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CubeSat swarm in LEO orbit is an attractive alternative to present-day expensive and bulky satellite-based remote sensing systems. This paper presents the design and optimization rules to achieve omnidirectional, high speed, long-range (more than 100 km) data communication among CubeSats. The unprecedented size, weight, power, and cost constraints imposed by the CubeSat platform and the availability of the commercial-off-the-shelf components are considered in the analyses. Analytical studies related to the scanning mirror-based beam steering system as well as scanning mirrors smallest step angle requirement are presented. In addition, we demonstrate the relations and dependencies among scanning mirrors smallest step angle, laser beam divergence, optics dimensions, communication distance, and scanning area filling efficiency, etc. Furthermore, the optimization challenges of the transmit laser beam size considering the interplay among beam divergence, beam clipping, and scattering are studied in detail. This paper also presents the effect of laser peak power, initial beam size, and communication distance on effective communication beam width to maintain a long-distance (more than 100 km) communication with SNR ≥ 10 dB at a data rate greater than 500 Mb/s.

A mode-locked laser that can produce a broadband spectrum and ultrashort pulse has been applied for many applications in an extensive range of scientific fields. To obtain stable mode-locking during a long time alignment-free, a semiconductor saturable absorber is one of the most suitable devices. Dynamics from noise to a stable mode-locking state in the spectral-domain are known as complex and a non-repetitive phenomenon with the time scale from nanoseconds to milliseconds. Thus, a conventional spectrometer, which is composed of a grating and line sensor, cannot capture the spectral behavior from noise to stable mode-locking. As a powerful spectral measurement technique, a time-stretch dispersive Fourier transformation (TS-DFT) has been recently used to enable a successive single-shot spectral measurement over a couple of milliseconds time span. Here, we experimentally demonstrate real-time spectral evolution of femtosecond pulse build-up in a homemade passive mode-locked Yb fiber laser with a semiconductor saturable absorber mirror using TS-DFT. Capturing 700 consecutive spectra (~ 17 µs time window) in real-time using the time-stretch technique, we are able to resolve the transient dynamics that lead to stable mode-locking. Before setting stable mode-locking, an oscillating or shifting fringe pattern in the consecutive spectra was detected. This signature proves the existence of multiple pulses (including a soliton molecule) which is temporally separated with a different relative phase. The dynamics on multiple pulses is originated from a fast relaxation time of the saturable absorption effect. This study provides novel insights into understanding the pulse behavior during the birth of an ultrafast mode-locked laser pulse and the stable single-pulse operation which is highly stabilized.

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Spin transfer torque magnetic random access memory (STT-MRAM) is a promising candidate for next generation memory as it is non-volatile, fast, and has unlimited endurance. Another important aspect of STT-MRAM is that its core component, the nanoscale magnetic tunneling junction (MTJ), is thought to be radiation hard, making it attractive for space and nuclear technology applications. However, studies on the effects of ionizing radiation on the STT-MRAM writing process are lacking for MTJs with perpendicular magnetic anisotropy (pMTJs) required for scalable applications. Particularly, the question of the impact of extreme total ionizing dose on perpendicular magnetic anisotropy, which plays a crucial role on thermal stability and critical writing current, remains open. Here we report measurements of the impact of high doses of gamma and neutron radiation on nanoscale pMTJs used in STT-MRAM. We characterize the tunneling magnetoresistance, the magnetic field switching, and the current-induced switching before and after irradiation. Our results demonstrate that all these key properties of nanoscale MTJs relevant to STT-MRAM applications are robust against ionizing radiation. Additionally, we perform experiments on thermally driven stochastic switching in the gamma ray environment. These results indicate that nanoscale MTJs are promising building blocks for radiation-hard non-von Neumann computing.

We present a symmetric physical layer based secret key generation scheme for Point-to-Point Optical Link (PPOL) communication by exploiting Polarization Mode Dispersion (PMD) as a random and inimitable channel characteristic. The randomness and security strength of generated cryptographic keys based on PMD is significantly high. In this paper, we present that random modulation of a probe signal caused by PMD in a high-speed data communication network (40Gb/s and 60Gb/s) is reciprocal with average Pearson correlation coefficient of 0.862, despite the presence of optical nonlinearities, dispersion, and noise in the system. 128-bit symmetric cryptographic key has been successfully generated using the proposed scheme. Moreover, PMD based encryption keys passed the National Institute of Standards and Technology (NIST) tests. We have shown through simulations with a 50km link that, with optimal key generation settings, symmetric keys can be generated with high randomness (high P-values for NIST randomness tests) and with sufficient generation rates (>50%). Furthermore, we considered an attack model of a non-invasive adversary intercepting at 10km into the link and found that the generated keys have high average key bit mismatch rates (>40%).

We propose a novel scheme for enhancing the quality factor (Q factor) of coupled resonators optical waveguides (CROWs) side coupled to a straight waveguide when operating near a degenerate band edge (DBE). The DBE is an exceptional point of degeneracy occurring without the need of loss or gain when four Bloch eigenwaves coalesce, providing a resonance condition with field enhancement and other unique properties associated with such frozen mode. We derive an analytic expression that describes the flatness of the dispersion diagram at the DBE and show how this is related to engineering the quality factor. We report an anomalous scaling law of the quality factor for a cavity made of the DBE-CROW with the fifth power of the number of rings when operating at the resonance frequency closest to the DBE frequency, even in the presence of losses and structural perturbations. Remarkably, the Q factor of the proposed DBE-CROW can be engineered to exceed that of a single ring resonator having a diameter equal to the total DBE-CROW length; hence, the DBE leads to an overall huge area reduction. We also demonstrate the robustness of the DBE-CROW's Q factor scaling near the DBE against perturbations and disorders that could arise from tolerances in fabrication. The findings reported in this paper are critical for enhancing field's amplitudes to giant levels and the Q factor of ring resonators, and are very beneficial for various applications including four-wave mixing, Q switching, lasers, and highly sensitive sensors.

The integration of a leaky-wave antenna with a ring resonator is presented based on the leaky-wave theory and integrated waveguide models. The device consists of a ring resonator fed by a directional coupler, where the ring resonator path includes a segment that is turned into a leaky-wave antenna. We devise an analytical model of the guided wave propagation along a directional coupler and the ring resonator path, including the antenna and non-radiating segments. The resonator integration provides two main advantages: 1) the high-quality factor resonance ensures effective control of radiation intensity by controlling the resonance conditions and 2) the efficient radiation from a leaky-wave antenna even when its length is much smaller than the propagation length of the leaky wave. The tradeoffs regarding the quality factor of resonance and the antenna efficiency of such a design are reported in terms of the coupler parameters, leaky-wave constant, and radiation length. Finally, a CMOS-compatible OLWA suitable for the ring resonator integration is designed where silicon is utilized as the waveguide material for a possible electronic control of radiation intensity. The simulation results together with the analytical model show that slight variations in the leaky wave's propagation constant, realized through excitation of excess carriers in the Si domain, is sufficient to control the far-field radiation modulation with high extinction ratio.

We theoretically demonstrate optical trapping using a silicon nitride (Si3 N4 ) trench waveguide on which bow-tie plasmonic nanoantennas are employed for enhancing optical forces. The electric field tailing away from the waveguide is transformed and then enhanced by the plasmonic nanoantennas deposited on the waveguide surface. We show that, with gold bow-tie nanoantennas, the waveguide system exhibits outstanding trapping capability on a 10 nm radius polystyrene nanoparticle, due to a 60-fold electric field enhancement in the proximity of the nanoantenna gap. This enhancement causes a boost of the optical trapping force by 3 orders of magnitude. The gradient force in the vertical direction is also calculated semi-analytically by using a dipole approximation of a scattering polystyrene nanosphere, and the analytical solution well matches the full-wave simulations. Mode polarization effects are discussed in this paper as a way to switch trapping. These investigations indicate that the patterned Si3 N4 trench waveguide is suitable for optical trapping and nanoparticle sensing applications.

We present a new approach for electronic control of optical tweezers by using space-Time-wavelength mapping (STWM), a technique that uses time-domain modulation to control local intensity values and hence the resulting optical force in space. The proposed technique enables direct control of magnitude, location, and polarity of force hot spots created by Lorentz force (gradient force). In this paper we develop an analytical formulation of the proposed STWM technique for optical tweezing. In the case study presented here we show that 150 fs optical pulses are dispersed in time and space to achieve a focused elliptical beam that is ∼20 μm long and ∼2 μm wide. By choosing the appropriate RF waveform and electro-optic modulator we can generate multiple hot spots with >200 pN force per pulse.

We demonstrate the fabrication of a highly nonlinear sub-micron silicon nitride trench waveguide coated with gold nanoparticles for plasmonic enhancement. The average enhancement effect is evaluated by measuring the spectral broadening effect caused by self-phase-modulation. The nonlinear refractive index n2 was measured to be 7.0917×10-19 m2/W for a waveguide whose Wopen is 5 μm. Several waveguides at different locations on one wafer were measured in order to take the randomness of the nanoparticle distribution into consideration. The largest enhancement is measured to be as high as 10 times. Fabrication of this waveguide started with a MEMS grade photomask. By using conventional optical lithography, the wide linewidth was transferred to a 100 wafer. Then the wafer was etched anisotropically by potassium hydroxide (KOH) to engrave trapezoidal trenches with an angle of 54.7°. Side wall roughness was mitigated by KOH etching and thermal oxidation that was used to generate a buffer layer for silicon nitride waveguide. The guiding material silicon nitride was then deposited by low pressure chemical vapor deposition. The waveguide was then patterned with a chemical template, with 20 nm gold particles being chemically attached to the functionalized poly (methyl methacrylate) domains. Since the particles attached only to the PMMA domains, they were confined to localized regions, therefore forcing the nanoparticles into clusters of various numbers and geometries. Experiments reveal that the waveguide has negligible nonlinear absorption loss, and its nonlinear refractive index can be greatly enhanced by gold nano clusters. The silicon nitride trench waveguide has large nonlinear refractive index, rendering itself promising for nonlinear applications.

The possibility of integration of two important categories of optical components, i.e., circular polarizer and lens, into a thin plasmonic metasurface is examined, for the realistic case when metal losses cannot be neglected, for example when operating in the visible spectrum, or at infrared when non-noble metals are used. We introduce a metasurface made of nanoantennas that offer enough degrees of freedom to control both amplitude and phase of the reflection coefficient. First a theoretical formulation is developed and then an optimal design for a polarizing lens at mid-infrared wavelengths near 4.3 μmis presented.Atwo-dimensional array of Y-shaped nanoantennas with polarization-dependent and spatially varying phase response offers the possibility of balancing the losses experienced by the x- and y-polarized incident fields and is the basis for such a compact polarizing lens.

We provide for the first time the detailed study of the radiation performance of an optical leaky wave antenna (OLWA) integrated into a Fabry-Pérot resonator. We show that the radiation pattern can be expressed as the one generated by the interference of two leaky waves counter-propagating in the resonator leading to a design procedure for achieving optimized broadside radiation, i.e., normal to the waveguide axis. We thus report a realizable implementation of the OLWA made of semiconductor and dielectric regions. The theoretical modeling is supported by full-wave simulation results, which are found to be in good agreement. We aim to control the radiation intensity in the broadside direction via excess carrier generation in the semiconductor regions. We show that the presence of the resonator can provide an effective way of enhancing the radiation level modulation, which reaches values as high as 13.5 dB, paving the way for novel promising radiation control capabilities that might allow the generation of very fast optical switches, as an example. © 2014 IEEE.

Reduction in the operating voltage of electrooptic modulators is needed, in order to remove the bottleneck in the flow of data between electronics and optical interconnects. We report an experimental demonstration of a tenfold reduction in an electrooptic modulator's half-wave voltage up to 50 GHz. This was achieved by employing optical sideband-only amplification.

We investigate the radiation of an optical leaky-wave antenna embedded in a Fabry-Pérot resonator (FPR), resonating in the direction of the guided leaky wave. Leaky-wave radiation is achieved via the generation of a -1 Floquet harmonic in a dielectric waveguide due to the inclusion of a periodic set of perturbations. The FPR is formed by confining the dielectric waveguide and the leaky-wave section between two partially reflective mirrors. We report the design principles that are required to achieve a pencil beam at broadside as a superposition of leaky waves that travel inside the FPR in two opposite directions. We also investigate the tunability of the radiation by using semiconductor regions in the waveguide and thereby exciting and controlling excess carriers. We report simulation results related to a realistic design as a proof of the concept. © 2013 IEEE.

We provide analytical modeling and the detailed procedure that is used in recently proposed arbitrary waveform generation technique by using MEMS digital micro-mirror arrays. We estimate the achievable temporal resolution, repetition rate, modulation index and the rise/fall times of the final waveform as figure of merit in the proposed systems. We show that reducing the diffraction limit via increasing the ratio of beam size to lens focal length (>0.075) and the spatial modulation down to single mirror pitch size (10.8μm), waveforms up to 18GHz repetition rates with >90% modulation index and

We analyze the theoretical and physical properties of a CMOS compatible optical leaky wave antenna (OLWA) integrated into a Fabry-Pérot resonator (FPR) at 193.4 THz (wavelength ?0 = 1550 nm). The presented OLWA design is composed of a silicon (Si) dielectric waveguide sandwiched between two silica glass (SiO2) domains, and it comprises periodic perturbations (cavities of vacuum). We first describe the radiation of the isolated OLWA whose radiation pattern is due to the excitation of a leaky wave, slowly decaying while traveling. The perturbations are indeed designed to obtain a leaky wave harmonic with very low attenuation and phase constants. Then, we integrate the same OLWA into a FPR where two leaky waves with the same wavenumber are travelling in opposite directions inside the resonator. We show that the radiation level at the broadside direction can be effectively controlled by modifying the optical properties of the Si waveguide through electron-hole excess carrier generation (found to be highly enhanced when it is integrated into a FPR). The design of the integrated OLWA is properly set to guarantee the constructive interference of the two radiated beams provided by the two leaky waves in the FPR. The modal propagation constant in the integrated OLWA can be then altered through excess carrier generation in Si, thus the antenna can be tuned in and out of the resonance thanks to the high FPR quality factor, and the LW modal dispersion relation. This allows for enhanced radiation level control at broadside, and preliminary results show up to 13 dB beam modulation. © 2012 SPIE.

We investigate the directive radiation at 1550 nm from an optical leaky wave antenna (OLWA) with semiconductor perturbations made of silicon (Si). We study the radiation pattern dependence on the physical dimensions, number of perturbations and carrier densities in these semiconductor perturbations through optical excitations at a visible wavelength, 625 nm. In this detailed theoretical study we show the correlation between the pump power absorbed in the perturbations, the signal guided in the waveguide and the radiation through leakage. To overcome the limited control of the radiation intensity through excess carrier generation in Si, we present a new design with the OLWA integrated with a Fabry-Pérot resonator (FPR). We provide analytical and numerical studies of the enhanced radiation performance of the OLWA antenna inside the FPR, and derive closed-form formulas accounting for LW reflection at the edges of the FPR. A discussion on the constructive and destructive radiation by the direct and reflected leaky waves in the FPR resonator is provided. Results shown in this paper exhibit 3 dB variation of the radiation and pave the way for further optimization and theoretical developments.

We propose a highly directive optical leaky wave antenna (OLWA) radiating at 1550 nm composed of a dielectric waveguide comprising periodic silicon (Si) perturbations. The antenna working principle is based on the excitation of a leaky wave guided mode in the perturbed waveguide. Here we study the radiation properties for two sets of perturbation dimensions, and show beam scanning capabilities of the antenna (radiation level and direction) at broadside by varying the free space wavelength. Moreover, the use of Si offers the electronic/optical tunability of its complex refractive index by excess electron-hole carrier density generation via current injection (electronic control) or optical absorption (optical control). Therefore, by changing the Si refractive index we vary the leaky wave attenuation constant and the input impedance of the antenna, which in turn allow for beam control capabilities. © 2012 IEEE.

Erbium-based plasmonic-assisted vertical emitters at telecommunication wavelengths have been investigated. We show that net gain and array of lasers are achievable. © 2011 IEEE.

We propose the control of the radiation of an optical leaky wave antenna through optical pumping schemes. A bi-directional pumping is eventually adopted, and the tunability of the radiation is observed © 2011 IEEE.

An optical leaky wave antenna (OLWA) is a device that radiates a light wave into the surrounding space from a leaky wave (LW) guided mode or receives optical power from the surrounding space into a guided optical mode. In this work, we propose and provide a 3D analysis of a novel CMOS compatible OLWA made of a silicon nitride (Si3N4) waveguide comprising periodic silicon perturbations which allow electronic tuning capability. The analysis presented here includes the effect of the number of semiconductor perturbations, the antenna radiation pattern and directivity. We show that the number of the silicon perturbations has to be large to provide a long radiating section required to achieve radiation with high directivity. In other words, the proposed structure allows for a very narrow-beam radiation. Preliminary results are confirmed by exploiting leaky wave and antenna array factor theory, as well as verified by means of two full-wave simulators (HFSS and COMSOL). Our purpose is to ultimately use PIN junctions as building blocks for each silicon implantation for the electronic control of the radiation. In particular, the electronic tunability of the optical parameters of silicon (such as refractive index and absorption coefficient) via current injection renders itself the ideal platform for optical antennas that can facilitate electronic beam control, and boost the efficiency of optoelectronic devices such as light-emitting diodes, lasers and solar cells, and bio-chemical sensors. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

We propose a design of a dielectric (silicon nitride) optical leaky wave antenna (OLWA) with periodic semiconductor (silicon) corrugations, capable of producing narrow beam radiation. The optical antenna radiates a narrow beam because a leaky wave (LW) with low attenuation constant is excited at one end of the corrugated dielectric waveguide. We show that pointing angle, beam-width, and operational frequency are all related to the LW complex wavenumber, whose value depends on the amount of silicon perturbations in the waveguide. In this paper, the propagation constant and the attenuation coefficient of the LW in the periodic structure are extracted from full-wave simulations. The far-field radiation patterns in both glass and air environments predicted by LW theory agree well with the ones obtained by full-wave simulations. We achieve a directive radiation pattern in glass environment with about 17.5 dB directivity and 1.05 degree beam-width at the operative free space wavelength of 1.55 mu m, pointing at a direction orthogonal to the waveguide (broadside direction). We also show that the use of semiconductor corrugations facilitate electronic tuning of the radiation pattern via carrier injection. (C)2011 Optical Society of America

Silicon photonics has great potential for mid-wave-infrared applications. The dispersion of waveguide can be manipulated by waveguide dimension and cladding materials. Simulation shows that < 3 mu m wide conversion can be achieved by tuning the pump wavelength. (C) 2010 Optical Society of America

An ultra-broadband wavelength conversion is presented and experimentally demonstrated based on nondegenerate four-wave mixing in silicon waveguides. Two idlers can be generated and their wavelengths can be freely tuned by using two pumps where the first pump is set close to the signal and the second pump is wavelength tunable. Using this scheme, a small phase-mismatch and hence an ultra-broad conversion bandwidth is realized in spite of the waveguide dispersion profile. We show that the experimental demonstrations are consistent with the theoretical estimations. Total conversion bandwidth is estimated to reach > 500 nm and it can provide a feasible approach to realize one-to-two wavelength conversion among different telecommunication bands between 1300 nm and 1800 nm. (C) 2010 Optical Society of America