A 4-bit polymer optoelectronic true time delay device is demonstrated. The device is composed of monolithically integrated, low loss, passive polymer waveguide delay lines and 2x2 polymer thermo-optic 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 range from 0 to 177 ps in 11.8 ps increments. The packaged device has an insertion loss of 14.5 dB and the delay switching speed is 2 ms. The delays generated by the device are suitable for steering a 1D or 2D sub-array of an X-band phased array antenna system.
A novel optoelectronically-controlled wideband 2-D phased-array antenna system is demonstrated. The inclusion of WDM devices makes a highly scalable system structure. Only (M+N) delay lines are required to control a M×N array. The optical true-time delay lines are combination of polymer waveguides and optical switches, using a single polymeric platform and are monolithically integrated on a single substrate. The 16 time delays generated by the device are
measured to range from 0 to 175 ps in 11.6 ps. Far-field patterns at different steering angles in X-band are measured.
Continuously tunable optical true time-delay (TTD) modules based on dispersion-enhanced photonic crystal fibers (DEPCFs) are demonstrated to provide continuous microwave squint-free beam scanning for an X-band (8 to 12 GHz) phased-array antenna (PAA) system. The dispersion of the fabricated photonic crystal fibers (PCFs) is as high as –600 ps/nm km at 1550 nm. By employing PCFs to increase the dispersion, the TTD module size can be proportionally reduced. The time delay is continuously tunable from –31 ps 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 1×4 subarray were measured from –45 to 45 deg scanning angles. Squint-free operation is experimentally confirmed. Wavelength conversion is also demonstrated to confirm that time-delay information can be successfully transferred from one wavelength to the other without being changed, which is suitable to be implemented in 2-D phased-array antenna systems. The TTD formation idea presented is suitable for not only the X band, but also the other higher microwave frequencies, such as the K band.
A wavelength-controlled continuous beam-steering four-element X-band (8- to 12-GHz) phased array antenna system is presented. The system is based on the continuously tunable optical true-time-delay technique. Dispersion-enhanced waveguide holograms were proposed and used to fabricate the optical true-time-delay devices. The devices are characterized both theoretically and experimentally. The wavelength of a laser was tuned within the system to get continuously tunable true time delay. The time delay was measured for a wavelength tuning range from 1537 to 1547 nm in 10-nm steps. The far-field radiation patterns of the antenna system were measured at 9 and 10.3 GHz, and they showed no beam squint. The true-time-delay formation idea presented here is suitable for not only X-band, but also for higher microwave frequencies, such as K-band.
Nanophotonics including photonic crystals promises to have a revolutionary impact on the landscape of photonics technology. Photonic crystal line defect waveguides show high group velocity dispersion and slow photon effect near transmission band edge. By using photonic crystal waveguides to build true time delay based phased array antenna or other optical signal processing systems, the length of the tunable true time delay lines can be dramatically reduced inversely proportional to group velocity dispersion in dispersion enhanced system architecture or reduced inversely proportional to group index in slow photon enhanced system architecture. The group index of the fabricated silicon photonic crystal line defect waveguide is experimentally demonstrated as high as 40 at optical wavelength around 1569 nm. The group velocity dispersion of the fabricated silicon photonic crystal line defect waveguide is as high as 50 ps/nm∙mm at wavelength around 1569 nm, which is more than 107 times the dispersion of the standard telecom fiber (D = 3 ps/nm∙km). Due to the integration nature of photonic crystals, system-on-chip integration of the true time delay modules can be easily achieved.
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.
The design and fabrication of a polymer optical waveguide based true time delay (TTD) device is described. Optimization of the fabrication process decreased the waveguide propagation loss from more than 1.55 dB/cm to 0.38 dB/cm at a wavelength of 1.55um. Waveguide bend loss structures were fabricated and measurement results were compared to simulations. A bend radius of 3 mm provides low insertion loss and small device size. 2x2 thermo-optic TIR switches were fabricated with insertion losses of 2.8 dB. A 4-bit TTD device for use with a 4x4 sub-array of a 10GHz phased array antenna was calculated to have an insertion loss of 23.88 dB.
•A two-dimensional optically controlled phased array antenna (PAA) system is proposed. The system employs highly dispersive photonic crystal fibers (HDPCFs) to provide the true-time-delays (TTD). Independent azimuth and elevation control is obtained through a mid-stage optical wavelength conversion process. The dispersion of the fabricated is as high as -600 ps/nmkm around 1550 nm which is 33 times of conventional telecom SMF. By employing the PCFs to increase the dispersion, the TTD module size can be proportionally reduced. A 64-element (8x8) PCF-based PAA system is under construction. Simulation results operating at X-band are shown in this paper.
Photonic crystal based structures have been considered for optical communication applications. A class of novel symmetric structures consisting of cavities and waveguides have been proposed to serve as optical add-drop multiplexers. Light transfer processes in these structures are analyzed briefly. The problem of deviating from the perfect accidental degeneracy is addressed for practical designs, and the backscattering intensities are shown low for the slight deviations. Anomalous light refraction at a surface of a photonic crystal has also been studied. The limitations of prior theoretical methods for the transmission problem are discussed. An outline of a new analytic theory that overcomes these limitations is presented. Photonic crystals are fabricated on polymer multi-layer films and integrated with conventional channel waveguides.
The holographic-grating based wavelength-controlled true-time-delay devices are presented in the paper. The optical true-time-delay can be continuously controlled by continuously tuning the wavelength of a single laser within the devices. The dispersion ability of the devices is greatly enhanced by increasing the diffraction angles of the holographic gratings. The fabricated true-time-delay devices work within 1550nm region. The loss performance of the devices were calculated and measured. The wavelength-controlled true-time-delay was also characterized both theoretically and experimentally.
To find the optimal driving voltage and bandwidth for electro-optic polymer-waveguide-based directional couplers, four electrode structures are investigated. They are the microstrip line (MSL), the asymmetric coplanar waveguide with ground (ACWG), the coplanar waveguide with ground (CPWG), and the edge-coupled microstrip line (CMSL). UV15:Polymethyl methacrylate/dispersed-red 1:UV11-3-based directional couplers are evaluated. The CPWG and the ACWG have almost the same driving voltages, which are about twice the driving voltage of the CMSL. The MSL has the largest driving voltage, which is 20 to 25% higher than the diving voltages of the CPWG and ACWG. Simulation results further conclude that the MSL has the largest bandwidth, and its bandwidth is about 1.6 times that of the bandwidth of the CMSL, which has the narrowest bandwidth. The bandwidths of the ACWG and CPWG are 1.4 and 1.2 times that of the CMSL, respectively. The driving voltages for the four different devices are experimentally confirmed.
Wavelength-controlled true-time delay modules based on the dispersive hologram-waveguide are presented here to provide continuous beam-scanning for a X-band phased-array antenna system. The true-time delay modules operating in the 1550nm region were fabricated with continuously tunable time delays from 5ps to 64ps. All-optical wavelength conversion in the semiconductor optical amplifiers was proposed in the system to extend the beam-scanning scope from one dimension to two dimensions. The wavelength-controlled time delays were measured across the x-band (8-12GHz) in the experiment.
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