The demand for increased data and communications services is driving many carriers to upgrade their legacy optical systems in the metro-metro-edge region of the communication network. When such upgrades require extending the transmission distance, dispersion compensation techniques are required that compensate for signal degradations while conforming to tight operating budgets.
We have used both channelized and non-channelized, fiber Bragg grating (FBG)-based dispersion-compensating modules (DCM) to compensate for the chromatic dispersion of 60-km fiber links operating at 1550 nm. Using typical SONET/SDH lasers with a large spectral linewidth (~1 nm at the 20-dB point), including significant chirp, our BER experiments show that the system performance depends on whether the grating-based compensators are channelized or non-channelized. Our measurements show that the performance of FBG-based channelized DCMs is a function of the amplitude of the dispersion ripple at the boundaries of the channel bandwidth. Non-channelized DCMs performed well despite their exhibiting more chromatic-dispersion and insertion-loss ripple in the immediate proximity of the laser center wavelength.
First-order system simulation was found to be in general agreement with these experimental observations and singles out the large variations in chromatic dispersion at the boundaries of the channel as the primary reason for the degraded system performance.
A point-scan based laser imaging system is described in this paper. A diode-pumped Nd:YAG laser with high efficiency and high pulse repetition rate is used as the laser source. Any interested area of an object can be imaged and investigated with the system. The technique can have many applications in the field like industry, medical application, defense system and many other fields.
A homodyne CO<SUB>2</SUB> laser radar vibration system is investigated in this paper. A loudspeaker as a cooperative object is used as a vibration source. The vibration frequency of the loudspeaker varied with the supplied voltage can be measured and can be compared with the pre-set frequency. A simple and feasible method is presented to measure the vibration frequency and amplitude. The vibration amplitude in the magnitude of micro meter can be measured precisely.
A short coherence length of a laser diode (LD) is required in coherent resolved interferometers. The coherence length of a LD can be reduced by modulating the source with a high frequency signal, which is superposed on the driving current for the LD. A 980nm laser diode in this paper is modulated with a frequency 40MHz and modulation depth 0.5, where its coherence length is compressed 20 times. The first side-band peak in the coherence function is reduced by 10dB, but it is hard to suppress them completely.