Recent advance in hollow-core fiber high-temperature and high-pressure sensing technology [Invited]

The pure-silica hollow-core fiber(HCF) has excellent thermostabilities that can benefit a lot of high-temperature sensing applications.The air-core microstructure of the HCF provides an inherent gas container, which can be a good candidate for gas or gas pressure sensing.This paper reviews our continuous efforts to design, fabricate, and characterize the hightemperature and high-pressure sensors with HCFs, aiming at improving the sensing performances such as dynamic range,sensitivity, and linearity.With the breakthrough advances in novel anti-resonant HCFs, sensing of high temperature and high pressure with HCFs will continuously progress and find increasing applications.

Low-noise amplification of dissipative Kerr soliton microcomb lines via optical injection locking lasers

The dissipative Kerr soliton microcomb provides a promising laser source for wavelength-division multiplexing(WDM)communication systems thanks to its compatibility with chip integration.However,the soliton microcomb commonly suffers from a low-power level due to the intrinsically limited energy conversion efficiency from the continuous-wave pump laser to ultra-short solitary pulses.Here,we exploit laser injection locking to amplify and equalize dissipative Kerr soliton comb lines,superior gain factor larger than 30 dB,and optical-signal-to-noise-ratio(OSNR)as high as 60 dB obtained experimentally,providing a potential pathway to constitute a high-power chip-integrated WDM laser source for optical communications.

Fiber nonlinearity compensation for CO-OFDM transmission with 10.7-Gb/s NRZ-OOK neighbors

Fiber nonlinearity limits the use of coherent optical orthogonal frequency division multiplexing （CO- OFDM） to upgrade wavelength-division multiplexing （WDM） systems using legacy non-return-to-zero-on- off-keying （NRZ-OOK） channels. This letter proposes to compensate for the fiber nonlinearity of COOFDM with NRZ-OOK neighbors by combining digital signal processing （DSP）-based self-phase modulation （SPM） post-compensation with pilot-tone-based cross-phase modulation （XPM） compensation. The simulation results demonstrate that the optimum low-pass filter bandwidth for pilot-tone-based XPM compensation depends on the pilot-to-signal ratio value and launch optical power. Our method allows a 4-dB increase in the launch power for a 40-Gb/s single polarization CO-OFDM channel placed in the middle of six 10.7-Gb/s NRZ channels in a 50-GHz space and 1 200-km WDM system.

High energy efficiency soliton microcomb generation in high coupling strength,large mode volume,and ultra-high-Q micro-cavity

The nonlinear physics dynamics of temporal dissipative solitons in a microcavity hinder them from attaining high power from pump lasers with a typical nonlinear energy conversion efficiency of less than 1%.Here,we experimentally demonstrate a straightforward method for improving the output power of soliton combs using a silica microrod cavity with high coupling strength,large mode volume,and high-Q factor,resulting in a low-repetition-rate dissipative soliton(∼21 GHz)with an energy conversion efficiency exceeding 20%.Furthermore,by generating an∼105 GHz 5×FSR(free spectral range)soliton crystal comb in the microcavity,the energy conversion efficiency can be further increased up to 56%.

MLSE-assisted decision feedback equalizer for error-propagation suppression in high-speed IM-DD transmission systems

We propose a trellis-compressed maximum likelihood sequence estimation(TC-MLSE)-assisted sliding-block decision feedback equalizer(DFE)to suppress the error propagation resulting from the DFE in high-speed systems.We use an out-ofrange detector to detect the end of burst errors from the DFE and activate the optional TC-MLSE to correct burst errors.We conduct experiments to transmit a 201-Gbit/s PAM-8 signal.The results show that the proposed method achieves a bit error rate of 3.65×10^(-3),which is close to that of MLSE.The optional MLSE is only activated when needed and processes 11.4%of the total symbols.Moreover,the proposed method compresses the maximum length of burst errors from 19 to 5.

Precise control of micro-rod resonator free spectral range via iterative laser annealing

We demonstrate a novel method to control the free spectral range(FSR) of silica micro-rod resonators precisely.This method is accomplished by iteratively applying laser annealing on the already-fabricated micro-rod resonators.Fine and repeatable increasing of resonator FSR is demonstrated, and the best resolution is smaller than 5 MHz, while the resonator quality-factor is only slightly affected by the iterative annealing procedure.Using the fabricated micro-rod resonators, single dissipative Kerr soliton microcombs are generated, and soliton repetition frequencies are tuned precisely by the iterative annealing process.The demonstrated method can be used for dual-comb spectroscopy and coherent optical communications.

All-polymer solar cells with over 16%efficiency and enhanced stability enabled by compatible solvent and polymer additives

Considering the robust and stable nature of the active layers,advancing the power conversion efficiency(PCE)has long been the priority for all-polymer solar cells(all-PSCs).Despite the recent surge of PCE,the photovoltaic parameters of the stateof-the-art all-PSC still lag those of the polymer:small molecule-based devices.To compete with the counterparts,judicious modulation of the morphology and thus the device electrical properties are needed.It is difficult to improve all the parameters concurrently for the all-PSCs with advanced efficiency,and one increase is typically accompanied by the drop of the other(s).In this work,with the aids of the solvent additive(1-chloronaphthalene)and the n-type polymer additive(N2200),we can fine-tune the morphology of the active layer and demonstrate a 16.04%efficient all-PSC based on the PM6:PY-IT active layer.The grazing incidence wideangle X-ray scattering measurements show that the shape of the crystallites can be altered,and the reshaped crystallites lead to enhanced and more balanced charge transport,reduced recombination,and suppressed energy loss,which lead to concurrently improved and device efficiency and stability.

Multi-service small-cell cloud wired/wireless access network based on tunable optical frequency comb

In this paper,we demonstrate a novel multi-service wired/wireless integrated access architecture of cloud radio access network(C-RAN) based on radio-over-fiber passive optical network(RoF-PON) system,which utilizes scalable multiple-frequency millimeter-wave(MF-MMW) generation based on tunable optical frequency comb(TOFC).In the baseband unit(BBU) pool,the generated optical comb lines are modulated into wired,RoF and WiFi/WiMAX signals,respectively.The multi-frequency RoF signals are generated by beating the optical comb line pairs in the small cell.The WiFi/WiMAX signals are demodulated after passing through the band pass filter(BPF) and band stop filter(BSF),respectively,whereas the wired signal can be received directly.The feasibility and scalability of the proposed multi-service wired/wireless integrated C-RAN are confirmed by the simulations.

Transfer-learning multi-input multi-output equalizer for mode-division multiplexing systems

We propose a transfer-learning multi-input multi-output(TL-MIMO)scheme to significantly reduce the required training complexity for converging the equalizers in mode-division multiplexing(MDM)systems.Based on a built three-mode(LP01,LP11a,and LP11b)multiplexed experimental system,we thoughtfully investigate the TL-MIMO performances on the three-typed data,collecting from different sampling times,launching optical powers,and inputting optical signal-to-noise ratios(OSNRs).A dramatic reduction of approximately 40%–83.33%in the required training complexity is achieved in all three scenarios.Furthermore,the good stability of TL-MIMO in both the launched powers and OSNR test bands has also been proved.