Benn C. Thomsen

Burst Mode Receiver for 112 Gb/s DP-QPSK with parallel DSP.

We demonstrate a burst mode 112Gb/s DP-QPSK digital coherent optical receiver with parallel DSP suitable for implementation in a CMOS ASIC (437.5MHz clock speed). A convergence time of less than 200ns is reported.

Dynamic linewidth measurement technique using digital intradyne coherent receivers

The linewidth settling time of a fast switching tuneable laser is investigated using a dynamic coherent receiver and we show that a minimum linewidth can be realised within 70ns of a wavelength switching event.

Cascadability Properties of Optical 3R Regenerators Based on SOAs

This paper assesses the regenerative properties of nonlinear semiconductor optical amplifier (SOA)-based optical regenerators cascaded in high-speed transmission networks. It is shown that the fundamental condition that must be ensured to maintain optimum and constant regenerative properties along a chain of concatenated nonlinear optical regenerators is that the extinction ratio at the input of each regenerator is kept constant. This condition determines an important requirement on the regenerator; signal reshaping and noise suppression must take place while performing the necessary extinction ratio enhancement to maintain cascadability. Starting from the SOA nonlinear transfer function, we derive the relationship between the extinction ratio enhancement and the noise suppression for different SOA-based gate configurations and assess their cascadability properties. This analysis is supported by experimental results of transmission with cascaded optical regeneration in a reconfigurable transmission network over transoceanic distances on standard fiber.

Digital dual-rate burst-mode receiver for 10G and 1G coexistence in optical access networks

A digital dual-rate burst-mode receiver, intended to support 10 and 1 Gb/s coexistence in optical access networks, is proposed and experimentally characterized. The receiver employs a standard DC-coupled photoreceiver followed by a 20 GS/s digitizer and the detection of the packet presence and line-rate is implemented in the digital domain. A polyphase, 2 samples-per-bit digital signal processing algorithm is then used for efficient clock and data recovery of the 10/1.25 Gb/s packets. The receiver performance is characterized in terms of sensitivity and dynamic range under burst-mode operation for 10/1.25 Gb/s intensity modulated data in terms of both the packet error rate (PER) and the payload bit error rate (pBER). The impact of packet preamble lengths of 16, 32, 48, and 64 bits, at 10 Gb/s, on the receiver performance is investigated. We show that there is a trade-off between pBER and PER that is limited by electrical noise and digitizer clipping at low and high received powers, respectively, and that a 16/2-bit preamble at 10/1.25 Gb/s is sufficient to reliably detect packets at both line-rates over a burst-to-burst dynamic range of 14,5 dB with a sensitivity of -18.5 dBm at 10 Gb/s.

Performance of an Adaptive Threshold Receiver in a Dynamic Optical Burst-Switched Network

We compare the performance of a digital receiver operating with both a fixed and adaptive decision threshold in response to gain transients arising from network operation of an optically gain-clamped erbium-doped fiber amplifier. An optical burst switching link, based on a recirculating transmission loop, is used to study the effect of transients accumulated across a number wavelength-routing nodes linked by amplified fiber spans where bursts are added and dropped at each node. The use of an adaptive threshold reduces the amount of optical feedback required by a factor of 6 and, in some cases, allows for unclamped operation.

Performance of an optical equalizer in a 10 G wavelength converting optical access network

A centralized optical processing unit (COPU) that functions both as a wavelength converter (WC) and optical burst equaliser in a 10 Gb/s wavelength-converting optical access network is proposed and experimentally characterized. This COPU is designed to consolidate drifting wavelengths generated with an uncooled laser in the upstream direction into a stable wavelength channel for WDM backhaul transmission and to equalize the optical loud/soft burst power in order to relax the burst-mode receiver dynamic range requirement. The COPU consists of an optical power equaliser composed of two cascaded SOAs followed by a WC. Using an optical packet generator and a DC-coupled PIN-based digital burst-mode receiver, the COPU is characterized in terms of payload-BER for back-to-back and backhaul transmission distances of 22, 40, and 62 km. We show that there is a compromise between the receiver sensitivity and overload points that can be optimized tuning the WC operating point for a particular backhaul fiber transmission distance. Using the optimized settings, sensitivities of -30.94, -30.17, and -27.26 dBm with overloads of -9.3, -5, and >-5 dBm were demonstrated for backhaul transmission distances of 22, 40 and 62 km, respectively.

10 Gb/s AC-Coupled Digital Burst-Mode Optical Receiver

A 10 Gb/s NRZ digital burst-mode optical receiver without any line-coding has been realized using an AC-coupled photodiode and asynchronous 20 GS/s ADC. Symbol timing, amplitude and baseline wander corrections are implemented with digital signal processing.

Impact of network load and traffic sparsity on the performance of a digital burst-mode receiver

The packet error-rate (PER) for a digital burst-mode receiver is measured for different traffic loads and maximum and minimum traffic sparsity. We found a negligible impact of the burst sparsity and an increased performance for reduced network load on PER.

Cluster processing for the study of optical burst-mode digital signal processing receivers and subsystems for dynamic optical burst switching networks

The development of fast analog-to-digital converters makes feasible the use of DSP techniques for burst-mode digital receivers operating at 10 Gb/s. MATLAB offers an easy and rapid route for the development and offline validation of new processing algorithms, but is somewhat limited by the slow processing time. Whilst real time development is possible using FPGA technology the cost and slower design cycle make this approach less attractive in a research environment. To overcome the processing time limitation of MATLAB based DSP for the evaluation of parameters that require the capture of a great number of bursts, we present a cluster based processing system for investigating the performance of digital burst-mode receivers in the context of dynamic OBS networks. Using this cluster processing system we measured dynamic range, bit error rate and packet error rate of a digital burst-mode receiver.