Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2001-01-19
2002-09-03
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06445478
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical transmission system, particularly to an optical time division multiplexing technique. This invention can be applied to a measuring system, particularly to a temperature sensor and a pressure sensor.
2. Description of the Related Art
In an optical transmission system according to the related art, a transmitting apparatus performs TDM (Time Division Multiplexing) of a plurality of low-speed signals by processing in an electronic circuit and generates high-speed signals. A receiving apparatus or a node performs DEMUX (Demultiplexing) of the high-speed signals by processing in an electronic circuit and regenerates the low-speed signals. A transmission system with a transmission level of 10 Gb/s (bits per second) has been already realized by adopting the TDM technique in an electronic circuit. However, a processing speed of the electronic circuit is likely to become a bottle neck for a future transmission system with a larger capacity. Therefore, the time division multiplexing technique (optical TDM technique) for performing optical processing is currently under intense studies.
According to the optical TDM technique, an optical signal is processed without being converted to an electric signal. Optical pulse strings inputted from various transmission lines must be multiplexed synchronously. However, the optical pulse strings are transmitted in the transmission lines at different transmission rates depending on environmental factors such as a temperature, etc. Further, pulse positions (phases) of inputted optical pulse strings change constantly. Therefore, it is necessary to provide a method for detecting the pulse positions. The pulse positions are relative time relationships of standard clock signals with repetitive frequencies of the optical pulse strings and inputted pulses.
A technique for detecting a pulse position is disclosed by Ohteru, et. al.
A block chart in “Optical Time-Division-Multiplexer Based on Modulation Signal to Optical Modulators,” B-1118 in Proceedings of the 1996 Institute of Electronics, Information and Communication Engineers (IEICE) General Conference is revised in FIG.
43
.
In
FIG. 43
, an optical pulse string input terminal
1
, an optical multiplexer
2
, an optical modulator
3
for modulating an optical power level, a phase shifter
4
, an oscillator
5
, optical power meters
6
a
and
6
b
for detecting power levels of optical signals and a transmittancy rate detector
7
are illustrated.
In
FIG. 43
, an optical pulse string is inputted from the optical pulse string input terminal
1
and multiplexed into two transmission lines by the optical multiplexer
2
A first output from the optical multiplexer
2
is inputted to the first optical power meter
6
a
and a second output from the optical multiplexer is inputted to the optical modulator
3
. A standard clock signal outputted from the oscillator
5
drives the optical modulator
3
via the phase shifter
4
. An optical signal outputted from the optical modulator
3
is inputted to the second power meter
6
b
. The transmittancy rate detector
7
performs a comparative operation of outputs from the first and second optical power meters
6
a
and
6
b
, and detects a transmittancy rate of a pulse in the optical modulator. Since the comparative operation of the outputs from the first and second power meters
6
a
and
6
b
is performed, even if the optical power level of the inputted optical pulse string fluctuates, the transmittancy rate in the optical modulator
3
can be measured. As discussed below, the transmittancy rate of a pulse in the optical modulator is determined from a phase of a clock signal for driving the optical modulator and a position (phase) of an optical pulse string inputted to the optical modulator. Therefore, a pulse position can be known from the transmittancy rate. The phase shifter
4
is controlled manually to increase a value of the transmittancy rate. Accordingly, the phase of the inputted optical pulse and the phase of the standard clock signal can be synchronized.
An operation of
FIG. 43
is discussed with reference to FIG.
44
.
In
FIG. 44
, pulse positions (a) in an optical pulse string inputted to the optical modulator
3
are illustrated. A relation (b) of a time and a transmittancy rate in the optical modulator
3
is also shown. The relation corresponds to the clock signal which drives the optical modulator
3
. A relation (c) of a time and a transmittancy rate of a pulse is also shown.
In
FIG. 44
, three pulse positions (a) of pulse
1
, pulse
2
and pulse
3
in the optical pulse string correspond to transmittancy rates
1
,
2
and
3
in (c) Since the pulse positions and the transmittancy rates correspond, the pulse positions can be known by detecting the transmittancy rates.
In technique illustrated in
FIG. 43
, it is assumed that a pulse position detector is provided as an error signal detecting circuit for controlling pulse positions Therefore, it is not necessary to detect an accurate pulse position. It is only necessary to detect a sign relationship (left-or-right from position A in (b) of
FIG. 44
) of the detected pulse position.
However, when it is necessary to detect the pulse positions accurately, following problems arise from the technique illustrated in FIG.
43
. As apparent from (c) of
FIG. 44
, the transmittancy rates
1
,
2
and
3
correspond to pulses
1
′,
2
′ and
3
′ as well as pulses
1
,
2
and
3
. A range for detecting positions is limited to field T in (b) of FIG.
44
. Since the transmittancy rate in the optical modulator corresponds to two phase shift amounts, it is difficult to optimize the phase shift amounts. As shown in (c) of
FIG. 44
, the relation of the transmittancy rate and the pulse position is not a straight-line but a sine function curve, a complicated operation circuit is necessary to detect the accurate pulse positions.
It is necessary to detect the accurate pulse positions to simplify a controlling circuit of the pulse positions and to perform more complicated optical processing. Detection of the accurate pulse positions is also necessary for various sensors that utilize changes of a transmission delay time in transmission lines.
Another technique for detecting a pulse position is disclosed in Japanese Unexamined Published Patent Application HEI 2-1828.
FIG. 1
in HEI 2-1828 is revised in
FIG. 45
for this specification.
In
FIG. 45
, the optical pulse string input terminal
1
, an optical demultiplexer
33
, a fully-optical modulator
43
for modulating an optical pulse string with an optical clock pulse and a photo detector
8
are illustrated. In
FIG. 45
, an optical delayer controlling circuit
34
, an optical clock pulse generating circuit
44
, an optical delayer
24
and a phase shift amount output terminal
10
are also illustrated. An optical signal is inputted from the optical pulse string input terminal
1
and inputted to the photo detector
8
via the fully-optical modulator
43
. Then, the photo detector
8
outputs a signal to the optical clock pulse generating circuit
44
, and the optical clock pulse generating circuit
44
outputs an optical clock pulse. The optical delayer
24
delays the optical clock pulse and the optical demultiplexer
33
inputs the delayed optical clock pulse to the fully-optical modulator
43
. The fully-optical modulator
43
is designed to have a higher transmittancy rate when an optical signal with a higher power is inputted. Therefore, when phases of the optical signal inputted from the optical pulse string input terminal
1
and the optical clock pulse synchronize, the photo detector
8
detects a maximum optical power. When the optical delayer
24
is controlled to maximize the output from the photo detector
8
, the optical clock pulse synchronizes with the inputted optical pulse. A pulse position of the inputted optical pulse string can be detected by monitoring an amount of delay for the optical delayer
24
from the phase shift amount output
Edagawa Noboru
Kitayama Tadayoshi
Komiya Takeshi
Matsushita Kiwami
Mizuochi Takashi
Pascal Leslie
Phan Hanh
LandOfFree
Optical pulse position detecting circuit and an optical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical pulse position detecting circuit and an optical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical pulse position detecting circuit and an optical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2845760