Yian Chang

Recent advances in electrooptic polymer modulators incorporating highly nonlinear chromophore

Based on a nonlinear optical polymer with a highly nonlinear chromophore (CLD) dispersed in an amorphous polycarbonate (APC), we have developed electrooptic (EO) polymer modulators operating at 1550-nm wavelength with low loss and good thermal stability. By incorporating polymer insulation layer, push-pull poling was successfully performed without film damages. We also demonstrated that the propagation loss of the EO polymer waveguide could be reduced as low as 1.2 dB/cm at 1550 nm when the large core waveguide structure was incorporated. The long-term reliabilities of the EO polymer modulator made of CLD/APC polymer were investigated. When the modulator was hermetically sealed in an inert gas, the V/sub /spl pi// change of a Mach-Zehnder modulator was negligible over 30 d of operation with 20-mW exposure to the waveguide input. In the thermal stability measurement, 25% V/sub /spl pi// increase was observed from the sample heated to 60/spl deg/C over 40 d, though the sample left at room temperature showed no decay of nonlinearity.

Push–pull electro-optic polymer modulators with low half-wave voltage and low loss at both 1310 and 1550 nm

Push–pull polymeric electro-optic Mach–Zehnder (MZ) modulators with Vπ of 1.2 and 1.8 V at 1310 and 1550 nm, respectively, with an interaction length of 2 cm are demonstrated. These devices were made from second-order nonlinear optic guest–host polymers that consisted of a phenyltetraene bridged high μβ chromophore guest and an amorphous polycarbonate host. Poling was done in N2 atmosphere to avoid chromophore bleaching by oxidation. A MZ-like two-arm microstrip line was used as the driving electrode in these devices. The optical response dropped 3 dB electrical from 2 to 20 GHz. These 3 cm long devices have 5 dB total chip loss at both wavelengths and good thermal stability.

Microwave phase conjugation using antenna arrays

A technique has been developed and tested for achieving phase conjugation in the microwave and millimeter-wave regime. The effective nonlinearity required for this phase-conjugation process is provided by electronic mixing elements feeding an array of antennas. Using these balanced mixing circuits in conjunction with a one-dimensional array antenna, we have demonstrated two-dimensional free-space phase conjugation at 10.24 GHz. A critical factor of this technique is the delivery of a 2/spl omega/ pump signal to each array element with the same phase. Two types of interconnects, electrical and a more versatile optical technique, have been implemented to distribute the pump signal in our demonstrations. In both systems, two-dimensional free-space phase conjugation was observed and verified by directly measuring the electric-field amplitude and phase distribution under various conditions. The electric-field wave-fronts exhibited retro-directivity and the auto-correction characteristics of phase conjugation. Furthermore, these experiments have shown amplified conjugate-wave power up to ten times of that of the incoming wave. This amplifying ability demonstrates the potential of such arrays to be used in novel communications applications.

Demonstration of a photonically controlled RF phase shifter

Integrated photonic radio frequency (RF) phase shifters with dc voltage control have been realized using a nested dual Mach-Zehnder modulator configuration in a new nonlinear optical polymer, CLD2-ISX. These modulators have a V/sub /spl pi// of 10.8 V and exhibit excellent frequency performance measured up to 20 GHz. A near linear phase shift exceeding 108/spl deg/ was obtained for a 16-GHz microwave signal by tuning the dc control voltage over a 7.8-V range. It is expected that these integrated polymer phase shifters will find widespread applications in new types of lightweight optically controlled phased array systems.

Optically controlled serially fed phased array sensor

A new type of RF-photonic sensor design which uses an optical serially fed phased array is proposed for applications in radar and communication systems. This sensor has the advantages of true time delay and yet only requires one tunable laser and one fiber optic grating delay for beam steering. In addition to discussing the system operation in transmit and receive modes, we also present initial experiments establishing the viability of the basic serial-feed design approach.

Laser-fabricated delay lines in GaAs for optically steered phased-array radar

We have used laser direct fabrication techniques to implement optical delay lines on an epitaxial GaAs/AlGaAs substrate. These integrated photonic circuits, which are important for optically-controlled phased-array radar, include asymmetric splitters with various splitting ratios, smoothly curved 90/spl deg/ bends, as well as linear waveguides. The delay lines were tested and found to have the desired delay and a power-output uniformity of /spl plusmn/2-4%. >

Phased-array optically controlled receiver using a serial feed

Extension of a new optically controlled serially fed phased-array system to the receive mode of operation has been demonstrated. Our system uses the pulsed nature of microwave radars in a manner similar to clocked systems used in digital configurations. This novel approach requires only the use of one tunable laser, one optical modulator, and one chirped fiber grating unit. In this letter, we present an experimental demonstration of a two-element serially fed wide frequency range receiver that validates the feasibility of this novel concept. Our system can. Be readily expanded with multiple elements and transmit/receive modules for a complete phased array system.

Photonic control of terahertz systems

The use of optical control for millimeter wave systems has been extended recently to frequencies well over 100 GHz. New types of optical modulators, detectors and mixers can now be used to make novel systems for the first time operating at submillimeter wavelengths. In addition to the fabrication of the next generation of traveling wave polymer modulators and phototransistors, we have also developed novel approaches to high frequency testing. These involve both high frequency mixing and femtosecond pulse techniques. Applications of this technology to high frequency, electro-optical oscillators and integrated phase conjugation surfaces are now in their initial stages.

Microwave phase conjugation using optically interconnected phased arrays

A new technique has been developed to achieve phase conjugation in the microwave and millimeter wave regime. Using optically interconnected microwave mixing circuits in conjunction with one-dimensional array antennas, two-dimensional free space phase conjugation at 10.24 GHz has been observed and verified by directly measuring the electric field amplitude and phase distribution under various conditions.

Video broadcast using an optically controlled serially fed phased-array antenna

A new type of RF-photonic antenna design which uses an optical serially-fed phased array is proposed for applications in radar and communication systems. This antenna has the advantages of true time delay and yet only requires one tunable laser and one fiber optic grating delay for beam steering. In addition to discussing the system operation in transmit mode, we also present initial experiments establishing the viability of the basic serial-feed design approach by experimentally demonstrating the concept of optically controlled directional video broadcast using a 9 GHz sub-carrier. Our video transmission results are the first use of an optically controlled serially-fed phased array antenna as a communication device. KEYWORDS: true-time delay, fiber Bragg gratings, phased-array, video broadcast, photonic antenna, wireless communication