Optical time division multiplexing - wavelength division multiplexing (OTDM-WDM), intensity modulation (IM) systems employing optical amplification and dispersion management (DM) are analyzed with and without the introduction of an optical narrowband bandpass filter placed right after optical time demultiplexing. The use of the filter was found to improve the performance of the demultiplexed channels by reducing amplitude jitter while possessing high intersymbol interference (ISI) tolerance. The OTDM-WDM link shows good performance up to 2000km with the OTDM filter providing a Q gain of 0.7 - 1.1dB. The optimal input power reduces for longer distances due to increased significance of nonlinear effects. A 900km link showed good performance for spectral efficiencies as low as 0.52bits/s/Hz, though the Q gain provided by the OTDM filter reduces as channel spacing decreases.
Gain clamping in double-pass short-wavelength band erbium-doped fiber amplifier (S-band EDFA) is demonstrated. It uses a fiber Bragg grating, which operates in conventional-band to form an oscillating laser in the cavity using an erbium-doped fiber (EDF) gain at around 1530nm. This new technique has shown a good gain clamping effect with gain variation of less than 1.0dB from -40 to -14dBm input signal powers for 1500nm signal. The gain can be controlled within 18 to 20dB by varying a variable optical attenuator from 0 to 8dB. Compared with an unclamped amplifier, the noise figures for small signals are slightly improved due to the suppression of amplified spontaneous emission (ASE). However, the noise figure level is still considerably high due to the double-pass scheme and unoptimised splicing between a depressed cladding EDF and a standard single mode fiber. The advantage of this gain clamped amplifier is that the oscillating light operates at wavelength outside S-band region, which prevent the wavelength division multiplexed system from being disturbed.
Described in this paper is a system for the real-time image monitoring of electromagnetic near-field distributions over devices and circuits at a specific radio frequency (RF), which is the first to the best of our knowledge. It is based on a 64-channel parallel electro-optic heterodyne detection scheme, in which arrays of photodiodes and mixers allow simultaneous acquisition of 8 × 8pixel data. Its highest frame rate of 10Hz enables even a motion picture display of RF near-field images. It has been applied to a patch antenna and a moving RF emitter for performance demonstration.