Recently there has been increased interest on the part of federal and state regulators to detect and quantify emissions of methane, an important greenhouse gas, from various parts of the oil and gas infrastructure including well pads and pipelines. Pressure and/or flow anomalies are typically used to detect leaks along natural gas pipelines, but are generally very insensitive and subject to false alarms. We have developed a system to detect and localize methane leaks along gas pipelines that is an order of magnitude more sensitive by combining tunable diode laser spectroscopy (TDLAS) with conventional sensor tube technology. This technique can potentially localize leaks along pipelines up to 100 km lengths with an accuracy of ±50 m or less. A sensor tube buried along the pipeline with a gas-permeable membrane collects leaking gas during a soak period. The leak plume within the tube is then carried to the nearest sensor node along the tube in a purge cycle. The time-to-detection is used to determine leak location. Multiple sensor nodes are situated along the pipeline to minimize the time to detection, and each node is composed of a short segment of hollow core fiber (HCF) into which leaking gas is transported quickly through a small pressure differential. The HCF sensing node is spliced to standard telecom solid core fiber which transports the laser light for spectroscopy to a remote interrogator. The interrogator is multiplexed across the sensor nodes to minimize equipment cost and complexity.
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.
We have fabricated proton-implanted photonic crystal (PhC) vertical-cavity surface-emitting lasers (VCSELs) emitting
in the visible spectrum. The active region of the VCSELs is composed of multiple InGaAlP quantum wells resulting in
an emission wavelength of 674 nm. A threshold current of 1.3 mA and single mode output power higher than 1 mW at
room temperature have been achieved. The maximum continuous wave (CW) lasing temperature was found to be 55° C.
The PhC VCSELs operate in a single fundamental mode with a side-mode suppression ratio (SMSR) larger than 30 dB
and show a constant beam divergence of 8 degree (full angle) for all levels of injection current and various ambient
temperatures. We compare ion-implanted and photonic crystal VCSELs and demonstrate that the controllable refractive
index guidance effect of the PhC results in a stable beam output which makes these red VCSELs interesting for imaging
applications.
Compact, non-contact, and low operating power sensors are desirable for position sensing applications. Vertical-cavity
surface-emitting lasers integrated monolithically with PIN photodetectors have been designed and fabricated for optical
position sensing. This compound semiconductor component has in turn been integrated onto a Si-platform to form a
microsystem. Using a metallic grating as a position gauge, the sensor microsystem can measure differences in reflected
power from the grating as it travels parallel to the sensors. This measurement technique allows for a high spatial
resolution. Calculations indicate that such a device can detect spatial changes on the order of the wavelength of light
emitted from the laser. Measurements from the work described here show the potential to use VCSEL/PIN chips to
determine position with an accuracy of sub-micron resolution.
We describe the hybrid integration of vertical-cavity surface-emitting lasers with a network of microfluidic channels to
form a compact microfluidic microsystem. VCSEL dies, created by standard fabrication techniques, are integrated on a
silicon substrate which is merged with a micro-fluidic network of PDMS channels to form an opto-fluidic microsystem.
The fabrication and integration process of VCSEL dies, silicon host substrate, and microfluidic network are discussed.
Absorption measurements of the laser output power using IR absorbing dyes indicate a detection limit of 13 μM of dye
concentration. A future integration scheme using monolithically integrated VCSEL / PIN photodetector dies is
proposed.
We describe a robust manufacturing process for single-mode photonic crystal (PhC) vertical-cavity surface-emitting
lasers (VCSELs). The fabrication of the PhC VCSELs is based on a high tolerance manufacturing process only using
optical lithography. We investigate various photonic crystal designs to determine endlessly single mode designs,
whereby the same photonic crystal design yields single mode operation for three different wavelengths (780 nm, 850 nm,
and 980 nm). The PhC VCSELs demonstrate a maximum output power greater than 1 mW under continuous wave
operation with side-mode suppression ratio greater than 35 dB.
With the emergence of the internet, the demand for high data transmission rates in short haul area networks and fiber-to-the-
desktop applications is increasing every year. Densely packed one-dimensional and two-dimensional vertical-cavity
surface-emitting laser (VCSEL) arrays offer new possibilities for future short haul parallel optical links, free-space
optical interconnects at the chip-to-chip, board-to-board, and on-board level. In this paper, we describe the
manufacturing process of individually addressable two-dimensional VCSEL arrays, PIN detector arrays, and integrated
VCSEL / PIN detector arrays. We also present measurement results of the fabricated devices and comment on the
reliability.
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