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Method For Imaging Neurotransmitters In Vitro and In Vivo Using Functionalized Carbon Nanotubes

Neurotransmitters play a central role in complex neural networks by serving as chemical units of neuronal communication.  Quantitative optical methods for the detection of changes in neurotransmitter levels has the potential to profoundly increase our understanding of how the brain works. Therapeutic drugs that target neurotransmitter release are used ubiquitously to treat a vast array of brain and behavioral disorders.  For example, new methods in this sphere could provide a new platform by which to validate the function of drugs that alter modulatory neurotransmission, or to screen antipsychotic and antidepressant drugs.  However, currently in neuroscience, few optical methods exist that can detect neurotransmitters with high spatial and temporal resolution in vitro or in vivo.  Brain tissue also readily scatters visible wavelengths of light currently used to perform biological imaging, and neuronal tissue and has an abundance of biomolecules that are chemically or structurally similar and therefore hard to specifically distinguish.  Furthermore, neurotransmission relevant processes occur at challenging spatial  and temporal scales.    UC Berkeley investigators have developed polymer-functionalized carbon nanotubes for in vitro and in vivo quantification of extracellular modulatory neurotransmitter levels using optical detectors. The method uses the fluorescent optical properties of polymer-functionalized carbon nanotubes to selectively report changes in concentration of specific neurotransmitters. The scheme is novel in that the detection method applies to wide variety of specific neurotransmitters, it is an optical method and therefore gives greater spatial information, and enables the potential for imaging of one or more neurotransmitters. The optical method also produces less damage to the surrounding tissue than methods that implant electrodes or cells and allows high resolution localization with other methods of optical investigation. The invention takes advantage of favorable fluorescence properties of carbon nanotubes, such as carbon nanotube emission in the near infrared and infinite fluorescence lifetime.  The near infrared emission scatters less than shorter wavelengths, enabling greater signal recovery from deeper tissue, and allows greater compatibility with other techniques. The optical properties also enable long term potentially even chronic use. 

Direct Optical Visualization Of Graphene On Transparent Substrates

96 Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:Calibri; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;} The ∼10% optical contrast of graphene on specialized substrates like oxide-capped silicon substrates, together with the high-throughput and noninvasive features of optical microscopy, have greatly facilitated the use and research of graphene research for the past decade.  However, substantially lower contrast is obtained on transparent substrates. Visualization of nanoscale defects in graphene, e.g., voids, cracks, wrinkles, and multilayers, formed during either growth or subsequent transfer and fabrication steps, represents yet another level of challenge for most device substrates.     UC Berkeley researchers have developed a facile, label-free optical microscopy method to directly visualize graphene on transparent inorganic and polymer substrates at 30−40% image contrast per graphene layer.  Their noninvasive approach overcomes typical challenges associated with transparent substrates, including insulating and rough surfaces, enables unambiguous identification of local graphene layer numbers and reveals nanoscale structures and defects with outstanding contrast and throughput. We thus demonstrate in situ monitoring of nanoscale defects in graphene, including the generation of nano-cracks under uniaxial strain, at up to 4× video rate.  

Pseudo Light-Field Display

Creating correct focus cues (blur and accommodation) has become a critical issue in the development of the next generation of 3D displays, particularly head-mounted displays.  Withough correct focus cues, current 3D displays create undue visual discomfort and reduce visual performance.  Current attempts to solve the focus cues problem are limited in their practical use.  For example, volumetric displays are limited because the viewable scene is restricted to the size of the display volume.  Multi-plane displays require very accurate alignment between the display and the viewer’s eyes.  Light field displays often require demanding resolution requirements and computational workload.   Researchers at UC Berkeley have developed a system and method to correct focus cues with a conventional display, a dynamic lens in front of each eye, and a method to measure the current focus or an estimate of the current focus of each eye.  Most of the system components are currently commercially available and the technology solves the speed and resolution problems in current light field displays. 

Apparatus and Method for 2D-based Optoelectronic Imaging

The use of electric fields for signaling and manipulation is widespread, mediating systems spanning the action potentials of neuron and cardiac cells to battery technologies and lab-on-a-chip devices. Current FET- and dye-based techniques to detect electric field effects are systematically difficult to scale, costly, or perturbative. Researchers at the University of California Berkeley have developed an optical detection platform, based on the unique optoelectronic properties of two-dimensional materials that permits high-resolution imaging of electric fields, voltage, acidity, strain and bioelectric action potentials across a wide field-of-view.

A New Method For Improving 3-D Depth Perception

The ability to see depth is a key visual function, as three-dimensional vision is used to guide body movements. Although many visual cues are used to infer spatial relationships, depth perception relies primarily on stereopsis, or the perception of depth based on differences in the images in the two eyes. More than 5% of the US population, however, is unable to see in three dimensions due to stereo-blindness and stereo-anomaly. Without depth perception, basic activities such as catching a ball or driving a car are not possible. Current therapeutic methods to address this issue include a set of eye-training exercises that aim to equalize the input from the eyes to the brain, which are collectively called orthoptics.   Researchers at UC Berkeley have developed an orthoptic method to train stereo depth perception. This method includes devices and systems for implementation, and it can be used in the home. 

Compressive Plenoptic Imaging

Better understanding the brain's architecture and the behavior of neural networks requires non-invasive probes capable of monitoring brain activity at the scale of individual neurons.  Functional neuro-imaging methods have the advantage of being minimally invasive and can potentially resolve individual action potentials.  An ideal imaging method would be capable of quantifying many neurons simultaneously, have high spatial and temporal resolution, be non-invasive, and be accurate even in deep layers of brain tissue. There are a variety of current techniques available, many of which use mechanical scanning to reduce the effects of optical scattering and therefore have low temporal resolution. UC Berkeley researchers have developed a device capable of quantitative functional neuro-imaging in the thick brain tissue of live animals. By combining a detection method with algorithmic data processing, this device achieves single neuron resolution and fast sampling rates with high spatial and temporal resolution.  

BRIGHT: Building With Radiant And Insulated Green Harvesting Technology

People spend a large part of the day inside a building for different purposes, e.g. living, working, and shopping. Lighting is one of the largest categories of end-use energy consumption in the commercial sector. In 2014, the Department of Energy reported that approximately 40% of total U.S. energy was consumed in residential and commercial buildings and costing $50 billion each year. Commercial buildings account for over 70% of U.S. electricity use and lighting accounts for approximately 30% of the building use. Traditional approaches have implemented passive or active efficient energy strategies, like electronic ballasts, LED technologies, compact fluorescent lamps, occupancy sensors, and common light bulb standards. One problem is that each of these technologies require a power supply or battery. Another problem is all of these have a lifetime and a replacement cost. To address these challenges, researchers at the University of California, Berkeley, have demonstrated a smart dynamic panel system for capturing and channeling daylight without gains and/or losses of heat and without compromising the structure of the building. The designed translucent panel for building envelopes (i.e. facades and/or roof) is a modular element that can be used as the primary physical separator between the conditioned and unconditioned environment, or can also be used in specific parts of the designed building, or can be used in retrofitting existing buildings. The prototype panel has validated many useful aspects of the innovation including observations that report improvements of around 150-300% in the maximum light that is transmitted with light concentrators and modified optical fiber tips compared to a translucent panel with only embedded optical fibers with flat tips. From the analysis of operational energy, the panel is also shown to reduce the total energy consumption (heating, cooling, lighting, and fans) by 36%, which in turn curtails CO2 emissions by 34%. 

Low Capacitance/High Speed Bipolar Phototransistor

The performance of optoelectronic links is very strongly related to the sensitivity of the detector on the receiver end. Conventional receivers include a photodiode whose signal is sent to amplifiers until it is strong enough to be used in microelectronic circuits. The energy cost of amplification is very high and could be significantly reduced if the capacitance of the photodiode and first stage of amplification were smaller. In order to be useful for this application, a phototransistor must have several features: - Low capacitance - High speed - Large photon absorption volume Unfortunately, for conventional bipolar phototransistors, these requirements are contradictory. Indeed the photon absorption length in typical semiconductors is on the order of microns, while the speed requirement only allows transit regions for amplified carriers of a few tens of nanometers at best. This is over a 100x size mismatch. Increasing any other dimension (that is not the transit direction) results in prohibitively high capacitances. This invention offers a solution to these issues consisting of a new kind of semiconductor phototransistor device, which integrates a large PIN-photodiode with a bipolar junction transistor (or Heterojunction Bipolar transistor). 

Nanoscale Imaging

Cathodoluminescence (CL) is used for nanoscale imaging by detecting the light generated in the sample by the application of an electron beam. Direct CL has also been used to image biological samples, but typically causes damage to the sample and can result in poor imaging quality.  Methods which incorporate inorganic cathodoluminescent nanoparticle labels into a biological sample result in less sample damage, but imaging with nanoparticle labels requires the electron beam to penetrate into the sample, which precludes repeated measurements or observations of dynamics. A UC Berkeley researcher has developed an optical imaging system and method for producing nanoscale images with high resolution, images of fragile samples without damaging the samples and that can be used for repeated imaging of a sample which allows observation of sample dynamics.  

Eyeglasses-Free Display Towards Correcting Visual Aberrations With Computational Light Field Displays

Almost 170 million people in the United States (~55% of the total U.S. population) wear vision correction. Of this population, more than 63 million people (53%) up to age 64 have presbyopic vision. Eyeglasses have been the primary tool to correct such aberrations since the 13th century. In more modern times, contact lenses and refractive surgery have become viable alternatives to wearing eyeglasses. Unfortunately, these approaches require the observer to either use eyewear or undergo surgery, which is often uncomfortable and costly, and can lead to complications, in the case of surgery. To address these challenges, researchers at the University of California, Berkeley, and MIT have developed vision correcting screen technology which involves digitally modifying the content of a display so that the display can be seen in sharp focus by the user without requiring the use of eyeglasses or contact lenses. By leveraging specialized optics in concert with proprietary prefiltering algorithms, the display architecture achieves significantly higher resolution and contrast than prior approaches to vision-correcting image display. The teams have successfully demonstrated light field displays at low cost backed by efficient 4D prefiltering algorithms, producing desirable vision-corrected imagery even for higher-order aberrations that are difficult to be corrected with conventional approaches like eyeglasses.

Accurate and Robust Eye Tracking with a Scanning Laser Ophthalmoscope

The tracking scanning laser ophthalmoscope (TSLO) provides fast and accurate measurements of fixational eye motion with flexible field of views. Currently, this system is the most accurate, fast and functional eye-tracking system used in a standard ophthalmic instrument. At a basic research level, the benefits of accurate eye-tracking are especially useful for delivering stimuli to targeted retinal locations as small as a single cone. In the clinical domain, advances in imaging and tracking technology help render accurate images which can lead to better outcomes in treating eye disease. Scanning laser ophthalmoscopy (SLO) uses both a horizontal and vertical scanner to image a specific region of the retina. Current state of the art tracking SLO systems are only suitable for observing a narrow field of view (FOV < five degrees) and will lose signal with certain types of eye motion. This is problematic for patients suffering from varying retinal or neurological disorders, where unstable fixation hinders accurate eye-tracking and image acquisition. These include retinal diseases of the macula such as: age-related macular degeneration, or neurological disorders such as: Alzheimer's and Parkinson's disease. In cases such as these, it would be desirable to capture a larger field of view whose image quality is sufficient to track the retina for larger and more rapid eye movements. To help address this problem, researchers at the University of California, Berkeley have developed systems, software, and methods for an image-based high-performance TSLO. Early laboratory experimentation results suggest significantly enhanced eye-tracking in terms of: sampling uniformity of eye motion traces, detection of eye rotation, increased frame rate of image capture, expandable/adjustable FOV, stabilization accuracy of 0.66 arcminutes, and tracking accuracy of 0.2 arcminutes or less across all frequencies. The Berkeley system and techniques show promise for observing detailed structural and functional changes in the eye as a result of age and/or disease like never before.

Partially Coherent Phase Recovery By Kalman Filtering

Phase imaging has applications in biology and surface metrology, since objects of interest often do not absorb light but cause measurable phase delays (e.g. biological cells or uneven surface heights).  Here, a new extension to an experimentally simple method for imaging quantitative phase information is described, which uses a Kalman filter algorithm with a stack of intensity images taken through focus. The extended method involves incorporation of information about the microscope source shape in Koeler configuration, so that the coherence of the illumination may be included into the phase retrieval algorithm in order to produce more accurate phase results with arbitrary source shapes and sizes. Investigators have optimized and extended the Kalman filtering method to reduce computational complexity and to produce images using partially coherent illumination. This new software and method is faster and more efficient than previous methods, and in addition is robust to noise. It is compatible with a range of imaging systems, including optical, electron, X-ray and synchrotron, for example. Further, modifications are described for variations on the phase contrast mechanism, such that any complex transfer function (including but not limited to defocus) may be used. 

Active color controllable membrane

Being able to actively change the color of objects is highly desirable for a variety of applications, including sensing, anti-counterfeit, camouflage, jewelry and visual art. Conventional optical coating consists of one or multiple layers of thin films, relying on accumulative optical interference of the layers. However, these traditional coating methods do not provide means to actively control color.   To address this challenge, UC Berkeley researchers invented a color-controllable membrane with color tuning capability either by active actuation or passive stimulation. Colors are controllable via photonic, mechanical or electro stimulation. The active color display is promising for making artificial chameleon skin for camouflage and the color coating of visual arts. The color change ability via passive stimulation can be applied toward labeling mechanical changes at visible wavelength resolution. Other structural color applications include beam-steering devices for a fixed wavelength.

Silicon Photonic Switch

Optical (photonic) switches are used in datacenter networks to switch signals carried by optical fibers from one circuit to another. They deliver reconfigurable bandwidth, which improves network performance and reduces power consumption. Currently, optical switches are limited either by their slow switching time (ms) or small switch size as well as high cost, which restricts their use in data-intensive applications. Investigators at UC Berkeley have developed a photonic switch that can be monolithically integrated on a silicon chip. It has a fast switch time (microsecond), large port count (~ 100 or larger), and low optical loss. Furthermore, the switch can be mass-produced at a low cost, allowing for easy scale up. These advances will be particularly beneficial in high traffic datacenter networks that require fast switching times. A prototype of the switch has been experimentally demonstrated at Berkeley Marvell Nanolab.

MEMS Ultrasonic Fingerprint ID System

Two-dimensional optical fingerprint analysis has been used for a variety of personal identification applications over the years.  However, automated optical fingerprint scanning techniques have a number of limitations that block their use in broader applications. For example, automated optical fingerprint scanning techniques sense only the epidermal layer of a fingerprint. As a result, they are prone to errors created by finger contamination.  The marketplace has reflected the limitations of optical fingerprint identification, as many optical fingerprint scanners have been removed from most later models due to these limitations. They lacked the necessary robustness to perform predictably in such everyday environments.  Ultrasonic fingerprint scanners have been developed in an effort to minimize the limitations of currently available optical fingerprint scanning, and avoid some of the resulting errors.  However, currently available ultrasonic fingerprint scanners devices are limited in their applications because of large size, the requirement of a physically moving scanning device, and cost.   UC researchers have developed a micro-machined ultrasonic transducer fingerprint identification system (MUT fingerprint ID system) to address these issues.  MUT fingerprint ID system has advantages of a small size, robust solid-state construction, easy fabrication, easy integration with electronics, and fast electronic scanning. These features represent a game-changing advancement over currently available bulky, failure prone mechanical scanners.  The system also has orders of magnitude lower cost per unit than current systems.  Conventional fingerprint sensors used in consumer electronics applications are capacitive sensors and are extremely prone to errors due to wet, dry or oily fingers. Optical sensors are sensitive to dirt on fingers. Unlike both capacitive and optical sensors, which measure the fingerprint on the epidermis (skin surface), the ultrasonic sensor at the core of the MUT fingerprint ID system can detect the fingerprint on both the epidermis and dermis (subcutaneous) layers.  

A Drift-Corrected, High-Resolution Optical Trap

Optical trapping systems are commercially available through several companies. In these systems, the optical trap precision relies on the passive stability of the instrument itself, and therefore demands costly engineering solutions to limit environmental noise that can be coupled into the optomechanical components. Consequently, high-resolution measurements are not possible in common biological laboratory settings that typically lack appropriate vibration isolation and temperature stability.  Researchers at the University of California, Berkeley have developed an invention that addresses a critical problem currently limiting the performance of high-resolution optical traps: that the mechanical drift of optical components often results in physical drift in the location of an optical trap that obscures the displacement-of-interest. The motion of biological motor proteins that are specific to interacting with DNA often take steps along the double helix that is on the order of 0.3 nanometers in size. Accurate measurement of displacements on this scale requires that drift of the trap positions be limited to no more than a few angstroms. However, the current best-performing optical traps suffer from instrumental drift that is almost twice what can be tolerated. Owing to the critical role of these components in all optical trapping systems, and the previously undetectable levels of mechanical drift they undergo, we sought to measure the trap drift with angstrom-level precision using a new approach. This new approach has successfully measured for and corrected for the mechanical drift of these components and demonstrated that this novel invention is capable of consistently reducing the noise floor to levels that have not previously been accomplished.       

High-sensitivity Angular Interferometer

Researchers at the University of California, Berkeley have developed an invention that consists of an angular interferometer able to measure angle variations of a coherent, collimated light source with an accuracy below 30 nrad. The optical setup is compact and consists of a few simple optical components. The novelty of this innovation lies in the use of a simple, cost-effect technique to amplify the sensitivity of the instrument. The disclosed invention is in principle capable of being integrated into more compact, high-sensitivity commercial instruments for a fraction of the cost of current, state-of-the-art instruments (currently exceeding $30,000).   Commercial devices used to measure the angular deviation of a single beam include autocollimators and interferometers. The highest resolution offered by a commercial system is 25 nrad. The disclosed angular interferometer is able to measure relative angle variations (of a sample beam relative to a reference beam) below 30 nrad, though the resolution is known to currently be limited by the specific details of the current application and can therefore be further reduced with minor, inexpensive improvements.

Nanophotonic Graphene Transistor

Conventional approach to controlling and modulating carrier transport in transistor is by utilizing external electric field. In a typical setting, metal or heavily doped silicon gate is separated by dielectric materials from the active region of semiconductor, forming a metal-insulator semiconductor structure. However, such approach requires physical metal interconnections to the device for electrical modulation, which are constructed up to at least 10 interconnection layers in the state-of-the-art complementary metal-oxide-semiconductor (CMOS) technology. As the technology advances, these interconnections become more and more complicated, and significantly burden the operation of the transistor due to increased parasitic components of the circuit (i.e. parasitic resistance/capacitance). In order to address such challenges, researchers at the University of California, Berkeley have developed optical interface capable of wireless modulation of electrical current, instead of complicated physical metal interconnects. In particular, they have developed a interface to demonstrate the free-space optical modulation of current. The new capability of optical modulation allows a new class of transistor optical transistor - with unprecedented performance and tunability. Furthermore, The two critical applications of the new transistor - multi functional logic gates, and ultra-sensitive electrical detection of biomolecules – enable completely new possibilities for multifunctional electronics and ultra-sensitive detection of chemical and bio- molecules. The uniqueness of wavelength-specific modulation of nanophotonic transistors lead to the creation of multi-functional nanophotonic logic gates and circuits where different component generate multiple functionalities in a same circuit layout. In addition, local field enhancement provides a unique opportunity to substantially improve sensitivity of field-effect transistor (FET) based biosensors.

Solar Optics-Based Active Panels (Soap) For Greywater Reuse And Integrated Thermal (Grit) Building Control

It is estimated that half of the world will be under water stress by 2030. Water stress is especially strong in arid climate zones, where water scarcity combined with daily temperature swings make good energy and water management a must. Attempts have been made to integrate thermal regulation and water recycling into the building structure ? but as separate solutions. Most waste (greaywater) treatment technologies involve multiple independent steps, making them difficult to implement. The most advanced means to recycle greywater in buildings is bio-filtration, but it requires large spaces to be efficient. There have been attempts to develop new greywater recycling technologies based on optics, but in order to be efficient they need to adapt to variable light angles, requiring large and heavy mechanical control systems. Researchers at UC Berkeley created an integrated system of filtration, disinfection, and organic compound removal viable in small spaces (thin building exterior walls). The invention is based on solar optics-based active panels (SOAP) for greywater reuse coupled with integrated thermal (GRIT) building control. The system uses sun light for water disinfection, and can also act as a thermal mass to control daily temperature swings by absorbing heat during the day and releasing it through the night. SOAP for GRIT establishes a new exterior wall building system that can decrease substantially both water and energy use.

Plasmon Laser at Deep Sub-Wavelength Scale

The data bandwidth needs of the 21st century rely on the progress of Photonic Integrated Circuits (PICs), which are able to provide ultra high bandwidths at low cost. PICs appeared as the result of miniaturization of discrete optical components, similar to the miniaturization of electrical components that caused a revolution in electronics. However, in case of PICs, the diffraction limit of light fundamentally restricts how small the components can be scaled. The most critical devices in PICs are electro-optical transducers, such as light sources and detectors, which convert electrical signals into optical ones and need to be fast, efficient, and integrable. While many PIC components have been successfully developed, the on-chip laser light source is still facing many challenges. Researchers at UC Berkeley invented a semiconductor plasmonic laser that surpasses the diffraction limit, offering true PIC scaling. The laser uses a hybrid plasmonic waveguide consisting of a semiconductor nanowire separated from a metal surface by a thin insulating gap. Because plasmonic modes have no cutoff, the lateral dimensions of both the device and the optical mode can be downscaled. This invention overcomes the difficulties encountered by previous attempts to use plasmons in creating a truly nano-scale laser and opens the door to constructing other types of optical transducers. 

Method For Patterning Crystalline Indium Tin Oxide Using Femtosecond Laser

96 Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:Calibri; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;} In order to improve the device characteristic of optoelectronic products, such as solar cells and flat-panel displays, the amorphous material such as the transparent conductive oxide has to be transferred by thermal treatment into crystalline material so as to reduce the resistivity and enhance the transparency. Generally, six runs of process (five for pattern transfer and one for thermal treatment) are required to complete the crystalline pattern. To overcome the problems due to the multi-step and high-cost process, laser machining is used in some processing steps to ablate the undesired portion of the thin films. However, convention long pulse laser results in thermal effects to cause elevated ridges on the edge and defects in the layers below.   US Berkeley researchers have discovered a method for patterning crystalline indium tin oxide using a femtosecond laser which overcome the above-mentioned problems by using a focusing device with the laser to heat up the amorphous indium tin oxide (ITO).    

Nanoparticle Transistor Photodetector for Sensing Applications

Quantum dots show great potential for use in next generation optical devices, including photodetection in sensing applications, due to their third order optical response and fast response times. To achieve stability and processability with these nanoparticles, it is ideal to incorporate them into a polymer matrix forming a hybrid material, commonly known as nanocomposites. However, patterning these nanoparticles into nanocomposites is challenging. To address this challenge, researchers at UC Berkeley have developed a novel approach and method for patterning nanocomposites. Using this new Berkeley approach, a nanocomposite film can be patterned and incorporated into a transistor structure in which the film acts as a semiconducting active layer. Additionally, with optical stimulation matching the absorption spectrum of the nanoparticles, the resulting photoconduction can be optimized to create a novel, polymer, transistor-based photodetector. Unlike previous nanocomposite transistors, this new design is simpler to fabricate and uses readily available, inexpensive materials.

Improved Photodetection for Mobile Sensing Applications

Photodetection, especially for fluorescence applications, requires various optics including lenses and filters. The optics surrounding the detection and illumination system are complex and can often weigh more than the photodetector and illumination sources. Therefore in order to make such photodetection equipment mobile, much of the optics needs to be integrated and micro-sized. However that causes various microfabrication problems -- especially in yields and throughput. To address this situation, researchers at UC Berkeley have developed a new design for fluorescence detection subsystems. This new design integrates and miniaturizes the photodetection functionality and thereby makes it suitable for mobile application as well as efficient microfabrication.

Axial Light-force Sensor

Commercially available optical tweezers can move objects using laser light, but they are generally not used to measure forces exerted on those objects, since accurate force calibration is difficult. Research in the field of optical trapping has led to the development of optical tweezers that measure forces (transverse to optic axis) by changes in light-momentum. Force calibration is greatly simplified by using this method. However, in measuring the light force on a trapped object, it is also desirable to obtain all three vector components of that force. Representing an improvement on the light-momentum force-sensor, researchers at the University of California, Berkeley have developed an axial light-force sensor. A system incorporating the Berkeley improvement permits simultaneous measurements of the axial and transverse forces acting on a trapped particle. Like the transverse sensor, the axial force sensor is calibrated from measured constant values: the speed of light, the objective focal length, and the power sensitivity of the planar photo-diode. Thus calibration is not affected by particle shape, laser power, particle refractive index, or sharpness of the trap focus. In addition, a highly-miniaturized, ultra stable, optical trap system has been developed that should permit a low cost instrument with force-measuring capabilities for use in normal lab environments.

Broad Bandwidth And Highly Reflective Gratings

Broadband mirrors with very high reflectivity are essential for applications such as telecommunications, surveillance, sensors and imaging. Among the various conventional mirror designs, metal mirrors have larger reflection bandwidths but lower reflectivities; as a result they are not suitable for fabricating transmission-type optical devices such as etalon filters. Dielectric distributed Bragg reflectors (DBRs) can achieve a higher reflectivity but deposition methods for DBRs are often not precise enough to yield the reflectivities of 99% or better needed for demanding applications, and typical material combinations constrain the mirror bandwidth and can be incompatible with conventional semiconductor processing technologies. In addition the tuning range is often limited for tunable etalon type devices such as MEM vertical cavity surface emitting lasers (VCSELs), filters, and detectors. There is a need for a mirror with broadband reflection, low loss, and compatibility with conventional optoelectronic processing methods. Researchers at the UC Berkeley have developed a single layer, sub-wavelength grating with a very broad reflection spectrum and very high reflectivity. The grating design facilitates monolithic integration of optoelectronic devices at a wide range of wavelengths from visible to far infrared, as well as integration with electronic circuits and other optoelectronic devices. Grating spectral characteristics can be tailored by choice of materials and structure to maximize both reflectivity and spectral coverage. The grating design developed at Berkeley has potential application in MEM tunable devices and reconfigurable focal plane arrays for such high value applications as optical communications, chemical/biological sensors, and imaging.

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