The detection and measurement of gas concentrations using the characteristic optical absorption of the gas species is important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. This study reviews the field, covering several individual gas detection techniques including non-dispersive infrared, spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy. We present the basis for each technique, recent developments in methods and performance limitations. The technology available to support this field, in terms of key components such as light sources and gas cells, has advanced rapidly in recent years and we discuss these new developments. Finally, we present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.

/pdf/optical-gas-sensing-a-review-4uaf589xiq.pdf

Optical gas sensing: a review

We present, to the best of our knowledge, the first demonstration of coherent solid-state light detection and ranging (LIDAR) using optical phased arrays in a silicon photonics platform. An integrated transmitting and receiving frequency-modulated continuous-wave circuit was initially developed and tested to confirm on-chip ranging. Simultaneous distance and velocity measurements were performed using triangular frequency modulation. Transmitting and receiving optical phased arrays were added to the system for on-chip beam collimation, and solid-state beam steering and ranging measurements using this system are shown. A cascaded optical phase shifter architecture with multiple groups was used to simplify system control and allow for a compact packaged device. This system was fabricated within a 300 mm wafer CMOS-compatible platform and paves the way for disruptive low-cost and compact LIDAR on-chip technology.

Coherent solid-state LIDAR with silicon photonic optical phased arrays

An overview of the most recent developments and improvements to the low-loss TriPleX Si3N4 waveguide technology is presented in this paper The TriPleX platform provides a suite of waveguide geometries (box, double stripe, symmetric single stripe, and asymmetric double stripe) that can be combined to design complex functional circuits, but more important are manufactured in a single monolithic process flow to create a compact photonic integrated circuit All functionalities of the integrated circuit are constructed using standard basic building blocks, namely straight and bent waveguides, splitters/combiners and couplers, spot size converters, and phase tuning elements The basic functionalities that have been realized are: ring resonators and Mach–Zehnder interferometer filters, tunable delay elements, and waveguide switches Combination of these basic functionalities evolves into more complex functions such as higher order filters, beamforming networks, and fully programmable architectures Introduction of the active InP chip platform in a combination with the TriPleX will introduce light generation, modulation, and detection to the low-loss platform This hybrid integration strategy enables fabrication of tunable lasers, fully integrated filters, and optical beamforming networks

/pdf/low-loss-si3n4-triplex-optical-waveguides-technology-and-1qqqpecafn.pdf

Low-Loss Si3N4 TriPleX Optical Waveguides: Technology and Applications Overview

Abstract The emergence of silicon photonics over the past two decades has established silicon as a preferred substrate platform for photonic integration. While most silicon-based photonic components have so far been realized in the near-infrared (near-IR) telecommunication bands, the mid-infrared (mid-IR, 2–20-μm wavelength) band presents a significant growth opportunity for integrated photonics. In this review, we offer our perspective on the burgeoning field of mid-IR integrated photonics on silicon. A comprehensive survey on the state-of-the-art of key photonic devices such as waveguides, light sources, modulators, and detectors is presented. Furthermore, on-chip spectroscopic chemical sensing is quantitatively analyzed as an example of mid-IR photonic system integration based on these basic building blocks, and the constituent component choices are discussed and contrasted in the context of system performance and integration technologies.

/pdf/mid-infrared-integrated-photonics-on-silicon-a-perspective-31psns51w2.pdf

Mid-infrared integrated photonics on silicon: a perspective

The problem of attitude sensor and payload alignment calibration for spacecraft systems is addressed. An absolute alignment error model and a gyro error model are derived and implemented in a Kalman e lter using UD factorization. Advantage is taken of the structure of the model to compute efe ciently the factors of the process noise matrix. Simulation results illustrate the ill effects of misalignment on attitude estimation and illustrate the performance of the absolute alignment calibration e lter. The presence of unobservable degrees of freedom associated with the absolute alignment error model is demonstrated in these results. We also offer a simple modie cation of the typical onboard real-time attitude estimator that is useful in mitigating the effects of minor miscalibration (misalignment and gyro scale factor error ) without requiring estimation of calibration parameters.

Kalman Filtering for Spacecraft System Alignment Calibration

Liquid crystal waveguides for dynamically controlling the refraction of light. Generally, liquid crystal materials may be disposed within a waveguide in a cladding proximate or adjacent to a core layer of the waveguide. In one example, portions of the liquid crystal material can be induced to form refractive or lens shapes in the cladding that interact with a portion (e.g. evanescent) of light in the waveguide so as to permit electronic control of the refraction/bending, focusing, or defocusing of light as it travels through the waveguide. In one example, a waveguide may be formed using one or more patterned or shaped electrodes that induce formation of such refractive or lens shapes of liquid crystal material, or alternatively, an alignment layer may have one or more regions that define such refractive or lens shapes to induce formation of refractive or lens shapes of the liquid crystal material. In another example, such refractive or lens shapes of liquid crystal material may be formed by patterning or shaping a cladding to define a region or cavity to contain liquid crystal material in which the liquid crystal materials may interact with the evanescent light.

Liquid crystal waveguide having refractive shapes for dynamically controlling light

An external cavity laser apparatus and method wherein wavelenght or channel selection (66) is carried independently from adjustment of external cavity optical path length. The apparatus comprises a wavelenght or channel selection tuner (66) and an external cavity tuner, wherein the wavelength tuner is uncoupled from the external cavity tuner. The tuning mechanisms for wavelenght selection (70) and cavity optical path length (68) are configured to operate independently or orthogonally with respect to each other. The wavelength tuner may operate according to a first, channel selection signal, while the external cavity tuner operates according to a second, external cavity adjustment signal. The wavelength tuner and external cavity tuner may operate under the control of the same, or of separate controllers. The channel selection signal may be derived from a look-up table of adjustment parameter data accessed by a controller, and the external cavity adjustment signal may be derived from an error signal from a detector configured to measure external cavity loss.

Tunable laser having liquid crystal waveguide

Vescent Photonics Inc. and Jet Propulsion Lab are jointly developing an innovative ultra-compact (volume < 10 cm 3 ), ultra-low power (<10 -3 Watt-hours per measurement and zero power consumption when not measuring), completely non-mechanical electro-optic Fourier transform spectrometers (EO-FT S) that will be suitable for a variety of remote-platform, in-situ measurements. These devices are made possible by a novel electro-evanescent waveguide architecture, enabling chip-scale EO-FTS sensors. The potential performance of these EO-FTS sensors include: i) a spectral range throughout 0.4-5 µ m (25000  2000 cm -1 ), ii) high-resolution ( 0.1 nm), iii) high-speed (< 1 ms) measurements, and iv) rugged integrated optical construction. This performance potential enables the detection and quantification of a large number of different atmospheric gases simultaneously in the same air mass and the rugged construction will enable deployment on previously inaccessible platforms. The sensor construction is also amenable for analyzing aqueous samples on remote floating or submerged platforms. To date a proof-of-principle prototype EO-FTS sensor has been demonstrated in the near-IR (range of 1450-1700 nm) with a 5 nm resolution. This performance is in good agreement with theoretical models, which are being used to design and build the next generation of EO-FTS devices.

/pdf/compact-liquid-crystal-waveguide-based-fourier-transform-253j1zdhr7.pdf

Compact Liquid Crystal Waveguide Based Fourier Transform Spectrometer for In-Situ and Remote Gas and Chemical Sensing

A new electro-optic waveguide platform, which provides unprecedented electro-optical phase delays (> 1mm), with very
low loss (< 0.5 dB/cm) and rapid response time (sub millisecond), is presented. This technology, developed by Vescent
Photonics, is based upon a unique liquid-crystal waveguide geometry, which exploits the tremendous electro-optic
response of liquid crystals while circumventing historic limitations of liquid crystals. The exceedingly large optical
phase delays accessible with this technology enable the design and construction of a new class of previously unrealizable
photonic devices. Examples include: a 1-D non-mechanical, analog beamsteerer with an 80° field of regard, a chip-scale
widely tunable laser, a chip-scale Fourier transform spectrometer (< 5 nm resolution demonstrated), widely tunable
micro-ring resonators, tunable lenses, ultra-low power (< 5 microWatts) optical switches, true optical time delay (up to
10 ns), and many more. All of these devices may benefit from established manufacturing technologies and ultimately
may be as inexpensive as a calculator display. Furthermore, this new integrated photonic architecture has applications
in a wide array of commercial and defense markets including: remote sensing, micro-LADAR, OCT, laser illumination,
phased array radar, optical communications, etc. Performance attributes of several example devices are presented.

/pdf/a-new-electro-optic-waveguide-architecture-and-the-44tv1hrone.pdf

A new electro-optic waveguide architecture and the unprecedented devices it enables

A waveguide and method for controllably altering an optical phase delay (OPD) of light traveling along a propagation direction through the waveguide. Many embodiments are disclosed, and in one example, a waveguide may include a core for guiding the light through the waveguide; at least one cladding adjacent the core, wherein the at least one cladding has liquid crystal molecules disposed therein; at least one electrode for receiving a first voltage for controllably altering the optical phase delay of the TE polarized light traveling through the waveguide; and at least one electrode for receiving a second voltage for controllably altering the optical phase delay of the TM polarized light traveling through the waveguide.

Liquid crystal waveguide having two or more control voltages for controlling polarized light

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