Brie Howley

Dispersion-enhanced photonic crystal fiber array for a true time-delay structured X-band phased array antenna

Tunable optical true time-delay modules based on highly dispersive photonic crystal fibers (PCFs) are demonstrated to provide continuous radio-frequency squint-free beam scanning for an X-band (8-12 GHz) phased array antenna system. The dispersion of the fabricated PCF is as high as -600 ps/nm /spl middot/ km at 1550 nm. The time delay is continuously tunable from -31 to 31 ps between adjacent delay lines by tuning the laser wavelength continuously from 1528 to 1560 nm. The far field radiation patterns of a 1/spl times/4 subarray were measured from -45/spl deg/ to 45/spl deg/ scanning angles. Squint-free operation is experimentally confirmed.

Fringing-field minimization in liquid-crystal-based high-resolution switchable gratings

A liquid-crystal (LC)-based high-resolution switchable grating is proposed by using a double-sided structure, where striped electrodes are patterned on both sides of the LC cell. A unique biasing configuration is employed to successfully minimize the distortion of the LC director profile due to the fringing-field effects under two-dimensional electric fields. A first order diffraction angle of 14.5° with a diffraction efficiency of 33% for transmission light at 1.55μm is experimentally achieved. This result approaches the theoretical upper limit of 33.8% for a sinusoidal phase grating. The device efficiency is enhanced 80 times compared to a conventional single-sided device. Experimental results indicate the tolerance of electrode misalignment is 2μm.

2-bit reconfigurable true time delay lines using 2/spl times/2 polymer waveguide switches

A 2-bit (four delays) polymer waveguide delay device is demonstrated and characterized. The device is composed of polymer waveguide delay lines, optical fiber delay lines, and polymer thermooptical 2/spl times/2 switches. The insertion loss for the fully integrated device ranges between 8.12 and 9.81 dB depending on the delay path chosen. The polarization-dependant loss is 0.04 dB. Measured delays are 0, 37.8, 160.4, and 199.2 ps. The switching speed is less than 4 ms. The designed polymer waveguide delays match well with the measured values.

Reconfigurable Delay Time Polymer Planar Lightwave Circuit for an X-band Phased-Array Antenna Demonstration

A 4-bit polymer optoelectronic true-time delay (TTD) device is demonstrated. The planar lightwave circuit (PLC) is composed of monolithically integrated low-loss passive polymer waveguide delay lines and five cascaded 2 times 2 polymer thermooptic switches. Waveguide junction offsets and air trenches simultaneously reduce the bending loss and device area. Simulations are used to optimize the trench and offset structures for fabrication. The 16 time delays generated by the device are measured to be in the range from 0 to 177 ps in 11.8-ps increments. The packaged PLC has an insertion loss of up to 14.9 dB, and the delay switching speed is 2 ms. An eight-element X-band phased-array antenna system is constructed to demonstrate the beam-steering capabilities of the 4-bit-delay devices. The TTD devices are shown to steer the far-field radiation pattern between 0deg and -14.5deg

Phase error corrected 4-bit true time delay module using a cascaded 2 × 2 polymer waveguide switch array

A fully integrated 4-bit true time delay device using polymer optical switches and waveguide delay lines is demonstrated. The fabricated device, which contains five 2x2 thermo-optic switches, has a maximum power consumption of 143 mW and a switching time less than 3 ms. The rf phase error, which is affected by the optical switch cross talk, is also theoretically analyzed and proved to be negligible by experimental results.

Polarization-independent all-wave polymer-based TIR thermooptic switch

The optimal design of a polymer-based thermooptic (TO) switch using a total internal reflection (TIR) effect is proposed to improve switching performance. Numerical calculations show that this type of optical switch can achieve an ultrabroad optical bandwidth as well as a low polarization dependent loss. The devices fabricated with different half branch angles consume driving powers from 25 to 66 mW. The switches also show fiber-to-fiber insertion losses at 2.8 dB and polarization dependent losses (PDLs) at 0.2 dB. The measured rising and falling times are 1.5 and 2 ms, respectively. The optical bandwidth of the devices, which is limited by the material absorption from the fluorinated polymer, is quite large extending from 630 to 1630 nm

Experimental evaluation of curved polymer waveguides with air trenches and offsets

Excess waveguide bend loss can be minimized through the use of offsets and air trenches. Offsets, used for reducing the junction loss between straight and curved waveguides, and air trenches, which prevent bend radiation loss, were simulated by a three-dimensional, semivectorial beam propagation method. Low loss polymer waveguide bend structures, employing both offsets and trenches, were fabricated. A reduction of the 180° bend insertion loss from 17.7to3.0dB with a bending radius (BR) of 1.5mm is experimentally confirmed at λ=1.55μm. BR ranging from 5to0.5mm are evaluated with decent match when compared with simulation results. The polarization dependent loss is BR dependent with a maximum value of 0.4dB when the BR is reduced to 0.5mm. The experimental results confirm that the joint use of air trenches and junction offsets is effective in reducing the bend radii of low index contrast polymer waveguides in planar lightwave circuits.

Crosstalk-minimized polymeric 2/spl times/2 thermooptic switch

A thermooptic 2/spl times/2 switch based on the total internal reflection effect is demonstrated. The device, made of ultraviolet curable fluorinated polymer, has an increased half-branch angle of 5/spl deg/. The purpose of a large half-branch angle is to overcome the volume relaxation phenomenon, which is an intrinsic characteristic of polymers. The device successfully decreases the crosstalk below -40 dB in both the cross and bar states. The fabricated device has a power consumption of only 66 mW in the bar state.

4

A polymeric 4times4 nonblocking thermo-optic switch matrix that uses the total internal reflection effect, is designed and fabricated. The switch matrix has a total device length of 39.3 mm, a fiber-to-fiber insertion loss ranging from 8.7 to 4.5 dB, and a worst case cross talk of -23.3 dB. The device also achieves a low power consumption of 96 mW and a switch response time of 2.1 ms

,times,

A thermo-optic switch using total internal reflection waveguide was fabricated for optical true time delay. Experimental result shows that the crosstalk in the bar state is as low as -42dB and the total insertion loss is only -4dB at the wavelength of 1.55μm. A power consumption of 130mWand switching speeds of 2ms are obtained as well, which makes the device qualified to be used in the application of optical true time delay.