Research Interests

Aerospace and Defense

Riza’s Defense Optics activities started from his Caltech Ph.D. student days in the mid-80’s where he showed for the first time how Acousto-Optics could be used to control transmit and receive mode phased array radars/antennas. Later work revolved around developing next generation highest phase stability acousto-optic (AO) signal processors such as convolvers, correlators, and spectrum analyzers for wideband Electronic Warfare (EW) applications. Additional AO signal processing innovations included powerful Range-Doppler and transversal filter optical implementations suited for extreme bandwidth and signal complexity radar signal processing. In 1992, Riza invented a 2-D Spatial Light Modulator (SLM)-based powerful high tap and weight count time-delay-based transversal Radio Frequency (RF) filter. In 2004, introduced was a compact polarization independent version of this RF filter. Another aspect of the Riza group innovations includes a series of novel photonic beamforming control systems for Phased Array Radars/Antennas for both narrowband and wideband operations. The group has also pioneered optical security systems using multi-dimensional optical ID cards and a new Hybrid Photonic Signal Processing technique that combines the worlds of optics-based analog and digital signal processing leading to world record numbers of RF time delay controls using photonics.

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Health and Imaging

Riza’s interest in optics for health and imaging goes back to his 1989 General Electric (GE) days with the development of the simplest control liquid crystal electronic lens motivated by vision applications. In 1995, Riza’s group introduced the use of optics for phased array ultrasound controls including the concept of intracavity imaging using optical wavelength-to-image space mapping using a single optical fiber probe and wavelength coding of the spatial array space. Since 1995, the group has also proposed several world first novel optical imaging systems such as the first acousto-optics-based Optical Coherence Tomography (OCT) system and a first wavelength coded optical imager with transmit/receive (T/R) optical amplification and agile wavelength switching & gain controls for 3-D sensing and optical energy delivery for ablation, cutting/surgery. Other inventions include wavelength coded interferometric optical imaging, Angstrom sensitivity high speed scanning interferometric imagers, fiber-based scanning imaging endoscopes, confocal programmable spectral microscopes, agile no-moving parts microscopes, and endoscopes and human vision testers using Electronically controlled Variable Focal Length Lens (ECVFL), also called the E-lens. Another world first is the invention of the Spatial Light Modulator (SLM)-based agile pixel imager (e.g., using the DMD) including the Coded Access Optical Sensor (CAOS) camera for extreme dynamic range smart imaging.

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Riza and his group’s contributions in the field of communications include pioneering works in both RF wireless communications as well as optical communications.

Specifically, optical communications innovations have ranged from both the optical fiber domain to the freespace optical communications wireless arena. In the fiber-optic signal attenuation arena, the group has pioneered the most diverse set of variable optical attenuator (VOA) modules using optical MEMS, Acousto-Optic (AO), liquid and Liquid Crystal (LC) technologies. The group for example proposed and demonstrated the world’s first fault-tolerant variable attenuators, all-digital fiber-optic switches, spectral equalizers, and wavelength sensitive add-drop filters. These novel fiber-optic signal conditioning modules are based on a number of device technologies such as optical MEMS. LCs, AOs, and liquids. Riza invented the Hybrid MEMS/LC design for fiber-optic applications including the hybrid analog-digital design for producing world record performance VOAs. Other inventions include super low noise LC switches and low loss MEMS, LC, and hybrid MEMS-LC 3-D cross-connect switches and digital MEMS/LC tunable laser designs.

In the free-space wireless domain, Riza invented Multiplexed Optical Scanner Technology (MOST), a new method for no-moving parts three dimensional steering and imaging of light. The group also developed the most advanced theoretical models for freespace-to-Single Mode Fiber (SMF) lens coupling that has realized near zero loss SMF-to-freespace-to-SMF optical power transfer for short distances as well as for longer range optical wireless link distances, including the use of smart optical 3-D beamforming and weak lensing via the self-imaging mechanism to form ultra-low loss point-to-point optical datacom links. In addition, the group introduced and demonstrated the first smart indoor optical wireless concepts using agile 3-D optical beamforming-based reconfigurable light to produce  both Line of Sight (LOS) and Non Line of Sight (NLOS) robust and high efficiency indoor optical wireless communications (today for example called Li-Fi) including its first application for data centers. Another novel optical communications method introduced by Riza and co-workers is called spatial optical CDMA that deploys spatial coding of light to provide multi-access communications using both fiber and freespace communication channels.

Riza is a pioneer in multiple simultaneous RF beams optical beamforming systems for RF wireless communications phased array antennas. His 1989 Caltech Ph.D proposed such smart beamforming systems and in particular, in 1995, he pioneered the use of optical beamforming systems for RF wireless Base-Station antennas for cellular systems including use of  optical beamforming for mm-wave (today called 5G and 6G) high data rate wireless phased array antennas on a variety of fixed and mobile platforms including automobiles.

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Extreme Environment Systems

Generation and control of clean energy such as via combined cycle gas-fired power plants is an important research area for greener economies. Such power plants operate in extreme and hazardous environments and require operations at the newer higher temperatures ranges for better efficiencies and cleaner operations. Riza and co-workers have demonstrated novel extreme environment optical sensors needed for these extreme temperature (> 1500 deg-C) Zero Emissions fossil fuel-based power generation systems. These Riza group inventions include Silicon Carbide-based extreme temperature hybrid design sensors to measure temperature and pressure. Temperature sensing experiments using the silicon carbide thermometer placed in a commercial rig has reached world record high temperatures of 1600 deg-C. In addition, the Riza group has proposed and developed non-contact liquid level sensors to measure caustic fluid liquid levels. The Riza group has also proposed and developed non-contact E-lens based non-contact highest transverse spatial resolution 3-D shape sensors suited to measure shapes of 3-D objects in extreme environments. Another world first is the invention of the Spatial Light Modulator (SLM)-based agile pixel imager (e.g., using the DMD) including the Coded Access Optical Sensor (CAOS) camera for extreme dynamic range smart imaging. See Health and Imaging section for relevant light irradiance measurement instrumentation inventions.

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