Implementation of a high speed time resolved error detector utilising a high speed FPGA

Abstract

We demonstrate a time-resolved bit error rate detector utilising a field programmable gate array. The proposed detector offers 93 ps resolution operating at 10.7 Gb/s and allows for all the data received to contribute to the measurement allowing low bit error rates to be measured at high speed. Via synchronisation of both the detector and a high speed scope, the bit error rate and the corresponding individual eyes are identified. The operation of the detector is demonstrated by characterising a fast switching tuneable laser. INTRODUCTIONRecently there has been increasing interest in optical transmission systems that are capable of operating in burst mode. An important requirement for such burst mode systems is the ability to start transmitting data as quickly as possible after the network requests that a burst begin. In order to optimise the transient performance, associated with such burst operation it is important to accurately find the bit error rate (BER) at time intervals relative to the burst start time e.g. how long it takes for the BER to drop below the forward error correction (FEC) limit (i.e. BER = 1E-3). Such information allows for networks to be designed to be tolerant to the initial channel setup with minimal blanking times or to optimise more resilient FEC codes for use at the start of a burst window. As such it is necessary to measure the time-resolved BER (TRBER).A number of methods for measuring TRBER already exist. One such method involves carrying out an Exclusive OR (XOR) operation between an error free version of the transmitted data (i.e. transmitted from a stable transmitter) and a version of the transmitted data containing errors (i.e. due to burst mode operation) and then recording the output on a scope triggered using the burst trigger. This method has achieved a TRBER resolution of 10 ns [1], with data sets recorded at a few Hz. While the proposed method in [1] is reasonably fast it suffers from poor temporal resolution. Another TRBER method has been demonstrated using a standard BER test set with a time resolution of 2 ns having been shown by gating the error detector with the burst trigger. It is possible to improve the temporal resolution by moving the error gate in small steps i.e. 100 ps [2] and deconvolving the measurement window. Unfortunately [2] can only take a BER measurement at one time delay at a time making the measurement extremely slow.In this paper we demonstrate a TRBER detector utilising an FPGA which is capable of carrying out TRBER analysis on data transmitted at 10.7 Gb/s and return BER data with 93 ps resolution (corresponding to one bit slot). The time axis of the TRBER detector and the scope are both calibrated relative to each other so that measured BERs can be associated with an individual eye on a scope. It is also demonstrated that unlike gated error detection techniques which suffer from only measuring the BER in a small window at any one time the approach demonstrated in this paper allows for all data in a burst event to be recorded so that BER values for ...

Time Resolved Bit Error Rate Analysis of a Fast Switching Tunable Laser for Use in Optically Switched Networks

“…The transition times associated with the SGDBR laser modulated with different direct detection modulation formats are investigated. The transition time is characterized using a time resolved bit error rate (TRBER) detector utilizing a field programmable gate array (FPGA) which is capable of carrying out TRBER analysis on data transmitted at 10.7 Gb/s and return bit error rate (BER) data with 93 ps resolution (corresponding to one bit slot) [5]. Unlike a gated error detection technique [6,7], which suffers from only measuring the BER in a small window, this FPGA based TRBER detector allows for all received data to contribute to the TRBER, allowing for measurements to be made much more quickly [5].…”