Optics: measuring and testing – By dispersed light spectroscopy – With synchronized spectrum repetitive scanning
Reexamination Certificate
2000-03-16
2003-01-28
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
With synchronized spectrum repetitive scanning
C356S326000, C356S332000
Reexamination Certificate
active
06512582
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the technology of measuring the wavelength characteristics of an optical filter and a light transmission channel using an optical spectrum analyzer which measures the spectra of optical signals and a wavelength tunable light source capable of outputting light at different wavelengths.
2. Description of the Related Art
FIG. 4
is a block diagram showing the configuration of a prior art wavelength tracking system using an optical spectrum analyzer and a wavelength tunable light source. Indicated by
1
is an optical spectrum analyzer,
2
is a control unit in the optical spectrum analyzer
1
,
3
is a communication circuit for performing communication with external equipment, {circle around (2)} is an I/O terminal providing an interface with the communication circuit
3
,
4
is a spectroscope which performs spectral resolving to extract a specified wavelength from the light to be measured and outputs the extracted wavelength,
5
is a light input terminal at which the light to be measured is input to the spectroscope
4
,
6
is a motor for tuning the wavelength being extracted with the spectroscope
4
,
7
is a drive circuit for driving the motor
6
,
8
is a photodetector that receives the extracted light being output from the spectroscope
4
and which converts it to an electrical signal,
9
is an amplifier circuit for amplifying the small electrical signal being output from the photodetector
8
,
10
is an A/D converter with which the analog signal being output from the amplifier circuit
9
is converted to a digital signal,
11
is a display unit for displaying the measured data,
12
is a position detector circuit for detecting the rotating position of the motor,
14
is a wavelength tunable light source,
15
is a control unit in the wavelength tunable light source
14
,
16
is a communication circuit for performing communication with external equipment, {circle around (2)}′ is an I/O terminal providing an interface with the communication circuit
16
,
17
is a display unit for displaying conditions and the like,
18
is a light source drive circuit for driving a light source unit
20
and performing, for example, temperature control of the light source unit,
19
is a wavelength control circuit for controlling the wavelength being output from the light source unit,
20
is the light source unit that oscillates a single-mode spectrum and which is so adapted as to be capable of turning the oscillating wavelength,
21
is a light output terminal at which the optical signal being output from the light source unit
20
is output externally, and
22
is the device under measurement.
On the basis of motor control information preliminarily stored in the control unit
2
, the optical spectrum analyzer
1
drives the motor
6
via the drive circuit
7
and sets the wavelength which is to be extracted by the spectroscope
4
. The control unit
2
monitors and controls the position information being sent from the position detector circuit
12
coupled to the motor
6
and after confirming the setting of a specified wavelength, reads data from the A/D converter
10
, performs arithmetic operations on the data and displays the result in the display unit
11
. On the basis of a preset wavelength range and a preset number of measurements, the control unit
2
determines equally spaced wavelengths to be extracted with the spectroscope
4
, intermittently determines data for the respective settings of extraction wavelength, and plots the data on the display unit
11
so that it is displayed as a single waveform.
On the basis of the light source drive information and wavelength information that are preliminarily stored in the control unit
15
, the wavelength tunable light source
14
controls the light source drive circuit
18
and the wavelength control circuit
19
so as to tune the single-mode oscillating wavelength of the light source unit
20
and the optical power of its oscillation. The control unit
15
performs mathematical operations to determine relevant parameters from the settings of conditions displayed on the display unit
17
and controls the light source drive circuit
18
and the wavelength control circuit
19
so that the light source unit
20
is oscillated at the desired settings of conditions. The control unit
15
is also capable of intermittent tuning over a certain wavelength range at predetermined intervals.
The optical spectrum analyzer
1
functions as a host that controls the wavelength tunable light source
14
connected to external equipment. The control unit
2
in the optical spectrum analyzer
1
sends out a control instruction from the communication circuit
3
and the I/O terminal {circle around (2)} and supplies it to the control unit
15
in the wavelength tunable light source
14
via the I/O terminal {circle around (2)}′ and the communication circuit
16
, thereby setting the wavelength and optical power of signal light to be output from the wavelength tunable light source
14
.
We now describe the prior art wavelength tracking system using an optical spectrum analyzer and a wavelength tunable light source by referring to
FIG. 5
, which is a flowchart for the sequence of steps in measurement by the prior art tracking system shown in FIG.
4
.
First, the technician (the person who performs measurement) sets a plurality of conditions for measurement (e.g. &lgr;0 or the wavelength at which the measurement starts, &lgr;e or the wavelength at which the measurement ends, and the number of samples to be measured) in the spectrum analyzer
1
, which then determines wavelength interval &Dgr;&lgr; and other parameters by arithmetic operations (this is step S
1
; in the following description, symbol S is used without being preceded by the word “step”). In accordance with the determined conditions, the control unit
2
sends a signal to the drive circuit
7
, drives the motor
6
so that the wavelength to be extracted with the spectroscope
4
is set at the initial value, monitors the position information being output from the position detector circuit
12
, and confirms the setting of the initial wavelength. The control unit
2
also sends out a command for shift to the initial wavelength and supplies it to the externally connected wavelength tunable light source
14
via the communication circuit
3
(S
2
).
By performing arithmetic operations from the command sent from the optical spectrum analyzer
1
, the control unit
15
in the wavelength tunable light source
14
determines parameters to be imparted to the light source drive circuit
18
and the wavelength control circuit
19
, sets the light source unit
20
at the initial wavelength and, after the end of the setting, sends a SETTING COMPLETE command to the control unit
2
in the optical spectrum analyzer
1
via the communication circuit
16
(S
3
). In response to a technician's instruction for starting measurement (S
4
), the control unit
2
in the optical spectrum analyzer
1
sends a control signal to the drive circuit
7
such that the wavelength &lgr; being extracted with the spectroscope
4
becomes equal to &lgr;0, drives the motor
6
while waiting for the end of its necessary motion while monitoring the position information being output from the position detector circuit
12
. The control unit
2
also sends out a command for shift to &lgr;, supplies it to the externally connected wavelength tunable light source
14
via the communication circuit
3
and waits for the return of a WAVELENGTH SETTING COMPLETE command from the wavelength tunable light source
14
(S
5
).
When wavelength setting has completed with the optical spectrum analyzer
1
and the wavelength tunable light source
14
(S
6
), the control unit
2
actuates the A/D converter
10
and picks up a digital signal (S
7
), as well as performs arithmetic operations to determine the value of optical power from factors such as preset conditions for the amplifier circuit
9
and plots the result on the display unit
11
Funakawa Seiji
Mori Tohru
Ando Electric Co. Ltd.
Evans F. L.
Fish & Richardson P.C.
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