Alphion Corporation

Lucent Technologies Inc.

Agere Systems Inc.

Bharat P Dave

Boris Stefanov

Tan Buu Thai

Ronald Simprini

Kwang S Kim

Doruk Engin

Julio Martinez

Olga Nedzhvetskaya

Jithamithra Sarathy

Niraj K Jha

Roman Antosik

Mohammad Laham

Jiten Sarathy

David Lidsky

Michael Evans

Ganesh Lakshminarayana

Chinnabbu Ekambaram

Adriaan J De Lind Van Wijngaarden

Jayanta Das

Rudiger L Urbanke

Edward Ryszard Sokolowski

James S Lavranchuk

Brij Bhushan Garg

Frank N Hujber

Paul Grabbe

Gaurav Naik

Olga Nedzhvetska

Roanld Simprini

Aleksandr Miglo

Scott Kaminski

Boris B Stefanov

Raj Acharya

Jayantha Das

Khem Gandhi

David Lowe

Frederick Renner

Ravi Vora

Murali Sampath

Kuo-Ming Lee

Tan Thai

David B Lidsky

In a fiber-optic communications system, a backup or redundant optical link is provided at the central office in parallel with the primary one in use. Parameters associated with the backup link, including its signal delay, its attenuation, etc. are stored at the time of installation. Upon failure of the primary link, switchover can be automatic, and the stored parameters are used to make adjustments necessary for the differences between the primary link and the backup link. In addition, having information on the differences between the two links, the central office is able to send control information downstream which is used at the remote site to control changes that must be made for upstream signals. For example, customer equipment can be signaled to adjust its timing for the next time slot or interface amplifiers can be adjusted to account for the change in attenuation. The central office could be provided with a corrected interface to accommodate the new link and a substantial buffer to account for the change in timing, and switchover to the new timing could be done gracefully.

Apparatus and method for ensuring continuity of fiber optic

Methods and apparatus for implementing synchronous Optical Time Division Multiplexing are presented. Namely, a method of upconverting and combining N input NRZ optical data signals, each having an approximately equal pulse width and period, into one time-division multiplexed output signal, as well as a method for the inverse, i.e., down converting the N demultiplexed component signals are presented. Apparatus to implement these functionalities is also presented.

Synchronous OTDM: gapped clock creation and duty cycle multiplication

Method and apparatus are presented for the generation and detection of maintenance signals in an optical data network. The maintenance signals are such that they can be read both by high bit-rate and low bit-rate receivers. Detection of the maintenance signals occurs in two stages. In a low bit-rate first stage each nodal input port is sampled in a round robin fashion to detect the presence of a maintenance signal. In a high bit-rate second stage the maintenance signal is verified and read by a high speed receiver, along with other high bit-rate information transmitted with it. One second stage high speed receiver is shared among M input channels for cost and circuit efficiency.

Generation and detection of optical maintenance signals in optical networks

A method and apparatus for a tunable optical spectrum analyzer that can measure the optical spectrum of a demultiplexed DWDM signal are presented. The signal level and Optical Signal to Noise Ratio (OSNR) of an individual channel of the DWDM signal can be obtained from the measured optical spectrum. The device employs a rapid tuning and detection technique to obtain the optical spectrum of the incoming signal. In a preferred embodiment the apparatus is fabricated on a single chip resulting in a compact measurement device. Using the device of the preferred embodiment, single channel OSNR can be determined in as small a time interval as approximately 225 microseconds. Using an array of these devices an entire DWDM mixed signal can be monitored as to OP and OSNR in the same time interval.

Method and apparatus for bit-rate and format insensitive performance monitoring of lightwave signals

The present invention provides an optical signal quality selection system for optimizing the quality of information transmission. The system splits an incoming optical signal into two equal signals. The split signals are evaluated in optical performance monitors, transmitting an electrical output message to a signal selector relating to the quality of the respective signal. A second electrical message is sent from the optical performance generator to an alarm indicator signal generator, which sends an optical signal to the signal selector to drop the one of the split signals and transmit the non-dropped split signal. An unequipped optical signal from an optical idle signal generator is triggered if no active optical signal is being transmitted.

Optical signal quality selection system

Fault tolerance is provided in a cross-connect system having only duplicated switch fabrics, instead of the triplicated switch fabrics of the prior art. In addition to the two information switch fabrics, the cross-connect system has a relatively small code switch fabric which switches check-code signals generated at each input interface for each input signal sent to an information switch fabric. Fault-detection and error-recovery components in each output interface (1) generate local check-code signals for each outgoing signals received from an information switch fabric and (2) compare those local check-code signals to the corresponding check-code signal received from the code switch fabric to detect a failure and to select a healthy signal as the output signal for that output interface. In one embodiment, input and output interfaces are clustered, and the corresponding input and output check-code signals are multiplexed, for even greater savings in overhead (e.g., fewer check-code cables to and from the code switch fabric).

Low-overhead fault-tolerance techniques for optical and other cross-connect systems

A method and circuit are presented for an all-optical format independent preprocessor that processes an arbitrary optical input signal by converting a NRZ signal to a PRZ signal, or if the input optical signal is RZ, by merely amplifying it. The method involves subtracting a delayed copy of the signal from the original, thereby effectively doubling its frequency, and inserting a pulse at each transition of the original signal, whether rising or falling. In a preferred embodiment this stage is implemented via an integrated SOA in each arm of an asymmetric interferometric device. The asymmetry consists of a delay element in one arm. In a preferred embodiment the entire device is fabricated on a semiconductor substrate, allowing for compactness as well as minimization of interconnectivity losses and overall power consumption. The output of the preprocessor, having a significant frequency component at its original clock rate, can then be fed to a clock recovery stage for all-optical clock recovery.

Format insensitive and bit rate independent optical preprocessor

A method and circuit are presented for the all optical recovery of the clock signal from an arbitrary optical data signal. The method involves two stages. A first stage preprocesses the optical signal by converting a NRZ signal to a PRZ signal, or if the input optical signal is RZ, by merely amplifying it. In a preferred embodiment this stage is implemented via an integrated SOA in each arm of an asymmetric interferometric device. The output of the preprocessing stage is fed to a clock recovery stage, which consists of a symmetric interferometer that locks on to the inherent clock signal by using the second stage input signal to trigger two optical sources to self oscillate at the clock rate. In a preferred embodiment the second stage is implemented via SOAs integrated in the arms of an interferometer, with two DFB lasers as terminuses. The output of the interferometer is an optical clock signal at the clock rate of the original input.

Bit-rate and format insensitive all-option clock extraction circuit

Bit-rate and format insensitive all-optical clock extraction circuit

A method and system for AO R functionality is presented. The system includes an AO R device followed by an AOCR clock recovery module and an AOR retiming device. The AOR retiming device takes as input a recovered clock signal extracted from the output of the AO R by the AOCR clock recovery module. The output is the recovered clock signal gated by the regenerated and reshaped input signal, and a monitor circuit is used to set the optimum operations of the retiming device. In a first embodiment the output of the AOR retiming device is fed to an AOC code and wavelength conversion output stage, which returns the signal to the NRZ coding, on a service wavelength converted to match the fixed wavelength connection with the DWDM transmission system. In a second embodiment the code conversion is incorporated into the AOR retiming device, and wavelength conversion is accomplished in the AOCR clock recovery device.

Bit-rate and format insensitive all-optical circuit for reshaping, regeneration and retiming of optical pulse streams

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Howell, NJ, United States of America

Bharat P Dave