In this paper, firstly, the principle, advantages and disadvantages of measurement of laser linewidth by delayed self-heterodyne method is introduced，and the essence of the method is analyzed theoretically. The core components of the measurement system are introduced in detail.Secondly, the self-developed scheme of semiconductor laser with external dual- cavity self-injection structure of the adjustable time-delay fiber is proposed. The linewidth results of lasers with different lengths of time-delay fiber are tested for the single-mode optical fiber system. The power variation of different structures is analyzed. Finally, A narrow-linewidth semiconductor laser with a mean power of 4 mW, a mean linewidth of 1.96 kHz and the side mode suppression ratio is more than 35 dBm is obtained.
KEYWORDS: Free space optics, Telecommunications, Atmospheric turbulence, Free space optical communications, Signal to noise ratio, Atmospheric optics, Turbulence, Acquisition tracking and pointing, Modulation, Transmitters
The performance of a free-space optical communication system is highly affected by the atmospheric turbulence in terms of scintillation. An optical communication system based on intensity-modulation direct-detection was built with 1-km transmission distance to evaluate the bit error rate (BER) performance over real atmospheric turbulence. 2.5-, 5-, and 10-Gbps data rate transmissions were carried out, where error-free transmission could be achieved during over 37% of the 2.5-Gbps transmissions and over 43% of the 5-Gbps transmissions. In the rest of the transmissions, BER deteriorated as the refractive-index structure constant increased, while the two measured items have almost the same trend.