The capability of brass as a real time substrate for surface enhanced Raman scattering applications is investigated. In this article, we showed that, using just the ultra-pure water as the electrolyte and the brass electrodes, ions extracted from the anode form nanoparticles on the anode surface in matter of minutes, and these nanoparticles are used for enhancing Raman signal intensity in real time. We observed enhancement factor of more than five orders of magnitude in Raman spectrum of Rhodamine B. We show that the nanoparticles formed on the brass anode surface are copper oxide nanoparticles and the enhancement of Raman signal intensity is due to these (copper oxide) nanoparticles. The zinc atoms do not affect the enhancement factor due to absence of zinc oxide nanoparticles on the anode surface. We present number of reasons to support this view in detail.
Metal-insulator-metal (MIM) diodes are highly considered in high frequency applications in form of rectennas for energy harvesting applications due to their fast speed, small size, and ease of fabrication and IC compatibility. In these diodes, insulators are integral part of the device, determining performance parameters. In this study, we have evaluated HfO<sub>2</sub> and Al2O<sub>3</sub> based MIM diode structures to compare and determine performance parameters, with conversion efficiency being prioritized. The fabrication processes in physical vapor deposition (PVD) systems for the MIM diodes resulted in the devices having high non-linearity and responsivity. Also, to achieve uniform and very thin insulator layer atomic layer deposition (ALD) was used. We implemented the same MIM structure in 10x10 array form, with active area of 200x325 nm<sup>2</sup>. The efficiency values of same arrays tested with 1200 and 1600 nm wavelength LEDs for 200x325 nm<sup>2</sup> diode active area without applying bias. The conversion efficiency value of the HfO<sub>2</sub> based structures calculated as 5% for 1200 nm wavelength. These measured values of conversion efficiency are reported for the first time in the literature for MIM diodes in SWIR operation.
The metal-insulator-metal (MIM) diodes have high speed and compatibility with integrated circuits (IC’s) making MIM diodes very attractive to detect and harvest energy for infrared (IR) regime of the electromagnetic spectrum. Due to the fact that small size of the MIM diodes, it is possible to obtain large volume of devices in same unit area. Hence, MIM diodes offer a feasible solution for nanorectennas (nano rectifiying antenna) in IR regime. The aim of this study is to design and develop MIM diodes as array format coupled with antennas for energy harvesting and IR detection. Moreover, varying number of elements which are 4x4, and 40x30 has been fabricated in parallel having 0.040, 0.065 and 0.080 μm<sup>2</sup> diode area. For this work we have studied given type of material; Ti-HfO<sub>2</sub>-Ni, is used for fabricating MIM diodes as a part of rectenna. The effect of the diode array size is investigated. Furthermore, the effect of the array size is also investigated for larger arrays by applying given type of material set; Cr-HfO<sub>2</sub>-Ni. The fabrication processes in physical vapor deposition (PVD) systems for the MIM diodes resulted in the devices having high non-linearity and responsivity. Also, to achieve uniform and very thin insulator layer atomic layer deposition (ALD) was used. The nonlinearity 1.5 mA/V<sup>2</sup> and responsivity 3 A/W are achieved for Ti-HfO<sub>2</sub>-Ni MIM diodes under low applied bias of 400 mV. The responsivity and nonlinearity of Cr-HfO<sub>2</sub>-Ni are found to be 5 A/W and 65 μA/V<sup>2</sup>, respectively. The current level of Cr-HfO<sub>2</sub>-Ni and Ti-HfO<sub>2</sub>-Ni is around μA range therefore corresponding resistance values are in 1-10 kΩ range. The comparison of single and 4x4 elements revealed that 4x4 elements have higher current level hence lower resistance value is obtained for 4x4 elements. The array size is 40x30 elements for Cr-HfO2-Ni type of MIM diodes with 40, 65 nm<sup>2</sup> diode areas. By increasing the diode area, the current level increases for same size of array. The current level is increased from10 μA to100 μA with increasing the diode area. Therefore resistance decreased in the range of 10 kΩ and nonlinearity is increased from 58 μA/V<sup>2</sup> to 65 μA/V<sup>2</sup>.
In this work, we utilize the electrolysis effect to prepare a semi-colloidal substrate for surface enhanced Raman spectroscopy (SERS) applications in which the nanoparticles created on the anode surface act as an active medium for SERS. The experiments carried out with copper (Cu) as the electrode and Rhodamine B (RhB) as the electrolyte. The measured enhancement factor (EF) of the Raman peaks of RhB is more than five orders of magnitude. The proposed method has some key advantages: it is a very simple and low cost technique and also can be used in real time since it is a quite fast process.
The metal-insulator-metal (MIM) diodes are considered to be very attractive candidate for infrared energy harvesting and detection applications. The high speed and compatibility with integrated circuits (IC’s) makes MIM diodes good choice for infrared (IR) regime of the electromagnetic spectrum. Moreover, it is possible to obtain large volume of devices in same unit area due to smaller active area required for MIM diodes. The aim of this work is to design and develop MIM diodes for energy harvesting and IR detection. For this work three different sets of materials; Au-Al<sub>2</sub>O<sub>3</sub>-Al, Au-Cr<sub>2</sub>O<sub>3</sub>-Cr, Au-TiO2-Ti Al<sub>2</sub>O<sub>3</sub>, are used for fabricating MIM diodes. Furthermore, the effect of the insulator thickness and diode active areas are investigated for Au-Al<sub>2</sub>O<sub>3</sub>-Al MIM diode to study diode characteristics further. The optimization of fabrication processes in physical vapor deposition (PVD) systems for the MIM diodes resulted in the devices having high non-linearity and responsivity. The non-linearity of 80 μA/V<sup>2</sup> and a responsivity of 15 A/W are achieved for Al-Al<sub>2</sub>O<sub>3</sub>-Au MIM diodes under low applied bias of 50 mV. The responsivity of Au-Cr<sub>2</sub>O<sub>3</sub>-Cr and Au-TiO<sub>2</sub>-Ti diodes with insulating layers of Cr<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> are found to be 8 A/W and 2 A/W respectively.
In this work we have proposed a new configuration based on a tilted charged coupled device (CCD) camera and bandpass sampling theorem which not only decreases the spectrometer size but also operates in the traditional spectrometers wavelength range of 400 nm – 1100 nm. The static Michelson interferometer is built by attaching a quartz cube and a prism together, and a CCD camera is attached to the quartz cube in 45 degree to record path length differences (PLD). An algorithm is developed to process the signal and calculate the Fourier transform of the recorded interferograms on the CCD camera.
Here we present the development of a 3D holographic endoscope with an interferometer built around a commercial
rigid endoscope. We consider recording the holograms with coherent and incoherent light separately without
compromising the white light imaging capacity of the endoscope. In coherent light based recording, reference
wave required for the hologram is obtained in two different ways. First, as in the classical holography, splitting the
laser beam before the object illumination, and secondly creating the reference beam from the object beam itself.
This second method does not require path-length matching between the object wave and the reference wave,
and it allows the usage of short coherence length light sources. For incoherent light based holographic recordings
various interferometric configurations are considered. Experimental results on both illumination conditions are
Antenna-coupled metal-insulator-metal devices are most potent candidate for future energy harvesting devices. The reason for that they are ultra-high speed devices that can rectify the electromagnetic radiation at high frequencies. In addition to their speed, they are also small devices that can have more number of devices in unit area. In this work, it is aimed design and develop a device which can harvest and detect IR radiation.
There is increasing demand for devices operating at room temperature for IR sensing and imaging. Antenna coupled metal-insulator-metal (MIM) diodes are potential candidates in this field. The reasons are miniaturizing features and femtosecond operation of these devices: smaller sizes lead to more pixels in limited areas and quantum tunneling phenomenon leads to faster operation. In this work, it is aimed to design and develop a device that can act as IR detector at room temperature.
Here we consider a derivative based method for phase recovery and demonstrate a numerical method that can be described as differentiate and cross multiply operation to obtain the phase gradient. This method uses quadrature phase data that is in sine and cosine form, which is a natural outcome many interferometric measurements including that of digital holographic reconstruction. Since the differentiation is performed on trigonometric functions which are discrete, it is shown that the method of differentiation and the sampling rate are important considerations especially for the noise corrupt signals. The method is initially developed for 1D phase signals, and then later extended to 2D. Noise performance of the method is also investigated, and it is shown that for extremely noisy signals the method can be adapted to an iteration routine which recovers the phase successfully. We present simulations and the experimental results which show the validity of the approach.
In digital holography, computing a focused image of an object requires a prior knowledge of the distance of the object from the camera. When this distance is not known, it is necessary to repeat the image reconstruction at a range of distances followed by evaluation of each image with a sharpness metric to determine the in-focus distance of the object. Here, we present a method to nd the focus distance by processing the image transverse to the object plane instead of the processing in the image plane as it is usually done. Since the reconstructed hologram image is spatially symmetric around the focus point along the propagation axis, simply nding the symmetry points in the image cross-section speci es the focus location, and no other sharpness metrics are necessary to use. Also with this method, it is possible to nd the focus distances of multiple objects simultaneously, including the phase only objects without any staining. We will present the simulations and the experimental results obtained by a digital holographic microscope.
Digital holography allows the acquisition of 3D profiles of objects. Digitally captured holograms are reconstructed
at the respective distances of the objects to reveal the phase and the intensity profiles. However, computing an
object’s 3D profile with only a single reconstruction requires prior knowledge of the distance of the object from
the camera. Otherwise, by performing several reconstructions at different distances and by evaluating each image
with sharpness estimation, one can determine the in-focus distance of the object. Moreover, it is not practical
to perform several reconstructions in real-time systems since reconstruction is the most computationally heavy
part in digital holographic imaging. In this paper, we compare common sharpness functions applied to digitally
recorded holograms for autofocus algorithms found in the literature. In addition, we show that automatic focus
distance search can be done in real-time with scaled-down holograms obtained from the original hologram. This
new method improves the speed of autofocus algorithms on the order of square of the scaling ratio. We show
that numerical simulations and experimental results are in good agreement.
Digital holography made it possible to capture and reconstruct holograms in a computer environment. In a conventional CPU, the real-time reconstruction is not possible when the size of the holograms increase to several mega-pixels range. However, a graphics processor can provide the required computational power. The rapid developments in commercial graphics card technology provide an opportunity to process large blocks of data in a very short amount of time which reduces the hologram reconstruction time significantly. In this manuscript, basics of GPU programming for hologram reconstruction is introduced, and the efficiency of CPU and GPU implementations of the three reconstruction algorithms (Fresnel transformation, angular spectrum method, convolution with free space propagation) are compared. Experimental results indicate that, on average, 100 fps reconstruction rate is achieved with all methods.
A new numerical method for in-line hologram reconstruction is proposed. It is shown that the object image is
successfully recovered by applying Hartley transform to the difference of two phase shifted holograms followed
by the application of a phase retrieval type of an algorithm. The algorithm is explained in detail and simulation
results are presented.
Here we describe a new holographic recording method in which a separate reference wave is not required. Object
wave is split into two beams and one of them is spatially filtered to create a plane reference wave. This method
allows the use of low coherence light sources since pathlengths of the interfering waves are matched automatically
which will lead to holographic recording of objects at any distance rather easily. Optical setup will be discussed
and the experimental results will be presented.
In recent years the field of digital holography became an attractive research area following the developments of
CCD-arrays and an ever increasing computational power of computers. Here we investigate digital holography
reconstruction methods and compare them for the accuracy and the computational speed. In addition, possible
discrepancies in the calculation of the diffraction integral via fourier transform is clarified and it is compared
to convolution methods. The proper evaluation of discrete Fresnel diffraction equation is demonstrated by
creating artificial holograms and numerically reconstructing them. Simulation results and experimental work is
A gyroscope based on Sagnac interferometer measures the rotation rate relative to an inertial frame of reference.
Sagnac effect originally has been derived and experimentally demonstrated with optical waves. Later, matter
wave based Sagnac interferometers were developed due to inherent sensitivity over a photon based system.
However in any interferometer whether it is photon or matter wave based the resultant phase shift due to
counter-rotating waves is independent of the wave velocity. Here we show that one can have a larger phase shift
with slower matter waves using Aharonov-Bohm effect: the phase difference of the counter propagating waves is
proportional to the inverse square of the particle velocity.
In recent years there has been significant activity in research and development of high sensitivity accelerometers and gyroscopes using atom interferometers. In these devices, a fringe shift in the interference of atom de Broglie waves indicates the rotation rate of the interferometer relative to an inertial frame of reference. In both optical and atomic conventional Sagnac interferometers, the resultant phase difference due to rotation is independent of the wave velocity. However, we show that if an atom interforemeter is enclosed in a Faraday cage which is at some potential, the phase difference of the counter-propagating waves is proportional to the inverse square of the particle velocity and it is proportional to the applied potential. This is due to Aharonov-Bohm effect and it can be used to increase the rotation sensitivity of atom interferometers.
A surface plasmon resonance (SPR) sensor for sensing displacement of a thin membrane is described. We assume a thin membrane is located in close proximity of a metal film in the usual SPR configuration. A displacement of the membrane changes the plasmon resonance condition and by processing the reflectance we can deduce the deflection amount. In particular, we analyze the reflectance of this system using Fresnel's formulas for multilayer films and we discuss the angular scanning, differential phase measurement and wavelength scanning methods to obtain the amount of displacement. We propose that such a system can be used as a pressure sensor or an optical microphone. If one uses a cantilever instead of a membrane, same system might have a use in atomic force microscopy applications. The minimum resolvable displacement can be as low as 10<sup>-4</sup>Å/√Hz limited by the laser phase noise and the shot noise of the detection system.
External cavity lasers (ECL) based on semiconductor diode gain
elements and Fiber Bragg Gratings (FBG) have been developed for
Telecom (OC-48) nd Analog (CATV, QAM) applications. They possess
very narrow linewidth (100 kHz) and exceptional wavelength stability.
These qualities makes them attractive platform for implementation of
heterodyne sources and Optical Phase Locked Loops (OPLL) for
Microwave Photonics applications.
We discuss two types of such heterodyne sources: heterodyne
oscillator based on heterodyning of two ECL, and fixed frequency
heterodyne oscillators based on ECL with FBG written in the polarization maintaining fiber.
All two types of heterodyne sources were built based on industry
standard 14-pin butterfly package. All of them exhibited excellent
wavelength stability (less than 1 pm/mA and 1-2 pm/°C).
Fixed frequency sources provided beat oscillation around 40 GHz.
We present performance characteristics and measurement data on
(linewidth, phase noise, heterodyne mixing, etc.) and discuss the merits of ECL use as heterodyne sources for Microwave Photonics applications.