Optics: measuring and testing – Lens or reflective image former testing – For optical transfer function
Reexamination Certificate
2000-01-06
2002-12-10
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Lens or reflective image former testing
For optical transfer function
C356S073100, C250S227180
Reexamination Certificate
active
06493074
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for measuring an optical transfer characteristic, each of which is capable of measuring an optical transfer characteristic of an optical device in a wide optical frequency bandwidth with high resolution, on optical frequency axis or on optical wavelength axis.
2. Description of the Related Art
In case of measuring an optical transfer characteristic (characteristic of amplitude, dispersion, delay, phase, gain or the like) of an optical device such as an optical filter, an optical fiber, an optical transmission system or the like, there is currently used an apparatus for measuring an optical transfer characteristic (an optical transfer characteristic measuring apparatus) having been constructed, for example, as shown in FIG.
4
. The optical transfer characteristic measuring apparatus includes two light sources one of which is a variable wavelength sweep type light source
10
for measurement (hereinafter referred to as variable wavelength sweep type measurement light source or measurement light source), and the other of which is a variable wavelength light source
20
for reference (hereinafter referred to as variable wavelength reference light source or reference light source). In the variable wavelength sweep type measurement light source
10
, the wavelength of an optical or light signal generated thereby can be switched stepwise and also the optical frequency of the optical signal can be swept in a predetermined frequency range. In the variable wavelength reference light source
20
, the wavelength of an optical or light signal generated thereby can be switched stepwise, but the optical frequency of the optical signal cannot be swept.
An output end of the variable wavelength sweep type measurement light source
10
is optically coupled to an input end of an optical device whose optical transfer characteristic is to be measured (optical device under measurement) DUT via a first optical coupler
30
. In the illustrated example, the first optical coupler
30
has four ports, i.e., the first through the fourth ports
301
,
302
,
303
and
304
. The first and the second ports
301
and
302
are used as input ports, respectively, and the third and the fourth ports
303
and
304
are used as output ports, respectively. The first port (the first input port)
301
is terminated in reflectionless termination, the second port (the second input port)
302
is coupled to the output end of the variable wavelength sweep type measurement light source
10
via an optical fiber, the third port (the first output port)
303
is coupled to an input end of the optical device under test DUT via an optical fiber, and the fourth port (the second output port)
304
is coupled to the second port of a second optical coupler
31
which will be discussed later. As a result, an optical signal generated from the measurement light source
10
is optically branched into two, one of which is supplied to the input end of the optical device under measurement DUT and the other of which is supplied to the second port of the second optical coupler
31
.
The output end of the variable wavelength reference light source
20
is coupled to the second optical coupler
31
via an optical fiber. The second optical coupler
31
also has four ports, i.e., the first through the fourth ports
311
,
312
,
313
and
314
. The first and the second ports
311
and
312
are used as input ports, respectively, and the third and the fourth ports
313
and
314
are used as output ports, respectively. The first port (the first input port)
311
is coupled to the output end of the variable wavelength reference light source
20
via an optical fiber, the second port (the second input port)
312
is coupled to the second output port
304
of the first optical coupler
30
as mentioned above, the third port (the first output port)
313
is terminated in reflectionless termination, and the fourth port (the second output port)
314
is coupled to an input end of a light receiving device
21
via an optical fiber. As a result, an optical signal generated from the reference light source
20
is inputted to the second optical coupler
31
via its first input port
311
, and also an optical signal generated from the measurement light source
10
is inputted to the second optical coupler
31
via its second input port
312
, so that the two light signals can be optically heterodyned.
Since the illustrated optical transfer characteristic measuring apparatus monitors the amount of frequency sweep (a frequency being swept) using an optical heterodyne detection, the optical signals generated from the variable wavelength sweep type measurement light source
10
and the variable wavelength reference light source
20
are first set to signals having the same frequency (the same reference wavelength), and then the frequency of the optical signal generated from the measurement light source
10
is swept within a predetermined frequency range so that both the optical signals are optically heterodyned in the second optical coupler
31
. After that, an electrical signal having a frequency difference between both the optical signals, i.e., an electrical signal having an optical beat frequency is detected by the light receiving device
21
coupled to the second output port
314
of the second optical coupler
31
.
As the light receiving device
21
is used, in this example, a photodetector for converting light into an electrical signal such as a photodiode, and the electrical signal having the optical beat frequency detected by the light receiving device
21
is supplied to a high frequency counter
50
after it has been amplified by an amplifier
22
. Further, the light receiving device
21
and the amplifier
22
constitute a wide-band or broad-band optical receiver
29
.
The high frequency counter
50
measures, based on the electrical signal having the optical beat frequency supplied from the wide-band optical receiver
29
, the amount of sweep of the frequency of the optical signal generated from the variable wavelength sweep type measurement light source
10
, and supplies the measured result to a measurement/analysis/display part
90
. On the other hand, an optical or light signal for measurement (hereinafter referred to as optical measurement signal) inputted to the optical device under measurement DUT via the first optical coupler
30
is transmitted through the optical device under measurement DUT into the measurement/analysis/display part
90
. The measurement/analysis/display part
90
carries out a measurement/analysis of the inputted optical signal, and displays the results of the measurement/analysis, if necessary. In addition, the measurement/analysis/display part
90
supplies a control signal to a variable wavelength light source control part
80
, as the case may be.
Control terminals of the measurement light source
10
and the reference light source
20
are connected to output terminals of the variable wavelength light source control part
80
, respectively, and the reference wavelengths of both the optical signals generated respectively from these light sources
10
and
20
are determined on the basis of wavelength setting signals supplied from the variable wavelength light source control part
80
to the control terminals of both the light sources, respectively. In addition, the variable wavelength light source control part
80
supplies a frequency sweep instruction or command signal to the control terminal of the variable wavelength sweep type measurement light source
10
at a predetermined timing, thereby to cause the frequency of the optical signal generated from the measurement light source
10
to be swept within the predetermined frequency range.
Incidentally, an optical frequency bandwidth that can be covered by one sweep is determined by the performance of the variable wavelength sweep type measurement light source
10
, and this bandwidth is approximately several 10 GHz or so in the current technology l
Imamura Motoki
Ryu Shiro
Advantest Corporation
Font Frank G.
Gallagher & Lathrop
Lathrop, Esq. David N.
Stock Gordon
LandOfFree
Method and apparatus for measuring an optical transfer... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for measuring an optical transfer..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for measuring an optical transfer... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2919672