Frequency upconversion technique, where the infrared signal is nonlinearly translated into the visible band to leverage the silicon sensors, offers a promising alternation for the mid-infrared (MIR) imaging. However, the intrinsic field of view (FOV) is typically limited by the phase-matching condition, thus imposing a remaining challenge to promote subsequent applications. Here, we demonstrate a wide-field upconversion imaging based on the aperiodic quasi-phase-matching configuration. The acceptance angle is significantly expanded to about 30°, over tenfold larger than that with the periodical poling crystal. The extended FOV is realized in one shot without the need of parameter scanning or post-processing. Consequently, a fast snapshot allows to facilitate high-speed imaging at a frame rate up to 216 kHz. Alternatively, single-photon imaging at room temperature is permitted due to the substantially suppressed background noise by the spectro-temporal filtering. Furthermore, we have implemented high-resolution time-of-flight 3D imaging based on the picosecond optical gating. These presented MIR imaging features with wide field, fast speed, and high sensitivity might stimulate immediate applications, such as non-destructive defect inspection, in-vivo biomedical examination, and high-speed volumetric tomography. 

/pdf/wide-field-mid-infrared-single-photon-upconversion-imaging-1c3ksvhh.pdf

Wide-field mid-infrared single-photon upconversion imaging

Mid-Infrared Single-Photon Edge Enhanced Imaging Based on Nonlinear Vortex Filtering

We have proposed and implemented a novel scheme to obtain high-precision repetition rate stabilization for a polarization-maintaining mode-locked fiber laser. The essential technique lies in the periodic injection of electronically modulated optical pulses into a nonlinear amplifying loop mirror within the laser resonator. Thanks to the nonlinear cross-phase modulation effect, the injected pulses referenced to an external clock serves as a stable and precise timing trigger for an effective intensity modulator. Consequently, synchronous mode-locking can be initiated to output ultrafast pulses with a passively stabilized repetition rate. The capture range of the locking system reaches to a record of 1 mm, which enables a long-term stable operation over 15 hours without the need of temperature stabilization and vibration isolation. Meanwhile, the achieved standard deviation is as low as 100 μHz with a 1-s sample time, corresponding to a fluctuation instability of 5.0×10-12. Additionally, the repetition rate stabilization performance based on the passive synchronization has been systematically investigated by varying the average power, central wavelength and pulse duration of the optical injection.

High-precision passive stabilization of repetition rate for a mode-locked fiber laser based on optical pulse injection

: Optical soliton molecules in ultrafast lasers present striking analogies with their matter molecule counterparts, such as internal vibrations. However, the vibrations of soliton molecules are nonlinear, with frequencies that are sensitive to the system parameters, thus presenting an opportunity of control. Here, we experimentally demonstrate the synchronization of the internal vibrations of self-excited vibrating soliton molecules through a modulated optical injection. We show efficient sub-harmonic, fundamental and superharmonic synchronization, forming a pattern of Arnold tongues with respect to the injection strength. Our observations are supported by numerical simulations.

Synchronization of the internal dynamics of optical soliton molecules

Abstract Electromagnetic vortex carries the orbital angular momentum, one of the most fundamental properties of waves. The order of such vortex can be unbounded in principle, thus facilitating high-capability wave technologies for optical communications, photonic integrated circuits and others. However, it remains a key challenge to generate the high-order vortex beams in a reconfigurable, broadband and cost-effective manner. Here, inspired by the balanced-ternary concept, we demonstrate the reconfigurable generation of order-controllable vortices via cascaded N-layer metasurfaces. We theoretically showed that 3 N − 1 ${3}^{N}-1$ different vortex modes can be generated by cascading N metasurfaces, each one serving as an individual vortex beam generator for the order of 3 k ${3}^{k}$ (k = 0,1,2 …, N − 1 $N-1$ ). As a proof-of-concept demonstration, a reconfigurable generation of 26 different vortex beams, with orders from 1 to 13 and from −1 to −13, is showcased in a broad millimeter-wave region by a cascade of 3 metasurfaces. Our method can be easily extended to vortex beam generator of arbitrary orders in a reconfigurable and easily implementable manner, paving a new avenue towards tremendous practical applications.

/pdf/balanced-ternary-inspired-reconfigurable-vortex-beams-using-2ruucezl.pdf

Balanced-ternary-inspired reconfigurable vortex beams using cascaded metasurfaces

Optical detectors with single-photon sensitivity and large dynamic range would facilitate a variety of applications. Specifically, the capability of extending operation wavelengths into the mid-infrared region is highly attractive. Here we implement a mid-infrared frequency upconversion detector for counting and resolving photons at 3 μm. Thanks to the spectrotemporal engineering of the involved optical fields, the mid-infrared photons could be spectrally translated into the visible band with a conversion efficiency of 80%. In combination with a silicon avalanche photodiode, we obtained unprecedented performance with a high overall detection efficiency of 37% and a low noise equivalent power of 1.8×10−17  W/Hz1/2. Furthermore, photon-number-resolving detection at mid-infrared wavelengths was demonstrated, for the first time to our knowledge, with a multipixel photon counter. The implemented upconversion detector exhibited a maximal resolving photon number up to 9 with a noise probability per pulse of 0.14% at the peak detection efficiency. The achieved photon counting and resolving performance might open up new possibilities in trace molecule spectroscopy, sensitive biochemical sensing, and free-space communications, among others.

Mid-infrared photon counting and resolving via efficient frequency upconversion

We demonstrate highly sensitive photon counting in the infrared region based on two-photon absorption (2PA) in a silicon avalanche photodiode, where the required photon energy for inducing effective conductivity is provided by an intense midinfrared (MIR) field at 3 $\ensuremath{\mu}\mathrm{m}$. The used MIR pumping scheme can not only benefit from the enhanced 2PA coefficient in the nondegenerate regime, but also eliminate the detrimental background noises due to the pump harmonic excitation of the pump. Consequently, the enhancement factor for the signal counting rate unprecedentedly reached about ${10}^{5}$ with input infrared pulses at the femtojoule level. Additionally, the noise equivalent power is substantially improved by 2 orders of magnitude in comparison to conventional schemes with near-infrared pumping. Therefore, the presented configuration might provide an alternative to realize sensitive infrared detection and imaging with desirable features of room-temperature operation, no phase-matching requirement, and broadband responding window, which can find a variety of applications, including remote ranging, sensitive sensing, biochemical imaging, and trace spectroscopy.

Jianan Fang

Papers

Mid-infrared photon counting and resolving via efficient frequency upconversion

Wide-field mid-infrared single-photon upconversion imaging

Mid-Infrared Single-Photon Edge Enhanced Imaging Based on Nonlinear Vortex Filtering

Highly Sensitive Detection of Infrared Photons by Nondegenerate Two-Photon Absorption Under Midinfrared Pumping

High-precision passive stabilization of repetition rate for a mode-locked fiber laser based on optical pulse injection