Optical waveguides – Planar optical waveguide
Reexamination Certificate
1998-12-09
2003-11-11
Font, Frank G. (Department: 2877)
Optical waveguides
Planar optical waveguide
C359S285000, C359S305000
Reexamination Certificate
active
06647196
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an optical device and, more particularly, to an optical device having an optical wave guide produced in the presence of acoustic standing wave.
DESCRIPTION OF THE RELATED ART
A typical example of the optical wave guide is an optical fiber. In order to confine light in the optical fiber, the optical fiber has a multilayer structure shown in
FIG. 1. A
core
1
a
is enclosed in a clad
1
b
, and the core
1
a
and the clad
1
b
are, by way of example, formed of quartz glass and compound glass, respectively. The quartz glass is larger in refractive index than the compound glass, and incident light L
1
repeats the total reflection on the boundary between the core
1
a
and the clad
1
b
. As a result, the light L
1
proceeds along the core
1
a
, and is radiated from the other end. The multilayer structure is achieved by a double crucible pulling down method and so on.
Another example of the optical wave guide is known as “diffusion type optical wave guide”. The diffusion type optical wave guide has an elongated portion with a large refractive index by replacing an element of single crystal material with another element.
FIG. 2
illustrates the diffusion type optical wave guide. A piece
2
a
of single crystal compound of LiNbO
3
is available for the diffusion type optical wave guide, and Li-site of the single crystal material is replaced with H
+
or Ti
3+
in an elongated portion
2
b
indicated by hatching lines. The elongated portion
2
b
is higher in refractive index than the remaining portion
2
e
of the single crystal compound, and serves as a wave guide. Incident light L
2
is propagated along the elongated portion
2
b
or the wave guide, and is radiated from the other end.
Another example of the optical wave guide is illustrated in FIG.
3
. The optical wave guide is categorized in the thin film wave guide, and has a plane wave guide of active material grown by using a liquid-phase epitaxy. The thin film wave guide increases the energy density of optically pumped laser light/oscillation light generated in the active material, and, accordingly, improves the oscillation threshold and the slope efficiency or input-and-output characteristics.
FIG. 3
illustrates a thin film wave guide or a planar optical wave guide disclosed by D. Pelenc et. al. in “High slope efficiency and low threshold in a diode-pumped epitaxially grown Yb:YAG wave guide laser”, Optics Communications, vol. 115, 1995, pages 491 to 497. A plane wave guide
3
a
, which is indicated by hatching lines, is sandwiched between Yb-doped YAG
3
b
and
3
c
. Al
3+
site is partially replaced with Ga
3+
, and the active material is epitaxially grown on the Yb-doped YAG substrate
3
b
so as to form the plane wave guide
3
a
. Yb-doped YAG with Ga
3+
is grown on the plane wave guide
3
a
, and the plane wave guide
3
a
is overlain by the Yb-doped YAG layer
3
c.
Various optical devices have been developed, and several optical devices are known as “acousto-optic device”. An interaction between optical material and an acoustic wave is known as an acousto-optic effect, and the acousto-optic effect is available for an optical device.
FIG. 4
illustrates an optical deflector analogous to the electro-acoustic element disclosed in Japanese Patent Publication of Unexamined Application No. 50-143547. The optical deflector has an electro-acoustic transducer
4
a
attached to a block
4
b
of optic material. The electro-acoustic transducer
4
a
generates an ultrasonic wave
4
c.
Laser light L
3
is obliquely incident onto the block
4
b
, and is propagated through the block
4
b
. The transmitted light L
4
is radiated from the block
4
b
. When the electro-acoustic transducer
4
a
is driven for generation of the ultrasonic wave
4
c
, Bragg reflection takes place due to the ultrasonic wave
4
c
due to an interaction between photon and phonon. If the electro-acoustic transducer
4
a
changes the frequency of the ultrasonic wave
4
c
, the laser light L
3
is diffracted, and is radiated from the block
4
b
as indicated by L
4
′.
In this instance, the acoustic wave is applied as a progressive wave. If the acoustic wave does not serve as a progressive wave, the diffraction intensity is drastically decreased, because the interaction between the photon and phonon causes the diffraction to take place.
A surface acoustic wave is also available for an optical device.
FIG. 5
illustrates an optical filter for changing the spectrum distribution of an incident laser light L
5
. The optical filter is analogous to an optical deflector with a comb-like electro-acoustic transducer disclosed in Japanese Patent Publication of Unexamined Application No. 62-257133. The filter comprises a block
5
a
of optical material, an optical wave guide
5
b
formed on the block
5
a
and a comb-like electro-acoustic transducer
5
c
. The comb-like electro-acoustic transducer
5
c
generates an ultrasonic wave
5
d
, and the laser light L
5
is propagated in the optical wave guide
5
b
in such a manner as to cross the ultrasonic wave
5
d
. The laser light L
5
is radiated from the other side as transmitted light L
6
. However, when the laser light L
5
is interfered with the ultrasonic wave
5
d
, the ultrasonic wave
5
d
diffracts a predetermined frequency component L
6
′. If the electro-acoustic transducer
5
c
varies the intervals
5
e
of the ultrasonic wave
5
d
, the filter changes the diffracted frequency component.
The prior art optical wave guide device encounters a problem in the production cost. As described hereinbefore, the optical wave guide requires a refractive index higher than the other portion, and the higher refractive index is achieved by bonding different materials to each other, replacing an element of the optical material with another element, diffusing a dopant into an optical element or using a hetero-epitaxy. These modifying techniques are carried out on a part of the optical material, and a masking step and/or lithography is necessary for the selective modification. This results in a complicated fabrication process. The complicated fabrication process requires various kinds of apparatus such as, for example, a sputtering apparatus, a thin film growing apparatus, an etching apparatus, a cleaning apparatus and an annealing apparatus. Therefore, the prior art optical device with an optical wave guide is so expensive.
The second problem inherent in the prior art optical wave guide is poor reproducibility. A part of the optical material is converted to a high refractive index portion through a chemical reaction, and various parameters dominate the chemical reaction. It is impossible to exactly control all the parameters. For this reason, the reproducibility is poor.
The third problem is that the prior art optical wave guide can not be formed in all the optical materials. Some optical materials do not widely change the refractive index, and the crystal structure of another optical material is destroyed through the selective modification.
SUMMARY OF THE INVENTION
It is therefore an important object of the present invention to provide an optical device which has an optical wave guide inexpensive, reliable and formed in an optical material which is not available for the prior art optical wave guide.
To accomplish the object, the present invention proposes to partially change a refractive index of optical material by using an acoustic standing wave.
In accordance with the present invention, there is provided an optical device comprising a block of optical material, and at least one acoustic wave generator for creating an acoustic wave existing as a standing wave in the block, and the standing wave changes a refractive index of a part of the block through an acousto-optic effect so as to form an optical wave guide in the block.
REFERENCES:
patent: 3947780 (1976-03-01), Rice et al.
patent: 3958863 (1976-05-01), Isaacs et al.
patent: 3964825 (1976-06-01), Eschler
patent: 4354735 (1982-10-01), Stowe et al.
patent: 4460250 (1984-07-01),
Font Frank G.
Mooney Michael P
NEC Corporation
Sughrue & Mion, PLLC
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