Tristan J. Tayag

Spatial power splitting and combining based on the Talbot effect

The Talbot effect, a multimode interference phenomenon, is investigated as a technique for combining power from solid-state devices in order to generate higher levels of microwave and millimeter-wave power in a process referred to as quasioptical or spatial power combining. We explore the feasibility of using the Talbot effect to implement a 1 /spl times/ 8 power splitter and an 8 /spl times/ 1 power combiner at 94 GHz. We report the first demonstration of the multimode interface phenomenon in a planar waveguide at 8 GHz.

Polarization separation/combination based on self-imaging

An integrated optical device for the separation/combination of orthogonal polarizations is described. The device relies on simultaneous symmetric and antisymmetric 1 x 1 off-center self-imaging. Calculations show that 90% throughput and 0.1% crosstalk can often be attained, with device length less than or comparable to other integrated optical polarization separation devices. The device is passive, requires only a single mask, and is not restricted to a specific fabrication method or material system. Devices can even be made in isotropic material systems with a deep etch. Simulation results are presented for the lithium niobate and glass waveguide material systems.

Optical fiber interferometer for measuring the in situ deflection characteristics of microelectromechanical structures

An optical fiber interferometer is described for measuring the out-of-plane displacement of microelectromechanical structures. The in- terferometric system has a theoretical measurement dynamic range greater than 10 8 . Experimental results characterizing an electrostatically actuated polysilicon flexure beam are presented. The results are in good agreement with modeling data based on coupled boundary-element and finite-element analysis.

Quantum-noise-limited sensitivity of an interferometer using a phase generated carrier demodulation scheme

The quantum-noise-limited sensitivity is derived for a two-beam interferometer, which uses a phase generated carrier demodulation scheme. For surface-disturbance-detecting sensors, this sensitivity limit is expressed in terms of the smallest displacement that may be detected if the signal-to-noise ratio is unity. We determine the quantum-noise-limited displacement of the classical Michelson interferometer to be 5 pm.

Rotating wall vessel system designed for fluorescent imaging

Fluorescent imaging of cells and tissues cultured within a rotating wall vessel bioreactor offers quantitative assessment of the 3-dimensional aggregation of cells into tissue constructs. We present the design of a rotating wall vessel system optimized for real-time fluorescent analysis. The modulation transfer function of our system is found to be superior to the commercially-available vessel used in previous fluorescence imaging studies. We demonstrate dynamic fluorescent imaging of DAPI-stained porcine pancreatic islets.

Simulation of an interferometric computed tomography system for intraocular lenses

In this paper, we present a metrology system to characterize the refractive index profile of intraocular lenses (IOLs). Our system is based on interferometric optical phase computed tomography. We believe this metrology system to be a key enabling technology in the development of the next generation of IOLs. We propose a Fizeau-based optical configuration and present a simulation study on the application of computed tomography to IOL characterization.

Digital processing of an interferometric velocimeter for ballistic shock measurement

We have developed a ballistic shock sensor based on interferometric velocimetry. The requirements of the sensor are that it should measure the motion of an impacted armored plate with velocities up to 10 m/s, frequencies up to 100 kHz, and displacements not exceeding about 3 mm. Our fiber optic system uses a 3 × 3 fiber directional coupler and digital demodulation for passive stabilization of the interferometer. In this paper, we describe the digital signal processing for phase drift compensation and automatic calibration of the system. Simulation results will be presented.

Digital demodulation algorithm for the interferometric characterization of RF MEMS structures

Microelectromechanical systems (MEMS) are under development as radio-frequency (RF) switches for a broad range of applications, where active and passive components can be switched into or out of RF circuits. Optical interferometry is well-suited to the characterization of MEMS structures due to its wide dynamic range, its fine resolution, and its non-invasive qualities. However, RF MEMS operate at frequencies ranging from a few megahertz to tens of gigahertz. These high operating frequencies offer challenges in the demodulation of the interferometric system. Our demodulation system consists of photodetecting the optical interferometric signal, converting the analog electronic signal to a digital signal, and digitally processing the signal to compute the MEMS structures vibration amplitude. In this paper, we present a digital signal processing algorithm for demodulating an interferometer developed for characterizing RF MEMS. Our algorithm is based on a phase-generated carrier modulation system and assumes that the target structure is oscillating at a fixed frequency. A key feature of our algorithm is that it permits determination of a structure’s vibration amplitude, where the structures vibration frequency is greater than the analog-to-digital converters (ADCs) sample frequency. Therefore, commercially-available low-cost ADCs and microprocessor systems may be used for real-time demodulation. Both simulation and experimental results will be presented.

Digital demodulation of an interferometer for the characterization of vibrating microstructures

The rapid expansion of the microelectromechanical systems (MEMS) industry and the increasing number of applications in communications, displays, and sensing has led to an increasing demand for robust characterization techniques capable of in situ characterization of MEMS structures. Interferometry is well suited to such characterization due to its wide measurement dynamic range, its fine resolution, and its non-invasive qualities. We have constructed a fiber optic interferometer for the in situ characterization of MEMS structures. We report the development and implementation of a real-time digital signal processing (DSP) algorithm to demodulate the interferometer. We have developed a computationally efficient algorithm for both stabilization of the interferometer at quadrature and determination of the target’s vibration amplitude. We have verified our demodulation scheme using a piezoelectric transducer driven mirror as the target. Our current system will measure vibration amplitudes down to 10 nm. Both theoretical and experimental results are presented.

Non-uniform projection angle processing in computed tomography

In this paper, we present a novel approach for the collection of computed tomography data. Non-uniform increments in projection angle may be used to reduce data acquisition time with minimal reduction in the accuracy of the reconstructed profile. The key is to exploit those projection angles which correspond to regions where the object contains few high spatial frequency components. This technique is applicable to optical phase computed tomography, as well as X-ray computed tomography. We present simulation results on intraocular lenses used in cataract surgery.