Monolithic Silicon based all-optical waveform analyser with terahertz bandwidth
A compact, inexpensive, easily manufactured device that enables simultaneous measurements of multi-impairments to a communications signal transmitted over an optical network, even at ultrahigh bandwidths
Modern communications systems require constant monitoring of the performance characteristics of the system (signal to noise, for example) and diagnostics to determine the causes of the degradation, for example dispersion-related effects. Measurement of these impairments using real time electronic detection schemes becomes extremely difficult and expensive in networks at 100 Gb/s and beyond, since they rely on detectors with bandwidths matching the spectral content of the modulation. Electronic detectors become extremely expensive at bandwidth beyond 50 GHz; furthermore, complex software algorithms are required to unfold information about impairments from the measured signal.
Our waveform analyser uses nonlinear optical cross-phase modulation to recover the RF spectrum of the data signal. Specific components of the RF spectrum, which can be isolated and measured using spectral filtering techniques, are due to different impairment mechanisms and so their measurement gives a direct measure of these impairments. We have shown that all these discrete optical functions – nonlinear mixing, filtering and signal detection with low bandpass detectors – can be integrated onto the one optical signal processing chip, which can be easily produced using lithography and interfaced to CMOS electronics for on-board digital signal processing. Our approach also yields RF spectral information for microwave photonic applications.
We published earlier work on this monitoring technique using a chalcogenide glass-based approach. This result showed that the technique worked, but chalcogenide has limitations for widespread commercial application. This work builds on that by demonstrating that similar performance can be obtained using silicon-based processors, despite this material's well-known limitations for high speed applications due with two photon absorption and free-carrier associated effects.
- This monitoring approach can be used to perform simultaneous multi-impairment analysis for long-haul optical transmission systems at single channel bit-rate of 40 Gbit/s to Tbit/s.
- This monitoring scheme can be applied to either current conventional intensity modulation formats or advanced coherent modulation format.
- This technique can also be used to characterise very short (hundreds of femtoseconds) pulses. This is routinely used in telecommunications and microwave photonics for characterizing distortions in amplitude or phase.
Trung D. Vo, Bill Corcoran, Mark D. Pelusi, David J. Moss, Benjamin J. Eggleton, and Jochen Schröder