Spectral recovery of broadband waveforms via cross-phase modulation based tunable Talbot amplifier.

Physical processes in the Fourier domain play a crucial role in various applications such as spectroscopy, quantum technology, ranging, radio-astronomy, and telecommunications. However, the presence of stochastic noise poses a significant challenge in the detection of broadband spectral waveforms, especially those with limited power. In this study, we propose and experimentally demonstrate a cross-phase modulation (XPM) based spectral Talbot amplifier to recover the broadband spectral waveforms in high fidelity.

Capacity enhancement through entropy loading with probabilistically shaped signals in a frequency comb-based transmission system.

We demonstrate a multichannel entropy loading mechanism in an optical frequency comb-based coherent communication system. In high-capacity wavelength division multiplexing communications, the individual laser sources can be replaced by an optical frequency comb, thus reducing the complexity and energy consumption of the transmitter. However, the power variation among different comb lines will lead to performance discrepancies.

Optimizing the probability mass function of complex modulated signals through adaptive channel characterization.

We propose a probability mass function (PMF) optimization scheme for quadrature amplitude modulation (QAM) signals by considering the parametric characteristic of the training sequence. The training sequence for optimization is mapped in standard Maxwell-Boltzmann (M-B) distribution, and the considered characterizing parameters incorporate either the noise variance or the error matrix of the received symbols. The proposed PMF optimization is based on independent reallocation within each constellation ring, generating new distribution with almost the same entropy and transmitted power as the original distribution.

Tunable optical frequency comb with hundred-GHz spacings generated on a silicon waveguide.

We demonstrate the generation of optical frequency combs with tunable spacing at the hundred-GHz range in the 1550-nm window. The widely spaced combs are realized through silicon-based cross-phase modulation. The optical pump is prepared by multiplication of a 10-GHz train of 1.

Constellation size for probabilistic shaping under the constraint of limited ADC resolution.

We investigate the optimal constellation size for probabilistic shaping (PS) under the constraint of different effective numbers of bits (ENOB) of the analog-to-digital converter (ADC) at the receiver. For a fixed entropy, increasing the constellation size brings a larger shaping gain, while it also leads to a higher peak-to-average-power ratio, which makes the signal more sensitive to the ENOB and fiber nonlinearity. Our experimental results show that PS-44 quadrature amplitude modulation (QAM) outperforms both PS-64 QAM and uniformly shaped 32 QAM (U-32 QAM) when the ENOB of ADC is lower than 4.

A silicon nitride waveguide-integrated chemical vapor deposited graphene photodetector with 38 GHz bandwidth.

We demonstrate a high-speed chemical vapor deposited graphene-on-silicon nitride waveguide photodetector. The device is designed with grating-like metal contact to reduce the channel spacing. Benefiting from the narrow channel spacing, a calculated transit-time-limited bandwidth of 111 GHz is derived.

Integrated germanium-on-silicon Franz-Keldysh vector modulator used with a Kramers-Kronig receiver.

We propose an integrated vector modulator based on two compact and high-speed germanium-on-silicon Franz-Keldysh electro-absorption modulators. The proposed vector modulator is extremely compact with a total footprint of only 1800  μm×200  μm. We further experimentally demonstrate a 4-quadrature-amplitude-modulation (4-QAM) at 40 Gb/s over a 20-km standard single-mode fiber transmission.

Surpassing the tuning speed limit of slow-light-based tunable optical delay via four-wave mixing Bragg scattering.

We demonstrate a tunable optical delay that surpasses the tuning speed limit of the conventional slow-light-based optical delay. A novel nonlinear optical coupler, implemented by the four-wave mixing (FWM) Bragg scattering process, is utilized to perform destructive interference of the slow-light delayed signal pulse and a nondelayed reference pulse. As a result, the Brillouin-induced frequency-dependent phase shift, as well as the group delay of the synthesized pulse, is amplified.

Carrier regeneration from a blockwise phase-switching signal for a frequency comb-based WDM system.

We demonstrate that an optical carrier can be extracted from a signal based on a blockwise phase-switching (BPS) technique for locking the frequency combs at the transmitter and the receiver in a wavelength division multiplexing (WDM) system. Two types of carrier regeneration techniques, optical injection locking and stimulated Brillouin scattering, are evaluated in the aspects of the injection ratio and pump power, respectively, under different carrier-to-signal power ratios. 7×16  Gbaud QPSK data channels with 25 GHz spacing are successfully transmitted over an 80 km fiber by the direct detection of a BPS-assisted central channel and coherent detection of the remaining channels.

Raman-enhanced optical phase conjugator in WDM transmission systems.

Optical phase conjugation (OPC) can be applied to boost the performance of long-haul transmission by mitigating the impairments from fiber nonlinearity. Unfortunately, noticeable nonlinear noise in the conjugator for optical orthogonal frequency division multiplexing (OFDM) systems often degrades the signal quality. In this paper, we demonstrate nonlinear distortion mitigation in OPC by introducing backward Raman amplification to the conjugator.

High-performance chemical vapor deposited graphene-on-silicon nitride waveguide photodetectors.

Waveguide photodetectors integrated with graphene have demonstrated potential for ultrafast response and broadband operation. Here, we demonstrate high-performance chemical vapor deposited graphene-on-silicon nitride waveguide photodetectors by enhancing the absorption of light propagating in the transverse-magnetic mode through a metal-graphene junction. A doubling in responsivity is experimentally observed.

Kramers-Kronig detection with the Brillouin-amplified virtual carrier.

We proposed a novel scheme for realizing Kramers-Kronig detection by utilizing the narrow-band and high-gain characteristic of stimulated Brillouin scattering. At the receiver, the weak virtual carrier located at the edge of the signal spectrum is Brillouin amplified by the output of a slave laser, which is injection locked by a weak pump seed provided by the transmitter. More than a 2.

Brillouin optical time domain analyzer sensors assisted by advanced image denoising techniques.

We have experimentally analyzed and compared the performance of Brillouin optical time-domain analyzer (BOTDA) sensors assisted by non-local means (NLM) and wavelet denoising (WD) techniques in terms of measurement accuracy and experimental spatial resolution, respectively. Degradation of the measurement accuracy and experimental spatial resolution after denoising by NLM and WD are observed, which originate from the fact that higher signal-to-noise ratio (SNR) improvement is achieved at the expense of sacrificing the details of BOTDA data, and smaller data sampling point number (SPN) gives rise to insufficient redundant information for denoising. The two parameters degrade to different extents depending on the amount of SNR improvement and SPN adopted in data acquisition.

Support vector machine assisted BOTDA utilizing combined Brillouin gain and phase information for enhanced sensing accuracy.

Benefiting from both Brillouin amplitude and phase spectral responses during Brillouin scattering, a support vector machine (SVM) assisted Brillouin optical time domain analyzer (BOTDA) enabling the improvement of sensing accuracy with only a slight sacrifice of processing speed has been proposed and demonstrated. Only one SVM model, i.e.

Photonically assisted microwave waveform generation by gain-transparent SBS-induced carrier processing: erratum.

In our previous work [Opt. Lett.42, 3852 (2017)OPLEDP0146-959210.

SBS-enhanced FWM for polarization division multiplexed signals in coherent communication systems.

Stimulated Brillouin scattering (SBS) is applied to improve the performance of polarization insensitive four-wave mixing (FWM) realized with two orthogonal pumps. By manipulating the phase matching condition with SBS-induced phase change, we achieve conversion efficiency improvement up to 6 dB with negligible polarization dependence. Our approach is implemented in a coherent communication system where polarization division multiplexing (PDM) quadrature phase shift keying (QPSK) signal is applied.

Photonically assisted microwave waveform generation by gain-transparent SBS-induced carrier processing.

We propose and experimentally demonstrate a new approach to generate microwave waveforms by phase modulation and optical carrier phase processing based on gain-transparent stimulated Brillouin scattering (SBS). By properly adjusting the SBS-induced-phase shift on the carrier and the following group velocity dispersion, microwave waveforms with controllable repetition rates and temporal profiles can be generated. In the experiment, we have successfully generated triangular waveforms at repetition rates of 5.

Cavity-enhanced thermo-optic bistability and hysteresis in a graphene-on-SiN ring resonator.

Cavity-enhanced thermo-optic bistability is studied in a graphene-on-SiN ring resonator. By engineering the coverage of the monolayer graphene on top of the SiN ring resonator, we observed a two-fold enhancement in the thermo-optically induced resonance shift rate and an 18-fold increase in the effective thermal nonlinear refractive index compared with the devices without graphene. The thermo-optic hysteresis loop was also characterized in this hybrid structure, where the experimental results agree well with the theoretical calculations.

Enhanced performance in serial-to-parallel data conversion via Raman-assisted time lens processing.

We have demonstrated a new approach to enhance the uniformity of conversion efficiency in serial-to-parallel data conversion via time lens processing. In our approach, Raman amplification is applied to enhance four-wave mixing in a highly nonlinear fiber. By carefully selecting the pump wavelength, the Raman gain profile can be exploited to compensate the roll-off in conversion efficiency resulted from the varying phase mismatch between the linearly chirped pump and the signal.

Synergistic Effects of Plasmonics and Electron Trapping in Graphene Short-Wave Infrared Photodetectors with Ultrahigh Responsivity.

Graphene's unique electronic and optical properties have made it an attractive material for developing ultrafast short-wave infrared (SWIR) photodetectors. However, the performance of graphene SWIR photodetectors has been limited by the low optical absorption of graphene as well as the ultrashort lifetime of photoinduced carriers. Here, we present two mechanisms to overcome these two shortages and demonstrate a graphene-based SWIR photodetector with high responsivity and fast photoresponse.

Raman enhanced polarization-insensitive wavelength conversion based on two-pump four-wave mixing.

Backward Raman amplification is applied to improve the conversion efficiency of two-orthogonal-pump four-wave mixing (FWM) with polarization insensitivity. Wavelength conversion with ~0dB efficiency and negligible polarization dependency is demonstrated by using a common highly nonlinear fiber without pump dithering. The conversion efficiency is increased by ~29dB with Raman enhancement.

High-responsivity graphene-on-silicon slot waveguide photodetectors.

We demonstrated strong optical absorption in a graphene integrated silicon slot waveguide. Due to the increase in light intensity and decrease of optical mode confinement in the silicon slot, the graphene experienced an increased interaction to the in-plane light. A waveguide absorption of 0.

Raman-Enhanced Phase-Sensitive Fibre Optical Parametric Amplifier.

Phase-sensitive amplification is of great research interest owing to its potential in noiseless amplification. One key feature in a phase-sensitive amplifier is the gain extinction ratio defined as the ratio of the maximum to the minimum gains. It quantifies the capability of the amplifier in performing low-noise amplification for high phase-sensitive gain.

Active control of gain saturation in fiber-optical parametric amplifier using stimulated Brillouin scattering.

We have demonstrated the use of stimulated Brillouin scattering (SBS) to control the gain saturation characteristics of fiber-optical parametric amplification (FOPA). The saturation can be dynamically deferred or expedited without changing the input FOPA pump and signal parameters. It is observed that the input signal power at saturation can be increased or decreased by up to 6 dB.