Wavelength tunable external resonator laser using optical...

Details Wavelength tunable external resonator laser using optical... Wavelength tunable external resonator laser using optical...

2002-06-27

2004-10-26

Wong, Don (Department: 2828)

Coherent light generators

Particular beam control device

Tuning

C372S016000, C372S054000, C372S100000, C372S102000

Reexamination Certificate

active

06810047

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to a wavelength tunable external resonator laser using an optical deflector driven by an electrical signal and can be applied in the external resonator laser of a Littman-Metcalf mode or a Littrow mode.
2. Description of the Prior Art
An external resonator for tuning a single mode light from a laser diode or other light sources having a predetermined range of bandwidth to select a specific wavelength, includes a Littman-Metcalf mode external resonator and a Littrow mode external resonator. A method by which a specific wavelength is selected using these types of the resonators has been applied to a dye laser technology that is widely researched in the field of a spectroscopy.
FIG. 1
is a structure of a conventional external resonator of a Littman-Metcalf mode.
Referring now to
FIG. 1
, the external resonator of a Littman-Metcalf mode includes a laser diode
101
having a wide band of wavelength, a first lens
102
a
for making the beam from the laser diode
101
in parallel, a diffraction grating
104
for diffracting the parallel beam and a reflection mirror
105
for reflecting the diffracted beam. The beam generated from the external resonator laser is reflected against a diffraction grating
104
and focused on an optical fiber
103
via a lens
102
b.
If a beam is generated from the laser diode
101
, the beam is converged in parallel by the first lens
102
a
. Then, the parallel beam is diffracted toward the reflection mirror
105
by means of the diffraction grating
104
. At this case, the angle of the reflection mirror
105
toward the diffraction grating
104
is controlled by a mechanical equipment (not shown). Thereby, the reflection mirror
105
reflects specific wavelengths that are vertically incident from the wavelengths incident to the reflection mirror
105
, to the diffraction grating
104
. The beam reflected by the reflection mirror
105
is diffracted by the diffraction grating
104
, so that it returns to the laser diode
101
via the first lens
102
a.
As shown in
FIG. 1
, if the reflection mirror
105
is positioned at a first angle
109
, a first beam
107
of a given wavelength is vertically incident to the reflection mirror
105
and is then reflected toward the diffraction grating
104
. Further, if the reflection mirror
105
is positioned at a second angle
110
, a second beam
108
having a different wavelength is vertically incident to the reflection mirror
105
and is then reflected toward the diffraction grating
104
. As a result, the wavelength of the beam returning to the laser diode
101
is different depending on the angle in which the reflection mirror
105
is positioned. The wavelength is also tuned depending on the angle of the reflection mirror.
As above, the external resonator of the Littman-Metcalf mode controls the angle of the reflection mirror to tune the wavelength. However, the external resonator of the Littrow mode controls the angle of the diffraction grating to tune the wavelength.
FIG. 2
is a structure of a conventional external resonator of a Littrow mode.
Referring now to
FIG. 2
, the external resonator of the Littrow mode is similar in structure to the external resonator of the Littman-Metcalf mode. Only different is that the external resonator of the Littrow mode does not use the reflection mirror but rotate the diffraction grating
104
to tune the wavelength.
If a beam is generated from the laser diode
101
, the beam
201
is in parallel converged by the lens
102
. A beam having a specific wavelength from the parallel beams is diffracted depending on the angle
106
of the diffracting grating
104
and is then reflected toward the lens
102
. The beam
201
reflected by the diffracting grating
104
returns to the laser diode
101
via the lens
102
.
As a result, the wavelength of the beam
201
returning to the laser diode
101
is different depending on the angle in which the diffracting grating
104
is positioned. That is, the wavelength of the beam is tuned depending on the rotation of the diffracting grating
104
.
As above, the external resonator tunable laser of the Littman-Metcalf or Littrow mode mechanically rotates the reflection mirror or the diffraction grating and then control the angles of them to select a beam of a specific wavelength. Therefore, as the reflection mirror or the diffraction grating must be mechanically finely rotated, there are problems that the stability of a laser is low, the size of the apparatus is great, the tunable speed is low and the manufacturing cost is high. In other words, the conventional resonator requires a rotation mechanical apparatus having a high accuracy in order to select a specific wavelength and is low in a tunable speed.
Various types of resonators that have been proposed to tune the wavelengths will be now described.
The external resonator laser structure includes two reflection mirrors fixed at both sides of the resonator centering on a laser medium capable of oscillating a plurality of wavelengths so that they can have a rapid variable speed of about 1 ms, and a reflection mirror linearly and in multiple arranged, for varying the length of the resonator by means of PZT.
As the reflection mirror and diffraction grating are simultaneously rotated centering on a given rotation axis located near the laser, the rotation for controlling the diffraction angle and the length of the resonator can be simultaneously controlled. Thus, an external resonator light source can consecutively select a wavelength without hopping a mode.
There is a high-speed wideband wavelength tunable laser system. The laser system includes various tunable components controlled via a microprocessor. The tunable components, being birefringence crystal body representing an electrical optical effect when applied with an electric field, consist of more than two tunable components. At this case, the two tunable components perform a coarse control and a fine control, respectively.
There is a laser resonator including more than two reflection components, positioned at both sides of the resonator, two curve overlapping mirrors, and couple-type reflection mirrors positioned at its output portion. A laser crystal body is installed at a reflection path within the laser resonator. A component for distributing the wavelength such as a prism is positioned at the reflection path within the resonator between one of the overlapping mirrors and the reflection components at its both ends, in order to tune and oscillate at least one wavelength within an expected range of the wavelength. At this time, tuning of the oscillated wavelength is made by a fine rotation of the reflection component.
There is an external resonator structure for tuning the wavelength using an electrical signal without mechanical movement. The external resonator includes two mirrors at its both ends, a crystal body as a laser medium positioned at the center of the mirror, and a crystal body for selecting the wavelength in a piezoelectric unit driven by a RF source as a sound wave input. Therefore, the grating is not moved in the external resonator since the crystal body installed at the piezoelectric unit driven by the RF source.
Also, there is a wavelength tunable laser diode rotates the grating using a stepper motor and controls it using a microprocessor. Further, there is a wavelength tunable laser diode moves the reflection mirror and diffraction grating by means of an actuator using a MEMS technology.
The above-mentioned conventional technologies have advantages in the structure and performance but have some problems. Major problem in the prior arts are as follows: they require mechanical movement and have a narrow wavelength tunable range, and the module size of them could not be miniaturized. In other words, there is a need for a new technology having a spectroscopy the wavelength of which is required to be tuned, a wide tunable range of the wavelength in a WDM optical communication, and a light source having the stability, miniaturizatio

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