Amplification through stimulated Brillouin scattering in optical fibers can totally modify the po... more Amplification through stimulated Brillouin scattering in optical fibers can totally modify the polarization properties of the light, enabling an all-optical polarization control and a direct estimate on the fiber birefringence.
The polarization-related properties of stimulated Brillouin scattering (SBS) processes in long, r... more The polarization-related properties of stimulated Brillouin scattering (SBS) processes in long, randomly birefringent, standard optical fibers are examined. Evolution equations for the pump and signal waves, in the presence of both birefringence and SBS, are provided in Jones and Stokes spaces. It is shown that in the undepleted pump regime, the amplification of the SBS signal wave is equivalent to that of a linear medium with polarization-dependent gain. The process is associated with a pair of orthogonal states of polarizations (SOPs) of the signal wave, which undergo maximum and minimum amplification. In long, standard fibers, the Jones vector of the probe SOP which corresponds to maximum amplification is aligned with the complex conjugate of the pump wave Jones vector. The maximum and minimum SBS gain coefficients in such fibers equal two-thirds and one-third of the gain coefficient that is predicted by scalar theory, respectively. The large differential gain of the SBS process gives rise to an effective pulling of the amplified Stokes probe wave SOP, towards that of maximum amplification. Lastly, Stokes wave pulses that are aligned for maximum and minimum amplification experience different group delays, which manifest as polarization-related distortions in SBS slow light setups.
Second European Workshop on Optical Fibre Sensors, 2004
A novel time-dependent Mueller-like formalism is used to optimize performance in fiber-optic sens... more A novel time-dependent Mueller-like formalism is used to optimize performance in fiber-optic sensing scenarios, where the RF envelope of the interrogating signal is distorted by PMD/PDL.
Stationary and localized Brillouin dynamic gratings are generated using phase modulation of both ... more Stationary and localized Brillouin dynamic gratings are generated using phase modulation of both pump waves by a pseudo-random bit sequence. The gratings are applied to long variable delay of pulses and to cm-level distributed sensing.
OFS2012 22nd International Conference on Optical Fiber Sensors, 2012
Distributed temperature measurements with 1.2 cm resolution based on stimulated Brillouin scatter... more Distributed temperature measurements with 1.2 cm resolution based on stimulated Brillouin scattering (SBS) in standard fibers are reported. High resolution is achieved by phase-coding both pump and probe waves with a high-rate, pseudorandom binary phase code. The SBS interaction is effectively confined to narrow correlation peaks. The separation between adjacent peaks, signifying the unambiguous measurement range, scales with the length of the modulation code and can therefore be made arbitrarily long. Measurements were performed over 40 meters of fiber, or 3300 resolution points. The technique is applicable to distributed measurements of birefringence and Brillouin frequency shift over polarization maintaining fibers.
Optical Fiber Communication Conference and National Fiber Optic Engineers Conference, 2009
Simple, continuous wave based beat length measurement technique is proposed, using statistics of ... more Simple, continuous wave based beat length measurement technique is proposed, using statistics of the states of polarization of stimulated Brillouin scattering amplified signals. Polarization statistics are studied analytically, numerically and experimentally.
Vector formalism for stimulated Brillouin scattering amplification in birefringent fibers is used... more Vector formalism for stimulated Brillouin scattering amplification in birefringent fibers is used to model the fiber as an equivalent, pseudo-linear, polarization-dependent gain medium. Implications on slow and fast light setups are discussed.
Stimulated Brillouin scattering slow light delay is shown to introduce an inherent polarization m... more Stimulated Brillouin scattering slow light delay is shown to introduce an inherent polarization mode dispersion, which can dominate the broadening and distortion of signal pulses. The effect is demonstrated in both simulations and experiments.
21st International Conference on Optical Fiber Sensors, 2011
Stimulated Brillouin scattering (SBS) amplification of probe signals is highly polarization depen... more Stimulated Brillouin scattering (SBS) amplification of probe signals is highly polarization dependent. Maximum and minimum gain values are associated with a pair of orthogonal states of polarization (SOP) at the fiber output. Since the maximum gain is much higher than the minimum, the output probe SOP is pulled towards that of the maximum amplification. Polarization pulling is restricted, however, by pump depletion. In this work, we propose, analyze and demonstrate a method for enhanced SBS polarization pulling, using two orthogonal pumps: the one amplifies the probe wave whereas the other attenuates it. The method provides the same polarization pulling as that of a single amplifying pump, however it is considerably more tolerant to depletion.
Frontiers in Optics 2009/Laser Science XXV/Fall 2009 OSA Optics & Photonics Technical Digest, 2009
ABSTRACT A flexible and simple scheme for generating ultra-wideband waveforms is proposed, using ... more ABSTRACT A flexible and simple scheme for generating ultra-wideband waveforms is proposed, using pulse compression in highly nonlinear fiber and differential detection. Center frequencies of 25 GHz, as well as FCC mask compliant waveforms, are demonstrated.
Optical spectral analysis of closely spaced, subcarrier multiplexed fiber-optic transmission is p... more Optical spectral analysis of closely spaced, subcarrier multiplexed fiber-optic transmission is performed, based on stimulated Brillouin scattering (SBS). The Brillouin gain window of a single, continuous-wave pump is scanned across the spectral extent of the signal under test. The polarization pulling effect associated with SBS is employed to improve the rejection ratio of the analysis by an order of magnitude. Ten tones, spaced by only 10 MHz and each carrying random-sequence on-off keying data, are clearly resolved. The measurement identifies the absence of a single subcarrier, directly in the optical domain. The results are applicable to the monitoring of optical orthogonal frequency domain multiplexing and radio over fiber transmission.
Self-assembled monolayers (SAMs) of organic molecules are widely employed in surface chemistry an... more Self-assembled monolayers (SAMs) of organic molecules are widely employed in surface chemistry and biology, and serve as ultra-fine lithographic resists. Due to their small thickness of only a few nanometers, the analysis of patterned monolayer surfaces using conventional methods requires thorough point-by-point scanning using complicated equipment. In the work reported herein, patterned monolayers are simply and directly observed using a bright-field optical microscope. The monolayers modify the spectral reflectivity pattern of a silica-on-silicon thin film, and introduce a contrast between bare and monolayer-coated regions of the substrate. The method can also distinguish between regions of single-layer and bi-layer coatings. The observations are supported by calculations, and by control experiments using atomic force microscopy, scanning Raman spectrometry and scanning reflection spectrometry. The results are useful for electro-optic devices, selective wafer-bonding protocols and lab-on-a-chip test systems. We show here that chemical reactions leading to the formation of a bi-layer of SAMs correspond to an optical contrast visible to the naked eye, enabling such detection to provide a simple, yet effective differentiation between monolayers and adsorbed analytes with possible applications for chemical and/or biological sensing.
ABSTRACT The monitoring of sub nano-liter pendant liquid droplets, during their evaporation from ... more ABSTRACT The monitoring of sub nano-liter pendant liquid droplets, during their evaporation from the cleaved facet of a standard optical fiber, is proposed and demonstrated. The combined reflections of incident light from the two boundaries, between fiber and liquid and between liquid and air, give rise to interference fringes as the fluid evaporates. The analysis of the fringe pattern allows for the reconstruction of the instantaneous size and evaporation rate of the droplets. These, in turn, provide information regarding the properties of the liquid itself, and the surface to which it is applied. The sensor readout is validated against direct video observation of evaporating droplets. Several examples illustrate the potential of the proposed sensor. Evaporation dynamics measurements identify the ethanol contents in binary ethanol-water mixtures with 2% certainty. The evaporation dynamics are modified by the application of a hydrophobic self-assembled monolayer coating to the tip of the fiber. Ten different organic solvents are accurately classified by clustering analysis of their evaporation data, collected using bare and coated fibers. Potential applications of the sensors could include quality control of water, beverages and oils, recognition of flexible fuel blends and fuel dilutions, mobile point-of-care diagnostics, and laboratory analysis of surface treatments.
Amplification through stimulated Brillouin scattering in optical fibers can totally modify the po... more Amplification through stimulated Brillouin scattering in optical fibers can totally modify the polarization properties of the light, enabling an all-optical polarization control and a direct estimate on the fiber birefringence.
The polarization-related properties of stimulated Brillouin scattering (SBS) processes in long, r... more The polarization-related properties of stimulated Brillouin scattering (SBS) processes in long, randomly birefringent, standard optical fibers are examined. Evolution equations for the pump and signal waves, in the presence of both birefringence and SBS, are provided in Jones and Stokes spaces. It is shown that in the undepleted pump regime, the amplification of the SBS signal wave is equivalent to that of a linear medium with polarization-dependent gain. The process is associated with a pair of orthogonal states of polarizations (SOPs) of the signal wave, which undergo maximum and minimum amplification. In long, standard fibers, the Jones vector of the probe SOP which corresponds to maximum amplification is aligned with the complex conjugate of the pump wave Jones vector. The maximum and minimum SBS gain coefficients in such fibers equal two-thirds and one-third of the gain coefficient that is predicted by scalar theory, respectively. The large differential gain of the SBS process gives rise to an effective pulling of the amplified Stokes probe wave SOP, towards that of maximum amplification. Lastly, Stokes wave pulses that are aligned for maximum and minimum amplification experience different group delays, which manifest as polarization-related distortions in SBS slow light setups.
Second European Workshop on Optical Fibre Sensors, 2004
A novel time-dependent Mueller-like formalism is used to optimize performance in fiber-optic sens... more A novel time-dependent Mueller-like formalism is used to optimize performance in fiber-optic sensing scenarios, where the RF envelope of the interrogating signal is distorted by PMD/PDL.
Stationary and localized Brillouin dynamic gratings are generated using phase modulation of both ... more Stationary and localized Brillouin dynamic gratings are generated using phase modulation of both pump waves by a pseudo-random bit sequence. The gratings are applied to long variable delay of pulses and to cm-level distributed sensing.
OFS2012 22nd International Conference on Optical Fiber Sensors, 2012
Distributed temperature measurements with 1.2 cm resolution based on stimulated Brillouin scatter... more Distributed temperature measurements with 1.2 cm resolution based on stimulated Brillouin scattering (SBS) in standard fibers are reported. High resolution is achieved by phase-coding both pump and probe waves with a high-rate, pseudorandom binary phase code. The SBS interaction is effectively confined to narrow correlation peaks. The separation between adjacent peaks, signifying the unambiguous measurement range, scales with the length of the modulation code and can therefore be made arbitrarily long. Measurements were performed over 40 meters of fiber, or 3300 resolution points. The technique is applicable to distributed measurements of birefringence and Brillouin frequency shift over polarization maintaining fibers.
Optical Fiber Communication Conference and National Fiber Optic Engineers Conference, 2009
Simple, continuous wave based beat length measurement technique is proposed, using statistics of ... more Simple, continuous wave based beat length measurement technique is proposed, using statistics of the states of polarization of stimulated Brillouin scattering amplified signals. Polarization statistics are studied analytically, numerically and experimentally.
Vector formalism for stimulated Brillouin scattering amplification in birefringent fibers is used... more Vector formalism for stimulated Brillouin scattering amplification in birefringent fibers is used to model the fiber as an equivalent, pseudo-linear, polarization-dependent gain medium. Implications on slow and fast light setups are discussed.
Stimulated Brillouin scattering slow light delay is shown to introduce an inherent polarization m... more Stimulated Brillouin scattering slow light delay is shown to introduce an inherent polarization mode dispersion, which can dominate the broadening and distortion of signal pulses. The effect is demonstrated in both simulations and experiments.
21st International Conference on Optical Fiber Sensors, 2011
Stimulated Brillouin scattering (SBS) amplification of probe signals is highly polarization depen... more Stimulated Brillouin scattering (SBS) amplification of probe signals is highly polarization dependent. Maximum and minimum gain values are associated with a pair of orthogonal states of polarization (SOP) at the fiber output. Since the maximum gain is much higher than the minimum, the output probe SOP is pulled towards that of the maximum amplification. Polarization pulling is restricted, however, by pump depletion. In this work, we propose, analyze and demonstrate a method for enhanced SBS polarization pulling, using two orthogonal pumps: the one amplifies the probe wave whereas the other attenuates it. The method provides the same polarization pulling as that of a single amplifying pump, however it is considerably more tolerant to depletion.
Frontiers in Optics 2009/Laser Science XXV/Fall 2009 OSA Optics & Photonics Technical Digest, 2009
ABSTRACT A flexible and simple scheme for generating ultra-wideband waveforms is proposed, using ... more ABSTRACT A flexible and simple scheme for generating ultra-wideband waveforms is proposed, using pulse compression in highly nonlinear fiber and differential detection. Center frequencies of 25 GHz, as well as FCC mask compliant waveforms, are demonstrated.
Optical spectral analysis of closely spaced, subcarrier multiplexed fiber-optic transmission is p... more Optical spectral analysis of closely spaced, subcarrier multiplexed fiber-optic transmission is performed, based on stimulated Brillouin scattering (SBS). The Brillouin gain window of a single, continuous-wave pump is scanned across the spectral extent of the signal under test. The polarization pulling effect associated with SBS is employed to improve the rejection ratio of the analysis by an order of magnitude. Ten tones, spaced by only 10 MHz and each carrying random-sequence on-off keying data, are clearly resolved. The measurement identifies the absence of a single subcarrier, directly in the optical domain. The results are applicable to the monitoring of optical orthogonal frequency domain multiplexing and radio over fiber transmission.
Self-assembled monolayers (SAMs) of organic molecules are widely employed in surface chemistry an... more Self-assembled monolayers (SAMs) of organic molecules are widely employed in surface chemistry and biology, and serve as ultra-fine lithographic resists. Due to their small thickness of only a few nanometers, the analysis of patterned monolayer surfaces using conventional methods requires thorough point-by-point scanning using complicated equipment. In the work reported herein, patterned monolayers are simply and directly observed using a bright-field optical microscope. The monolayers modify the spectral reflectivity pattern of a silica-on-silicon thin film, and introduce a contrast between bare and monolayer-coated regions of the substrate. The method can also distinguish between regions of single-layer and bi-layer coatings. The observations are supported by calculations, and by control experiments using atomic force microscopy, scanning Raman spectrometry and scanning reflection spectrometry. The results are useful for electro-optic devices, selective wafer-bonding protocols and lab-on-a-chip test systems. We show here that chemical reactions leading to the formation of a bi-layer of SAMs correspond to an optical contrast visible to the naked eye, enabling such detection to provide a simple, yet effective differentiation between monolayers and adsorbed analytes with possible applications for chemical and/or biological sensing.
ABSTRACT The monitoring of sub nano-liter pendant liquid droplets, during their evaporation from ... more ABSTRACT The monitoring of sub nano-liter pendant liquid droplets, during their evaporation from the cleaved facet of a standard optical fiber, is proposed and demonstrated. The combined reflections of incident light from the two boundaries, between fiber and liquid and between liquid and air, give rise to interference fringes as the fluid evaporates. The analysis of the fringe pattern allows for the reconstruction of the instantaneous size and evaporation rate of the droplets. These, in turn, provide information regarding the properties of the liquid itself, and the surface to which it is applied. The sensor readout is validated against direct video observation of evaporating droplets. Several examples illustrate the potential of the proposed sensor. Evaporation dynamics measurements identify the ethanol contents in binary ethanol-water mixtures with 2% certainty. The evaporation dynamics are modified by the application of a hydrophobic self-assembled monolayer coating to the tip of the fiber. Ten different organic solvents are accurately classified by clustering analysis of their evaporation data, collected using bare and coated fibers. Potential applications of the sensors could include quality control of water, beverages and oils, recognition of flexible fuel blends and fuel dilutions, mobile point-of-care diagnostics, and laboratory analysis of surface treatments.
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Papers by Avi Zadok