Coherent light generators – Particular beam control device – Optical output stabilization
Reexamination Certificate
2000-07-12
2002-11-05
Ip, Paul (Department: 2828)
Coherent light generators
Particular beam control device
Optical output stabilization
Reexamination Certificate
active
06477189
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser oscillation frequency stabilizer which controllably locks the oscillation frequency of a tunable laser source such as a semiconductor laser by making use of saturated absorption spectra of atoms or molecules.
2. Detailed Description of the Related Art
The oscillation frequency of a laser light source portion such as of a semiconductor laser device significantly depends on the temperature of the laser light source portion and the current allowed to flow through the laser light source portion. There is such a problem as the oscillation frequency varies due to slight changes in temperature of the laser light source portion and in current flowing therethrough, so that the laser device cannot easily provide stabilized oscillation frequencies.
For this reason, various types of laser oscillation frequency stabilizers have been proposed to stabilize the oscillation frequency of the laser light source portion of laser devices. As a typical technique for laser oscillation frequency stabilizers, such a technique which makes use of absorption spectra of atoms or molecules is known, for example, those using the absorption spectra of atoms or molecules as the reference.
Among them, a laser oscillation frequency stabilizer that uses saturated, absorption spectra of atoms or molecules as the reference can obtain a spectral line width narrower than a linear absorption spectral line width that is broadened due to the Doppler effect. Thus, the oscillation frequency of the laser light source portion can be stabilized with high sensitivity.
The laser oscillation frequency stabilizer for stabilizing the oscillation frequency of the laser light source portion with saturated absorption spectra of atoms or molecules used as the reference, the following method is employed. That is, first, a laser beam (which is called “pumping light”) having intensity enough to saturate the light absorption is introduced into an absorption cell so that the amount of the transmitted beam of light is detected by means of a first light-receiving device. At the same time, part of the transmitted beam of light that has passed through the absorption cell is reflected. Then, the reflected feeble laser light (which is called probe light) is introduced again into the absorption cell from the opposite direction. Then, the amount of the transmitted light that has been introduced into the absorption cell and passed therethrough is detected by means of a second light-receiving device. Thus, the oscillation frequency of the laser light source portion is controllably locked to a saturated absorption spectrum of a narrow line width in accordance with the light reception outputs of the two light-receiving devices.
FIG. 10
is an explanatory view showing one example of the conventional laser oscillation frequency stabilizer. In
FIG. 10
, reference numeral
1
designates a laser light source portion. The laser light source portion
1
generally includes a laser diode
2
, a thermistor
3
, a Peltier-effect device
4
, and a plate heat radiator
5
. The temperature of the laser diode
2
is controlled by means of a temperature control circuit
6
.
A laser beam emitted from the laser diode
2
is directed to a condensing lens
7
. Then, the beam is transmitted from an optical isolator
7
A to be introduced into a polarization beam splitter
8
. The laser beam is linearly polarized. The polarization beam splitter
8
reflects laser beams having components linearly polarized in a certain direction and transmits those linearly polarized in the direction orthogonal to that direction.
The linearly polarized laser beam that has passed through the polarization beam splitter
8
is guided into a quarter wavelength plate
9
to be circularly polarized. Then, the circularly polarized laser beam is introduced into a saturated absorption cell
10
as pumping light. In the saturated absorption cell
10
, sealed are gaseous atoms and/or molecules, which have absorption spectra at certain wavelengths.
The saturated absorption cell
10
is provided with electromagnets
11
. The magnetic. fields created by the electromagnets
11
are modulated by means of an oscillator
12
. A transmitted circularly polarized laser beam that has passed through the saturated absorption cell
10
passes through an ND filter
13
and then guided into a half mirror
14
. Part of the laser beam is reflected by the half mirror
14
in the direction opposite to that of travel, whereas the remainder of the laser beam passes through the half mirror
14
to be received by a first light-receiving device
15
. The laser beam that is reflected by the half mirror
14
and travels in the opposite direction passes again through the ND filter
13
to be allowed into the saturated absorption cell
10
as feeble probe light. Then, the laser beam passes through the saturated absorption cell
10
to be guided into the quarter wavelength plate
9
, where the laser beam is linearly polarized in the direction orthogonal to that of the original linearly polarized laser beam. This linearly polarized laser beam is guided into the polarization beam splitter
8
and then reflected by a polarized beam splitting plane
8
a to be received by means of a second light-receiving device
16
.
The light reception outputs of the first light-receiving device
15
and the second light-receiving device
16
are inputted to a divider
17
. The divider
17
is adapted to divide the light reception output of the second light-receiving device
16
by that of the first light-receiving device
15
. The division output from the divider
17
is inputted to a lock-in amplifier
18
, which in turn detects the division output in synchronization with the oscillation output of the oscillator
12
to output the lock-in signal to a current control circuit
19
. In accordance with the lock-in signal, the current control circuit
19
is adapted to control parameters, having wavelength dependency, such as LD injection current for locking the wavelength of the laser diode
2
to a wavelength of absorption spectra.
However, the laser oscillation frequency stabilizer of the prior art is adapted to Zeeman-modulate a saturated absorption spectrum and therefore has to be provided with electromagnets, a power source, and an oscillator of its own. This presents a problem of increasing the laser oscillation frequency stabilizer in size. In addition to this, the stabilizer also present another problem that the electromagnets generate heat to cause the laser diode
2
to increase in temperature and thus the laser diode
2
requires much power for controlling the temperature, thereby making it difficult to save power consumption.
SUMMARY OF THE INVENTION
The present invention was developed in view of the aforementioned circumstances. An object of the present invention is to provide a laser oscillation frequency stabilizer that can be reduced in size without deteriorating the accuracy of wavelength stability and can reduce power consumption.
According to the present invention as set forth in claim
1
, the laser oscillation frequency stabilizer is characterized by comprising a laser light source portion having a laser light source of which oscillation frequency can be controlled and for emitting a laser beam; a polarized beam splitter portion for splitting a laser beam from the above-mentioned laser light source portion into a first laser beam and a second laser beam, the above-mentioned laser beams having linearly polarized components orthogonal to each other; a quarter wavelength plate for converting the above-mentioned two laser beams, split by means of the above-mentioned polarized beam splitter portion, into laser beams circularly polarized in directions opposite to each other; an absorption cell which is disposed in an optical path of the above-mentioned circularly polarized laser beams and in which gaseous atoms or molecules with a certain absorption spectrum are sealed and to which a uniform magnetic field is applied; a half mirror for refle
Kawashima Hiroyuki
Saito Susumu
Takeda Noriko
Ip Paul
Kabushiki Kaisha TOPCON
Zahn Jeffrey
LandOfFree
Laser oscillation frequency stabilizer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Laser oscillation frequency stabilizer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Laser oscillation frequency stabilizer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2938393