Publications by Year: 2013

D. Sinefeld, “Adaptive optics for fast optical communication: Spatial solutions for spectral issues,” 2013. Publisher's VersionAbstract

In recent decades, the use of fast optical signals has become increasingly dominant, both in scientific research and in engineering applications. High speed photonics serves as the core of modern worldwide communication networks, as well as in many optical signal processing applications. Such applications rely on the ability to control, filter and manipulate large bandwidth signals. Traditionally, such control can be realized using fast electronics. However, continuous growth in data rates makes this option impractical, since the signals become too fast to control even for cutting edge electric circuit technology. The alternative is to use an all-optical system, where signal control is done in the frequency (spectral) domain. Such a system must be capable of manipulating large bandwidth signals with high spectral resolution. Such optical systems are essential in optical communication networks, for performing signal conditioning, impairment mitigation and WDM channel power equalization.

In this work I explore a family of optical sub-systems combining guided-wave and free-space optics for spectrally resolving optical signals at unprecedented resolution, and actively manipulating the spectral components with spatial light modulator (SLM) technology. The ability to combine the employed cutting edge technologies, including a high resolution planar lightwave circuit (PLC) arrayed waveguide grating (AWG), together with the state-of-the-art phase SLM, which was adapted from the light projection industry, enables the design and demonstration of high resolution photonic spectral processors (PSP). This system is capable of applying arbitrary spectral phase and amplitude at high spectral resolution to an optical signal and of controlling its properties in the time domain. A PSP can be configured for addressing the entire conventional optical communication band, at a price of poor resolution due to the finite space-bandwidth trade-off. Alternatively, the PSP can be designed as a colorless adaptive device, operating with a free spectral range (FSR) matching the channel plan, e.g. with a 100-GHz FSR, for in-band high-resolution wavelength division multiplexing (WDM) filtering applications. By using two-dimensional free-space optics achieved by crossing the PLC AWG with a bulk grating, a new broadband processor was introduced. This PSP is capable of controlling independent WDM channels on the 100 GHz grid at the high resolution of the colourless solution, thereby shattering the space-bandwidth limitation.

Based on these concepts, a family of novel systems and implementations were developed and investigated. In this thesis I introduce six papers which demonstrate the design and implementation of three PSP systems, based on hybrid waveguide/free space optics arrangements. The papers are divided into two groups: in the first group, three papers present the evolution of the spectral processing device, from the simplest version of colorless PSP up to two dimensional PSP arrangement with full spectral, control along the c-band. The second group contains three papers describing several implementations of these technologies, including amplitude filtering applications (Nyquist-WDM generation), phase filtering applications (tunable chromatic dispersion compensation and group delay stairs generation) and a demonstration of a new fiber laser which was built using the PSP platform. These high spectral resolution devices and systems can serve as an important element in controlling dispersion, enhancing signal quality and optimally filtering a distorted signal, and their development is essential for the progress in the optical fiber communication world.

O. Golani, “Photonic Analog-to-Digital Conversion Using Spatial Oversampling,” 2013.Abstract

Photonic analog to digital converters (ADC) have been the focus of much research interest in recent years, because of their potential for very high bandwidth and sampling rates. Using photonic techniques may help to surpass the limitations of traditional electronic analog to digital converters, providing unprecedented performance. A key parameter of any ADC is its conversion resolution. This works explores the technique of spatial oversampling as a means to increase resolution in photonic ADCs. Spatial oversampling is shown to be equivalent to temporal oversampling, a commonly used technique in the field of digital signal processing. The properties, benefits and requirements of spatial oversampling are derived, and the concept is demonstrated theoretically and experimentally. A photonic ADC design based on this technique is described, and an implementation as a photonic integrated circuit is presented. The design is based on electro-optic phase modulation, interferometric detection and spatial oversampling. The abilities and performance of this photonic ADC concept are demonstrated experimentally by digitizing analog signals with frequencies of up to 13GHz.

Photonic Analog-to-Digital Conversion Using Spatial Oversampling
M. Bin-Nun, “Polymeric waveguide platform fabrication optimization,” 2013. Publisher's VersionAbstract

In this work I report on the development of a platform of a polymeric waveguide composed of Cytop as the cladding and PFCB as the core. These two polymers were chosen due to their low loss in the optical communication regime (0.26 dB/cm for PFCB core and 0.022dB/cm for Cytop cladding). PFCB and Cytop have refractive indexes of 1.48 and 1.34 respectively and therefore offer high index contrast in comparison to glass waveguides. PFCB was chosen as the waveguide core since it has been proven a good host for nanocrystals (NCs).
In this work a lot of effort was invested in making the fabrication process compatible with semiconductor NCs that will in the long term be mixed in the PFCB core. Doping the core with nanocrystals is of interest, since the NCs properties are diverse, flexible and controllable. Choosing NCs with high third order susceptibility will allow us to fabricate nonlinear waveguides. Furthermore,specifying the NCs shape and size will allow us to align them by applying external electric voltage and by that enhance the macroscopic nonlinear properties of the composite.
Two fabrication configuration are proposed. Both are aimed at fabricating a square waveguide. The first configuration is the ridge-method where the PFCB core undergoes reactive ion etching (RIE).This method carries on with previously proposed methodology at the Photonic Devices Laboratory of Dr. Marom [1], however several key improvements were made.
The second configuration is the trench-method where only the Cytop undergoes RIE. By that method we wish to prevent roughness that might occur in the alternative method due to etching a composite made of PFCB and the NCs at the same time. In addition not all NC materials we would like to use are allowed into the RIE chamber since they may cause contamination to the RIE machine. Replacing the ridge method with the trench one will obviously overcome this obstacle. However both methods have their own challenges. In this work I tried to overcome some of the challenges and to produce reliable and reproducible method for fabricating a square polymeric waveguide compatible with NCs.

Polymeric waveguide platform fabrication optimization
Time-to-space conversion of ultrafast waveformsat 1.55 μm in a planarperiodically poled lithium niobate waveguide
D. Shayovitz, H. Herrmann, W. Sohler, R. Ricken, C. Silberhorn, and D. M. Marom, “Time-to-space conversion of ultrafast waveformsat 1.55 μm in a planarperiodically poled lithium niobate waveguide,” Optics Letters, vol. 38, no. 22, pp. 4708-4711, 2013. Publisher's VersionAbstract

We report the first demonstration, to our knowledge, of time-to-space conversion of subpicosecond pulses in a slab nonlinear waveguide. By vertically confining the nondegenerate sum-frequency generation interaction between a spatially dispersed 100 fs signal pulse at 1.55 μm and a reference pulse in a titanium indiffused planar periodically poled lithium niobate crystal waveguide, we have attained a conversion efficiency of 0.1% and a conversion efficiency slope of 4% per watt of reference beam power. This was achieved while maintaining high conversion resolution, with a measured time window of operation of 48 ps resulting in a serial-to-parallel demultiplexing factor of 90. © 2013 Optical Society of America

Effective permittivity and third-order nonlinearsusceptibility for a dilute composite consistingof partially aligned nanorods
Y. Lior and D. M. Marom, “Effective permittivity and third-order nonlinearsusceptibility for a dilute composite consistingof partially aligned nanorods,” Journal of the Optical Society of America B, vol. 30, no. 7, pp. 1864-1871, 2013. Publisher's VersionAbstract

The expected permittivity and third-order nonlinear susceptibility of a composite consisting of semiconductor nanorods (NRs) dispersed in a polymer host are derived using a generalized Maxwell Garnett model under various NR axis orientation statistics, achieved by an aligning electric field. The semiconductor NRs are analyzed as prolate spheroids and modeled as more realistic capsule shapes. From the angular distribution function of the NRs, the composite macroscopic characteristics are found for low filling fractions. As the alignment field strength increases, the composite optical properties asymptotically converge toward the nematic case. Aligning fields of order 107 V∕m are required for the optical properties to increase to half the value between random orientation and nematic array composites. © 2013 Optical Society of America

MEMS Spatial Light Modulator for Phase andAmplitude Modulation of SpectrallyDispersed Light
J. Dunayevsky and D. M. Marom, “MEMS Spatial Light Modulator for Phase andAmplitude Modulation of SpectrallyDispersed Light,” Journal of Microelectromechanical Systems, vol. 22, no. 5, pp. 1213-1221, 2013. Publisher's VersionAbstract

We present a new micro-electro-mechanical system (MEMS) spatial light modulator (SLM) with a two-dimensional array of tightly-spaced square micromirrors (or pixels) designed to sag (or piston motion). This diffractive MEMS modulator is to be used for independently applying amplitude attenuation and phase control to spectrally-dispersed light along one dimension. The spectral phase and amplitude modulator operate in conjunction with a dispersive optical setup, where spatially resolved frequency components are to be incident onto and independently modulated by the device. The MEMS design is based on two common actuators per array column, in order to set the two degrees of freedom of amplitude and phase for every spectral component. This MEMS SLM is thus optimal in actuator/electrode count, especially when compared to conventional SLM where each pixel is independently actuated. The MEMS sag range is compatible with near-IR wavelengths used in the fiber-optic communication band.

Nyquist-WDM filter shaping with a high-resolutioncolorless photonic spectral processor
D. Sinefeld, S. Ben-Ezra, and D. M. Marom, “Nyquist-WDM filter shaping with a high-resolutioncolorless photonic spectral processor,” Optics Letters, vol. 38, no. 17, pp. 3268-3271, 2013. Publisher's VersionAbstract

We employ a spatial-light-modulator-based colorless photonic spectral processor with a spectral addressability of 100 MHz along 100 GHz bandwidth, for multichannel, high-resolution reshaping of Gaussian channel response to square-like shape, compatible with Nyquist WDM requirements. © 2013 Optical Society of America