Power efficient nonlinear signal processing with Silicon nano-waveguides
Final Report Abstract
During the project we investigated the usage of SOI-based waveguides with p-i-n diode in different fields of application of all-optical signal processing. This approach turned out to be a feasible and more compact alternative to fiber-based optical signal processing. The employed p-i-n diode in many cases enabled comparable performance by removing carriers generated by TPA in silicon. Using phase-sensitive amplification in those waveguides, we could demonstrate a QPSK phase regenerator for processing a 14 GBd QPSK signal. It was placed in a dispersion-compensated link of 1040 km and was able to reduce the BER by an order of magnitude for high launch powers. The required pump powers of 26.6 dBm are comparable to a fiber-based implementation. While a fiber was used for harmonic generation in the first stage, it sounds feasible to replace it by improved versions of the current SOI waveguides. This would enable compact fully-integrated solutions for increased transmission ranges in future optical networks. A further goal was to achieve anomalous dispersion by using higher waveguides to improve bandwidth and potentially reach positive net gain in parametric amplification. Using waveguides with 500 nm width, 400 nm rib height and 80 nm slab height, significant anomalous dispersion could be attained over the C band. Using 26.6 dBm of pump power at 1539.8 nm, a reverse bias of 40 V and CW signals, a conjugated wavelength conversion with -8.5 dB peak output-output efficiency and about 40 nm bandwidth was realized. Using 0 V bias reduced the conversion efficiency by about 4 dB, demonstrating the benefits of the p-i-n diode. Later, the CW signal was replaced by a WDM signal consisting of 8×32 GBd 16QAM channels with a total data rate of 1.024 Tb/s. Under otherwise identical conditions, this WDM signal was converted with the same efficiency. All converted channels had an OSNR penalty of less than 0.6 dB compared to backto-back reception of the transmitted signals. Although the 400 nm waveguides exhibited the desired anomalous dispersion and improved bandwidth, the waveguide loss could not be reduced to levels comparable to the 220 nm waveguides. As positive parametric gain is based on anomalous dispersion and low waveguide losses, it could not be realized within this project. Another approach for improving signal quality for higher-order modulations in long-haul transmissions is the usage of optical phase conjugation (OPC) within the transmission link to compensate for fiber nonlinearities. This was also demonstrated with an SOI waveguide. For this experiment a 5x16 GBd 16QAM WDM signal was generated around 1540 nm. This signal was transmitted over multiple dispersion-compensated fiber spans of 644 km total length with an optional OPC stage in between. When the OPC stage was included, the maximum received Q-factor was increased by 1 dB. Therefore, the OPC enabled operation below the HD-FEC threshold, which (for this transmission link) was not possible without it. The performance and power requirements are similar to fiber-based approaches again, although it is much more compact. Finally, we started investigation of inter-modal four-wave mixing. Using two pumps in different modes of an SOI waveguide, the requirements of anomalous dispersion for broadband operation can be relaxed and it can be used to translate signals between bands that are far apart. Therefore multi-mode SOI waveguides, including on-chip mode multiplexing, have been designed and fabricated using standard 220 nm technology. Most of the components were working as expected, whereas the waveguide itself showed mode crosstalk higher than expected. This may be due to surface roughness, but requires further investigation. Nevertheless, in an experiment we could demonstrate wavelength conversion by 50 nm from C band to L band for up to three 32 GBd QPSK WDM channels, which were spread over 6 nm bandwidth. The OSNR penalty compared to the back-to-back case was less than 0.8 dB. After transmitting the converted signals over 100 km of SSMF, all channels were detected below the HD-FEC threshold. The feasibility of all-optical signal processing in SOI waveguides has been shown by numerous experiments. The required power and achievable performance is comparable to fiber-based approaches when free carriers are removed by a p-i-n diode, while smaller footprint and potential for more on-chip integration make it the more attractive choice for many applications.
Publications
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“QPSK Phase-Regeneration in a Silicon Waveguide Using Phase-Sensitive Processing”, in ECOC 2016; 42nd European Conference on Optical Communication, Sep. 2016, paper W.3.C.2.
I. Sackey et al.
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“1024 Tb/s wavelength conversion in a silicon waveguide with reverse-biased p-i-n junction”, Optics Express, vol. 25, no. 18, p. 21229, Sep. 2017
I. Sackey et al.
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“Performance Evaluation of a Silicon Waveguide for Phase Regeneration of a QPSK Signal”, Journal of Lightwave Technology, vol. 35, no. 6, pp. 1149–1156, Mar. 2017
E. Liebig et al.
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“Dual-polarization wavelength conversion of 16-QAM signals in a single silicon waveguide with a lateral p-i-n diode [Invited]”, Photon. Res., vol. 6, no. 5, pp. B23-B29, May 2018
F. Da Ros et al.
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“Silicon Waveguide with Lateral p-i-n Diode for Nonlinearity Compensation by On-Chip Optical Phase Conjugation”, in 2018 Optical Fiber Communications Conference and Exposition (OFC), Mar. 2018, paper W3E.4
A. Gajda et al.
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“Optical Phase Conjugation in a Silicon Waveguide With Lateral p-i-n Diode for Nonlinearity Compensation”, Journal of Lightwave Technology, vol. 37, no. 2, pp. 323–329, Jan. 2019
F. Da Ros et al.
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“Investigation of Inter-Modal Four Wave Mixing in p-i-n Diode Assisted SOI Waveguides”, in 2020 IEEE Photonics Society Summer Topicals Meeting Series (SUM), Jul. 2020, paper TuD2.3.
G. Ronniger et al.
