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To answer the question: “Is optical phase conjugation (OPC) capable of compensating nonlinear distortions caused by not only Kerr effect of optical fibre, but also the carrier dynamics of semiconductor optical amplifiers (SOAs)?", we investigate the effectiveness of OPC-based nonlinear compensation for SOAs amplifying a few-channel WDM signal modulated with m-QAM. We use a pair of SOAs with an OPC stage sandwiched between the two so that the combination works as a low-distortion amplifier. Symbol-period longer than the gain recovery time is chosen in our experiments to avoid bit-pattern effects introduced by the SOA. We amplify a 12Gbaud, 16QAM modulated three-channel WDM signal with this technique in the back-to-back configuration which remarkably outperforms a single SOA in the nonlinear regime of operation with an average Q2 improvement better than 4 dB for an output power of 4 dBm. We further demonstrate the practical advantage of the low distortion higher output power capability of the SOA shown in the back-to-back result by carrying out a transmission of the amplified signal through a 160-km fibre, where relatively high launch power is desirable. We also study the case of 64QAM signals and show that approximately a 3 dB Q2 factor improvement can be obtained over single SOA, while without nonlinear phase distortion compensation, the demodulation is nearly impracticable.

Optical frequency comb lines with poor carrier to noise ratio (CNR) are significantly improved by Brillouin amplification using its extreme narrow bandwidth gain to suppress out of band noise, enabling higher quality signal modulation. Its application to spectral lines of narrow 10 GHz pitch and poor CNR is shown to suppress the otherwise strong phase distortion caused by poor CNR after encoding with 96 Gb/s DP-64-QAM signals and restore the bit error rate (BER) to below the limit for standard forward error correction (FEC). This is also achieved with the required frequency shifted optical pump for amplification obtained by seeding it from the comb itself, sparing the need for lasers and frequency locking. Simultaneous CNR improvement for 38 comb lines is also achieved with BER restored to below the FEC limit, enabled by a multi-line pump that is pre-dispersed to suppress its spectral distortion from the Kerr effect in the gain medium. Carrier performance at minimum BER shows minimal noise impact from the Brillouin amplifier itself. The results highlight the unique advantage of Brillouin gain for phase sensitive communications in transforming otherwise noisy spectral lines into useful high quality signal carriers.

We demonstrate a nonlinear signal processing approach for compensating nonlinear distortion caused by the Kerr effect in optical fiber transmission. The concept relies on propagating the signal through a separate all-optical module outside the link to apply tunable nonlinear distortion and phase-conjugation in series. We show this uniquely enables tunable regeneration of phase-encoded 40 Gb/s signals of different data-formats and number of WDM channels, to allow significantly higher transmission powers through single and multi-span fiber links. An improvement in the receiver power penalty by 3~4 dB for a bit-error-rate (BER) of ≈10−5 is achieved.

We report the demonstration of automatic higher-order dispersion compensation for the transmission of 275 fs pulses associated with a Tbaud Optical Time Division Multiplexed (OTDM) signal. Our approach achieves simultaneous automatic compensation for 2nd, 3rd and 4th order dispersion using an LCOS spectral pulse shaper (SPS) as a tunable dispersion compensator and a dispersion monitor made of a photonic-chip-based all-optical RF-spectrum analyzer. The monitoring approach uses a single parameter measurement extracted from the RF-spectrum to drive a multidimensional optimization algorithm. Because these pulses are highly sensitive to fluctuations in the GVD and higher orders of chromatic dispersion, this work represents a key result towards practical transmission of ultrashort optical pulses. The dispersion can be adapted on-the-fly for a 1.28 Tbaud signal at any place in the transmission line using a black box approach.

We present automatic dispersion control of 1.28Tb/s optical time domain multiplexed signals. The dispersion is monitored by measuring the power of the 1.28THz tone of the RF spectrum using a photonic-chip-based radio-frequency spectrum analyzer (PC-RFSA) and the dispersion compensation is realized by means of a spectral pulse shaper, via computer-controlled feedback from the PC-RFSA.

We investigate an optical performance monitor based on Stimulated Brillouin scattering (SBS), for enabling the measurement of the in-band optical signal to noise ratio (OSNR) for multiple channels of a wavelength-division multiplexed (WDM) signal simultaneously. The principle relies on propagating the signal in a nonlinear waveguide so that each channel pumps SBS to produce a back-scattered Stokes wave of unique carrier wavelength, and with a power that depends on the in-band OSNR of the channel itself. We experimentally demonstrate a highly sensitive OSNR measurement for a 3 x 40 Gb/s signal, with a small sensitivity to the input state of polarization, and a large dynamic range (25 dB) in the Stokes power. Our results also reveal the insensitivity of SBS to both chromatic and polarization-mode dispersions, and the indirect role these effects can play in mitigating the suppression of SBS from the nonlinear Kerr effect.

We present the first demonstration of all optical wavelength conversion in chalcogenide glass fiber including system penalty measurements at 10 Gb/s. Our device is based on singlemode As2Se3 chalcogenide glass fiber which has the highest Kerr nonlinearity (n2) of any fiber to date for which either advanced all optical signal processing functions or system penalty measurements have been demonstrated. We achieve wavelength conversion via cross phase modulation over a 10 nm wavelength range near 1550 nm with 7 ps pulses at 2.1 W peak pump power in 1 meter of fiber, achieving only 1.4 dB excess system penalty. Analysis and comparison of the fundamental fiber parameters, including nonlinear coefficient, two-photon absorption coefficient and dispersion parameter with other nonlinear glasses shows that As2Se3 based devices show considerable promise for radically integrated nonlinear signal processing devices.

A femtosecond pulse characterization technique is developed using frequency-resolved optical gating based on the two-photon absorption in an InP crystal. The technique provides direct visual monitoring of pulse frequency chirping in the time-spectral domain for femtosecond pulses with a pulse energy as low as 3.8 pJ. Pulse chirping and pedestal wings of 10-GHz optical fiber solitons are characterized experimentally for the first time by this technique.

We demonstrate broadband wavelength conversion of a 40 Gb/s return-to-zero signal using four-wave-mixing (FWM) in a dispersion engineered chalcogenide glass waveguide. The 6 cm long planar rib waveguide 2 mum wide was fabricated in a 0.87 mum thick film etched 350nm deep to correspond to a design where waveguide dispersion offsets the material leading to near-zero dispersion in the C-band and broadband phase matched FWM. The reduced dimensions also enhance the nonlinear coefficient to 9800 W(-1)km(-1) at 1550 nm enabling broadband conversion in a shorter device. In this work, we demonstrate 80 nm wavelength conversions with 1.65 dB of power penalty at a bit-error rate of 10(-9). Spectral measurements and simulations indicate extended broadband operation is possible.

We introduce an all-optical, format transparent hash code generator and a hash comparator for data packets verification with low latency at high baudrate. The device is reconfigurable and able to generate hash codes based on arbitrary functions and perform the comparison directly in the optical domain. Hash codes are calculated with custom interferometric circuits implemented with a Fourier domain optical processor. A novel nonlinear scheme featuring multiple four-wave mixing processes in a single waveguide is implemented for simultaneous phase and amplitude comparison of the hash codes before and after transmission. We demonstrate the technique with single polarisation BPSK and QPSK signals up to a data rate of 80 Gb/s.

Compensation of nonlinear distortion of polarization-multiplexed (PolMux) signals in optical fiber is evaluated experimentally using all-optical signal pre-distortion and fiber loop phase-conjugation at the transmitter. An improved bit error rate is shown for high baud rate, 80 Gb/s RZ-DPSK PolMux signals before transmission in a 728 km long dispersion-managed fiber link employing a direct detection receiver. The partial compensation of nonlinear distortion for both single channel and 3 × 80 Gb/s WDM PolMux signals is observed, despite the impact from the inter-polarization nonlinearity and the associated polarization scattering. Evidence of the limited compensation of inter-polarization nonlinearity is shown.

We demonstrate all-optical wavelength conversion at 10 Gb/s for differential phase-shift keyed (DPSK) data signals in the C-band, based on four-wave mixing (FWM) in a silicon ring resonator. Error-free operation with a system penalty of ~ 4.1 dB at 10-9 BER is achieved.

We report the first demonstration of optical phase conjugation (OPC) transmission of phase encoded and wavelength-division multiplexed (WDM) signals by the Kerr effect in a planar structured waveguide. The phase conjugated electric field of the signal is produced by four wave mixing pumped by a CW laser during co-propagating with the signal in a highly nonlinear waveguide fabricated in As(2)S(3) glass. Experiments demonstrate the capability of the device to perform dispersion-free transmission through up to 225 km of standard single mode fiber for a 3 × 40 Gb/s WDM signal, with its channels encoded as return-to-zero differential phase shift keying and spaced either 100 or 200 GHz apart. This work represents an important milestone towards demonstrating advanced signal processing of high-speed and broadband optical signals in compact planar waveguides, with the potential for monolithic optical integration.

We demonstrate a terahertz bandwidth silicon nanowire based radio-frequency spectrum analyzer using cross-phase modulation. We show that the device provides accurate characterization of 640Gbaud on-off-keyed data stream and demonstrate its potential for optical time-division multiplexing optimization and optical performance monitoring of ultrahigh speed signals on a silicon chip. We analyze the impact of free carrier effects on our device, and find that the efficiency of the device is not reduced by two-photon or free-carrier absorption, nor its accuracy compromised by free-carrier cross-chirp.

We demonstrate all-optical time division demultiplexing from 160Gb/s to 10Gb/s in the C-band, based on four-wave mixing (FWM) in a silicon nanowire. We achieve error-free operation with a system penalty of approximately 3.9dB at 10(-9) BER.

A broadband photonic instantaneous frequency measurement system utilizing four-wave mixing in highly nonlinear fiber is demonstrated. This new approach is highly stable and does not require any high-speed electronics or photodetectors. A first principles model accurately predicts the system response. Frequency measurement responses from 1 to 40 GHz are demonstrated and simple reconfiguration allows the system to operate over multiple bands.

We report the first demonstration of high bit rate signal processing by a fiber-based photonic wire. We achieve 160 Gb/s demultiplexing via four wave mixing in a 1.9 microm diameter photonic wire tapered from As(2)S(3) chalcogenide glass single mode fibre, with very low pump power requirements ( < 20 mW average power, 0.45 W peak power), enabled by a very high nonlinearity (gamma approximately 7850 W(-1) km (-1) ) and greatly reduced dispersion.

We demonstrate broadband wavelength conversion of a 40 Gb/s return-to-zero signal by cross-phase modulation in a newly developed chalcogenide glass waveguide based photonic chip. These new serpentine As(2)S(3) waveguides offer a nonlinear coefficient approximately 1700 W(-1)km(-1) with 5x lower propagation loss over a length of 22.5 cm which ensures the full propagation length contributes towards the nonlinear process. This reduces the peak operating power thereby allowing a x4 increase in the data rate compared with previous results. Spectral measurements show the device operates over a span of 40 nm while system measurements show just over 1 dB of power penalty at a bit-error rate of 10(-9). This is primarily due to the compact planar waveguide design which minimizes the effect of groupvelocity dispersion.