Riza and his group’s contributions in the field of communications include pioneering works in RF wireless communications, optical wireless communications and fiber-optic communications.
Riza is a pioneer in the use of MEMS for fiber-optic switching (SPIE 1992, US Patent 1993). 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 (IEEE 1998). Riza invented the fault-tolerant all-digital paradigm for designing fiber-optic signal power conditioning and routing modules that include multi-wavelength equalizer modules (OSA 1999). This technique provides 100% repeatable and energy efficient controls for light flow controls in fiber communications. Riza pioneered the design of fiber-optic signal conditioning and routing modules using the reliable Texas Instruments (TI) Digital Light Processing (DLP) technology, namely using the Digital Micromirror Device (DMD). The group for example proposed and demonstrated using the DMD, the world’s first fault-tolerant variable attenuators, all-digital fiber-optic switches, spectral equalizers, tunable laser designs and wavelength sensitive add-drop filters. Riza also invented the Hybrid MEMS/LC design for fiber-optic applications including the hybrid analog-digital design for producing world record performance VOAs (IEEE 2005). Other Riza inventions include super low noise LC switches and low loss MEMS, LC, and hybrid MEMS-LC 3-D cross-connect switches. Specifically, Riza invented the world’s first N x N large port count crossconnect design using 3-D beamforming optics that allowed inherent light power attenuation control at localized fiber ports and also proposed and demonstrated the exceptionally low near zero coupling loss fiber-to-freespace-to-fiber connection designs such as using the self-imaging fiber-to-free-space-to-fiber design (IEEE 1998, US Patent 2000, SPIE 2000 and 2003, OSA 1999 and 2003). These methods have been deployed and extended in commercially deployed fiber-optic modules including the very large crossconnect optical circuit switches (e.g., Calient Technologies) that are performing ultra-low loss optical circuit switching operations in many data centers around the world with over 750,000 deployed fiber terminations. It is important to note that Riza’s near zero coupling loss fiber-to-freespace-fiber self-imaging designs reduced optical power losses with over an order of magnitude impact and in fact, with larger freespace propagation distance between fibers such as needed in crossconnect circuit switches, created many orders of magnitude reduction in optical losses. Thus vital energy savings occurred with such low loss Fiber-optic signal controls designs enabling acceleration and development of the modern internet for the world high bandwidth data communications. In effect, greener and wide spread operations for the internet data services were possible as the energy saved due to lower loss optical designs was energy well spent elsewhere such as in fiber-optical amplifiers that require additional pump laser energy to boost data signals in the fiber transmission lines typically placed every 40 km. Thus the Riza low losss designs also created in-direct and critical impact for the overall infrastructure of the growing and evolving internet.
Many of the Riza’s fiber-optical design inventions underwent prototyping and commercialization at Nuonics, Inc., a 1998 startup company founded by Riza. The Nuonics design technology underwent acquisition and sale to a global commercial corporation. This DMD-based design technology and its extension is deployed in many commercialized products (e.g., Newport Corp., Cidra Corp., Nistica Corp/NTT Electronics/Fujikura/Molex) such as fiber-optic multiwavelength equalizers and routers across the world fiber-optic communications and internet infrastructure.
In 1992, Riza & his GE colleagues pioneered spatial optical CDMA, a space division multiplexing (space MUX) method to transmit multiple simultaneous data channels, both for optical wireless and multi-fiber bundle optical data communications (SPIE 1992). The method combined space-time coding to realize a multiaccess optical network. A decade later, many efforts evolved around the world to deploy Space Mux in few mode fiber and multicore fiber to increase data carrying capacity of fiber networks. Realizing that coupling freespace interconnected light between single mode fibers (SMFs) can be a challenge, Riza in 1994 proposed the first use of a variable focus lens for SMF fed optical wireless short range interconnects (IoP 1994) and later extended the work to incorporate 3-D beamforming for robust SMF-freespace-to-SMF coupling controls (SPIE 1997).
Continuing with the same theme of SMF-freespace coupling, the group also developed the most advanced theoretical models for freespace-to-SMF lens coupling (OSA 1999, 2003) 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 (Elsevier 2006), including the use of smart optical 3-D beamforming combining cascaded strong and weak lensing via the self-imaging mechanism to form ultra-low loss point-to-point optical datacom links as well as for low loss optical wireless power transfer (IEEE 2012, US Patent Appl. 2014). These smart 3-D beamforming works have been incorporated around the world to maximize received link optical power for adequate signal-to-noise (SNR) to set optical wireless data transmission records for terrestrial, indoor and underwater links as well as highly efficient optical wireless power transfer links.
Riza introduced and demonstrated the first smart indoor multiple beams optical wireless concept (IEEE 1999) using agile 3-D optical beamforming-based reconfigurable light (for both laser and LED light) to produce both Line of Sight (LOS) and Non Line of Sight (NLOS) (SPIE 2013) robust and high efficiency indoor optical wireless communications, including its first application for data centers (JEOS 2011, IEEE 2012). Others around the world have used the Riza multibeam reconfigurable indoor optical wireless system to set world indoor optical wireless data records for eye safe telecom C-band operations and develop systems for IEEE Industry 4.0 Standard. In addition, designers have used the Riza lab SMF-freespace ultra-low loss coupling models and techniques to commercially deploy millions of SMF-freespace/solid optic-based components that are deployed across the world optical communications and internet infrastructure.
In the free-space optical wireless domain, Riza invented Multiplexed Optical Scanner Technology (MOST), a new powerful method using polarization (P-MOS), space (S-MOS), wavelength (W-MOS), and code (C-MOS) multiplexing, including hybrid mux-methods to realize no-moving parts three dimensional steering of light for optical wireless and imaging applications (IEEE 1999). These optical scanners set world records for large aperture 4-pi steradian coverage inertia less optical scanning (OSA 2004). Riza also invented the first de-centered variable focus electronically controlled lens including MEMS lens and liquid lens-based optical beam steering method (SPIE OE 2004, Elsevier 2009) and combined it with liquid lens focus/defocus methods to make smart search and lock-in low loss optical wireless data links (JEOS 2011) as well as fiber-optic attenuation and switching components (Elsevier 2000, 2009, 2010). In 2018, Riza introduced his newest invention, the camceiver, the world’s first combined camera plus data transceiver module with applications in data centers and indoor user ID tag locating systems (IEEE 2018). The camceiver features full spectrum UV to SWIR operations including designs for T/R operations with high speed fiber-optic data links.
Riza is also a pioneer in multiple simultaneous RF beams optical beamforming systems for RF wireless communications phased array antennas and his 1989 Caltech Ph.D. work proposed such smart beamforming systems. In particular, in 1995, he was the first to propose the use of optical multi-beamforming systems for RF wireless Base-Station antennas for cellular systems including 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 (SPIE 1995). He proposed the first design for frequency reuse and smart frequency allocations within a cell using spatially multiplexed antenna beams via a multi-beams optical beamformer. In addition, in the same 1995 SPIE paper to improve multi-user wireless data transfer performance, he proposed the first design combining the use of carrier/sub-carrier frequency multiplexing and spatial multiplexing of multiple simultaneous beams for RF cellular base-station phased array antennas (PAA). This approach was much like the 1996 proposed Orthogonal Frequency Division Multiplexing-Multiple Input Multiple Output (OFDM-MIMO) or spatial-spectral multiplexing MIMO PAA method that today is an IEEE standard for RF wireless communications. Several world labs have pursued both the combined frequency-space Multiplexing multi-beam PAA idea as well use of optical controls approach for mm-wave wireless communication array antennas.
In addition, in the same paper in 1995 (SPIE 1995), he extended the mm-wave RF multibeam multi-user beamforming approach for the optical wireless application creating the first use of multiple simultaneous beams for multiple users using passive as well as electronically programmable beamforming optics such as liquid crystal optical devices. Effectively, he pioneered Spatial Multiplexing via Optical Multi-beamforming and Spatial-Frequency Multiplexing for both the RF mm-wave and optical wireless domains of multi-access communications.