Abstract: A low profile, low cost receiver/transmitter system includes a planar waveguide-to-microstrip adapter, a dielectric loaded waveguide fed slot array antenna, and a downconverter all formed on a single dielectric substrate made of polytetrafluoroethylene. The waveguide antenna includes a set of slots disposed in a surface thereof to receive/transmit a microwave/millimeter wave signal. The waveguide-to-stripline adapter is connected to the waveguide antenna and includes a taper section attached to a microstrip line. The taper section, which may be linear or may follow some other more complex taper function such as a Chebyshev function, adapts a signal propagating within the waveguide antenna to the microstrip line or vise versa.

Abstract: An intensity modulator having a Mach-Zehnder structure with first and second waveguide arms formed of an electro-optic polymer. The active molecules of the waveguide arms are poled in first and second different and substantially orthogonal directions. Electrodes are arranged to receive a modulating voltage and generate first and second electric fields which are respectively aligned with the first and second directions. As a consequence, the modulation depth of an optical signal which is transmitted through the modulator is substantially insensitive to the polarization of the signal. Other embodiments combine mode splitters and combiners with first and second Mach-Zehnder modulators which have electro-optic polymer waveguides. The active molecules of the arms of the two Mach-Zehnder modulators are poled in orthogonal directions.

Abstract: Velocity-matched electrodes that are sufficiently index-matched to use in linearized directional-coupler modulators are provided by placing a low dielectric constant material layer over the travelling-wave modulator electrodes, followed by a metal layer that is electrically connected to a ground electrode. The low dielectric constant layer between the grounded metal layer and the active electrode lowers the effective RF dielectric constant, which lowers the RF index of refraction. The RF index of refraction is matched to the optical index of refraction by controlling the thickness of the low dielectric constant layer, which is deposited with standard RF sputtering techniques that allow for precise control over the layer thickness. As a result, more precise velocity matching and greater reproducibility than with prior velocity matching techniques is achieved.

Abstract: A simple, low-power feedback control loop is arranged to set the operating point of a photonic intensity modulator. The loop includes photodetectors which are respectively illuminated with a sample of the carrier signal into the modulator and the modulated signal out of the modulator. A comparison network develops an error signal which is integrated and applied to the voltage modulating port of the modulator. The comparison network includes voltage dividers for adjusting the transfer function operating point of the modulator. The control loop is especially suited for stabilizing Mach-Zehnder and directional coupler modulators.

Abstract: An optical receiver with an enhanced power capability and wide bandwidth is implemented by distributing a number of photodetectors along an optical transmission channel to convert respective portions of an optical signal into electrical signals. An electrical transmission line receives and accumulates signal inputs from the photodetectors. A velocity matching is established between the optical and electrical signals, allowing the photodetector outputs to accumulate coherently along the electrical transmission line, by loading the transmission line with distributed capacitance elements. The loading capacitances are preferably inherent in the photodetectors, which are designed and spaced apart from each other to yield the desired velocity matching.

Abstract: An electro-optic modulator such as a Mach-Zehnder interferometer has a segmented optical transmission network with a series of discrete electrodes for successive segments of the network. Respective modulating signals are supplied to the electrodes along transmission lines whose lengths differ from each other, so that modulating signals applied to the inputs of the transmission lines arrive at their respective electrodes in synchronism with the propagation of an optical signal through the optical transmission network. The modulating transmission lines are disposed lateral to and generally coplanar with the optical transmission network, preferably on a separate substrate. The desired differential in transmission line lengths can be achieved by positioning the input ends of the transmission lines along an edge of the input substrate that is at a desired angle to the optical transmission network.

Abstract: In accordance with the teachings of the present invention, an enhanced performance opto-electric modulator (30 or 70) is provided herein which compensates for phase velocity mismatches between optical modulation and an RF electric signal. The modulator (30) includes an optical waveguide (38, 40) formed in a substrate (32) and coupled to an optical input (56). An RF waveguide (46, 48) is formed on the substrate (32) for applying an electric field (59) to a modulation region (50) adjacent the optical waveguide so as to modulate an optical signal. The substrate (32) has a ferroelectric domain which includes periodically inverted and non-inverted regions (54) and (52) which compensate for phase differences within the modulation region (50). In a preferred embodiment, the optical waveguide includes two substantially parallel optical waveguides (38) and (40) which have outputs combined to provide for an amplitude modulated (AM) optical output signal (60).

Abstract: A travelling-wave Mach-Zehnder electro-optic modulator (10) for operation at microwave electrical input signal frequencies has an electrical modulation electrode structure (26,34) which constitutes a coplanar waveguide (24). An electrical input signal connector (80) is coupled to a microstrip line (38) having an output impedance which is significantly different from the input impedance of the waveguide (24). A Chebyshev impedance matching transformer (50) couples the input signal from the input connector (80) to the modulation electrode structure (26,34), while matching the output impedance of the microstrip line (38) to the input impedance of the waveguide (24) to maximize the coupling efficiency and minimize return loss. The modulatoGOVERNMENT RIGHTSThis invention was made with Government support under Contract No. N66604-87-C-1126 awarded by the Department of the Navy. The Government has certain rights in this invention.

Abstract: An electro-optic modulator (10) includes a pair of optical waveguide channels (20, 22) formed in an X-cut lithium niobate substrate (12) and an overlying RF coplanar waveguide (36). A periodic electrode structure (48) of the intermittent interaction type employs a plurality of middle stubs (52) to maintain the phase of the RF drive frequency in phase with the optical signal. The modulator (10) also utilizes shorter stubs (64) and tapered inlets (42) and outlets (44) to match and transform impedances.