This project involves the construction of a remote-controlled laboratory experiment that can be accessed by online students. The project addresses a need to provide a laboratory experience for students who are taking online courses to be able to provide an in-class experience. The chosen task for the remote user is an optical engineering experiment, specifically aligning a spatial filter. We instrument the physical laboratory set up in Tucson, AZ at the University of Arizona. The hardware in the spatial filter experiment is augmented by motors and cameras to allow the user to remotely control the hardware. The user interacts with a software on their computer, which communicates with a server via Internet connection to the host computer in the Optics Laboratory at the University of Arizona. Our final overall system is comprised of several subsystems. These are the optical experiment set-up, which is a spatial filter experiment; the mechanical subsystem, which interfaces the motors with the micrometers to move the optical hardware; the electrical subsystem, which allows for the electrical communications from the remote computer to the host computer to the hardware; and finally the software subsystem, which is the means by which messages are communicated throughout the system. The goal of the project is to convey as much of an in-lab experience as possible by allowing the user to directly manipulate hardware and receive visual feedback in real-time. Thus, the remote user is able to learn important concepts from this particular experiment and is able to connect theory to the physical world by actually seeing the outcome of a procedure. The latter is a learning experience that is often lost with distance learning and is one that this project hopes to provide.
The use of optical fibers to couple spectrographs to telescopes has been important in the search for extrasolar planets using radial velocity measurements. The ability of an optical fiber to partially scramble the input illumination enables a fiber feed to provide more uniform illumination to the spectrograph optics, but a limiting factor in fiber coupling is modal noise. Agitation of the fiber has been shown to reduce modal noise, but altering fiber transmission parameters by varying the length of the fiber may offer advantages. We report on tests comparing some of the alternative devices for reducing modal noise.
A magnetically actuated optical phase modulator is described. The phase of a reflected optical beam is modulated by deflecting a Mylar® membrane, coated with a magnetic iron/nickel film, with the field of an electromagnet. A phase change of for light of wavelength 0.633 µm was achieved with a driving voltage of only 4 V, much smaller than the voltage required for comparable, electrostatically-actuated devices. The modulator can be scaled to micron dimensions for fabrication in arrays, scaled for even lower drive voltage, and operated at megahertz frequencies.
A three element, 15.3 cm, fiber Bragg grating array (FBGA) operating at 1550 nm wavelength is fabricated using a single mode photosensitive fiber. The FBGA is initially simulated using in-house developed software based on the Transfer Matrix Method, then fabricated using a double frequency Argon laser and a phase mask technique, and interrogated using Optical Frequency Domain Reflectometry. A single fiber Bragg grating (FBG) is accurately strain calibrated using a Fabry-Perot interferometer and piezoelectric actuation. The piezoelectric is linearly ramped, and the shifts in the Bragg wavelength along with the fringe count from the Fabry-Perot interferometer are recorded. The fringe count is then used to determine the strain on the FBG and compared to changes in the Bragg wavelength in-order to calculate the strain gage factor. This result is used to calibrate the FBGA for strain measurements. The FBGA is then bonded to a cantilever beam with three electric strain gages attached next to each FBG in the array. The axial strain results obtained from the electric strain gages and FBGA are compared for various displacements of the cantilever beam. The Fabry-Perot interferometer and piezoelectric calibration method is a non-destructive process that eliminates the need to bond the FBG to an external support during the calibration process, and can also be used to calibrate electric strain gages.
An overall strategy in infrastructure health monitoring systems is given through the concept of Infrastructure Optics. The focus is to design and build optical devices and systems, primarily fiber optic communication technology, for health monitoring of infrastructure. Recent developments in the use of Optical Frequency Domain Reflectometry (OFDR) to demodulate Fiber Bragg Grating Arrays (FBGA) have shown promise in its use in infrastructure health monitoring systems. However, the number of papers on the simulation and characteristics of FBGA using OFDR demodulation for health monitoring purposes is not great. In this paper, a FBGA is simulated using OFDR demodulation technique to extract strain information from a simulated cantilever beam host. The structure is first simulated using a Finite Element Model (FEM) to determine displacement and strain response, and the results are used as inputs to the FBGA. An OFDR program then demodulates the array to extract the strain response of the cantilever beam. The characteristics of OFDR and FBGA system is analyzed and compared to actual FEM results.
Integrated optoelectronic circuits that are capable of very high speeds or high functionality have been demonstrated using InP-based heterojunction bipolar transistors (HBTs). Optoelectronic receivers contain photodetectors fabricated from the same epitaxial material structure as the HBTs. High-functionality digital receivers, analog receiver arrays as well as analog-to-digital converters have been realized. Optoelectronic modulation circuits for signal transmission also contain separately grown, surface-coupled multiple- quantum-well (MQW) modulators.
We demonstrate midwave infrared diode lasers than span the 3 - 4 micrometers range. Laser active regions are multiple quantum well structures with GaInSb/InAs, type-II, broken gap superlattices for the wells and GaInAsSb for the barriers. The superlattice constituents and dimensions were tailored to reduce losses from Auger recombination. AlSb/InAs superlattices are used for both n-type and p-type laser cladding regions. A device with emission at 3.2 micrometers lased up to 255 K. We have achieved 75 mW per facet at 3.0 micrometers at an operating temperature of 140 K with an 85 microsecond(s) ec input current pulse. Device output appears to be limited by resistive heating. A four-layer, strain-balanced superlattice design offers greater laser efficiency.
Mid-wave infrared lasers have been fabricated employing InAs/A1Sb superlattice cladding layers and multi-quantum well active regions consisting of Ga75In025Sb1InAs broken-gap superlattice wells and Ga75In025As023Sb,,77 barriers. Diodes demonstrated to date include lasers with emission wavelengths of 3.18j.tm at 255K, 3.40im at 195K, and 4.32p.m at 110K.
Keywords: infrared, laser, diode, superlattice, multi-quantum well
We demonstrate midwave infrared (MID-IR) diode lasers that span most of the 3 - 4 micrometers range. Laser active regions are multiple quantum well (MQW) structures with GaInSb/InAs, type-II, broken gap superlattices for the wells and GaInAsSb for the barriers. The superlattice constituents and dimensions were tailored to reduce losses from auger recombination. AlSb/InAs superlattices are used for both n-type and p-type laser cladding regions.
We examine optical limiting with C<SUB>60</SUB>-toluene for nanosecond optical pulses at 532 nm. When the input fluence is less than 50 J/cm<SUP>2</SUP>, optical limiting is due to a combination of reverse saturable absorption (excited state absorption) and self-defocusing. Nonlinear scattering was not observed. For a peak input fluence greater than 50 J/cm<SUP>2</SUP>, an acoustic report and broad-band emission indicate that optical breakdown occurs. We find C<SUB>60</SUB>- tetrahydronaphthalene to be a better optical limiter, at 532 nm, than tetrahydronaphthalene solutions of C<SUB>76</SUB>, C<SUB>78</SUB>, or C<SUB>84</SUB>. C<SUB>84</SUB>-tetrahydronaphthalene is shown to be an optical limiter at 1.064 micrometers .
We examine optical limiting with C<SUB>60</SUB> solutions for nanosecond optical pulses at 532 nm and 694 nm and microsecond pulses at 514 nm. When the input fluence is less than 50 J/cm<SUP>2</SUP>, optical limiting is due to a combination of reverse saturable absorption (excited state absorption) and self-defocusing. Nonlinear scattering was not observed. For a peak input fluence greater than 50 J/cm<SUP>2</SUP>, an acoustic report and broadband emission indicate that optical breakdown occurs. At 532 nm, optical limiting for C<SUB>60</SUB>-toluene is comparable to carbon black suspension (CBS). For use at 694 nm, C<SUB>60</SUB>-toluene has a larger excited state absorption than at 532 nm, which partially compensates a much smaller ground state absorption. For microsecond optical pulses, C<SUB>60</SUB> appears to be a better optical limiter than CBS.
We have investigated the nonlinear optical mechanisms responsible for optical limiting of both picosecond and nanosecond 532-nm optical pulses in the organometallic compound cyclopentadienyliron carbonyl tetramer (King's complex). For fluences below ~200 mJ/cm<sup>2</sup>, picosecond pump-probe measurements in solutions of the King's complex reveal a prompt reverse saturable absorption (RSA) that recovers with a time constant of 120 ps. We attribute this RSA to excited-state absorption within the singlet system of the King's complex, and we demonstrate that the RSA is completely characterized by a simple three-level model. We find, however, that the material parameters extracted from these picosecond measurements cannot account for the strong optical limiting previously observed in identical solutions of this compound using nanosecond excitation at higher fluences. Picosecond measurements at fluences greater than 200 mJ/cm<sup>2</sup> reveal the onset of an additional loss mechanism that appears ~1 ns after excitation. The magnitude of this loss depends on both the laser repetition rate and the solvent, indicating that the loss is not directly related to the intrinsic properties of the King's complex but is most likely thermal in origin. Using nanosecond excitation pulses, we have performed angularly resolved transmission and reflection measurements, which reveal strong forward- and backward-induced scattering at these fluences. Furthermore, when the King's complex is incorporated in a solid host, we observe negligible induced scatter and the response is completely described by the singlet parameters extracted from the picosecond measurements. These observations indicate that the nanosecond optical limiter response of solutions of King's complex is dominated by thermally induced scattering.
We have measured the photodynamics of reverse saturable absorption (RSA) in solutions of cyclopentadienyliron carbonyl tetramer (King's complex) using picosecond pump-probe techniques. Similar preliminary measurements in solutions of synthesized variations of the King's complex indicate that the excited state transition responsible for the observed RSA is most likely a second d-d transition within the metal core of the molecule. On time scales of hundreds of picoseconds, the observed RSA in the King's complex is well characterized by a three-level rate-equation, singlet-state absorption model, where the excited-state cross section is greater than that of the ground state. On nanosecond timescales and at fluences above 200 mJ.cm<SUP>-2</SUP>, however, we observe the onset of a response that is consistent with a thermally induced scattering process. Further evidence of this scattering is provided by angularly-resolved measurements of the transmitted and back-scattered signals for nanosecond excitation. When the King's complex is incorporated in a solid host negligible scatter was observed and the response is completely described by the singlet parameters extracted from the picosecond measurements. The observation of, scatter from solution, together with a time- resolved decay to the ground state that is rapid (approximately 120 ps) and largely nonradiative in this molecule, indicate that solutions of King's complex may provide a mechanism for efficiently generating thermal nonlinearities on a subnanosecond timescale.