Optical spectrum measurement system with very high resolution

Abstract

Since the discovery of semiconductor-optical fiber, the development of optical communication has been significant. In particular, a baseband modulation frequency in high-speed communication has been increased up to the order of 10 GHz at the research level and of 1 GHz at the practical level. A factor which is the obstacle for further improvement is the bandpass width limitation for a transmitted signal caused by the spread of an oscillation spectrum of LD and also the wavelength dispersion of an optical fiber. For long-distance and high-speed transmission, it is important to determine accurately the spread of the LD spectrum for designing an optical transmission system. The objective of the present study is to clarify the condition required for a high-resolution optical spectrum analysis system, which is essential for understanding the spectrum-spread and chirping of the LD laser at a time of high-speed modulation. A comparison of various measurement systems is made. A method of combining the diffraction grating system and the Fabry-Perot etalon system is proposed, and the optimization of the system is discussed in detail. The present paper describes for the first time the optimization of the tandem configuration of a diffraction grating and Fabry-Perot etalon systems. Based on those discussions, a prototype system has been constructed with which a maximum wavelength sweeping width of 200 MHz/div and resolution of 100 MHz were demonstrated.