Optical signal processing brings together various fields of optics and signal processing - namely, nonlinear devices and processes, analog and digital signals, and advanced data modulation formats - to achieve high-speed signal processing functions that can potentially operate at the line rate of fiber optic communications. Information can be encoded in amplitude, phase, wavelength, polarization and spatial features of an optical wave to achieve high-capacity transmission. We revisit advances in the key enabling technologies that led to recent research in optical signal processing for digital signals that are encoded in one or more of these dimensions. Various optical nonlinearities and chromatic dispersion have been shown to enable key sub-system applications such as wavelength conversion, multicasting, multiplexing, demultiplexing, and tunable optical delays. We review recent advances in high-speed optical signal processing applications in the areas of equalization, regeneration, flexible signal generation, and optical control information (optical logic and correlation).

All-Optical Signal Processing

Periodically poled lithium niobate (PPLN) waveguides are a powerful platform for efficient wavelength conversion. Conventional PPLN converters, however, typically require long device lengths and high pump powers due to the limited nonlinear interaction strength. Here we use a nanostructured PPLN waveguide to demonstrate an ultrahigh normalized efficiency of 2600%/W−cm2 for second-harmonic generation of 1.5 μm radiation, more than 20 times higher than that in state-of-the-art diffused waveguides. This is achieved by a combination of sub-wavelength optical confinement and high-fidelity periodic poling at a first-order poling period of 4 μm. Our highly integrated PPLN waveguides are promising for future chip-scale integration of classical and quantum photonic systems.

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Ultrahigh-efficiency wavelength conversion in nanophotonic periodically poled lithium niobate waveguides

On a single chip, sources of entangled photons are combined with optical elements that can perform complex manipulations of quantum signals.

On-chip generation and manipulation of entangled photons based on reconfigurable lithium-niobate waveguide circuits.

The state of the art of optical waveguide fabrication in lithium niobate is reviewed, with particular emphasis on new technologies and recent applications. The attention is mainly devoted to recently developed fabrication methods, such as femtosecond laser writing, ion implantation, and smart cut waveguides as well as to the realization of waveguides with tailored functionalities, such as photorefractive or domain engineered structures. More exotic systems, such as reconfigurable and photorefractive soliton waveguides, are also considered. Classical techniques, such as Ti in-diffusion and proton exchange, are cited and briefly reviewed as a reference standpoint to highlight the recent developments. In all cases, the application-oriented point of view is preferred, in order to provide the reader with an up-to date panorama of the vast possibilities offered by lithium niobate to integrated photonics.

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Optical waveguides in lithium niobate: Recent developments and applications

Multiprotocol label switching (MPLS) is rapidly emerging as an Internet Engineering Task Force (IETF) standard intended to enhance the speed, scalability, and service provisioning capabilities in the Internet. MPLS uses the technique of packet forwarding based on labels, to enable the implementation of a simpler high-performance packet forwarding engine. This also decouples packet forwarding from routing, facilitating the provision of varied routing services independent of the packet forwarding paradigm. The authors track the evolution of this technology in relation to other existing technologies. Then an overview of the MPLS architecture and design is provided. In addition, some of the work that was a precursor to MPLS is discussed, as well as related issues and debates.

Evolution of multiprotocol label switching

The authors present a review of all-optical signal-processing technologies based on /spl chi//sup (2)/ nonlinear interactions in guided-wave devices and their applications for telecommunication. In this study, the main focus is on three-wave interactions in annealed proton-exchanged periodically poled lithium niobate waveguides due to their suitable properties with respect to nonlinear mixing efficiency, propagation loss, and ease of fabrication. These devices allow the implementation of advanced all-optical signal-processing functions for next-generation networks with signal bandwidths beyond 1 THz. In this paper, integrated structures that will allow for improvements of current signal-processing functions as well as the implementation of novel device concepts are also presented.

All-optical signal processing using /spl chi//sup (2)/ nonlinearities in guided-wave devices

We demonstrate an optical half-subtracter and half-adder module that performs simultaneous bit-wise subtraction and addition of two 5 Gbit/s RZ data streams. We generate Borrow (/X*Y) and Difference/Sum (X plus sign in circleY, or XOR) outputs using cross-gain modulation (XGM) in two parallel SOAs. Taking advantage of the gain saturation inherent to SOAs, we generate two signals, /X*Y, and X*/Y, and combine them using a passive optical coupler to generate the XOR Difference/Sum output. We use difference-frequency-generation-based lambda-conversion in a PPLN waveguide to generate the Carry (X*Y) output. The PPLN waveguide allows bit-synchronous wavelength shifting, is wide-bandwidth, and offers no intrinsic chirp. Our module uses three active elements to perform simultaneous half-subtraction and addition, and carries a maximum power penalty of 1.0 dB.

Simultaneous optical digital half-subtraction and -addition using SOAs and a PPLN waveguide.

A method for generating high power pulsed RF waveforms comprises the steps of charging a transmission line in a pulse forming network with a high-voltage and discharging the voltage on the transmission line to ground utilizing a gallium nitride photoconductive switch.

Generation of flexible high power pulsed waveforms

A steerable high-power microwave beam array includes an optical sub-system comprising a laser and an optical time delay unit and a parallel set of RF time delay units. The optical system and/or the RF delay subsystem are utilized to precisely delay the pulses from the microwave antenna elements to provide steerable beam forming.

High-power microwave beam steerable array and related methods

A Multi-Cycle Digital High Power Microwave (MCD-HPM) source includes a microwave transmission line (MTL) to which a plurality electrically charged thin film transmission lines (TFTL's) are connected by switches. The switches are activated in sequence to generate a square wave at a microwave output frequency. The activation signal is controlled by a free space time delay, which can vary the timing and/or routing of the activation signal by modifying at least one free space element, thereby adjusting the switch activation timing and varying the output frequency. In embodiments, the switches are photo-conducting switches, the activation signal is a laser beam, and the switch timing is varied by reorienting and/or repositioning mirrors and/or other elements in the free space time delay. The elements can be manually adjusted, or mounted on motorized stages and automatically controlled. Optical amplifiers can be included to compensate for losses in the time delay elements.

Mcgeehan John E

Papers

All-optical signal processing using /spl chi//sup (2)/ nonlinearities in guided-wave devices

Simultaneous optical digital half-subtraction and -addition using SOAs and a PPLN waveguide.

Generation of flexible high power pulsed waveforms

High-power microwave beam steerable array and related methods

Frequency agile high power microwave generator