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We demonstrate a novel method for finding the coherent transfer matrix (CTM) of a multi-channel transmission medium utilizing backscattering and coherent optical time-domain reflectometry (COTDR). We measured the CTM for two polarizations of a single-mode fiber with ±0.3dB and ±8.5° amplitude and phase precisions.

This paper summarizes the recent advances of integrated hybrid InP/SOI lasers and transmitters based on edge coupling. First, we review the different integration methods between III–V material and silicon. Then, we focus on using an external III–V chip coupled via edge coupling to our silicon photonic integrated circuit. The paper reports on the results of wavelength tunable lasers containing one or two ring resonators as well as an integrated reflectivity tunable mirror. We demonstrate that a wide thermal tuning range, exceeding the C band, with a high side mode suppression ratio above 35 dB can be achieved. Design of external silicon cavities enables the realization of a broad range of on-chip functionalities as well as advanced hybrid transmitters. Parallel wavelength tunable cavities and compact variable optical attenuator-controlled arrayed waveguide gratings on silicon are integrated with a reflective semiconductor optical amplifiers, creating fast wavelength switching lasers. Furthermore, integrated transmitters that combine silicon modulators with tunable hybrid III–V/Si lasers are reported. The integrated transmitter for on–off keying signal generation exhibits more than 30 nm wavelength tunability and excellent bit-error-rate performance up to 40 Gb/s. A multichannel integrated transmitter is then reported with combined silicon-based arrayed waveguide gratings laser cavity and multiple ring modulators. Finally, an advanced wavelength-tunable hybrid III–V/Si transmitter with two microring modulators nested in a Mach–Zehnder interferometer is demonstrated for quadrature phase-shift keying generation where a BPSK signal is generated by each ring.

We report the transmission of probabilistically shaped (PS) 64-ary quadrature amplitude modulation (QAM) at 7.46 b/s/Hz over a 5523-km in-service trans-Atlantic fiber-optic cable that consists of 65–89-km spans of Erbium-doped fiber amplifier only amplified fiber. Using a looped-back system configuration, we achieve 5.68 b/s/Hz over a trans-Pacific-equivalent distance of 11 046 km. Net spectral efficiencies are increased by 18% and 80% by using PS, at 5523 km and 11 046 km, respectively, compared to uniform square QAM. Throughout our experiments, we pay particular attention that our claims are backed by implementable forward error correction schemes. In addition, we demonstrate real-time coherent transmission of single-carrier 200 and 250-Gb/s uniform 8-QAM and 16-QAM at 4 b/s/Hz over the 5523-km cable.

We theoretically and experimentally demonstrate a ring-assisted Mach–Zehnder interferometer modulator for intensity and phase modulation, leveraging both Mach–Zehnder modulator and single microring modulator. Differential drive of two microring modulators nested in a Mach–Zehnder interferometer offers several advantages for both intensity modulation and phase modulation. We first present a complete theoretical study of this differential ring modulator, including the operation principles, high-speed characteristics, system performance, and energy consumption. We then experimentally verify that this differential ring modulator provides low-chirp, low drive voltage, and large extinction ratio for intensity modulation, and low-chirp, low drive voltage, and drive-voltage insensitivity for phase modulation.

This chapter introduces the general architecture of an optical transponder and describes the three critical optical components that comprise the transponder, the laser, the optical modulator, and the photodetector. Following this, the subsystem consisting of the optical transmitter and the coherent receiver that are typically used for generating and detecting dual-polarization complex-modulated signals are explained. The typical characteristics of the components used in the transponder are presented both from current-generation products, as well as from more recent research demonstrations.

We experimentally demonstrate the rate/reach adaptability of probabilistically constellation-shaped quadrature amplitude modulation across from 80 km to 12,000 km using the same 32-GBaud transponder hardware and highlight the roles of template and shaping distribution.

We experimentally solve the problem of maximizing capacity under a total supply power constraint in a massively parallel submarine cable context, i.e., for a spatially uncoupled system in which fiber Kerr nonlinearity is not a dominant limitation. By using multi-layer neural networks trained with extensive measurement data acquired from a 12-span 744-km optical fiber link as an accurate digital twin of the true optical system, we experimentally maximize fiber capacity with respect to the transmit signal's spectral power distribution based on a gradient-descent algorithm. By observing convergence to approximately the same maximum capacity and power distribution for almost arbitrary initial conditions, we conjecture that the capacity surface is a concave function of the transmit signal power distribution. We then demonstrate that eliminating gain flattening filters (GFFs) from the optical amplifiers results in substantial capacity gains per Watt of electrical supply power compared to a conventional system that contains GFFs., Comment: arXiv admin note: text overlap with arXiv:1910.02050

We demonstrate both 100-GBaud PAM-4 and 80-GBaud PAM-8 transmissions over 10-km fiber using a 1315-nm 54-GHz distributed Bragg reflector laser with a transient chirp parameter of 1.0. The 80-GBaud PAM-8 system achieves a net bit rate of 200 Gb/s.

We experimentally achieve a 19% capacity gain per Watt of electrical supply power in a 12-span link by eliminating gain flattening filters and optimizing launch powers using deep neural networks in a parallel fiber context. (C) 2020 The Authors

We demonstrate an all-electronic digital-to-analog converter (DAC) with 100-GHz electrical bandwidth, sampling at 240 GSa/s, based on digital band interleaving (DBI). We discuss digital predistortion techniques for compensating the nonideal performance of the high-speed and radio-frequency components in our DBI architecture. We then test the DAC by generating up to 190-GBaud Nyquist-shaped pulse amplitude modulation. We analyze the performance of the digital band interleaved DAC and demonstrate coherent detection of single-polarization optical binary phase-shift keying at 140 GBaud.

We demonstrate the world-first single-channel direct detection beyond 1-Tb/s with 1.26-Tb/s line rate and 1.02-Tb/s net rate after 100-km SSMF, via an 86-GHz Stokes vector receiver that recovers totally single-polarization-equivalent 252-Gbaud probabilistic-shaped 64-QAM signal.

We investigate the impact of the opto-electronic front-end frequency response on Kramers-Kronig (KK) receivers. We demonstrate that adaptive equalization preceding KK processing can significantly improve optical field reconstruction.

Simulations and experiments using probabilistically shaped QAM quantify the impact of nonideal coding on the information rate. A coding gap induces an information rate loss that increases with the underlying constellation size, favoring lower-order QAM templates.

We review self-coherent receiver schemes that enable >100 Gb/s per-wavelength transmission over ∼100 km of fiber. We discuss in detail recent progress on Kramers-Kronig receivers.

This paper reviews recent progress in high spectral efficiency optical transmission using probabilistic constellation shaping (PCS), and discusses various aspects of PCS from theoretic and practical benefits to performance optimization.

We review the design and implementation of a digital- band-interleaved (DBI) digital-to-analog converter (DAC). We show the experimental generation of up to 1.6 Tb/s per wavelength using two synchronized 100-GHz DBI-DACs.

Electro-optic modulators translate high-speed electronic signals into the optical domain and are critical components in modern telecommunication networks

The emerging applications for inter and intradata center communications demand low-cost and small-from-factor optical transceivers with 100G/400G capacity. Various techniques, such as wavelength-division multiplexing (WDM), multilevel pulse-amplitude modulation, and discrete multitone (DMT), are heavily investigated in this field. Among these techniques, DMT can offer 100G capacity with 10–20G optical devices using direct detection, which provides a very promising low-cost 100G/400G solution. In this paper, we report silicon photonic four-channel DMT integrated circuits, which demonstrate net channel rates of 70 and 100 Gb/s detected by integrated germanium receivers and commercial receivers, respectively. The silicon photonic chip integrates four silicon Mach–Zehnder modulators and WDM multiplexers using thermally tuned second-order microring filters. Besides the wavelength multiplexing functionality, we also demonstrate that these microrings can serve as vestigial sideband filters to enhance the transmission performance in 20–40 km ranges. These demonstrations indicate the promise of using low-cost and high-integrated silicon photonic circuits in high capacity 100G/400G applications.

We demonstrate polarization-independent parametric amplification of a 2.048-Tbit/s 8-WDM PDM 16-QAM signal and simultaneous wavelength conversion and phase conjugation in a highly nonlinear fiber. Two high-power continuous-wave pumps with orthogonal polarizations and counter-phase modulation are used in the fiber optical parametric amplifier (FOPA) to achieve broadband flat gain, polarization independence, and high-quality idler generation. The polarization-independent FOPA is amplitude and phase preserving and has ∼10 dB on-off gain for the signal and ∼9 dB conversion efficiency for the idler with a 1-dB bandwidth of ∼16 nm. Compared to the back-to-back case, the amplified signals and the wavelength-converted conjugates have mean Q2 penalties of only 0.6 and 0.4 dB, respectively, with variances of Q2 factors across all the wavelength-division-multiplexed channels of only 0.3 dB. This demonstration shows the great promise of optical signal processing techniques to simultaneously process large-capacity multiple-channel multilevel signals with almost no latency and potentially low power consumption.