The increase in domestic natural gas production has brought attention to the environmental impacts of persistent gas leakages. The desire to identify fugitive gas emission, specifically for methane, presents new sensing challenges within the production and distribution supply chain. A spectroscopic gas sensing solution would ideally combine a long optical path length for high sensitivity and distributed detection over large areas. Specialty micro-structured fiber with a hollow core can exhibit a relatively low attenuation at mid-infrared wavelengths where methane has strong absorption lines. Methane diffusion into the hollow core is enabled by machining side-holes along the fiber length through ultrafast laser drilling methods. The complete system provides hundreds of meters of optical path for routing along well pads and pipelines while being interrogated by a single laser and detector. This work will present transmission and methane detection capabilities of mid-infrared photonic crystal fibers. Side-hole drilling techniques for methane diffusion will be highlighted as a means to convert hollow-core fibers into applicable gas sensors.
A Silicon Carbide Solid-State Photomultiplier (SiC-PM) was designed, fabricated and characterized for the first time. A die size of 3x3 mm2 has a 2x2 mm2 pixelated photosensitive area on it. The pixelated area consists of 16 sub-arrays of 0.5x0.5 mm2 with 64 pixels (60 μm pitch) in each sub-array. Each individual pixel has an integrated quenching resistor made of poly-silicon. Optical measurements of the SiC-PM were performed using fast UV LED with a wavelength of 300 nm demonstrating Geiger mode operation. Output signal waveforms measured at temperatures from 20°C to 200°C indicated temperature dependent time constants. The discrete nature of output signals indicated the capability of the SiC-PM to detect single photons from a faint UV light flux.
The technology for enhanced geothermal systems (EGS), in which fractures connecting deep underground wells are deliberately formed through high pressure stimulation for energy generation, is projected to enormously expand the available reserves of geothermal energy in the U.S. EGS could provide up to 100,000 MWe within the U.S. by the next 50 years. Pressure measurements, in particular, are important for determining the state of the fluid, i.e., liquid or steam, the fluid flow, and the effectiveness of the well stimulation. However, it has been especially difficult to accurately measure pressure at temperatures above ~200°C at a distance of 10 km below ground. MEMS technology has been employed for many years for extremely accurate pressure measurements through electrical readout of a MEMS fabricated resonator. By combining optical readout and drive at the end of a fiber optical cable with a MEMS resonator, it is possible to employ these highly accurate sensors within the harsh environment of a geothermal well. Sensor prototypes based on two beam and four beam resonator designs have been designed, fabricated and characterized for pressure response and accuracy. Resonant frequencies of the sensors vary between ~15 kHz and 90 kHz depending on sensor design, and laboratory measurements yielded sensitivities of frequency variation with external pressure of 0.9-2.2 Hz/psi. An opto-electronic feedback loop was designed and implemented for the field test. The sensors were packaged and deployed as part of a cable that was deployed at a geothermal well over the course of 2½ weeks. Error of the sensor versus the reference gage was 1.2% over the duration of the test. There is a high likelihood that this error is a result of hydrogen darkening of the fiber that is reducing the temperature of the resonator and, if corrected, could reduce the error to less than 0.01%.
We present the heterogeneous integration of a 3.8 μm thick InGaAs/GaAs edge emitting laser that was metal-metal
bonded to SiO2/Si and end-fire coupled into a 2.8 μm thick tapered SU8 polymer waveguide integrated on the same
substrate. The system was driven in pulsed mode and the waveguide output was captured on an IR imaging array to
characterize the mode. The waveguide output was also coupled into a multimode fiber, and into an optical head and
spectrum analyzer, indicating lasing at ~997 nm and a threshold current density of 250 A/cm2.
The integration of thin film edge emitting lasers onto silicon enables the realization of planar photonic structures for
interconnection and for miniaturized optical systems that can be integrated in their entirety at the chip scale. These thin
film emitters are compound semiconductor lasers that are optimized for operation without the growth substrate.
Removal of the laser growth substrate, coupled with bonding to the silicon host substrate, enable the integration of high
quality edge emitting lasers with silicon. This paper explores the challenges, approaches, fabrication processes, and
progress in the integration of thin film edge emitting lasers integrated onto silicon.
Miniaturized, portable sensing systems for medical and environmental diagnostics and monitoring are an excellent
application area for microresonator sensors. Polymer microresonators are attractive components for chip scale integrated sensing because they can be integrated in a planar format using standard semiconductor manufacturing technologies. Vertically coupled microresonators, where the waveguides lie below or above the microresonator, can be fabricated using standard photolithography, enabling low cost integrated sensor systems. Microresonators can be surface customized for discrimination in, for example, chemical sensing applications, or the surface can be functionalized for biological sensing applications. To create chip scale integrated sensing systems, microresonators can be integrated with planar optical system components, such as polymer waveguides and thin film photodetectors, onto silicon using heterogeneous integration. Heterogeneous integration can also be used to integrate optical sources with sensors onto host substrates such as silicon.
We present a new architecture for a programmable disperions matrix for optical beamforming. A 2-channel prototype is constructed to demonstrate beam steering for angles of ±70° in the receive/transmit mode in RF0.1-1 GHz frequency range.
This paper describes implemented methods for characterizing a 5-bit programmable dispersion matrix (PDM) that is built to control a two-channel Receive beamformer in the 1550 nm region. The architecture of the PDM, is based on an array of 5 delay lines each having two spliced fiber Bragg gratings. Phase measurements for 32 possible delay configurations of the PMD are presented. Beam-patterns of this Receive beamformer at RF frequencies of 0.2, 0.5 and 1 GHz agrees well with the theoretical calculations. The main lobe of the beam pattern is shown to be independent of frequency for several target positions thus demonstrating a 'squint-free' characteristic of this optical processor.