Olaf Adamczyk

Coherent optical communication: Towards realtime systems at 40 Gbit/s and beyond

Coherent optical communication systems promise superior performance, but their realization in real time also poses big technical challenges. After an introduction the potential of coherent optical transmission systems is shown as manifested in offline experiments. Then we present key components that are necessary to realize these systems in real time. We review recent achievements in realtime coherent communication and finally present the results of a realtime QPSK transmission system with a 3x3 coupler in the receiver. The achieved BER at a data rate of 1.4 Gbit/s is well below the FEC threshold.

First Real-Time Data Recovery for Synchronous QPSK Transmission With Standard DFB Lasers

For the first time, synchronous quadrature phase-shift keying data is recovered in real-time after transmission with standard distributed feedback lasers using a digital inphase and quadrature receiver. Forward-error-correction-compatible performance is reached at 800 Mb/s after 63 km of fiber. Self-homodyne operation with an external cavity laser is error-free

Coherent Digital Polarization Diversity Receiver for Real-Time Polarization-Multiplexed QPSK Transmission at 2.8 Gb/s

This letter presents a coherent digital polarization diversity receiver for real-time polarization-multiplexed synchronous quadrature phase-shift keying transmission with distributed feedback lasers at a data rate of 2.8 Gb/s. The tolerance against fast polarization changes and polarization-dependent loss is evaluated for different filter widths in the carrier recovery circuit. The minimum achieved bit-error rate is 3.4 times 10-7.

Frequency and Phase Estimation for Coherent QPSK Transmission With Unlocked DFB Lasers

This letter presents a hardware-efficient frequency estimator and an advanced phase estimation algorithm capable of tracking the phase noise of a 10-GBaud optical quadrature phase-shift-keying transmission system with standard distributed-feedback lasers in the presence of a frequency mismatch up to 1.2 GHz. This algorithm allows us to implement a digital coherent receiver without an analog frequency control circuit.

Multiplier-Free Real-Time Phase Tracking for Coherent QPSK Receivers

This letter presents a hardware-efficient phase estimation algorithm that can replace the common complex estimators for a coherent quadrature phase-shift keying transmission system.

Ultra-Fast Adaptive Digital Polarization Control in a Realtime Coherent Polarization-Multiplexed QPSK Receiver

A digital polarization control system integrated in a 2.8 Gbit/s realtime polarization-multiplexed coherent QPSK system compensates for endless polarization changes having a maximum gradient of 3.5 krad/s (12 krad/s) with 1 dB (3.9 dB) loss in receiver sensitivity.

PDL-Tolerant Real-time Polarization-Multiplexed QPSK Transmission with Digital Coherent Polarization Diversity Receiver

This paper presents the implementation of a real-time electronic polarization tracking algorithm which enables robust optical polarization-multiplexed synchronous quadrature phase shift keying transmission with DFB lasers. The achieved BER at a data rate of 2.8 Gbit/s is well below the FEC threshold.

1.6 Gbit/s Real-Time Synchronous QPSK Transmission with Standard DFB Lasers

Using standard DFB lasers, 1.6 Gbit/s QPSK data is demodulated and recovered coherently and synchronously in real-time, faster than ever before. BER after 63 km of fiber is well below the FEC threshold.

Fast Adaptive Polarization and PDL Tracking in a Real-Time FPGA-Based Coherent PolDM-QPSK Receiver

Fast polarization changes of 40 krad/s and 6-dB polarization-dependent loss (PDL) are tracked in a 2.8-Gb/s real-time coherent quadrature phase-shift keying receiver. The tolerance against fast polarization changes and PDL is measured for different polarization control time constants. The sensitivity penalty of the receiver at a polarization change speed of 40 krad/s is 0.7 dB at bit-error rate (BER) of 1times 10-3, with a BER floor of 6.1times10-7. With an additional PDL of 6 dB, these figures become 1.7 dB and 9.6 times 10-6, respectively.

5-bit 12.5 Gsamples/s analog-to-digital converter for a digital receiver in a synchronous optical QPSK transmission system

We present the implementation of an analog-to-digital converter in a SiGe BiCMOS technology. The converter has a resolution of 5 bits with a sampling rate >12.5 Gsamples/s and consumes 4.3 W of power.