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This Letter presents a method for the fabrication and integration of a thin LiNbO3 substrate with a Si handle wafer. An inverted ridge structure guides a single optical mode in an electro-optic modulator fabricated on a mechanically thinned substrate. To define an optical waveguide, a ridge structure is first patterned on a 500 μm thick X-cut LiNbO3 wafer; then a low dielectric constant adhesive layer is used to bond the etched LiNbO3 to Si. The LiNbO3 is mechanically thinned to 4 μm, and planar electrodes are patterned. Experimental results demonstrating modulation with a V(π)L of 7.1 V-cm were shown, optical loss was low enough, and film quality high enough, to enable an interaction length of 0.8 cm.

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We present a tightly coupled array antenna excited by high-power photodiodes for millimeter wave transmit operation. The design includes thinned photodiode substrates for improved bandwidth performance at high frequency combined with the inherently lightweight, low-loss, and direct feeding architecture afforded by the photonic approach. Circuit and full wave simulations are conducted for array design and compared against the traditional electronic arrays in the literature. A prototype 1 × 3 photonic array is developed and characterized to validate the design which achieves a 3 dB (VSWR < 1.4) radiated power bandwidth of 4.6:1 across 13-60 GHz and maintains a 3 dB bandwidth near 4:1 across scan angles up to 30 • . The fabricated array exhibits a 3 dB radiated power bandwidth of 1.8:1 across 30-55 GHz and a maximum measured effective isotropic radiated power of 19.4 dBm at 40 GHz.Index Terms-High-power photodiode, optically fed phased array, RF photonics, tightly coupled array (TCA) antenna, ultrawideband (UWB). I. INTRODUCTIONP HASED array antennas are essential in the development of advanced multifunctional RF systems that serve both commercial and defense sectors. Emphasis in the defense community is placed on the consolidation of RF front ends, signal processing algorithms, and control centers with adaptive subsystems effective for radar and communication [1], [2]. Consolidation of RF front ends with adaptive, multifunctional capabilities requires phased arrays with multioctave operational bandwidths, high transmit power and beam space diversity, frequency agility, scaling potential, and optimal size, weight, and power (SWaP). Similar requirements are of interest in the commercial sector where these benefits can be leveraged in the fifth-generation (5G) cellular communications and mobile networks [3]. Generally, 5G encapsulates the modern trend to continually increase wireless data capacity. Specifically, increasing data capacity ultimately requires increased Manuscript