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

Abstract

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.

Enhanced monolithically integrated coherent 120° downconverter with high fabrication yield

“…We will consider ideal behaviour of TIAs and DSP blocks. More details of the system simulation scenario can be found in [10].…”

“…As it was already studied in [5], in a 90° downconverter receiver amplitude and phase imbalances will distort IQ signal constellation due to: i) DC offset ii) rotation and imbalance of the reference axes iii) non-linear error proportional to the signal-to-LO power ratio. The standard procedure to correct the hybrid induced-distortion is the GSOP algorithm [6], which cannot remove the non-linear constellation distortion, and this makes this solution limited for high signal-to-LO power ratios [10]. However, the 120° downconverter was shown to be free from this limitation.…”

“…When compared with the traditional 90° hybrid receiver, the main advantages of the 120° downconverter are higher dynamic range, wider operating bandwidth and relaxed fabrication tolerances. Although these conclusions were stated in [10], the last one was only deduced from the others but not proven, since only optimized nominal designs (i.e. without fabrication errors) were considered.…”

“…The 120° downconverter has been reported several times for optical communications by making use of 3x3 fiber couplers [8,9]. Recently, authors have proposed [10] a monolithically integrated 120° downconverter based on a 2x3 MMI. This approach makes use of a simple linear calibration strategy to fully correct the receiver imbalances.…”

Amplitude and Phase Error Correction Algorithm for $3\times 3$ MMI Based Mach–Zehnder Interferometers

“…A correction algorithm can be applied to improve the accuracy of the phase estimation. Reyes et al proposed a linear correction scheme in a coherent receiver [9], by transmitting four pilot symbols. When the signal power changes, these pilot symbols would have to be retransmitted.…”