General Instrument Corporation of Delaware

Ganesh K Gopalakrishnan

A resonantly enhanced external electro-optic modulator reduces required drive power. The modulator has a coupling structure that efficiently couples power from a feed line into the resonator and eliminates the need for a terminal impedance. The modulator can be driven by a RF signal that is designed to suppress Stimulated Brillouin Scattering (SBS) in a long haul, high power fiber optic link, such as that used to transmit analog CATV signals. The modulator can also be used to depolarize an optical signal. A ring resonator includes a portion located outside the active area of the modulator in order to provide a space-efficient structure. The ring resonator can include one or more coaxial cable portions that are tuned to provide resonance at one or more frequencies that are matched to the input RF drive signal. A pre-chirping phase modulator and intensity modulator which are driven by a common RF/DC bias signal also provide a space- and power-efficient structure by eliminating the need for a separate DC bias electrode. Compared to other adjustable chirp devices, there is no need to pre-distort both branches of the intensity modulator. An integrated electro-optic device includes a resonantly enhanced modulator, a pre-chirping modulator, and an intensity modulator arranged serially and fabricated in a common substrate.

Optical modulator for CATV systems

A phase modulator is provided in an externally modulated, feed-forward linearized, analog cable television (CATV) link for reducing fiber-induced composite second order (CSO) distortion components. The system is compatible with existing commercially available modulators. CSO distortion is caused, in part, by self-phase modulation of the transmitted signal in the fiber optic link. The problem is particularly prevalent when data is transmitted at a wavelength other than the minimum dispersion wavelength of the fiber. Moreover, CSO distortion increases with the length of the fiber optic link and with the optical intensity modulation index of the primary modulator of the link. The phase modulator modulates an optical signal which is provided to the primary modulator in accordance with an optical phase modulation index k of an RF data signal to be transmitted. The phase modulator is effective with fiber optic links of varying lengths which carry amplitude-modulated vestigial sideband (AM-VSB) data signals such as cable television (CATV) signals.

Growing community of inventors

Huntingdon Valley, PA, United States of America

Ganesh K Gopalakrishnan