Synchronous Communications, Inc.

General Instrument Corporation

Innotrans Communications, Inc.

Hermann Gysel

Mani Ramachandran

Chandra Sekhar Jasti

Wilton J Hildenbrand, Jr

Chandra Jasti

A directly modulated optical transmitter for use with a fiber optical communications system operating in the 1550 nm wavelength band exhibits very low chirp. The chirp inherently present in a directly modulated laser is cancelled by a phase modulator which optically modulates the directly modulated laser light beam by applying a 180&#xb0; phase delay to a split-off portion of the input radio frequency signal. This provides a low cost transmitter capable of operating in the 1550 nm band and with laser chirp effectively cancelled or substantially reduced, thereby avoiding distortions due to laser chirp interactions with the downstream optical fiber.

Method and apparatus for low chirp transmitter for optical fiber communications

A dispersion compensator is provided that includes an input portfor receiving a WDM optical signal and a dispersion compensating elementcoupled to the input port for substantially compensating the WDM optical signal for dispersion that has accumulated along an external transmission path. The dispersion compensator also includes an output portfor directing the dispersion compensated WDM optical signal to an external element and a dynamic power controllerfor maintaining a total power of the WDM signal below a prescribed level prior to receipt of the WDM optical signal by the dispersion compensating element.

Method and apparatus for automatically adjusting the optical power directed to a dispersion compensating element

A method and apparatus is provided for power balancing an optical signal wavelength to be added to an OADM having at least one drop port and at least one add port. The method begins by monitoring a power level of a first signal wavelength being dropped on the drop port and a power level of a second signal wavelength being added on the add port. The power level of the first signal wavelength is compared to the power level of the second signal wavelength. Based on the step of comparing, the optical attenuation is adjusted along the add port so that the power level of the second signal wavelength becomes substantially equal to the power level of the first signal wavelength.

Method and apparatus for balancing the power of optical channels traversing an optical add drop multiplexer

An optical amplifier () splits an optical signal into two signals (). A first amplifier section () receives the first signal (). The first amplifier section () includes a first optical fiber (), having a first input, for generating a first output power (), and a first pump source () is coupled to the first input, for supplying a first energy amount to the first optical fiber (). The optical amplifier () also includes a second amplifier section () to receive the second signal (), which is arranged in parallel to, and under common control with, the first amplifier section (). The second amplifier section () includes a second optical fiber (), having a second input, for generating a second output power (), and a second pump source () is coupled to the second input, for supplying a second energy amount to the second optical fiber (). A total power () of the first output power () and the second output power () is at least about 600 mill Watts.

Optical amplifier apparatus and method

An optical transmission system is provided comprising a method and apparatus for cancelling noise in the output from a light source for broadening the line width of a light source so as to increase stimulated Brillouin scattering threshold in a standard single mode fiber with a dispersion null at 1310 nm and for using a linearized external modulator to modulate the amplified output of a distributed feedback laser providing an output at 1550 nanometers for use on a standard single mode fiber optic cable with a dispersion null at 1310 nm.

Optical transmission system

A cable TV signal transmission system comprising a Nyquist filter carrier recovery circuit, a mixer, a level shifter and a pre-emphasis circuit for transmitting scrambled TV-IF signals on an FM or digital signal link to a receiver section comprising a de-emphasis circuit, an amplitude modulator circuit and a VSB filter so as to provide to remote TV receivers a scrambled TV-IF signal with correct timing between the video and audio scrambling information.

Scrambled TV-IF signal transmission system

A scrambled frequency modulated video signal transmission system is provided with a headend station having a d.c. coupled amplitude demodulator for removing the amplitude modulation of a scrambled amplitude modulated baseband video signal. The low frequency components, e.g. 0-50 Hz, of the resulting scrambled baseband video signal are separated from the remaining high frequency components thereof for providing a pulse-code FSK modulated subcarrier. The subcarrier and the high frequency components are then combined and frequency modulated in a frequency modulator. The resulting scrambled frequency modulated video signal is then transmitted via fiber optic, coaxial and/or microwave transmission lines to a frequency demodulator in a hub station. In the hub station the output of a frequency demodulator is provided to a subcarrier demodulator for removing the pulse-code FSK modulated subcarrier producing the low frequency components, e.g. 0-50 Hz, which contain the scrambled sync pulse information. The resulting signals are then combined with the high frequency components thereof and provided to a d.c. coupled amplitude modulator before being transmitted to a TV set. In the TV set the output of the amplitude modulator is then provided to a descrambler. The descrambler restores the sync pulse information to the amplitude modulated video signal. The amplitude modulated video signal is then provided to an amplitude demodulator for restoring the original baseband video signal.

Scrambled video signal transmission system with pulse-code modulated

An electrical compensation circuit and an optical compensation circuit are provided for compensating for expansion-type and compression-type gain distortion due to the interaction of a laser and an optical amplifier. In the electrical compensation circuit there is provided a linear signal path and a nonlinear signal path. A delay circuit in the linear signal path compensates for a signal delay in the nonlinear signal path. In the nonlinear signal path there is provided an FET and a transformer. A modulation signal applied to the linear signal path and the nonlinear signal path is processed in the nonlinear signal path and combined with the signal in the linear signal path so as to provide a predistorted modulation signal which is substantially equal in amplitude and opposite in phase to the gain distortion in the optical signal at the output of the optical amplifier. In the optical compensation circuit there is provided a predetermined length of erbium-doped fiber which is inserted between a laser and an erbium-doped fiber amplifier (EDFA) so as to provide an absorption of the output of the laser which is equal in magnitude and opposite in phase to the gain distortion in the output signal of an uncompensated EDFA.

Method and apparatus to compensate for distortion in optical

A scrambled video digital transmission link comprising an amplitude modulator, a scrambler, an amplitude demodulator and frequency conversion apparatus for providing a scrambled video signal in a baseband format and a modified sound signal which includes video sync information which is used to restore the video signal for use in a subscriber's television set. The scrambled video signal in the baseband format and the modified sound signal are converted to a digital signal before transmission by a laser driven fiber optic transmission line to a hub station. In the hub station there is provided digital-to-analog signal converting apparatus, amplitude modulating apparatus and frequency conversion apparatus for recreating the scrambled video signal and modified sound signal generated in the head end station. The signals transmitted between the transmitter and the receiver may be in a digital pulse code modulation (PCM) format or in a format produced by digital modulation of an r.f. carrier, such as quarternary phase shift keying (QPSK) techniques.

Scrambled video digital transmission link

A delay distortion compensating circuit for a laser driven optical transmission system comprises a varactor network for producing a time shift of the instantaneous amplitude of the modulation signal applied to the laser that is inverse to the time shift caused by chromatic dispersion of a fiber optic cable used for propagating the output of the laser and laser chirp so that the sum of the two time shifts is substantially equal to a constant. In one embodiment the cathode of the varactor diode is coupled to a center tap of an inductor called a first order delay equalizer, the terminals of which are connected to a source of a modulating signal and the laser. A d-c bias is applied to the varactor by means of a choke. In another embodiment called a low pass structure, a modulating signal is coupled to the laser through an inductor and a parallel combination of a discrete capacitor and a varactor diode is coupled between ground and a node located between the inductor and the laser. D-c bias is provided to the varactor by means of a resistor.

Delay distortion compensating circuit for optical transmission system

A scrambled frequency modulated video signal transmission system is provided with a headend station having a DC coupled amplitude demodulator for removing the amplitude modulation of a scrambled amplitude modulated baseband video signal. The low frequency components, e.g. 0-50 Hz, of the resulting scrambled baseband video signal are separated from the remaining high frequency components thereof for modulating a sub-carrier. The sub-carrier and the high frequency components are then combined and frequency modulated in a frequency modulator. The resulting scrambled frequency modulated video signal is then transmitted via fiber optic, coaxial and/or microwave transmission lines to a frequency demodulator in a hub station. In the hub station the output of a frequency demodulator is provided to a sub-carrier demodulator for producing the low frequency components, e.g. 0-50 Hz, which contain the scrambled sync pulse information. The resulting signals are then combined with the high frequency components thereof and provided to a DC coupled amplitude modulator before being transmitted to a TV set. In the TV set the output of the amplitude modulator is then provided to a descrambler. The descrambler restores the sync pulse information to the amplitude modulated video signal. The amplitude modulated video signal is then provided to an amplitude demodulator for restoring the original baseband video signal.

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San Jose, CA, United States of America

Hermann Gysel