Pump Light Research Articles

Steering Nonlinear Chiral Valley Photons Through Optical Orbit–Orbit Coupling

AbstractTwo‐dimensional transition metal dichalcogenides feature a direct tunable bandgap and robust spin‐valley coupling, offering an additional valley degree of freedom for information carriers. While optical spin‐orbit coupling has traditionally facilitated valley manipulation, on‐chip control of nonlinear valley photons remains elusive. Here, the directional coupling of nonlinear chiral valley photons through optical orbit‐orbit coupling in monolayer tungsten disulfide at room temperature is demonstrated. The chirality of nonlinear valley photons is governed by the spin angular momentum of the pump light, adhering to nonlinear selection rules. Importantly, the coupling direction is controlled by the orbital angular momentum of the pump light, facilitated by the orbital momentum flux. This approach not only provides a novel method for manipulating the valley degree of freedom but also enhances the flexibility of directing valley photon emission and on‐chip routing. These developments hold promising prospects for advanced valley optoelectronic devices.

Mid-infrared enhanced Raman soliton generation in an erbium-doped ZBLAN with record energy and peak power

The advancement of tunable ultrafast sources in the mid-infrared spectrum would bring about significant progress in various scientific fields. This study suggests a gain-modulation technique to increase the peak power and pulse energy of mid-infrared tunable Raman solitons. By utilizing a high-power 2-2.23 µm Raman soliton pulse as a pump source, mid-infrared Raman solitons within the 2-3.2 µm tuning range can be generated in a segment of Er3+: ZBLAN fiber. Additionally, the introduction of 976 nm pump light into the Er3+: ZBLAN fiber leverages the gain of Er3+ to amplify the frequency shift velocity and pulse energy of the Raman soliton. Consequently, the frequency shift range of the Raman soliton is extended to 3.5 µm, with peak power and pulse energy reaching 0.93 MW and 107 nJ, respectively. These achievements represent the highest peak power and energy levels of Raman solitons generated in mid-infrared fibers to date.

Tunable silicon integrated quantum light source with on-chip FSR-free filters

In this work, we design and fabricate a telecom band quantum light source (QLS) on a silicon photonic chip, which integrates a piece of a long silicon waveguide as the nonlinear medium for spontaneous four-wave mixing (SFWM) and five narrow FSR-free bandpass filters based on a grating-assisted contra-directional coupler (GACDC). Two optical filtering functions of the silicon integrated QLS have been demonstrated. First, the QLS supports two tunable outputs of photon pair generations by four GACDC filters. A wavelength tunable range of 6 nm is demonstrated. Second, one GACDC bandpass filter is designed as an on-chip pump filter before the silicon waveguide. The performances of the QLSs with and without the on-chip pump filter are measured and compared. It shows that the on-chip pump filter has the effect to enhance the performance of the QLS by suppressing the Raman noise photons generated when a pump light propagated in optical fibers before it is injected into the chip. These results show that FSR-free filters would play important roles in developing silicon integrated QLSs.

Chiral polaritons in semiconductor perovskite metasurface enhanced by bound states in the continuum

Abstract The exploration of novel chiral optical platforms holds both fundamental and practical importance, which have shown great promise towards applications in valleytronics, chiral sensing and nanoscopic chiroptics. In this work, we combine two key concepts — chiral bound states in the continuum and exciton polaritons — to showcase a strong chiral response from polaritons. Using the Finite Element Method, we numerically design a CsPbBr3 based metasurface that supports intrinsically chiral bound states in the continuum and verify the chirality by calculating the reflection spectrum and eigen-polarization mapping. We further demonstrate chirality-dependent exciton polariton angular dispersion arising from the strong coupling between the chiral BIC and excitons in CsPbBr3 through simulating the polariton angle-resolved absorption spectrum. Reciprocity analysis reveals that the polariton photoluminescence in different momentum space locations is selectively enhanced by chiral pumping light. Our results suggest a promising first step towards chiral polaritonics.

A Dynamic Hybrid Luminescent Display for Multilevel Anticounterfeiting

AbstractIncorporating specific motifs to provide tangible evidence of authenticity is a direct and effective measure against counterfeiting. However, achieving multi‐level anticounterfeiting through multiple motifs requires utilizing numerous stimulus sources to configure region‐specific emissions with customizable colors, which is complex, costly, and inaccessible. To address this challenge, a hybrid luminescent display is developed by integrating an internal down‐conversion layer with an organic light‐emitting diode (OLED). The internal down‐conversion layer can effectively extract the substrate and waveguide modes, resulting in a very rare outcome where the efficiency of a hybrid down‐conversion white OLED exceeds that of the pump light source. More importantly, by combining voltage‐modulated color‐tunable electroluminescence (EL) with EL‐induced down‐conversion luminescence, this unique design can precisely create dynamic and configurable multi‐color display patterns using only electrical stimulation. For anticounterfeiting purposes, the further amalgamation of the dynamic hybrid luminescent display device with the Internet of Things for digital authentication, and with fingerprint features for physical unclonable functions showcases unprecedented security. These results herald a new generation of multilevel luminescent anticounterfeiting technology.

750 nm laser based on an BaGa4Se7 optical parametric oscillator

The red edge effect of plants is extensively utilized in vegetation remote sensing, particularly by applying hyperspectral LiDAR (HSL) technology. This technology effectively captures spectral information from targets together with range measurements by processing recorded waveforms in the red-edge spectral bands. Despite its widespread use, there is still potential for enhancing the tuning accuracy and the energy output of each channel. What we believe to be a novel nonlinear crystal, BaGa4Se7 (BGSe), has been employed to achieve laser output in the red edge spectral band with a wide tuning range and high tuning precision for the first time. Successful generation of laser radiation at 1512 nm was achieved, with an angular tuning resolution of 35.9 nm/°. When the pump light energy was 17.81 mJ, the energy of the 1512 nm near-infrared laser was 3.210 mJ, with a slope efficiency of 31.2% and an optical-to-optical conversion efficiency (pump to signal) of 18.0%. Subsequent pumping of the second harmonic generation crystal KTiOPO4 (KTP) with the 1512 nm laser output from the BGSe optical parametric oscillator (OPO) facilitated the generation of 756 nm red light laser output. Angle tuning of the BGSe OPO eventually enabled the tunable output of the red edge spectral laser ranging from 701 nm to 780 nm with output energy of approximately 2 mJ, which is several orders of magnitude higher than traditional supercontinuum laser source solution. Such improvement becomes a solid cornerstone for long-range HSL applications.

Dual-channel bistability modulation in a bilayer graphene-based optomechanical system.

We propose a flexible scheme for studying linear absorption response and optical bistability (OB) in a bilayer graphene-based optomechanical system. The results show that as the coupling between the G-mode phonon and excitons is turned on, the linear absorption spectrum will evolve from a single-peaked structure to a two-peaked one, and the spacing between two splitting peaks is equal to twice as large as the phonon-exciton coupling strength. Especially, we plot bistability phase diagrams within the system's parameter subspaces, demonstrating that the bistable switch can be controlled via no, single, or dual-channel by changing the intensity of the pump light in a weak phonon-exciton coupling regime. This holds promise for developing precision-measuring nanodevices and multi-channel optical bistable switches.

Modal phase-matching in thin-film lithium niobate waveguides for efficient generation of entangled photon pairs

Thin-film lithium niobate (TFLN) waveguides have emerged as a pivotal platform for on-chip spontaneous parametric down-conversion (SPDC), serving as a crucible for the generation of entangled photon pairs. The periodic poling of TFLN, while capable of generating high-efficiency SPDC, demands intricate fabrication processes that can be onerous in terms of scalability and manufacturability. In this work, we introduce a novel approach to the generation of entangled photon pairs via SPDC within TFLN waveguides, harnessing the principles of modal phase-matching (MPM). To address the challenge of efficiently exciting pump light typically in a higher-order mode, we have engineered a mode converter that couples two asymmetrically dimensioned waveguides. This converter adeptly transforms the fundamental mode into a higher-order mode, demonstrating a conversion loss of 1.55 dB at 785 nm with a 3 dB bandwidth exceeding 30 nm. Subsequently, we have showcased the device’s capabilities by characterizing the pair generation rate (PGR), coincidences-to-accidentals ratio (CAR), and spectral profile of the entangled photon source. Our findings present a simplified and versatile method for the on-chip generation of entangled photon sources, which may pave the way for the application in the realms of quantum information processing and communication technologies.

High-pulse-energy ultrafast 3 µm laser generation through OPG/DFG in PPMgLN

Abstract We report high-pulse-energy ultrafast 3 µm laser generation through optical parametric generation/difference frequency generation (OPG/DFG) in periodically poled magnesium-oxide-doped lithium niobate (PPMgLN). A commercial 1030 nm femtosecond laser is applied as the pump light and a homemade broadband nanosecond pulse laser around 1580 nm is used as the signal light in DFG. The broadband 1580 nm laser has a master oscillator power amplifier (MOPA) structure with a directly modulated superluminescent light-emitting diode (SLED) as the pulse seed and three stages of Er/Yb fiber amplifiers to lift its average power. A portion of the 1030 nm output pulse is converted to an electronic pulse via a pin detector, which is used as the trigger signal of the SLED driving circuit to ensure synchronization between the signal and the 1030 nm pump pulse. When injecting 2.12 W pump light into the PPMgLN, a broadband mid-infrared (MIR) output of 280 mW can be achieved directly through OPG with a center wavelength around 2.94 μm, a pulse width of 1.38 ps and a pulse repetition frequency of 500 kHz. The corresponding MIR pulse energy is 0.56 µJ. When injecting 2.62 W signal light simultaneously, a MIR output of 300 mW is achieved through the DFG process at the same pulse repetition frequency, corresponding to a pulse energy of 0.6 µJ. The conversion efficiency of the ultrafast pump laser to MIR reaches 14.1%. This high-pulse-energy 3 μm ultrafast laser has great prospects for applications in biological tissue ablation.

Raman-phonon-polariton condensation in a transversely pumped cavity

Phonon polaritons are hybrid states of light and matter that are typically realised when optically active phonons couple strongly to photons. We suggest a new approach to realising phonon polaritons, by employing a transverse-pumping Raman scheme, as used in experiments on cold atoms in optical cavities. This approach allows hybridisation between an optical cavity mode and any Raman-active phonon mode. Moreover, this approach enables one to tune the effective phonon–photon coupling by changing the strength of the transverse pumping light. We show that such a system may realise a phonon-polariton condensate. To do this, we find the stationary states and use Floquet theory to determine their stability. We thus identify distinct superradiant and lasing states in which the polariton modes are macroscopically populated. We map out the phase diagram of these states as a function of pump frequencies and strengths. Using parameters for transition metal dichalcogenides, we show that realisation of these phases may be practicably obtainable. The ability to manipulate phonon mode frequencies and attain steady-state populations of selected phonon modes provides a new tool for engineering correlated states of electrons.

Optical Properties and Applications of Diffraction Grating Using Localized Surface Plasmon Resonance with Metal Nano-Hemispheres.

This study investigates the optical properties of diffraction gratings using localized surface plasmon resonance (LSPR) with metal nano-hemispheres. We fabricated metal nano-hemisphere gratings (MNHGS) with Ga, Ag, and Au and examined their wavelength-selective diffraction properties. Our findings show that these gratings exhibit peak diffraction efficiencies at 300 nm, 500 nm, and 570 nm, respectively, corresponding to the LSPR wavelengths of each metal. The MNHGs were created through thermal nanoimprint and metal deposition, followed by annealing. The experimental and simulation results confirmed that the MNHGs selectively diffract light at their resonance wavelengths. Applying these findings to third-order nonlinear laser spectroscopy (MPT-TG method) enhances measurement sensitivity by reducing background noise through the selective diffraction of pump light while transmitting probe light. This innovation promises a highly sensitive method for observing subtle optical phenomena, enhancing the capabilities of nonlinear laser spectroscopy.

Subsurface Spectroscopy of Thermal Degradation Inside an Inert Plastic Bonded Explosive (PBX) Simulant Using Feedback-Assisted Wavefront Shaping.

We characterize the subsurface thermal degradation of an inert analog of high-explosive molecular crystals (Eu:Y(acac)3(DPEPO)) (EYAD) embedded inside of a plastic bonded explosive simulant using feedback-assisted wavefront shaping-based fluorescence and Raman spectroscopies. This technique utilizes wavefront shaping to focus pump light inside a heterogeneous material onto a target particle, which significantly improves its spectroscopic signature. We find that embedding the EYAD crystals in the heterogeneous polymer results in improved thermal stability, relative to bare crystal measurements, with the crystal remaining fluorescent to >612 K inside of the heterogeneous material, while the bare crystal's fluorescence is fully quenched by 500 K. We hypothesize that this improvement is due to the polymer restricting the effects of EYAD melting, which occurs at 400 K and is the primary mechanism for spectroscopic changes in the temperature range explored.

A low heat release cladding pump coupler

Few-mode erbium-doped fiber amplifiers (FM-EDFAs) have opened up the possibility of realizing the next generation of high-capacity, high-rate communication systems. However, the leakage of pump light during continuous operation of the FM-EDFA is likely to cause the temperature of the cladding pump coupler to be too high and thus destabilize the amplifier. In this work, a low heat release cladding pump coupler was designed and the corresponding FM-EDFA was constructed. The cladding pump coupler in the 8 hours of continuous operation of the FM-EDFA is at 27.8 °C for maximum, 23.7 °C for minimum, and 26 °C for average temperatures, respectively, which are in a low-temperature safe transmission state. The FM-EDFA performance test was performed on this basis, and the results show that when the input pump power is 7 W, the maximum gain fluctuation of each mode of FM-EDFA at 1550 nm in 0∼8 hours is only 1.5 dB, the gain of all modes is greater than 23 dB and the differential mode gain (DMG) is less than 2 dB. In addition, the FM-EDFA still has good performance in the C-band after 8 hours of continuous operation. The gain for all modes is greater than 21 dB, DMG is less than 2 dB, and wavelength flatness is 3.6 dB. The low heat release cladding pump coupler is conducive to the stable amplification transmission of FM-EDFA, which is of great significance to achieving the upgrading and expansion of the communication system.

Metalorganic Vapor‐Phase Epitaxy of +c/−c GaN Polarity Inverted Bilayer for Transverse Quasi‐Phase‐Matched Wavelength Conversion Device

Photon‐pair generation based on optical parametric down‐conversion has attracted for the application as a light source for quantum information. Highly efficient wavelength‐conversion devices require a polarity‐inversion structure when using nitride semiconductors. A transverse quasi‐phase‐matching (QPM) polarity‐inverted GaN bilayer channel waveguide device is suitable for efficient wavelength conversion. This study designed a cross‐section device to satisfy the modal dispersion phase‐matching condition between the TM02 mode pump light and the TM00 mode signal/idler light. Moreover, an AlN oxidation interlayer fabricates the Ga‐polar/N‐polar (+c/−c) GaN layers via metalorganic vapor‐phase epitaxy (MOVPE). A 145 nm thick film layer with a macro‐step‐free surface is grown by optimizing the −c‐GaN growth conditions and reducing the substrate off‐angle to 0.2°. Next, the AlN layer is oxidized in an electric furnace and MOVPE is used to regrow a 1500 nm thick +c‐GaN layer. A macrosteps‐free surface can be achieved by reducing the off‐angle to 0.2° and optimizing the −c‐GaN growth conditions to avoid hillock formation. These results pave the way for improving the efficiency of GaN transverse QPM wavelength‐conversion devices.

Dual-mode multifunctional switchable polarization conversion metasurface based on VO2, Si, and graphene in THz region

In this paper, a dual-mode multifunctional switching terahertz metasurface polarization converter based on vanadium dioxide (VO2), photosensitive semiconductor silicon (Si) and graphene is designed. The converter can switch between transmission and reflection modes by adjusting the state of VO2. In the insulating state of VO2, the converter operates in transmission mode and performs linear-to-linear polarization conversion (LTL-PC) with a relative bandwidth of 166.0 %. Conversely, when VO2 is in the metallic state, the converter works in reflection mode. By adjusting the pump light intensity to modulate the state of Si, linear-to-circular polarization conversion (LTC-PC) and LTL-PC function can be achieved. Moreover, the Fermi level of graphene can be adjusted via electrostatic gate to further enhance the working bandwidth of the converter. In reflection mode, the relative bandwidths for LTL-PC, linear to left-circularly and right-circularly polarization conversion are 98.1 %, 87.0 % and 4.0 %, respectively. The metasurface polarization converter proposed in this paper has a variety of functions and a variety of control modes, and has the advantages of high polarization conversion rate and wide operating band, showing great potential in switching and tunable wideband terahertz converters and related applications.

Enhancing the sensitivity of spin-exchange relaxation-free magnetometers using phase-modulated pump light with external Gaussian noise

An optical pumping scheme is proposed for reducing the gradient of electron spin polarization and suppressing light source noise in a spin-exchange relaxation-free magnetometer. This is achieved by modulating only the phase of a narrow-linewidth pump light field with external Gaussian noise. Compared to the absence of phase modulation, the uniformity of electron spin polarization was improved by over 40%, and the light-frequency noise suppression ratio of the magnetometer was enhanced by 4.3 times. Additionally, the response of the magnetometer was increased by 54%, resulting in a sensitivity of 0.34 fT/Hz1/2 at 30 Hz. The applicability of this scheme can extend to other optical pumping experiments involving large atom ensembles requiring uniform electron spin polarization distribution, which is beneficial for developing ultra-high sensitivity and high stability magnetometers essential for magneto-cardiography and magneto-encephalography research applications.

Narrow peaks in excitation spectrum of alkali spin polarization: non-adiabatic case of spin dynamics

We theoretically describe the phenomenon of non-adiabatic spin dynamics, which occurs in a gas cell filled by alkali vapor in the presence of a strong alternating magnetic field and pump light. Steep increase of the spin polarization occurs if the frequency of the magnetic field is equal to the certain value. The observable effect relies on the periodic field that consists of two perpendicular components defined by harmonics with the same amplitudes and different frequencies. The considered effect of the coherent spin motion cannot be explained by a resonance, because the Larmor precession is absent without a constant component of magnetic field. Moreover, there are some clearly visible peaks in the excitation spectrum of spin polarization, which are narrow in comparison to the relaxation rate. Detailed analysis according to proposed quantum model results in the reasoning of the effect via qualitative properties of non-adiabatic dynamics of atomic spin.

Doping engineering of NiO–Zn nanofilms for modulation of morphological structure and ultrafast nonlinear optical response at 515 nm

In this work, to investigate the metal doping on the third-order nonlinear optical properties of NiO thin films under femtosecond pulsed laser excitation, pure NiO and 2w,4w,6w,8w Zn doped-NiO nanofilms were prepared by DC-RF co-sputtering technique. Then, the nonlinear absorption properties and nonlinear refractive properties of the five samples were investigated using the femtosecond laser at a wavelength of 515 nm. The experimental results show that the nonlinear absorption and nonlinear refractive properties of NiO are enhanced by the doped metal as well as the effect of defects. In addition, by varying the pump light intensity, we observed the transition of nonlinear absorption from the coexistence of saturated absorption and reverse saturated absorption to reverse saturated absorption. We established a multi-energy level system to interpret the nonlinear absorption and nonlinear refractive results, which broadens the application of NiO thin films in the field of nonlinear optics.

Generating tunable picosecond pulses at 900 nm directly from the all-fiber structured parametric oscillator

In this work, we present an all-fiber structured parametric oscillator capable of directly generating pulses within the 900 nm wavelength range. Leveraging the four-wave mixing effect within photonic crystal fibers, the oscillator converts the 1030 nm pump light into two distinct sidebands centered at 900 nm and 1250 nm. Employing time-dispersion-tuning techniques, we achieved a remarkable continuously tunable wavelength range spanning 60 nm, from 865 nm to 925 nm. These pulses exhibited a pulse width of 3.2 ps and a peak power of 500 W at 900 nm, with a repetition rate of 30.6 MHz.

Highly sensitive optical thermometer based on Li+-doped erbium ytterbium silicate films

This work provides a new material, Li+-doped erbium ytterbium silicate, with reliable and high temperature sensing sensitivity for optical thermometers. The Li+-doped erbium ytterbium silicate films were prepared by RF magnetron sputtering. The film shows strong green visible emission, which is related to the radiation transitions from thermally coupled energy levels 2H11/2, 4S3/2 to 4I15/2. Lithium doping reduces the field symmetry around erbium and improves the radiation transition efficiency, and Yb doping improves the pump light absorption. Lithium or ytterbium is advantageous to enhance up-conversion luminescence and temperature sensing sensitivity of erbium ions. Therefore, the temperature dependence of green up-conversion luminescence in the range of 80–460 K of the Li+-doped erbium ytterbium silicate films have been found to be a promising optical thermometer material with a high relative sensitivity of 16.9 % K−1, which is higher than the optimum value of other Er3+ materials. In addition, we have provided a preliminary temperature measurement scheme based on the Li+-doped erbium ytterbium silicate film.