Broadband coherent anti-Stokes Raman scattering (CARS) microscopy promises non-invasive, high information content microscopic imaging for live cells and tissues. Generation of a broadband continuum with
appropriate characteristics to be used for Stokes light has been a roadblock for bringing this promise to fruition. Here we present numerical and experimental work towards generation of a suitable Stokes light continuum from a femtosecond pulse laser. In the simulations, the pulse propagation along the fiber is governed by the generalized nonlinear Schroedinger equation, including linear effects from the group velocity dispersion and the nonlinear effects from self phase modulation, delayed Raman scattering process and
self-steepening. The equations are integrated using a symmetrized split-step Fourier method. Optimal fiber-related simulation parameters used in the model, such as the nonlinear coefficient, dispersion coefficients and the fraction of the stimulated Raman scattering contribution etc, are systematically investigated and determined for the GeO<sub>2</sub> doped fiber.
An efficient and secure algorithm for random phase mask generation used in optical data encryption and transmission system is proposed, based on Diffie-Hellman public key distribution. Thus-generated random mask has higher security due to the fact that it is never exposed to the vulnerable transmitting channels. The effectiveness to retrieve the original image and its robustness against blind manipulation have been demonstrated by our numerical results. In addition, this algorithm can be easily extended to multicast networking system and refresh of this shared random key is also very simple to implement.
In electro-optic (EO) modulator devices ferroelectric crystals of strontium barium niobate (SBN) are attractive due to exceptional high EO coefficients and low half wave voltage. SBN single crystals grown by laser heated pedestal growth are investigated to explore frequency dependent EO property at low frequency and near resonant frequency range. The mechanism of its frequency dependence is discussed briefly.
A new method of phase-coded multiplexing is proposed and tested. The construction of this multiplexing scheme combines a rotating cylindrical-collimating lens system (RCCLS) with a random phase transparent mask. It is verified that such a system is capable
of storing over 1000 images in a doped LiNbO3 crystal. Experimental results and theoretical analyses presented in this paper demonstrate that a compact, all optical, secure and high capacity volume holographic memory system can be implemented with further exploitation
of the method.
A simple and intelligent technique of reducing the zero-order diffraction in an optical spectrographic processor is discussed and the corresponding nonbias optical architecture, by which spectrograms can indeed be obtained, is proposed. Reduction of zero-order diffraction in a Fourier optical system arises from the removal of the dc bias, which is usually needed when a conventional optical spectrographic processor is utilized. We have shown that discrimination sensitivity of the optical spectrograms is significantly enhanced and the dynamic range (DR) requirement for the spectrogram capturing device is also notably reduced due to the removal of the dc bias. In addition, energy utilization efficiency in the optical signal processing is drastically improved by our nonbias architecture. Simulated demonstration is provided.
In this research Electronic Fiber Speckle Pattern Interferometry (EFSPI) is proposed to investigate the area of directional sensing. Modal phasing caused speckle field phase variation was discussed and the sensor architecture based on electronic fiber speckle pattern interferometry (EFSPI) is proposed. The concept of vector sensing with EFSPI was analyzed and experimentally verified with fiber speckle interferogram results, signaling a great potential for directional sensing.
Optical windows have been widely used in optical spectrographic processing system. In this paper, various window profiles, such as rectangular, triangular, Hamming, Hanning, and Blackman etc., have been investigated in detail, regarding their effect on the generated spectrograms, such as joint time-frequency resolution ΔtΔw, the sidelobe amplitude attenuation etc.. All of these windows can be synthesized in a photorefractive crystal by angular multiplexing holographic technique, which renders the system more adaptive. Experimental results are provided.
Hetero-core fiber structure consists of a sandwiched structure of fibers with different core diameters. Hetero-core fiber structure has found its application in both intensity based and phase change based sensors. In this paper, an analysis of hetero-core fiber structure in photonic crystal fibers (PCF) and waveguides is presented. With the finite-difference time-domain (FDTD) method, the performance of such a structure in a fiber specklegram sensor and the refractive index modulation on PCF section are investigated. It is found that the unique photonic nanostructures can substantially enhance the sensitivity of the specklegram sensor with added dynamic range tunability, which can lead to many practical applications in optical sensors.
In this paper we report the design and implementation of a multimode fiber sensing technique for displacement sensing. To exploit the spatial information contents for sensing, a multimode fiber specklegram sensor with a hetero-core fiber structure is used. The sensor utilizes the inner product of multimode fiber speckle fields, which is highly sensitive on the geometrical shape change of the sensing section. The sensitivity and the dynamic range of the displacement sensing are investigated for hetero-core structure fiber specklegram sensor and straight multimode fiber specklegram sensor. It’s found that the sensitivity of the hetero-core FSS offers sensitivity as high as 0.1 μm, with a dynamic range of about 3 μm, which is superior to straight structure multimode fiber FSS. Dynamic response of the hetero-core FSS for displacement sensing was also studied.
Thermal electron dynamics at the interfaces of thin gold film/ferroelectric lithium niobate (LiNbO<sub>3</sub>) is studied by using step-function type laser irradiation. Our measurements reveal an anomalous transient optical transmission fluctuation caused by thermal electron dynamics at the interfaces. To our knowledge, such phenomenon and its theoretical explanation haven't been reported.
Optical spectrographic processing systems have been shown to be the most widely used techniques for time-varying signals that usually contain very distinct characteristics in spectral distributions and are difficult to categorize in time (spatial) domain. In this paper, an optical architecture for spectrograph generation, by which time-varying signal processing can be performed, is proposed and its implementation is described in detail. Some potential applications using optical spectrographic processing system in phonetics, linguistics, speech identification are investigated. Simulation results are also presented to demonstrate the effectiveness of the optical spectrographic processing system in those application areas. Other applications of the optical spectrographic analysis system in identifying individuals through "voice prints" or in detecting mechanical fatigue through abnormal noise are also indicated.
Optical fibers have been widely used for transmitting temporal signal. However, the transmission of spatial signal has not been fully exploited. Although multimode fiber has a large space-bandwidth product, transmitting spatial signals by using a fiber is rather difficult. When a laser beam is lached into a multimode fiber, the exit light field produces a complicated speckle pattern caused by the modal phasing of the fiber. It is difficult to recover the transmitted informati from the speckle field. However, the fiber speckle field can be used to fiber sensing with a hologrpahic method. In other words, if a hologram is made with the speckle fiber field, the information of the fiber status can be recovered. Thus by reading the hologram by the same speckle field, the reference beam can be reconstructed, which represents the detection of the speckle field. In other words, instead of exploiting the temporal content, the spatial content from a multimode fiber can be exploited for sensing. Our analyses and experimentations have shown that the fiber specklegram sensor (FSS) is highly senstiive to perturbation, and it is less vulnerable to the environment factors. Applications of the FSS to temperature, transversal displacement, and dynamic sensing are also included.