402 results about "Optical fiber transmission systems" patented technology

In an optical fiber system for delivering laser, a laser beam is focused onto an optical fiber at an injection port of the system. The end portions of the fiber have cladding treatments to attenuate stray light and cladding mode light, so as to enhance the protection of the outer layer joint points. Photodetector sensors monitor scattered stray light, cladding mode light, and / or transmitted cladding mode light. Sensor signals are provided to a control unit for analyzing the fiber coupling performance. If need be, the control unit can control a laser shutter or the like to minimize or prevent damage. In materials processing applications, the photodetector signals can be analyzed to determine the processing status of a work piece.

A transmitter (3) for generating a DQPSK-modulated optical signal, including: a splitter (7) for dividing an optical carrier signal into a first and second branch (8a, 8b), a first and second Mach-Zehnder interferometer (9, 10) in the first and second branch (8a, 8b), respectively, a phase shifter (11) in one of the branches (8b) generating a nominal phase shift of .pi. / 2, and a combiner (7′) for combining the optical output signals of the two branches (8a, 8b). The transmitter (3) has a feedback circuit (12) generating at least a first and second bias signal (15.1 to 15.3) for adjusting a bias of at least the first and second Mach-Zehnder interferometers (9, 10), the feedback circuit (12) includes a detector for generating at least a first and second feedback signal from a sample signal extracted from the optical signal after the combiner (7′), and for each bias signal: a local oscillator generating an auxiliary signal modulating the bias signal (15.1 to 15.3) at a pre-defined frequency (f1, f2, f3), a lock-in detector determining a phase difference between the feedback signal and the auxiliary signal, and a bias circuit for generating the bias signal (15.1 to 15.3) from an output signal of the lock-in detector, wherein the pre-defined frequencies of the auxiliary signals (f1, f2, f3) are different from one another (f1.noteq.f2.noteq.f3) and preferably no integer multiples of each other.