The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Leu-M

Lithium niobate (LN), an outstanding and versatile material, has influenced our daily life for decades—from enabling high-speed optical communications that form the backbone of the Internet to realizing radio-frequency filtering used in our cell phones. This half-century-old material is currently embracing a revolution in thin-film LN integrated photonics. The successes of manufacturing wafer-scale, high-quality thin films of LN-on-insulator (LNOI) and breakthroughs in nanofabrication techniques have made high-performance integrated nanophotonic components possible. With rapid development in the past few years, some of these thin-film LN devices, such as optical modulators and nonlinear wavelength converters, have already outperformed their legacy counterparts realized in bulk LN crystals. Furthermore, the nanophotonic integration has enabled ultra-low-loss resonators in LN, which has unlocked many novel applications such as optical frequency combs and quantum transducers. In this review, we cover—from basic principles to the state of the art—the diverse aspects of integrated thin-film LN photonics, including the materials, basic passive components, and various active devices based on electro-optics, all-optical nonlinearities, and acousto-optics. We also identify challenges that this platform is currently facing and point out future opportunities. The field of integrated LNOI photonics is advancing rapidly and poised to make critical impacts on a broad range of applications in communication, signal processing, and quantum information.

/pdf/integrated-photonics-on-thin-film-lithium-niobate-3tfumu49q8.pdf

Integrated photonics on thin-film lithium niobate

Lithium niobate (LN), an outstanding and versatile material, has influenced our daily life for decades: from enabling high-speed optical communications that form the backbone of the Internet to realizing radio-frequency filtering used in our cell phones. This half-century-old material is currently embracing a revolution in thin-film LN integrated photonics. The success of manufacturing wafer-scale, high-quality, thin films of LN on insulator (LNOI), accompanied with breakthroughs in nanofabrication techniques, have made high-performance integrated nanophotonic components possible. With rapid development in the past few years, some of these thin-film LN devices, such as optical modulators and nonlinear wavelength converters, have already outperformed their legacy counterparts realized in bulk LN crystals. Furthermore, the nanophotonic integration enabled ultra-low-loss resonators in LN, which unlocked many novel applications such as optical frequency combs and quantum transducers. In this Review, we cover -- from basic principles to the state of the art -- the diverse aspects of integrated thin-film LN photonics, including the materials, basic passive components, and various active devices based on electro-optics, all-optical nonlinearities, and acousto-optics. We also identify challenges that this platform is currently facing and point out future opportunities. The field of integrated LNOI photonics is advancing rapidly and poised to make critical impacts on a broad range of applications in communication, signal processing, and quantum information.

/pdf/integrated-photonics-on-thin-film-lithium-niobate-55z73oui6u.pdf

Electroencephalography (EEG) emerged in the second decade of the 20th century as a technique for recording the neurophysiological response. Since then, there has been little variation in the physical principles that sustain the signal acquisition probes, otherwise called electrodes. Currently, new advances in technology have brought new unexpected fields of applications apart from the clinical, for which new aspects such as usability and gel-free operation are first order priorities. Thanks to new advances in materials and integrated electronic systems technologies, a new generation of dry electrodes has been developed to fulfill the need. In this manuscript, we review current approaches to develop dry EEG electrodes for clinical and other applications, including information about measurement methods and evaluation reports. We conclude that, although a broad and non-homogeneous diversity of approaches has been evaluated without a consensus in procedures and methodology, their performances are not far from those obtained with wet electrodes, which are considered the gold standard, thus enabling the former to be a useful tool in a variety of novel applications.

Dry EEG Electrodes

An electro-optic, solid-state electric field sensor system for noncontact detection of energized objects at power frequency (60 Hz) was investigated. In laboratory testing, the sensor system was found to have a minimum detectable field amplitude of 4 mV/m/Hz1/2, which was further reduced by a factor of 2 through vector averaging over 20 cycles. In an experimental setup emulating the realistic scenario of an energized conducting structure (such as a street light or metal fence post), the detection of a 1-m object energized at 1 VAC at a distance of 2 m was demonstrated.

Detection of Energized Structures With an Electro-Optic Electric Field Sensor

Most on-chip optical isolators utilize nonreciprocal magneto-optic (MO) garnet-materials that require an external bias magnetic field to operate. The magnetic field is applied through incorporation of either a permanent magnet or an active electromagnet. Permanent magnets add significantly to device bulk and electromagnets increase fabrication complexity and power consumption. Hence, it is highly desirable to reduce or eliminate the magnetizing component in these devices. Here, we experimentally demonstrate a first of its kind bias-magnet-free (BMF) on-chip waveguide optical isolator with integrated Polarcor UltraThin polarizers. The BMF isolator device obviates the need for magnetizing components while possessing superior performance, relative to other on-chip isolators, with ≥25 dB of isolation ratio (IR), and ≤3.5 dB of insertion loss (IL) across the entire infrared optical C-band.

/pdf/broadband-bias-magnet-free-on-chip-optical-isolators-with-zuo5v6cx3j.pdf

Broadband Bias-Magnet-Free On-Chip Optical Isolators With Integrated Thin Film Polarizers

This paper describes a paradigm shift in the technology for sensing electro-physiological signals. In recent years, SRICO has been developing small lithium niobate photonic electrodes, otherwise called "Photrodes” for measuring EEG and ECG signals. These extrinsic fiber-optic sensing devices exploit the extremely high electrical input impedance of Mach-Zehnder Intensity (MZI) electro-optic modulators to detect microvolt and millivolt physiological signals. Voltage levels associated with electrocardiograms are typically on the order of several millivolts, and such signals can be detected by capacitive pickup through clothing, i.e., the Photrode may be used in a non-contact mode. Electroencephalogram signals, which typically have an amplitude of several microvolts, require direct contact with the skin. However, this contact may be dry, eliminating the need for conductive gels. The electrical bandwidth of this photonic electrode system stretches from below 0.1 Hz to many tens of kHz and is constrained mainly by the signal processing electronics, not by the Photrode itself. The paper will describe the design and performance of Photrode systems and the challenging aspects of this new technology.

Photrodes for physiological sensing

Photonic methods for electric field sensing have been demonstrated across the electromagnetic spectrum from near-DC to millimeter waves, and at field strengths from microvolts-per-meter to megavolts-per-meter. The advantages of the photonic approach include a high degree of electrical isolation, wide bandwidth, minimum perturbation of the incident field, and the ability to operate in harsh environments. Aerospace applications of this technology span a wide range of frequencies and field strengths. They include, at the high-frequency/high-field end, measurement of high-power electromagnetic pulses, and at the low-frequency/low-field end, in-flight monitoring of electrophysiological signals. The demands of these applications continue to spur the development of novel materials and device structures to achieve increased sensitivity, wider bandwidth, and greater high-field measurement capability. This paper will discuss several new directions in photonic electric field sensing technology for defense applications. The first is the use of crystal ion slicing to prepare high-quality, single-crystal electro-optic thin films on low-dielectricconstant, RF-friendly substrates. The second is the use of two-dimensional photonic crystal structures to enhance the electro-optic response through slow-light propagation effects. The third is the use of ferroelectric relaxor materials with extremely high electro-optic coefficients.

Advanced Materials and Device Technology for Photonic Electric Field Sensors

This paper reports the first demonstration of a high-speed electro-optic modulator in crystal ion sliced thin film lithium niobate (TFLN™). The device exhibits a Vπ·L of 4.75 V·cm, 8dB RF loss at 65 GHz and 40 GHz electro-optic bandwidth.

Wide-band electro-optic modulator in thin-film lithium niobate on quartz substrate

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