Highly sensitive photon detectors are regarded as the key enabling elements in many applications. Due to the low photon energy at the short-wave infrared (SWIR), photon detection and imaging at this band are very challenging. As such, many efforts in photon detector research are directed toward improving the performance of the photon detectors operating in this wavelength range. To solve these problems, we have developed an electron-injection (EI) technique. The significance of this detection mechanism is that it can provide both high efficiency and high sensitivity at room temperature, a condition that is very difficult to achieve in conventional SWIR detectors. An EI detector offers an overall system-level sensitivity enhancement due to a feedback stabilized internal avalanche-free gain. Devices exhibit an excess noise of unity, operate in linear mode, require bias voltage of a few volts, and have a cutoff wavelength of 1700 nm. We review the material system, operating principle, and development of EI detectors. The shortcomings of the first-generation devices were addressed in the second-generation detectors. Measurement on second-generation devices showed a high-speed response of ∼6 ns rise time, low jitter of less than 20 ps, high amplification of more than 2000 (at optical power levels larger than a few nW), unity excess noise factor, and low leakage current (amplified dark current ∼10 nA at a bias voltage of −3 V and at room temperature. These characteristics make EI detectors a good candidate for high-resolution flash light detection and ranging (LiDAR) applications with millimeter scale depth resolution at longer ranges compared with conventional p-i-n diodes. Based on our experimentally measured device characteristics, we compare the performance of the EI detector with commercially available linear mode InGaAs avalanche photodiode (APD) as well as a p-i-n diode using a theoretical model. Flash LiDAR images obtained by our model show that the EI detector array achieves better resolution with higher signal-to-noise compared with both the InGaAs APD and the p-i-n array (of 100×100 elements). We have designed a laboratory setup with a receiver optics aperture diameter of 3 mm that allows an EI detector (with 30-μm absorber diameter) to be used for long-range LiDAR imaging with subcentimeter resolution.
used for monitoring and profiling structures, range, velocity, vibration, and air turbulence. Remote sensing in the IR region has several advantages over the visible region, including higher transmitter energy while maintaining eye-safety requirements. Electron-injection detectors are a new class of detectors with high internal avalanche-free amplification together with an excess-noise-factor of unity. They have a cutoff wavelength of 1700 nm. Furthermore, they have an extremely low jitter. The detector operates in linear-mode and requires only bias voltage of a few volts. This together with the feedback stabilized gain mechanism, makes formation of large-format high pixel density electron-injection FPAs less challenging compared to other detector technologies such as avalanche photodetectors. These characteristics make electron-injection detectors an ideal choice for flash LiDAR application with mm scale resolution at longer ranges. Based on our experimentally measured device characteristics, a detailed theoretical LiDAR model was developed. In this model we compare the performance of the electron-injection detector with commercially available linear-mode InGaAs APD from (Hamamatsu G8931-20) as well as a p-i-n diode (Hamamatsu 11193 p-i-n). Flash LiDAR images obtained by our model, show the electron-injection detector array (of 100 x 100 element) achieves better resolution with higher signal-to-noise compared with both the InGaAs APD and the p-i-n array (of 100 x 100 element).
This article reports the progress on the development of a novel detector with the promise of addressing the needs of extreme AO (ExAO) in the near-IR band (NIR), 0.9-1.7 μm. The camera is based on the electron injection mechanism which resembles how the human eye processes light. The camera design allows high sensitivity operation at TEC reachable temperatures for ExAO at 1-4 kHz frame rates, and at the same time the concept produces sufficient gain to overcome the read noise of the device. Here we present the overall design, test results on Gen-1 (outdated but operable) camera, along with early results of our next generation of detectors.
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.
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.
We have introduce optomechanical nanoantennae, which showed dramatic changes in scattering
properties by minuscule changes in geometry. These structures are very compact, with a volume 500
times smaller than free space optical wavelength volume. Through these optical elements, far-field can
directly control the near-field of antenna by mechanical reconfiguration. Here we present the functionality
of the optomechanical nanoantenna and challenges in fabricating and measuring these devices.
Our group has designed and developed a novel telecom band photon detector called the electron-injection detector. The detector provides a high avalanche-free internal-amplification and a stable excess noise factor of near unity while operating at linear-mode with low bias voltages. In our previous reports on un-isolated detectors, the large dark current of the detectors prevented long integration times in the camera. Furthermore, the bandwidth of the un-isolated detectors was in the KHz range. Recently, by changing the 3D geometry and isolating the detectors from each other, we have achieved 3 orders of magnitude reduction in dark current at same bias voltage and temperature compared to our previous results. Isolated detectors have internal dark current densities of 0.1nA/cm2 at 160 K. Furthermore, they have a bandwidth that is 4 orders of magnitude higher than the un-isolated devices. In this paper we report room temperature and low temperature characteristics of the isolated electron-injection detectors. We show that the measured optical gain displays a small dependence on temperature over our measured range down to 220 K.
Plasmonic structures produce well-known enhancement of the near-field optical intensity due to sub-wavelength optical confinement. These properties can produce a significant change of transmission and reflection upon small mechanical change of the antenna configuration. We have developed a method based on this enhanced sensitivity for cooling and amplification of a moving mirror. Using finite difference time domain method and standard optomechanical coupled-equation, different regimes of operation such as laser detuning and cavity length were studied to compare the effect of the near-field enhancement with the conventional radiation pressure. Using practical microcavity parameters, we demonstrate significantly higher cooling - or amplification- efficiency for the near-field plasmonic effect. Moreover, the volume of the system is very small. We believe that the significant efficiency improvement and reduced volume due to the proposed near-field effect can make this approach practical for many applications ranging from gravitational wave detection to photonic clocks, high precision accelerometers, atomic force microscopy, laser cooling and parametric amplification.
In order to lessen the strain of cooling requirements on mid-infrared detectors, reducing the volume of the detecting medium is one promising solution. It is necessary to augment the absorption (quantum efficiency) lost when shrinking the detector volume. We present a Quantum Well Infrared Photodetector with a plasmonic structure embedded within and around the detection media. This device has a self-aligned plasmonic-hole array designed for 8μm wavelength and a planar top contact to the array of detector material. This arrangement has an expected field enhancement of an order of magnitude and lends itself to making a Focal Plane Array.
Our group has designed and developed a new SWIR single photon detector called the nano-injection detector that is conceptually designed with biological inspirations taken from the rod cells in human eye. The detector couples a nanoscale sensory region with a large absorption volume to provide avalanche free internal amplification while operating at linear regime with low bias voltages. The low voltage operation makes the detector to be fully compatible with available CMOS technologies. Because there is no photon reemission, detectors can be formed into high-density single-photon detector arrays. As such, the nano injection detectors are viable candidates for SPD and imaging at the short-wave infrared band. Our measurements in 2007 proved a high SNR and a stable excess noise factor of near unity. We are reporting on a high speed version of the detector with 4 orders of magnitude enhancement in speed as well as 2 orders of magnitude reduction in dark current (30nA vs. 10 uA at 1.5V).
We report mechanical frequency and amplitude modulation of a quantum cascade laser (QCL) integrated with a
plasmonic antenna operating at ~6.1 μm. We have observed a shift in the lasing frequency by over 30 GHz and an
intensity modulation of ~74% when an atomic force microscope (AFM) tip approaches the hot spot of a metal-dielectricmetal
(MDM) bow-tie antenna integrated onto the facet of the laser. The tip diameter is ~λ/60 and in non-contact mode
its amplitude of motion is ~λ/120. We have presented a theoretical model based on the rate equations for a QCL which
affirms our experimental observations. Our experiment demonstrates the strong influence of the hot spot on the laser
cavity modes, despite the fact that the former is many orders of magnitude smaller than the latter. We have compared
our device to a previous mechanically frequency modulated QCL and calculated a figure of merit, change in frequency
divided by change in distance of the mechanical component (Δf/Δd), which is an order of magnitude higher, while our
design uses a volumetric change per λ3 that is five orders of magnitude smaller. Our device differs from optical gradient
force actuated devices in that our device is externally mechanically actuated while those devices are self actuated
through the optical force. This sensitivity of the laser cavity mode to the position of a nanometer-scale metallic absorber
opens up the opportunity for modulating large amount of optical power by changing the optical properties of a miniscule
volume in an integrated, chip-scale device.
Here we present an antenna-integrated QCL which can be actively and optically modulated using light in the near infrared, creating an optical nanocircuit – coupling two different frequency antennas with a nonlinear active switching element. For our design, we chose two cross-polarized bow-tie antennas with an aligned central spot. We have used detailed FDTD simulations to choose the length of each bow-tie. The larger bow-tie antenna is resonant with the QCL at 6.1 μm wavelength and is aligned perpendicular to the active region of the device because QCL emits TM polarized light. The smaller bow-tie is resonant with the incoming modulating light at 1550 nm and is aligned perpendicularly to the first bow-tie. There is a rectangular region of amorphous germanium below the smaller bow-tie which acts as an absorber at 1550 nm. When light at 1550 nm is incident upon the device, it is focused and enhanced by the smaller bowtie, creating a region of large absorption in the germanium rectangle below. Free carriers are generated, shorting the larger bow-tie which is already focusing and enhancing light from the QCL mode. When the bow-tie arms of the larger bow-tie are shorted by these free carriers, the focusing and enhancement of the light by the larger bow-tie of the QCL mode is severely diminished, affecting the entire laser output, even the far field. Simulation results, fabrication details, and finally experimental results are discussed. Such an all-optical switch could be useful for telecommunications, free space communications, or rangefinding applications.