Frequency Up-conversion Research Articles

Optical Single-Sideband Generation by Dual-Stage Four-Wave Mixing Bragg Scattering

In this letter, we propose a novel approach for optical single-sideband (SSB) generation by utilizing four-wave mixing Bragg scattering (FWM-BS). The scheme comprises three stages: the initial FWM-BS stage, the spectral phase control stage, and the final FWM-BS stage. Constructive or destructive interference can occur between the sidebands generated in the two FWM-BS stages, depending on the spectral phase mask applied between the stages. By applying an appropriate phase mask, one sideband can be eliminated by destructive interference, while the other sideband is magnified by constructive interference, thus realizing SSB generation. Both upconverted and downconverted SSB generations can be achieved. To verify the scheme, we experimentally demonstrate 50-GHz optical frequency upconversion and downconversion separately for multi-channel 16-Gbaud QPSK signals.

Characterization of the NEP of Mid-Infrared Upconversion Detectors

We present a scheme to estimate the noise equivalent power (NEP) of the frequency upconversion detectors (UCDs), detecting mid-infrared (MIR) light. The NEP of the UCD is a combined contribution of NEPs from the upconversion process and from the photodetector, used for detecting the upconverted signal. The 2–5- $\mu \text{m}$ MIR range is particularly investigated in this letter using a bulk periodically poled lithium niobate-based CW-intracavity UCD. We measured the NEP of UCD as 20 fW/ $\sqrt {\text {Hz}}$ at the MIR wavelength of $3.39~\mu \text{m}$ . Here, we showed that the limiting factor is not the noise from the upconversion process (estimated NEP is 2.3 fW/ $\sqrt {\text {Hz}}$ at $3.39~\mu \text{m}$ ) but from the electrical noise in the photodetector itself. We also compared the performance of our UCD with the previously published results and with market available direct MIR detectors. In addition, we measured the optical noise of the UCD over its working spectral range (2.9– $3.6~\mu \text{m}$ ) and compared with the numerical simulation.

Nonlinear response in a noncentrosymmetric topological insulator

Nonlinear phenomena are inherent in most systems in nature. Second or higher-order harmonic generations, three-wave and four-wave mixing are typical phenomena in nonlinear optics. To obtain a nonzero signal for second-harmonic generation in the long-wavelength limit ($q\rightarrow0$), the breaking of inversion symmetry is required. In topological materials, a hexagonal warping term which breaks the rotation symmetry of the Fermi surface is observed by angular-resolved photo-emission spectroscopy (ARPES). If a gap opens (e.g., by doping with magnetic impurities) the inversion symmetry will be broken. Here we use a nonlinear response theory based on a generalized Kubo formula to explain the frequency up-conversion in topological materials.

A Microwave Polarimeter Demonstrator for Astronomy with Near-Infra-Red Up-Conversion for Optical Correlation and Detection.

This paper presents a 10 to 20 GHz bandwidth microwave polarimeter demonstrator, based on the implementation of a near-infra-red frequency up-conversion stage that allows both the optical correlation, when operating as a synthesized-image interferometer, and signal detection, when operating as a direct-image instrument. The proposed idea is oriented towards the implementation of ultra-sensitive instruments presenting several dozens or even thousands of microwave receivers operating in the lowest bands of the cosmic microwave background. In this work, an electro-optical back-end module replaces the usual microwave detection stage with Mach–Zehnder modulators for the frequency up-conversion, and an optical stage for the signals correlation and detection at near-infra-red wavelengths (1550 nm). As interferometer, the instrument is able to correlate the signals of large-format instruments, while operating as a direct imaging instrument also presents advantages in terms of the possibility of implementing the optical back end by means of photonic integrated circuits to achieve reductions in cost, weight, size, and power consumption. A linearly polarized input wave, with a variable polar angle, is used as a signal source for laboratory tests. The receiver demonstrator has proved its capabilities of being used as a new microwave-photonic polarimeter for the study of the lowest bands of cosmic microwave background.

Germanium oxide glass based metal-dielectric nanocomposites: fabrication and optical characterization: a review of new developments

We review recent experimental results with germanate glasses containing rare-earth ions (RE) and silver nanoparticles (Ag-NPs) nucleated by appropriate heat-treatment of samples. In one study, the photoluminescence (PL) due to an infrared-to-visible frequency upconversion (UC) process was investigated in Bi2O3–GeO2 (BGO) glasses co-doped with ytterbium (Yb3+) and erbium (Er3+) ions when low concentration of AgNO3 was added to the starting glass composition. By exciting the samples at 980 nm, in resonance with the Yb3+ transition, we investigated the influence of the Ag-NPs on the UC process. The Er3+ PL was enhanced, up to 100%, due to the increased local-field sensed by the RE and to the efficient Yb3+ → Er3+ energy-transfer. In another set of experiments, we studied the behavior of BGO glasses containing thulium ions (Tm3+) and Ag-NPs. The role of energy-transfer from bismuth centers to Tm3+ was investigated. PL and relative gain enhancements of ≈ 56% and 500%, respectively, were observed due to the influence of Ag-NPs. Using a pump laser operating at 808 nm (6 W) and a probe laser at 1470 nm (0.6 mW) the relative gain measured at 1470 nm was 4.5 dB/cm. The results from the two sets of experiments indicate that Yb3+/Er3+ co-doped BGO glass with Ag-NPs is an efficient upconverter and Tm3+ doped BGO glass with Ag-NPs can be used as efficient optical amplifier in the short-wave infrared region.

Photonic generation of MMW-UWB monocycle and doublet signals based on frequency up-conversion and delay-line filter

A photonic approach to generate millimeter-wave (MMW) ultra-wideband (UWB) monocycle and doublet signals using stimulated Brillouin scattering (SBS) selective sideband amplification technique and delay-line filter is proposed and theoretically analyzed. In the proposed approach, a dual-drive Mach–Zehnder modulator (DDMZM) is used as a first-order differentiator to produce a monocycle UWB signal. Then the generated monocycle signal is single-sideband (SSB) modulated by SBS effect for up-conversion. A balanced photodetector (BPD) is further employed for both photodetection and first-order differentiation. Consequently, an MMW-UWB monocycle signal or an MMW-UWB doublet signal can be attained in electrical field with controlling an optical switch. The frequency spectra of the generated MMW-UWB monocycle and doublet signals meet well with the Federal Communication Committee (FCC) mask with power efficiency of 50.63% and 40.53%. Besides, the produced MMW-UWB signals can be employed to realize multiple modulation formats, such as on–off keying modulation (OOK), pulse position modulation (PPM) and pulse amplitude modulation (PAM).

HV discharges triggered by dual- and triple-frequency laser filaments.

We study the use of frequency upconversion schemes of near-IR picosecond laser pulses and compare their ability to guide and trigger electric discharges through filamentation in air. Upconversion, such as Second Harmonic Generation, is favorable for triggering electric discharges for given amount of available laser energy, even taking into account the losses inherent to frequency conversion. We focus on the practical question of optimizing the use of energy from a given available laser system and the potential advantage to use frequency conversion schemes.

A bio-inspired host-parasite structure for broadband vibration energy harvesting from low-frequency random sources

Energy harvesting for low-power sensing has drawn great attention, but still faces challenges in harnessing broadband random motions. Inspired by the parasitic relationship in plants, a host-parasite vibration harvester is designed to scavenge random low-frequency vibrations by incorporating bi-stability and frequency up-conversion within such a design. A hosting beam is formed in a buckled condition by clamping it at both ends and applying an axial compression load. Two parasitic piezoelectric beams are fixed at the center of the hosting beam and plucked at the free ends by two plectra on the hosting beam, while it oscillates in an inter-well mode. The low-frequency hosting beam oscillation is converted to high-frequency parasitic beam's vibration at resonance due to the plucking effect, allowing the harvester to convert the broadband low-frequency motion into electricity effectively. The electromechanical dynamics are modeled and the design is validated experimentally. The harvester is capable of harnessing low-frequency random vibration (0.0018 g2/Hz @ 5–400 Hz) over a wide bandwidth. More than 1 mJ energy was collected over 100 s under this pseudorandom vibration.

Up-Conversion Imaging Processing With Field-of-View and Edge Enhancement

Spiral phase contrast is an important and convenient imaging processing technology in edge detection, and a broader field-of-view (FOV) of imaging is a long-pursuing aim to see more regions of the illumination objects. Compared with near-infrared (NIR) spectrum, the up-conversion imaging in visible spectrum benefits from the advantages of higher efficiency detection and lower potential speckle. FOV enhanced and spiral phase contrast up-conversion imaging processing methods by using second order nonlinear frequency up-conversion from NIR spectrum to visible spectrum in two different configurations are presented in this work. By changing the temperature of crystal, controllable spatial patterns of imaging with more than 4.5 times enhancement of FOV is realized in both configurations. Additionally, we present numerical simulations of the phenomenon, which agree well with the experimental observations. Our results provide a very promising way in imaging processing, which may be widely used in biomedicine, remote sensing and up-conversion monitoring.

Design methodology of a frequency up-converting energy harvester based on dual-cantilever and pendulum structures

Mechanical frequency up-conversion is a technique whereby a high-frequency oscillation is induced from a low-frequency source and aims to address inherent problems in low frequency vibration energy harvesting. This work presents a novel 1:2:6 internal resonances based frequency up-converting harvester in which the operation frequency is 6 times up-converted. Compared to traditional conceptual mechanisms (e.g. mechanical impact, mechanical plucking, impulsive acceleration), the proposed harvester can operate at much lower acceleration level, the missing of sound during the frequency conversion also reduces the energy consumption. Experimental measurements and theoretical simulations demonstrate that the proposed design can collect energy from ultra-low frequency (< 5 Hz) vibration sources. In addition, the harvester shows very high performance compared to the current state-of-the-art devices, a maximum 2.07 mW of average power is obtained from the fabricated prototype at the excitation frequency and level of 1.71 Hz & 0.19 g, respectively.

Microwave-Photonics Frequency Up-Converter for Telecom and Measurement Equipment

An ultra-wideband tunable frequency converter scheme for microwave and millimeter-wave signal generation based on optical recirculating loop and microwave-photonics technique, is proposed and demonstrated. The scheme consists of standard, commercially available elements such as dual parallel Mach-Zehnder modulator, optical filter, wideband photodiode and does not require ultra-broadband RF components. A recirculating loop acts as an optical frequency comb generator and allows obtaining multiple local oscillator signals at frequencies that significantly higher than the RF reference used. Up-converted signals of frequencies in mm-wave band are demonstrated experimentally with spectra free of spurious products. The converter proposed could be used as an alternative solution to microwave mixers in telecom and measurement equipment.

SHG (532 nm)-induced spontaneous parametric downconversion noise in 1064-nm-pumped IR upconversion detectors.

As a novel technique for infrared detection, frequency upconversion has been successfully deployed in many applications. However, investigations into the noise properties of upconversion detectors (UCDs) have also received considerable attention. In this Letter, to the best of our knowledge, we present a new noise source-second-harmonic generation (SHG)-induced spontaneous parametric downconversion-experimentally and theoretically shown to exist in short-wavelength-pumped UCDs. We investigate the noise properties of two UCDs based on single-pass 1064-nm-pumped periodically poled LiNbO3 bulk crystals. One UCD is designed to detect signals in the telecom band and the other in the mid-infrared regime. Our experimental demonstration and theoretical analysis reveal the basic properties of this newly discovered UCD noise source, including its dependence on crystal temperature and pump power. Furthermore, the principle behind the generation of this noise source can also be applied to other UCDs, which utilize nonlinear crystals either in waveguide form or with different bulk materials. This study may also aid in developing methods to suppress the newly identified noise in future UCD designs.

Nanoscale Vector dc Magnetometry via Ancilla-Assisted Frequency Up-Conversion.

Sensing static magnetic fields with high sensitivity and spatial resolution is critical to many applications in fundamental physics, bioimaging, and materials science. Even more beneficial would be full vector magnetometry with nanoscale spatial resolution. Several versatile magnetometry platforms have emerged over the past decade, such as electronic spins associated with nitrogen vacancy (NV) centers in diamond. Achieving vector magnetometry has, however, often required using an ensemble of sensors or degrading the sensitivity. Here we introduce a hybrid magnetometry platform, consisting of a sensor and an ancillary qubit, that allows vector magnetometry of static fields. While more generally applicable, we demonstrate the method for an electronic NV sensor and a nuclear spin qubit. In particular, sensing transverse fields relies on frequency up-conversion of the dc fields through the ancillary qubit, allowing quantum lock-in detection with low-frequency noise rejection. In combination with the Ramsey detection of longitudinal fields, our frequency up-conversion scheme delivers a sensitive technique for vector dc magnetometry at the nanoscale.

Generation of deep ultraviolet sub-2-fs pulses.

We demonstrate the generation of few-cycle deep ultraviolet pulses via frequency upconversion of 5-fs near-infrared pulses in argon using a laser-fabricated gas cell. The measured spectrum extends from 210 to 340 nm, corresponding to a transform-limited pulse duration of 1.45 fs. We extract from a dispersion-free second-order cross-correlation measurement a pulse duration of 1.9 fs, defining a new record in the deep ultraviolet spectral range.

Tunable microwave generation utilizing monolithic integrated two-section DFB laser

Tunable microwave generation and frequency up-conversion are demonstrated utilizing a monolithically integrated two-section DFB laser. The frequency of the microwave signal is tuned from 13 GHz to 40 GHz, which can be further improved by adjusting the wavelengths of the DFB lasers. Utilizing the sideband optical injection locking technique, frequency-doubled microwave signals with low phase noise of −100.9 dBc/Hz at 10 kHz and narrow linewidth of 102 Hz are obtained. In addition, the tunable range of frequency-doubled and frequency-quadrupled microwave signals are also investigated respectively.

A tunable frequency up-conversion wideband piezoelectric vibration energy harvester for low-frequency variable environment using a novel impact- and rope-driven hybrid mechanism

This paper presents a tunable frequency up-conversion wideband piezoelectric vibration energy harvester using a novel impact- and rope-driven hybrid mechanism, in which a high frequency generating beam is triggered by the rope or impacted directly by the low frequency driving beam. A mass-spring-damper equivalent model was built to understand the operation mechanism of the proposed piezoelectric vibration energy harvester. Based on the theoretical model, the effect of the rope-margin on the performance of the proposed piezoelectric vibration energy harvester was numerically analyzed. Both the simulation and experimental results showed that the central working frequency of the proposed piezoelectric vibration energy harvester can be changed easily from 74.75 Hz to 106 Hz by adjusting the rope-margin from 0.5 mm to 2 mm without any structure re-fabrication. Moreover, a bandwidth 4.2 times wider than the conventional frequency up-conversion piezoelectric vibration energy harvester based on impact-driven mechanism can be achieved. The tunable performance of the proposed piezoelectric vibration energy harvester system make it promising for vibration energy harvesting in wideband environments with low frequency.

On the Frequency Up-Conversion Mechanism in Metamaterials-Inspired Vibro-Impact Structures

Conventional acoustic absorbers like foams, fiberglass or liners are used commonly in structures for industrial, infrastructural, automotive and aerospace applications to mitigate noise. However, these have limited effectiveness for low-frequencies (LF, <~500 Hz) due to impractically large mass or volume requirements. LF content being less evanescent is a major contributor to environmental noise pollution and induces undesirable structural responses causing diminished efficiency, comfort, payload integrity and mission capabilities. There is, therefore a need to develop lightweight, compact, structurally-integrated solutions to mitigate LF noise in several applications. Inspired by metamaterials, tuned mass-loaded membranes as vibro-impact attachments on a baseline structure are considered to investigate their performance as an LF acoustic barrier. LF incident waves are up-converted via impact to higher modes in the baseline structure which may then be effectively mitigated using conventional means. Such Metamaterials-Inspired Vibro-Impact Structures (MIVIS) could be tuned to match the dominant frequency content of LF acoustic sources. Prototype MIVIS unit cells were designed and tested to study energy transfer mechanism via impact-induced frequency up-conversion and sound transmission loss. Structural acoustic simulations were done to predict responses using models based on normal incidence transmission loss tests. Simulations were validated using experiments and utilized to optimize the energy up-conversion mechanism using parametric studies. Up to 36 dB of sound transmission loss increase is observed at the anti-resonance frequency (326 Hz) within a tunable LF bandwidth of about 300 Hz for the MIVS under white noise excitation. Whereas, it is found that under monotonic excitations, the impact-induced up-conversion redistributes the incident LF monotone to the back plate’s first mode in the transmitted spectrum. This up-conversion could enable further broadband transmission loss via subsequent dissipation in conventional absorbers. Moreover, this approach while minimizing parasitic mass addition retains or could conceivably augment primary functionalities of the baseline structure. Successful transition to applications could enable new mission capabilities for aerospace and military vehicles and help create quieter built environments.

Nonlinear optical response of a two-dimensional semi-Dirac system in the terahertz regime

We demonstrate a strong nonlinear optical response in a two-dimensional semi-Dirac system in the terahertz regime. By applying the Boltzmann transport theory for the intra-band process and a quantum mechanics method for the inter band process, we obtained the three-photon current response. It is found that both the intra- and inter-band excitations make significant contributions to the nonlinear response. The third order conductivities (TOCs) are about two magnitudes higher than that of . Interestingly, for the inter-band TOCs, there is a sign change when the chemical potential varies across the saddle point in the conduction band in direction (that is parabolic), due to the competition between the two opposite nonlinear current contributed by the electrons at states and , respectively. Finally, we show that the nonlinear response in the terahertz regime is significant at experimentally accessible field strengths. Our results suggest that this system could be of potential applications in photonic device for frequency up-conversion.

A dual electromagnetic array with intrinsic frequency up-conversion for broadband vibrational energy harvesting

This letter proposes a dual electromagnetic array to transform low frequency rectilinear vibrations into electricity with frequency up-conversion. The free of mechanical contact harvester consists of a rectilinear oscillator (RLO) and an array of two identical rotary oscillators (RTO). The RTO includes a rotor and a stator. The rotor has eight cubic magnets distributed centrosymmetrically, and the stator has eight coils. Under rectilinear vibrational excitations, the RLO drives the rotor of the RTO to rotate through magnetic torque acting on the rotors. A slight fluctuation of the rectilinear motion can lead to a great change of torque, which converts the low frequency vibrations into high frequency rotational motions. By adopting the frequency up-conversion mechanism, a high instantaneous output voltage is produced and maintained from 3.0 Hz to 9.5 Hz. Experiments show that with the dual rotor array, the output power is improved and the RLO is able to oscillate at its resonance even if the input frequency is greater than its resonant frequency, which implies a potential solution to suppress and harvest vibration energy during an earthquake if properly arraying multiple rotors. Under the excitation of 0.5 g and 4.0 Hz, the harvester can provide a stable DC power of 3.1 mW after AC-DC conversion.

A near-infrared frequency upconversion probe for nitroreductase detection and hypoxia tumor in vivo imaging

Nitroreductase (NTR) acts as a detective enzyme that can be used to judge the hypoxic level of solid tumors. To date, only a few optical probes can effectively and selectively monitor NTR in vivo. Therefore, it is important to develop an ideal probe with near-infrared (NIR) excitation and emission for NTR detection and imaging. In this study, we report a NIR frequency upconversion luminescence (FUCL) probe (Cy7-NO2) based on a cyanine structure decorated with an aromatic nitro group to detect NTR in vivo. Cy7-NO2 not only was excited at 850 nm and emitted at 790 nm, but also showed a fast and selective response to NTR. Docking calculations revealed that NTR was able to form hydrogen bonds with Cy7-NO2 and underwent an enzyme-catalyzed reduction reaction. Compared with absorption and the Stokes emission methods, FUCL method exhibited a lower detection limit (3.4 ng mL−1). In addition, Cy7-NO2 was used for FUCL bioimaging of NTR in living cells and mice. All of these results proved that Cy7-NO2 as a FUCL probe supplies a new method for biodetection and bioimaging of NTR in vitro and in vivo.