Wideband multi-stage CROW filters with relaxed fabrication tolerances

Agile THz-range spectral multiplication of frequency combs using a multi-wavelength laser

A breakthrough technology, on-chip frequency comb sources offer broadband combs while being compact, energy-efficient, and cost-effective solutions for various applications from lidar to telecommunications. Yet, these sources encounter a fundamental trade-off between controllability and bandwidth: broadband combs, generated in microresonators, lack free-spectral range or spectral envelope control, while combs generated with electro-optic modulators can be carefully tailored but are limited in bandwidth. Here, we overcome this trade-off through agile spectral multiplication of narrowband combs. Exploiting the nonlinear dynamics of a multi-wavelength laser under modulated optical injection, we achieve spectral multiplication at frequency offsets from 26 GHz to 1.3 THz. Moreover, on-chip control allows for nano-second switching of the frequency offset. Compatible with generic platforms, our approach can be scaled up to cover several THz. When combined with THz photomixers, our system could enable low-cost, compact, and power-efficient THz comb sources, paving the way towards a new generation of THz applications.

Flexible channel selection method based on optical combs for broadband signals receiving

A flexible channel selection method based on optical combs is proposed for reconfigurable optical channels in this paper. Optical-frequency combs with a large frequency interval are used to modulate broadband radio frequency (RF) signals, and an on-chip reconfigurable optical filter [Proc. of SPIE, 11763, 1176370 (2021).10.1117/12.2587403] is used to perform periodic carrier separation of wideband and narrowband signals and channel selection. In addition, flexible channel selection is achieved by presetting the parameters of a fast-response programmable wavelength-selective optical switch and filter device. Channel selection only relies on the combs through the Vernier effect of the combs and the passbands for different periods and does not require the use an additional switch matrix. Finally, flexible switching between and selection of specific channels for 13 GHz and 19 GHz broadband RF signals are experimentally verified.

Fundamental limitations of spectrally-sliced optically enabled data converters arising from MLL timing jitter

The effect of phase noise introduced by optical sources in spectrally-sliced optically enabled DACs and ADCs is modeled and analyzed in detail. In both data converter architectures, a mode-locked laser is assumed to provide an optical comb whose lines are used to either synthesize or analyze individual spectral slices. While the optical phase noise of the central MLL line as well as of other optical carriers used in the analyzed system architectures have a minor impact on the system performance, the RF phase noise of the MLL fundamentally limits it. In particular, the corresponding jitter of the MLL pulse train is transferred almost one-to-one to the system-level timing jitter of the data converters. While MLL phase noise can in principle be tracked and removed by electronic signal processing, this results in electric oscillator phase noise replacing the MLL jitter and is not conducive in systems leveraging the ultra-low jitter of low-noise mode-locked lasers. Precise analytical models are derived and validated by detailed numerical simulations.

8-channel WDM silicon photonics transceiver with SOA and semiconductor mode-locked laser

We demonstrate an integrated 8 by 14 Gbps dense wavelength division multiplexed silicon photonics transceiver that makes use of an external mode-locked laser as a light source and a single semiconductor optical amplifier for post-modulation signal amplification. Remaining components necessary for modulation, filtering and (de‑)multiplexing are monolithically integrated in a single chip. In all system experiments, all eight channels are jointly operated with independent data streams in order to include impairments arising out of nonlinear effects inside the SOA while benchmarking the system performance. The transmitter, measured with a commercial reference receiver, supports on-off keying data transmission with an uncorrected BER ranging between 1e-5 and 5e-7 for all channels in back-to-back configuration and between 8e-4 and 1e-5 after 10 km transmission (both PRBS 2³¹-1). The three best channels of the full link consisting in the silicon photonics transmitter operated with the silicon photonics receiver in back-to-back configuration maintain a BER better than the targeted 5e-5. Based on link budget modeling, we expect this target to be reached for all 8 channels pending improvement of the receiver offset compensation loop.