Coherent light generators – Particular beam control device – Modulation
Reexamination Certificate
1998-06-30
2001-02-06
Font, Frank G. (Department: 2877)
Coherent light generators
Particular beam control device
Modulation
C372S028000, C372S096000, C372S020000, C372S026000, C372S032000, C372S102000, C372S046012, C372S003000, C372S005000, C372S034000, C372S043010, C372S036000
Reexamination Certificate
active
06185232
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to lasers, and more specifically to communication devices using semiconductor lasers for optical communication.
BACKGROUND OF THE INVENTION
Cable television systems typically include a headend section for receiving satellite signals and demodulating the signals to baseband. The baseband signal is then converted to an optical signal for transmission from the headend section over fiber optic cable. Optical transmitters are distributed throughout the cable system for splitting and transmitting optical signals, and optical receivers are provided for receiving the optical signals and converting them to radio frequency (RF) signals that are further transmitted along branches of the system over coaxial cable rather than fiber optic cable. Taps are situated along the coaxial cable to tap off the cable signals to subscribers of the system.
In conventional communication systems, such as cable television systems, the fiber optic cable is characterized by small material variations or inhomogeneities that can cause reflection of the optical signal in the reverse direction, i.e., a Rayleigh backscattered signal. The backscattered signal then encounters further fiber variations which cause generation of yet another reflected signal in the forward direction. This signal is referred to as a double Rayleigh backscattered signal. As a result, two signals, the initial forward optical signal and the double Rayleigh backscattered signal, travel in the forward direction and are received by the optical receiver. This generates interference and intensity beats in the receiver, which can cause erroneous demodulation.
Thus, what is needed is a way to reduce interference generated by Rayleigh backscattering in an optical communication system.
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P.B. Hansen, L. Eskildsen, U. Koren, B.I. Miller, M.G. Young, K.J. Dryer, “SBS Suppression using a Temperature Wavelength-modulated Laser Diode with Low Residual AM”, Optical Fiber Communication OFC '96 Conference, vol. 2, 1996 Technical Digest Series, Conference Edition, Feb. 25-Mar. 1, 1996, pp. 302-303.
Hess, Jr. Doren W.
Pidgeon, Jr. Rezin E.
Barnhardt III Hubert J.
Flores Ruiz Delma R.
Font Frank G.
Gardner Kelly A.
Massaroni Kenneth M.
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