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Approaches to provide chip-scale aqueous chemical sensing for environmental and health monitoring via a photonic integrated circuit (PIC) technology are showing promise. To meet future U.S. Army demand, we have investigated waveguide structures compatible with feature sizes offered by modern mass-manufacturing PIC foundries. We have found that wide subwavelength grating (SWG) waveguide structures can maximally interact with an encapsulating analyte capture material with low propagation loss. We describe the analyte/light interaction component of our general integrated photonics chemical detector sensitivity model and use it to compare the effectiveness of waveguide geometries for sensing. The structures we have investigated afford superior detection to strip and slot waveguides. Finally, we introduce a novel tapered SWG waveguide geometry with improved transmission and similar sensitivity to nontapered SWG designs.

Sweat provides direct information of the real-time emotional and cognitive state of the subject, with applications ranging from situational awareness and mission effectiveness of armed forces to disease diagnosis for clinicians. Development of a broad class of human performance monitoring devices to quantify sweat biomarkers necessitates non-invasive, real-time monitoring of ultra-low concentrations (μM to fM) of hormones, proteins, and neurotransmitters. Field effect transistors are the predominant sensor approach whereby the gate electrode is modified with a selective bio-recognition element (BRE). However, FETs have diminished sensitivity in high ionic strength environments associated with sweat. Alternatively, BRE-modified photonic integrated circuits (PICs) have high sensitivity in high ionic strength fluids, low cost at the manufacturing scale, and enable a number of novel device concepts to achieve ultra-low levels of detection. One major technological challenge is to predict the limit of detection (LoD), or sensor response function, for a particular PIC geometry in a microfluidic chamber. LoD is highly dependent on analytic capture efficiency, fluid dynamics and affinity, analyte/light interaction, and analyte concentration. This work presents finite element simulations to emulate microfluidic BRE sweat sensors and provide a predictive limit of detection for different sensing structures or elements. Specifically, the optimum mass transfer and kinetics for sensing approaching single molecule detection is discussed, including flow characteristics, biomarker size, adsorption and desorption kinetics, and sensor geometry. Key metrics include capture efficiency (molecules being captured over molecules entering channel ), time to reach steady state, and temporal adsorption site occupancy to predict PIC system LoD. It is found that these systems are kinetically controlled, with capture efficiencies remaining below 1% even for kads/kdes ratios of 1010 . The need for adsorption kinetics measured for flow systems instead of stationary fluid systems is stressed, as these parameters are what need to be optimized to greatly increase analyte capture.

Due to its appreciable electro-optical properties, potassium tantalate niobate (KTN) thin films of high quality are expected to enhance the functionality of integrated photonics optical modulators. Unfortunately, they are inherently hard to synthesize. Herein, the authors present atomic layer deposition (ALD) of oriented KTN for the first time. They study the variability in phase content with respect to potassium concentration across a variety of substrates. Films grown with a slight overstoichiometry in potassium show excellent crystal quality of a pure perovskite phase. Highly oriented films were obtained on substrates of a similar lattice constant to bulk potassium tantalate niobate. Nearly stoichiometric potassium contents yield films with similar quality, albeit with trace amounts of pyrochlore. Potassium deficient films consist of an overwhelming amount of pyrochlore. Phase control and orientation control are essential when considering device integration of optical modulators. The authors believe that ALD is an ideal technique to obtain KTN thin films with high growth control.Due to its appreciable electro-optical properties, potassium tantalate niobate (KTN) thin films of high quality are expected to enhance the functionality of integrated photonics optical modulators. Unfortunately, they are inherently hard to synthesize. Herein, the authors present atomic layer deposition (ALD) of oriented KTN for the first time. They study the variability in phase content with respect to potassium concentration across a variety of substrates. Films grown with a slight overstoichiometry in potassium show excellent crystal quality of a pure perovskite phase. Highly oriented films were obtained on substrates of a similar lattice constant to bulk potassium tantalate niobate. Nearly stoichiometric potassium contents yield films with similar quality, albeit with trace amounts of pyrochlore. Potassium deficient films consist of an overwhelming amount of pyrochlore. Phase control and orientation control are essential when considering device integration of optical modulators. The authors believe th...

Extreme skin depth engineering (e-skid) can be applied to integrated photonics to manipulate the evanescent field of a waveguide. Here we demonstrate that e-skid can be implemented in two directions in order to deterministically engineer the evanescent wave allowing for dense integration with enhanced functionalities. In particular, by increasing the skin depth, we enable the creation of large gap, bendless directional couplers with large operational bandwidth. Here we experimentally validate two-dimensional e-skid for integrated photonics in a CMOS photonics foundry and demonstrate strong coupling with a gap of 1.44 {\mu}m., Comment: 13 pages, 9 figures

Grating waveguide structures have the opportunity to greatly improve photonic integrated circuit sensor sensitivity. We have examined the impact of wide subwavelength grating waveguide geometries on sensor performance. We present the progress of our design exploration and compare performance to existing slot and strip waveguide structures.

Development of a sensor consisting of a molecularly imprinted polymer integrated onto a photonic chip is discussed. This sensor has applications for threat detection, including current known and emerging hazards, and chemical and biological material via target specific sensing, concentrating and filtering. The photonic device that the MIP is integrated onto allows for the measurement of small quantities of target material, thus demonstrating potential application to materials like acute toxic chemicals or even low-incidence high-consequene pathogens. This paper highlights the recent early work to progress this capability focusing on MIP development for deposition onto a photonic sensing chip.

Recent advances in subwavelength grating (SWG) structures have shown promise in sensing applications. Though prior sensors have obtained high index sensitivities, their designs have not focused on providing strong analyte/light interaction efficiency for low analyte concentration flows. We have explored high-contrast grating “fish-bone” and segmented SWG structures in the hopes of improving this aspect. We present below the progress of our design exploration of these structures and compare their performance to a typical slot waveguide to understand their impact on spectral transmission and analyte interaction. The best performing structures will be experimentally functionalized with label-free analyte capture materials to sense specific threat molecules via index change. We envision building manyanalyte multiplexed sensor arrays from these devices to enable simultaneous monitoring of multiple chemical and biological threats or human biomarkers with high sensitivity, specificity, and low probabilities of false alarm.

We are studying the viability of a chip-scale integrated photonics based sensor assay array for wearable soldier health monitoring and environmental hazard warning applications. We propose using label-free analyte capture material clad wide subwavelength grating (SWG) waveguides as the sensor elements in a multiplexed array to probe the myriad variety and concentration ranges of chemical hazards and biomarker health molecules expected in these applications. We present here the simulated behavior of both rectangular and tapered wide SWG geometries. We discuss their transmission spectra, effective index, bulk sensitivity, and cladding dependence on waveguide width alongside strip and slot waveguide geometries. Experimental transmission and effective index measurements validating our simulation techniques are also given.

A symmetric gain optoelectronic mixer based on an indium gallium arsenide (In0.53Ga0.47As)/indium phosphide (InP) symmetric heterojunction phototransistor structure is being investigated for chirped-AM laser detection and ranging (LADAR) systems operating in the “eye-safe” 1.55 μm wavelength range. Signal processing of a chirped-AM LADAR system is simplified if the photodetector in the receiver is used as an optoelectronic mixer (OEM). Adding gain to the OEM allows the following transimpedance amplifier’s gain to be reduced, increasing bandwidth and improving the system’s noise performance. A symmetric gain optoelectronic mixer based on a symmetric phototransistor structure using an indium gallium arsenide narrow bandgap base and indium phosphide emitter/collector layers is proposed. The devices are simulated with the Synopsis TCAD Sentaurus tools. The effects of base–emitter interface layers, base thickness and the doping densities of the base and emitters on the device performance are investigated. AC and DC simulation results are compared with a device model. Improved responsivity and lower dark current are predicted for the optimized InGaAs/InP device over previously reported devices with indium aluminum arsenide emitter/collector layers.

An efficient Si hybrid external cavity laser with a micro-ring reflector is fabricated on SOI platform. The laser output power reaches 20 mW and the highest wall-plug efficiency of 7.8% is measured in an un-cooled condition.

A highly efficient silicon (Si) hybrid external cavity laser with a wavelength tunable ring reflector is fabricated on a complementary metal-oxide semiconductor (CMOS)-compatible Si-on-insulator (SOI) platform and experimental results with high output power are demonstrated. A III-V semiconductor gain chip is edge-coupled into a SOI cavity chip through a SiN(x) spot size converter and Si grating couplers are incorporated to enable wafer-scale characterization. The laser output power reaches 20 mW and the highest wall-plug efficiency of 7.8% is measured at 17.3 mW in un-cooled condition. The laser wavelength tuning ranges are 8 nm for the single ring reflector cavity and 35 nm for the vernier ring reflector cavity, respectively. The Si hybrid laser is a promising light source for energy-efficient Si CMOS photonic links.

We demonstrate improved optical interlayer coupling based on grating couplers with backside metal reflectors. Losses of 1.5dB and 2.0dB are achieved with 145nm and 220nm grating etch depth on a 130nm SOI CMOS platform, respectively.

Uncooled mid-infrared photoconductors are used in situations where hot objects (such as fire, explosions, engines, etc.) need to be detected using compact, low-cost systems. We have experienced trouble obtaining reliable detector data from mid-infrared photoconductor vendors. The purpose of this report is to give a detailed discussion of how to characterize the signal and noise properties of photodetectors with an emphasis on avoiding the measurement pitfalls associated specifically with room temperature and near room temperature mid-infrared photoconductors. The report ends with a discussion of where it is appropriate to use a commonly used figure of merit.

Optical modulators are a key element of optical data communication systems. All modulators demonstrated to date rely on the free-carrier plasma dispersion effect. This method absorbs light, which changes the material's index of refraction. This absorption requires carrier transport and, in present implementations, suffers from slow minority carrier diffusion. Reducing the active thickness over which the carriers must diffuse in an attempt to improve speed reduces the strength of the effect, trading efficiency for speed. Here we investigate an entirely new type of silicon electro-optic modulator that does not have any of these trade-offs. It utilizes the Kerr induced refractive index change in silicon nanocrystals, which has been reported to be large (5E-17cm2/W) [1]. The proposed microdisk resonator modulator is shown in Figure 1. An oxide layer (grey) separates the active device layers from the silicon Si substrate (green). Light enters the waveguide on the right and is alternately exchanged between the microdisk resonator and the output of the waveguide. Figure 1 shows an estimate of the expected refractive index change versus applied voltage. An index change of ∼2 × 10−4 is enough to modulate the light, corresponding to a voltage of only 0.5–1.5 V. Confinement of light in the waveguide and microdisk is accomplished via a slot waveguide design. Speeds of more than 100Gbit/s are possible with this design.

Here we report direct observation of DC Kerr electro-optic modulation using silicon nanocrystals. The enhanced DC Kerr effect could enable ultrafast CMOS compatible electro-optic modulators.

Optoelectronic mixing devices mix a modulated optical signal with a reference electrical signal to obtain an electrical low frequency difference signal. These devices are particularly attractive for chirped-FM laser detection and ranging (LADAR) systems. The Army Research Laboratory (ARL) has been developing chirped-FM LADAR systems for applications such as reconnaissance, terrain mapping, force protection, facial recognition, robotic navigation and weapons fuzing [1]. Signal processing of a chirped-FM LADAR system is simplified if the photodetector in the receiver is used as an optoelectronic mixer (OEM). While a DC biased phototransistor can be used as an optoelectronic mixer [2], a symmetric I–V characteristic photodetector allows driving the OEM directly with the local oscillator (LO) signal, without a DC bias [3]. Sensitivity to background light is reduced, as the response from background light averages to zero. An additional 3 dB signal processing gain is also obtained. As the OEM output is the low frequency difference signal, the gain of the following transimpedance amplifier (TZA) can be increased, improving LADAR performance. ARL has previously demonstrated chirped FM LADAR systems with GaAs and InGaAs metal-semiconductor-metal (MSM) Schottky photodetector OEMs for operation at the 800 nm and 1550 nm wavelengths [3,4]. A symmetric photodetector with gain would improve overall system performance, while preserving the advantages offered by MSM OEM devices. We previously reported on symmetric gain optoelectronic mixers based on a symmetric heterojunction phototransistor using In 0.52 Al 0.48 As/ In 0.53 Ga 0.47 As heterostructures [5]. In this work, the In 0.52 Al 0.48 As wide bandgap layers are replaced with InP to improve thin film growth quality and device performance.

Peripheral coupled waveguide (PCW) electro-absorption modulator (EAM) with different dimensions is studied. By incorporating a waveguide taper in the PCW to reduce the absorption at the input facet of the EAM, we show that the saturation effect due to high current density can be reduced.

Designs patterned by electron beam lithography without applying process effect correction exhibit overexposed dense features and underexposed sparse features for most practical exposure scenarios. This is typified by the limited exposure latitude of hydrogen silsesquioxane resist on silicon-on-insulator substrates used for silicon photonics, which commonly display very high density features (vertical grating couplers, ring resonators) mixed with very sparse features (inverse tapered waveguides, lone waveguides) in a single pattern. The authors have optimized a proximity effect correction (PEC) based on our analysis of a single 1D process control monitor characterization sample. Our PEC verification sample, which includes electron backscatter and process-related microloading effects, achieved linewidths with an RMS error of ±5.0 nm for features with pattern densities spanning 1%–67%. Ignoring the pattern density-dependent microloading effect limits the resolvable pattern density span to a smaller range and degrades the linewidth error.

Isothermal solidification metal waferbonding is well suited to heterogeneously integrate high-speed/high-power density RF and microwave devices with standard CMOS technology. It is capable of forming efficient electrical and thermal interconnects as well as bonded-microstrip waveguide structures. Accurate means of characterizing the electrical, thermal, and microwave properties of these structures are necessary to enable heterogeneous monolithic microwave integrated circuits (HMMICs). This article describes a bond layer thermal conductivity measurement method, a bond-metal microstrip microwave waveguide characterization method, and the fabrication method developed to support the measurement structures. As a result, an In-Pd bond alloy thermal conductivity of 2.51 W/(m K) was measured for GaAs devices bonded to Si. Also, an optimized bonded-microstrip waveguide was simulated based upon measured microwave results of the measurement structure, projecting a 0.56 dB/mm loss, a microwave index of 2.91, and a characteristic impedance of 41.3+6i Ω at 15 GHz, thus advocating this approach as a means of realizing high power HMMICs.

Wafer bonding has traditionally focused on producing either insulating or nonlinear heterostructure interfaces; low-resistance Ohmic interfaces would offer the advantage of more efficient current delivery. In this study, doped GaAs was bonded to doped Si using indium and palladium interlayers. During heating above the lower melting point metal indium, a solid alloy is formed bonding the GaAs and Si together, this process is typically referred to as isothermal solidification. This method universally created Ohmic bond interfaces for all doping types. A metric was devised to measure the bond resistivity revealing a resistivity of 1.03×10−5Ωcm2 for n-GaAs bonded to p-Si.

Silicon-on-insulator (SOI) substrates were created from two methods of ion cutting: thermal exfoliation (TE) and mechanical exfoliation (ME). These SOI films are characterized to discern the differences in electrical and other properties induced by the ME and TE processes. p-metal-oxide-semiconductor field-effect transistor were fabricated on these SOI substrates as well as on bulk silicon and their I-V characteristics measured and compared to point out materials differences created by the two methods. X-ray diffraction measurements were also performed to supplement the exploration of the TE and ME material properties. Overall the FETs fabricated from the ME SOI outperformed those made from the TE SOI and had similar Ion∕Ioff ratios and off-state drain-source leakage currents to the FETs fabricated from bulk Si.