Trw Limited

Eospace Inc.

The Boeing Company

Suwat Thaniyavarn

David Emil Moilanen

Walter Charczenko

Electro-optic modulation of multiple phase modulator waveguides with a single electrode is made possible by determining places of equal electric field strength. Substrate extensions support edges of a wide hot electrode and ground electrodes equally spaced from the wide hot electrodes. Waveguides are positioned in the extensions separated from the electrodes by buffer layers. A wide microstrip hot electrode on a buffer layer, wider substrate and ground has multiple waveguides in the substrate below the buffer layer. A thinned substrate has a microstrip hot electrode and spaced coplanar grounds with multiple waveguides located on both sides. Decreasing substrate thickness flattens the electric field strength between the electrodes and allows multiple waveguides located between the central hot and outer ground electrodes. Adjacent waveguides with different asymmetric waveguide index portion staged along their length eliminate cross talk.

Electro-optic modulation of multiple phase modulator waveguides with a single electrode

A Dual-polarization optical modulator that can be used to modulate light in both polarization states, in which the operating points of each polarization state can be set at any arbitrary point independently from each other. A novel architecture for an optically-controlled Phased-array beam forming system utilizing this unique dual-polarization is proposed to facilitate simple and practical implementation.

Dual polarization optical modulator with independent phase tuning for each polarization state and its application in an optical integrated circuit architecture for optically-controlled RF phased-array beam forming

Improved optical interferometric modulators have a small waveguide spacing so that the waveguide pair are close to the central electrode, to enhance electro-optic interaction. Asymmetric waveguides with differential indices are used to effectively de-couple the waveguide pair. Multiple sections of asymmetric waveguide pairs with alternating differential indices are used to achieve chirp-free operation. Another version of the device utilizes transmission-line electrode that weave closer to one of the waveguide pair alternately between sections. Another version of the device utilizes waveguide structure that one of the waveguide is closer to the central electrode in alternate section. To improve efficiency further, a DC bias is provided on the outer electrodes configured as an RF-ground but DC-float electrodes. Another improvement is to have a slot is cut underneath the waveguide region to effectively reduce to thickness of the substrate. These improvements lead to higher modulator efficiency.

Advanced techniques for improving high-efficiency optical modulators

Wide band phase modulators used with high power laser carriers convert high-frequency RF signals to phase-modulated optical signals. Higher laser optical power to the modulator produces larger RF signal sidebands. A carrier attenuation filter passes the attenuated carrier and non-attenuated RF modulation sidebands. Carrier attenuation leaves the larger RF signal sidebands. A demodulation filter used with a photodetector or a balanced photodetector pair converts the phase-modulated optical signal back to an electrical signal. Carrier-only attenuation allows high power laser use, avoids photodetector damage or saturation, and provides increased RF link gain, low noise figure (NF) and high spurious-free dynamic range (SFDR). Filtered-out carrier power fed back to the laser source increases to overall system efficiency. An additional optical delay filter with dual outputs used with a polarization multiplexer or a coherent combiner coupler combines signal power to a single photodetector to further increase electro-optic signal conversion efficiency.

High-RF frequency analog fiber-optic links using optical signal processing techniques

A new High-Z optical modulator has a waveguide and electrodes on a substrate, a buffer layer with a low dielectric constant between the waveguide and the substrate, and a substance between the waveguide and the substrate with a dielectric constant lower than a dielectric constant of the substrate to the side and below the plane of the waveguide, thereby improving electro-optic field overlap, increasing RF speed and increasing transmission line impedance. The material with a dielectric constant lower than the substrate extends between the waveguide and the electrodes to a depth below the waveguide equal to or greater than the lateral distance between the waveguide and electrodes. This material may be air and may be introduced by cutting away portions of the substrate around the waveguide with a precision dicing saw. The electrodes may be placed even with the waveguide or below the waveguide on the cut-away portion of the substrate.

High-efficiency optical modulators and implementation techniques

A cw-laser source transmits low-noise, narrow-linewidth optical power via an optical fiber to a bias-free electro-optic phase modulator at a remote site, where an antenna or an RF sensor is located. The RF electrical signal modulates the phase modulator at the remote site, converting an electrical signal into an optical signal. The phase-modulated optical signal is fed back via the optical fiber to an optical filter whose filter transfer characteristics can be tuned and reconfigured to cancel the intermodulation distortion terms, particularly the dominant 3order intermodulation, as well as the 2order. The filtered optical signal is converted to the RF signal at the photodetector. The optical filter is used to effectively 'linearize' the signal at the receiver end, rather than at the modulator end.

High-dynamic-range analog fiber-optic link using phase modulation and tunable optical filter

Optical switches based on the balanced bridge interferometer design require precisely made (or half a coupling length) directional couplers to achieve minimum crosstalk for the two switch outputs. Precision 3 dB-directional couplers require the waveguide dimensions and fabrication parameters of the evanescent region to be tightly controlled making a low crosstalk switch difficult to manufacture and expensive. A new type of balanced bridge interferometer type switch is disclosed where the input and output directional couplers are asymmetrically biased to induce a certain difference in the propagation constants between the two waveguide in the directional couplers. By using the asymmetrically biased directional couplers with a certain tuning a bias voltage for the directional couplers. Low crosstalk switches can be achieved for a very wide range of directional coupler strengths, relaxing the precise half-coupling length directional couplers required in conventional design. This relaxation of the precise directional coupler waveguide regions allows a relaxation in the manufacturing tolerance of the devices and therefore make the switch much easier to make. Because low crosstalk switches can be a device with an extended operating range and broader directional coupler parameters, switches can be used for a much broader wavelength bandwidth. In one of the embodiments, this new design allows a device to switch both TE and TM mode optical signals simultaneously at low crosstalk levels to result in a polarization-independent optical switch.

Polarization independent broad wavelength band optical switches/modulators

A photonic device for controlling phased array beam direction includes an electro-optic substrate; a plurality of waveguides formed in the substrate, each of which is capable of simultaneously propagating light signals with orthogonal polarizations; an input waveguide for inputting into each one of the plurality of waveguides a pair of copropagating polarized light signals having orthogonal polarizations and different frequencies; a plurality of electrodes on the substrate configured to phase shift the signals traveling through each waveguide by a different amount in response to applied voltages, thereby creating phase shifted polarized signals; and means for combining the phase shifted polarized signals within each one of the waveguides and propagating these combined signal to an antenna element. The basic operating principle of the invention is based on the differential phase shift between optical waves of orthogonal polarizations traveling in an electro-optic optical waveguide. This differential phase shift is directly proportional to the voltage applied to a control electrode and to the length of that electrode. If the two optical waves are slightly offset in optical frequency, they produce a beat frequency when photodetected whose phase shift equals the optical differential phase shift. An array of such phase shifters forms the basis for the photonic beam controller of the invention.

Phased array beam controller using integrated electro-optic circuits

An optical switching network includes one or more planar substrates with an optical waveguide switching array formed thereon butt-coupled to a waveguide component. The waveguide component is a planar substrate with a plurality of passive optical waveguides thereon. The input ends and output ends of the waveguides are disposed along the butt-coupled edge(s) of the waveguide component substrate. The waveguides and switches are arranged with the waveguides interconnecting the input and output switch arrays so that an incoming optical signal can be directed to any desired output on the output array. The use of planar substrates with electro-optic and passive waveguide circuits allows for a modular approach, where the active switch array substrate and the passive waveguide substrates can be optimized individually. An N.times.N switch array circuit can be formed of N sets of N.times.1 switch arrays on the input substrate and N sets of N.times.1 switch arrays on the output substrate. The input and output switch arrays are then interconnected by butt-coupling to a passive waveguide array fabricated on another substrate to form a complete N.times.N switch array circuit.

N.times.N optical switch array using electro-optic and passive waveguide

A photonic device for controlling phased array beam direction includes an electro-optic substrate; a plurality of waveguides formed in the substrate, each of which is capable of simultaneously propagating light signals with orthogonal polarizations; an input waveguide for inputting into each one of the plurality of waveguides a pair of copropagating polarized light signals having orthogonal polarizations and different frequencies; a plurality of electrodes on the substrate configured to phase shift the signals traveling through each waveguide by a different amount in response to a common applied voltage, thereby creating phase shifted polarized signals; and means for combining the phase shifted polarized signals within each one of the waveguides and propagating these combined signal to an antenna element. The basic operating principle of the invention is based on the differential phase shift between optical waves of orthogonal polarizations traveling in an electro-optic optical waveguide. This differential phase shift is directly proportional to the voltage applied to a control electrode and to the length of that electrode. If the two optical waves are slightly offset in optical frequency, they produce a beat frequency when photodetected whose phase shift equals the optical differential phase shift. An array of such phase shifters forms the basis for the photonic beam controller of the invention.

An optical time delay device includes a switching component butt-coupled to one or two delay line components. The switching component is a planar substrate with an optical waveguide switching array formed thereon. The delay line component is a second planar substrate with a plurality of optical waveguides of different optical lengths. The input ends and output ends of the waveguides are disposed along the butt-coupled edge of the second substrate. The waveguides and switches are arranged so that the switches direct an incoming optical signal to a selected one or more of said waveguides. In a preferred embodiment, one of the waveguides has an optical length .DELTA.L, and the remaining waveguides have optical lengths which are multiples of .DELTA.L. The use of planar substrates with electro-optic and passive waveguide circuits allows for a modular approach, with interchangeable delay line components chosen for a particular application and butt-coupled to the switching component.

Programmable signal time delay device using electro-optic and passive

An optical switch that does not require precise voltage control to produce the crossover and straight-through states. The switch comprises an electro-optic substrate in which a pattern of optical waveguides is formed, the pattern including an input waveguide that branches to form first and second output waveguides. The output waveguides pass through a coupling region within which evanescent field coupling can occur. A first pair of electrodes produces a first propagation constant difference .DELTA..beta..sub.1 in a first section of the coupling region, and a second pair of electrodes produces a second difference .DELTA..beta..sub.2 in a second section of the coupling region. By forming the first and second sections to have different lengths, and by causing .DELTA..beta..sub.1 and .DELTA..beta..sub.2 to have opposite polarities, an optical swtich is provided having wide voltage tolerances for the crossover and straight-through states.

Optical switch based on 1.times.2 directional coupler

An electrooptically tunable waveguide array combined with a semiconductor phase-locked laser array, to provide both amplitude shaping and phase control of the optical output. The tunable waveguide array includes an input waveguide array section with an array spacing matching that of the laser array, a tunable coupling array section for tailoring power distribution among the array elements, a tunable phase shifter array section for tailoring the relative phase distribution among the array elements, and an output waveguide array section of various possible configurations. The tunable waveguide array can be implemented either externally, independent of the laser array, or incorporated into the laser array to form a composite cavity-array.

Electrooptically tunable phase-locked laser array

A directional coupler having two coupled waveguides that receive a single optical input through a Y-junction power splitter, and two outputs from the coupled waveguides. Electrodes positioned over the coupled waveguides apply opposite electric fields to the waveguides and, through the electrooptical effect, modulate the optical outputs. For a zero applied voltage and zero electric field, the outputs are both equal to approximately half of the maximum possible output intensity, and no bias voltage is needed for operation as a modulator. As the voltage is varied from zero, positively or negatively, the optical intensity from either of the outputs varies linearly over a useful range. Moreover, the voltage required to switch full power from one output to the other is less than that required for conventional electrooptical modulators or switches.

Electrooptical switch and modulator

An improved electro-optic coupled waveguide interferometer (50) is provided. The device comprises a single input (52), a Y-junction splitter (54), two interferometric arms (56a, 56b), a Y-junction combiner (58), a single output (60) and multiple equal-length sections of electrodes (62a-d) with alternating applied voltage polarities. The device of the invention permits use of much smaller Y-junction branching angle, which reduces scattering losses, or a shorter branching waveguide section, which allows construction of a device having an overall shorter length than prior art interferometers. The device takes advantage of a close placement of the interferometer arms, which results in a transfer of optical energy and facilitates a single-gap electrode structure for efficient push-pull operation. The use of multiple-section electrodes restores the high modulation depth otherwise destroyed by the close placement of the interferometric arms.

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Bellevue, WA, United States of America

Suwat Thaniyavarn