Upconversion Detection Research Articles

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.

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.

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing.

We present a protocol for performing gas spectroscopy using infrared degenerated four-wave mixing (IR-DFWM), for the quantitative detection of gas species in the ppm-to-single-percent range. The main purpose of the method is the spatially resolved detection of low-concentration species, which have no transitions in the visible or near-IR spectral range that could be used for detection. IR-DFWM is a nonintrusive method, which is a great advantage in combustion research, as inserting a probe into a flame can change it drastically. The IR-DFWM is combined with upconversion detection. This detection scheme uses sum-frequency generation to move the IR-DFWM signal from the mid-IR to the near-IR region, to take advantage of the superior noise characteristics of silicon-based detectors. This process also rejects most of the thermal background radiation. The focus of the protocol presented here is on the proper alignment of the IR-DFWM optics and on how to align an intracavity upconversion detection system.

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing

Compact all-fiber polarization-independent up-conversion single-photon detector

We demonstrate a compact all-fiber polarization-independent up-conversion single-photon detector based on integrated reverse proton exchanged periodically poled lithium niobate waveguides. The horizontally and vertically polarized components of randomly polarized signals are separated with a fiber-coupled polarization beam splitter, launched into two orthogonally polarized polarization maintaining fibers and fetched into two adjacent independent waveguides on the same device. The up-converted outputs from both waveguide channels are then combined with a multi-mode fiber combiner and detected by a silicon detector. With this configuration, the polarization-independent single-photon counting at 1.55 μm is achieved with a system detection efficiency of 29.3%, a dark count rate of 1600 counts per second, and a polarization dependent loss of 0.1dB. This compact all-fiber system is robust and has great application potential in practical quantum key distribution systems.

Facile approach for the periodic poling of MgO-doped lithium niobate with liquid electrodes

Leakage current elimination by the SiO2 dielectric layer for high-quality periodic poling of 76.2 mm-diameter Mg:LN wafers using liquid electrodes.

Numerical investigation of mid-infrared single-photon generation

Single-photon creation through parametric downconversion underpins quantum technology for quantum sensing and imaging. Here we numerically study the creation of single photons in the near- and mid-infrared regime from 1.5 - 12 um in a range of novel nonlinear semiconductor and chalcopyrite materials. We identify phase-matching conditions and single out regimes in which group-velocity matching can be achieved with commercially available pump lasers. Finally, we discuss how mid-infrared single photons can be detected. Using our numerical results, we identify materials and pump lasers for up-conversion detection in conventional wavelength bands. Our study provides a complete recipe for mid-IR single-photon generation and detection, opening up quantum enhancements for mid-IR applications such as bio-medical imaging, communication, and remote sensing.

Enhancing the detectivity of an upconversion single-photon detector by spatial filtering of upconverted parametric fluorescence.

Due to advantages of low dark-count rate, reduced dead-time, and room-temperature operation, single-photon upconversion detectors for the telecom band are gaining strong interest as an alternative to other single-photon counters. In this work, we investigate the spatial and spectral distribution of upconverted spontaneous parametric downconversion (USPDC) noise, which is the typical dominant noise source in short-wavelength-pumped single-photon upconversion detectors for 1.5 µm - 1.6 µm. Our upconversion detector relies on a bulk periodically poled lithium niobate (PPLN) crystal and a 1064 nm intracavity pump system that spectrally translates the signal to the visible (~630 nm) where efficient, uncooled, and low dark-count Si based single-photon detectors operate. Experimental results show that the spectral and spatial distribution of the USPDC noise has a relatively broadband and radially modulated pattern that depends on the PPLN temperature, which is in good agreement with our numerical simulations. We also demonstrate that for narrow-linewidth 1575 nm signal photons, the dark-count rate can be significantly reduced by (1) using a phase-matched signal angle that corresponds to an upconverted output angle where the USPDC noise is at a "local minimum" and (2) applying a spatial filter (instead of an ultra-narrow bandpass filter) at the output. This simple spatial filtering technique resulted in a 14 dB dark-count rate reduction. Due to a corresponding decrease in the interaction length of the signal with the pump, the upconversion efficiency also decreased, but only with a 2.2 dB penalty.

Upconversion single-photon detectors based on integrated periodically poled lithium niobate waveguides [Invited

We demonstrate up-conversion single-photon detectors based on integrated periodically poled lithium niobate waveguides, which incorporate two mode filters and a directional coupler. The two mode filters are optimized for the fiber-waveguide coupling efficiencies for 1550 nm and 1950 nm respectively while the directional coupler plays the role of wavelength combiner, making the overall system portable and low-cost. The two wavelengths pump each other in our detection system. We achieve detection efficiencies of 28% for 1550 nm and 27% for 1950 nm, respectively. This scheme provides an efficient integrated single-photon detection method for any two well-separated spectral bands in the whole low-loss range of lithium niobate waveguides.

Electronically delay-tuned upconversion cross-correlator for characterization of mid-infrared pulses.

In this Letter, a novel method for the characterization of mid-infrared pulses is presented. A cross-correlator system, with no moving parts, combining ultra-broadband pulsed upconversion detection with fast active electronic delay tuning was built to perform time-resolved spectral characterization of 1.6ns mid-infrared supercontinuum pulses. Full wavelength/time spectrograms were acquired in steps of 20ps over a range that can, in theory, extend to microseconds in a matter of seconds, with 48ps temporal resolution and 22 cm-1 spectral resolution in the 2700-4300nm range. This work proves the potential for the use of electronic delay tuning instead of mechanical delay tuning for applications such as cross-correlators and laser spectroscopy, where their fast precise tunability and long delay ranges are a strong asset.

Mode selective up-conversion detection for LIDAR applications.

We study mode selective up-conversion detection as a viable approach to improving signal-to-noise and ranging resolution in LIDAR applications. It involves pumping a nonlinear waveguide at the edge of phase matching with picosecond pulses, so that only the backscattered signal photons in a single or few desirable time-frequency modes are efficiently up-converted while the broadband background noise in all other modes is rejected. We demonstrate a 41-dB increase in the signal-to-noise ratio for single-photon counting compared to that of direct detection using a commercial InGaAs single-photon detector, while achieving sub-millimeter ranging resolution with few detected photons. The proposed technique implies new LIDAR capabilities for ranging and imaging.

Upconversion detection of long-wave infrared radiation from a quantum cascade laser

Broadly tunable upconversion is demonstrated for long-wave infrared (LWIR) detection. The upconversion system is evaluated by the detection of 50 ns pulses from a narrow linewidth tunable quantum cascade laser (QCL) in the 9.4 to 12 µm range. The LWIR signal is mixed with a 1064 nm laser beam in a silver gallium sulfide (AgGaS2) crystal, resulting in an upconverted signal in the 956 to 977 nm range, using angle tuning for optimal phase-matching. This allows for efficient, high speed detection using a standard silicon detector. A theoretical model including absorption and diffraction shows qualitative agreement with experimental data.

Upconversion detector for range-resolved DIAL measurement of atmospheric CH4.

We demonstrate a robust, compact, portable and efficient upconversion detector (UCD) for a differential absorption lidar (DIAL) system designed for range-resolved methane (CH4) atmospheric sensing. The UCD is built on an intracavity pump system that mixes a 1064 nm pump laser with the lidar backscatter signal at 1646 nm in a 25-mm long periodically poled lithium niobate crystal. The upconverted signal at 646 nm is detected by a photomultiplier tube (PMT). The UCD with a noise equivalent power around 127 fW/Hz1/2 outperforms a conventional InGaAs based avalanche photodetector when both are used for DIAL measurements. Using the UCD, CH4 DIAL measurements have been performed yielding differential absorption optical depths with relative errors of less than 11% at ranges between 3 km and 9 km.

Thermal noise in mid-infrared broadband upconversion detectors.

Low noise detection with state-of-the-art mid-infrared (MIR) detectors (e.g., PbS, PbSe, InSb, HgCdTe) is a primary challenge owing to the intrinsic thermal background radiation of the low bandgap detector material itself. However, researchers have employed frequency upconversion based detectors (UCD), operable at room temperature, as a promising alternative to traditional direct detection schemes. UCD allows for the use of a low noise silicon-CCD/camera to improve the SNR. Using UCD, the noise contributions from the nonlinear material itself should be evaluated in order to estimate the limits of the noise-equivalent power of an UCD system. In this article, we rigorously analyze the optical power generated by frequency upconversion of the intrinsic black-body radiation in the nonlinear material itself due to the crystals residual emissivity, i.e. absorption. The thermal radiation is particularly prominent at the optical absorption edge of the nonlinear material even at room temperature. We consider a conventional periodically poled lithium niobate (PPLN) based MIR-UCD for the investigation. The UCD is designed to cover a broad spectral range, overlapping with the entire absorption edge of the PPLN (3.5 - 5 µm). Finally, an upconverted thermal radiation power of ~30 pW at room temperature (~30°C) and a maximum of ~70 pW at 120°C of the PPLN crystal are measured for a CW mixing beam of power ~60 W, supporting a good quantitative agreement with the theory. The analysis can easily be extended to other popular nonlinear conversion processes including OPO, DFG, and SHG.

Comparison of an InSb Detector and Upconversion Detector for Infrared Polarization Spectroscopy.

This paper compares the signal-to-noise ratio obtained using an InSb photodiode for infrared (IR) polarization spectroscopy to that obtained using an upconversion detector, and shows a factor 64 improvement by the change. Upconversion detection is based on using sum frequency generation to move the IR optical signal to near-visible wavelengths to improve the sensitivity.

Single Molecule Upconversion-Linked Immunosorbent Assay with Extended Dynamic Range for the Sensitive Detection of Diagnostic Biomarkers.

The ability to detect disease markers at the single molecule level promises the ultimate sensitivity in clinical diagnosis. Fluorescence-based single-molecule analysis, however, is limited by matrix interference and can only probe a very small detection volume, which is typically not suitable for real world analytical applications. We have developed a microtiter plate immunoassay for counting single molecules of the cancer marker prostate specific antigen (PSA) using photon-upconversion nanoparticles (UCNPs) as labels that can be detected without background fluorescence. Individual sandwich immunocomplexes consisting of (1) an anti-PSA antibody immobilized to the surface of a microtiter well, (2) PSA, and (3) an anti-PSA antibody-UCNP conjugate were counted under a wide-field epifluorescence microscope equipped with a 980 nm laser excitation source. The single-molecule (digital) upconversion-linked immunosorbent assay (ULISA) reaches a limit of detection of 1.2 pg mL-1 (42 fM) PSA in 25% blood serum, which is about ten times more sensitive than commercial ELISAs, and covers a dynamic range of three orders of magnitude. This upconversion detection mode has the potential to pave the way for a new generation of digital immunoassays.

Self-gated mid-infrared short pulse upconversion detection for gas sensing.

Pulsed nonlinear-optical upconversion is used for mid-infrared signal detection. A setup for both mid-infrared generation and upconversion based on a single pump laser enables sensitive light detection and is utilized for gas spectroscopy. With the demonstrated pulsed setup, quantum efficiencies above 80 % for the upconversion of a Gaussian beam signal and 25 % for the upconversion of backscattered radiation are achieved and in agreement with theoretical predictions. Combined with efficient background suppression due to spectral and temporal gating, this results in highly sensitive detection of the infrared signals. As a demonstration of application, the presented system is used for methane sensing in an open path geometry, highlighting the potential for stand-off leak detection with a concentration resolution better than 1.5 ppm·m.

Spectrally Multiplexed Upconversion Detection With C-Band Pump and Signal Wavelengths

We demonstrate a multiplexing scheme for upconversion-based single-photon detection using a waveguide with multiple phase-matching peaks. Two different signal wavelengths are upconverted using two distinct pump wavelengths, where all the wavelengths are in the 1550-nm band. Background photon generation rates $ per pulse with high internal conversion efficiencies are observed using 20-ps-long pump pulses.

1.064-μm-band up-conversion single-photon detector.

Based on the technique of periodically poled lithium niobate waveguide, up-conversion single-photon detection at 1.064-μm is demonstrated. We have achieved a system photon detection efficiency of 32.5% with a very low noise count rate of 45 counts per second by pumping with a 1.55-μm-band single frequency laser using the long-wavelength pumping technique and exploiting volume Bragg grating as a narrow band filter. Replacing the volume Bragg grating with a combination of adequate dielectric filters, a detection efficiency of up to 38% with a noise count rate of 700 counts per second is achieved, making the overall system stable and practical. The up-conversion single-photon detector operating at 1.064 μm can be a promising robust counter and find usage in many fields.

Ultra-broadband mid-wave-IR upconversion detection.

In this Letter, we demonstrate efficient room temperature detection of ultra-broadband mid-wave-infrared (MWIR) light with an almost flat response over more than 1200 nm, exploiting an efficient nonlinear upconversion technique. Black-body radiation from a hot soldering iron rod is used as the IR test source. Placing a 20 mm long periodically poled lithium niobate crystal in a compact intra-cavity setup (>20 W CW pump at 1064 nm), MWIR wavelengths ranging from 3.6 to 4.85 μm are upconverted to near-infrared (NIR) wavelengths (820-870 nm). The NIR light is detected using a standard low-noise silicon-based camera/grating spectrometer. The proposed technique allows high conversion efficiency over a wider bandwidth without any need for a shorter crystal length. Different analytical predictions and numerical simulations are performed a priori to support the experimental demonstrations.