Coherent light generators – Particular beam control device – Tuning
Reexamination Certificate
2002-06-13
2004-02-24
Scott, Jr., Leon (Department: 2828)
Coherent light generators
Particular beam control device
Tuning
Reexamination Certificate
active
06697389
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a tunable laser source device employed in evaluating or manufacturing the optical communication system or device.
A configuration of the tunable laser source device in the prior art will be explained with reference to
FIG. 4
hereunder.
In
FIG. 4
, the light emitted from the tunable laser source portion
11
is output to the outside of the tunable laser source device via the optical coupler
18
a
as the optical output.
Further, the light branched by the optical coupler
18
a
is branched by the optical coupler
18
b
. One branched output is fed to the wavelength measuring device
16
that measures the wavelength by utilizing the periodical change of the interference power generated based on the deviation between optical path lengths in the etalon, etc. The other branched output is fed to the gas cell as a reference for callibrating wavelength
15
and the wavelength measuring device
16
.
Further, detected outputs of the gas cell as a reference for callibrating wavelength
15
and the wavelength measuring device
16
are converted into electric signals and then fed to the control circuit
14
that is constructed by CPU.
Further, the control circuit
14
controls the wavelength of the light, that is output from the tunable laser source portion
11
via the motor driving circuit
12
and the LD current driving circuit
13
, in response to the set signal from the user interface portion
17
.
Next, the details of the tunable laser source portion
11
will be explained with reference to
FIG. 3
hereunder.
FIG. 3
is a view showing a detailed configuration of the tunable laser source portion
11
. This configuration includes the semiconductor laser (LD)
21
, the lenses
22
a
,
22
b
, the diffraction grating
23
, the mirror
24
, and the motor
25
.
The light emitted from the semiconductor laser
21
is shaped into the parallel light by the lens
22
a
and then enters into the diffraction grating
23
.
Only the light having the wavelength, which is decided by the positional relationship between the diffraction grating
23
and the mirror
24
, out of the light incident into the diffraction grating
23
can be fed back to the semiconductor laser
2
l once again. As a result, the light having the particular wavelength is output from the semiconductor laser
21
via the lens
22
b.
If the external cavity length is changed by driving the motor
25
to rotationally move the position of the mirror
24
around the center O of rotation, the wavelength of this output light can be changed.
In this case, if the motor
25
is set simply to a predetermined position, sometimes the infinitesimal error is generated in the position of this mirror
24
. Therefore, as shown in
FIG. 4
, the detected output of the wavelength measuring device
16
is fed back to the control circuit
14
such that the control is carried out by driving the motor
25
to mate always the measured wavelength with the predetermined wavelength.
Further, the wavelength of the light generated by the semiconductor laser can be controlled by adjusting the driving current of the semiconductor laser. Therefore, the wavelength of the light can be controlled by feeding back the detected output of the wavelength measuring device to the driving circuit of the semiconductor laser.
As described above, the wavelength measuring device that measures the wavelength by utilizing the periodical change of the interference power based on the deviation between optical path lengths in the etalon, etc. is employed as the wavelength measuring device in the tunable laser source device in FIG.
4
. Therefore, in order to compensate the change in the deviation between the optical path lengths due to the change of the ambient temperature, the temperature controlling device for maintaining the wavelength measuring device at the constant temperature (temperature control) is provided.
Further, the gas cell as a reference for callibrating wavelength
15
is provided to the tunable laser source device in FIG.
4
and is used to calibrate the wavelength measuring device.
In this case, the gas cell as a reference for callibrating wavelength
15
in
FIG. 4
looks for the wavelength at one point from already-known absorbed line wavelengths as the reference wavelength.
This already-known wavelength is set as the reference wavelength of the wavelength measuring device
16
in which, as shown in
FIG. 5
, the periodical change of the interference power is present.
As shown in
FIG. 5
, the wavelength linearity correction table by which the output of the wavelength measuring device
16
in which the periodical change of the interference power is present is corrected on the basis of the reference wavelength is formulated, and then is stored in a memory means (not shown) in the control circuit
14
.
As shown in
FIG. 5
, the gas cell
15
has the characteristic to absorb the wavelength at the particular already-known one point. The absorbed line wavelengths of the gas cell are very stable to the environmental change such as the change of the ambient temperature, and others.
In contrast, as shown in
FIG. 5
, the measured output of the wavelength measuring device
16
that utilizes the deviation between the optical path lengths changes to have peaks and notches of the power periodically.
However, the interval between the peak (notch) and the peak (notch) has the characteristic that depends on the change of the ambient temperature.
More particularly, as shown in
FIG. 5
, even though the wavelength linearity correction table is formulated at a certain ambient temperature while employing the absorbed line wavelength, that is indicated by an arrow, of the gas cell as a reference for callibrating wavelength
15
as the reference value of the measured output of the wavelength measuring device
16
, such measured output of the wavelength measuring device
16
in
FIG. 5
is expanded and contracted in the lateral axis direction if the ambient temperature is changed. As a result, the error is generated in the wavelength linearity correction table.
Accordingly, there exists the following problem in the tunable laser source device set forth in
FIG. 4
in the prior art.
Although the temperature control is applied to the wavelength measuring device, the infinitesimal temperature change is caused in the device if the ambient temperature of the device in formulating the wavelength linearity correction table at the time when the device is carried out of the factory is different from that of the device in user's employment. For this reason, such temperature change exerts not a little effect upon the wavelength measuring accuracy.
In order to maintain the wavelength accuracy obtained at the time when the device is carried out of the factory against the variation in the atmospheric temperature, the wavelength measuring device must be installed into the high performance temperature controlling mechanism (thermostatic bath). Normally, these high performance thermostatic baths are large in size and high in cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the problems of the tunable laser source device set forth in
FIG. 4
in the prior art, more particularly the problem such that, when an ambient temperature of the device in user's employment becomes different from that of the device in preparing a wavelength linearity correction table at the time when the device is carried out of a factory, a minute temperature change is caused in the device to have not a little effect on a wavelength measuring accuracy.
In order to overcome the above subjects, there is provided a tunable laser source device for branching a light output from a tunable laser source portion to supply to a wavelength measuring device and a wavelength calibrating reference device and then controlling the tunable laser source portion in response to an output of the wavelength measuring device,
wherein at least one peak and one notch or two peaks or two notches or more in a measurement interference period of the wa
Ema Nobuaki
Funakawa Seiji
Ando Electric Co. Ltd.
Fish & Richardson P.C.
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