Fabry-Pérot optical frequency comb based mm-wave RoF system using pilot-assisted equalizer.

The emergence of the millimeter wave (mm-Wave; 30 GHz to 300 GHz) frequency band holds a lot of promise for addressing the congestion at low frequency in future mobile networks. Among many mm-Wave generation schemes, optical heterodyning is considered one of the most promising approaches due to its scalability and potential for integration on chip. Employing optical frequency combs (OFC) for optical heterodyning alleviates the significant phase distortions/noise introduced by the optical sources. However, any residual phase noise in these systems can deteriorate the transmission performance. Here we demonstrate a high-capacity mm-Wave radio-over-fiber (RoF) system using Fabry-Pérot (FP) laser comb overcoming the typical limitations of this source. The temporal phase perturbation induced by the frequency fluctuation of the FP laser is theoretically analyzed, and then estimated and compensated by a pilot-based phase equalizer. Performance evaluation of the proposed phase equalizer is conducted through experiment and simulation. Enabled by the proposed compensation scheme, ten 200 MHz filtered orthogonal frequency division multiplexing (f-OFDM) signal bands modulated by 16-quadrature amplitude modulation (QAM) are transmitted over 10 km fiber, with the ability to serve multiple users. The transmission of 16-QAM modulated single carrier signals with 2 GBd and 8 Gbps data rate is also performed for comparison, which offers better resilience to phase noise, demonstrating the first commercial Quantum Well FP laser-based optical heterodyning mm-Wave RoF system for both multi-carrier and single carrier signals.

30 Gbit/s PAM4 transmission using an 8-GHz directly modulated multi-section laser.

This paper describes the characterization of a novel directly modulated multi-section laser with a master-slave configuration. Amplitude and phase noise measurements show relative intensity noise values of around -150 dB/Hz and a 3-dB linewidth of around 3 MHz. The laser's suitability for optical access networks, enabled by the chirp reduction from the external injection locking, is shown by demonstrating unamplified 30 Gbit/s C-band transmission over 25 km and 50 km of single mode fiber using PAM4, as well as 30 Gbit/s PAM4 and PAM8 amplified transmission over 75 km.

28 GBd PAM-8 transmission over a 100 nm range using an InP-Si3N4 based integrated dual tunable laser module.

This paper describes the detailed characterization of a novel InP-Si3N4 dual laser module with results revealing relative intensity noise (RIN) as low as -165 dB/Hz and wide wavelength tunability (100 nm). The hybrid coupled laser is deployed in an unamplified 28 GBd 8 level pulse amplitude modulation (PAM) short-reach data center (DC) transmission system. System performance, which is experimentally evaluated in terms of received signal bit error ratio (BER), demonstrates the ability of the proposed laser module to support PAM-8 transmission across a 100 nm tuning range with less than 1 dB variance in receiver sensitivity over the operating wavelength range. Comparative performance studies not only indicate that the proposed source can outperform a commercial external cavity laser (ECL) in an intensity modulation/direct detection (IM/DD) link but also highlight the critical impact of RIN in the design of advanced modulation short-reach systems.

Active demultiplexer enabled mmW ARoF transmission of directly modulated 64-QAM UF-OFDM signals.

In this Letter, we experimentally demonstrate an unamplified analog RoF distribution of 60 GHz 5G signals. The system entails the heterodyning of two optical tones from an externally injected gain switched laser (EI-GSL) based optical frequency comb to generate a millimeter wave (mmW) signal. A fixed frequency separation and a high level of phase correlation, between the EI-GSL comb lines, results in the generation of a high-quality signal. An active demultiplexer is used to filter and amplify two comb tones, thus alleviating the need for an external optical amplifier to boost the low power comb tones. Furthermore, the same demultiplexer is also used to modulate one of the tones with a 64-QAM UF-OFDM signal. Such an approach enables the remote generation of a mmW downlink data signal as well as an unmodulated RF carrier that could be used to downconvert the mmW signals to an intermediate frequency. Using the abovementioned scheme, we demonstrate the distribution of the downlink signal over 25 km of fiber, achieving a BER of 2.4e-3 (below the HD-FEC limit of 3.8e-3) and only a 0.5 dB penalty at the FEC limit in comparison to the BtB case.

56 Gb/s/λ over 1.3 THz frequency range and 400G DWDM PAM-4 transmission with a single quantum dash mode-locked laser source.

The continued evolution of high capacity data center interconnects (DCI) requires scalable transceiver design. The Gigabit Ethernet (GbE) family of standards targets cost-effective and increased capacity transmission through the use of coarse wavelength division multiplexing (CWDM) and direct detection. Moving beyond near-term GbE deployments, multi-wavelength optical sources will be required to enable spectrally efficient WDM transmission, as well as small form-factor transceiver design. This work highlights the capability of a single section 32.5 GHz quantum-dash mode locked laser to provide >Tb/s capacity by demonstrating successful 50 Gb/s/λ pulse amplitude modulation transmission on modes spanning a >1 THz frequency range. Additionally, true 400G DWDM (8×56 Gb/s) C-band transmission is successfully demonstrated with the Q-Dash MLL, resulting in a spectral efficiency of 1.54 b/s/Hz.

Power efficient optical frequency comb generation using laser gain switching and dual-drive Mach-Zehnder modulator.

We propose and experimentally demonstrate a power efficient dual-stage optical frequency comb using laser gain switching followed by a dual-drive Mach-Zehnder modulator (DD-MZM). The laser is initially gain switched at ∼ 9.5 GHz and the resultant comb is then expanded using a dual-drive Mach-Zehnder modulator driven at ∼ 19 GHz with signal amplitudes below 1.5 V. The setup generates an optical frequency comb, with 12 lines within 3 dB flatness, in a power efficient manner. Theoretical analysis is presented and verified through simulation and experimental results.

Tapless and topology agnostic calibration solution for silicon photonic switches.

We leverage the photo-conductance (PC) effect in doped phase-shifter heaters for both controlling and calibrating Mach-Zehnder interferometer (MZI) switch elements. Both the steady-state and the transient response are experimentally characterized, and compact models for the PC current are developed. Utilizing the PC effect, a topology-agnostic algorithm is then outlined. The calibration procedure is experimentally verified against calibration with external photo-detectors using a non-blocking 4×4 Benes switch consisting of six 2×2 MZIs. It is shown that our PC-based approach agrees with the PD-based procedure within less than 2.5% of difference between the obtained calibrated values. Based on the calibrated PC values, all possible routing configurations are measured for extinction ratio (9.92-21.51dB), insertion loss (0.88-4.59dB), and exhibiting performances far below the 7% FEC limit (bit error rate of 3.8 × 10- 3) using 25 Gbps 4-level pulse-amplitude-modulation signals (PAM4).

Software-defined control-plane for wavelength selective unicast and multicast of optical data in a silicon photonic platform.

We demonstrate a programmable control-plane based on field programmable gate array (FPGA) with a power-efficient algorithm for optical unicast, multicast, and broadcast functionalities in a silicon photonic platform. The platform includes a silicon photonic 1×8 microring array chip which in conjunction with a fast tunable laser over the C-band is capable of delivering software controlled wavelength selective functionality on top of spatial switching. We characterize the thermo-optic response of microring resonators and extract key parameters necessary for the development of the control-plane. The performance of the proposed architecture is tested with 10 Gb/s on-off keying (OOK) optical data and error-free operation is verified for various wavelength and spatial switching scenarios. Lastly, we evaluate electrical power and energy consumption required to reconfigure the silicon photonic device for all possible wavelength operations and output ports combinations and show that unicast, multicast of two, three, four, five, six, seven, and broadcast functions are achieved with energy overheads of 0.02, 0.07, 0.18, 0.49, 0.76, 1.01, 1.3, and 1.55 pJ/bit, respectively.

Single-section quantum well mode-locked laser for 400 Gb/s SSB-OFDM transmission.

Successful use of a single-section quantum well (QW) passively mode-locked laser (MLL) as a comb source for optical interconnects is demonstrated for the first time. Sixteen comb lines spaced by 37.6 GHz are modulated using 25 Gb/s compatible single sideband orthogonal frequency division multiplexed (SSB-OFDM) signals and transmitted over 50 km of standard single-mode fiber with bit error ratio below the 7% forward error correction limit. The system performance, analyzed on the basis of the relative intensity noise of the device, reveal the suitability of single-section QW MLLs as inexpensive comb sources for inter- and intra-data center communication scenarios.