This PDF file contains the front matter associated with SPIE Proceedings Volume 9609, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

In this paper, we review selected imaging and related technology development programs in the Defense Advanced Research Projects Agency (DARPA) Microsystems Technologies Office (MTO). An overview is presented for the evolution of Joule-Thomson (J-T) micro-cryogenic cooler (MCC) technology. The initial design of a system on a chip method is shown for these micro-coolers to be used in conjunction with high operating temperature mid-wave infrared (MWIR) and long-wave infrared (LWIR) focal plane arrays. For the reflective visible band, results are shown for a gigapixel monocentric multi-scale camera design to solve the scaling issues for high pixel count and wide field of view. Lastly, we discuss two different approaches to multiband imaging and the potential advantages of this technology for the enhanced detection, recognition, and identification of targets.

Schottky barriers formed between metal (Au) and semiconductor (GaAs) can be used to detect photons with energy lower than the bandgap of the semiconductor. In this study, photodetectors based on Schottky barriers were fabricated and characterized for the detection of light at wavelength of 1280 nm. The device structure consists of three gold fingers with 1.75 mm long and separated by 0.95 mm, creating an E shape while the middle finger is disconnected from the outer frame. When the device is biased, electric field is stretched between the middle finger and the two outermost electrodes. The device was characterized by measuring the current-voltage (I-V) curve at room temperature. This showed low dark current on the order of 10^-10 A, while the photocurrent was higher than the dark current by four orders of magnitude. The detectivity of the device at room temperature was extracted from the I-V curve and estimated to be on the order of 5.3x10¹⁰ cm.Hz^0.5/W at 5 V. The step response of the device was measured from time-resolved photocurrent curve at 5 V bias with multiple on/off cycles. From which the average recovery time was estimated to be 0.63 second when the photocurrent decreases by four orders of magnitude, and the average rise time was measured to be 0.897 second. Furthermore, the spectral response spectrum of the device exhibits a strong peak close to the optical communication wavelength (~1.3 μm), which is attributed to the internal photoemission of electrons above the Schottky barrier formed between Au and GaAs.

A key design feature of P⁺-on-n HgCdTe detectors is the depth of the p-type region. Normally, homojunction architectures are utilized where the p-type region extends into the narrow-gap absorber layer. This facilitates the collection of photo-carriers from the absorber layer to the contact; however, this may result in excess generation-recombination (G-R) current if defects are present. Alternatively, properly adopting a heterojunction architecture confines the p-type region (and the majority of the electric field) solely to the wide-gap layer. Junction placement is critical since the detector performance is now dependent on the following sensitivity parameters: p-type region depth, doping, valence band offset, lifetime and detector bias. Understanding the parameter dependence near the hetero-metallurgical interface where the compositional grading occurs and the doping is varied as either a Gaussian or error function is vital to device design. Numerical modeling is now essential to properly engineer the electric field in the device to suppress G-R current while accounting for the aforementioned sensitivity parameters. The simulations reveal that through proper device design the p-type region can be confined to the wide-gap layer, reducing G-R related dark current, without significantly reducing the quantum efficiency at the operating bias V = -0.100V.

Gallium (Ga)-free InAs/InAsSb superlattices (SLs) are being actively explored for infrared detector applications due to the long minority carrier lifetimes observed in this material system. However, compositional and dimensional changes through antimony (Sb) segregation during InAsSb growth can significantly alter the detector properties from the original design. At the same time, precise compositional control of this mixed-anion alloy system is the most challenging aspect of Ga-free SL growth. In this study, the authors establish epitaxial conditions that can minimize Sb surface segregation during growth in order to achieve high-quality InAs/InAsSb SL materials. A nominal SL structure of 77 Å InAs/35 Å InA_s0.7Sb_0.3 that is tailored for an approximately six-micron response at 150 K was used to optimize the epitaxial parameters. Since the growth of mixed-anion alloys is complicated by the potential reaction of As2 with Sb surfaces, the authors varied the deposition temperature (Tg) under a variety of Asx flux conditions in order to control the As2 surface reaction on a Sb surface. Experimental results reveal that, with the increase of Tg from 395 to 440 °C, Sb-mole fraction x in InA_s1-xSb_x layers is reduced by 21 %, under high As flux condition and only by 14 %, under low As flux condition. Hence, the Sb incorporation efficiency is extremely sensitive to minor variations in epitaxial conditions. Since a change in the designed compositions and effective layer widths related to Sb segregation disrupts the strain balance and can significantly impact the long-wavelength threshold and carrier lifetime, further epitaxial studies are needed in order to advance the state-of-the-art of this material system.

A Ge-on-SOI uni-traveling carrier (UTC) photodetector was reported for high-power high-speed applications. The performances, in terms of dark-current, photocurrent responsivity and 3-dB bandwidth, were characterized for analog and coherent communications applications. The responsivity was 0.18 A/W at 1550 nm. The detector with a 40μmdiameter demonstrated an optical bandwidth of 2.72 GHz at -5V for 1550nm. The -1dB compression photocurrent at 1 GHz under -7V for 40μm-diameter device was about 16.24mA, the RF output power came to be 4.6 dBmw.

Electron-injection detectors are designed based on a new photon sensing mechanism. Here we demonstrate significant improvements in the device performance as a result of scaling the injector diameter with respect to the trapping/absorbing layer diameter. Devices with an order of magnitude smaller injector area with respect to the trapping/absorbing layer areas show more than an order of magnitude lower dark current, as well as an order of magnitude higher optical gain compared with devices of same size injector and trapping/absorbing layer areas. Devices with 10 μm injector diameter and 30 μm trapping/absorbing layer diameter show an optical gain of ~ 2000 at bias voltage of -3V with a cutoff wavelength of 1700 nm. We also derive analytical expressions for the electroninjection detector optical gain to qualitatively explain the significance of scaling the injector with respect to the absorber.

Electron-injection detectors are used in a high-speed swept source optical coherence tomography system for the first time. Compared to a commercial p-i-n detector, electron-injection detectors show more than 20 dB higher SNR.

Avalanche photodiodes (APD) manufactured at RMD are fabricated using deep diffusion processes, resulting in a thick reach-through APD with excellent performance characteristics. These include a high quantum efficiency (<50% for visible photons) and low excess noise (F ~ 2). Due to the structure of the APD, the devices have very low junction capacitance (~0.7pF/mm²). These devices have been made as squares or hexagons on the order of 2-4” dimensionally and require <1000 V for operation. Due to the high operating bias, studies on the Geiger behavior were dismissed. The low capacitance is conducive to developing large-area devices, and the large drift region allows for charge steering toward the high breakdown field region. These results provide initial data on the performance characteristics of RMD’s APDs when operated in Geiger mode. Due to the thickness of these devices, they provide a high gain-bandwidth product for near IR single photon counting. A small area (~4 mm²) APD was biased beyond the reverse bias breakdown voltage (~1700 V at -50 C), where the device showed typical Geigermode behavior with a low dark count rate (<54 kHz at 1700 V at an excess bias of 3 V). The data indicates a uniform response over the diode region, yet due to the large dark currents, the device was only operated to 5 V in excess bias beyond the breakdown voltage. The Geiger probability at 5V excess bias was measured as 3%, which is consistent with simulations that suggest an excess bias of ~300 V is required for 100% Geiger probability.

Electro-optical/infrared sensors are being developed for a variety of defense and commercial systems applications. One of the critical technologies that will enhance EO/IR sensor performance is the development of advanced antireflection coatings with both broadband and omnidirectional characteristics. In this paper, we review our latest work on high quality nanostructure-based antireflection structures, including recent efforts to deposit nanostructured antireflection coatings on large area substrates. Nanostructured antireflection coatings fabricated via oblique angle deposition are shown to enhance the optical transmission through transparent windows by minimizing broadband reflection losses to less than one percent, a substantial improvement over conventional thin-film antireflection coating technologies. Step-graded antireflection structures also exhibit excellent omnidirectional performance, and have recently been demonstrated on 6-inch diameter substrates.

Previously, we have reported measurements of the temperature-dependent surface resistivity of pure and multi-walled carbon nanotubes doped Polyvinyl Alcohol (PVA) thin films. In the temperature range from 22 °C to 40 °C, with a humidity-controlled environment, we found the surface resistivity to decrease initially but to rise steadily as the temperature continued to increase. Correspondingly, we have measured the temperature-dependent pyroelectric coefficient of doped polyvinylidene difluoride (PVDF) thin films, very well. While the physical mechanism of the pyroelectric phenomenon in PVDF thin films is quite well known, the surface resistivity behavior of PVA thin films is not so well known. Here, we address this concern by reporting the electrical mechanistic phenomena that contribute to surface resistivity of pure and doped PVA thin films, and give preliminary surface resistivity detectivity and other relevant quality factors for infrared (IR) and motion sensors. Regarding the pyroelectric effect of doped PVDF thin films, we give materials Figures-of-Merit based on our measurements. In addition, pyroelectric and surface resistivity infrared fundamentals, IR sensor uniqueness, and innovative techniques are presented.

We theoretically investigate the properties of the series-coupled fiber double-ring resonator in a Mach–Zehnder interferometer as highly sensitive temperature sensor. By comparison of phase difference between two arms, we acquired suitable phase difference of 0.5π between two arms in a Mach–Zehnder interferometer for sharpest asymmetric line shape around the resonance wavelength. We also analyze the effect of parameters on the sensitivity and the detection limit by measuring the intensity change at a fixed wavelength. For the 30dB signal-to-noise ratio system, the sensitivity and the detection limit can achieve 720.8/°C and 4.16×10−6 °C, respectively. These results indicate that this structure is suitable for highly sensitive, compact and stable sensors.

Recently, we have developed a new detector structure, which is known as the resonator- QWIP or R-QWIP. With the new structure, we demonstrated quantum efficiency (QE) as high as 70% in single detectors and 30 - 40% in focal plane arrays (FPAs) with 9 μm cutoff. In this study, we designed a broadband, 10 μm cutoff R-QWIP FPA using a more accurate refractive index. To achieve the theoretical prediction, the substrates of the detectors have to be removed completely to prevent the escape of unabsorbed light out of the detectors. The height of the diffractive elements (DE) and the thickness of the active resonator must also be uniformly produced within 0.05 μm accuracy. To achieve these specifications, two optimized inductively coupled plasma (ICP) etching processes are developed. Using these etching techniques, a number of single detectors were fabricated to verify the analysis before FPA production. In general, test data support the theoretical predictions.

In this paper we present an all-optical silicon modulator, where a silicon slab (450 μm) thick is coated on both sides to get a Fabry-Perot resonator for laser beam at wavelength of 1550nm. Most of the modulators discussed in literature, are driven by electrical field rather than by light. We investigate new approaches regarding the dependence of the absorption of the optical signal on the control laser pulse at 532 nm having 5nm pulse width. Our silicon based Fabry-Perot resonator increases the intrinsic c-Si finesse to >10, instead of the uncoated silicon with natural finesse of 2.5. The improved finesse is shown to have significant effect on the modulation depth using a pulsed laser. A modulation of 12dB was attained. The modulation is ascribed to two different effects - The Plasma Dispersion Effect (PDE) and the Thermo- Optic Effect (TOE). The PDE causes increase in the signal absorption in silicon via the absorption of the control laser light. On top of that, the transmission of the signal can decrease dramatically in high finesse resonators due to change in the refractive index due to TOE. The changes in the signal's absorption coefficient and in the refractive index are the result of incremental change in the concentration of free carriers. The TOE gives rise to higher refractive index as opposed to the PDE which triggers a decrease in the refractive index. Finally, tradeoff considerations are presented on how to modify one effect to counter the other one, leading to an optimal device having reduced temperature dependence.

The circular polarizers were mostly made of meta-atom based chiral metamaterials (CMMs). Here we propose an ultra-thin metallic grating based circular polarizer, which can convert any polarization into circular polarization. The circular polarizer consists of two layers: an ultra-thin metallic grating embedded in the substrate and a silicon grating on the substrate surface. The ultra-thin metallic grating, which is thinner than the skin depth and was shown to hold anomalous resonant reflection for transverse magnetic (TM) wave, functions as a quarter-wave plate. We show that the ultra-thin metallic grating based quarter-wave plate can transmit circular polarized wave when the incident linear polarized wave is oriented properly. The silicon grating acts as a linear polarizer which restricts the polarization of the light that reaches the metallic grating. Unlike some of the CMMs, our structure is independent of the incident polarization state. Moreover, the fabrication of our circular polarizer is easier than other double-layer-CMMs, in which the relative position between the two layers must be precisely controlled. Our structure can find its application integrated photonic devices.

SiGe offers a low-cost alternative to conventional infrared sensor material systems such as InGaAs, InSb, and HgCdTe for developing near-infrared (NIR) photodetector devices that do not require cooling and can offer high bandwidths and responsivities. As a result of the significant difference in thermal expansion coefficients between germanium and silicon, tensile strain incorporated into Ge epitaxial layers deposited on Si utilizing specialized growth processes can extend the operational range of detection to 1600 nm and longer wavelengths. We have fabricated SiGe based PIN detector devices on 300 mm diameter Si wafers in order to take advantage of high throughput, large-area complementary metal-oxide semiconductor (CMOS) technology. This device fabrication process involves low temperature epitaxial deposition of Ge to form a thin p⁺ seed/buffer layer, followed by higher temperature deposition of a thicker Ge intrinsic layer. An n+-Ge layer formed by ion implantation of phosphorus, passivating oxide cap, and then top copper contacts complete the PIN photodetector design. Various techniques including transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) have been employed to characterize the material and structural properties of the epitaxial growth and fabricated detector devices. In addition, electrical characterization was performed to compare the I-V dark current vs. photocurrent response as well as the time and wavelength varying photoresponse properties of the fabricated devices, results of which are likewise presented.

GeTe₄ waveguides were designed and fabricated on silicon substrates with a ZnSe isolation layer. GeTe₄ has a refractive index of 3.25 at a wavelength of 9 μm and a lower refractive index isolation layer is needed to realise waveguides on silicon. Numerical modelling was carried out to calculate the thickness of the isolation layer (ZnSe, refractive index ~2.4) required to achieve low loss waveguides. For a loss between 0.1 and 1.0 dB/cm it was found that a ~ 4 μm thick ZnSe film is required at a wavelength of 9 μm. ZnSe thin films were deposited on silicon, GeTe4 waveguides were fabricated by lift-off technique and were characterised for mid-infrared waveguiding.

We propose an integrated microfluidic optical system device design for a monolithic integration of blood plasma analysis in a single step using microfluidic channels on a tri wavelength LED source emitting wavelengths in ultraviolet, infrared and visible. The device is a miniature disposable Lab-on-a-Chip as small as 6x 1.5mm with a blood plasma reservoir volume of 2μl providing instantaneous results. The device is fabricated using minimal lithographic fabrication steps and consists of a microfluidic Polydimethylsiloxane (PDMS) layer on top of a quantum well (QW) structure. The PDMS layer has three 100μm thick microfluidic channels connected to the 2μl reservoir where the blood plasma is injected. The three microfluidic channels pass over the QW substrate which is micro fabricated to produce three LEDs that emit light in three different wavelengths on a single structure. The LEDs emit light in UV, infrared and visible and can be controlled individually for specific plasma testing or can emit light simultaneously depending on the application. To operate the device, first current is injected into the LEDs to turn on light emission. Light travels within the LED structure and at the same time light is emitted through the surface. Light can be either collected from the top of the device or the output facets by focusing the channels output on a spectrometer to collect the spectra of the device and analyze the output. The device is compact in size and provides fast, low power consumption and cost effective point of care devices with minimal heat output.

The modal characteristics of tapered single mode optical fibers and its strain sensing characteristics by using mechanically induced long period fiber gratings are presented in this work. Both Long Period Fiber Gratings (LPFG) and fiber tapers are fiber devices that couple light from the core fiber into the fiber cladding modes. The mechanical LPFG is made up of two plates, one flat and the other grooved. For this experiment the grooved plate was done on an acrylic slab with the help of a computer numerical control machine. The manufacturing of the tapered fiber is accomplished by applying heat using an oxygen-propane flame burner and stretching the fiber, which protective coating has been removed. Then, a polymer-tube-package is added in order to make the sensor sufficiently stiff for the tests. The mechanical induced LPFG is accomplished by putting the tapered fiber in between the two plates, so the taper acquires the form of the grooved plate slots. Using a laser beam the transmission spectrum showed a large peak transmission attenuation of around -20 dB. The resultant attenuation peak wavelength in the transmission spectrum shifts with changes in tension showing a strain sensitivity of 2pm/μɛ. This reveals an improvement on the sensitivity for structure monitoring applications compared with the use of a standard optical fiber. In addition to the experimental work, the supporting theory and numerical simulation analysis are also included.

In this work, we present experimental results of a cost-efficient photonic system capable to discriminate Polyvinyl Chloride (PVC) bottles from those made of Polyethylene Terephthalate (PET). The proposed array uses a semiconductor laser emitting at 810 nm, whose output is diverged employing a line lens in order to obtain a line light pattern. Given the lower attenuation coefficient of the PVC in comparison to PET at this wavelength, the received optical power is higher for the PVC than for the PET, which results in higher photogenerated current and, consequently, higher voltage after the transimpedance amplifier. Experiments considering several samples reveal an average voltage difference of 10% between materials, probing its feasibility for future industrial applications.

A previous paper described LWIR Pupil Imaging with a sensitive, low-flux focal plane array, and behavior of this type of system for higher flux operations as understood at the time. We continue this investigation, and report on a more detailed characterization of the system over a broad range of pixel fluxes. This characterization is then shown to enable non-uniformity correction over the flux range, using a standard approach. Since many commercial tracking platforms include a “guider port” that accepts pulse width modulation (PWM) error signals, we have also investigated a variation on the use of this port to “dither” the tracking platform in synchronization with the continuous collection of infrared images. The resulting capability has a broad range of applications that extend from generating scene motion in the laboratory for quantifying performance of “realtime, scene-based non-uniformity correction” approaches, to effectuating subtraction of bright backgrounds by alternating viewing aspect between a point source and adjacent, source-free backgrounds.

Spectrally encoded microscopy (SEM) is a new microscopic imaging technique in which a grating is used to illuminate different positions along a line on the sample with different wavelengths, reducing the size of system and imaging time. In this paper, a SEM device is described which is based on a swept source and a balanced detection. A fixed gain balanced detector (BD) was employed in the system for detecting the low sample light without amplifier. Compared to conventional SEM detection method, our BD-SEM device has two significant advantages, one is its capability of suppressing common-mode noise and thermal noise, resulting in the lateral resolution better than direct detection, the other is that it can amplify the signal intensity which is particularly helpful for tissue reflectance imaging. The lateral resolution was measured by imaging a USAF resolution target. The images of onion cells were obtained. The data showed that both the lateral resolution and signal noise ratio are better than non-BD method. The method presented in this work is helpful for developing miniature endoscopic probe for in vivo tissue visualization with high acquisition speed and high imaging quality.

High-resolution imaging in ultraviolet (UV) bands has many applications in defense and commercial systems. The shortest wavelength is desired for increased spatial resolution, which allows for small pixels and large formats. The next frontier is to develop UV avalanche photodiode (UV-APD) arrays with high gain to demonstrate high-resolution imaging. We compare performance characteristics of front-illuminated Al0.05Ga0.95N UV-APDs grown on a free-standing (FS) GaN substrate and a GaN/sapphire template. UV-APDs grown on a FS-GaN substrate show lower dark current densities for all fabricated mesa sizes than similar UV-APDs grown on a GaN/sapphire template. In addition, stable avalanche gain higher than 5×10⁵ and a significant increase in the responsivity of UV-APDs grown on a FS-GaN substrate are observed as a result of avalanche multiplication at high reverse bias. We believe that the high crystalline quality of Al_0.05Ga_0.95N UVAPDs grown on a FS-GaN substrate with low dislocation density is responsible for the observed improvement of low leakage currents, high performance photodetector characteristics, and reliability of the devices.

The Center for Detectors at Rochester Institute of Technology and Raytheon Vision Systems (RVS) are leveraging RVS capabilities to produce large format, short-wave infrared HgCdTe focal plane arrays on silicon (Si) substrate wafers. Molecular beam epitaxial (MBE) grown HgCdTe on Si can reduce detector fabrication costs dramatically, while keeping performance competitive with HgCdTe grown on CdZnTe. Reduction in detector costs will alleviate a dominant expense for observational astrophysics telescopes. This paper presents the characterization of 2.5μm cutoff MBE HgCdTe/Si detectors including pre- and post-thinning performance. Detector characteristics presented include dark current, read noise, spectral response, persistence, linearity, crosstalk probability, and analysis of material defects.

Selective laser melting (SLM) is an additive manufacturing (AM) technology that uses a high-power laser beam to melt metal powder in chamber of inert gas. The process starts by slicing the 3D CAD data as a digital information source into layers to create a 2D image of each layer. Melting pool was formed by using laser irradiation on metal powders which then solidified to consolidated structure. In a selective laser melting process, the variation of melt pool affects the yield of a printed three-dimensional product. For three dimensional parts, the border conditions of the conductive heat transport have a very large influence on the melt pool dimensions. Therefore, melting pool is an important behavior that affects the final quality of the 3D object. To meet the temperature and geometry of the melting pool for monitoring in additive manufacturing technology. In this paper, we proposed the temperature sensing system which is composed of infrared photodiode, high speed camera, band-pass filter, dichroic beam splitter and focus lens. Since the infrared photodiode and high speed camera look at the process through the 2D galvanometer scanner and f-theta lens, the temperature sensing system can be used to observe the melting pool at any time, regardless of the movement of the laser spot. In order to obtain a wide temperature detecting range, 500 °C to 2500 °C, the radiation from the melting pool to be measured is filtered into a plurality of radiation portions, and since the intensity ratio distribution of the radiation portions is calculated by using black-body radiation. The experimental result shows that the system is suitable for melting pool to measure temperature.

Non-subjective and early diagnostic technique for liver fibrosis may decrease morbidity in patients and reduce medical costs. Liver fibrosis results in changes in density and thermal properties of tissue. In this work, we evaluate numerically the feasibility of using the optical beam deflection method (OBDM) by means of a thermo-optic material in contact with liver tissue to quantitate changes in thermal conduction. We use the finite-difference method to model the heat transfer in liver and acrylic slab. The response required for thermal characterization for different fibrosis stages is assessed by calculating the deflection angle using ray trace analysis. Numerical study shows the potential of the OBDM for developing an optical-integrated sensor as non-subjective diagnostic technique for liver fibrosis.