Signal phase regeneration through multiple wave coherent addition enabled by hybrid optical phase squeezer.

A newly proposed concept, which is called hybrid optical phase squeezer (HOPS), achieves multi-level optical phase quantization through coherent addition of two (dual-wave scheme) or three (triple-wave scheme) optical waves exploiting optical parametric processes and electro-optic modulation. The triple-wave scheme enables signal phase regeneration free from phase-to-amplitude noise transfer, which is inevitable in the dual-wave scheme. By using HOPS in the dual-wave scheme, 3-fold phase-noise reduction was achieved for 24-Gb/s QPSK signals with a slight increase of amplitude noise. On the other hand, HOPS in the triple-wave scheme allowed phase regeneration of 12-Gb/s BPSK signal with a suppression of phase-to-amplitude noise transfer.

Phase regeneration of phase encoded signals by hybrid optical phase squeezer.

We present a new method to perform phase regeneration of phase encoded signals. In our concept called "hybrid optical phase squeezer (HOPS)," a multilevel phase-quantized signal is synthesized through the coherent addition of a phase-conjugate copy of the signal and a phase harmonic of the signal with a frequency shifter. Unlike the conventional method by phase sensitive amplification, HOPS does not use any optical parametric gain such that only optical elements with low optical nonlinearity are necessary for optical phase quantization. In the proof-of-concept experiment, it is confirmed that a 2-level HOPS can perform quadrature squeezing with an extinction ratio of 40 dB. Simultaneous phase regeneration of two coherent wavelength-division-multiplexed 10.75-Gb/s binary phase-shift keyed signals is successfully demonstrated using a 2-level HOPS based on a semiconductor optical amplifier.

Transmission and pass-drop operations of mixed baudrate Nyquist OTDM-WDM signals for all-optical elastic network.

We propose the use of Nyquist OTDM-WDM signal for highly efficient, fully elastic all-optical networks. With the possibility of generation of ultra-coarse yet flexible granular channels, Nyquist OTDM-WDM can eliminate guard-bands in conventional WDM systems, and hence improves the spectral efficiency in network perspective. In this paper, transmission and pass-drop operations of mixed baudrate Nyquist OTDM-WDM channels from 43 Gbaud to dual-polarization 344 Gbaud are successfully demonstrated over 320 km fiber link with four FlexGrid-compatible WSS nodes. A stable clock recovery is also carried out for different baudrate Nyquist OTDMs by optical null-header insertion technique.

Baud-rate flexible clock recovery and channel identification in OTDM realized by pulse position modulation.

We propose a novel scheme of OTDM utilizing pulse position modulation, where optical null headers (ONH) are inserted between the signal pulses periodically to allow channel identification. The ONH also achieves in-band clock distribution through the generation of high contrast pilot tone on the signal power spectra, enabling baud-rate flexible clock recovery. Using the novel scheme, clock recovery with a timing jitter of less than 200 fs is achieved at different baud rates up to 344 Gbaud. We demonstrate stable clock recovery with channel identification in 344-Gb/s OTDM transmissions over dispersion managed 3-km SMF.

No guard-band wavelength translation of Nyquist OTDM-WDM signal for spectral defragmentation in an elastic add-drop node.

We demonstrate a seamless spectral defragmentation in an elastic all-optical add-drop node based on wavelength division multiplexing (WDM) channels of Nyquist optical time division multiplexing (OTDM) signal. A 172 Gbaud Nyquist OTDM signal occupying a 215 GHz range is elastically shifted adjacent to its neighboring channel, completely filling a variable spectral gap caused by the dropped channel. The frequency shift is done in a dual-stage polarization-diversity four wave mixing-based converter using polarization-maintaining highly nonlinear fiber. The spectrally defragmented signals are successfully transmitted over a 80 km fiber link with BER<10(-9).

Evolution of the gain extinction ratio in dual-pump phase sensitive amplification.

We have experimentally achieved a gain extinction ratio (GER) of 30 dB at 21.75 dBm pump power in a dual-pump phase sensitive amplifier based on highly nonlinear fiber, which is more efficient than what we predict with the conventional three-wave model. We point out that high-order sidebands play a key role. Then we scrutinize the trajectories of the output signal vector in the complex plane with increasing nonlinear phase shift and understand the roll-over behavior of GER versus pump power curve. We found that the phase "flip" of the output signal occurs around the largest GER. Adjusting design parameters, we show how to improve GER.

Parametric tunable dispersion compensation for the transmission of sub-picosecond pulses.

Parametric tunable dispersion compensator (P-TDC), which allows format-independent operation owing to seamlessly wide bandwidth, is expected to be one of the key building blocks of the future ultra-high speed optical network. In this paper, a design of ultra-wide band P-TDC is presented showing that bandwidth over 2.5 THz can be achieved by compensating the chromatic dispersion up to the 4th order without employing additional method. In order to demonstrate the potential application of P-TDC in the Tbit/s optical time division multiplexing transmissions, 400 fs optical pulses were successfully transmitted through a dispersion managed 6-km DSF fiber span.

High-speed optical transmissions over a second- and third-order dispersion-managed DSF span with parametric tunable dispersion compensator.

A wideband and fast tunable chromatic dispersion compensator is one of the key components for the future high-speed optical transmissions. We have so far proposed and demonstrated a new tunable dispersion compensation scheme called parametric tunable dispersion compensator (P-TDC), which is based on the combination of parametric frequency conversion and frequency dependent dispersive media. The P-TDC has many attractive features such as a seamlessly wideband operation, wide tunable range and fast dispersion tuning. In fact, with appropriate configurations of dispersive media, the P-TDC can compensate the dispersion slope of transmission fibers even though the second-order dispersion is small. In this paper, we use such a P-TDC scheme and successfully achieve high-speed optical transmissions over a second- and third-order dispersion managed dispersion shifted fiber (DSF) span. The transmission experiments show low-penalty 172 Gbit/s return-to-zero on-off-keying transmissions over 126-km DSF.

Continuously tunable 22 ns delay for wideband optical signals using a parametric delay-dispersion tuner.

We present a concept of parametric delay-dispersion tuner (PDDT) that is capable of the continuous tuning of delay and dispersion for wideband optical signals in a simultaneous and independent manner. We experimentally demonstrate a tunable delay of 22 ns for 2.6 ps return-to-zero optical signals without distortion and error-free transmissions at 43 gigabits per second. We show that PDDT has a bandwidth of ~0.9 THz, resulting in the delay-bandwidth product of ~20,000, and exhibits an excellent performance in terms of stability and reproducibility.