A demultiplexing scheme based on semiconductor optical amplifier（SOA）and optical filter for optical time division multiplexing differential quadrature phase shift keying（OTDM-DQPSK）system is proposed and investigated experimentally.With only a common half baudrate electrical clock modulated 33%duty cycle return-to-zero（RZ-33）optical clock signal as pump,this scheme is cost-effective,energy-efficient,and integration-potential.A proof-of-concept experiment is carried out for the demultiplexing of a 2×40-GBd OTDM-DQPSK signal.Error-free performance is demonstrated,and the average power penalty for both channels is about 3 dB.
An improved optoelectronic oscillator scheme for an optical time division multiplexing （OTDM） system based on cascaded Mach-Zehnder modulator （MZM） and polarization modulator （PolM） is experimentally investigated. The system can simultaneously realize clock recovery and demultiplexing. With the MZM working at peak point to generate return-to-zero-33 optical pulses and the PolM working as an equivalent intensity modulator, a high-quality clock signal with 35-fs timing jitter is extracted from the 160-GBaud OTDM-differential quaternary phase-shift keying signal. Narrow short optical switch gates （4 ps） are also generated to demultiplex 160-GBaud signals to 40-GBaud signals. Error-free performance is achieved with 2.4-dB power penalty in the worst case.
A scheme for the photonic generation of frequency-tunable millimeter wave and terahertz wave signals based on a highly flat optical frequency comb is proposed and demonstrated experimentally.The frequency comb is generated using two cascaded phase modulators（PMs）and an electro-absorption modulator（EAM）.The frequency comb covers a 440-GHz frequency range,with 40-GHz comb spacing and less than 2-dB amplitude variation.By filtering out two of the comb lines with 50 dB out of the band suppression ratio,high frequency-purity and low phase noise millimeter wave or terahertz wave signals are successfully generated,with frequencies ranging from 40 to 440 GHz.
A simple design procedure is used to generate photonic crystal fibers （PCFs） with ultra-flattened chromatic dispersion. Only four parameters are required, which not only considerably saves the computing time, but also distinctly reduces the air-hole quantity. The influence of the air-hole diameters of each ring of hexagonal PCFs （H-PCF, including 1-hole-missing and 7-hole-missing H-PCFs）, circular PCFs （C-PCF）, square PCFs （S-PCF）, and octagonal PCFs （O-PCF） is investigated through simulations. Results show that regardless of the cross section structures of the PCFs, the 1st ring air-hole diameter has the greatest influence on the dispersion curve followed by that of the 2nd ring. The 3rd ring diameter only affects the dispersion curve within longer wavelengths, whereas the 4th and 5th rings have almost no influence on the dispersion curve. The hole-to-hole pitch between rings changes the dispersion curve as a whole. Based on the simulation results, a procedure is proposed to design PCFs with ultra-flattened dispersion. Through the adjustment of air-hole diameters of the inner three rings and hole-to-hole pitch, a flattened dispersion of 0±0.5 ps/（nm·km） within a wavelength range of 1.239 – 2.083 μm for 5-ring 1-hole-missing H-PCF, 1.248 – 1.992 μm for 5-ring C-PCF, 1.237 – 2.21 μm for 5-ring S-PCF, 1.149 – 1.926 μm for 5-ring O-PCF, and 1.294 – 1.663 μm for 7-hole-missing H-PCF is achieved.
We show that absorbed and stored electromagnetic energy are proportional to the reflection group delay in highly reflective dispersive dielectric mirrors over the high-reflectivity band.Our theoretical considerations are verified by numerical simulations performed on different dielectric mirror structures.The revealed proportionality between group delay and absorbed energy sets constraint on the application of ultrabroadband and/or dispersive dielectric mirrors in broadband or widely tunable,high-power laser systems.
An all-optical serial-to-parallel converter （SPC） utilizing two cascaded phase modulators and optical bandpass filters （OBPFs） is experimentally investigated and applied to demultiplex an 80-GBd optical timedivision multiplexing （OTDM） return-to-zero （RZ） differential quadrature phase-shift keying （QPSK） signal. Two 40-GBd OTDM tributaries are error-free demultiplexed with a power penalty of approximately 4 dB in the worst case. With its advantages of compact structure, high speed, low power penalty, simultaneous two-tributary operation, and no assistance from a light source, the SPC has potential for use in future OTDM networks. However, the performance of the SPC still needs imDrovement.
