USA As Represented by Secretary of the Navy

Other

Keith J Williams

Shane J Strutz

Vincent J Urick

Jason D McKinney

Ronald D Esman

Preetpaul S Devgan

John F Diehl

Lew Goldberg

Irl N Duling, Iii

Michael L Dennis

Carl A Villarruel

Edward M Alexander

Paul D Biernacki

Meredith N Hutchinson

Lee T Nichols

Joseph M Singley

Christopher E Sunderman

Allan Ward

An apparatus includes an input radio frequency waveguide. The apparatus includes a radio-frequency-to-optical-radio-frequency-impedance-matching interface communicating with the input radio frequency waveguide. The apparatus includes a plurality of optical modulators communicating with the radio-frequency-to-optical-radio-frequency-impedance-matching interface. The apparatus includes a plurality of respective optical waveguides communicating with the plurality of optical modulators. The plurality of respective optical waveguides in operation includes a plurality of respective optical waveguide fields. The input radio frequency waveguide in operation includes an input radio frequency waveguide field. The input radio frequency waveguide field interacts with the plurality of respective optical waveguide fields to convert an input radio frequency signal into a plurality of optical signals.

Multi-element optical links

Systems and method are provided to for suppressing interference signals in optical systems, without prior knowledge of the type of location of the interferers, while maintaining a linear response to small signals of interest (SOI). By exploiting the unique power (or voltage) dependent transmission function of an externally angle-modulated photonic link, embodiments of the present disclosure are configured to provide strong, wideband interference suppression without requiring detailed knowledge of the interfering signal.

Interference suppression based on power-dependent transfer function of angle-modulated optical links

A system for suppressing even-order distortion in a photonic link includes a laser for providing laser light to a first input of a Mach-Zehnder modulator (MZM), where the MZM has a second input for receiving an RF input signal, a third input for applying a DC bias voltage to the MZM, and an optical signal output. A dc-voltage-biased photodiode has an input, coupled to the MZM optical signal output, and a modulated RF signal output. The MZM DC bias voltage is set at a value to generate an even-order distortion amplitude substantially equal to an even-order distortion amplitude from the photodiode and 180 degrees out of phase so as to substantially cancel the photodiode even-order distortion. The invention provides the cancellation of photodiode even-order distortion via predisortion linearization with a MZM biased slightly away from quadrature, employing a single fiber run and a single photodiode. The invention provides an improvement in carrier-to-intermodulation ratio (CIR) upwards of 40 dB.

System and method for suppression of even-order photodiode distortions

A multi-mode optoelectronic oscillator (MM-OEO) includes an OEO cavity having an input for receiving an RF signal and an RF output. The OEO cavity includes a) a first laser having a first laser output, a second laser having a second laser output, b) a modulator having i) a first input coupled to the first laser output, ii) a second input coupled to the second laser output, iii) a third input, iv) a first modulator output, and v) a second modulator output, c) a semiconductor optical amplifier (SOA) having an input coupled to the first modulator output and having an SOA amplified output, d) a photodetector coupled to the SOA amplified output and having an output, and e) a coupler having an input coupled to the photodetector output and having a first output coupled to the third modulator input and a second output, whereby an amplified RF signal is produced at the OEO RF output.

Multi-mode optoelectronic oscillator

A method and system for processing analog optical signals to produce a single RF output free from even-order harmonic distortion. Two analog optical signals of different wavelengths &#x3bb;are input into a dual-output Mach-Zehnder modulator (MZM), where one wavelength input is high-biased and one wavelength is low-biased. The complementary high- and low-biased wavelengths are output from each arm of the MZM to a multiplexer, which filters out the unwanted high- or low-biased wavelengths from each MZM arm so that both wavelengths are low-biased or high-biased. The signals are passed to a pair of photodiodes, and the photocurrents from the photodiodes are differenced to produce the final RF output. Because of the complementary phase differences between the two low- or high-biased signals generating the photocurrent, all components of the photocurrent except the fundamental and odd-order harmonics cancel each other, resulting in a high-quality RF output free from harmonic distortion.

Even-order harmonic cancellation and increased RF gain using dual-output mach-zehnder modulator with two wavelength input

An apparatus and method to increase the output power from LiNbO3 MZM style optical intensity modulating without exceeding the optical power damage threshold imposed by LiNbO3 is described. The optical path from a laser source is divided into two paths by a polarization maintaining (PM) coupler. The two paths form a Mach Zender Modulator (MZM) with a LiNbO3 phase modulator in one path and a fiber looped PZT in the other. The LiNbO3 phase modulator imprints an RF signal onto one path of the MZM cavity, while the fiber wrapped PZT is used to control the path length difference between the two optical paths. The two optical paths are recombined in a second PM coupler. The second PM coupler and a 1-2% coupler are used to sample a small portion of the MZM output signal which is fed back to a phase locked loop (PLL) circuit for providing feedback voltage to the fiber wrapped PZT in the second arm of the MZM, and ensures the phase of the signals in the two arms of the MZM are matched to within a fraction of the laser linewidth. The present invention increases the amount of optical power by using a LiNbO3 modulator within a fiber Mach-Zender cavity.

High power fiber optic modulator system and method

The remotable, ultrawide band optical image rejection downconverter uses sub-carrier modulation techniques without concern for image frequency interferences in the shifted signal, thereby allowing telecommunications systems to downconvert densely multiplexed communications channels into a low frequency band where conventional electronics can perform signal-processing functions. This invention has the image rejection (>120 dB) to provide unambiguous signals for direction finding applications and exhibits an efficient image that permits multi-octave microwave frequency reception and compression. This invention is intrinsically remoteable, and due to the various optical and electrical components proves to be very useful and practical in numerous fiber optic and antenna systems.

Optical image reject down converter

An optical image reject down-converter for mapping a received radio frequency (RF) into an arbitrary intermediate frequency range and for precluding interference between the received signals. A received radio frequency signal is down-converted into an intermediate frequency band for use by an electronic circuit in other devices. Optical light is divided into a first path and a second path. Light in the first path is transferred into an optical sideband by a first optical modulator or phase modulator. Light in a second path is converted into sidebands by a second, non-cascaded optical modulator and then passed through a tunable narrow-band optical filter which selects the desired sideband. The optical spectrum of the second path then primarily includes light at the frequency equal to the original laser frequency plus the additional sidebands. The filtered sideband is heterodyned with the light from the first path, resulting in a down-conversion to the desired intermediate frequency. Image frequencies initially present in the optical link are thereby filtered and rejected.

All optical image reject down-converter

A method and apparatus to enable the use of low cost high RIN optical sources for microwave photonic links by combining the wide-gain bandwidth and low cost of an EDFA, with the narrow gain bandwidth of a Brillouin amplifier. The hybrid Brillouin/EDFA (&ldquo;hybrid amplifier&rdquo;) apparatus of the present invention includes at least two couplers, a phase modulator, an Erbium-doped fiber, a laser source to pump the Erbium fiber, an optical circulator, and a length of fiber used for Brillouin amplification. Optical signals from the laser source are split into two optical paths by a polarization maintaining coupler. Optical signals passing through a first path are amplified by the Erbium doped fiber, and the amplified signals are passed through the optical circulator before sending the optical signals into one end of a spool of fiber in order to pump the Brillouin acoustic wave. Optical signals that follow a second path are phase modulated in a phase modulator at the Brillouin frequency and injected into an opposite end of the fiber spool in order to seed the Brillouin amplifier and improve its low frequency stability. The output of the Brillouin section of the hybrid amplifier is directed through the optical circulator, and the output may be used as an optical source for a photonic link.

Hybrid brillouin/erbium doped fiber amplifier apparatus and method

The optical image reject down converter maps a received radio frequency (RF) into an arbitrary intermediate frequency range and precludes interference between the received signals. A received radio frequency signal is downconverted into an intermediate frequency band for use by an electronic circuit in other devices. Optical light is divided, in a first path light is transferred into an optical sideband by a first optical modulator or phase modulator. Light in a second path is converted into 18 GHz sidebands. The signal is amplified and additional sidebands are generated by a received 9 GHz signal. The filtered sideband is heterodyned with the 25 GHz signal of path one, resulting in downconversion to 2 GHZ. Image frequencies which are present in the optical link are filtered and are rejected.

An image rejecting microwave photonic downconverter uses a microwave sub-carrier modulation technique without concern for image frequency interference in the shifted signal, thereby allowing telecommunications systems to downconvert densely multiplexed communications channels into a low frequency band where conventionqal electronics can perform signal-processing functions. The image rejecting microwave photonic downconveter incoming microwave signals can be processed without ambiguity in direction finding applications, allowing remotable, multioctave microwave signal processing for frequency and phase determination. A first laser providing an optical carrier that is modulated by a first electro-optic modulator with a sinusoidal electrical signal generated by a first local oscillator and a second laser providing optical carrier that is modulated by a second electro-optic modulator with a sinusoidal electrical signal generated by the second local oscillator for a signal generated by a second local oscillator; are transmitted independently through two polarization-maintaining (PM) optical fibers of arbitrary length to a distant point. There the first modulated optical signal is converted to an electrical domain and mixed with an input from an ultra-broadband radio frequency (RF) antenna receive-array, shifting the entire RF band to a higher frequency band equal to the original RF signal plus the modulated optical frequency signal.

Image rejecting microwave photonic downconverter

An optical receiver for receiving a signal from an optical fiber in a fiber-optic digital transmission system that includes a first low noise optical amplifier to amplify an input optical signal. The first low noise optical amplifier has an input 3 dB compression point lower than the desired system input sensitivity at a desired bit rate. A high power optical amplifier further amplifies the amplified optical signal, and has an automatic gain control for output signal leveling at a desired operation point of the transmission system. A high current photodetector converts the further amplified optical signal from the high power optical amplifier to an electrical signal that drives a retiming circuit without requiring further amplification of the electric signal.

High-sensitivity, high-speed digital optical photoreceiver

The broadband microwave frequency shifter is an electro-optical device that accomplishes frequency shifting, or translation by the use of serrodyning or mixing techniques. A first optical signal is modulated with the radio frequency signal desired to be translated and processed to produce an upconverted lower sideband optical signal. A second optical signal is frequency shifted using an optical phase shifter utilizing serrodyning techniques or by offset phase locking it to another optical signal. When the frequency shifted optical signal is combined with the upconverted optical signal and converted to an output radio frequency signal thereby producing an output microwave signal that duplicates the input microwave signal in all aspects except that its center frequency has been shifted.

Electro-optical broadband microwave frequency shifter

An attenuator/filter is disclosed that is inherently tuned and provides for a stimulated Brillouin scattering effect having a predetermined threshold that fixes the output thereof at a predefined power level. The stimulated Brillouin scattering effect is disclosed as being provided by either a fused silica optical fiber or a fiber-optic ring resonator both of which act as a filter to allow selected frequencies to pass. The SBS threshold is selected to improve the sideband to carrier power ratio which, in turn, determines the modulation depth for the modulated signal.

Stimulated Brillouin scattering for fiber-optic links

In the transmission electrical signals using an optical carrier the signal power carried by an optical carrier is proportional to the optical power. High optical power levels are desired for optical carriers that are modulated by weak electrical signals, however, significant unmodulated power is left in the original carrier after processing. To maximize the radio frequency (RF) signal power generated by a given (maximized) photodetector current (for a given input power), in this invention, the optical carrier power is reduced. This is accomplished by the addition of a narrowband optical filter, such as a Fabry-Perot filter, to reduce the average optical carrier power without reducing the modulation sidebands, which results in an increased modulation depth. Therefore, greater RF and microwave power is generated by a photodetector with the same photocurrent. With a laser source exhibiting a beam whose linewidth is narrow compared to the filter bandwidth, the filter is tuned, or frequency locked, to match the filtering resonance with the optical carrier wavelength. With the high finesse filter and narrow-linewidth laser beam, the frequency range of operation is extended from the filter half-bandwidth to the next resonance of the filter. Thus, broadband effective gain results without introducing additional noise.

Growing community of inventors

Dunkirk, MD, United States of America

Keith J Williams