This tutorial describes the basic principles and performance analysis of optical intensity modulators using electrooptic and electroabsorption effects, for use in analog and digital communication systems. These include lithium niobate modulators, semiconductor electroabsorption modulators, semiconductor Mach-Zehnder modulators, and polymer modulators.

Optical intensity modulators for digital and analog applications

Integrated Microwave photonics (IMWP) signal processing using Photonic Integrated Circuits (PICs) has attracted a great deal of attention in recent years as an enabling technology for a number of functionalities not attainable by purely microwave solutions. In this context, integrated waveguide Bragg grating (WBG) devices constitute a particularly attractive approach thanks to their compactness and flexibility in producing arbitrarily defined amplitude and phase responses, by directly acting on coupling coefficient and perturbations of the grating profile. In this article, we review recent advances in the field of integrated WBGs applied to MWP, analyzing the advantages leveraged by an integrated realization. We provide a perspective on the exciting possibilities offered by the silicon photonics platform in the field of MWP, potentially enabling integration of highly-complex active and passive functionalities with high yield on a single chip, with a particular focus on the use of WBGs as basic building blocks for linear filtering operations. We demonstrate the versatility of WBG-based devices by proposing and experimentally demonstrating a novel, continuously-tunable, integrated true-time-delay (TTD) line based on a very simple dual phase-shifted WBG (DPS-WBG).

Integrated waveguide Bragg gratings for microwave photonics signal processing

A plurality of one-dimensional planar beam forming and steering optical phased array chips form a two-dimensional-scanning solid-state lidar, enabling manufacturing of threedimensional mapping time-of-flight lidars at high yield and low cost resulting from the simplicity of said one-dimensional optical phased array chips.

Three-dimensional-mapping two-dimensional-scanning LIDAR based on one-dimensional-steering optical phased arrays and method of using same

A fiber laser amplifier system including a master oscillator that generates a signal beam. A splitter splits the signal beam into a plurality of fiber beams where a separate fiber beam is sent to a fiber amplifier for amplifying the fiber beam. A tapered fiber bundle couples all of the output ends of all of the fiber amplifiers into a combined fiber providing a combined output beam. An end cap is optically coupled to an output end of the tapered fiber bundle to expand the output beam.

All-fiber integrated high power coherent beam combination

Binary and multilevel phase-only sampling functions are proposed for the sampled fiber Bragg gratings (FBGs) with high channel count, which require significantly less refractive-index modulation than that does the sampled grating with amplitude sampling. The design using the new simulated quenching optimization with temperature rescaling results in high channel uniformity and minimum energy in the out-of-band channels. The technique can be applied to the sampled FBGs with very high channel count. A five-channel nonlinearly chirped multilevel phase-only sampled FBG for tunable chromatic dispersion compensation is demonstrated.

https://www.intranet.copl.ulaval.ca/sheng/publications/JLT03.pdf

Phased-only sampled fiber Bragg gratings for high-channel-count chromatic dispersion compensation

In this paper, we review our recent developments in the design and fabrication techniques for high-channel-count fiber Bragg gratings (FBGs). We have presented a theory for the phase-only sampled FBG and demonstrated that a sampled FBG of N channels would require radicN/etamiddot times higher maximum reflective index modulation than that of the single-channel FBG. We experimentally demonstrate a 45- and 81-channel linearly chirped FBG for nearly whole C-band dispersion compensation, which is fabricated with a novel diffraction precompensated phase mask. The grating specifications obtained agree well with the theoretical design. We have presented a novel method for multichannel FBG design, which enables us to design any kind of multichannel FBGs, where the spectrum response of each channel could be either identical or nonidentical. Particularly, the nine-channel nonlinearly chirped FBG, which is used as a simultaneous dispersion and dispersion slope compensator, has been demonstrated.

Advances in the Design and Fabrication of High-Channel-Count Fiber Bragg Gratings

Fiber Bragg gratings with phase-only superstructure ("sampling") are shown to greatly increase the reflectivity of large channel count designs. Grating fabrication is facilitated by the standard mask side-writing technique, where the entire sampling pattern is included in the phase mask. A novel phase sampling design based on binary Dammann gratings as well as continuous phase sampling functions is demonstrated and exhibits excellent channel-to-channel uniformity.

https://www.intranet.copl.ulaval.ca/sheng/publications/JoshPTL2002.pdf

Dammann fiber Bragg gratings and phase-only sampling for high channel counts

A plurality of coherent and incoherent light beams are combined into a composite high power diffraction limited beam by N oscillators (11), each transmitting light at one of N different wavelengths, each wavelength being split into M constituent beams. M beams in each of N groups are phase locked by a phase modulator (14), amplified, and coupled into an M x N fiber array (19). Beams from the array are collimated and incident 'on an optical beam combiner. The N single beams are incident and spectrally combined on a grating (25) which outputs a composite beam at a nominal 100% fill factor. A low power sample beam, taken from the N beams emerging from the optical combiner, is measured for phase deviations, from which phase correction signals are derived and fed back to the phase modulators (14).

Method and system for hybrid coherent and incoherent diffractive beam combining

An optical beam combiner and a related method for its operation, in which multiple coherent input beams are directed onto a diffractive optical element (DOE) along directions corresponding to diffraction orders of the DOE, such that the DOE generates a single output beam in a direction corresponding to a desired diffraction order, and suppresses outputs in directions corresponding to unwanted diffraction orders. The phases of the input beams are actively controlled to ensure and maintain the condition that only a single diffraction mode is present in the output of the DOE.

Joshua E. Rothenberg

Papers

Phased-only sampled fiber Bragg gratings for high-channel-count chromatic dispersion compensation

Advances in the Design and Fabrication of High-Channel-Count Fiber Bragg Gratings

Dammann fiber Bragg gratings and phase-only sampling for high channel counts

Method and system for hybrid coherent and incoherent diffractive beam combining

Coherent fiber diffractive optical element beam combiner