Technology
Key Innovations from IFOS
IFOS develops photonic computing, sensing, and signal processing technologies. The advancement of these technologies has yielded a basis for industrial products now available for purchase via Opterro, Inc.
- Fiber Bragg grating (FBG)-based wavelength-division multiplexed sensing technology platform: i*Sense®
- Raman scattering in optical fibers for distributed temperature sensing: r*Sense®
- Brillouin scattering in optical fibers for distributed temperature and strain sensing: b*Sense™
- Fabry-Perot interferometry (FPI) multi-functional sensors: FPI*Sense™
- Interferometric fiber-optic gyroscopic (I-FOG) for tracking and navigation: g*Sense®
- Photonic computing modules and subsystems
i*Sense® family of FBG Interrogators
The most comprehensive collection of solution for optical sensing of high-value assets are available commercially from Opterro, Inc.
i*Sense® FBG Interrogation Principle and Architecture
IFOS’s i*Sense® parallel processing interrogation module comprises an optical interface port for connecting to the multiplexed FBG sensors, sensor-specific front-end modifiers, a parallel-architecture Photonic Spectral Processor (PSP) module involving customized photonic processors, micro controllers, and any required wired or wireless network interfaces. A broadband optical source sends light out via a circulator to the FBG sensors. The sensors then return selected wavelengths depending upon strain and temperature.
The interrogator’s PSP subsystem processes the returned light, which subsequently is converted by the optoelectronic interface (detectors) to multiple wavelength-dependent currents that are then processed by the Electronic Data Acquisition and Digital Signal Processing (EDA/DSP) subsystem and interpreted by algorithms in the software subsystem. PIC-based PSP chips based on IFOS’s patented designs are core to functionality of the miniature module.
r*Sense® Raman Distributed Temperature Sensing (R-DTS)
The r*Sense® system was incorporated into IFOS’s technology portfolio during IFOS’s its 2006 acquisition of VC-funded Oluma, Inc in Carlsbad, CA. This system has demonstrated temperature measurement up to 200°C in oil and gas applications; although fire detection can be achieved at temperatures below 100°C in standard operating conditions, higher temperature measurement capability could be valuable during battlefield damage assessment in providing crew and engineers an understanding of the structural integrity of ship components at prolonged high temperatures.
In contrast to FBG sensing, where sensors are discrete sensing ‘points’ up to several millimeters long located at chosen positions along an optical fiber, the r*Sense® R-DTS system consists of a whole fiber length (up to kilometers long), which acts as a sensor along which a temperature is measured. The R-DTS sensing system uses a narrow-band laser source that launches light through the fiber. The interaction of the light with the fused silica in the fiber causes light to scatter backwards along the fiber. A typical reflected spectrum contains Rayleigh, Brillouin, and Raman components. The r*Sense® system exploits the Raman peaks; specifically, the intensity of the anti-Stokes Raman peak is dependent on temperature and therefore used to infer temperature change along the fiber. Raman sensing is not sensitive to strain, and responds only to temperature.
Opterro offers a range of r*Sense® products for various industrial applications.
The optical fiber configuration used for Raman sensing is different from that used for FBG sensing; strain monitoring and fire detection will each use their own fiber and supporting interrogator. This allows for greater flexibility in routing for required sensing locations. For example, shipboard electrical conduits for which strain information is not necessary would benefit greatly from having distributed fire detection along the length of electrical wiring to detect electrical fires.
The IFOS r*Sense® system was originally developed for harsh downhole oil and gas applications and has been field-proven in such applications, meaning that the technology risk is relatively low. In addition to oil and gas applications, the IFOS r*Sense® technology has been used to demonstrate feasibility of fire detection in collaboration with the Department of Homeland Security.
g*Sense® Fiber-Optic Gyroscopes
The FOG operates as an interferometer with two oppositely propagating beams – clockwise and counterclockwise. The two beams have opposite phase shift sensitivities to rotation about the fiber coil axis. Specifically, the “Sagnac” optical phase difference (Sagnac) between the clockwise and counterclockwise light beams induced by a rotation rate about the coil axis (Ω) is given by
= (2π/c)*F*Ω = K(L,D) * Ω (1)
where D and L are the fiber sensing coil average diameter and length, respectively, is the mean wavelength of the light reaching the detector, c is the speed of light in vacuum, F = LD/λ, and K(L,D) is the open-loop scale factor. The two beams pass through the phase modulator at different times. This time difference is fixed, based on the length and refractive index of the fiber in the coil. From Equation (1) we see that the FOG response to the input rate is larger for larger D and L and for smaller λ. The factor F = LD/λ can therefore be used as a top-level figure of merit for the scaling of the FOG’s response.
The IFOS team has a proven track record in developing low-SWaP-C systems for harsh environments to sense shock, vibration, temperatures, and radiation. IFOS’s FOG development programs have already resulted in more compact, less expensive, higher bandwidth, and lower noise devices. IFOS FOGs offer performance that approaches the high-end, tactical-grade performance levels for guidance, navigation, and control (GN&C) instrumentation needed for deployment in defense and space applications.