Low Pump Power Research Articles

Automotive Silicon Carbide Power Module Cooling With a Novel Modular Manifold and Embedded Heat Sink

Abstract The next generation of integrated power electronics packages will implement wide-bandgap devices with ultrahigh device heat fluxes. Although jet impingement has received attention for power electronics thermal management, it is not used in commercial electric vehicles (EVs) because of the associated pressure drop and reliability concerns. In this paper, we present a modular thermal management system designed for automotive power electronics. The system achieves superior thermal performance to benchmarked EVs while adhering to reliability standards and with low pumping power. The system utilizes a low-cost and lightweight plastic manifold to generate jets over an optimized heat sink, which is embedded in the direct-bonded-copper (DBC) substrate. The embedded heat sink concept leverages additive manufacturing to add elliptical pin fins to the DBC substrate. The heat sink geometry is optimized for submerged jet impingement using a unit-cell model and an exhaustive search algorithm. The model predictions are validated using unit-cell experiments. A full-scale power module model is then used to compare the DBC-embedded heat sink against direct DBC cooling and baseplate-integrated heat sinks for single-sided (SS) and double-sided (DS) cooling concepts. Using the SS and DS DBC-embedded cooling concepts, the models predict a thermal resistance that represents a reduction of 75% and 85% compared to the 2015 BMW i3, respectively, for the same water-ethylene glycol inverter flowrate. We have shown that an inverter with a 100-kilo-Watt-per-liter power density is achievable with the proposed design.

Broadband multi-wavelength Brillouin-Raman fiber laser with frequency switching

We purpose and demonstrate the switchable multi-wavelength Brillouin–Raman fiber laser (MBRFL) through a bi-directional Raman pumping scheme. The laser structure is arranged in a linear cavity by including a physical mirror at one side of the cavity. The switching operation for MBRFL with single- and double-wavelength spacing is implemented by optimizing the Raman power distribution through a variable optical coupler. This effect on feedback power of the physical mirror provides the difference between odd- and even-order Stoke lines’ maximum power on different sides of the cavity with 10 GHz and 20 GHz spacing. A 90/10 coupler is found to be the optimal. Up to 460 flat-amplitude lines within only a 0.5-dB flatness range, average −5 dBm Stokes peak power (SPP), 10 GHz frequency spacing, and an average optical signal-to-noise ratio (OSNR) of 26 dB are observed. All the counted laser lines are spread across a 37 nm bandwidth. Simultaneously, 170 Stoke lines with overall −2 dBm SPP, 28 dB OSNR, and 20 GHz frequency spacing are attained on other side of the cavity. These are achieved when the Raman pump power is set only at 900 mW. To date, this is the simplest cavity design with the flattest spectrum and highest output power for both wavelength spacing and excellent OSNR achieved in multi-wavelength fiber lasers that incorporate a single low-power Raman pump unit.

Optomechanical ring resonator for efficient microwave-optical frequency conversion

Phonons traveling in solid-state devices are emerging as a universal excitation for coupling different physical systems. Phonons at microwave frequencies have a similar wavelength to optical photons in solids, enabling optomechanical microwave-optical transduction of classical and quantum signals. It becomes conceivable to build optomechanical integrated circuits (OMIC) that guide both photons and phonons and interconnect photonic and phononic devices. Here, we demonstrate an OMIC including an optomechanical ring resonator (OMR), where co-resonant infrared photons and GHz phonons induce significantly enhanced interconversion. The platform is hybrid, using wide bandgap semiconductor gallium phosphide (GaP) for waveguiding and piezoelectric zinc oxide (ZnO) for phonon generation. The OMR features photonic and phononic quality factors of >1 × 105 and 3.2 × 103, respectively. The optomechanical interconversion between photonic modes achieved an internal conversion efficiency {eta }_{i}=(2.1pm 0.1)% and a total device efficiency {eta }_{{tot}}=0.57{times 10}^{-6} at a low acoustic pump power of 1.6 mW. The efficient conversion in OMICs enables microwave-optical transduction for quantum information and microwave photonics applications.

Dual-Stage Double-Pass Extended L-Band Erbium-Doped Fiber Amplifier with Improved Gain Performance

Extended L-band erbium-doped fiber amplifiers (EDFAs) have attracted much attention in recent years despite their relatively low gain levels. In this paper, a dual-stage extended L-band EDFA with improved gain level is demonstrated by using an Er/Yb/P co-doped fiber-based double-pass structure assisted by a low noise pre-amplifier. High gain levels of up to 48.79 dB at 1566 nm and 20.05 dB at 1621.4 nm are achieved with saturated output power at 1605 nm of 20.58 dBm under a total pump power of only 400 mW. Bandwidths with the gain of more than 20 and 30 dB are reached up to 66 nm (1555.4–1621.4 nm) and 58.4 nm (1557.5–1615.9 nm), respectively. The noise figure benefited by using the low noise pre-amplifier is 5.40 ± 1.55 dB in the 1565–1610 nm range. The wide gain bandwidth, high gain level and relatively low pump power give it great potential for future high-capacity optical fiber communication systems.

Flexible composite film with enhanced upconversion emission for ultrasensitive gas detection

Lanthanide-doped upconversion nanoparticles (UCNPs) were found promising in photovoltaic devices and nanoscale sensing due to their excellent optical properties. However, the low quantum yields severely limit their practical applications. In this work, we reported the enhanced upconversion emission by near-field modulation on all dielectric interfaces. The flexible polystyrene (PS) sphere array @UCNPs composite was fabricated by self-assembly and the NIR excitation can be highly localized and amplified in the array with proper sphere size, thus promoting the upconversion process. Based on this efficient upconversion composite film, the sensing performance on acetic acid gas were discussed in detail. The good linear relationship between the upconversion luminescence intensity and acetic acid concentration can be achieved with a detection limit of 5.2 ppm at room temperature, which is comparable with the best level reported so far. In addition, such optical signal-based sensors possessed other unique advantages such as easy fabrication, high sensitivity, long-term stability, reusability and flexibility. And the fluorescence signal enhancement factor showed less dependence on the excitation power and can emit effectively at low pump power. This all dielectric fluorescent composite with high efficiency and sensing performance can be helpful in biosensor and flexible security label applications.

Polarization-dependent intensity ratios in double resonance spectroscopy.

Double Resonance is a powerful spectroscopic method that unambiguously assigns the rigorous quantum numbers of one state of a transition. However, there is often ambiguity as to the branch (ΔJ) of that transition. Spectroscopists have resolved this ambiguity by using the dependence of the double resonance intensity on the relative polarization directions of pump and probe radiation. However, published theoretical predictions for this ratio are based upon a weak (i.e., non-saturating) field approximation. This paper presents theoretical predictions for these intensity ratios for cases where the pump field is strongly saturating in the two limits of transitions dominated by homogeneous or of inhomogeneous broadening. Saturation reduces but does not eliminate the magnitude of the polarization effect (driving the intensity ratio closer to unity) even with strong pump saturation. For the case of an inhomogeneously broadened line, such as when Doppler broadened linewidth dominates over the power-broadened homogeneous line width, a large fraction of the low pump power polarization anisotropy remains. This paper reports predicted polarization ratios for both linear and circular pump and probe field polarizations. The present predictions are compared with experimental measurements on CH4 ground state → ν3 → 3ν3 transitions recently reported by de Oliveira et al.63 and these are in better agreement than with the weak field predictions.

Ultra-efficient second harmonic generation via mode phase matching in integrated lithium niobate racetrack resonators.

High-efficiency second harmonic generation (SHG) relying solely on intermodal dispersion engineering remains a challenge. Here, we realize highly efficient SHG using a double-waveguide coupled racetrack microring resonator on X-cut lithium niobate on insulator (LNOI), where both pump and second harmonic (SH) approach critical coupling. Through precise temperature tuning, simultaneous pump and SH resonance is attained in the resonator, dramatically enhancing SHG efficiency. With low pump power, a normalized conversion efficiency of 9972%/W is achieved. Moreover, the resonator provides a 25.73 dB enhancement in SHG efficiency compared to a 4 mm straight waveguide with identical phase matching in our experiment. This work enables efficient wavelength conversion and quantum state generation on integrated X-cut LNOI platforms.

Fiber laser strain sensor based on an optical phase-locked loop.

In this Letter, we present a high-strain resolution fiber laser-based sensor (FLS) by a novel optical phase-locked loop (OPLL) interrogation technique based on a root mean square detector (RMSD). The sensor consists of a distributed feedback (DFB) fiber laser as a master laser for strain sensing and a fiber Fabry-Perot interferometer (FFPI) as a reference. The laser carrier locks to the reference by the PDH technique, and the single sideband laser working as a slave laser locks to the DFB sensing element using the OPLL technique, respectively. A strain resolution of 8.19 pε/√Hz at 1 Hz and 35.5 pε in 10 s is achieved in the demonstrational experiments. Significantly, the noise behaves a 1∕f distribution below 0.2 Hz due to the very low pump power for the DFB sensor and an active thermostat testing environment. The proposed OPLL interrogation brings new thinking for the demodulation of FLS. This strain sensor based on FLS has a great performance in strain measurement and can be a powerful tool for geophysical research.

Highly efficient on-chip erbium–ytterbium co-doped lithium niobate waveguide amplifiers

The ability to amplify optical signals is of paramount importance in photonic integrated circuits (PICs). Recently, lithium niobate on insulator (LNOI) has attracted increasing interest as an emerging PIC platform. However, the shortage of efficient active devices on the LNOI platform limits the development of optical amplification. Here, we report an efficient waveguide amplifier based on erbium and ytterbium co-doped LNOI by using electron beam lithography and an inductively coupled plasma reactive ion etching process. We have demonstrated that signal amplification emerges at a low pump power of 0.1 mW, and the net internal gain in the communication band is 16.52 dB/cm under pumping of a 974 nm continuous laser. Benefiting from the efficient pumping facilitated by energy transfer between ytterbium and erbium ions, an internal conversion efficiency of 10% has been achieved, which is currently the most efficient waveguide amplifier under unidirectional pumping reported on the LNOI platform, to our knowledge. This work proposes an efficient active device for LNOI integrated optical systems that may become an important fundamental component of future lithium niobate photonic integration platforms.

A new type of supercontinuum generation in hexagonal lattice C6H6-core PCF with broadband and low-power pump

Most of the spectral bandwidths of previous publications are still limited by high input powers making them economically less than ideal. By using a benzene core (C6H6) photonic crystal fiber (PCF) as a new supercontinuum (SC) light source, it is possible to achieve a very large spectral broadening with hundreds of times lower peak power. Due to the change in the diameter of air holes in the first ring near the core, near-zero flattened dispersion, high nonlinearity and small attenuation can be achieved for spectral broadening. The structural geometries of two C6H6-PCFs are optimized to generate wide SC at low input energy. The SC spectrum produced in 1[Formula: see text]cm long of all dispersion fiber extends from a part of visible light to the near-infrared range at 1.3[Formula: see text][Formula: see text]m wavelength and a small pulse energy of 18[Formula: see text]pJ (or 450[Formula: see text]W of electrical input). The second PCF shows wide soliton-induced SC from 0.8 to 4.2[Formula: see text][Formula: see text]m with 71[Formula: see text]pJ pulse energy (or input power approximately 790[Formula: see text]W) at 1.5[Formula: see text][Formula: see text]m wavelength within a fiber of 12[Formula: see text]cm. The proposed structures have the potential to become a new class of microstructured optical fibers for low-cost, broad-spectrum SC generation.

Transparent nanopaper for ultrashort pulse generation in the near-infrared region.

Transparent nanopaper (T-paper) can be applied in the field of electromagnetic shielding materials, antistatic materials, composite conductive materials, electric pool materials, super capacitors, and thermal management systems. However, this kind of T-paper has not been employed in ultrafast photonics yet. For the first time, to our knowledge, transparent electrical nanopaper is used in fiber lasers, different from the conventional pulsed fiber laser, which operates in the Q-switched regime under low pump power and then in the mode-locked regime under high pump power. Mode-locking is achieved first with a pulse duration of 550fs under low pump power (166mW). When further increasing the pump power up to 198mW, the proposed fiber laser can be converted from a mode-locked to Q-switched state, which is a result of the two-photon absorption effect. The proposed fiber laser based on T-paper can be potentially applied in optical tomography, metrology, spectroscopy, micro-machining technology, and biomedical diagnostics.

A numerical study of battery thermal management system with square spiral ring-shaped liquid cooling plate

The battery thermal management system is critical to the operating safety of power batteries. To alleviate the temperature gradient effect caused by the high local temperature of the battery, a centrally dispersed square-spiral-ring (SSR) mini-channel liquid cooling plate is designed for power batteries in this study. Through the simplification of the battery model, this liquid cooling plate battery thermal management system is investigated numerically. The effects of the number of SSR channel laps, channel width, channel bend radius and inlet mass flow rate on the temperature characteristics of the battery and coolant pressure drop are investigated. The results indicate that increasing the SSR channel laps and narrowing the channel width have a beneficial role in improving the battery and liquid cooling plate temperature distribution. The maximum battery temperature can be significantly dropped and the uniformity of battery temperature distribution can be considerably improved by enhancing the inlet mass flow rate. Moreover, additional branch channels could further improve the uniformity of the temperature distribution and the gradient effect of the battery. The maximum temperature decreases to 33.63 °C and the maximum temperature difference reduces to 6.45 °C during the 2C discharge process at a temperature of 25 °C. Furthermore, the SSR liquid cooling plate with a 5 mm-wide branch channel enables lower maximum battery temperatures and better temperature uniformity with lower pump power consumption than the existing serpentine plate. All these results and evidence provide an option for the development of novel mini-channel liquid cooling plates for battery thermal management.

Prolonged dephasing time of ensemble of moiré-trapped interlayer excitons in WSe2-MoSe2 heterobilayers

The moiré superlattices of transition metal dichalcogenide heterobilayers have a pronounced effect on the optical properties of interlayer excitons (IXs) and have been intensively studied in recent years. However, the impact of moiré potentials on the temporal coherence of the IXs has not yet been investigated in detail. Here, we systematically investigate the coherence properties of both the ensemble of delocalized and the ensemble of localized IXs trapped in moiré potentials of the hexagonal boron nitride encapsulated WSe2-MoSe2 heterostructures. Our low-temperature first-order correlation measurements show that prolonged T2 dephasing times with values up to 730 fs can be obtained from the ensemble of localized IXs under moderate pump powers. We observed up to almost a five-fold increase over the values we obtained from the delocalized IXs, while more than two-fold over the previously reported values of T2 ~ 300 fs from the delocalized IXs. The prolonged values of T2 dephasing times and narrow photoluminescence (PL) linewidths for the ensemble of moiré-trapped IXs compared to delocalized one indicate that dephasing mechanisms caused by exciton-low energy acoustic phonon and exciton-exciton scattering are significantly suppressed due to the presence of localization potentials. Our pump power-dependent T2 results show that ultra-long dephasing times can be expected if the dephasing time measurements are performed with the narrow photoluminescence emission line of a single moiré-trapped IX at a low pump power regime. The prolonged values of IX dephasing times would be critical for the applications of quantum information science and the development of two-dimensional material-based nanolasers.

Low-cost, low-power, clockwork syringe pump

A low-cost ($120 NZD, $75 USD), low-power (1-year battery life), portable, and programmable syringe pump design is presented, which offers an alternative to high-cost commercial devices with limited battery life. Contrary to typical motor-driven syringe pumps, the design utilizes a compression spring coupled with a clockwork escapement mechanism to advance the syringe plunger. Full control over flow-rate and discrete (bolus) deliveries is achieved through actuation of a clockwork escapement using programmable, low-power electronics. The escapement mechanism allows the syringe plunger to advance a fixed linear distance, delivering a dose size of 0.001ml in the configuration presented. The modular pump assembly is easily reconfigured for different applications by interchanging components to alter the minimum dose size. Testing to IEC 60601-2-24(2012), the average error of the clockwork syringe pump was 8.0%, 4.0%, and 1.9% for 0.001ml, 0.002ml, and 0.01ml volumes, respectively. An overall mean error of 1.0% was recorded for a flow-rate of 0.01mlh−1. Compared to a commercial insulin pump, the clockwork pump demonstrated reduced variability but greater average error due to consistent over-delivery. Further development of the design and/or manufacture should yield a device with similar performance to a commercial pump.

Efficiency optimization of E-band bismuth-doped ring-cavity fiber laser with low pump power

We demonstrate an efficient ring-cavity E-band bismuth-doped fiber laser with a low threshold power. The laser output power and efficiency are optimized for two operating wavelengths near the luminescence peak, 1430 nm and 1437.6 nm, by experimentally changing the laser output coupling ratio. Using a single co-propagating 1320 nm laser diode pump and a 100 m long bismuth-doped fiber, we achieve an output power of 114 mW with a slope efficiency of 24.5 % and an OSNR of 64 dB for an optimal coupling ratio of 70 % for a pump threshold below 64 mW. With added spectral tunability, this fiber laser will find application forthe characterization of E-band devices and components, such as optical amplifiers, and experimentation in transmission systems.

Broadband supercontinuum generation in hollow-core photonic crystal fibers infiltrated with chloroform

The chloroform-infiltrated square lattice photonic crystal fibers (PCFs) are designed with the difference of the air hole diameters in the cladding to improve chromatic dispersion and nonlinear properties. Based on numerical simulation results, two optimal structures with flat dispersion, high nonlinear coefficient, and small confinement loss are used for supercontinuum (SC) generation. The first fiber has an all-normal dispersion regime, a nonlinear coefficient of 486.355[Formula: see text]W[Formula: see text].km[Formula: see text] generating an SC spectrum of 640.3[Formula: see text]nm within 30 dB levels at a pump wavelength of 0.945[Formula: see text][Formula: see text]m with peak power as low as 1.44[Formula: see text]kW. With anomalous dispersion properties, the second fiber gives a very broad SC spectrum of 1471.8[Formula: see text]nm within 30 dB levels at a 1.4[Formula: see text][Formula: see text]m pumping wavelength with a peak power of 20[Formula: see text]kW. All-fiber SC sources operating with low-power pump lasers can use these fibers to effectively replace glass-core fibers.

NIR activated Er3+/Yb3+ doped LiYF4 upconverting nanocrystals for photothermal treatment, optical thermometry, latent fingerprint detection and security ink applications

This work reports the upconversion (UC) emission studies on Er3+/Yb3+ doped LiYF4 nanoparticles for radiation-to-heat conversion, optical thermometry using thermally coupled and uncoupled levels, latent fingerprint detection and security ink applications. LiYF4:Er3+/Yb3+ nanoparticles have been synthesized using the thermal decomposition reaction method using oleic acid and 1-octadecane as reaction medium. Crystal phase, crystallinity and size have been investigated using XRD and TEM techniques. UC emission ability of the prepared phosphor was tested using a CW laser source having 980 nm excitation. Under 980 nm excitation, synthesized nanoparticles have shown emission bands around 522 nm, 550 nm and 668 nm corresponding to transitions from 2H11/2, 4S3/2, and 4F9/2 levels to 4I15/2 level of Er3+ ions, respectively. Further, the number of photons involved in the UC process has been calculated using a pump power UC study. Decay time analysis of the most intense green (550 nm) and red (668 nm) emission bands is performed to study the emission dynamics. A study on the radiation-to-heat conversion phenomenon has revealed photothermal conversion efficiency of 29.5% which is important for photothermal therapy. The green and red UC emissions from the sample under stimulation at very low pump power (35 mW) are used to study the optical temperature sensing characteristics. The findings of this study suggest that the Er3+/Yb3+ co-doped LiYF4 phosphor may be particularly useful for creating NIR to visible upconversion and temperature sensing. Moreover, latent fingerprint detection and security ink for anti-counterfeiting applications are also demonstrated.

Low threshold photon avalanche upconversion emission for temperature sensing based on Yb(III)/Er(III) Co-doped NdVO4 with sphere 3D self-assembled structure microparticles

Upconversion luminescent microcrystals (UCMs) due to their optical characteristics have been applicated in temperature detecting fields. However, the accuracy of traditional temperature probes based on UCMs is limited by the low intensity of upconversion luminescence (UCL). Herein, Yb3+ and Er3+ ions co-doped NdVO4 (NdVO4:Yb/Er) UCMs with a 3D self-assembled structure were designed via a hydrothermal method. This innovative structure enables the realization of a photon avalanche (PA) emission process. The Yb3+ and Er3+ co-doping in NdVO4:Yb/Er UCMs significantly reduces the PA threshold compared to NdVO4:Er UCMs. Obvious PA process produced by Yb3+/Er3+ doping is observed at low excitation threshold (～13 mW) in NdVO4:Yb/Er UCMs, enhancing the whole UCL intensity. Additionally, the NdVO4:Yb/Er UCMs exhibit a high temperature sensitivity of 3.5% K−1 at low pump power, indicating that UCMs have the potential application in optical temperature sensor.

Characterization of NbTiN Films With Thicknesses Below 20 nm for Low Power Kinetic Inductance Amplifiers

A quantum-limited amplification chain is a fundamental advantage for any application that may benefit from the detection of very faint signals. Reading out arrays of superconducting detectors (TESs or MKIDs), resonant cavities, or qubits, calls for large bandwidth amplifiers in addition to having the lowest possible noise. At millikelvin temperatures, Kinetic Inductance Traveling-Wave Parametric Amplifiers (KI-TWPAs) working in 3-way-mixing (3WM) and fabricated from a 20 nm thick NbTiN film have shown promising noise performances, as they can operate close to the quantum limit [1]. However, they still require fairly high pump power. Devices that would require lower pump power would be easier to implement in readout chains, could reach the quantum limit and they would be compatible with qubit readout. A possible solution for obtaining this optimal configuration is to use a thinner superconducting film. In this work we explore the properties of NbTiN films with a thickness less than 20 nm and we report the obtained experimental characterizations in terms of critical temperature, normal resistivity, and kinetic inductance. A new design for a 3WM KI-TWPA amplifier, based on these developed superconducting films, is introduced and discussed.

On the cooling performance and entropy generation characteristics of a heat sink under ultrasonic vibration: Exploring the impact of porous medium

Ultrasonic vibration and porous medium utilization are both proven to be beneficial techniques to improve cooling performance of heat sinks. Present work aims at exploring the impacts of using porous medium in heat sinks under ultrasonic vibration effect on the cooling performance and entropy generation characteristics, hence, the interrelation of these two techniques is evaluated. Simulations are performed for a constant Reynolds number (Re=2000) and ultrasonic vibration frequency (f = 30 kHz), whereas five different porosities (ε=0.75 to 0.95) along with five different pore diameters (dp=1 to 17 mm) determining the permeability of the porous structure are considered. The results are compared to the non-porous case to determine the effects of porous medium on the ultrasonically vibrated heat sink. It is found that using porous medium increases convective heat transfer coefficient by up to 84.5% attaining a temperature reduction of 10.22 K. Low porosity along with high pore diameter attains an effective cooling, while high porosity with high pore diameter ensures lower pumping power requirement, which is only 1.2-folds of the non-porous case. Frictional entropy generation rises by up to 23% due to porous structure restricting fluid flow depending on its porosity and permeability, while thermal entropy generation can be even decreased below that of non-porous case by 8% with appropriate choice of parameters. Yet, considering the total irreversibility, the frictional entropy generation is significantly dominant compared to the thermal entropy generation. Overall, using ε=0.95 and dp=17 mm along with 30 kHz of ultrasonic vibration is recommended for significantly enhanced heat transfer together with lowest possible pressure drop penalty and low thermal entropy generation.