Shlomo Zach

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Papers by Shlomo Zach

A THz Integrated Circuit Based on a Pixel Array to Mode Multiplex Two 10-Gbit/s QPSK Channels Each on a Different OAM Beam

Journal of Lightwave Technology, Feb 15, 2023

Experimental Demonstration of Generating a 10-Gbit/s QPSK Laguerre-Gaussian Beam using Integrated Circular Antenna Arrays to Tune Both Spatial Indices

Conference on Lasers and Electro-Optics, 2022

We experimentally generate a Laguerre-Gaussian (LG ℓ , p ) beam with tunable spatial indices (LG0... more

Demonstration of Recovering Orbital-Angular-Momentum Multiplexed Channels Using a Tunable, Broadband Pixel-Array-Based Photonic-Integrated-Circuit Receiver

Journal of Lightwave Technology, Mar 1, 2022

We experimentally utilize a tunable, broadband pixel-array-based integrated receiver for recoveri... more We experimentally utilize a tunable, broadband pixel-array-based integrated receiver for recovering orbital-angular-momentum (OAM) multiplexed channels. The OAM receiver comprises a pixel-array-based mode converter, four phase controllers, and a pixel-array-based 4-to-3 coupler. Utilizing the mode converter, a free-space data-carrying OAM beam (<inline-formula><tex-math notation="LaTeX">$\ell \ = \ - 1$</tex-math></inline-formula> or <inline-formula><tex-math notation="LaTeX">$\ell \ = \ + 1$</tex-math></inline-formula>) is vertically coupled into four waveguides. The resulting waveguide modes carry an OAM-order-dependent phase delay between each other. Subsequently, a 4-to-3 coupler coherently combines four waveguide inputs with the specific phase delay into a specific output port. By further tuning the relative phase delay of the waveguides using the phase controllers, the data channel carried by a specific OAM beam (<inline-formula><tex-math notation="LaTeX">$\ell \ = \ - 1$</tex-math></inline-formula> or <inline-formula><tex-math notation="LaTeX">$\ell \ = \ + 1$</tex-math></inline-formula>)) could be routed to different ports. As there is no specific resonant wavelength, the OAM receiver could be operated with a relatively broad bandwidth. The experimental results show that: (a) the target OAM mode to be received by the OAM receiver could be tuned from (<inline-formula><tex-math notation="LaTeX">$\ell \ = \ - 1$</tex-math></inline-formula> to <inline-formula><tex-math notation="LaTeX">$\ell \ = \ + 1$</tex-math></inline-formula>) with a <−14-dB inter-modal power coupling; (b) in a wavelength range of ∼6 nm, two OAM-carried 50-Gbaud quadrature-phase-shift-keying (QPSK) data channels (<inline-formula><tex-math notation="LaTeX">$\ell \ = \ - 1$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">$\ell \ = \ + 1$</tex-math></inline-formula>) could be recovered by the tunable OAM receiver with a bit error rate (BER) performance below the 7% forward error correction threshold; and (c) a 400-Gbit/s OAM-multiplexed and wavelength-division-multiplexed (WDM) QPSK link is demonstrated with a <2-dB optical signal-to-noise ratio (OSNR) penalty compared to that of a single-beam link.

Utilizing multiplexing of structured THz beams carrying orbital-angular-momentum for high-capacity communications

Optics Express, Jun 29, 2022

Structured electromagnetic (EM) waves have been explored in various frequency regimes to enhance ... more Structured electromagnetic (EM) waves have been explored in various frequency regimes to enhance the capacity of communication systems by multiplexing multiple co-propagating beams with mutually orthogonal spatial modal structures (i.e., mode-division multiplexing). Such structured EM waves include beams carrying orbital angular momentum (OAM). An area of increased recent interest is the use of terahertz (THz) beams for free-space communications, which tends to have: (a) larger bandwidth and lower beam divergence than millimeter-waves, and (b) lower interaction with matter conditions than optical waves. Here, we explore the multiplexing of THz OAM beams for high-capacity communications. Specifically, we experimentally demonstrate communication systems with two multiplexed THz OAM beams at a carrier frequency of 0.3 THz. We achieve a 60-Gbit/s quadrature-phase-shift-keying (QPSK) and a 24-Gbit/s 16 quadrature amplitude modulation (16-QAM) data transmission with bit-error rates below 3.8 × 10−3. In addition, to show the compatibility of different multiplexing approaches (e.g., polarization-, frequency-, and mode-division multiplexing), we demonstrate an 80-Gbit/s QPSK THz communication link by multiplexing 8 data channels at 2 polarizations, 2 frequencies, and 2 OAM modes.

Experimental mitigation of the effects of the limited size aperture or misalignment by singular-value-decomposition-based beam orthogonalization in a free-space optical link using Laguerre–Gaussian modes

Optics Letters, Nov 13, 2020

Limited-size receiver (Rx) apertures and transmitter–Rx (Tx–Rx) misalignments could induce power ... more Limited-size receiver (Rx) apertures and transmitter–Rx (Tx–Rx) misalignments could induce power loss and modal crosstalk in a mode-multiplexed free-space link. We experimentally demonstrate the mitigation of these impairments in a 400 Gbit/s four-data-channel free-space optical link. To mitigate the above degradations, our approach of singular-value-decomposition-based (SVD-based) beam orthogonalization includes (1) measuring the transmission matrix H for the link given a limited-size aperture or misalignment; (2) performing SVD on the transmission matrix to find the U , Σ , and V complex matrices; (3) transmitting each data channel on a beam that is a combination of Laguerre–Gaussian modes with complex weights according to the V matrix; and (4) applying the U matrix to the channel demultiplexer at the Rx. Compared with the case of transmitting each channel on a beam using a single mode, our experimental results when transmitting multi-mode beams show that (a) with a limited-size aperture, the power loss and crosstalk could be reduced by ∼ 8 and ∼ 23 dB , respectively; and (b) with misalignment, the power loss and crosstalk could be reduced by ∼ 15 and ∼ 40 dB , respectively.

Receiver aperture and multipath effects on power loss and modal crosstalk in a THz wireless link using orbital-angular-momentum multiplexing

Scientific Reports, Aug 18, 2022

The channel capacity of terahertz (THz) wireless communications can be increased by multiplexing ... more The channel capacity of terahertz (THz) wireless communications can be increased by multiplexing multiple orthogonal data-carrying orbital-angular-momentum (OAM) beams. In THz links using OAM multiplexing (e.g., Laguerre-Gaussian LG ℓ,p beams with p = 0), the system performance might degrade due to limited receiver aperture size and multipath effects. A limited-size aperture can truncate the received beam profile along the radial direction. In addition, due to beam divergence, part of the beam might interact with reflectors in the environment, causing the signal to reflect and interfere at the receiver with the directly propagating part of the beam; this is known as the multipath effect. In this paper, we simulate and analyze the impact of both effects on the equality of the THz OAM link by considering a full two-dimensional (2-D) LG modal set. The simulation results show (i) a limitedsize receiver aperture can induce power loss and modal power coupling mainly to LG modes with the same ℓ but p > 0 for directly propagated OAM beams; (ii) the multipath effect can induce modal power coupling across multiple 2-D LG modes, which leads to inter-channel coupling among the different channels in an OAM multiplexed link; (iii) the interference between the reflected and direct beams can induce intra-channel coupling between the received signals from the reflected and direct beams; and (iv) beams with a higher OAM order (e.g., from ± 1 to ± 5) or a lower carrier frequency (e.g., from 0.1 to 1 THz) experience larger intra-and inter-channel coupling. The intra-and inter-channel coupling in an OAM-multiplexed THz link can degrade the signal-to-noise ratio (SNR) and induce SNR penalty when compared to a single-channel system. Structured electromagnetic (EM) waves have gained much interest partially due to their unique spatial beam structures with tailored amplitude and phasefronts 1,2 . One type of structured EM wave is orbital-angular-momentum (OAM) . A beam carrying OAM has a unique spatial structure, such that the amplitude has a ring-like doughnut profile and the phasefront "twists" in a helical fashion as it propagates. OAM beams are a subset of the complete Laguerre Gaussian (LG ℓ, p ) modal basis set, which has two modal indices: (i) ℓ represents the number of 2π phase shifts in the azimuthal direction, which is the OAM order, and (ii) p + 1 represents the number of concentric intensity rings . OAM beams with different OAM orders are orthogonal to each other. This orthogonality between different OAM modes could enable the data-multiplexing technique of mode-division multiplexing (MDM), which is a subset of space-division multiplexing (SDM) . In this approach, multiple independent data-carrying OAM beams can be efficiently multiplexed at the transmitter, spatially co-propagate through the same medium, and

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Experimental demonstration of object identification by analyzing 2-dimensional complex spectra of Laguerre-Gaussian modes (Conference Presentation)

We recover the shape and orientation of an object by analyzing the spatial phase and amplitude of... more We recover the shape and orientation of an object by analyzing the spatial phase and amplitude of a transmitted optical beam using a single pixel. We experimentally demonstrate using the complex spatial spectrum of multiple sequential measurements of a varying probe beam. Specifically, we transmit a structured beam that is tailored to have one mode of the Laguerre-Gaussian (LG) modal basis set, and the beam is varied to sequentially have a unique azimuthal (l) and radial (p) value. When each uniquely structured beam probes an object, there will be coupling of power from the pure mode to other LG modes. The complex phase and amplitude coefficients of this modal power coupling will provide a “signature” of the probed object’s 2D structure, and this signature can be detected using a single pixel. We identify a “fan-shaped” object with an opening angle of 120˚ and different angular orientations by analyzing the corresponding complex spatial spectrum of multiple sequential measurements, such that each subsequent tailored mode has l and p indices in the range -15 - +15 and 0-30, respectively. Results show that the amplitude spectrum is insensitive to the object’s angular orientation, whereas the phase spectrum predictably shifts with orientation. Additionally, we demonstrate that an irregular image with a ‘SC’ logo can be reconstructed using the complex modal spectrum. The structural similarity (SSIM) of the reconstructed image increases as the number of modes increases. Specifically, the SSIM increases by 83.5% when the number of modes increases from 36 (6 by 6) to 961 (31 by 31).

Experimental Characterization of Low-Latency Multiple and Tunable Delays of Wideband Analog LFM Signal Using Concatenated Linearly Chirped and Sampled FBGs

Conference on Lasers and Electro-Optics, May 5, 2019

Concatenated chirped and sampled fiber Bragg gratings are used to simultaneously generate multipl... more

Coarse and Fine Continuously Tunable Optical Delay Using the Time-of-flight in Fiber Bragg Gratings and Wavelength Conversion

We use the time-of-flight in arrayed, channelized and chirped fiber Bragg gratings along with wav... more We use the time-of-flight in arrayed, channelized and chirped fiber Bragg gratings along with wavelength conversion in PPLN waveguides to build continuously coarse- and fine-tunable delay line. More than 20 ns continues tuning range is achieved with less-than-0.6dB OSNR penalty for a 10 Gbaud QPSK signal.

Analog and Digital Performance of Multiple Discrete Time Delays based on a Fiber Loop with an Internal Frequency Shifter

A fiber loop with an internal frequency shifter is used to produce the delayed copies of an incom... more A fiber loop with an internal frequency shifter is used to produce the delayed copies of an incoming data signal. The linear phase response of the system is verified and the spurious free dynamic range (SFDR) is measured. Also, the BER and constellation diagrams of 10Gbaud QPSK signals are obtained.

Analog Performance of Multiple, Discretely Tunable Time Delays based on a Frequency Comb and a Chromatic Dispersion Element

We demonstrate the analog performance of multiple, coherent, and discretely tunable time delays b... more We demonstrate the analog performance of multiple, coherent, and discretely tunable time delays based on a frequency comb and a chromatic dispersion element. The amount of 0.6ns delay is measured between adjacent selected comb lines. The linear phase frequency response of the system is verified and the SFDR is measured.

Spurious-Free Dynamic Range Characterization of a χ2-Based PPLN Waveguide

We experimentally characterize the spurious-free dynamic range performance of a χ2-Based PPLN wav... more

Demonstration of Using Multiple Orthogonal Spatial Modes for Channel Header Information and Channel Encoding

45th European Conference on Optical Communication (ECOC 2019), 2019

Optical pulse-burst position modulation for antenna beam forming

Optical Engineering, Apr 1, 2009

We present a realization of an optically controlled pulse-burst position modulator to be used for... more We present a realization of an optically controlled pulse-burst position modulator to be used for a radio-frequency photonic circuit aiming to produce beam forming for a Radar-transmitting antenna. The configuration uses a set of fiber ring resonators that contain erbium-doped fiber amplifiers. By controlling the pumping in each loop, the gain of the doped fibers is changed, which results with

Contour superresolved imaging of static ground targets using satellite platform

Applied Optics, Aug 15, 2012

We propose a method for increasing the contour resolution of static ground targets and to overcom... more We propose a method for increasing the contour resolution of static ground targets and to overcome the diffraction limit of an optical system installed on top of a satellite. The resolution improvement is obtained by using a sequence of low-resolution images taken from different angles realized by the movement of the satellite platform. The superresolving process is obtained by the generation of relative movement between the inspected object and the a priori known high-resolution background. The relative movement is caused because the images are taken from different angles. The captured set of lowresolution images are decoded by the a priori known high-resolution background obtained from a set of reference images taken only once by a high-resolution camera. The proposed concept is demonstrated via Matlab simulation and laboratory experiments.

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Ka-band satellite systems: current state of development

21st IEEE Convention of the Electrical and Electronic Engineers in Israel. Proceedings (Cat. No.00EX377), Nov 11, 2002

Abstract This paper presents an overview of research targets, technologies and technical decision... more

Grating Lobe Mitigation in Ultra-wideband Phased Arrays

A numerically efficient optimization technique aimed at the suppression of grating lobes in ultra... more A numerically efficient optimization technique aimed at the suppression of grating lobes in ultra-wideband phased array antenna is proposed. Low computational complexity is achieved through efficient representation of the array factor over the desired band of frequencies and domain of main beam and observation directions. Subarray approach and fast array factor evaluation algorithm further reduce the computational cost. Significant grating lobe suppression in Cartesian and hexagonal array geometries has been demonstrated.

Phase-only Beam Broadening for Array Antennas

Modal Purity and LG Coupling of an OAM Beam Reflected by a Rough Surface for NLoS THz Links

We simulate the modal purities and Laguerre-Gaussian (LG) modal coupling of orbital-angular-momen... more We simulate the modal purities and Laguerre-Gaussian (LG) modal coupling of orbital-angular-momentum (OAM) beams reflected by a rough surface for a non-line-of-sight (NLoS) THz communication link. The reflection of the THz OAM beams is simulated using the finite-difference time-domain (FDTD) method. The simulation results show that: (i) an OAM beam reflected by a metal or dielectric rough surface would experience modal coupling in the 2-dimensional LG modal spectra; (ii) reflected by a metal surface, the modal purities of both transverse-electric (TE) and transverse-magnetic (TM) OAM beams increase as the incident angle increases from 0° to 70° or the carrier frequency of the OAM beams decreases from 1 THz to 0.1 THz; and (iii) reflected by a dielectric surface (n = 1.5), the modal purity and received power of the transmitted TE OAM beam also increase with an increase in the incident angle. However, for TM polarization, the modal purity exhibits a dip near the Brewster’s angle. Moreover, with a limited-size receiver aperture, the simulation results for a rough metal surface show that: (i) when the aperture size decreases, the received power of the desired mode decreases by >30 dB while the modal purity of that mode firstly increases and then decreases; and (ii) with the same aperture size, the link could experience ~10 dB higher total power loss and ~12 dB higher channel crosstalk when the standard deviation of the surface height increases from 0.08 mm to 0.20 mm.

A novel photonic Rotman-lens design for radar phased array antennas

2009 IEEE International Conference on Microwaves, Communications, Antennas and Electronics Systems, Nov 1, 2009

... Digest MWP'99, 271-274 (November 1999). [7] RA Sparks, “Progress in optical Rotman beamf... more

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