Fiber optic distributed temperature sensing based on Raman scattering of light in optical fibers has become a very attractive solution for distributed temperature sensing (DTS) applications. The Raman scattered signal is independent of strain within the fiber, enabling simple packaging solutions for fiber optic temperature sensors while simultaneously improving accuracy and robustness of temperature measurements due to the lack of strain-induced errors in these measurements. Furthermore, the Raman scattered signal increases in magnitude at higher fiber temperatures, resulting in an improved SNR for high temperature measurements. Most Raman DTS instruments and fiber sensors are designed for operation up to approximately 300˚C. We will present our work in demonstrating high temperature calibration of a Raman DTS system using both Ge doped and pure silica core multi-mode optical fiber. We will demonstrate the tradeoffs involved in using each type of fiber for high temperature measurements. In addition, we will describe the challenges of measuring large temperature ranges (0 – 600˚C) with a single DTS interrogator and will demonstrate the need to customize the interrogator electronics and detector response in order to achieve reliable and repeatable high temperature measurements across a wide temperature range.
Fiber Bragg gratings are reported that are optimized for low wavelength drift, making them suitable for high-
accuracy temperature measurements over extended periods of time. Our gratings show drift in the order of a
few 10's of pm over 1,300 h at up to 650°C.
Photo-acoustic spectroscopy (PAS) has been successfully applied to detect various gases and chemicals due to its high selectivity and sensitivity. However, the performance of the conventional acoustic sensors prohibits the application of PAS for harsh environment gas species real-time monitoring. By replacing conventional acoustic sensors, such as microphone and piezo-transducers, with a high-temperature Fiber Bragg Grating (FBG) vibration sensor, we developed a fiber-optic PAS sensing system that can be used in high-temperature and high-pressure harsh environments for gas species identification and concentration measurement. A resonant acoustic chamber is designed, and FBG vibration sensor is embedded in the molybdenum membrane. An OPO laser is used for spectrum scanning. Preliminary test on water vapor has been conducted, and the result is analyzed. This sensing technology can be adapted into harsh environments, such as Integrated Gasification Combined Cycle (IGCC) power plant, and provide on-line real-time monitoring of gases species, such as CO, H2O, and O2. Presently, our FBG-based vibration sensor
can withstand the high temperature up to 800°C.
Dynamic response characteristics of silica fiber long-period grating with a modified cladding, composed of
∼10-100 nm nanoparticle palladium oxides thin film material prepared by a magnetron sputtering
technique, have been investigated at several elevated temperatures with a 2%H2/98%N2 mixing gas
concentration. The fiber cladding modified grating, without cladding chemical etching process,
demonstrates 540 pm per 1% H2 sensitivity, a better than 1sec response times at 160oC, respectively. The
thermal responses of the prototype have demonstrated increased dynamic wavelength shift while reducing
response time simultaneously. The observed thermal dependence of the prototype could be attributed to a
combined effect of thermal dependent hydrogen atoms diffusion rate and hydrogen atoms solubility.
It is very critical to develop sensor that can operate in high temperature and chemically harsh environments. Sapphire (Al2O3) material, which possesses a melting point of 2050°C and a wide transmission wavelength region as high as ~3.5μm, has been demonstrated to be an ideal candidate for high temperature fiber-based environmental sensing applications. Under harsh environment, the performance of conventional blackbody radiation based sapphire fiber high temperature sensor could be easily affected due to the lack of cladding. In this paper, a fiber-optic temperature sensor with a single-crystal sapphire fiber as the light guide and a high temperature ceramic coating as the sensing element as well as the protection layer was presented. The radiance emitted from the ceramic coating is used to measure the temperature, and it is transmitted to optical receiver through the sapphire fiber. This ceramic coating greatly improved the stability and dynamical range of pyrometer. Preliminary experimental results demonstrated that the sensor is very promising for measuring ultra-high temperature up to 1900°C in the harsh environment.
The commercialization of CD ROM drives has clearly demonstrated the ability of optical storage devices to meet the growing demand for archival data storage. However, with the continued expansion of electronic information resources, storage capacity requirements are expected to approach the terabit level for personal users and exceed the petabit level for databases and data warehouse systems. Further, many data intensive applications will also require real time access data access rates. Thus, designers for the next generation of archival storage systems have the challenging task of providing storage capacities several orders of magnitude larger than existing systems while maintaining current data access times. To meet this challenge, we have been developing a 'smart' read-head device for large capacity, page-oriented optical storage systems. Further the device is designed to operate as a data filter that will pass only valid data between the optical storage system and the host computer. Based on a photonic VLSI device technology, our data filter monolithically integrates optical detectors, photoreceivers circuits, data manipulation logic, and filter control circuitry onto a single CMOS chip that can be readily fabricated using a standard VLSI fabrication facility. Thus, our device is compatible with existing electronic device manufacturing technology and shares all of the reliability, uniformity, and manufacturability benefits associated with current, electronic hardware. This paper will present an evaluation of our latest smart pixel circuits and detail our performance expectations for a 32 X 32 bit data filter chip currently under development.
The design, characterization and evaluation of CMOS based silicon photodetectors/photoreceivers suitable for smart-pixel based applications are presented. Implemented with a conventional CMOS fabrication process, these photodetectors/receiver circuits can be reliably fabricated for smart-pixel based photonic information processing systems that combine the parallelism associated with optics and the data processing capabilities associated with CMOS logic. Several different CMOS based photodetector structures including p-n junction detectors and bipolar phototransistors are presented. Simulation results indicate that the p-n junction detectors will provide photocurrents in the range of nanoamps with rise/fall times on the order of picoseconds. Although slower response is expected with the phototransistor structure, the optoelectronic gain increases the photocurrent to the microamps range. In addition to fabrication and evaluation of individual photodetectors, we present the design and evaluation of high gain photoreceiver array. Based on a standard 1.2 micrometer CMOS fabrication process the monolithic photodetector/receiver circuit includes a bipolar phototransistor, a three-stage current amplifier and a differential amplifier that produces output at digital logic levels. The photoreceiver with high gain and adjustable threshold has a wide dynamic range. For a reference voltage of 3.2 V, the optical power threshold has been measured at less than 1 nW. A page-oriented optical data detection is demonstrated using a 5 X 5 smart-pixel photoreceiver array.
Silica-based photonic integrated circuits (PICs) have been making major advances and are finding increasing applications in optical communications, networking, and signal processing. For the next generation of photonic integrated circuits, it is desirable to add more functionality as well as to increase the integration level. This would involve introducing a variety of heterogenous materials and devices on the same substrates, using a monolithic and/or hybrid integration method. In this paper we describe the results of our efforts of developing/incorporating new functions to the silica-based integrated circuits. 1) Optical amplifiers, suitable for monolithic integration with other guided-optic devices, are promising as loss-compensating devices for photonic integrated circuits. 2) Silicon is the most commonly used substrate for silica-based PICs. A novel method has been developed for forming 2D waveguides on silicon substrates, utilizing the photoelastic effect in Si induced by thin-film stress. This method does not require any separate guiding layer nor etching of silicon, and therefore is expected to increase the flexibility in designing/implementing advanced PICs on Si. 3) Ferroelectric materials possess various functional properties and are expected to play an important role in advanced PICs. The major challenges and progress are discussed in achieving monolithic integration of functional films, such as PZT, on silica and Si substrates.
We have grown epitaxial GaN and ZnO films on sapphire and silicon substrates, and investigated the possibility of forming channel waveguides utilizing the effect of thin- film-induced index change. 2D confinement of light was clearly observed in the channel region of GaN defined by a SiN cladding layer of a stripe window pattern. The lateral confinement of light in the window region indicates that the effective guide index in the window region of GaN is higher than that in the SiN-loaded outer region. We carried out numerical analyses on the various possible effects that might contribute to the overcompensation of the negative loading effect of a SiN cladding window. This includes the photoelastic, piezoelectric, and electro-optic effects in GaN induced by a SiN window layer. The analysis result suggests that the observed phenomenon can be ascribed to a combination of both the photoelastic and electro-optic effects, and especially that the spontaneous polarization field in GaN might play an important role in forming a channel waveguide in the window region.
We developed waveguide beamsplitters integrated with an Er- doped thin-film optical amplifier. A 1 to 2-cm-long Er-doped optical amplifier is monolithically cascaded to a beamsplitter in order to compensate for the losses of the beamsplitter. Both devices use a highly Er-doped silicate glass film as a guiding layer. Two different types of structures were investigated for a beamsplitter, i.e., a Y-branch type and a self-imaging multimode interference (MMI) type device. The beam propagation method (BPM) was used for the analysis and design of the beamsplitter structures. The beamsplitter part was designed to be much shorter than the amplifier (i.e., 1 - 2 mm versus 1 - 2 cm) in order to minimize the absorption of a signal beam by Er ions in the potentially underpumped splitter section. Both the amplifier and the beamsplitter parts have a ridge waveguide structure. A novel process technique was developed and used in forming the ridges. The process does not require etching of an Er-doped film in defining the lateral dimension of a waveguide, but involves a lift-off process with a collimated magnetron sputtering. A 1.7-cm-long waveguide thus fabricated shows a 1.55-micrometer signal enhancement of 15.4 dB with a 980 nm pump power of 40 mW. This enhancement fully compensates for both Er absorption and waveguide losses, and results in a gain of 7.2 dB. This demonstrates that 1 - 2-cm-long waveguide amplifiers can provide an optical gain sufficient to compensate for the 1 by 2 or 1 by 4 splitter losses.