referred to as “PD”) by a detection lens system
90
including a detection lens and a cylindrical lens. The photodetector
91
performs signal detection. With the optical pickup
2100
, a high-density optical disk of about 10 GB or more can be reproduced.
Uchida et al., the Spring Convention of the Institute of Electronics, Information and Communication Engineers of Japan, C3. 28, 1994 reports a technique in which a 45° cut is made in an optical waveguide to form a total reflection surface so that output light is in a direction substantially perpendicular to a substrate (see FIG.
22
). In this case, an optical waveguide
93
of glass is formed by conducting double ion exchange on a glass substrate
92
. A 45° cut
94
is provided in the optical waveguide
93
by microprocessing. The processing is performed using an appropriate blade. The sides of the cut
94
are polished at the time of cutting so that a reflection surface whose loss is as low as 0.3 dB can be obtained.
Recently, there is a demand for small and thin optical pickups as computers are being downsized. In order to achieve smaller and thinner optical pickups, it is important to downsize not only a light source of the optical pickup, but also the configuration of the optical pickup. In this case, it is also important to take measures against returning light, interference noise, or the like described below.
1) Small and thin optical pickup
In the configuration of the conventional optical pickup
2100
of
FIG. 21
, the optical axis of the module is parallel to the optical axis of the optical pickup
2100
. Therefore, the optical pickup
2100
is longer in the optical axis direction than in the width. When a semiconductor laser chip is employed, such an element is about 1 mm or less long, which is not problematic. In contrast, the SHG blue laser
2000
includes the optical waveguide type tunable device and the semiconductor laser. This causes the module size to be as long as 10 mm. The optical pickup
2100
becomes extremely long. Further, in the configuration of
FIG. 21
, the light detection system (the detection lens, the cylindrical lens, and the PD) is separated from the other parts of the optical pickup, causing the optical pickup to be large.
2) Measures against returning light
In the module including the semiconductor laser and the optical waveguide device, light reflected off the light-exiting facet of the optical waveguide is returned to the semiconductor laser. This causes the semiconductor laser to be in a multi-longitudinal mode, whereby noise characteristics are impaired.
3) Reduction in interference noise
In the SHG blue laser
2000
, blue light is obtained by converting the wavelength of the semiconductor laser light which is used as a fundamental wave. Therefore, even if part of reflected light from the outside is returned to the semiconductor laser, the returning light does not contribute to noise. As a result, the semiconductor laser can be operated in a single mode, thereby obtaining a low level of noise (about −140 dB/Hz or less). However, blue light is highly coherent, so that if a cavity structure is externally provided, the amplitude of the blue light varies due to interference as the cavity condition is changed. In the configuration of the optical pick
2100
of
FIG. 21
, the surface of an optical disk
95
and the light emitting facet of the optical waveguide type wavelength conversion device form a confocal optical system. Therefore, as the optical disk is rotated changing a cavity condition, the intensity of light received by the PD
91
varies, causing deterioration of a signal waveform upon reproduction of the optical disk
95
.
SUMMARY OF THE CONVENTION
According to one aspect of the present invention, an optical waveguide device comprises a substrate having first and second surfaces; and an optical waveguide provided on the first surface of the substrate, having a light-incoming facet and a facet inclined with respect to the optical waveguide. Guided light incident to the optical waveguide through the light-incoming facet is totally reflected off the inclined facet, and the guiding light is transmitted through the first or second surface of the substrate.
In one embodiment of this invention, the guided light is transmitted through the first surface of the substrate.
In one embodiment of this invention, the guided light is transmitted through the second surface of the substrate.
In one embodiment of this invention, the substrate is made of a nonlinear optical ma

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