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Additive manufacturing at small scales enables advances in micro- and nanoelectromechanical systems, micro-optics, and medical devices. Materials that lend themselves to AM at the nanoscale, especially for optical applications, are limited. State-of-the-art AM processes for high-refractive-index materials typically suffer from high porosity and poor repeatability and require complex experimental procedures. We developed an AM process to fabricate complex 3D architectures out of fully dense titanium dioxide (TiO₂) with a refractive index of 2.3 and nanosized critical dimensions. Transmission electron microscopy (TEM) analysis proves this material to be rutile phase of nanocrystalline TiO₂, with an average grain size of 110 nm and

A free-space coupled superconducting nanowire single-photon detector with high efficiency at 1550 nm, sub-0.1 Hz dark count rate, and sub-15 ps timing jitter is demonstrated.

Superconducting Nanowire Single Photon Detectors (SNSPDs) excel at a wide variety of performance criteria for single photon counting. They combine unprecedented high detection efficiency, high timing resolution, high count rates, low intrinsic dark count rates, and are sensitive to ultraviolet through mid-infrared single-photons. At JPL, we are working on several projects to push the performance limits of SNSPDs to achieve higher maximum count rates, larger active areas, higher timing resolution, and a wider spectral range. Our recent advances enable new applications for dark matter detection, imaging, and space-to-ground communication and provide insight into the fundamental physics of single-photon detection in superconducting nanowires.

We demonstrate large-area superconducting nanowire single-photon detectors (SNSPDs) with simultaneous high system detection efficiency and low system jitter. We describe the device architecture and discuss optimal readout setup for practical applications.

Improvements in temporal resolution of single-photon detectors enable increased data rates and transmission distances for both classical and quantum optical communication systems, higher spatial resolution in laser ranging, and observation of shorter-lived fluorophores in biomedical imaging. In recent years, superconducting nanowire single-photon detectors (SNSPDs) have emerged as the most efficient time-resolving single-photon-counting detectors available in the near-infrared, but understanding of the fundamental limits of timing resolution in these devices has been limited due to a lack of investigations into the timescales involved in the detection process. We introduce an experimental technique to probe the detection latency in SNSPDs and show that the key to achieving low timing jitter is the use of materials with low latency. By using a specialized niobium nitride SNSPD we demonstrate that the system temporal resolution can be as good as 2.6 ± 0.2 ps for visible wavelengths and 4.3 ± 0.2 ps at 1,550 nm. Knowledge about detection latency provides a guideline to reduce the timing jitter of niobium nitride superconducting nanowire single-photon detectors. A timing jitter of 2.6 ps at visible wavelength and 4.3 ps at 1,550 nm is achieved.

While single-pixel superconducting nanowire single photon detectors (SNSPDs) have demonstrated remarkable efficiency and timing performance from the UV to near-IR, scaling these devices to large imaging arrays remains challenging. Here, we propose a new SNSPD multiplexing system using thermal coupling and detection correlations between two photosensitive layers of an array. Using this architecture with the channels of one layer oriented in rows and the second layer in columns, we demonstrate imaging capability in 16-pixel arrays with accurate spot tracking at the few-photon level. We also explore the performance trade-offs of orienting the top layer nanowires parallel and perpendicular to the bottom layer. The thermally coupled row-column scheme is readily able to scale to the kilopixel size with existing readout systems and, when combined with other multiplexing architectures, has the potential to enable megapixel scale SNSPD imaging arrays.

A free-space coupled superconducting nanowire single photon detector with high efficiency and sub-hertz false count rate is demonstrated using stacked short pass filters, a bandpass filter, and optimized cryostat design to block thermal photons.

Many of the high accuracy Earth science survey missions are planned to use laser-based remote sensing instruments. The 2-μm laser wavelength is of particular interest due to the presence of many CO2 and H20 absorption lines in its vicinity1. Transmitter architectures are typically composed of an optically pumped, frequency-stable, solid-state seed laser and a high-power optical amplifier.2, 3 Taking advantage of the reliability and relative simplicity of semiconductor lasers, this architecture can substantially improve by replacing the solid-state light source with semiconductor lasers of comparable performance. This approach will greatly improve the system reliability, and will simplify instrument integration and space qualification. There are currently very limited semiconductor lasers operating in the 2-μm range with performance satisfactory enough for use as an injection seed in a laser absorption spectrometer. Optimally, seed lasers producing greater than 50 mW of continuous-wave (CW), with frequency jitter of less than 1 MHz are desired to reliably resolve the CO2 absorption lines near 2-μm. In this paper, we report the demonstration of high-power, single-longitudinal-mode laterally coupled distributed feedback (LC-DFB) lasers at 2.05 μm wavelength. We measured more than 80 mW of CW power at -10 oC for devices with a 4-μm-wide ridge and 2-mm-long cavity.

We developed superconducting nanowire single-photon detectors based on tungsten silicide, which show saturated internal detection efficiency up to a wavelength of 10 μm. These detectors are promising for applications in the mid-infrared requiring sub-nanosecond timing, ultra-high gain stability, low dark counts, and high efficiency, such as chemical sensing, LIDAR, dark matter searches, and exoplanet spectroscopy.

We present a simple experimental scheme for estimating the cryogenic thermal transport properties of thin films using superconducting nanowires. In a parallel array of nanowires, the heat from one nanowire in the normal state changes the local temperature around adjacent nanowires, reducing their switching current. Calibration of this change in switching current as a function of bath temperature provides an estimate of the temperature as a function of displacement from the heater. This provides a method of determining the contribution of substrate heat transport to the cooling time of superconducting nanowire single-photon detectors. Understanding this process is necessary for successful electrothermal modeling of superconducting nanowire systems.

The Deep Space Optical Communication (DSOC) project at the Jet Propulsion Laboratory aims to perform a bidirectional laser communication technology demonstration from deep space, at ranges from 0.1 - 3 AU. To support high data rates over such distances while keeping the mass and power on the spacecraft comparable to radio-frequency communication systems, extremely high-performance single photon detectors are required at the ground receiver. To this end, JPL has been developing 64-pixel tungsten silicide superconducting nanowire single photon detector (WSi SNSPD) arrays suitable for use in the DSOC ground terminal. To efficiently couple to a 5-meter telescope aperture in the presence of atmospheric seeing, the arrays are free-space coupled and have a combined 320-micron diameter active area. The development is targeting 70% system detection efficiency at an operating wavelength of 1550 nm, 150 ps time resolution, a maximum count rate approaching 109 counts per second, a numerical aperture capable of supporting an f/1.2 beam, a background-limited dark count rate, and an operating temperature of 1 Kelvin. In this paper, we will present our progress toward these goals, both in terms of focal plane array development and cryogenic readout technology.

We report on optically sensitive 15 nm thick, 100 nm wide MgB 2 nanowires in the operating-temperature range 4–11 K.

We developed a 64-pixel 320 μm diameter array of WSi SNSPDs for the ground receiver of a deep-space optical communication link. The SNSPD array exhibits a free-space system detection efficiency of 40% at 1550 nm.

We have demonstrated ∼ 80% detection efficiency of 370 nm photons using superconducting nanowire single-photon detectors (SNSPDs) operating at 4.2 K, with system dark count rates below 1 count/s. Prospects for detecting shorter wavelengths are discussed.

We report on room-temperature, continuous-wave operation of single-mode quantum cascade lasers designed for minimal threshold power consumption in the 4 to 10 μm spectral range. Narrow-ridge distributed feedback lasers were developed with plasma-etched sidewall corrugations and infrared-transparent dielectric cladding, enabling fabrication without any epitaxial steps beyond the initial growth of the planar laser wafer. The devices exhibit single-mode emission with stable, mode-hop-free tuning and side-mode suppression greater than 25 dB. We demonstrate packaged single-mode devices with continuous-wave threshold power consumption near 1 W above room temperature.

We demonstrate high-efficiency detection of 370 nm photons using superconducting nanowire single-photon detectors. The detectors employ amorphous MoSi (bulk T c = 6.8 K) to enable operation on a compact cryocooler system.

We report on 5 nm thick, 100 nm wide MgB 2 nanowires with single-photon sensitivity at 635 nm wavelength in the operating-temperature range 3–10 K.

Lasers employing a new double-ridge waveguide design emit 18 mW at 3.57 μm and 20 mW at 3.37 μm. The top ridge confines the optical mode while the bottom ridge limits lateral current spreading.

We have demonstrated WSi-based superconducting nanowire single-photon detectors coupled to SiN x waveguides with integrated ring resonators. This photonics platform enables the implementation of robust and efficient photon-counting detectors with fine spectral resolution near 1550 nm.

We fabricated and characterized the optical response of MgB 2 nanowires with critical temperature T C = 33 K. The devices showed optical response at 4 K and sub-nanosecond relaxation time. The detectors responded to the simultaneous absorption of three photons, but not to single photons.

Composed of optical waveguides and power-splitting waveguide junctions in a network layout, resonant guided wave networks (RGWNs) split an incident wave into partial waves that resonantly interact within the network. Resonant guided wave networks have been proposed as nanoscale distributed optical networks (Feigenbaum and Atwater, Phys. Rev. Lett. 2010, 104, 147402) that can function as resonators and color routers (Feigenbaum et al. Opt. Express 2010, 18, 25584-25595). Here we experimentally characterize a plasmonic resonant guided wave network by demonstrating that a 90° waveguide junction of two v-groove channel plasmon polariton (CPP) waveguides operates as a compact power-splitting element. Combining these plasmonic power splitters with CPP waveguides in a network layout, we characterize a prototype plasmonic nanocircuit composed of four v-groove waveguides in an evenly spaced 2 × 2 configuration, which functions as a simple, compact optical logic device at telecommunication wavelengths, routing different wavelengths to separate transmission ports due to the resulting network resonances. The resonant guided wave network exhibits the full permutation of Boolean on/off values at two output ports and can be extended to an eight-port configuration, unlike other photonic crystal and plasmonic add/drop filters, in which only two on/off states are accessible.

We demonstrate index-coupled distributed-feedback diode lasers at 2.65 μm that are capable of tuning across strong absorption lines of HDO and other isotopologues of H2O. The lasers employ InGaAsSb/AlInGaAsSb multi-quantum-well structures grown by molecular beam epitaxy on GaSb, and single-mode emission is generated using laterally coupled second-order Bragg gratings etched alongside narrow ridge waveguides. We verify nearcritical coupling of the gratings by analyzing the modal characteristics of lasers of different length. With an emission facet anti-reflection coating, 2-mm-long lasers exhibit a typical current threshold of 150 mA at 20 °C and are capable of emitting more than 25 mW in a single longitudinal mode, which is significantly higher than the output power reported for losscoupled distributed-feedback lasers operating at similar wavelengths. © 2013 Optical Society of America.

We demonstrate efficient coupling into channel plasmon polariton waveguides from Si ridge waveguides at λ0 = 1520nm, using near-field scanning-optical measurements. We further demonstrate optical power splitting at ultracompact 90-degree 4-way splitters and 2x2 resonators.

We demonstrate single-mode distributed-feedback quantum cascade lasers at 4.75 μm with etched index-coupled surface gratings and spin-on dielectric infilling. We observe continuous wave laser emission at room temperature with 5 W of electrical power consumption.

We report continuous-wave operation of single-mode quantum cascade (QC) lasers emitting near 7.4 µm with threshold power consumption below 1 W at temperatures up to 40 °C. The lasers were fabricated with narrow, plasma-etched waveguides and distributed-feedback sidewall gratings clad with sputtered aluminum nitride. In contrast to conventional buried-heterostructure (BH) devices with epitaxial sidewall cladding and in-plane gratings, the devices described here were fabricated without any epitaxial regrowth processes, yet they exhibit power consumption comparable to the lowest-dissipation BH QC lasers reported to date. These low-dissipation devices are designed primarily as light sources for infrared spectroscopy instruments with limited volume, mass, and power budgets.

We report on the phase noise properties of DFB lasers operating near 2.0 μm. Measured noise spectra indicate intrinsic linewidths below 1 kHz. Less than 200 kHz effective linewidth is estimated for 5 ms measurement time.

We demonstrate single-mode laterally coupled distributed-feedback diode lasers at 2.05 μm employing low-loss etched gratings. Single-facet CW output exceeds 50 mW near room temperature with linewidth below 1 MHz over 10-ms observation times.

International audience; We report the experimental realization of a compact, efficient coupler between silicon waveguides and vertical metal-insulator-silicon-metal (MISM) plasmonic waveguides. Devices were fabricated using complementary metal-oxide-silicon technology processes, with copper layers that support low-loss plasmonic modes in the MISM structures at a wavelength of 1550nm. By implementing a short (0.5µm) optimized metal-insulator-silicon-insulator structure inserted between the photonicand plasmonic waveguide sections, we demonstrate experimental coupling loss of 2.5dB, despite the high optical confinement of the MISM mode and mismatch with the silicon waveguide mode.

Crystalline Si wires, grown by the vapor–liquid–solid (VLS) process, have emerged as promising candidate materials for lowcost, thin-film photovoltaics. Here, we demonstrate VLS-grown Si microwires that have suitable electrical properties for high-performance photovoltaic applications, including long minority-carrier diffusion lengths (L_n » 30 µm) and low surface recombination velocities (S « 70 cm·s^(-1)). Single-wire radial p–n junction solar cells were fabricated with amorphous silicon and silicon nitride surface coatings, achieving up to 9.0% apparent photovoltaic efficiency, and exhibiting up to ~600 mV open-circuit voltage with over 80% fill factor. Projective single-wire measurements and optoelectronic simulations suggest that large-area Si wire-array solar cells have the potential to exceed 17% energy-conversion efficiency, offering a promising route toward cost-effective crystalline Si photovoltaics.

Resonant plasmonic and metamaterial structures allow for control of fundamental optical processes such as absorption, emission and refraction at the nanoscale. Considerable recent research has focused on energy absorption processes, and plasmonic nanostructures have been shown to enhance the performance of photovoltaic and thermophotovoltaic cells. Although reducing metallic losses is a widely sought goal in nanophotonics, the design of nanostructured 'black' super absorbers from materials comprising only lossless dielectric materials and highly reflective noble metals represents a new research direction. Here we demonstrate an ultrathin (260 nm) plasmonic super absorber consisting of a metal–insulator–metal stack with a nanostructured top silver film composed of crossed trapezoidal arrays. Our super absorber yields broadband and polarization-independent resonant light absorption over the entire visible spectrum (400–700 nm) with an average measured absorption of 0.71 and simulated absorption of 0.85. Proposed nanostructured absorbers open a path to realize ultrathin black metamaterials based on resonant absorption.

Si microwire-array solar cells with Air Mass 1.5 Global conversion efficiencies of up to 7.9% have been fabricated using an active volume of Si equivalent to a 4 μm thick Si wafer. These solar cells exhibited open-circuit voltages of 500 mV, short-circuit current densities (J_(sc)) of up to 24 mA cm^(-2), and fill factors >65% and employed Al_2O_3 dielectric particles that scattered light incident in the space between the wires, a Ag back reflector that prevented the escape of incident illumination from the back surface of the solar cell, and an a-SiN_x:H passivation/anti-reflection layer. Wire-array solar cells without some or all of these design features were also fabricated to demonstrate the importance of the light-trapping elements in achieving a high J_(sc). Scanning photocurrent microscopy images of the microwire-array solar cells revealed that the higher J_(sc) of the most advanced cell design resulted from an increased absorption of light incident in the space between the wires. Spectral response measurements further revealed that solar cells with light-trapping elements exhibited improved red and infrared response, as compared to solar cells without light-trapping elements.

We have integrated lithographically patterned VO2 thin films grown by pulsed laser deposition with silicon-on-insulator photonic waveguides to demonstrate a compact in-line absorption modulator for use in photonic circuits. Using single-mode waveguides at lambda=1550 nm, we show optical modulation of the guided transverse-electric mode of more than 6.5 dB with 2 dB insertion loss over a 2-microm active device length. Loss is determined for devices fabricated on waveguide ring resonators by measuring the resonator spectral response, and a sharp decrease in resonator quality factor is observed above 70 degrees C, consistent with switching of VO2 to its metallic phase. A computational study of device geometry is also presented, and we show that it is possible to more than double the modulation depth with modified device structures.

The use of silicon nanostructures in solar cells offers a number of benefits, such as the fact they can be used on flexible substrates. A silicon wire-array structure, containing reflecting nanoparticles for enhanced absorption, is now shown to achieve 96% peak absorption efficiency, capturing 85% of light with only 1% of the silicon used in comparable commercial cells. Si wire arrays are a promising architecture for solar-energy-harvesting applications, and may offer a mechanically flexible alternative to Si wafers for photovoltaics1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17. To achieve competitive conversion efficiencies, the wires must absorb sunlight over a broad range of wavelengths and incidence angles, despite occupying only a modest fraction of the array’s volume. Here, we show that arrays having less than 5% areal fraction of wires can achieve up to 96% peak absorption, and that they can absorb up to 85% of day-integrated, above-bandgap direct sunlight. In fact, these arrays show enhanced near-infrared absorption, which allows their overall sunlight absorption to exceed the ray-optics light-trapping absorption limit18 for an equivalent volume of randomly textured planar Si, over a broad range of incidence angles. We furthermore demonstrate that the light absorbed by Si wire arrays can be collected with a peak external quantum efficiency of 0.89, and that they show broadband, near-unity internal quantum efficiency for carrier collection through a radial semiconductor/liquid junction at the surface of each wire. The observed absorption enhancement and collection efficiency enable a cell geometry that not only uses 1/100th the material of traditional wafer-based devices, but also may offer increased photovoltaic efficiency owing to an effective optical concentration of up to 20 times.

We investigate the light emission properties of electrical dipole emitters inside 2-dimensional (2D) and 3-dimensional (3D) silicon slot waveguides and evaluate the spontaneous emission enhancement (F(p)) and waveguide coupling ratio (beta). Under realistic conditions, we find that greater than 10-fold enhancement in F(p) can be achieved, together with a beta as large as 0.95. In contrast to the case of high Q optical resonators, such performance enhancements are obtained over a broad wavelength region, which can cover the entire emission spectrum of popular optical dopants such as Er. The enhanced luminescence efficiency and the strong coupling into a limited set of well-defined waveguide modes enables a new class of power-efficient, CMOS-compatible, waveguide-based light sources.

For high-sensitivity absorption spectroscopy, single-mode light sources capable of emitting high optical output power in the 3 to 5 µm wavelength range are vital. Here, we report on interband cascade lasers that emit 20 mW of optical power in a single spectral mode at room temperature and up to 40 mW at 0 °C using second-order laterally coupled Bragg gratings for distributed feedback. The lasers employ a double-ridge design with a narrow 3-µm-wide top ridge to confine the optical mode and a 9-µm-wide ridge for current confinement. The lasers were developed for an integrated cavity output spectroscopy instrument for stratospheric detection of hydrogen chloride at a wavelength of 3.3746 µm and emit at the target wavelength with more than 34 mW of single-mode power.

We report on single-mode distributed-feedback quantum cascade lasers emitting at 4.8 μm with continuous-wave threshold power consumption as low as 0.76 W at 20 °C and 0.98 W at 50 °C. Following growth of the laser active region and semiconductor cladding layers by a single molecular beam epitaxy process, devices with 4-μm-wide ridges and vertical sidewall gratings were fabricated using plasma etching and standard dielectric and metal deposition processes. In terms of mode stability, output power, and efficiency, we show that lasers with 1-mm cavity length and high-reflectivity back-facet coatings can match the performance of buried heterostructure devices, but with the advantage of requiring only a single epitaxial growth step.

We report on the performance and reliability of laterally-coupled distributed-feedback (DFB) interband cascade lasers designed to operate at 3.6 μm wavelength. A two-step ridge etch process ensures single-transverse-mode operation with minimal lateral current spreading, and a second-order Bragg grating etched alongside the ridge waveguide imposes single-mode DFB operation. Life tests performed on four randomly selected lasers, continuously operating at 40 °C with output power >10 mW, showed no measurable degradation after each laser was operated continuously for more than 1500 h.

We report on GaSb-based laterally coupled distributed-feedback (DFB) diode lasers designed to operate at wavelengths near 2.05 μm. Second-order Bragg gratings were etched alongside narrow ridge waveguides to enable single-mode DFB operation in 2-mm-long laser diodes. At a heat-sink temperature of 10 °C, the lasers emit more than 40 mW continuous-wave in a single longitudinal mode, while increasing the current beyond 300 mA results in multimode operation due to spectral shifting of the laser gain with respect to the peak grating reflectivity. At −10 °C, we observe DFB operation at higher current, with single-facet emission exceeding 80 mW.

The linewidth of a gallium antimonide-based laterally-coupled 2.05 µm DFB laser emitting 40 mW of power at 9 C is measured. The measured linewidth is 1.7 MHz for 500 ms and 1.4 MHz for 10 ms observation time, respectively. The combination of high power and low frequency jitter makes this laser useful for detecting CO2 in air in both in-situ and remote sensing applications. The linewidth measurement is also discussed.

We fabricated horizontal Si slot waveguides with a 25 nm SiO2 slot layer by bonding thin Si-on-insulator wafers. After removing the Si substrate and buried oxide from one side of the bonded structure, grating-coupled waveguides and ring resonators were partially etched into the Si/SiO2/Si device layers. The gratings exhibit efficiencies of up to 23% at 1550 nm and the ring resonators were measured to have loaded quality factors near 42 000 for the lowest-order transverse-electric mode, corresponding to a propagation loss of 15 dB/cm. The leaky lowest-order transverse-magnetic mode was also observed with a propagation loss of 44 dB/cm.