Optical switching system

Details Optical switching system Optical switching system

2003-11-26

2004-12-21

Ullah, Akm Enayet (Department: 2874)

Optical waveguides

With optical coupler

Switch

C385S015000, C359S107000, C359S108000

Reexamination Certificate

active

06834135

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an optical switching system for routing optical signals that contain address information indicating destinations of the optical signals in an optical communication network.
(2) Description of the Related Art
In optical communication networks, switching apparatuses are placed at switching points where they receive optical signals from optical transmission apparatuses and switch the destinations of the received signals. At the switching points, the switching apparatuses route the optical signals according to the address information contained in packets that constitute the optical signals, where each signal, either electrical or optical, is a sequence of packets. The electric signals are converted into the optical signals through a modulation and then an electrical-to-optical conversion. Each of the packets constituting the signals is composed of transmission data and a header that contains address information indicating the destination of the signal. The packets constituting the optical signals are hereinafter referred to as optical packets.
In earlier days, when conventional switching apparatuses receive an optical signal composed of optical packets, they convert each optical packet into an electric-signal packet by performing an optical-to-electrical conversion and then a demodulation so as to extract the address information from the header of each electric-signal packet.
The conventional switching apparatuses then update the address information if necessary, re-convert the electric signal into the optical signal, and transmit the re-converted optical signal to the destination (another switching apparatus or a destination apparatus) in accordance with the extracted address information (see Patent Document 1: Optical Label Multiplexing,
FIG. 4
, listed below).
As understood from the above description, each switching apparatus performs the two-way conversion, namely optical-to-electrical and electrical-to-optical, to extract the address information from each packet. As a result, the conventional system has a problem that the transmission speed in the optical communication network is limited by the two-way conversion performed by the switching apparatuses.
For the purpose of solving the above-mentioned problem, various methods based on the optical label switching have been proposed so far (see, for example, the Patent Document 1 (especially
FIG. 6
) and Non-Patent Documents 1 and 2, listed below).
In the optical label switching, an optical transmitting unit transmits an optical signal that contains the address information (hereinafter referred to as a label) in each header of each packet, and an optical switching unit that receives the optical signal causes the received optical signal to branch into two optical signals that have the same information, extracts and extracts only the label of each packet contained in one branched optical signal, and outputs the other branched optical signal after switching its route based on each extracted label.
As described above, in the known optical label switching, the optical switching unit need not convert optical signals of the entire packet into electrical, but reads only a part (the label) of each packet. Further, the optical switching unit need not re-convert the electric signal into an optical signal after it extracts the label. Such an arrangement in this technology is considered to have increased the speed in switching the destinations of the optical signals.
However, in this known optical label switching method, the optical transmitting unit needs to perform a modulation and a frequency conversion on a label signal that is generated based on the label, so that the label signal has a higher frequency than the other portions of the electric signal. The optical switching unit performs a frequency conversion and a demodulation on the received label signal to extract the label.
Accordingly, the optical signal switching speed at the optical switching unit is limited by the modulation, demodulation, and frequency conversion of the label signal.
The above-mentioned problem in the known optical label switching will be described in detail with reference to
FIGS. 9-11
.
Known Optical Label Switching Method
FIG. 9
is a functional block diagram showing the construction of an optical transmitting unit included in an optical label switching system.
FIG. 10
is a functional block diagram showing the construction of an optical switching unit included in the optical label switching system.
An optical transmitting unit
60
converts data into an optical signal and transmits the optical signal into an optical communication network as a sequence of optical packets.
An optical switching unit
61
assigns each optical packet it receives from the optical transmitting unit
60
to an appropriate port in accordance with the destination of the optical packet, and outputs the optical packet to the assigned port.
First, the operation of the optical transmitting unit
60
will be explained.
A data signal generating unit
604
generates a data signal representing data to be transmitted, and outputs the generated data signal.
A label generating unit
601
generates a label signal based on the label contained in each packet, where the label indicates the address information of the packet constituting the data signal.
A label modulation unit
602
modulates the label signal and outputs a modulated label signal. The label modulation unit
602
is achieved by, for example, a BPSK (Binary Phase Shift Keying) modulator.
FIG. 11
shows the frequency allocation of the data signal and the label signal. Since the label signal is a modulated signal, it has a predetermined band width, with its center at f0.
A frequency conversion unit
603
converts the frequency of the modulated label signal into a desired frequency, and outputs the modulated label signal having the desired frequency.
An electrical-to-optical conversion unit
605
outputs a continuous optical signal.
An external modulation unit
606
performs the intensity modulation on the continuous optical signal received from the electrical-to-optical conversion unit
605
in accordance with (i) the modulated label signal received from the frequency conversion unit
603
and (ii) the data signal received from the data signal generating unit
604
, and outputs an optical signal composed of packets.
An optical switching unit
61
extracts a label contained in an optical signal that has been received via an optical line
11
, selects one among n output ports based on the extracted label, and outputs the optical signal to the selected port, where n is an integer no smaller than “2”.
As shown in
FIG. 10
, an optical branching unit
62
of the optical switching unit
61
receives the optical signal via the optical line
11
, and causes the received optical signal to branch to a label identifying unit
63
and a port switching unit
64
.
An optical-to-electrical conversion unit
631
of the label identifying unit
63
receives one of the outputs from the optical branching unit
62
, and converts the branched optical signal into an electric signal.
A filter
632
extracts a modulated label signal from the electric signal output from the optical-to-electrical conversion unit
631
.
A frequency conversion unit
633
converts the frequency of the modulated label signal.
A label demodulation unit
634
demodulates the electric signal output from the frequency conversion unit
633
, and outputs a demodulated label signal.
A label detecting unit
635
detects the address information, namely the label, from the label signal output from the label demodulation unit
634
.
A port control unit
636
determines a port among the n output ports based on the address information detected by the label detecting unit
635
, and controls the port switching unit
64
to output the other branched optical signal to the determined port.
As described above, in the known optical label switching method, the optical transmitting unit performs a modulation and a fre

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