Optical multiplexing/demultiplexing module

Details Optical multiplexing/demultiplexing module Optical multiplexing/demultiplexing module

2001-07-25

2003-04-08

Healy, Brian (Department: 2874)

Optical waveguides

With optical coupler

Plural

C385S011000, C385S036000, C359S199200, C359S199200, C359S494010

Reexamination Certificate

active

06546165

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an optical multiplexing/demultiplexing module having a function of synthesizing polarized waves and a function of demultiplexing a wave into polarized waves.
BACKGROUND OF THE INVENTION
Recently, optical multiplexing/demultiplexing modules are widely used in optical communication systems and in the field of optical measurement and the like. In general, an optical multiplexing/demultiplexing module functions as an optical multiplexer and as an optical demultilexer. Optical multiplexing/demultiplexing modules include optical multiplexers based on a method in which a plurality of incident beams having different wavelengths are multiplexed (or synthesized) to emit and obtain a multiplexed beam. By using such an optical multiplexing/demultiplexing module based on the wavelength multiplex/demultiplex method, a plurality of lights having different wavelengths can be transmitted as a multiplexed signal beam. Further, when the optical multiplexing/demultiplexing module is used as an optical demultiplexer, a multiplexed signal beam is demultiplexed into signal beams having different wavelengths.
Optical multiplexing/demultiplexing modules include optical multiplexers based on a method in which two linearly polarized incident beams having planes of polarization orthogonal to each other are multiplexed to emit and obtain a single multiplexed beam and in which the multiplexed beam is demultiplexed into two linearly polarized waves. An optical multiplexing/demultiplexing module based on the linearly polarized beam multiplexing/demultiplexing method is also referred to as “polarized beam combiner/splitter. For example, an optical multiplexing/demultiplexing module based on the linearly polarized beam multiplexing/demultiplexing method is used for synthesizing laser beams from a semiconductor laser or the like to provide higher optical power, as described later.
The plane of polarization implies a plane having a direction in which a linearly polarized beam is propagated and a direction in which an electric vector (electric field) oscillates.
Although the semiconductor lasers are widely used as light sources in the field of optical communication, it is presently difficult to provide a semiconductor laser having high power that can satisfy requirements in the field. Further, it is known that when a semiconductor laser oscillates laser beams that are linearly polarized beams, improved laser beam optical power can be achieved by synthesizing two laser beams having planes of polarization orthogonal to each other.
Conventional optical multiplexing/demultiplexing modules based on the linearly polarized beam multiplexing/demultiplexing method include devices utilizing a uniaxial birefringent crystal and devices utilizing a polarization beam splitter.
FIG. 6
is an illustration of an example of an optical multiplexing/demultiplexing module based on the linearly polarized beam multiplexing/demultiplexing method. The optical multiplexing/demultiplexing module is an example of an optical multiplexing/demultiplexing module in which a uniaxial birefringent crystal is used to multiplex linearly polarized beams having planes of polarization orthogonal to each other. In
FIG. 6
, a uniaxial birefringent crystal
78
multiplexes a first linearly polarized beam
71
which is emitted by a first polarization-maintaining optical fiber
70
and collimated by a first lens
72
and a second linearly polarized beam
73
which is emitted by a second polarization-maintaining optical fiber
74
and collimated by a second lens
76
.
As shown in
FIG. 6
, the polarization-maintaining optical fibers
70
and
74
are provided substantially in parallel with each other at an interval, and the first linearly polarized beam
71
and second linearly polarized beam
73
enter the uniaxial birefringent crystal
78
with their optical axes substantially in parallel with each other. When the first linearly polarized beam
71
and second linearly polarized beam
73
enter an entrance surface
77
of the uniaxial birefringent crystal
78
, the linearly polarized beams
71
and
73
are multiplexed at an exit surface
79
of the uniaxial birefringent crystal
78
. The multiplexed beam
75
is converged by a lens
80
to enter an optical fiber
82
.
SUMMARY OF THE INVENTION
An optical multiplexing/demultiplexing module according to the invention comprises:
a first optical input section for inputting a first linearly polarized beam;
a second optical input section provided at an interval from the first optical input section for inputting a second linearly polarized beam having a plane of polarization orthogonal to that of the first linearly polarized beam;
a uniaxial birefringent crystal for multiplexing the first linearly polarized beam and the second linearly polarized beam:
an optical output section for outputting a multiplexed beam multiplexed by the uniaxial birefringent crystal; and
an optical path converting member for converting at least either of the optical path of the first linearly polarized light propagating from the first input section and the optical path of the second linearly polarized beam propagating from the second input section when they enter the uniaxial birefringent crystal,
wherein the optical path converting member performs the optical path conversion such that the distance between the points of entrance of the first linearly polarized beam and second linearly polarized beam entering the entrance surface of the uniaxial birefringent crystal becomes smaller than the distance between the first optical input section and second optical input section.


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