Optical waveguides – With optical coupler
Reexamination Certificate
2001-04-24
2003-03-18
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
C385S014000, C385S024000, C359S107000, C359S199200
Reexamination Certificate
active
06535661
ABSTRACT:
This application is based on Japanese Patent Application Nos. 2000-125516 filed Apr. 26, 2000 and 2000-262115 filed Aug. 31, 2000 in Japan, the contents of which are incorporated here into by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical signal processing method and apparatus that inputs an optical pulse train such as optical packets, and carries out serial-to-parallel conversion or generates an optical clock pulse train and so on.
In addition, the present invention relates to a label processing method and apparatus for recognizing address information and the like of high-speed optical packets.
Furthermore, the present invention relates an optical memory method and apparatus that allows a memory composed of an electronic circuit to write freely a high-speed optical packet signal, and to read and output it as an optical packet signal, again.
Moreover, the present invention relates to implementing higher order functions such as a router or optical computer by combining techniques such as serial-to-parallel conversion, optical clock pulse generation, label processing and optical memory.
2. Description of the Related Art
Recently, with the explosive growth of data communications typified by the Internet, the need for enhancing the speed of optical signals has been increasing. In such an environment, a problem arises about processing directly an electrical signal with a rate greater than 10 Gbps by a conventional electronic circuit after converting an optical signal into an electrical signal by a photo detector. For example, such a router in optical packet communications needs a label recognition function in order to decide an output port by decoding the address information contained in the label of the optical packet, and a buffer memory function for delaying packet signals by a desired time period in order to avoid collision between optical packets. In such a case, since the conventional label recognition processing or memory processing function is usually carried out by silicon based LSIs, their speed is limited to less than 1 Gbps.
Thus, it is becoming increasingly difficult for employing conventional silicon-based electronic circuits to implement the label recognition processing or memory processing for the high-speed optical packet signals.
In view of this, such a technique as shown in
FIG. 17
has been proposed recently. In
FIG. 17
, a high-speed optical packet signal is converted into an electrical signal by an O/E (optical-to-electrical) receiver
1
using a photo detector. Then, a clock signal is extracted from the electrical signal by an electrical clock signal generator
2
using InP- or GaAs-based high-speed electronic circuit technology. Using the clock signal, the high-speed electrical signal is converted into a plurality of parallel low-speed electrical signals by an electric serial-to-parallel converter
3
, thereby enabling label recognition. On the other hand, as the memory processing, the following scheme is conceived. The electrical signals passing through the parallel conversion are stored into a memory cell array
4
consisting of an SRAM. When reading the electrical signals, the plurality of low-speed output electrical signals read out of the memory cell array
4
are rearranged into a high-speed serial electrical signal by an electrical parallel-to-serial converter
5
using the electronic circuit technology, and the high-speed serial electrical signal is finally converted into an optical packet signal by an E/O (electrical-to-optical) transmitter
6
.
The method, however, is considered to have a limit of about 40 Gbps because it entirely depends on electronic circuits
2
,
3
and
5
to implement the clock signal generation, serial-to-parallel conversion and parallel-to-serial conversion. Furthermore, to achieve the serial-to-parallel conversion to convert the serial signal to the plurality of low-speed signals by the InP- or GaAs-based high-speed electronic circuit technology, the high-speed electrical signal must be successively halved in frequency (such as 40 GHz→20 GHz→ . . . →several hundred MHz), which requires not a few stages, and hence presents a problem about clock extraction, phase control and the like at each stage. Besides, using the electronic circuits will increase the total power consumption considerably. In addition, since it is necessary for the conventional clock extraction by the electronic circuit to lock the oscillation frequency of the VCO (Voltage-Controlled Oscillator) using the feedback in the PLL (Phase Locked Loop), it is impossible to extract the clock signal instantaneously for the packet signal input in a burst.
Apart from the foregoing systems, several researches are conducted about parallel conversion (also called “time to space conversion”) of a high-speed serial optical signal. As a conventional optical serial-to-parallel conversion method, such a scheme is conceived as splitting a high-speed optical signal into a plurality of optical signals, followed by converting the individual optical signals into low-speed optical signals using high-speed all-optical switches. For example, to carry out parallel conversion of a 100 Gbps high-speed optical signal to ten 10 Gbps low-speed optical signals, ten all-optical switches are used.
As other optical serial-to-parallel conversion methods, the following techniques are proposed. A method using a plurality of surface emitting second harmonic generation processes (Shih-Chen Wang et al., J. Lightwave Technol. Vol. 14, No. 12, P. 2736 (1996)); a method using exciton giant non-linear effect (K. Ema et al., Appl. Rhys. Lett. Vol. 59, No. 25, p. 2799 (1991)); and a method using hologram (P. C. Sunetal., Opt. Lett. Vol. 20, No. 16, p. 1728 (1995)).
However, the conventional method using the plurality of all-optical switches for the all-optical serial-to-parallel conversion has a problem of requiring a large scale apparatus, and increasing the power consumption. The conventional method using the surface emitting second harmonic generation has a problem of extremely low efficiency and large loss because of using non-resonant optical nonlinear effect. The conventional method using the exciton giant nonlinear effect has a problem of a need for cooling the nonlinear medium to the liquid helium temperature to achieve large nonlinear effect. Finally, the conventional method using the hologram has a problem of an extremely large loss because of using diffraction effect. Thus, all the conventional methods offer problems of demanding extremely large running costs, and being ineffective and difficult to maintain stable performance for a long time.
SUMMARY OF THE INVENTION
To solve the foregoing problems of the conventional techniques, a first object of the present invention is to implement optical signal processing by various silicon-based electronic circuits with low power consumption and rather simple configuration by allowing the high-speed input optical packet signal to convert itself into low-speed parallel optical signals.
To solve the foregoing problems of the conventional techniques, a second object of the present invention is to implement instantaneous reading of the label information in a high-speed optical packet that is input in a burst mode by generating a single optical pulse from the input optical packet, by converting the label of the optical packet into parallel signals at once using the optical pulse, and by leading the parallel signal to a label recognition circuit used as the silicon-based electronic circuit.
To solve the foregoing problems of the conventional techniques, a third object of the present invention is to implement a high-speed, low power consumption optical memory method and apparatus capable of handling a burst mode signal.
A fourth object of the present invention is to implement higher order functions of a router, optical computer or the like by combining techniques such as serial-to-parallel conversion, optical clock pulse generation, label processing and optical memory.
The optical si
Itoh Hiroki
Nakahara Tatsushi
Suzuki Hiroyuki
Takahashi Ryo
Takenouchi Hirokazu
Fitch Even Tabin & Flannery
Knauss Scott
Lee John D.
Nippon Telegraph and Telephone Corporation
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