Sepideh T. Naimi

Simulations of an OSNR-Limited All-Optical Wavelength Conversion Scheme

We present simulations of a scheme to perform wavelength conversion of signals that eliminates phase-noise transfer from the pump to the converted signal. Nondegenerate four-wave mixing in a semiconductor optical amplifier is used to convert the signal to a new wavelength, and if an optical comb generator is used as the multiple-pump source, then the signal can be converted without incurring any phase-noise transfer from the pumps. We highlight the capabilities of this scheme by simulating the conversion of 16-QAM signals at 10 GBd and showing that errors due to phase-noise accumulation are eliminated, thus enabling conversion whose only impairment would be the total additive optical noise.

Detailed Investigation of the Pump Phase Noise Tolerance for Wavelength Conversion of 16-QAM Signals Using FWM

All-optical wavelength conversion (WC) of advanced modulation formats could have a significant role in the next generation of high-capacity optical networks. Four-wave mixing (FWM) occurring within a semiconductor optical amplifier is one of the most advantageous methods to implement all-optical WC. We demonstrate the WC of 16-quadrature amplitude modulation (16-QAM) using degenerate and nondegenerate FWM in a semiconductor optical amplifier. We pay particular attention to the phase noise transfer from the pump(s) to the converted signal. The class of laser that can be used as the pump source to implement the scheme is highlighted by the calculations of the required pump laser linewidths to achieve specific system bit error rate performance at the forward error correction threshold. Our results are consistent with theories of phase noise transfer between the pump and converted signals.

All Optical Wavelength Conversion of Nyquist-WDM Superchannels Using FWM in SOAs

In this paper, the performance of all-optical wavelength conversion (WC) of Nyquist-WDM superchannels is investigated for future implementation in optical networks. We consider advanced modulation formats of DQPSK and 16-QAM for the subchannel modulation format achieving raw bit rates of 448 and 896 Gb/s, respectively. We demonstrate through simulations the WC of Nyquist-WDM superchannel using degenerate and nondegenerate four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). We consider the effects of raised cosine (RC) and root raised cosine (RRC) signal pulse shaping within the wavelength conversion process. We find that the performance of the converted superchannel is severely impaired by crosstalk due to cross-gain modulation of the pump by the superchannel. Optimum performance of the converted superchannel is achieved by setting the detuning between the continuous-wave pump and the central wavelength of the superchannel to be around 200 GHz and using pumps of double the gain saturation power of the SOA with 23 dB pump to signal power ratio.

Numerical generation of laser-resonance phase noise for optical communication simulators

We generate random numerical waveforms that mimic laser phase noise incorporating laser-resonance enhanced phase noise. The phase noise waveforms are employed in system simulators to estimate the resulting bit error rate penalties for differential quadrature phase shift keying signals. The results show that baudrate dependence of the bit error rate performance arises from laser-resonance phase noise. In addition, we show with supporting experimental results that the laser-resonance phase noise on the pumps in four-wave-mixing-based wavelength converters is responsible for large bit error rate floors.

All-optical wavelength conversion of spectrally-efficient modulation formats for future networks

We present simulation results of a wavelength conversion scheme that adds no additional phase-noise to the converted signal. The scheme uses an optical comb generator as the pump source in a wavelength converter based on nondegenerate four-wave mixing. The comb source ensures that no phase noise is transferred from the pumps to the converted signal. We underscore the ability of this conversion scheme by showing that after a two-stage conversion, that the only impairment is the additive noise from the active elements. Such a scheme is necessary for implementing multiple conversions of spectrally efficient modulation formats in future optical networks.

Novel Implementation of SOA-Based All-Optical Wavelength Conversion of DQPSK Signals Using Fast Switching Tunable Lasers

We investigate the feasibility of SOA-based wavelength conversion of DQPSK signals using wavelength tunable SGDBR pump lasers. Our results indicate that it is possible to build fast reconfigurable wavelength convertors with <5 ns switching time.

Phase noise tolerant wavelength conversion of Nyquist-WDM superchannels using FWM in SOAs

Nyquist-WDM superchannel technology, which involves the combination of several lower data rate optical wavelength carriers (sub-channels), is a suitable technique to increase the spectral efficiency of WDM systems, and satisfy the growing demand for bandwidth in future networks. These superchannels will need to be routed through the optical network as a single entity. This work will present the use of four-wave mixing (FWM) in a semiconductor optical (SOA) to wavelength convert an 896 Gbit/s optical superchannel comprising of 8 × 28 Gbaud 16-QAM. The use of a dual correlated pumping technique ensures that the wavelength conversion process is not limited by phase noise on the optical pumps.

Phase noise tolerant wavelength conversion of Tb/s Nyquist-WDM superchannels based on 64-QAM and using FWM in SOAs

We present results of all-optical wavelength conversion of a 1.008 Tb/s 6×28 Gbaud Nyquist-WDM superchannel based on 64-QAM using four-wave mixing in in a semiconductor optical amplifier. We employ the phase noise tolerant dual-correlated pumping scheme to eliminate phase noise transfer from the pumps to the converted 64-QAM superchannel and thus achieving minimal implementation OSNR penalty of 2.5 dB.

Impact of four-wave mixing phase noise transfer on wavelength converted QPSK signals

Future high capacity wavelength division multiplexed (WDM) optical networks will rely on transmitting signals with information encoded on both the amplitude and phase of multiple optical carriers. To optimise the efficiency of these networks, they are likely to employ some level of wavelength switching [1], and a key function required by wavelength switching is wavelength conversion [1]. Wavelength conversion of phase modulated signals in wavelength switched optical networks will need to be undertaken using a coherent nonlinear process, such as four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) [2] employing a fast wavelength tuneable pump laser to ensure an optical channel can be dynamically routed to different wavelengths. A crucial issue that is likely to have a major impact on the wavelength conversion of such high capacity signals using FWM is the phase noise transfer to the converted signal. A detailed study of FWM wavelength converted continuous-wave signals in [3] showed that the phase noise transfer from the pump to the idler, increased the linewidth of the idler by a factor of 4 relative to the pump. Such a large line broadening is highly detrimental to the detection of phase-encoded signals, especially since the tuneable lasers that exhibit small wavelength switching times (<;50 ns) and would be employed in wavelength switched networks tend to have linewidths of the order of a few MHz [4]. Therefore estimating the linewidth limits that enable FWM wavelength conversion using this scheme is vital to select a tuneable pump laser with suitable linewidth.