Abstract

The increased information throughput requirements for optical communications systems are placing increasingly stringent demands on the linewidth, modulated spectra, and bandwidth performance of lasers and optical modulators. In addition, increased DWDM channel densities have resulted in a need for significantly higher resolution optical spectrum measurement than is available from the current generation of diffraction grating-based optical spectrum analyzers. One powerful technique to improve resolution is optical heterodyne,^1–3 where two lasers operate at optical frequencies whose difference is within the frequency range of a microwave spectrum ana-lyzer used to detect the heterodyne beat signal.^4–6 In this approach, the upper frequency limit of the microwave spectrum analyzer (20 to 50 GHz) limits the range of the optical frequencies covered in a single sweep. This becomes a very serious limitation when high-resolution spectrum analysis is required over the frequency range corresponding to the DWDM C and L bands (>10 THz). With the recent advances in widely tunable mode-hop-free lasers,⁷ a dramatic simplification of the heterodyne optical spectrum analysis is possible by using the traditional radio concept of the tunable local oscillator (LO).^8–11 Here, we report on a novel polarization diverse coherent optical spectrum analyzer based on a continuously tunable optical LO.

© 2002 Optical Society of America