Photonics Processing Laboratory

Principal Investigators:
Aaron Peled, Nina Mirchin, Raya Margolin, Itzhak Baal-Zedaka, Meir Zagon

Students watching an experiment of interaction between a hydrosol colloid and argon laser beam
Students watching an experiment of interaction between a hydrosol colloid and argon laser beam
Design of Diffractive Optical Elements (DOE) and optical

Laser based Photo-excited processes will be used in this investigation to create planar elements for miniaturized optical and optoelectronic applications. We investigate processes for laser writing Diffractive Optical Elements (DOE) by directly photodepositing from solutions and engraving methods. We use computer based programs to design and simulate the optical diffractive profile of the elements. Lasers and discharge UV lamps are used to produce various elements such as linear gratings and other DOE profiles

Computerized Visualization of fast processes by FFT and Image Processing Methods Visualization techniques of dynamic processes are developed using computer generated micrographs using 2D Fourier transform techniques. Models are developed to predict spatio-temporal processes evolution visualized by 'snapshots' and time movies. The simulations in this work can track for instance rapid diffusive fronts in deposition experiments, starting from initial microscopy micrographs such as SEM and AFM. The surface microstructure time 'tracking' scheme relies on transforming the original image of the particles spatio-temporal dependent morphology into a synthetic image in the Fourier spatial frequency domain. The modeling of the material deposition and subsequent surface redestribution by diffusion and other driving mechanisms are sought. The 2D-Inverse Fourier Transform (IFT) is used to obtain the real - space, time dependent 'snapshots'. This enables us to observe dynamic processes of extremely fast rates where spatio-temporal details cannot be followed experimentally.
Simulations of fast photodeposition of colloid particles on a surface
Simulations of fast photodeposition of colloid particles on a surface

Simulation of photo-excited TOF experiments by the generalized Ramo-Theorem The spatio-temporal spreading features of charge packets from time of flight (TOF) current transients in molecular doped polymer systems are analysed using TOF currents simulation by the generalized Ramo-Theorem and the experimental results related to the thermal and electric field dependences of the dispersion parameters and charge carrier mobility. The parameters describing the charge spatial spread are the velocity distributions within the moving charge packet, the trapping time and the trapping lengths. These parameters are used for a better understanding of charge transport in laser printers and photocopiers systems.

Design and implementation of proximity optoelectronic systems for collision avoidance
Automotive sensor systems are increasing in complexity as functionality becomes more demanding. Radar, Lidar, ultrasound and video components are investigated to provide the vehicle with a view of what is happening around it. This picture needs to be both comprehensive and accurate. Forward looking ranging sensors must look ahead up to 100 m in order to anticipate the actions of the vehicles in front. What is needed are solutions that will allow the sensors to align and lock-on obstacles ahead of the vehicle very fast and maintain lock under software control. This feature is useful in safety systems for collision avoidance and pre-crash.

Simulation of Soliton propagation in fiber optics
 The information transfer by means of fiber optics communication systems (FOCS) with pulse-code modulation is limited by the dispersion of group velocities. The influence of this effect can be suppressed efficiently if one uses sufficient powerful pulses of light. The non-linear effect of pulses under certain conditions can be transformed into solitons and their propagation in FOCS then is not prone to dispersive broadening. In the FOCS field our current research focuses on the development of extremely high bit-rate links, of the order of 100GB/second. We consider in our investigations the soliton as an approach for real life non-linear pulses in fibers at specific conditions.

Investigation of Photo-excitation effects using Imaging methods
 The nanoscopic patterns created by an Ar+ laser while irradiating photoexcitable solutions creates a volume pattern of regions possessing a varying refractive index and optical density. The dynamic processes during the volume photo-excitation are measured by a He-Ne probing laser and corroborated with in situ optical microscopy. The thermal properties of the solutions particles in the irradiated volume are controlled by the high laser powers, and vary also under a variety of environmental and chemical conditions are investigated by image CCD and CMOS acquiring methods.

Investigation of FO systems for optimized performance using noise figure

Unlike long-distance RF links, where thermal noise dominates, optical links are more likely to be subsequently limited by nonlinearities once the link budget OSNR is satisfied-such as dispersion. The result is that some new methods inthe area of optimizing the link properties are worked out. Dispersion compensation in the optical domain is implemented in very-high speed electronics in much the same way it is implemented in electronic communication receivers-even adaptively. Thus methods for comparing optical and electrical links and devices are in high demand. Our laboratory activities are aimed at simplifying the cumbersome Optical-electrical-optical (OEO) conversion required for combined links. We continue to develop a technique for determining relative degradations of FO links using noise figure concepts similar to radar and microwave links. This uses the equivalent noise figure in optical and electronic components to quantize the degradation space of S/N quality etc. The optimized parameters required to characterize the performance of these systems are channel count, signal wavelength, signal power, optical signal to noise ratio (OSNR) , and spectral flatness.

Developing a sensitive photorecording method for laser beam profilometry and Light profile microscopy
 (LPM)Light profile microscopy (LPM) is a technique of optical inspection that is used to record micrometer-scale images of sources and structural cross-sections. LPM provides image contrast based on changes of the depth profile due to changes of the optical absorption coefficient of the analyzed structures. We develop a novel approach to lensless and maskless projection of optical patterns, which we call Photo-Deposition Profiling (PDP). In traditional optical profilometry light from the laser is recorded only on 2D space loosing z information. The central idea in PDP is that the pattern of light that emerges from the laser for instance evolves into a relief thin film containing the light integrated dosimetry information also. A prototype PDP projector is constructed including a target recording region far away from the source. The resulting optical pattern contains useful information not only of the instantaneous laser profile but also its varation in time for a preset period of time.

Investigating Submicrometric recording methods
 The advent of near-field optical microscopy allows to overcome the lateral resolution limit of the classical optical microscopes imposed by far-field diffraction phenomena. This limit is given by the well-known Rayleigh-Abbe criterion. The principle of SNOM consists in the detection of the evanescent components of the light scattered by a nanostructure. These evanescent components of the electromagnetic field contain information on the high spatial frequencies of the sample surface. The SNOM is a complementary optical tool to other Scanning Probe Microscopes such as AFM and Scanning Tunneling Microscope (STM) which can only provide topographic and mechanical and electronic information respectively. A particular advantage of SNOM is to allow a various and powerful means of local analysis such as fluorescence near-field imaging and spectroscopy which are highly sensitive and selective techniques to determine the physical and chemical properties of surfaces.

Investigating the Write/Erase properties of photodeposition processes
 The principles and mechanisms of image printing by the photodeposition effect in colloid solutions is investigated for various materials. The light beam is projected by lasers and other high power sources on a photoactive aqueous medium. The photons are absorbed by colloid particles and trigger a sequence of photoexcitation events by which nanoparticles are deposited onto substrates. By irradiating the cell/solution interface with laser beams, various lines, dots and more intricate material shapes can be directly written as if the laser beam consists of a "stylus" which deposits the colloidal material in proportion to the photon irradiation dose. The rate of the process for each material is controlled by the laser fluence, temperature of the cell and laser wavelength. Write and erase thin film patterns can be obtained by in-situ consecutive photodeposition and photoablation cycles. The submicrometric structures of photodeposited and photoablated thin films are examined by optical new methods and checked against high resolution scanning electron microscope (SEM) and AFM. High magnifications will be used to establish the morphology of the particles and islands on the substrate before and after the ablation cycle.
Simulation of colloid particles in liquid vortices
Simulation of colloid particles in liquid vortices

Theoretical investigation in disordered materials
Theoretical investigation of carrier mobility in disordered materials is essential to a deeper understanding of charge transport in such materials and for interpreting the time of flight and photoconductivity data. The characteristics of these p-conjugated polymers suggest that the electron or hole is in a polaronic state extended over one or more rings or over a number of sites along the backbone, as dictated by the geometry of the material. Ladder or double-stranded polymers are then expected to have better transport properties i.e., higher conductivity and photoconductivity, than the usual conjugated polymers because if there is a break or serious configuration defects in one strand, there is another strand for the carrier to proceed on.The p-conjugated polymers can be expected to have also interesting third-order nonlinear optical properties since such effects along with charge transport and photoconducting properties are related to common structural origins. Their outstanding mechanical properties and high temperature stability in conjunction with large nonlinear optical effects would make this class of polymers potential photonic materials. In contrast to other known nonlinear optical materials, these high temperature polymers were found to exhibit the largest optical damage threshold (>50 GW/cm2) for high intensity infrared laser light.

Laboratory Facilities
 The laboratory facilities are used also for educational purpopses such as the optical characterization of electro-optical materials, devices and systems. The laboratory is equipped with various PC Computers, electronics hardware and Software to perform the various controlling functions needeed as well as for acquiring data in situ and its processing. Labs which support the research activity with additional accesible equipment are the Microelectronics Lab and Sciences Department including X-ray photoelectron,spectroscopy (XPS), scanning electron microscope (SEM), surface profilometer and sputtering deposition systems.