P. J. Reyes-Iglesias

High-performance monolithically integrated 120° downconverter with relaxed hardware constraints

A coherent receiver based on a 120° downconverter architecture, inherited from previous approaches at the microwave and optical fields, is proposed, analyzed, numerically evaluated and compared to the conventional 90° downconverter alternative. It is shown that, due to its superior calibration procedure, the new downconverter architecture allows full compensation of the imbalances in its optical front-end thus leading to an extended dynamic range and a broader operating bandwidth than its 90° counterpart. Simulation results from monolithically integrated downconverters show that our approach can be an interesting alternative to support efficient modulation schemes such as M-QAM that is being studied as potential candidate for the next generation of optical communication systems.

Colorless monolithically integrated 120° downconverter.

We numerically demonstrate colorless reception of dense wavelength division multiplexed channels in the C-band for high-order QAM (16-64 QAM) signals on a 120° monolithically integrated downconverter, based on a 2x3 MMI with calibrated analog IQ recovery. It is shown that the proposed calibrated 120° downconverter can increase up to 80 the number of coincident channels in an efficient way, exhibiting good signal dynamic range and high fabrication yield. As this downconverter makes use of the minimum number of power outputs required for perfect recovery of IQ signals, it becomes an interesting alternative to conventional 90° based downconverters.

Enhanced monolithically integrated coherent 120° downconverter with high fabrication yield

Conventional monolithically integrated 90° downconverter suffers from hardware-induced non-linear constellation distortion, which gets worse far away from the central wavelength or when fabrication errors are taken into account. To overcome these problems, a 120° monolithically integrated downconverter with full compensation of hardware non-idealities has been proposed. It is numerically demonstrated that, in a realistic scenario exposed to the combined effects of fabrication tolerances and limited ADC resolution, this approach exhibits a significantly better signal dynamic range and a remarkable improvement of fabrication yield.

Sensitivity penalty induced by non-ideal dual polarization downconverter in digital coherent receivers

The implementation agreement of the Optical Internet Forum for a dual polarization (DP) I/Q downconverter defines strict requirements for the phase diversity network, resulting in a negligible penalty, but does not specify the extinction ratio (ER) of the polarization beam splitters (PBS) on which the polarization diversity network is based. We propose a novel metric, based on the Frobenius norm of the Jones receiver matrix, to accurately estimate the sensitivity penalty from receiver non-idealities, stablishing a precise interface for hardware specification. Results will be numerically verified for the reception of 112 Gbps DP-QPSK signals in a realistic receiver scenario with subsequent state-of-art DSP algorithms. The proposed metric highlights the benefits of the polarization diversity scheme based on two PBS, compared to the common alternative based on a PBS and a BS, as it achieves an improvement in the receiver sensitivity of at least 3 dB for the same ER. Furthermore, this paper shows than the sensitivity penalty is negligible for an ER higher than 16 dB and that it less than 2 dB for an ER of 8 dB. These results can have an important impact in monolithically integrated DP downconverters in which practical integration of PBS with high ER is still challenging.

Polarization-beam-splitter-less integrated dual-polarization coherent receiver

Conventional dual-polarization coherent receivers require polarization beam splitters for either the signal or the local oscillator path. This severely hinders monolithic integration, since integrated polarization splitting devices often exhibit stringent fabrication tolerances. Here we propose a dual-polarization monolithically integrated coherent receiver architecture that completely avoids the use of polarization splitting elements. Polarization management is instead achieved by adequately engineering the birefringence of the interconnecting waveguides. The resultant receiver is highly tolerant to fabrication deviations and thus offers a completely new route for monolithic integration of dual-polarization receivers without any type of active tuning.

Colorless devices and reception techniques for polarization multiplexed communications

Future optical networks call for flexible, high performance and low cost coherent optical receivers. We present here several advances towards such receivers, including integrated optical couplers with ultra-broad bandwidth, as well as novel reception techniques and architectures that will enable high performance coherent reception without filtering and polarization splitting elements.

Monolithic integrated InP receiver chip for coherent phase sensitive detection in the C- and L-band for colorless WDM applications

We demonstrate a monolithically integrated coherent receiver PIC on an InP substrate with a 120° optical hybrid and 40GHz pin-photodetectors. Moreover, the performance of the device for colorless detection of 28Gbaud 16-QAM signals in the C- and L-band is investigated.