Roman V. Kruzelecky

Optical switching of vanadium dioxide thin films deposited by reactive pulsed laser deposition

The parameters of reactive pulsed laser deposition were successfully optimized for fabrication of vanadium dioxide thin films. It is observed that the O2 concentration in Ar gas and the total deposition pressure are critical in stabilizing the single VO2 phase. Thermochromic VO2 and V1−xWxO2 (x=0.014) thin films were synthesized on various substrates (silicon, quartz, and sapphire) at 5% of O2/Ar ratio gas and total pressure of 90 mTorr. The structural properties of the deposited films were analyzed by x-ray diffraction, while their semiconductor-to-metal phase transitions were studied by electrical resistivity using the four-point technique and infrared transmittance from room temperature up to 100 °C. The observed transition temperature was about 36 °C for W-doped VO2 compared to 68 °C for VO2 films. This transition temperature was then lowered by about 22.85 °C per 1 at. % of W added. The temperature coefficient of resistance was about 1.78%/°C for VO2 and about 1.90%/°C for W-doped VO2. Using the pump...

Micro-optical switch device based on semiconductor-to-metallic phase transition characteristics of W-doped VO2 smart coatings

The authors have successfully fabricated planar micro-optical switch device exploiting the transmitting semiconductor (on) to the reflecting metallic (off) phase transition of thermochromic W(1.4at.%)-doped VO2 smart coatings and driven by an external voltage. The starting W-doped VO2-coated Al2O3 exhibited infrared transmittance switching about 45%. After the microfabrication, the temperature dependence of electrical resistance of the micro-optical switch showed clearly its well-known semiconductor-to-metallic phase transition at a transition temperature of 36°C. A reversible transmittance switching (on/off) as high as 28dB was achieved with this device at λ=1.55μm. In addition, the transmittance switching modulation of the device was demonstrated at 1.55μm by switching the micro-optical switch simultaneously with dc and ac voltages.

In-plane silicon-on-insulator optical MEMS accelerometer using waveguide fabry-perot microcavity with silicon/air bragg mirrors

A novel in-plane Silicon-On-insulator (SOI) optical accelerometer using a Fabry-Perot microcavity with two distributed Bragg reflectors (DBR) is presented, in which one DBR mirror is attached to two suspended proof masses. As a consequence of acceleration, the relative displacement of the movable mirror with respect to the fixed one changes the cavity length and modifies the Fabry-Perot resonance. All of the device components are fabricated by using one single fabrication step. The sensor performance could reach μg resolution with a demonstrated 2.5 nm/g sensitivity and 400 µg resolution.

Fabrication of stationary micro-optical shutter based on semiconductor-to-metallic phase transition of W-doped VO2 active layer driven by an external voltage

The authors have successfully fabricated stationary micro-optical shutter arrays based on the well-known transmitting semiconductor (on) to the reflecting metallic (off) phase transition of thermochromic W-doped VO2 active layers operating at room temperature and driven by an external voltage. This shutter consists of 16 active planar micro-optical slits for which the optical switching (either transmittance or reflectance) can be controlled individually. This allows performing any desirable on-off switching combinations. The current-voltage characteristic of the micro-slit shows that the current jumps when the phase transition occurs. Transmittance switching as high as 25 dB and reflectance switching of about 6 dB were achieved with this device at λ=1.55 μm. Therefore, this electrically controllable VO2-array can be used as a stationary Hadamard shutter to increase the sensitivity of infrared spectrometers.

Multichannel laser vibrometer and its applications

A multi-channel laser measurement system based on a commercially available single-channel laser vibrometer has been developed to measure the vibrations of low mass flexible space structures. The first generation of the multi-channel laser vibrometer is bulk-optic based system with laser being switched by an acousto-optical modulator. To overcome some of its drawbacks, for instance, being physically large and cumbersome, requiring tedious alignment, the second generation of the system was developed which employs fiber-optic technique to distribute the laser signal to the desired fiber-optic laser head. The design of the fiber-optic switch minimizes the power loss of laser beam in such a way that the vibrometer can work in its optimal range. Both bulk-optic and fiber-optic multi-channel vibrometers were verified using accelerometers on a light weight communication satellite antenna reflector. The modal parameters of the reflector were identified using measured frequency response functions both from laser vibrometer and from accelerometers. The result show that the laser system gives virtually the same result as the accelerometers.

Advanced MEMS and Integrated-Optic Components for Multifunctional Integrated Optical Micromachines

Optical technologies can play a strategic role in improving the performance, functionality, and reducing the mass of various spacecraft technologies, such as true time-delay T/R modules for phased-array antennas and optical sensor systems for satellite navigation and systems status. However, current photonic and fiber-optic systems tend to be bulky relative to the requirements for space applications. Micro integrated-optic circuits increase the integration of optical components on a single substrate, to provide multi-function optical processing and switching similar to electronic integrated circuits. This minimizes the number of external optical interconnections required and sensitivity to external vibrations; maximizing the system information capacity, optical throughput, and reliability, while minimizing the overall system size and weight. This paper considers a systematic development of MEMS integrated-optic circuits on SOI for various space application. A unique blend of MEMS, smart-material and photonic technologies is employed to miniaturize the size of the basic components, while improving on the attainable performance.

Passive dynamically-variable thin-film smart radiator device

This paper describes a new approach to spacecraft thermal control based on a passive thin-film smart radiator device (SRD) that employs a variable heat-transfer/emitter structure. The SRD employs an integrated thin-film structure based on V 1 - x - y M x N y O n that can be applied to existing Al thermal radiators. The SRD operates passively in response to changes in the temperature of the space structure. The V 1 - x - y M x N y O n exhibits a metal/insulator transition with temperature, varying from an IR transmissive insulating state at lower temperatures, to a semiconducting state at higher temperatures. Dopants, M and N, are employed to tailor the thermo-optic characteristics and the transition temperature of the passive SRD. The transition temperature can be preset over a wide range from below -30°C to above 68°C using suitable dopants. A proprietary SRD structure has been developed that facilitates emissivities below 0.2 to dark space at lower temperatures to reduce heater requirements. As the spacecraft temperature increases above the selected transition temperature, the thermal emissivity of the SRD to dark space increases by a factor of 2.5 to 3. The thin-film SRD methodology has significant advantages over competitive technologies in terms of weight, cost, power requirements, mechanical simplicity and reliability Preliminary results on an active electrochromic SRD based on the VO 2 system are also presented.

High-performance miniature integrated infrared spectrometers for industrial and biochemical sensing

High-resolution, miniature integrated spectrometers have been constructed for the NIR and MIR spectral ranges, based on MPBTs proprietary IOSPEC technology. Advanced slab-waveguide integrated optics have been employed to extend the performance of the miniature IR spectrometers to rival that of much larger FT-JR spectrometers. Monolithic integration of the miniature spectrometer, input optics and detector array provides a very compact and robust package that is suitable for industrial and field environments. Despite the compact size of the spectrometers, resolutions of 4 to 8 cm-1 are achievable over dedicated spectral ranges (2000 to 4000 nm, respectively). These spectrometers are coupled to 256channel linear detector arrays controlled by software based on Visual C++ to provide rapid spectral acquisition and analysis. This technology facilitates on-line infrared spectral analysis of an industrial or biochemical process at scan rates exceeding 200 spectra/sec. Since the spectral data is measured directly, significantly less data processing is required than for FT-JR techniques, allowing more CPU time for spectral identification and analysis. Multi-channel, time-resolved spectral measurements permit the study of the intermediate steps in a process or reaction. This paper discusses recent advances in the performance of the miniature integrated spectrometers. New detector geometries and data processing techniques have facilitated a substantial improvement in the overall system SNR over that feasible with typical sequentially-scanned detector arrays. Preliminary experimental transmittance spectra of optical filters and plastics are presented.

Development of a miniaturized integrated optical spectrometer for the infrared spectral range

A miniaturized, planar-grating optical spectrometer for the 2 to 6 micrometer range has been designed and fabricated. This has entailed development of a slab waveguide structure suitable for the infrared, a broad-band optical grating structure and fiber-based, IR input/output optics. Broad- band light is coupled into the spectrometer through a pig- tailed IR fiber and is subsequently dispersed into its spectral components and can be focused either onto a thermo- electrically (TE) cooled HgCdZnTe detector array or an IR fiber array. Integration of the optics and detector provides exceptional optical alignment and a very compact package that is suitable for various airborne and terrestrial applications.

VOA-based optical MEMS accelerometer

A novel in-plane double silicon-on-insulator optical MEMS accelerometer based on variable optical attenuator is presented. It is designed for micro-satellite navigation applications and it uses multimode waveguides integrated with MEMS providing a compact and reliable device.