In this paper, an achromatic quarter waveplate scheme at terahertz frequency range is proposed. The waveplate is based on a silicon grating with large fill factor and period close to the wavelengths of the terahertz wave. Owing to the grating structure, the frequency dependence of waveplate is compensated. An achromatic QWP is fabricated and experimentally demonstrated to show an excellent wideband feature at the range of [0.47, 0.8] THz, which is more than 6 times wider than a conventional QWP working at single frequency 0.5 THz, by assuming ± 3% variance of phase retardation.

In this paper, we propose a novel method to depict 2-dimension (2-D) phase portrait by using single-channel-sampling (SCS) technique, which can be used for optical performance monitoring. Single low speed sampling scheme reduces cost and complexity of monitoring system setup significantly. In the experimental demonstration, optical signal to noise ratio (OSNR) is monitored from 10 dB to 30 dB by statistical analysis on pattern evolution of the generated 2-D phase portrait in both NRZ and RZ systems. The chromatic dispersion (CD) influence on OSNR monitoring performance is also investigated.

In this letter, we propose and experimentally demonstrate an all-optical modulation format conversion scheme from amplitude shift keying (ASK) and quadrature phase shift keying (QPSK) to 8-ary quadrature amplitude modulation (8QAM), using four-wave mixing (FWM) effect in highly nonlinear fiber. In the FWM process, a 20-Gbits/s return-to-zero QPSK (RZ-QPSK) signal and a 10-Gbit/s ASK signal are utilized as probe light and pump light, respectively. A 30-Gbits/s RZ-8QAM signal, which is the idler light, is successfully obtained with optical signal-to-noise ratio larger than 30 dB and bit-error rate lower than 10 −5 .Index Terms-8-ary quadrature amplitude modulation (8QAM), cross phase modulation (XPM), four-wave mixing (FWM), highly nonlinear fiber (HNLF).