Pump-probe detuning dependence of four-wave mixing pulse in an SOA

Four-wave mixing (FWM) between 2-ps pulses in a multiquantum-well semiconductor optical amplifier (SOA) is presented. The conjugate pulses are fully characterized using the frequency-resolved optical gating technique. The detuning between the pump and probe is varied, leading to a compression of the FWM signal from 3.71 to 2.77 ps as the detuning is increased from 5 to 25 nm. The output conjugate pulse is always broader than the injected probe signal due to gain saturation effects. A reshaping of the conjugate pulse is also measured. However, large nonlinearities are introduced to the frequency chirp across the pulse for large detunings which may degrade the performance of four-wave-mixing-based all-optical processing applications in SOAs

All-optical processing for terabit/s wavelength division multiplexed systems using two-photon absorption in a semiconductor micro-cavity

Due to continued growth of the Internet and the introduction of new broadband services, such as video-on-demand and mobile telephony, there is a constant requirement for higher speed communications. It is expected that next generation optical communications systems will evolve towards higher capacities by increasing individual line rates rather than the number of wavelength channels. To implement these high-speed optical networks operating at individual channel rates above 100 Gb/s, all-optical processing techniques are necessary. A novel approach based on two photon absorption nonlinearity within a resonance cavity enhanced structure is explored within this thesis. High-speed transmission is severely limited by optical impairments requiring frequent and expensive signal regeneration. Chromatic dispersion, considered as one of the main limiting factors, has to be mitigated in order to achieve satisfactory system performance. Continuous monitoring and adaptive compensation of accumulated dispersion fluctuations within a transmission line is likely to be necessary in future systems. Asynchronous all-optical nonlinear techniques can be utilized for high-speed signal temporal characterization and monitoring without the necessity of timing extraction, or optical to electrical conversion. Two-photon absorption within a resonant microcavity is an ideal candidate for high-speed transmission line performance monitoring, and can be easily integrated with a dispersion compensation module. The major advantage of using a microcavity structure is that the signal is only enhanced over a narrow wavelength range, which is defined by the structure and design of the micro-cavity. In addition, by varying the angle of the incident signal, the resonance response peak of the device can be tuned, thereby isolating individual wavelength channels without the need for external optical filtering. The novelty of this work lies in the ability of using a single photodetector for sequential monitoring of different wavelength channels, operating at line rates exceeding conventional electrical processing-speeds limits. Experimental work included characterization and testing of the fabricated TPA micro-cavities for 160 Gb/s OTDM chromatic dispersion monitoring. A theoretical model explaining the cavity influence on the nonlinear detection is introduced. The main attribute of this work is the experimental investigation of the performance TPA based micro-cavities laboratory prototype, in a multi-wavelength high-speed optical system. The results have demonstrated the applicability of the TPA micro-cavity to monitor accumulated dispersion fluctuations in future high speed optical networks

Pulse pedestal suppression using four-wave mixing in an SOA

Experimental results are presented demonstrating how four-wave mixing in a semiconductor optical amplifier can be used to remove pulse pedestals introduced due to nonlinearities which occur upon pulse propagation in an optical system. Such pedestals would degrade the performance of an optical time-division-multiplexed system due to coherent interaction between channels. An improvement of the temporal pulse suppression ratio to greater than 30 dB is achieved regardless of the level of the pulse pedestal on the input signal. This improvement takes place simultaneously with wavelength conversion and compression of the optical pulse

Detuning dependence of four-wave mixing between picosecond pulses in a multi-quantum well semiconductor optical amplifier

Four-wave mixing is investigated experimentally using frequency resolved optical gating in a multi-quantum well semiconductor optical amplifier. Demultiplexing is carried out from 80 GHz to 10 GHz using two picosecond pulses. The pump-probe detuning is varied and it is found that the probe phase is preserved in the four- wave mixing signal across the central portion of the pulse. Also, the pedestals present in the four-wave mixing waveform are measured and it is found that the impact of these pedestals increases as a function of the detuning due to the carrier dynamics in the device

High-speed chromatic dispersion monitoring of a two-channel WDM system using a single TPA microcavity

Chromatic dispersion monitoring of two 160 Gb/s wavelength channels using a TPA Microcavity is presented. As the microcavity exhibits a wavelength resonance characteristic, a single device could monitor a number of different WDM-channels sequentially

Chromatic dispersion monitoring for high-speed WDM systems using two-photon absorption in a semiconductor microcavity

This paper presents a theoretical and experimental investigation into the use of a two-photon absorption (TPA) photodetector for use in chromatic dispersion (CD) monitoring in high-speed, WDM network. In order to overcome the inefficiency associated with the nonlinear optical-to-electrical TPA process, a microcavity structure is employed. An interesting feature of such a solution is the fact that the microcavity enhances only a narrow wavelength range determined by device design and angle at which the signal enters the device. Thus, a single device can be used to monitor a number of different wavelength channels without the need for additional external filters. When using a nonlinear photodetector, the photocurrent generated for Gaussian pulses is inversely related to the pulsewidth. However, when using a microcavity structure, the cavity bandwidth also needs to be considered, as does the shape of the optical pulses incident on the device. Simulation results are presented for a variety of cavity bandwidths, pulse shapes and durations, and spacing between adjacent wavelength channels. These results are verified experimental using a microcavity with a bandwidth of 260 GHz (2.1 nm) at normal incident angle, with the incident signal comprising of two wavelength channels separated by 1.25 THz (10 nm), each operating at an aggregate data rate of 160 Gb/s. The results demonstrate the applicability of the presented technique to monitor accumulated dispersion fluctuations in a range of 3 ps/nm for 160 Gb/s RZ data channel

Wavelength tuneable pulse monitoring using a Two-Photon-Absorption microcavity

Two Photon Absorption (TPA) is a non-linear optical-to-electrical conversion process that can be significantly enhanced by placing the active region within a resonance microcavity. The experiment confirmed the potential use of the microcavity structure for monitoring a single channel in multi-wavelength systems. The cavity can be designed for different applications depending on desired resonance width or cavity life time allowing the contrast ratio to be further improved. Due to the possibility of tuning the resonance wavelength by cavity tilting, a single device can be used to monitor a number of WDM channels without the need for additional optical filters

Chromatic dispersion monitoring of 80-Gb/s OTDM data signal via two-photon absorption in a semiconductor microcavity

In this letter, a novel method of chromatic dispersion monitoring via two-photon absorption (TPA) is investigated. A specially designed semiconductor microcavity is employed as a TPA detector for monitoring data signals operating at rates up to 80Gb/s. As the microcavity has a wavelength-dependent response, a single device can be used to monitor multiple channels in a multiwavelength optical telecommunication syste

Suppression of residual single-photon absorption relative to two-photon absorption in high finesse planar microcavities

Suppression of residual single-photon absorption (SPA) relative to two-photon absorption (TPA) in a high finesse GaAs planar microcavity is explored. The TPA photocurrent becomes larger than the SPA photocurrent as long as the incident continuous-wave optical power exceeds 0.09 mW. An optical power of 5 mW would be required if the relative SPA suppression did not exist

All-optical pulse processing for advanced photonic communication system

This paper investigates the use of a two-photon absorption photodetector for high speed processing of ultrashort optical pulses in advanced photonic communication systems. Specifically the paper describes how the two-photon absorption photodetector maybe employed for chromatic dispersion monitoring in high-speed, wavelength division multiplexed networks, and also for reducing multiple access interference noise in an optical code division multiplexed system