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Now showing items 1 - 16 of 163

  • SYSTEMS FOR COHERENT LIGHT DETECTION AND RELATED METHODS

    Systems for coherent light detection are provided, including a system comprising a light source configured to generate light; a first optical assembly configured to split the light into a reference arm and a sample arm; a second optical assembly configured to illuminate a sample with light of the sample arm, thereby generating a sample signal; a third optical assembly configured to combine the sample signal with light of the reference arm, thereby generating an interference signal; and a detector assembly comprising an array of carrier injection photodetectors, the array arranged to collect the interference signal. Methods of using the systems are also provided.
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  • Emerging technologies for high performance infrared detectors

    Tan, Chee Leong   Mohseni, Hooman  

    Infrared photodetectors (IRPDs) have become important devices in various applications such as night vision, military missile tracking, medical imaging, industry defect imaging, environmental sensing, and exoplanet exploration. Mature semiconductor technologies such as mercury cadmium telluride and III-V material-based photodetectors have been dominating the industry. However, in the last few decades, significant funding and research has been focused to improve the performance of IRPDs such as lowering the fabrication cost, simplifying the fabrication processes, increasing the production yield, and increasing the operating temperature by making use of advances in nanofabrication and nanotechnology. We will first review the nanomaterial with suitable electronic and mechanical properties, such as two-dimensional material, graphene, transition metal dichalcogenides, and metal oxides. We compare these with more traditional low-dimensional material such as quantum well, quantum dot, quantum dot in well, semiconductor superlattice, nanowires, nanotube, and colloid quantum dot. We will also review the nanostructures used for enhanced lightmatter interaction to boost the IRPD sensitivity. These include nanostructured antireflection coatings, optical antennas, plasmonic, and metamaterials.
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  • Engineering the gain-bandwidth product of phototransistor diodes

    Bianconi, Simone   Rezaei, Mohsen   Park, Min-Su   Huang, Wenyuan   Tan, Chee Leong   Mohseni, Hooman  

    In recent years, phototransistors have considerably expanded their field of application, including for instance heterodyne detection and optical interconnects. Unlike in low-light imaging, some of these applications require fast photodetectors that can operate in relatively high light levels. Since the gain and bandwidth of phototransistors are not constant across different optical powers, the devices that have been optimized for operation in low light level cannot effectively be employed in different technological applications. We present an extensive study of the gain and bandwidth of short-wavelength infrared phototransistors as a function of optical power level for three device architectures that we designed and fabricated. The gain of the photodetectors is found to increase with increasing carrier injection. Based on a Shockley-Read-Hall recombination model, we show that this is due to the saturation of recombination centers in the phototransistor base layer. Eventually, at a higher light level, the gain drops, due to the Kirk effect. As a result of these opposing mechanisms, the gain-bandwidth product is peaked at a given power level, which depends on the device design and material parameters, such as doping and defect density. Guided by this physical understanding, we design and demonstrate a phototransistor which is capable of reaching a high gain-bandwidth product for high-speed applications. The proposed design criteria can be employed in conjunction with the engineering of the device size to achieve a wide tunability of the gain and bandwidth, hence paving the way toward fast photodetectors for applications with different light levels. Published under license by AIP Publishing.
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  • Sensitivity Limit of Nanoscale Phototransistors

    Rezaei, Mohsen   Park, Min-Su   Tan, Chee Leong   Mohseni, Hooman  

    In this letter, the optical gain mechanism in phototransistor detectors (PTDs) is explored in low light conditions. An analytical formula is derived for the physical limit on the minimum number of detectable photons for the PTD. This formulation shows that the sensitivity of the PTD, regardless of its material composition, is related to the square root of the normalized total capacitance at the base layer. Since the base total capacitance is directly proportional to the size of the PTD, the formulation shows the scaling effect on the sensitivity of the PTD. Our proposed model can be used to explore a wide range of PTDs, including nanowire, monolayer, and bulk devices. For the illustration of the ability of the model, two different PDTs, one with bottom-up fabrication for ultraviolet and the other with top-down fabrication for short-wave infrared (SWIR) detection, are used. For the SWIR PTD, a scaling effect is explored on InGaAs-based devices. Our modeling predicts that this PTD with a nanoscale electronic area can reach to a single photon noise equivalent power even at room temperature. To the best of our knowledge, this is the first comprehensive study on the sensitivity of the PTD for extreme low light detection.
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  • Heterojunction phototransistor for highly sensitive infrared detection

    Rezaei, Mohsen   Park, Min-Su   Tan, Chee Leong   Rabinowitz, Cobi   Wheaton, Skyler   Mohseni, Hooman  

    In this work, we have proposed a model for the ultimate physical limit on the sensitivity of the heterojunction bipolar phototransistors (HPTs). Based on our modeling we have extracted the design criteria for the HPT for high sensitivity application. HPT with the submicron emitter and base area has the potential to be used for the low number photon resolving in near-infrared (NIR) wavelength. However, in practice, the quality of materials, processing, and the passivation plays an important role in the realization of the highly sensitive HPT. For short wave infrared (SWIR) HPTs based on lattice matched InGaAs to InP is studied. For these devices, conditions to reach to the highest possible sensitivity is examined. We have made an HPT based on InGaAs collector and base on the InP substrate. After developing proper processing combination of wet and dry etching and the surface passivation for the device we made an imager with 320x256 pixels based with a 30m pixel pitch. The imager shows the sensitivity less the 30 photons for each pixel with the frame rate more than 1K frames per second.
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  • On the Sensitivity of Electron-Injection Detectors at Low Light Level

    Fathipour, Vala   Nia, Iman Hassani   Bonakdar, Alireza   Mohseni, Hooman  

    We present the signal-to-noise performance of a short-wave infrared detector, which offers an internal avalanche-free gain. The detector is based on a similar mechanism as the heterojunction phototransistor and takes advantage of a type-II band alignment. Current devices demonstrate a noise-equivalent sensitivity of similar to 670 photons at 260 K and over a linear dynamic range of 20 dB. While this level of sensitivity is about an order of magnitude better than an ideal p-i-n detector attached to the same low-noise amplifier, it was still limited by the amplifier noise (similar to 2600 electrons root mean square) due to the insufficient device gain. Performance comparison with other SWIR detector technologies demonstrates that the so-called electron-injection detectors offer more than three orders of magnitude better noise-equivalent sensitivity compared with state-of-the-art phototransistors operating at similar temperature.
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  • SYSTEMS, APPARATUSES AND METHODS FOR CONVERTING LIGHT WAVELENGTHS

    In one aspect, an apparatus for converting light having a first wavelength to a light having a second wavelength is provided. The apparatus includes an interband light detector configured to detect light with the first wavelength, a light emitting device configured to emit light with the second wavelength, and a connector connecting the light detector to the light emitting device. In another aspect, an apparatus includes an absorber layer configured to absorb light having a first wavelength, a barrier and trap layer adjacent the absorber layer, an injector layer adjacent the barrier and trap layer, and an emitting device configured to emit light having a second wavelength. In a further aspect, a method is provided and includes absorbing an input light having a first wavelength, converting the first wavelength to a second wavelength different in size than the first wavelength, and emitting an output light having the second wavelength.
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  • Embedded plasmonic-enhanced quantum well infrared photodetector

    Brown, Robert L.   Bonakdar, Alireza   Jang, Sung Jun   Memis, Omer G.   Mohseni, Hooman  

    Quantum Well Infrared Photodetector (QWIP) is an attractive candidate for long-wave infrared detection but is limited due its low quantum efficiency and its polarization sensitivity. Here we propose a detector with an embedded plasmonic structure surrounding the detector that is protected. Our detector uses an array of pillars surrounded by a plasmonic metal and contacted from the top making one "super pixel". This structure is within close proximity of the active medium and is protected by the top contact. This configuration also eliminates non-absorbing semiconductor eliminating significant dark current.
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  • Demonstration of Shot-noise-limited Swept Source OCT Without Balanced Detection

    Fathipour, Vala   Schmoll, Tilman   Bonakdar, Alireza   Wheaton, Skylar   Mohseni, Hooman  

    Optical coherence tomography (OCT) has been utilized in a rapidly growing number of clinical and scientific applications. In particular, swept source OCT (SS-OCT) has attracted many attentions due to its excellent performance. So far however, the limitations of existing photon detectors have prevented achieving shot-noise-limited sensitivity without using balanced-detection scheme in SS-OCT, even when superconducting single-photon detectors were used. Unfortunately, balanced-detection increases OCT system size and cost, as it requires many additional components to boost the laser power and maintain near ideal balanced performance across the whole optical bandwidth. Here we show for the first time that a photon detector is capable of achieving shot noise limited performance without using the balanced-detection technique in SS-OCT. We built a system using a so-called electron-injection photodetector, with a cutoff-wavelength of 1700 nm. Our system achieves a shot-noiselimited sensitivity of about -105 dB at a reference laser power of -350 nW, which is more than 30 times lower laser power compared with the best-reported results. The high sensitivity of the electron-injection detector allows utilization of micron-scale tunable laser sources (e.g. VCSEL) and eliminates the need for fiber amplifiers and highly precise couplers, which are an essential part of the conventional SS-OCT systems.
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  • Near-field Back-action Cooling and Amplification

    Nia, Iman Hassani   Fathipour, Vala   Mohseni, Hooman  

    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.
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  • Hybrid optical antenna with high directivity gain

    Bonakdar, Alireza   Mohseni, Hooman  

    Coupling of a far-field optical mode to electronic states of a quantum absorber or emitter is a crucial process in many applications, including infrared sensors, single molecule spectroscopy, and quantum metrology. In particular, achieving high quantum efficiency for a system with a deep subwavelength quantum absorber/emitter has remained desirable. In this Letter, a hybrid optical antenna based on coupling of a photonic nanojet to a metallo-dielectric antenna is proposed, which allows such efficient coupling. A quantum efficiency of about 50% is predicted for a semiconductor with volume of similar to lambda(3)/170. Despite the weak optical absorption coefficient of 2000 cm(-1) in the long infrared wavelength of similar to 8 mu m, very strong far-field coupling has been achieved, as evidenced by an axial directivity gain of 16 dB, which is only 3 dB below of theoretical limit. Unlike the common phased array antenna, this structure does not require coherent sources to achieve a high directivity. The quantum efficiency and directivity gain are more than an order of magnitude higher than existing metallic, dielectric, or metallo-dielectric optical antenna. (C) 2013 Optical Society of America
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  • Precise Formation of Dovetail Structures for InP-Based Devices

    Nia, Iman Hassani   Mohseni, Hooman  

    Anisotropic etching of InP along specific crystallographic directions leads to negative sidewall angles along dovetail direction. This is an important process for self-alignment of electrical contacts where sub-micron alignment is needed. However, existing etching methods are only suitable for shallow etching, and for stress-free layers. Here we demonstrate a new etching method that is capable of producing dovetail patterns with 10 times larger etch depth, and where interface stress exists. We believe this new etching method is useful for many electronic and optoelectronic devices that require precise negative angle sidewalls in their fabrication scheme. (C) 2013 The Electrochemical Society. All rights reserved.
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  • A proposal for Coulomb assisted laser cooling of piezoelectric semiconductors

    Nia, Iman Hassani   Mohseni, Hooman  

    Anti-Stokes laser cooling of semiconductors as a compact and vibration-free method is very attractive. While it has achieved significant milestones, increasing its efficiency is highly desirable. The main limitation is the lack of the pristine material quality with high luminescence efficiency. Here, we theoretically demonstrate that the Coulomb interaction among electrons and holes in piezoelectric heterostructures could lead to coherent damping of acoustic phonons; rendering a significantly higher efficiency that leads to the possibility of cooling a broad range of semiconductors. (c) 2014 AIP Publishing LLC.
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  • Optomechanical beam steering by surface plasmon nanoantenna

    Bonakdar, Alireza   Kohoutek, John   Mohseni, Hooman  

    Controlling the far field pattern of the electromagnetic (EM) waves has many applications including wireless communications, radar detection, and industrial applications. The dynamic control of EM patterns is called beam steering. Despite advantages in each technique, the speed, angular range, and spectral range of beam steering is limited due to mechanical and optical properties of such systems. Here we present a beam steering method by means of an array of optomechanical nanoantennas in which the generated optical force of each antenna results in changes to the antenna response due to mechanical reconfiguration. As a result, the antenna far field phase is changed due to the mechanical movement generated by the optical force. Depending on the mechanical properties of the movable component of the antenna, the phase of the antenna can be tailored for a given optical source power. FDTD simulations are used to calculate the optical response of antenna. A phase array of optomechanical nanoantennas is used to do beam steering. The main far field lobe is steered by 0.5 degrees as a result of the mechanical reconfiguration of the phased array.
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  • Interlevel Cascade Transition in Electrically Confined Quantum Wire Arrays

    Wu, Wei   Hassani, Iman   Mohseni, Hooman  

    Vertical stacks of electrically confined quantum wires were demonstrated in devices with large areas. Multiple current plateaus and strong differential conductance oscillations were observed at above liquid nitrogen temperatures because of interlevel cascade transition of carriers. Our simulation results for charge transport, as well as interlevel infrared photoresponse red-shift, due to lateral electric field confinement show good agreement with experimental data.
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  • A Low-Power,High-Speed Readout for Pixel Detectors Based on an Arbitration Tree

    Fahim, Farah   Joshi, Siddhartha   Ogrenci-Memik, Seda   Mohseni, Hooman  

    In this article, a low-power, high-speed arbitration tree for pixel detector readout is presented. The synchronized, binary tree priority encoder establishes a position-dependent priority list at the start of every time frame. Pixels that indicate the presence of data for readout are sequentially granted access to a shared bus for data transfer to the periphery, without the use of an additional global strobe signal. It can be used for either full frame imaging or zero-suppressed readout, in which case it can simultaneously generate the pixel address. To increase the readout frame rate, the pixel array is subdivided into two halves, which allow interleaved latching of data at the output serializer. The design was implemented in a 65-nm LP-CMOS process for the readout of a 64 x 64x pixel array. Measurement results demonstrate a deadtimeless, full frame imaging rate of similar to 50 kfps, achieved with a dedicated output for every (32x32) 1024 pixels and for a pixel data packet of 11 bits, with no bit errors detected over 1000 frames. The measured energy per bit is 0.94 pJ.
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