Christos Riziotis

Direct ultraviolet writing of channel waveguides in congruent lithium niobate single crystals

We report the fabrication of optical channel waveguides in congruent lithium niobate single crystals by direct writing with continuous-wave ultraviolet frequency-doubled Ar+ laser radiation (244 nm). The properties and performance of such waveguides are investigated, and first results are presented.

Development of channel waveguide lasers in Nd3+-doped chalcogenide (Ga:La:S) glass through photoinduced material modification

We report the development of a waveguide laser source in a neodymium-doped chalcogenide (Ga:La:S) glass. Channel waveguide structures were directly written via above band gap (=244 nm) illumination provided by a focused UV-laser beam with fluencies 1.5–150 J/cm2. Effects of photoinduced material modification in the form of surface compaction and photodensification were evident. Characterization revealed a low threshold waveguide laser with emission at 1075 nm and slope efficiency of 17%. The active device was spatially single mode and exhibited laser operation with 8.6 mW peak power and attenuation <0.5 dB cm–1.

Design considerations in optical add/drop multiplexers based on grating-assisted null couplers

The performance of a fully optimized optical add/drop multiplexer (OADM), based on null couplers and tilted Bragg gratings, is studied in detail. It is shown that maximization of the device performance involves three main optimization steps. First, the waveguide asymmetry (V/sub 2//V/sub 1/ ratio) should be optimized in order to minimize the extinction ratio of the unwanted mode at the null coupler waist. Second, the coupler taper shape should he optimized in order to further minimize the aforementioned extinction ratio. Third, the grating tilt angle and relative width can be also optimized to give negligible backreflections at the input port and minimize radiation losses. The results show that the proposed high-performance OADM configuration can meet stringent telecom specifications.

UV written waveguides using crosslinkable PMMA-based copolymers

Crosslinkable copolymers poly(methylmethacrylate/2-methacryloylethylmethacrylate) (P(MMA/MAOEMA)) were developed for waveguide applications. P(MMA/MAOEMA) can crosslink under either UV exposure or heating. The UV-induced refractive index change in unreacted P(MMA/MAOEMA) is found to depend on the fluence. UV exposure of thermally crosslinked P(MMA/MAOEMA) can induce further structure change and thus index change, and therefore, was found to be useful for creating the core layers in optical waveguides. The photosensitivity of the thermally crosslinked polymers is sufficient for the fabrication of low loss (<1 dB/cm) channel waveguides in the thermally crosslinked copolymer system.

Planar Bragg Grating Sensors—Fabrication and Applications: A Review

We discuss the background and technology of planar Bragg grating sensors, reviewing their development and describing the latest developments. The physical operating principles are discussed, relating device operation to user requirements. Recent performance of such devices includes a planar Bragg grating sensor design which allows refractive index resolution of 1.9×10−6 RIU and temperature resolution of 0.03∘C. This sensor design is incorporated into industrialised applications allowing the sensor to be used for real time sensing in intrinsically safe, high-pressure pipelines, or for insertion probe applications such as fermentation. Initial data demonstrating the ability to identify solvents and monitor long term industrial processes is presented. A brief review of the technology used to fabricate the sensors is given along with examples of the flexibility afforded by the technique.

Novel full-cycle-coupler-based optical add-drop multiplexer and performance characteristics at 40-Gb/s WDM networks

A novel configuration of an interferometric device, based on a full-cycle full (100%) coupler structure, loaded with a Bragg grating symmetrically placed into the uniform coupler waist, is proposed for use as an optical add-drop multiplexer (OADM) with simultaneously optimized add and drop actions. A general method for designing a suitable Bragg grating for optimal inscription in to the uniform coupler waist is also proposed for use in to the device design and development. The performance of the device is characterized at 40-Gb/s wavelength-division-multiplexing (WDM) networks using theoretical systems simulations and is compared directly with other alternative OADM architectures.

Growth and characterization of pulsed laser deposited lead germanate glass optical waveguides

AbstractLead germanate thin films have been grown on BK7 and silica substrates, using pulsed excimer laser deposition(PLD) at wavelengths of 193 and 248 nm, from a bulk lead germanate target under various partial pressures of oxygen.The films produced vary in colour from brown, through clear, to yellow, and a parametric study has been undertaken ofthe film properties as a function of the growth conditions. The measured losses of the lead germanate films grown onglass substrates varied from ˘2.5 to 7 dB cm y1 depending on the oxygen partial pressure used. O 1999 Elsevier ScienceB.V. All rights reserved. 1. IntroductionPulsed laser deposition (PLD) has been exten-sively researched within the past decade as acomparatively fast, easy, and flexible technique forgrowing thin films of a wide range of materials [1].Amorphous, polycrystalline, and single crystallayers are routinely grown, depending on experi-mental parameters that include target composi-tion, substrate temperature, target–substratedistance, and the presence of an ambient gas, of-ten oxygen, at moderately low partial pressures.Recent successes in crystalline growth by PLDhave permitted the demonstration of e†cient la-sing action in 2–10 lm thick layers of gadoliniumgallium garnet, GGG, grown on YAG [2,3], andalso Ti:sapphire, grown on undoped sapphire [4].The losses reported in Ref. [3], of 0.3–0.5dB cm

Effect of in-band group delay ripple on WDM filter performance

The effects of time-delay-ripple period and amplitude in 25 GHz and 100 GHz filters for operation at 10 Gb/s and 40 Gb/s, respectively, are studied. It is shown that maximum transmission penalties occur at time-delay periods of /spl sim/75% of the -20 dB data bandwidth.

Continuous wave ultraviolet radiation induced frustration of etching in lithium niobate single crystals

Illumination of the -z face of congruent lithium niobate single crystals with continuous wave (c.w.) ultraviolet (UV) laser radiation modifies the response of the surface to subsequent acid etching. A frequency doubled Ar+ laser (lambda=244 nm) was used to illuminate the -z crystal face making it resistive to HF etching and thus transforming the illuminated tracks into ridge structures. This process enables the fabrication of relief patterns in a photolithographic manner. Spatially resolved Raman spectroscopy indicates preservation of the good crystal quality after irradiation.

Fiber and Integrated Waveguide-Based Optical Sensors

1The Institute of Photonic Sciences (ICFO) and ICREA, Mediterranean Technology Park, Avenue del Canal Oĺimpic s/n, 08860 Castelldefels (Barcelona), Spain 2Photonics for Nanoapplications Laboratory, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation (NHRF), 48 Vassileos Constantinou Avenue, 11635 Athens, Greece 3Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, UK 4Department of Electrical and Computer Engineering, National Technical University of Athens, 15780 Athens, Greece