Nano-Plasmonics possesses unique physical properties that enable localization of optical fields beyond the diffraction
limit. These highly confined/nanoscale optical modes will enhance light/matter interactions in systems with free
electrons in micro/nanoscale geometric structures. Metal-dielectric fluid interfaces can support surface plasmon
polaritons (SPPs), which are electromagnetic modes interacting with free electron oscillations. Research work is
described on using optofluidic plasmonic chips for implementation of an optofluidic plasmonic sensor, demonstrating in
situ, real time, label-free detection of protein-protein interaction. SPP lineshape is modified from Fano to Lorentz for
increase of the figure of merit to increase the limit of detection. Novel metal-dielectric nanoresonator composites is
presented to increase the surface sensitivity by exciting localized surface plasmon resonance (LSPR) in combination with
SPP readout, enabling higher surface field localization. In order to solve the long time challenging issue of overlapping
molecule of interest onto LSPR to realize the maximal interaction cross-section, micro-nanofluidics integrated nanochip
was developed. We employed electrokinetic forces to control and manipulate the nanoparticles onto the predefined
An interference microscope based on a wavelength-to-depth encoding technique is presented. The wavelength-to-depth encoding is realized by using a diffractive lens and wavelength tuning. The coherence degree of the interference fields versus wavelength is analyzed. A depth discrimination of 0.71µm is obtained with 0.90 NA objective lenses. Experimental results of a four-level grating measurement are presented with results are comparable to those obtained with a Dektak profilometer and the same interference microscope using mechanical depth-scanning. The system is promising for fast, noncontact, high- resolution three-dimensional imaging.
We describe several concepts for real time shaping and detection of femtosecond laser pulses using optical nonlinearities. Cascaded second order wave mixing is used for real-time conversion of spatial-domain images to ultrafast time-domain optical waveforms. We experimentally demonstrate a cascaded nonlinearity arrangement allowing generation of complex amplitude femtosecond waveforms with high fidelity and good conversion efficiency. Single-shot, phase-sensitive detection of femtosecond pulses is demonstrated using both nonlinear wave-mixing and 2-photon absorption in semiconductor detector arrays. Using commercial silicon charge-coupled device (CCD), the latter approach allows detection of broadband ultrashort signals in the important wavelength range around 1.5 microns without phase-matching limitations. Finally we describe an approach to characterization of the multimode fiber using ultrashort pulse interferometry.
We describe various optical techniques for processing and detection of femtosecond laser pulses. Photorefractive and cascaded second order nonlinear wave mixing are used for space-to-time conversion, transforming space domain information into ultrafast temporal waveforms. An inverse operation that transforms a femtosecond pulse sequence into a quasi-stationary spatial image is performed with spectral domain three wave-mixing. We also demonstrate single-shot phase sensitive femtosecond pulse detection with two-photon absorption in a conventional silicon detector array. This approach allows efficient detection of wide-bandwidth ultrafast signals in the wavelength range of 1-2 μm.
We demonstrate several nonlinear optical techniques that allow spatial-temporal processing of femtosecond laser pulses. Photorefractive and cascaded second order nonlinear wave mixing is used to convert space domain information into ultrafast temporal waveforms. Spectral domain three wave mixing allows time imaging of femtosecond signals as well as characterization of the signal complex amplitude. Femtosecond pulse interferometry is applied for spatial and temporal characterization of the multimode optical fiber.
Nonlinear optical processing techniques that produce space-time information processing are introduced and experimentally demonstrated. The basic concept of such space-time processors closely resembles conventional Fourier optical processors of the space domain. By using ultrafast short pulses and nonlinear optics, we can perform not only real-time optical information conversion between the space and time domains, but also the processing and imaging of temporal information.
Nonlinear optical processing techniques that produce space- time information processing are introduced and experimentally demonstrated. The basic concept of such space-time processors closely resembles conventional Fourier optical processors of the space domain. By using ultrafast short pulses and nonlinear optics, we can perform not only real-time optical information conversion between the space and time domains, but also the processing and imaging of temporal information.
In this paper, we show two optical storage and retrieval techniques: a technique to record/readout data in serial format with real time detection, and an orthogonal-code multiplexed recording/readout system with nonlinear gated detection. Both of these techniques are based on femtosecond optical short pulses. In the former storage and detection technique, a train of pulses is recorded via spectral holography into a photorefractive crystal at wavelength 460 nm and the recorded hologram is read at the wavelength 920 nm, allowing nonvolatile readout of information from the photorefractive crystal. For detection and demultiplexing of a femtosecond pulse sequence whose time duration is much longer than the pulse width, a new pulse correlation technique is developed that is capable of real-time conversion of a femtosecond pulse sequence into its spatial image. Our technique uses a grating at the entrance of the system, thus introducing a transverse time delay (TTD) into the transform-limited reference pulse. The shaped signal pulses and the TTD reference pulse are mixed in a nonlinear optical crystal, producing a second-harmonic field that carries the spatial image of the temporal shaped signal pulse. In the orthogonal-code multiplexed recording technique with spectral holography, a signal pulse that contains a 1-D spatial information is recorded with a unique spectral phase-coded reference pulse, and multiplexing is performed by orthogonal phase-coding of reference pulses. Information readout is performed employing a nonlinear time- grating technique with the use of wave mixing in nonlinear optical crystals. We present the basic principles and experimental results for those femtosecond optics systems.
The existing mismatch between the bandwidth capacity of optical fiber and electronic devices, can be used to increase the speed, provide security and reliability in the transmission and distribution of information. To implement these applications, all-optical multiplexer performing space-to-time (i.e., parallel-to-serial) transformation at the transmitter and demultiplexer performing time-to-space (i.e., serial-to-parallel) transformation at the receiver will need to be constructed. For efficient bandwidth utilization, these processors need to be operated at rates determined by the bandwidth of the optical pulses. Ultrashort pulse laser technology has recently experienced significant advances, producing high peak power waveforms of optical radiation in the femtosecond duration range. These ultrafast waveforms can be synthesized and processed in the temporal frequency domain by spatially dispersing the frequency components in a spectral processing device (SPD) and performing operations on the spectrally decomposed wave (SDW). Space-to-time multiplexing via waveform synthesis using SDW filtering has been demonstrated with prefabricated masks, spatial light modulators and holograms. These filters are limited in their adaptability rate -a new filter can be implemented only as fast as the modulator response time or recording time ofa new hologram - typicallywell over a microsecond. To fulfill our goal of real-time SDW processing, we utilize a nonlinear wave mixing process based on four-wave mixing via cascaded second-order nonlinearities (CSN) in a 2)medium performed inside the SPD. The CSN arrangement consists of a frequency-up conversion process followed by a frequency-down conversion process satisfying the type-Il non-collinear phase matching condition. Our experiments are concerned with ultrafast information exchange between spatially parallel signals and higher bandwidth temporal signals. For the waveform synthesis experiment, we introduce two spatial information modulated waves carried by quasi-monochromatic light and a SDW of a ultrashort femtosecond pulse. The four wave mixing process produces a SDW that is a product of three waveforms: a spatial Fourier Transform (FT) of the two spatial information carrying waves and the SDW (i.e., temporal FT) of a femtosecond laser pulse. The spatial-temporal information exchange (i.e., the generated SDW) results in a synthesized waveform that is a time-scaled version of the spatial image, performed on a single shot basis with femtosecond-rate response time due to the fast nonlinearity. The inverse time-to-space transformation for detection of femtosecond pulse sequences is achieved using nonlinear three-wave mixing in a crystal. The two input waves are the SDW of a sequence of ultrashort pulses that need to be detected and a reference pulse. The nonlinear interaction between the two SDW's results in generating a quasimonochromatic second harmonic wave. The frequency ofthe second harmonic fields is twice the center frequency ofthe incident fields. The generated second harmonic fields contain spatial frequencies determined by the time delay between the reference pulse and the pulses in the signal. Thus a 1-D spatial FT of the second harmonic field produces a l-D spatial image equivalent to the temporal cross-correlation between the reference and the signal pulses. With short pulses, the spatial image has one-to-one correspondence with the signal pulse, implementing the desired time-to-space demultiplexing at femtosecond rates.
We have investigated the use of a 19-channel micromachined membrane deformable mirror (MMDM) for correcting aberrations of the eye to improve the resolution of fundus imaging. A Hartmann-Shack wavefront sensor (HSWS) and the MMDM are used to measure and correct aberrations existing in the anterior segments of the eye, respectively. Zernike polynomials are used to represent the MMDM surface shape as well as the optical wavefront shape. In order to control the MMDM, which has nonlinear and coupled responses to electrostatic controls, we have developed an adaptive control algorithm to iteratively adjust the control voltages of all channels, thus modulating the shape of the MMDM to reduce the variance of the optical wavefront measured using the HSWS. Experimental results using an artificial eye show that the adaptive system can compensate for low-order and some high- order aberrations, thereby improving the resolution of retinal images. The capability for correcting ocular aberrations is limited by the number of channels and the deflection range of the MMDM. Our new adaptive control algorithm allows effective use of the low-cost, compact MMDM, making adaptive optics a viable and practical technique for clinical high-resolution fundus cameras and other ophthalmic imaging instruments.
Optical information processing, traditionally employed in the spatial domain, has been experiencing a renaissance with femtosecond laser pulse technology. Temporal optical information can now be manipulated via linear and nonlinear processes, and stored and retrieved, by converting optical signals between the spatial and temporal domains. In this manuscript, we review the state-of-the-art in the spatio-temporal optical signal processing techniques for information data coding, data conversion, signal recording, as well as signal characterization. Applications of these techniques for future computing, communication, storage, and signal processing systems are discussed.
Confocal microscopy is a powerful tool that has been used in the development of 3D profilometers for depth-section image capture and surface measurements. Previously developed confocal microscopes operated by scanning a single point, or array of points, over the surface of a sample. The 3D profilometer we constructed acquires measurement data using a confocal microscopy technique, where transverse surface scanning is performed by a digital micromirror device (DMD). The DMD is imaged onto the object's surface allowing for confocal surface scanning of the field of view at a rate faster than video rate without physical movement of the sample. 3D reconstruction is performed a posteriori from stacks of 2D image planes acquired at different depths. A description of the experimental setup with system design issues and solutions are presented. Backscatter noise and diffraction noise due to the periodic micromirror structure is minimized using spatial filtering and polarization coding techniques. Using a 100x objective, the longitudinal point spread function was measured at 2.1 micrometers , with simultaneous transverse resolution of 228.0 lines/mm. The optical resolution performance of our microscope with real-time scanning provided by the DMD, is shown to be effectively equivalent to those of conventional confocal microscopes. The 3D images capabilities of our scanning system using the DMD were demonstrated on various objects.
We demonstrate a novel single shot autocorrelation technique for characterization of ultrashort pulses. Unlike existing single shot autocorrelation techniques, our new technique is capable of characterizing optical pulses over a femtosecond to picosecond pulse-width range. Our technique uses a grating at the entrance of the system, introducing a Transverse-Time- Delay (TTD) into the reference pulse. The pulse front in the resulting field is decoupled from the wave front. The signal pulse to be characterized and the TTD reference pulse are mixed in a nonlinear optical crystal, producing a second harmonic field whose transverse spatial extent is proportional to the signal pulse width. Since our technique allows for decoupling of the time delay from the propagation direction (unlike the commercial single shot autocorrelators), we can select the angle between the intersecting pulses to satisfy the phase matching conditions, achieving best efficiency while setting the resolution independently in the orthogonal direction. In addition, by controlling the slope of the TTD, the system can adapt to a wide range of input pulse widths. In this paper we will present the basic principles as well as experimental results for this new autocorrelation technique.
Optical signal processing, traditionally employed in the spatial domain, has been experiencing a renaissance with femtosecond laser pulse technology. Temporal optical information can now be manipulated via linear and nonlinear processes, and stored and retrieved, by converting optical signals between the spatial and temporal domains. In this manuscript, we review the state-of-the-art in the spatio- temporal optical signal processing techniques for information data coding, data conversion, signal recording, as well as signal characterization. Applications of these techniques for future computing, communication, storage, and signal processing systems are discussed.
Novel diffractive optical elements (DOE) with multifunctionality in polarization or color are reviewed. We review three technological approaches for construction of such DOEs with multifunctionality in polarization: the two- substrate birefringent computer generated hologram (BCGH), the multiple order delay BCGH, and the form birefringent computer generated hologram approaches. We also discuss the accurate design of such DOEs enabled by our modeling tools based on rigorous coupled wave analysis. Microfabrication techniques developed for realization of these three types of polarization selective DOEs are described. The developed DOEs with multifunctionality in polarization or color are used to package a 3D optoelectronic VLSI chip, a transparent optical multistage interconnection network, and a wavelength division demultiplexer, providing mechanical and thermal stability, light efficiency, reduced volume, weight, and cost, and increased reliability.
An attempt to eavesdrop a quantum cryptographic channel reveals itself through errors it inevitably introduces into the transmission. We investigate the relationship between the induced error rate and the maximum amount of information the eavesdropper can extract, both in the two-state B92 and the four-state BB84 quantum cryptographic protocols. In each case, the optimal eavesdropping method that on average yields the most information for a given error rate is explicitly constructed. Analysis is limited to eavesdropping strategies where each bit of the quantum transmission is attacked individually and independently form other bits. Subject to this restriction, however, we believe that all attacks not forbidden by physical laws are included. Unlike previous work, the eavesdropper's advantage is measured in terms of Renyi information, and with respect only to bits received error-free by Bob. This alters both the maximum extractable information and the optimal eavesdropping attack. The result can be used directly at the privacy amplification stage of the protocol to accomplish secure communication over a noisy channel.
Utilization of ultrahigh bandwidth available in optical fiber networks will require development of fast and efficient parallel-to-serial and serial-to-parallel all- optical multiplexing techniques. Such multiplexers are also useful for interfacing to optical storage devices. In this presentation we will review the application of space/time optical processing with femtosecond laser pulse to implement such multiplexers. We will focus on a novel real time optical space-time processor based on 3-wave mixing in a nonlinear optical crystal. This processor allows conversion of temporal signal sequence to a 1D spatial image, thereby realizing a serial-to-parallel multiplexer. The processor is also used to generate a wigner distribution function, which allows to determine both amplitude and phase of ultrashort temporal signals.
We introduce a novel polarizing beam splitter that uses the anisotropic spectral reflectivity (ASR) characteristics of a high spatial frequency multilayer binary grating. By combining the form birefringence effect of a high spatial frequency grating with the resonant reflectivity of a periodic multilayer structure, the ASR characteristics for the two orthogonal linear polarizations are obtained. Such ASR effects allow us to design an optical element that is transparent for TM polarization but reflective for TE polarization. The properties of the polarizing beam splitter are investigated using rigorous coupled-wave analysis. The design results show that an ASR polarization beam splitter can provide a high polarization extinction ratio for optical waves from a wide range of incident angles and a broad optical spectral bandwidth. Such ASR polarizing beam splitters are uniquely suitable for image processing and optical interconnection applications.
A realistic quantum cryptographic system must function in the presence of noise and channel loss inevitable in any practical transmission. We examine the effects of these channel limitations on the security and throughput of a class of quantum cryptographic protocols known as four-state, or BB84. Provable unconditional security against eavesdropping, which is the principal feature of quantum cryptography, can be achieved despite minor channel defects, albeit at a reduced transmission throughput. We present a semi-empirical relation between the fully-secure throughput and the loss and noise levels in the channel. According to this relation, a particular implementation of BB84, based on the frequency-division multiplexing scheme and utilizing commercially available detectors, can reach throughputs as high as 10<SUP>4</SUP> - 10<SUP>5</SUP> secure bits per second over a practical channel of reasonable quality.
The next generation of distributed imaging and visualization environments for diagnostic radiography and C<SUP>4</SUP>I will require the delivery of a guaranteed quality-of-service by a ultra-high bit rate network. Two aspects of the quality-of-service, the link bit rate and the round-trip packet latency, can be met through the use of transparent third-generation photonic networks. These networks can be implemented using ultra-short optical pulses in conjunction with spectral-domain processing to construct links. These links are combined with transparent photonic packet switches to form the network switching fabric. The quality-of-service is guaranteed by using virtual circuit-switching.
We introduce a novel method of modeling PLZT phase modulators. Traditionally, modeling has been based upon fitting the constant quadratic electro-optic coefficient to empirical data. Our characterization has shown that the electro-optic coefficient is not a constant and that the electro-optic effect saturates at electric field strengths that exist in standard surface electrode device configurations. We have also found that the additional effects of light scattering and depolarization, which depend on the strength of the applied electric field, are significant factors for modeling device design and optimization.
Photorefractive volume holography for processing ultrashort optical pulses carrying spatial, temporal, and spatio-temporal optical information is introduced. These new holographic methods can process 4-dimensional information that in addition to the 3 spatial coordinates also include the temporal evolution of optical signals on nanosecond to femtosecond scale. Photorefractive volume holographic materials provide the medium necessary for recording and reconstruction in real-time. Applications of direct time domain and spectral domain holography for image processing, temporal matched filtering, optical pulse shaping, 3-D optical storage, and optical interconnects are discussed. Furthermore, the combined space-time holographic processing that allows the conversion between spatial and temporal optical information carrying channels is introduced. This method is used to demonstrate experimentally parallel-to-serial and serial-to-parallel data conversion for 1-D images and image-format data transmission. This holographic processor provides the advantages of self- referenced signal transmission and self-compensation for optical dispersion induced by the holographic materials, communication channel, as well as other optical components. Finally, future research directions for optical information processing with complex spatio-temporal signals are identified and discussed.
Diffraction characteristics of high-spatial-frequency gratings (HSF) are evaluated for application to polarization-selective computer generated holograms using two different approaches, second order effective-medium theory (EMT) and rigorous coupled-wave analysis (RCWA). The reflectivities and the phase differences for TE and TM polarized waves are investigated in terms of various input parameters, and results obtained with second order EMT and RCWA are compared. It is shown that while the reflection characteristics can be accurately modeled using the second order EMT, the phase difference created by form birefringence for TE and TM polarized waves requires the use of a more rigorous, RCWA approach. Design of HSF gratings in terms of their form birefringence and reflectivity properties is discussed in conjunction with polarization-selective computer generated holograms. A specific design optimization example furnishes a grating profile that provides a trade-off between largest form birefringence and lowest reflectivities.
Electronic holography for imaging through biological tissue is described. A number of processes are given, including the holographic implementation of the first arriving light method, the broad source method, as well as variations on these methods. The equipment is discussed in some detail, including the camera-computer interactions.