Optics: measuring and testing – By light interference – Using fiber or waveguide interferometer
Reexamination Certificate
2000-07-19
2002-07-23
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
Using fiber or waveguide interferometer
Reexamination Certificate
active
06424420
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a measuring device for an arrayed-waveguide diffraction grating, and in particular, to a measuring device for an arrayed-waveguide diffraction grating that demultiplexes optical signals of different wavelengths.
This application in based on patent application No. Hei 11-205423 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Wavelength multiplex communications in which optical signals of multiple different wavelengths are multiplexed and sent in one optical fiber have entered practical application in recent years. An optical multiplexer/demultiplexer, which multiplexes and demultiplexes the light according to its wavelength, is one important element in this type of communications system.
It is conventionally known that bulk diffraction gratings, dielectric multilayers and the like may be used for this optical multiplexer/demultiplexer. However, these conventional devices have a variety of defects. Namely, the selected wavelength is difficult to set, the devices are expensive because the manufacturing steps are complicated, and they experience considerable loss. Thus, the application of these conventional devices to wavelength multiplex communications in which multiple wavelengths are multiplexed/demultiplexed is difficult.
Accordingly, in recent years, attention has been given to arrayed-waveguide diffraction gratings such as recorded in “Compilation 1, C-3, p. 162 of lectures given at the 1996 meetings of the electronics society of the Institute of Electronics, Information and Communication Engineers of Japan”.
FIG. 3
is a planar view showing an example of an arrayed-waveguide diffraction grating.
As shown in
FIG. 3
, an arrayed-waveguide diffraction grating consists of a plurality of input waveguides
50
; an input-side slab waveguide
52
onto which optical signals from input waveguides
50
are incident; an arrayed-waveguide
54
consisting of a plurality of waveguides attached to the opposite end of the input-side slab waveguide
52
; an output-side slab waveguide
56
attached to the other end of arrayed-waveguide
54
; and a plurality of output waveguides
58
attached to the other end of the output-side slab waveguide
56
.
Optical signals being incident from input waveguides
50
are incident on the input-side slab waveguide
52
, and then are incident with the same phase on arrayed-waveguide
54
consisting of a plurality of waveguides.
The input terminal of arrayed-waveguide
54
and the output terminal of input waveguides
50
are each disposed on respective circles. The radius of the circle on which the input terminal of arrayed-waveguide
54
is disposed is two-fold greater than the radius of the circle on which the output terminal of input waveguides
50
is disposed. The center of the circle on which the input terminal of arrayed-waveguide
54
is disposed is located on the circle on which the output terminal of input waveguides
50
is disposed.
Each of the waveguides in arrayed-waveguide
54
is adjusted so as to provide an equivalent interval phase difference. An output-side slab waveguide
56
is disposed to the other end of arrayed-waveguide
54
. With regard to the disposition of arrayed-waveguide
54
, output-side slab waveguide
56
, and output waveguide
58
, the output terminal of arrayed-waveguide
54
and the input terminal of output waveguide
58
are each disposed on respective circles, as was the case on the input side. The radius of the circle on which the output terminal of arrayed-waveguide
54
is disposed is two-fold greater than the radius of the circle on which the input terminal of output waveguide
58
is disposed. The center of the circle on which the output terminal of arrayed-waveguide
54
is disposed is located on the circle on which the input terminal of output waveguide
58
is disposed.
Cross-talk is one performance indicator for this arrayed-waveguide diffraction grating. This cross-talk is defined as the ratio of the optical power of a wavelength with respect to the optical power of the wavelength which is to be selected. Cross-talk expresses the signal spill-over between channels.
It is necessary to realize a low level of cross-talk in order to achieve high-quality communications. In order to realize a low level of cross-talk, the length of the optical path in arrayed-waveguide
54
(i.e., the product of length and the refractive index) needs to be controlled with an accuracy that is on the order of {fraction (1/10)} of the wavelength. As a result, accurate measurement of the optical path length and trimming thereof based on the results of this measurement are required.
It is known that a method employing a Mach-Zehnder interference optical system and Fourier transform demultiplexing method as disclosed in K. Takada, H. Yamada, Y. Inoue, Optical Low Coherence Method for Characterizing Silica-Based Arrayed-Waveguide, Journal of Lightware Technology, Vol. 14, No. 7., p. 1677, 1996, can be used as a method for measuring the optical path length in arrayed-waveguide
54
.
FIG. 4
is a block diagram showing the structure of the conventional measuring device for an arrayed-waveguide diffraction grating.
The numeral
100
in
FIG. 4
indicates a LED (light emitting diode) that radiates light of a sufficiently short coherent length having a wavelength of 1.5 &mgr;m.
102
is a LD (laser diode) that radiates light of a sufficiently long coherent length having a wavelength of 1.3 &mgr;m.
104
is an optical coupler that multiplexes the light radiated from LED
100
and LD
102
, splits the light into equal intensities, and then radiates it from each of two radiating terminals. An arrayed-waveguide diffraction grating
106
, which is to be measured, is connected to one radiating terminal of the optical coupler, and an optical path length varying device
108
for changing the optical path length is connected to the other radiating terminal.
110
is an optical coupler which is identical to optical coupler
104
. The output terminal of arrayed-waveguide diffraction grating
106
and the output terminal of optical path length varying device
108
are connected to respective input terminals of optical coupler
110
.
The above-described optical coupler
104
, arrayed-waveguide diffraction grating
106
, optical path length varying device
108
, and optical coupler
110
form a Mach-Zehnder interference optics system.
Numeral
112
is a wavelength demultiplexer which is connected to one output terminal of optical coupler
110
, and which radiates input light from different radiating terminals at each wavelength.
Optical detector
116
is connected to one of the radiating terminals of wavelength demultiplexer
112
via optical fiber
114
. Optical detector
116
converts the incident optical signal to an electric signal and outputs this result. The output electric signal is output to waveform recording device
120
via signal line
118
.
Optical detector
124
is connected to the other radiating terminal of wavelength demultiplexer
112
via optical fiber
122
. Like optical detector
116
, optical detector
124
converts the incident optical signal to an electric signal and then outputs this result. The electric signal output from optical detector
124
is input to clock generator
128
via signal line
126
. Clock generator
128
outputs a frequency clock in response to the value of the electric signal that is input. Note that clock generator
128
is connected to waveform recording device
120
by signal line
130
. It is also possible to record the output of clock generator
128
.
The principle for measuring the optical path length of arrayed-waveguide diffraction grating
106
in the aforementioned design is as follows. Namely, light having a wavelength of 1.5 &mgr;m that was radiated from LED
100
is incident on the Mach-Zehnder interference optics system via optical coupler
104
. When this light is incident on the Mach-Zehnder interference optics system, then 1.5 &mgr;m light which has propa
Connolly Patrick
McGinn & Gibb PLLC
NEC Corporation
Turner Samuel A.
LandOfFree
Measuring device for arrayed-waveguide diffraction grating does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Measuring device for arrayed-waveguide diffraction grating, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Measuring device for arrayed-waveguide diffraction grating will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2875570