Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-08-18
2001-08-07
Negash, Kinfe-Michael (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C375S308000
Reexamination Certificate
active
06271950
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to optical transmission systems and, more particularly, to an optical Differential Phase Shift Keying (DPSK) transmission system having multiplexing, routing and add/replace capabilities.
BACKGROUND OF THE INVENTION
Cost is an important parameter in optical Local Area Networks (LANs) and Metropolitan Area Networks (MANs). The cost of lasers is a prime component of the costs in such networks. Also, the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocols (e.g., Ethernet, IEEE 802.3, etc.) of traditional LANs may not readily be adopted for optical LAN/WANs because of the longer distances involved.
What is desired is an optical LAN/MAN network where multiple users can share the same laser source and at the same time provide an efficient way of allocating bandwidth among users.
SUMMARY OF THE INVENTION
The apparatus and method of the present invention solves the above problems in a Differential Phase Shift Keying (DPSK) optical transmission system which provides time division multiplexing, channel routing and channel add/replace functions. Our techniques also provide a flexible way of allocating bandwidth among multiple users. This makes DPSK attractive for LAN/MAN applications because the cost of one laser (or several lasers in case of a WDM system) can be shared among multiple users.
More particularly, our DPSK transmitter comprises a laser to generate an optical carrier signal; a delay encoder to provide a different delay for each of a plurality, M, of input signal channels; and a M channel phase modulator to phase modulate the optical carrier signal with each of the differently delayed M input signal channels to form a Time Division Multiplexed (TDM) phase modulated optical signal. A TDM phase modulated DPSK system is formed by combining the transmitter with a receiver for demodulating a received TDM phase modulated optical signal.
In another embodiment, an add node is disclosed for adding a signal channel to an empty time slot channel of a received TDM phase modulated optical signal. The add node includes a receiver to demodulate the received TDM phase modulated optical signal to form an output TDM signal including the empty time slot channel; a clock recovery circuit to provide a synchronization signal for the add signal; and a flip-flop to gate the add signal onto a phase modulator. As a result, the add signal is added into the empty time slot channel of the received TDM signal.
In yet another embodiment, a channel replace node is disclosed for replacing a selected channel of a received TDM phase modulated optical signal with a new channel signal. The channel replace node includes a receiver to demodulate the received TDM phase modulated optical signal to form an output signal; a demultiplexer and clock recovery circuit to recover data and clock signals of all TDM channels; a channel reset circuit; a flip-flop to add the new channel to the TDM signal; and a channel phase modulator to phase modulate the product signal so as to overwrite the selected channel of the received TDM signal.
REFERENCES:
patent: 5181136 (1993-01-01), Kavehrad et al.
patent: 5228043 (1993-07-01), Naito et al.
patent: 5355243 (1994-10-01), King
patent: 5491575 (1996-02-01), Neidlinger et al.
patent: 5907421 (1999-05-01), Warren et al.
Hansen Per Bang
Nielsen Torben N.
Caccuro John A.
Lucent Technologies - Inc.
Negash Kinfe-Michael
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