Center for Photonics Technology

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https://hdl.handle.net/10919/24790

The Center for Photonics Technology at Virginia Tech is focused on innovation in fiber optics, fiber optic sensors, and biomedical and applied optics. With five faculty and over 30 students and research staff, CPT is a world leader in fiber optic sensor research.

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Optical Image Recognition Of Three-Dimensional Objects
Poon, Ting-Chung; Kim, Taegeun (Optical Society of America, 1999-09-01)
A three-dimensional (3-D) optical image-recognition technique is proposed and studied. The proposed technique is based on two-pupil optical heterodyne scanning and is capable of performing 3-D image recognition. A hologram of the 3-D reference object is first created and then is used to modulate spatially one of the pupils of the optical system; the other pupil is a point source. A 3-D target object to be recognized is then scanned in two dimensions by optical beams modulated by the two pupils. The result of the two-dimensional scan pattern effectively displays the correlation of the holographic information of the 3-D reference object and that of the 3-D target object. A strong correlation peak results if the two pieces of the holographic information are matched. We analyze the proposed technique and thereby lay a theoretical foundation for optical implementations of the idea. Finally, computer simulations are performed to verify the proposed idea. (C) 1999 Optical Society of America.
Manufacturing Of A Fiber Optic Young's Double Pinhole Interferometer For Use As A 3D Profilometer
Pennington, Timothy L.; Wang, Anbo; Xaio, Hai; May, Russell G. (Optical Society of America, 2000-05-01)
The method used to manufature a Young's double pinhole interferometer is discussed. This interferometer is destined to be used in a surface profilometer using two wavelengths so that the zero order fringe can be determined. Hence stringent requirements are placed on the absolute length difference between the two output fibers of a single mode coupler. These requirements are discussed along with the manufacturing process. The interferometer is shown along with measurements showing a length difference on the order of 6 mu m. (C) 2000 Optical Society of America.
Grating-Assisted Demodulation Of Interferometric Optical Sensors
Yu, B.; Wang, Anbo (Optical Society of America, 2003)
Accurate and dynamic control of the operating point of an interferometric optical sensor to produce the highest sensitivity is crucial in the demodulation of interferometric optical sensors to compensate for manufacturing errors and environmental perturbations. A grating-assisted operating-point tuning system has been designed that uses a diffraction grating and feedback control, functions as a tunable-bandpass optical filter, and can be used as an effective demodulation subsystem in sensor systems based on optical interferometers that use broadband light sources. This demodulation method has no signal-detection bandwidth limit, a high tuning speed, a large tunable range, increased interference fringe contrast, and the potential for absolute optical-path-difference measurement. The achieved 40-nm tuning range, which is limited by the available source spectrum width, 400-nm/s tuning speed, and a step resolution of 0.4 nm, is sufficient for most practical measurements. A significant improvement in signal-to-noise ratio in a fiber Fabry-Perot acoustic-wave sensor system proved that the expected fringe contrast and sensitivity increase. (C) 2003 Optical Society of America.
Fiber Fabry-Perot Sensors For Detection Of Partial Discharges in Power Transformers
Yu, Bing; Kim, Dae Woong; Deng, Jiangdong; Xiao, Hai; Wang, Anbo (Optical Society of America, 2003-01-01)
A diaphragm-based interferometric fiber optic sensor that uses a low-coherence light source was designed and tested for on-line detection of the acoustic waves generated by partial discharges inside high-voltage power transformers. The sensor uses a fused-silica diaphragm and a single-mode optical fiber encapsulated in a fused-silica glass tube to form an extrinsic Fabry-Perot interferometer, which is interrogated by low-coherence light. Test results indicate that these fiber optic acoustic sensors are capable of faithfully detecting acoustic signals propagating inside transformer oil with high sensitivity and wide bandwidth. (C) 2003 Optical Society of America.
Observation Of The Enhanced Backscattering Of Light By The End Of A Tilted Dielectric Cylinder Owing To The Caustic Merging Transition
Marston, Philip L.; Zhang, Yibing; Thiessen, David B. (Optical Society of America, 2003-03-01)
The scattering of light by obliquely illuminated circular dielectric cylinders was previously demonstrated to be enhanced by a merger of Airy caustics at a critical tilt angle. [Appl. Opt. 37, 1534 (1998)]. A related enhancement is demonstrated here for backward and near-backward scattering for cylinders cut with a flat end perpendicular to the cylinder's axis. It is expected that merged caustics will enhance the backscattering by clouds of randomly oriented circular cylinders that have appropriately flat ends. (C) 2003 Optical Society of America.
Optical Scanning Cryptography For Secure Wireless Transmission
Poon, Ting-Chung; Kim, Taegeun; Doh, K. (Optical Society of America, 2003-09-01)
We propose a method for secure wireless transmission of encrypted information. By use of an encryption key, an image or document is optically encrypted by optical heterodyne scanning and hence encryption is performed on the fly. We call this technique optical scanning cryptography. The output of the heterodyne encrypted signal is at radio frequency and can be directly sent through an antenna to a secure site for digital storage to be prepared for decryption. In the secure site, an identical optical scanning system to that used for encryption is used, together with a decryption key, to generate an electrical signal. The electrical signal is then processed and sent to a computer to be used for decryption. Utilizing the stored information received from the encryption stage and the electrical information from the secure site, a digital decryption unit performs a decryption algorithm. If the encryption key and the decryption key are matched, the decryption unit will decrypt the image or document faithfully. The overall cryptosystem can perform the incoherent optical processing counterpart of the well-known coherent double-random phase-encoding technique. We present computer simulations of the idea. (C) 2003 Optical Society of America.
Exact Analysis Of Low-Finesse Multimode Fiber Extrinsic Fabry-Perot Interferometers
Han, M.; Wang, Anbo (Optical Society of America, 2004-02-01)
A straightforward theory is presented to accurately model the light inferences in a low-finesse multimode fiber extrinsic Fabry-Perot (FP) interferometer. The effect on the fringe visibility of the gap length, sensor structure imperfections, and modal power distributions is explored. The analysis is particularly useful in the design and optimization of sensors that use an extrinsic FP cavity as the sensing element. (C) 2004 Optical Society of America.
Self-Compensating Fiber Optic Flow Sensor System And Its Field Applications
Peng, W.; Pickrell, Gary R.; Huang, Z. Y.; Xu, J. C.; Kim, D. W.; Qi, B.; Wang, Anbo (Optical Society of America, 2004-07-01)
A self-compensating fiber optic flow sensor system based on the principle of broadband white-light interferometers and cantilever beam bending is described. The fiber optic sensor system uses two fiber ferrule sensors that are bonded on either side of a cantilever beam to measure the flow rate by monitoring the air-gap changes caused by the bending of the cantilever beam. Cross sensitivity of the temperature and pressure dependence of the sensor can be compensated for automatically. The prototype sensor system was constructed, laboratory characterized, and field tested. The results from the field testing have demonstrated high resolution, repeatability, and stability for on-line detection of the flow rates of fluids. (C) 2004 Optical Society of America.
Frequency-Estimation-Based Signal-Processing Algorithm For White-Light Optical Fiber Fabry-Perot Interferometers
Shen, F. B.; Wang, Anbo (Optical Society of America, 2005)
A novel signal-processing algorithm based on frequency estimation of the spectrogram of single-mode optical fiber Fabry-Perot interferometric sensors under white-light illumination is described. The frequency-estimation approach is based on linear regression of the instantaneous phase of an analytical signal, which can be obtained by preprocessing the original spectrogram with a bandpass filter. This method can be used for a relatively large cavity length without the need for spectrogram normalization to the spectrum of the light source and can be extended directly to a multiplexed sensor system. Experimental results show that the method can yield both absolute measurement with high resolution and a large dynamic range. Performance analysis shows that the method is tolerant of background noise and variations of the source spectrum. (c) 2005 Optical Society of America.
In-Fiber Reflection Mode Interferometer Based on A Long-Period Grating For External Refractive-Index Measurement
Kim, D. W.; Zhang, Y.; Cooper, K. L.; Wang, Anbo (Optical Society of America, 2005-04-01)
We present two novel schemes for refractometry based on a long-period fiber grating- (LPG-) based Michelson interferometer. These schemes are designed to overcome the measurement dependence of previously demonstrated LPG-based refractometry on the immersion depth. The first utilizes an unshielded LPG and the second, a shielded one. Both schemes were tested over a certain refractive-index range, and the measurement of glucose concentration in water was experimentally demonstrated. In addition, the temperature sensitivity of the two schemes is discussed. (c) 2005 Optical Society of America.
Surface-Mount Sapphire Interferometric Temperature Sensor
Zhu, Y. Z.; Wang, Anbo (Optical Society of America, 2006-02-01)
A fiber-optic high-temperature sensor is demonstrated by bonding a 45 degrees-polished single-crystal sapphire fiber on the surface of a sapphire wafer, whose optical thickness is temperature dependent and measured by white-light interferometry. A novel adhesive-free coupling between the silica and sapphire fibers is achieved by fusion splicing, and its performance is characterized. The sensor's interference signal is investigated for its dependence on angular alignment between the fiber and the wafer. A prototype sensor is tested to 1170 degrees C with a resolution of 0.4 degrees C, demonstrating excellent potential for high-temperature measurement. (C) 2006 Optical. Society of America.
Micro-Air-Gap Based Intrinsic Fabry-Perot Interferometric Fiber-Optic Sensor
Chen, X. P.; Shen, F. B.; Wang, Z. A.; Huang, Z. Y.; Wang, Anbo (Optical Society of America, 2006-05-01)
A simple intrinsic Fabry-Perot interferometric (IFPI) sensor is developed. The sensor is fabricated by two micro air gaps as reflective mirrors in a fiber to form a Fabry-Perot cavity. Theoretical and experimental studies of the sensor are described. Experimental results show that high resolution and high sensitivity can be achieved. Two structures of micro-air-gap-based IFPI sensors offer more applications than other IFPI sensors. (c) 2006 Optical Society of America.
Fast-Fourier-Transform Based Numerical Integration Method For The Rayleigh-Sommerfeld Diffraction Formula
Shen, F. B.; Wang, Anbo (Optical Society of America, 2006-08-01)
The numerical calculation of the Rayleigh-Sommerfeld diffraction integral is investigated. The implementation of a fast-Fourier-transform (FFT) based direct integration (FFT-DI) method is presented, and Simpson's rule is used to improve the calculation accuracy. The sampling interval, the size of the computation window, and their influence on numerical accuracy and on computational complexity are discussed for the FFT-DI and the FFT-based angular spectrum (FFT-AS) methods. The performance of the FFT-DI method is verified by numerical simulation and compared with that of the FFT-AS method. (c) 2006 Optical Society of America.
Implementation Of A Loss-Compensated Recirculating Delayed Self-Heterodyne Interferometer For Ultranarrow Laser Linewidth Measurement
Chen, X. P.; Han, M.; Zhu, Y. Z.; Dong, Bin; Wang, Anbo (Optical Society of America, 2006-12-01)
Ultranarrow laser linewidth measurement using an optimized loss-compensated recirculating delayed self-heterodyne interferometer is described. An experimental setup is constructed to measure subkilohertz laser linewidths. The system parameters are optimized to obtain the best beat signals. The experimental results agree well with the theoretical analysis. Two methods of linewidth interpretation are presented and analyzed based on the experimental results. It is proved that a loss-compensated recirculating delayed self-heterodyne interferometer is an effective tool for measuring an ultranarrow laser linewidth. (c) 2006 Optical Society of America.
Behavior of Random Hole Optical Fibers under Gamma Ray Irradiation and Its Potential Use in Radiation Sensing Applications
Alfeeli, Bassam; Pickrell, Gary R.; Garland, Marc; Wang, Anbo (MDPI, 2007-05-24)
Effects of radiation on sensing and data transmission components are of greatinterest in many applications including homeland security, nuclear power generation, andmilitary. A new type of microstructured optical fiber (MOF) called the random hole opticalfiber (RHOF) has been recently developed. The RHOFs can be made in many differentforms by varying the core size and the size and extent of porosity in the cladding region.The fibers used in this study possessed an outer diameter of 110 _m and a core ofapproximately 20 _m. The fiber structure contains thousands of air holes surrounding thecore with sizes ranging from less than 100 nm to a few _m. We present the first study ofthe behavior of RHOF under gamma irradiation. We also propose, for the first time to ourknowledge, an ionizing radiation sensor system based on scintillation light from ascintillator phosphor embedded within a holey optical fiber structure. The RHOF radiationresponse was compared to normal single mode and multimode commercial fibers(germanium doped core, pure silica cladding) and to those of radiation resistant fibers (puresilica core with fluorine doped cladding fibers). The comparison was done by measuringradiation-induced absorption (RIA) in all fiber samples at the 1550 nm wavelength window(1545 25 nm). The study was carried out under a high-intensity gamma ray field from a 60Co source (with an exposure rate of 4x104 rad/hr) at an Oak Ridge National Laboratory gamma ray irradiation facility. Linear behavior, at dose values less than 106 rad, was observed in all fiber samples except in the pure silica core fluorine doped cladding fiber which showed RIA saturation at 0.01 dB. RHOF samples demonstrated low RIA (0.02 and 0.005 dB) compared to standard germanium doped core pure silica cladding (SMF and MMF) fibers. Results also showed the possibility of post-fabrication treatment to improve the radiation resistance of the RHOF fibers.
Method Of Multiple References For 3D Imaging with Fourier Transform Interferometry
Lally, Evan M.; Gong, Jianmin; Wang, Anbo (Optical Society of America, 2010-03-01)
This letter presents an improved phase referencing technique, called Method of Multiple References, for optical profilometry. Based on a lookup table, the method eliminates several major drawbacks of single-reference Fourier Transform Interferometry by enabling surface error correction for steep slopes and step discontinuities, and by allowing mapping of multiple discrete objects using a single image set. The algorithm is tested using a fiber optic coupler-based FTI system and shown to have RMS surface error less than 0.03mm. (C) 2010 Optical Society of America
Multimode Excitation-Induced Phase Shifts in Intrinsic Fabry-Perot Interferometric Fiber Sensor Spectra
Ma, Cheng; Wang, Anbo (Optical Society of America, 2010-11-01)
We report the modal analysis of optical fiber single-mode-multimode-single-mode intrinsic Fabry-Perot interferometer sensors. The multimode nature of the Fabry-Perot cavity gives rise to an additional phase term in the spectrogram due to intermodal dispersion-induced wavefront distortion, which could significantly affect the cavity length demodulation accuracy. By using an exact model to analyze the modal behavior, this phase term is explained by employing a rotating vector approach. Comparison of the theoretical analysis with experimental results is presented. (c) 2010 Optical Society of America
Decoding The Spectra Of Low-Finesse Extrinsic Optical Fiber Fabry-Perot Interferometers
Ma, Cheng; Dong, Bin; Gong, Jianmin; Wang, Anbo (Optical Society of America, 2011)
A theoretical model is developed to address the fringe visibility and additional phase in the interference spectra of low-finesse extrinsic optical fiber excited Fabry-Perot interferometers. The model described in the paper applies to both single-mode and multimode fiber excitations; according to the theory, the fringe visibility and additional phase term are primarily determined by the working wavelength and angular power density distribution outputting from the excitation fiber, rather than based on spatial and temporal degree of coherence. Under certain approximations, the output interference intensity and the spatial power density distribution projected onto the fiber axis form a Fourier-transform pair, which potentially provides a tool for spatial density distribution analysis of fiber output. With excellent agreement with experiments, the theory presented in this paper leads to design guidelines for Fabry-Perot interferometric sensors and insightful physical understanding of such devices. (C) 2011 Optical Society of America
Long Period Gratings in Random Hole Optical Fibers for Refractive Index Sensing
Wang, Ke; Pickrell, Gary R. (MDPI, 2011-02-01)
We have demonstrated the fabrication of long period gratings in random hole optical fibers. The long period gratings are fabricated by a point-by-point technique using a CO2 laser. The gratings with a periodicity of 450 µm are fabricated and a maximum coupling efficiency of −9.81 dB has been achieved. Sensing of different refractive indices in the surrounding mediums is demonstrated by applying standard liquids with refractive indices from 1.400 to 1.440 to the long period grating.
Photonic Biosensor Assays to Detect and Distinguish Subspecies of Francisella tularensis
Cooper, Kristie L.; Bandara, Aloka B.; Wang, Yunmiao; Wang, Anbo; Inzana, Thomas J. (MDPI, 2011-03-07)
The application of photonic biosensor assays to diagnose the category-A select agent Francisella tularensis was investigated. Both interferometric and long period fiber grating sensing structures were successfully demonstrated; both these sensors are capable of detecting the optical changes induced by either immunological binding or DNA hybridization. Detection was made possible by the attachment of DNA probes or immunoglobulins (IgG) directly to the fiber surface via layer-by-layer electrostatic self-assembly. An optical fiber biosensor was tested using a standard transmission mode long period fiber grating of length 15 mm and period 260 µm, and coated with the IgG fraction of antiserum to F. tularensis. The IgG was deposited onto the optical fiber surface in a nanostructured film, and the resulting refractive index change was measured using spectroscopic ellipsometry. The presence of F. tularensis was detected from the decrease of peak wavelength caused by binding of specific antigen. Detection and differentiation of F. tularensis subspecies tularensis (type A strain TI0902) and subspecies holarctica (type B strain LVS) was further accomplished using a single-mode multi-cavity fiber Fabry-Perot interferometric sensor. These sensors were prepared by depositing seven polymer bilayers onto the fiber tip followed by attaching one of two DNA probes: (a) a 101-bp probe from the yhhW gene unique to type-A strains, or (b) a 117-bp probe of the lpnA gene, common to both type-A and type-B strains. The yhhW probe was reactive with the type-A, but not the type-B strain. Probe lpnA was reactive with both type-A and type-B strains. Nanogram quantities of the target DNA could be detected, highlighting the sensitivity of this method for DNA detection without the use of PCR. The DNA probe reacted with 100% homologous target DNA, but did not react with sequences containing 2-bp mismatches, indicating the high specificity of the assay. These assays will fill an important void that exists for rapid, culture-free, and field-compatible diagnosis of F. tularensis.

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