Abstract: A servo control loop for tuning a center frequency of a tuning device to a desired frequency. More specifically, the dynamic range and response time of the servo loop are improved by closing the loop when the sign of the dither signal is such that the center frequency of filter would move towards the desired frequency when the loop is closed and by shifting the phase of the residual dither so that it adds at least partially in phase with the dither signal. The two components thus added are used to supply the control signal for the tuning device.

Abstract: A method of transmitting data and commands on a communication link so as to efficiently distinguish between commands and data. This invention encodes information symbols before transmission on the communication link. A unique code symbol S which does not equal any encoded information symbol is defined along with a unique encoded command symbol ESOTX. Encoded data information symbols are transmitted by sending S followed by ESOTX, and then the encoded data information symbols. Encoded command information symbols, not including ESOTX, are transmitted by sending S immediately followed by the encoded command information symbols. The receiver interprets any encoded information symbol immediately following S as a command. If the encoded command equals ESOTX, the following symbols are treated as data until S is received again. If the encoded command is not ESOTX, the following symbols are treated as commands until S is received again.

Abstract: This invention discloses a method and apparatus for providing high speed optical tuning. With this invention, light is spatially routed through a tree of optical switches interconnected by waveguides to a selected fixed tuned optical filter in an array of such filters. Each of the optical switches can be controlled by a binary signal thereby permitting digitally controlled optical filtering.