Optics: measuring and testing – By dispersed light spectroscopy – With synchronized spectrum repetitive scanning
Reexamination Certificate
2000-04-28
2003-10-14
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
With synchronized spectrum repetitive scanning
C356S326000, C356S332000
Reexamination Certificate
active
06633380
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a wavelength characteristic measurement apparatus for measuring the light wavelength characteristic of an optical component such as an optical filter or an optical transmission line and more particularly to a wavelength tracking control technique in wavelength characteristic measurement using an optical spectrum analyzer for measuring the spectrum of an optical signal and a wavelength variable light source capable of outputting different wavelengths.
2. Description of the Related Art
FIG. 21
is a block diagram to show an apparatus configuration example in a related art for embodying wavelength tracking in wavelength characteristic measurement using an optical spectrum analyzer and a wavelength variable light source. In the figure, numeral
100
denotes an optical spectrum analyzer for measuring an optical spectrum and numeral
101
denotes a wavelength variable light source capable of outputting different wavelengths.
The optical spectrum analyzer
100
comprises a control section
102
for controlling the whole operation of the optical spectrum analyzer
100
, a communication circuit
103
for carrying out communications with an external machine (in this case, the wavelength variable light source
101
), a terminal {circle around (3)} used as an input/output interface of the communication circuit
103
, a spectroscope
104
for extracting and outputting a specific wavelength from measured light by a spectrum using a spectral element of a diffraction grating, a prism, an interference filter, etc., an optical input terminal
105
for inputting measured light given from the outside to the spectroscope
104
, a motor
106
for varying the extracted wavelength of the spectroscope
104
, a drive circuit
107
for driving the motor
106
in accordance with the conditions of the motor rotation speed, rotation quantity, etc., set from the control section
102
, a position detection circuit
108
for detecting the rotation quantity and the rotation position of the motor
106
, a photodetector
110
for receiving the extracted light output from the spectroscope
104
and converting the light into an electric signal, an amplification circuit
111
for amplifying the minute electric signal output from the photodetector
110
, an A/D (analog-digital) converter
112
for quantizing an analog signal output from the amplification circuit
111
and converting the signal into a digital signal, and a display section
113
for displaying an optical spectrum provided by plotting measurement data output from the A/D converter
112
.
The control section
102
drives the motor
106
by the drive circuit
107
to set the extracted wavelength of the spectroscope
104
to any desired value based on motor control information previously stored in the control section
102
. The control section
102
checks position information provided by the position detection circuit
108
connected to the motor
106
to ensure that the extracted wavelength of the spectroscope
104
is set to the desired value, then reads measurement data from the A/D converter
112
, performs predetermined operation processing, and displays the operation result on the display section
113
.
At this time, the control section
102
finds each wavelength at equal intervals as the extracted wavelength of the spectroscope
104
based on the wavelength range and the number of measurement samples set by the measurer and while intermittently finding measurement data provided when the extracted wavelength of the spectroscope
104
is set to each wavelength at equal intervals, the control section
102
plots the measurement data on the display section
113
, whereby it is made possible to display the measurement waveform of the spectrum concerning the measured light.
The optical spectrum analyzer
100
has a function as a host for controlling the external wavelength variable light source
101
connected Lo the optical spectrum analyzer
100
. That is, the control section
102
transmits a control instruction to a control section
115
(described later) of the wavelength variable light source
101
via the communication circuit
103
and the terminal {circle around (3)} and a terminal {circle around (3)}′ and a communication circuit
116
(both described later) of the wavelength variable light source
101
, thereby setting the wavelength and light power of signal light output by the wavelength variable light source
101
.
A measured object is an optical component whose wavelength characteristic such as a wavelength versus loss characteristic is to be measured, such as an optical component for WDM (wavelength division multiplexing), an optical fiber grating, or a dielectric multilayer film filter. Measured light is supplied from the measured object
114
to the optical spectrum analyzer
100
by wavelength tracking measurement using single mode signal light supplied from an optical output terminal
118
(described later) of the wavelength variable light source
101
, and the wavelength characteristic of the measured object
114
is measured.
On the other hand, the wavelength variable light source
101
comprises a control section for controlling the whole operation of the wavelength variable light source
101
, the communication circuit
116
for carrying out communications with an external machine (in this case, the optical spectrum analyzer
100
), the terminal {circle around (3)}′ used as an input/output interface of the communication circuit
116
, the optical output terminal
118
for outputting an optical signal output from a light source
122
(described later) to the external measured object
114
, the light source
122
for oscillating a single mode spectrum with its oscillation wavelength being variable, a light source drive circuit
123
for driving the light source
122
and performing temperature control, etc., of the light source
122
, a display section
124
for displaying conditions of the measurement wavelength range, etc., set by the measurer (described later in detail), and a wavelength control circuit
126
for controlling the wavelength of the optical signal output from the light source
122
.
The control section
115
controls the light source drive circuit
123
and the wavelength control circuit
126
based on the light source drive information and the wavelength information previously stored in the control section
115
and varies single mode oscillation wavelength and oscillation light power of the light source
122
. That is, the control section
115
finds parameters of the measurement wavelength interval, etc., (described later in detail) based on the setup conditions by performing operations, gives instructions to the light source drive circuit
123
and the wavelength control circuit
126
, and oscillates the light source
122
under an arbitrary setup condition. In addition, the control section
115
intermittently changes the oscillation wavelength of the light source
122
at predetermined wavelength intervals throughout the wavelength range set by the measurer. Like the optical spectrum analyzer
100
, the wavelength variable light source
101
also uses a spectral element (not shown) and a motor (not shown) for driving the spectral element to vary the oscillation wavelength of the light source
122
.
Next, the procedure of wavelength tracking control performed in the wavelength characteristic measurement apparatus in the related art will be discussed according to a flowchart shown in FIG.
22
. The control in the optical spectrum analyzer
100
and the wavelength variable light source
101
as described below may be performed using a computer, etc., provided aside from them. First, the measurer sets measurement conditions of measurement start wavelength &lgr;
0
, measurement end wavelength &lgr;e, the number of measurement samples, etc., in the optical spectrum analyzer
100
. Then, the control section
102
derives parameters of wavelength interval &Dgr;&lgr;, etc., by performing operations based on the setup measureme
Iwasaki Takashi
Mori Tohru
Ando Electric Co. Ltd.
Fish & Richardson P.C.
Font Frank G.
Lee Andrew H.
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