Coherent light generators – Particular beam control device – Tuning
Reexamination Certificate
2001-10-31
2003-09-09
Ip, Paul (Department: 2828)
Coherent light generators
Particular beam control device
Tuning
C372S028000, C372S029011, C372S038010, C372S038020
Reexamination Certificate
active
06618401
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a tunable laser source device, particularly to a tunable laser source device having a tunable laser source of an external resonance type that varies the wavelength of emitted light by changing the resonator length of the external resonator by driving a driver such as a motor, the above tunable laser source device employing a technology capable of sweeping the wavelength of the emitted light at a high speed and capable of outputting the accurate information of the wavelength to be swept.
BACKGROUND ART
Generally in many cases, the measurement of optical characteristics by an optical device is performed by a measurement system, in which the emitted light from the tunable laser source device capable of varying the wavelength is input to a device under test (DUT) and various kinds of the optical characteristics of the DUT are measured based on the change of the output light from the DUT with respect to the wavelength of the input light.
FIG. 9
schematically shows the constitution of the prior art as the optical characteristics measuring system for such an optical device.
That is, in the optical characteristics measuring system for the optical device, for example, the input light whose wavelength is variable to a DUT
100
such as an optical band-path filter is input to a tunable laser source device
201
constituting an optical transmitter
200
via an optical transmission path
101
such as an optical fiber.
The output light from the DUT
100
is output to, for example, an optical characteristics measuring device
301
such as an optical spectrum analyzer constituting an optical receiver
300
via an optical transmission path
102
such as the optical fiber.
Then, in the optical characteristics measuring device
301
, as described later, various kinds of the optical characteristics, for example, band-pass characteristics of the optical band-path filter are measured based on the change of the output light from the DUT
100
with respect to the wavelength of the input light by performing data processing in a data processor, after an electric signal which is obtained by photoelectric conversion at a light receiving unit is sampled in a sampling unit.
In this case, wavelength information of the input light necessary for each processing of the optical characteristics measuring device
301
on the side of the optical receiver
300
, for example, a tunable start wavelength, an stop wavelength, a tunable range and the like, are transmitted by the so-called CPU communication from a CPU
202
included in a controller on the side of the optical transmitter
200
to a CPU
302
included in the controller on the side of the optical receiver
300
.
FIG. 10
is a block diagram exemplifying a concrete constitution of a controller
130
on the side of the optical transmitter
200
used in the foregoing measurement system and a tunable laser source
121
of the external resonance type which can be controlled by the controller
130
.
Here, the tunable laser source
121
of the external resonance type is constituted so as to vary the wavelength of an omitted light by changing the resonator length of the resonator constituted of a diffraction grating
1
c
rotatively driven by a motor
123
as the driver, an optical lens
1
b
and a laser diode (LD)
1
a.
It is to be noted that a stepping motor is used as the motor
123
herein.
Wavelength information input means
131
in the controller
130
is used to input information for determining a point wavelength for measurement including a start wavelength &lgr;s and a stop wavelength &lgr;e for sweep by, for example, key operation.
Further, point information measurement means
132
in the controller
130
stores and sets, as point information, in a point information memory
133
, a step number m of the motor
123
corresponding to each point wavelength including the start wavelength &lgr;s and the stop wavelength &lgr;e for the sweep, based on the information input from the wavelength information input means
131
and the information stored in a memory table
133
.
Furthermore, in the memory table
133
in the controller
130
, for example, a state where the emitted wavelength of the tunable laser source
121
is longest is set as a reference, and wavelengths &lgr;(
0
), &lgr;(
1
) . . . &lgr;(N) in the case that the entire tunable wavelength range is indicated by a predetermined unit wavelength (for example, 0.01 nm) and the step numbers
0
,
1
. . . N of the motor
123
corresponding to these wavelengths are stored in advance.
Furthermore, in the case where the start wavelength &lgr;s and the stop wavelength &lgr;e for the sweep and a point number M are input from, for example, the wavelength information input means
131
, the point information setting means
133
in the controller
130
obtains a wavelength distance &Dgr;&lgr; by dividing a difference between the start wavelength &lgr;s and the stop wavelength &lgr;e by a number smaller than the point number M by 1, and then obtains the point wavelengths of M pieces, &lgr;p(
1
)=&lgr;s, &lgr;p(
2
)=&lgr;s+&Dgr;&lgr;, &lgr;p(
3
)=&lgr;s+2&Dgr;&lgr;, . . . &lgr;p(M−1)=&lgr;e−&Dgr;&lgr;, &lgr;p(M)=&lgr;e.
Then, this point information setting means
33
selects the step numbers m(
1
), m(
2
) . . . m(M) which correspond to these point wavelengths, respectively, from the memory table
133
, and stores and sets in the point information memory
134
.
It is to be noted that, in the case that the wave distance &Dgr;&lgr; is designated instead of the stop wavelength &lgr;e, the point wavelengths of M pieces, &lgr;p(
1
)=&lgr;s, &lgr;p(
2
)=&lgr;s+&Dgr;&lgr;, &lgr;p(
3
)=&lgr;s+2&Dgr;&lgr;, . . . &lgr;p(M−1)=&lgr;s+(M−2)&Dgr;&lgr;, &lgr;p(M)=&lgr;s+(M−1)&Dgr;&lgr;=&lgr;e are obtained, and the step numbers m(
1
), m(
2
) . . . m(M) which correspond to these point wavelengths are stored and set in the point information memory
134
.
Further, when drive control means
135
in the controller
130
receives a start instruction of measurement from an operation unit or the like not shown, it obtains the step number m(
1
) corresponding to the start wavelength &lgr;s from the point information memory
134
.
Then, the drive control means
135
outputs an up-pulse to positively rotate the motor
123
, if the obtained m(
1
) is positive.
Alternatively, the drive control means
135
outputs a down-pulse to reversal rotate the motor
123
, if the obtained m(
1
) is negative.
Then, the drive control means
135
initially sets the emitted wavelength to one step before the start wavelength &lgr;s, and thereafter, sweeps the wavelength of the emitted light in a range of from the start wavelength &lgr;s to the stop wavelength &lgr;e by continuously outputting the up-pulse for positively rotating the motor
23
by a number equal to a difference m(M)−m(
1
) between the step number m(
1
) corresponding to the start wavelength &lgr;s and the step number m(M) corresponding to the stop wavelength &lgr;e.
Here, the drive control means
135
gradually shortens a pulse frequency from the initial period of the drive until reaching a predetermined speed, and gradually lengthens the pulse frequency from the predetermined speed until stopping, in order to control the motor
123
in a trapezoid.
Further, a driver
136
in the controller
130
supplies the up-pulse and the down-pulse output from the drive control means
135
to the motor
123
, thereby driving the motor
123
in steps.
Furthermore, sweep signal output means
141
in the controller
130
is constituted of voltage data generation means
141
a,
a voltage data memory
141
b,
voltage data reading means
141
b
an a D/A converter
141
d.
Here, among the point wavelengths &lgr;p(
1
), &lgr;p(
1
) . . . &lgr;p(M) determined by the information input from the wavelength information input means
131
, the voltage data generation means
141
a
generates a predetermined sweep starting voltage Vs
Ozaki Toshiyuki
Takizawa Masanori
Tanimoto Takao
Anritsu Corporation
Frishauf Holtz Goodman & Chick P.C.
Ip Paul
Rodriguez Armando
LandOfFree
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