D. Syvridis

IMPROVED PERFORMANCE OF A WAVELENGTH CONVERTER BASED ON DUAL PUMP FOUR-WAVE MIXING IN A BULK SEMICONDUCTOR OPTICAL AMPLIFIER

Very high conversion efficiency (6.5 dB for 23.4 nm down-wavelength shift and 4.5 dB for 16 nm up-wavelength shift) is reported, using four-wave mixing in a bulk semiconductor optical amplifier. Based on a dual pump configuration where wavelength conversion is achieved by shifting one of the pumps, superior performance has been achieved in terms of both efficiency and the converted signal-to-background amplified spontaneous emission noise ratio, especially for very large wavelength shifts. Simple theoretical considerations are also discussed for the explanation of the improved performance of the converter.

Study of polarization-insensitive wave mixing in bulk semiconductor optical amplifiers

A detailed experimental investigation of polarization-insensitive dual-pump wave mixing in bulk, polarization-insensitive semiconductor optical amplifier (SOA) is reported. Measurements of the phase conjugated, polarization-insensitive four-wave mixing (FWM) efficiency are reported versus: (1) pump-signal wavelength spacing while keeping the wavelength spacing between the two orthogonally polarized pumps constant and (2) wavelength spacing between the pumps while keeping the signal wavelength constant. The achieved wavelength conversion bandwidth of the polarization-insensitive scheme is approximately 60 nm with efficiency between 8 and -20 dB. The obtained results are in good agreement with theoretical predictions.

Quality of transmission estimation in WDM and elastic optical networks accounting for space–spectrum dependencies

We develop a framework for estimating the quality of transmission (QoT) of a new lightpath before it is established, as well as for calculating the expected degradation it will cause to existing lightpaths. The framework correlates the QoT metrics of established lightpaths, which are readily available from coherent optical receivers that can be extended to serve as optical performance monitors. Past similar studies used only space (routing) information and thus neglected spectrum, while they focused on old-generation noncoherent networks. The proposed framework accounts for correlation in both the space and spectrum domains and can be applied to both fixed-grid wavelength division multiplexing (WDM) and elastic optical networks. It is based on a graph transformation that exposes and models the interference between spectrum-neighboring channels. Our results indicate that our QoT estimates are very close to the actual performance data, that is, to having perfect knowledge of the physical layer. The proposed estimation framework is shown to provide up to 4 × 10-2 lower pre-forward error correction bit error ratio (BER) compared to the worst-case interference scenario,which overestimates the BER. The higher accuracy can be harvested when lightpaths are provisioned with low margins; our results showed up to 47% reduction in required regenerators, a substantial savings in equipment cost.

Experimental evaluation of subcarrier modulation in chaotic optical communication systems

Data streams with bit rates of up to 1 Gbit/s have been applied though the subcarrier modulation technique in an experimentally deployed optical communication system based on chaos data encryption and have been recovered efficiently. By shifting the spectral components of the encrypted data in regions where the chaotic carrier is powerful, a more efficient encryption and final message recovery is recorded with respect to the baseband modulation technique, improving the up-to-date performance of analogous systems.

On the polarisation sensitivity and performance optimisation of a dual pump four wave mixing based wavelength converter

This paper presents a detailed investigation of the performance of a wavelength conversion scheme. The converter is based on four wave mixing in semiconductor optical amplifiers using two parallel polarised pumps. Measurements of the conversion efficiency and the signal to background noise ratio of the two replicas of the signal, for the cases of the signal polarisation being either parallel or orthogonal relative to the pump waves have been carried out. These measurements will reveal the polarisation sensitivity of this scheme which appears to be less than 1 dB when the wavelength spacing between the signal and its closest spaced pump is larger than 12 nm. The experimental results are supported in a satisfactory way by theoretical considerations. A simple theoretical expression describing the polarisation sensitivity have been derived and the theoretical results are in good agreement with those experimentally obtained. A performance comparison of the conversion scheme using semiconductor optical amplifiers with different lengths but the same structure is also performed. Through the following study the optimum operational conditions for this wavelength conversion scheme will be determined.

PSA-based phase regeneration of DPSK signals in a silicon germanium waveguide

We demonstrate a polarization-assisted PSA-based phase regenerator in a passive low-birefringence SiGe waveguide at low CW pump power. A PSER of 28.6-dB enables a six-fold reduction in phase-error and BER improvement of approximately 2-dB in the regenerated signal.

Transmission induced limitations in optical communication systems with chaotic signals

The transmission impairments induced by the optical medium in optical communication systems that employ chaotic carrier data encryption are discussed after theoretical consideration and experimental evaluation.

High speed optical transmission at 2 μm in subwavelength waveguides made of various materials

We report the transmission of a 10 Gbps telecommunication signal at 2 μm in waveguides made of three different materials: Si, SiGe and TiO2. Bit error rates below 10−9 can be achieved after transmission in the devices with subwavelength dimensions.

Optical injection in semiconductor lasers: Physics and applications

This paper presents a comprehensive overview of the underlying physics of optical injection mechanisms in lasers highlighting the determining influence of important parameters as the injection strength, the frequency detuning and the free running oscillation frequency of the interacting lasers. The paper particularly sheds light on the different properties exhibited by inter-band diode lasers and intersubband quantum cascade lasers under external injection. Finally, the paper presents experimental results which demonstrate the utilization of optical injection in telecom, metrology and mid-infrared gas sensing applications leveraging its optical signal processing capabilities.

Scaling multimode fibre IM/DD transmission capacity through spatial-spectral multiplexing

Data centre connections can greatly benefit from parallel transmission channels on one multimode fibre (MMF). Shortwave wavelength division multiplexing (SWDM) achieves parallel transmission through spectral multiplexing. Furthermore, MMFs offer a spatial dimension that should be exploited to increase parallel transmission, albeit in a cost-effective way. In this paper, it is shown that SWDM and spatial multiplexing can be combined in intensity modulation and direct detection MMF transmission systems that use selective offset excitation and mode-selective spatial filtering.