Description:
OBJECTIVE: To develop and demonstrate an ultra-sensitive, room-temperature, long-wavelength detector that utilizes the coupling between a combined mechanical-optical-cavity system at the micro-to-nanoscale to achieve operational performance that exceeds the state-of-the-art in the Far-IR and THz regions. DESCRIPTION: Optical forces are known to produce significant mechanical effects in micro- and nano-optomechanical systems [1-5]. Such interactions have been proposed as a means of constructing novel optomechanical components [6], such as tunable filters, couplers and lasers. Additionally, the static and dynamical manifestations of the coupling between the mechanical and optical degrees of freedom [1, 2] in such systems have been exploited in the development of electromechanical oscillators, tunable filters and switches, in enhancing the sensitivity of gravitational wave detectors, and in the study of the quantum dynamical properties of both light and mechanical systems. Therefore, the inherent physical advantages of light-based interactions with very small mechanical systems suggest basic paradigms for detectors that should be able offer very high detection sensitivities across very broad electrical bandwidths at the long wavelength end of the spectrum, e.g., far-infrared (Far-IR) and even beyond to terahertz (THz) regime. Indeed, prior investigations [3-5] have demonstrated the basic advantages of using the available radiation pressure to affect the static and dynamical behavior of very high quality (Q) factor mechanical systems. These observations are very important because detection devices of this type are inherently optical, thereby being free of electrical interference. Furthermore, micro-to-nano size systems have the inherent potential for producing extremely high sensitivity at room temperature, and they can be tailored to operate at long wavelengths. Most importantly, the combined results of recent studies [6-8] indicate that electromagnetic (EM) field driven changes in mechanical resonators can be efficiently sensed by monitoring their influence on optical modes of a combined mechanical-optical-resonator system. Specifically, schemes employing the use of Whisper Gallery Mode (WGM) resonators have achieved Q-factors of 10**11 [7] under laboratory conditions and 10**8 in practical devices [8]. Hence, these micro-scale resonator systems have already demonstrated minimum detectable powers (or temperature changes) on the order of 10**-9 watts (or 10**-4 K) [6-8]. These breakthroughs, and technical observations noted above, are already significant when compared the existing state-of-the-art. Presently, bolometric and pyroelectric sensors are the two leading classes of Far-IR and THz radiation detectors. However, bolometric sensors require liquid helium temperature operation in order to achieve the level of sensitivity of interest, so that they are cumbersome to use and therefore of no interest for comparison at room temperature. Conversely, pyroelectric sensors do operate at room temperature and they have high sensitivity at room temperature (micro-to-nanoscale watt level in the range 0.1 to 30 THz) but they are inherently electrical which means they are prone to noise problems, and they have a non-linear temperature coefficient which is problematic. All these facts strongly motivate further research into EM-field-driven mechanical-optical coupled cavities, which employ for example the response of WGM resonances [6] to incident radiation, for the purpose of realizing ultra-sensitive room-temperature detectors for application at the Far-IR and THz regimes. In addition, the research should be extended into mechanical-optical-cavity (MOC) detectors that employ external modulation of the incident radiation field and that utilize novel materials for optimizing the sensor time constant because these measures [8, 9] could lead to a ten times improvement in the room temperature sensitivity at very long wavelengths. As these ultra-sensitive, room-temperature, MOC detectors would offer significant potential for enhancing the operation of many Far-IR sensing systems of relevance to the military and it could open new opportunities for fundamental research into Far-IR and THz sensing science and micro-to-nanoscale phenomenology, a new research and development program is proposed. One particular scientific area of importance to the Joint Chemical and Biological Defense Program is the interaction of THz radiation with biological systems which could provide new methods for detecting hazardous organisms. These interactions may also prove useful in new methods of medical diagnosis. Hence, the associated long wavelength technological investigations would have significant relevance to biological and medical science. PHASE I: Studies will be executed to explore the use of novel mechanical-optical-cavity (MOC) structures consisting of various geometries and materials to determine their potential for detecting long wavelength (Far-IR and/or THz regimes) radiation with very high sensitivity performance. This work will include physical modeling of the coupling between MOC elements and design simulations to optimize specific MOC structures and operational modalities. The Phase I effort should include fabrication experiments and optical and/or mechanical benchmarking testing that will demonstrate the general potential for the future implementation of an ultra-sensitive, room-temperature detector for operation with the Far-IR and/or THz regimes. The merit of the project will also be increased by defining micro-to-nanoscale phenomenology experiments that have potential for discovery in regards to long wavelength radiation and biological systems. PHASE II: A prototype Mechanical-Optical-Cavity (MOC) detector will be developed that demonstrates ultra-sensitive, room-temperature performance that exceeds the state-of-the-art at long wavelengths (Far-IR and/or THz regimes). The expected technology development work should include but is not necessarily limited to: systematic studies of the MOC detector characteristics as a function of the structural parameters of the combined mechanical and optical resonators; detailed investigations into the use of various types of materials and coatings; development and implementation of a fully operational integrated detector platform with heat sinks, fibers and/or waveguide based optical coupling; and investigation into robustness and reliability issues in the context of a field sensor. The merit of the project will also be increased if micro-to-nanoscale sensing phenomenology research is performed to investigate the use of the technology for interfacing to, and interrogating, biological systems. PHASE III: Refine the sensitivity and functionality of a new type of Mechanical-Optical-Cavity (MOC) detector concept, and design fabrication and integration procedures for defining a robust and reliable field sensor. The base technology would have direct applicability to point detection and standoff scanning imaging systems. The Phase III development work could also be expanded to perfecting the optical signal interface and to defining integration methods for potentially implementing the technology into focal plane arrays. Therefore, this new detector technology will have commercialization opportunities for such military relevant applications as detection of BW agents with obvious extensions to chemical and explosive threats. PHASE III DUAL USE APPLICATIONS: This technology is relevant to scientific studies on the interaction of micro-to-nanoscale MEC systems with biological (and possibly chemical and explosive) targets. Hence, the technology work conducted in conjunction with this project could find applicability in many sensing areas, and especially in areas related to biological and medical science. REFERENCES: [1] H. G. Craighead,"Nanoelectromechanical Systems,"Science 290, 1532 (2000). [2] T.J. Kippenberg and K.J. Vahala,"Cavity Opto-Mechanics,"Optics Express 15, 17172 (2007). [3] Y. Wu, J. M. Ward, V. G. Minogin and S. N. Chormaic,"Trapping of a Microsphere Pendulum Through Cavity-enhanced Optical Forces,"Phys. Scr., T140, 014040 (2010). [4] R. Ma, A. Schliesser, P. Del'Haye, A. Dabirian, T. J. Kippenberg,"Radiation Pressure Driven Vibrational Modes in Ultra-high-Q Silica Microspheres,"arXiv:physics/0702252v1 [physics.optics] 28 Feb (2007). [5] M. Eichenfield, C. P. Michael, R. Perahia and O. Painter,"Actuation of Micro-Optomechanical Systems via Cavity-enhanced Optical Dipole Forces,"Nature Photonics 1, 416 (2007). [6] A. Schweinsberg, S. Hocde, N. N. Lepeshkin, R. W. Boyd, C. Chase, J. E Fajard,"An environmental sensor based on an integrated optical whispering gallery mode disk resonator,"Sensors and Actuators B: Chemical 123, 727 (2007). [7] J. Lutti, W. Langbein, P. Borri"A monolithic optical sensor based on whispering gallery modes in polystyrene microspheres,"Applied Physics Letters 93, 151103 (2008). [8] G Guan, S Arnold, M V Otugen"Temperature measurements using a microoptical sensor based on whispering gallery modes,"AIAA Journal 44, 2385 (2006). [9] T. Ioppolo, M. Kozhevnikov, V. Stepaniuk, M V. Otgen, V. Sheverev,"Micro-optical force sensor concept based on whispering gallery mode resonators,"Applied Optics 47, 3009 (2008). [10] A.B. Matsko et. al.,"Fabrication, Characterization and Applications of Crystalline Whispering Gallery Mode Resonators,"in ICTON"07, 9th International Conference on Transparent Optical Networks, 2007. [11] I.S. Grudnin et. al.,"Ultra high Q Crystalline Microcavities,"Optics Communications, 265, 33 (2006). [12] V. Otugen and V. A. Sheverev,"Micro-Optical Wall Shear Stress Sensor"; US Patent #: US 7,701,586 B2, 2010. [13] V. A. Sheverev and V. Stepuniuk,"Load Cell and System for Measuring Forces Based on Optical Spectral Shifts,"US Patent Application #: US 2009/0282928 A1, 2009. [14] T. Carmon,"Wavelength-independent coupler from fiber to an on-chip cavity, demonstrated over an 850nm span,"Optics Express 15, 7677 (2007).
