Ultrahigh-speed fiber lasers operating at up to 40 GHz offer a clean longitudinal comb and a narrow linewidth. This makes them suitable for applications including optical comb generation, ultrahigh-speed optical pulse transmission including PSK, and as opto-microwave oscillators. In this paper, we describe recent progress on ultrafast fiber lasers and their applications to optical metrology.

We present and demonstrate a novel method of generating a π phase-alternated return-to-zero (RZ) signal together with pulse-amplitude equalization in a rational harmonic mode-locked fiber ring laser, by using a dual-drive Mach-Zehnder modulator. By adjusting the voltages applied to both arms of the modulator, amplitude-equalization and π phase shift can be achieved successfully at a 9.95 GHz repetition rate. The generated alternate-phase RZ signals show enhanced transmission performance in the single-mode fiber (SMF) links without dispersion compensation.

Progress on a single wavelength channel OTDM terabit/s transmission is described. In particular, we focus on 1.28 Tbit/s OTDM transmission over 70 km which we realized recently. A pre-chirping technique using a high speed phase modulator is emphasized to simultaneously compensate for third- and fourth-order dispersion. The input pulse width was 380 fs, and the pulse broadening after a 70 km transmission was as small as 20 fs. All 128 channels time-division-demultiplexed to 10 Gbit/s had a bit error rate of less than 110-9, in which we employed a lot of new technique for pulse generation, dispersion compensation and demultiplexing. These techniques help pave the path for OTDM technology of the 21 century.