Zan Shi

Polymeric electro-optic modulator based on 1×2 Y-fed directional coupler

We have demonstrated a polymeric electro-optic modulator based on a 1×2 Y-fed directional waveguide coupler. The symmetric geometry of the 1×2 Y-fed directional coupler provided the modulator unique characteristics of intrinsic 3 dB operating point and two complementary output ends. A low switching voltage of 3.6 V and a high extinction ratio of 26 dB were obtained with the modulator operating at a wavelength of 1.34 μm. The modulator was fabricated with a novel electro-optic polymer that was synthesized from polyurethane cross-linking with a chromophore.

Highly efficient linear waveguide modulator based on domain-inverted electro-optic polymers

A Y-branch waveguide directional coupler modulator based on domain-inverted electro-optic polymers is demonstrated for highly ef- ficient analog modulation. A detailed theoretical analysis is given to show its working principles based on coupled-mode theory. Domain-inverted electro-optical polymers are obtained by using a high-voltage pulsed pol- ing technique. The demonstrated domain-inverted polymers represent a promising technology for creating a new class of electro-optic modula- tors with superior performance over conventional counterparts. By using domain inversion in a Y-branch waveguide directional coupler, the poly- meric electro-optic waveguide modulator provides a highly linear modu- lation transfer curve that shows a ;100% modulation efficiency with an intermodulation distortion less than 230 dB. The demonstrated modula- tor also features a switching voltage of 10 V and an extinction ratio of 228 dB at operation wavelength of 1.32 mm. A linear modulation transfer curve and a 3-dB operating point are obtained without a bias voltage or an asymmetric device structure through a single uniform electrode.

Wavelength division multiplexers/demultiplexers for optical interconnects in massively parallel processing

Communication between computing systems is recognized as the main limitation to increase the speed of all-electronic systems beyond levels currently achieved in existing supercomputers. Optical in- terconnects hold great promise in eliminating current communication bottlenecks because of properties that stem from optics inherent paral- lelism. Wavelength-division multiplexing (WDM) technology, by which multiple optical channels can be simultaneously transmitted at different wavelengths through a single optical transmission medium, is a useful means of making full use of optics parallelism in an application of inter- connects for massive parallel processing. We first briefly review the bottlenecks of electrical interconnects in massively parallel processing. Then we discuss the advantages of optical interconnects and present our approach of optoelectronic interconnects in massively parallel pro- cessing by WDM technology. We then review the working principles of wavelength division (de) multiplexers (WD(D)M) for optical interconnects in massively parallel processing and address the optical design issues of WD(D)Ms. Finally, we report experimental data of WD(D)Ms for this ap- plication. The devices exhibit low insertion loss, high reliability, and low cost.

High-speed traveling-wave electrodes for polymeric electro-optic modulators

A detailed design and fabrication procedure of high-speed traveling-wave electrodes for EO polymer-based modulator has been developed. Design consideration, thick photoresist deposition and electroplating are specially focused on. A lot of practical experiences are introduced as well. This kind of modulator can be used in satellite receiver systems, remote connection of cellular radio systems, and LANs.

Switched optical polymeric waveguide true-time-delay lines for wideband photonics phased array antennas

It has been realized that the lack of enabling technology of beam forming and steering devices significantly slows down the process of implementing wideband phased array antenna systems. In this paper, we present our research in developing an integrated electro-optic switched true-time-delay module as a boradband beam forming device for wideband phased array antennas. The unique feature of our approach is that both the true-time-delay waveguide circuit and electro-optic switching elements are monolithically integrated in a single substrate. As a result, this integration significantly reduces the device size while eliminating the most difficult packaging problem associated with the delicate interfaces between optical fibers and optical switches. Such a monolithic approach offers greater precision for the RF phase control than the fiber-delay-lines thanks to the sub-micrometer accuracy of lithography-defined polymeric waveguides. More important, the proposed optical switched true-time-delay network requires very low electrical power consumption due to the low power soncumption of electrically-switchable waveguide gratings. Furthermore, the electrically-switchable waveguide gratings have a very fast switching speed (<50 μm) that is at least 100 times faster than any existing commercial optical switching matrix. Photonic phased array antenna based on optical true-time delay lines offers improved performance and reduced weight and power consumption over existing parabolic dish antenna presently used for communications.

An integrated 4-bit optical true-time-delay module for synthetic aperture radars

We demonstrate a 4-bit optical true time-delay module for synthetic aperture radars based on the integration of polymer channel waveguide and electro-optic Bragg gratings. The demonstrated device is a truly integrated module that eliminates the most difficult packaging problem associated with the delicate interfaces between optical fibers and optical switches. The total insertion loss of the 4-bit optical true-time-delay line is less than 3 dB with switching time <50 □s and driving voltage of 25 V.

1x2 Y-fed directional coupler modulator based on electro-optic polymer

We have demonstrated a polymeric electro-optic modulator based on a 1 X 2 Y-fed directional waveguide coupler. The symmetric geometry of the 1 X 2 Y-fed directional coupler provided the modulator unique characteristics of intrinsic 3 dB operating point and two complementary output ends. A low switching voltage of 3.6 V and a high extinction ratio of 26 dB were obtained with the modulator operating at a wavelength of 1.34 micrometers . The modulator was fabricated with a novel electro-optic polymer that was synthesized from polyurethane crosslinking with a chromophore.

Switching characteristic of wideband MSM and PIN photodetectors for photonic phased-array antennas

The switching characteristic of wide-band MSM and PIN photodetectors has been studied in theory and experiments. MSM detector has threshold bias voltage to activate its response and so has a better performance than PIN photodetectors when working as a photo-electronic switch. However, our study tells that through a suitable designed bias circuit, the PIN photodetector also can provide a switching operation with considerable performance. Especially for RF photonic signal, the extinction ratio can reach around 30dB. At different bias condition, the gain of PIN can be continually tuned and it has very important application in photonic phased-array antenna system.

Fabrication and testing of polyimide thermo-optic switches

CMOS compatible optical polyimide based thermo-optic switches have the potential use as low-power switches. These switches would have many advantages over other switches based on inorganic crystals. For one, they can be integrated into module-to-module systems using currently available VLSI fabrication techniques. Polyimide based, 1 by 2 thermo-optic switches are fabricated onto silicon wafers and tested. We report the properties and characteristics of digital thermo- optic switches designed to operate at 1.3 micrometers . Also, the switching characteristics at different heating electrode voltages are tested and compared.

Photonic applications in wireless terminal networks

Wireless communications are rapidly becoming the means of data and information transfer for a broad range of applications. As wireless communication applications continue to expand, the information transfer rates are evolving toward the Gigabit per second data rate and, for some applications, there is even a need for terabit per second data rate transfer in the wireless network. In addition, wireless terminals often require instantaneous switching and communications between network members. For most applications directional antennas are needed to support the high data throughput requirements, and phased array antennas are the only high gain, directional antennas that can be rapidly switched to provide instantaneous communications among network members scattered geographically. Wireless terminal equipment is currently designed to operate in the 1 to 60 GHz frequency range and, traditionally, these equipment are designed with RF hardware. More recently, optics technology has been demonstrated to play an important role in RF systems as the True-Time-Delay in the phased array antenna, and, for some systems operating at high data rates, optical interconnects at the baseband level require E-O and O-E conversions. This paper discusses the considerations in using optics technology in the design of the wireless terminal network including optical signal processing, optical backplanes, optical networking, optical interconnects, and optical components. This paper also describes the architecture of an RF wireless communications network using a range of optical technologies.