[pt] A presente tese tem por objetivo estabelecer uma metodologia de caracterização metrológica de redes de Bragg do tipo I, tipo II e tipo regenerada estimando e validando estatisticamente o resultado de medição para medições de altas temperaturas voltadas para aplicações em sensoriamento. Além das telecomunicações, as fibras óticas estão sendo empregadas em aplicações de sensoriamento, visto que, a sílica que as compõem apresenta grande eficiência como meio de transmissão de dados. A crescente demanda por medição em alta temperatura nos processos industriais possibilitou o desenvolvimento de novas tecnologias de medição além das tecnologias tradicionais já utilizadas atualmente. Desta forma, criaram-se as condições necessárias para se introduzir uma nova tecnologia de medição de temperatura com redes de Bragg que apresenta algumas vantagens se comparadas com as tecnologias tradicionais de medição. Apesar de já existirem várias pesquisas a respeito de medição de temperatura com redes de Bragg, nenhuma delas aprofundou as questões metrológicas com as respectivas estimativas das incertezas de medição que envolve todo o processo de medição e caracterização de redes de Bragg em alta temperatura. A adaptação de um sistema tradicional de calibração de instrumentos de medição de temperatura foi projetado e desenvolvido, de tal forma que possibilitou a caracterização dos diferentes tipos de redes. Observou-se que os resultados de medição e as estimativas das incertezas de medição obtidos para todas as redes, se aproximaram satisfatoriamente dos modelos teóricos utilizados, confirmando a adequação dos sistemas de medição de temperatura e sensoriamento ótico. / [en] This thesis aims to establish a methodology for the metrological characterization of Bragg gratings type I, type II and type regenerated statistically thereby estimating and validating the measurement results for high temperature sensing applications. Beyond telecommunications applications, optical fibers are still used for optical sensing, since the silica fiber has great optical efficiency for data transmission. The growing demand for high-temperature measurements in industrial processes has enabled the development of new measurement technologies beyond the traditional technologies already in use today. Thus were created the conditions necessary to introduce a new technology of temperature measurement with Bragg gratings which presents some advantages compared with traditional technologies of measurement. Although there are several prior studies none of those examined the by others about temperature measurement with Bragg gratings, metrological issues, and is particular, the estimate of the measurement uncertainties surrounding the whole process of measurement and characterization of Bragg gratings at high temperature. The adaptation of a traditional system of calibration instruments for temperature measurement was developed and designed in such a way that allowed the characterization of different types of gratings. It was observed that the measurement results and the estimated uncertainties of the measurements obtained for all gratings, successfully approached the theoretical models used, confirming the adequacy of the measurement of temperature and optical sensing.

This thesis discusses a new scheme for generating radiation in the mid infrared spectral region, especially the 3.5-5 µm range. The scheme uses established Nd3+-lasers at 1.06 µm and down conversion in nonlinear optical crystals. The down conversion is made by two optical parametric oscillators (OPO) in series. The second OPO is a classical OPO using a zink germanium phosphide (ZGP) crystal. ZGP is the best nonlinear material available for the 4-8 µm spectral range, but it is absorbing below 2 µm. The new development presented in this thesis is the OPO used to convert the 1.06 µm laser radiation to a suitable OPO pump near 2 µm. The OPO uses a type I quasi phase-matched crystal, which accesses high nonlinearities and avoids walk-off. The problem with type I OPOs close to degeneracy is the broad bandwidth of the generated radiation, which reduces the efficiency of a second OPO. This has been solved with a spectrally selective cavity using a volume Bragg grating output coupler. Unlike other bandwidth limiting schemes this introduces no intracavity losses and thus efficient OPO operation is achievable. Narrow linewidth (~0.5 nm) OPO operation has been achieved with periodically poled LiNbO3 (PPLN) and periodically poled KTiOPO4 (PPKTP) while locking the signal wavelength at 2008 nm and simultaneously generating an idler at 2264 nm. A high average power PPLN OPO with 36 % conversion efficiency and 47 % slope efficiency is reported. Operation very close to degeneracy at 2128 nm with the narrowband signal and idler peaks separated by 0.6 nm was demonstrated in a PPKTP OPO. Both the signal at 2008 nm and the combined signal and idler around 2128 nm from the PPKTP OPOs have been used to show efficient pumping of a ZGP OPO. The maximum conversion efficiency from 1 µm to the mid-IR demonstrated is 7 % with a slope efficiency of 10 %. This is not quite as high as what has been presented by other authors, but the experiments reported here have not shown the optimum efficiency of the new scheme. Relatively simple improvements are expected to give a significant increase in conversion efficiency. / QC 20101108

Laser beams can be manipulated by volume diffractive elements in addition to conventional optical elements like mirrors, lenses, and beam splitters. Conventional optical elements can be described by applying the basic laws of reflection and refraction at the surfaces of the elements. Even diffraction by surface gratings utilizes relatively simple mathematics. This is to be contrasted with the volume diffraction, which requires coupled wave theory in the slowly varying envelope approximation (SVEA) to obtain accurate results. Efficient spatially distributed diffraction of laser beams is possible due to the high coherence of laser light, and it occurs at specific resonant Bragg conditions. This research work is inspired and driven by the successful development of recording technology for robust, high-efficiency volume Bragg gratings (VBGs) in photo-thermo-refractive (PTR) glass. Mostly VBGs of the reflective type are discussed in this dissertation. Starting with an analysis of electro-magnetic wave propagation in layered media, we have reformulated Fresnel and volume reflection phenomena in terms of a convenient parameter – strength of reflection. The influence that the different non-uniformities inside a VBG have on its spectral properties has been examined. One important result of this work is the proposal of moiré VBG and the derivation of an analytical expression for its bandwidth. A multiplexed VBG used as a coherent combiner is discussed as well. Beam distortion via transmission through and/or reflection by a heated VBG due to residual absorption is analyzed.

Photo-thermo-refractive (PTR) glass is an ideal photosensitive material for recording phase volume holograms. It is a homogeneous multi-component silicate glass that demonstrates all the advantages of optical glass: thermal stability, high laser damage threshold, and a wide transparency range. Moreover the ability to record phase patterns (i.e. spatial refractive index variations) into PTR glass has resulted in the fabrication of volume holograms with diffraction efficiency greater than 99%. The conventional method of recording a hologram in PTR glass relies on exposure to continuous-wave ultraviolet laser radiation. In this dissertation the interaction between infrared ultrashort laser pulses and PTR glass is studied. It is shown that photosensitivity in PTR glass can be extended from the UV region to longer wavelengths (near-infrared) by exposure to ultrashort laser pulses. It is found that there exists a focusing geometry and laser pulse intensity interval for which photoionization and refractive index change in PTR glass after thermal development occur without laser-induced optical damage. Photoionization of PTR glass by IR ultrashort laser pulses is explained in terms of strong electric field ionization. This phenomenon is used to fabricate phase optical elements in PTR glass. The interaction between ultrashort laser pulses and volume holograms in PTR glass is studied in two laser intensity regimes. At intensities below ~10^12 W/cm^2 properties such as diffraction efficiency, angular divergence, selectivity, and pulse front tilt are shown to agree with the theory of linear diffraction for broad spectral width lasers. A volume grating pair arrangement is shown to correct the laser pulse distortions arising from pulse front tilt and angular divergence. At higher intensities of irradiation, nonlinear generation and diffraction of third harmonic is observed for three types of interactions: sum-frequency generation, front-surface THG generation, and THG due to phase-matching with a grating formed by modulation of the nonlinear refractive index of PTR glass.

Beam combining techniques have become an important tool in the design of high-power high-brightness laser systems. Spectral beam combining (SBC) is an incoherent combining technique that does not require phase control of sources, allowing for a stable and robust system. Using SBC, beams from an array of lasers with each element operated at a different wavelength are combined into a single near-diffraction-limited beam with the same aperture using dispersive optical elements. SBC by means of volume Bragg gratings (VBGs) utilizes unique spectral response of VBGs: diffraction efficiency is close to unity when the Bragg condition is satisfied and is close to zero at multiple points corresponding to particular wavelength offsets from Bragg condition. High-efficiency VBGs can be recorded in UV-sensitive photo-thermo-refractive (PTR) glass. Narrow-band reflecting VBGs allow multi-channel SBC with high spectral density of channels. In this dissertation, experimental results of SBC with high spectral density of combined channels in two spectral regions of interest (1064 and 1550 nm) are reported. The behavior of narrow-band VBGs under high-power laser radiation is investigated. A laser system with kW-level output power and near-diffraction-limited divergence of spectrally-combined output beam is demonstrated. The system combines five randomly-polarized Yb-doped fiber lasers with 0.5 nm spectral separation in central wavelengths using narrow-band reflecting VBGs with absolute efficiency of combining > 90%. A novel design of a multi-channel high-power SBC system is suggested. In this approach, a common-cavity is created for all channels such that wavelengths of the sources are passively controlled by the combination of a common output coupler and intra-cavity VBGs which also act as combining elements. Laser wavelengths are automatically selected to match resonant wavelengths of respective VBGs. We report successful demonstration of a passively-controlled SBC system consisting of two amplifiers in a common cavity configuration. A compact and rugged monolithic SBC module based on multiplexed VBGs is introduced. Experimental results of a four-channel implementation of such module are discussed. Modular design of high-power laser systems is suggested with multiple modules arranged in a series. We show that with basic combining parameters achieved up to date, laser systems with 10 kW output power can be constructed using this arrangement. Further scaling to 100 kW power level is discussed.

Few-mode fibers (FMFs) and multimode fibers (MMFs) can provide much higher data-carrying capacities compared with single-mode fibers. But in order to achieve this goal, one must address the challenge of intermodal coupling and dispersion. Therefore the ability to accurately control the optical signal propagation in FMFs/MMFs can play a pivotal role in FMF/MMF applications. This thesis demonstrates the ability to excite, in FMFs and MMFs, the desired linearly polarized (LP) modes as well as their superpositions through adaptive optics (AO). Specifically, in the case of step-index FMFs, a phase-only spatial light modulator (SLM) is employed to manipulate the light at the fiber input end, driven by the feedback signal provided by the correlation between the charge coupled device (CCD) camera captured images at the fiber output end and the target light intensity profile. Through such an adaptive optical system, any arbitrarily selected LP modes can be excited at the distal end of the four-mode and seventeen-mode fibers, respectively. For a graded-index MMF with a uniform Bragg grating, we use a deformable mirror (DM) to perform the wavefront modulation at the fiber input end, where the feedback is based on the ratio of the grating-reflected signal power to the transmitted signal power. At the Bragg grating position of this highly multimode fiber, any desired principal mode groups can be successfully chosen. These experimental results suggest that adaptive control of optical wavefront in FMFs/MMFs is indeed feasible. / Master of Science / Optical fibers, in terms of the number of modes they support, can be generally divided into single-mode fibers (SMFs), and few-mode fibers/multimode fibers (FMFs/MMFs). FMFs/MMFs can provide much higher data-carrying capacities than SMFs. For example, an FMF/MMF that supports M modes can ideally increase the data transmission rate by a factor of M, where each mode can serve as a distinct communication channel. However, in order to achieve good performance, one must accurately control signal propagation in FMFs/MMFs, which are often degraded due to the multiple-mode nature. This thesis demonstrates the ability, using adaptive optics (AO), to control signal propagation in FMFs and a highly MMF, respectively. Specifically, in the case of FMFs, a phase-only spatial light modulator (SLM) is employed to manipulate the light at the fiber input, driven by AO feedback signal provided by the similarity between the real-time fiber output image and the target mode profile. Through such an adaptive optical system, any desired linearly-polarized (LP) modes can be excited at the output of the four-mode and seventeen-mode fibers, respectively. For the highly MMF with uniform Bragg grating, we use a deformable mirror (DM) to perform the wavefront modulation at the fiber input, where AO feedback is provided by the fiber Bragg grating (FBG) reflectivity. At the FBG position, any desired principal mode groups can be successfully chosen. These experimental results suggest that adaptive control of optical wavefront in FMFs/MMFs is indeed feasible, and may find a large number of applications in optical communication, sensing, and imaging.

Few mode fibers and multimode fibers (MMFs) are traditionally regarded as unsuitable for important applications such as communications and sensing. A major challenge in using MMFs for aforementioned applications is how to precisely control the waveguide modes propagating within MMFs. In this thesis, we experimentally demonstrate a generic method for controlling the linearly polarized (LP) modes within a two-mode fiber (TMF). Our method is based on adaptive optics (AO), where one utilizes proper feedback signals to shape the wavefront of the input beam in order to achieve the desired LP mode composition. In the first part of this thesis, we demonstrate the feasibility of AO-based mode control by using the correlation between the experimentally measured field distribution and the desired mode profiles as feedback for wavefront optimization. Selectively excitation of pure LP modes or their combinations at the distal end of a TMF are shown. Furthermore, we demonstrate that selective mode excitation in the TMF can be achieved by using only 5×5 independent phase blocks. Afterwards, we extend our AO-based mode control method to more practical scenarios, where feedback signals are provided by all-fiber devices such as a directional fiber coupler or fiber Bragg gratings (FBGs). Using the coupling ratio of a directional coupler as feedback, we demonstrate adaptive control of LP modes at the two output ports of the directional coupler. With feedback determined by the relative magnitude of optical power reflected by a FBG and the transmitted power, selective excitations of the LP01 and the LP11 modes are experimentally shown. As the final component of this thesis, we experimentally combine the AO-based mode control with time-division-multiplexing. By choosing reflected pulses with appropriate arrival time for mode control, we can selectively excite the LP11 mode at different FBG locations within the TMF, based on the ratio of optical signals reflected by FBGs in the TMF and the transmitted signal. Using two lasers set at the two FBG peak reflection wavelengths associated with the LP01 and the LP11 modes, we can accomplish AO-based mode control within a TMF by using only the reflection signals from the FBG. By using the ratio of the reflected signals of two lasers as feedback, we demonstrate selective excitation of almost pure LP01 or LP11 mode at the FBG location within the TMF. The method developed in this thesis is generic and can be extended to many other applications using appropriately chosen feedback signals. It is possible to generalize the AO-based mode control method to MMF as well. This method may find important applications in MMF-based communication, sensing and imaging et. al. in the future. / Ph. D.

En utilisant la combinaison spectrale de faisceaux, des faisceaux provenant de plusieurs lasers opérant à des longueurs d'onde différentes sont combinés en un seul faisceau avec une divergence proche de la limite de diffraction. Cette thèse présente des résultats expérimentaux de combinaison spectrale de faisceaux avec une grande densité spectrale dans deux régions spectrales d'intérêt (1064 et 1550 nm). Un système laser avec une puissance de sortie de l'ordre du kW et une divergence du faisceau combiné proche de la limite de diffraction est démontré. Le système combine cinq fibres lasers dopées Ytterbium polarisées de façon aléatoire avec une séparation spectrale de 0.5 nm en utilisant des réseaux de Bragg volumiques réfléchissants présentant une largeur spectrale étroite et une efficacité de combinaison absolue supérieure à 90%. La projection d'un tel système pour des puissances de sortie de l'ordre de 100 kW est discutée. / Using spectral beam combining (SBC), beams from an array of lasers with each element operated at a different wavelength are combined into a single near-diffraction-limited beam with the same aperture using dispersive optical elements. In this thesis, experimental results of SBC with high spectral density of combined channels in two spectral regions of interest (1064 and 1550 nm) are reported. A laser system with kW-level output power and near-diffraction-limited divergence of spectrally-combined output beam is demonstrated. The system combines five randomly-polarized Yb-doped fiber lasers with 0.5 nm spectral separation in central wavelengths with absolute efficiency of combining > 90% using narrow-band reflecting volume Bragg gratings recorded in photo-thermo-refractive glass. Scaling of such systems to 100 kW power level is discussed.

The main objectives of this thesis were to develop a lowtemperature PECVD process suitable for optoelectronicintegration, and to optimize silica glass composition forUV-induced modifications of a refractive index in PECVDfabricated planar devices. The most important achievement isthe successful development of a low temperature silicadeposition, which for the first time makes it is possible tofabricate good quality low loss integrated components whilekeeping the temperature below 250oC during the entirefabrication process. Two strong absorption peaks thatappear at1.5 mm communication window due to N-H and Si-H bonds have beencompletely eliminated by process optimization. This openspossibilities for monolithic integration with other,temperature sensitive devices, such as semiconductor lasers anddetectors, or polymer-based structures on the common siliconplatform. PECVD technology for low loss amorphous silicon inapplication to SiO2/Si based photonic crystal structures hasbeen also optimized to remove hydrogen incorporated during thedeposition process, responsible for the porosity of thedeposited material and creation of similar to silica absorptionbands. Change of the refractive index of germanium doped silicaunder UV irradiation is commonly used for fabrication of UVinduced fiber Bragg gratings. Here we describe our achievementsin fabrication of fiber Bragg gratings and their application todistributed sensor systems. Recently we have built up a laserlab for UV treatment in application to planar technology. Wehave demonstrated the high photosensitivity of PECVD depositedGe-doped glasses (not thermally annealed) even without hydrogenloading, leading to a record transmission suppression of 47dBin a Bragg grating photoinduced in a straight buried channelwaveguide. We have also used a UV induced refractive indexchange to introduce other device modifications or functions,such as phase shift, wavelength trimming and control ofpolarization birefringence.The developed low temperature technology and the UVprocessing form a unique technology platform for development ofnovel integrated functional devices for optical communicationsystems. A substantial part of the thesis has been devoted tostudying different plasma deposition parameters and theirinfluence on the optical characteristics of fabricatedwaveguides to find the processing window giving the besttrade-off between the deposition rate,chamber temperatureduring the process, optical losses and presence of absorptionbands within the interesting wavelength range. The optimalconditions identified in this study are low pressure (300-400mTorr), high dilution of silane in nitrous oxide and high totalflow (2000 sccm), low frequency (380 KHz) RF source and high RFpower levels (800-1000 W). The thesis provides better understanding of the plasmareactions during the deposition process. RF Power is the keyparameter for increasing the rate of surface processes so as toaccommodate each atomic layer in the lowest energy statepossible. All the process conditions which favor a moreenergetic ion bombardment (i.e. low pressure, low frequency andhigh power) improve the quality of the material, making it moredense and similar to thermal oxide, but after a certain pointthe positive trend with increasing power saturates. As theenergy of the incoming ion increases, a competing effect setsin at the surface: ion induced damage and resputtering. Finally, the developed technologies were applied for thefabrication of some test and new concept devices for opticalcommunication systems including multimode interference (MMI)-based couplers/splitters, state-of-the-art arrayed waveguidegrating-based multi/ demultiplexers, the first Bragg gratingassisted MMI-based add-drop multiplexer, as well as moreresearch oriented devices such as a Mach-Zehnder switch basedon silica poling and a Photonic Crystal-based coupler. <b>Keywords:</b>silica-on-silicon technology, PECVD, plasmadeposition, photonic integrated circuits, planar waveguidedevices, UV Bragg gratings, photosensitivity, arrayed waveguidegratings, multimode interference couplers, add-dropmultiplexers.

I den här avhandlingen visas hur lasrar och optiska parametriska oscillatorer (OPO:er) kan styras spektralt med hjälp av volymbraggitter. Volymbraggitter utgörs av ett periodiskt varierande brytningsindex som skrivits i ett fototermorefraktivt glas. Gittret reflekterar därmed en specifik våglängd som bestäms av perioden hos modulationen, och kan tillverkas med smal bandbredd och hög reflektans beroende på modulationens längd och styrka. En teoretisk modell har utvecklats för reflektiva volymbraggitters egenskaper om den infallande strålen har en större vinkelspridning än gittrets vinkeltolerans. Detta kan bl.a. inträffa i en laserkavitet där gittret används vid snett infall, och en teoretisk beskrivning är därför ett viktigt redskap för att kunna designa sådana lasrar. Spektral kontroll av ett antal fasta tillståndslasrar med hjälp av volymbraggitter har i försök påvisats, och lasern har därvid både kunnat avstämmas spektralt samtidigt som en avsmalnad spektral bandbredd erhållits. Lasern kan göras väldigt enkel genom att byta ut en av kavitetsspeglarna mot gittret. Tack vare gittrets goda spektrala urvalsmekanism kan lasern låsas var som helst i förstärkningsspektrumet. De tekniker och lasrar som demonstrerats experimentellt är följande: Lasring i en enda longitudinell mod erhölls både för en diodpumpad ErYb:glas-laser vid 1553 nm med ca 10 mW:s effekt och 90 kHz linjebredd samt för en diodpumpad Nd:GdVO4-laser vid 1066 nm med 0.85 W:s effekt. Lasrarnas våglängd kunde avstämmas över större delen av gittrets bandbredd på ca. 30 GHz. Genom att bygga Nd:GdVO4-lasern med en monolitisk kavitet kunde även en spektralt synnerligen stabil laser erhållas med under 40 MHz bandbredd. Tillämpningar för dessa lasrar finns både inom spektroskopi samt som källor för intrakavitetsfördubbling till synliga våglängder. Genom att använda gittret som inkopplingsspegel går det även att framställa lasrar med en väldigt låg kvantdefekt, som därför får minskad värmeutveckling i lasermediet. Detta medger i sin tur att lasrar med höga medeleffekter kan konstrueras, som kan användas bl.a. för olika former av materialbearbetning. I detta arbete har lasrar med låg kvantdefekt byggts med Yb:KYW som laserkristall; både en laser vid 998 nm på 3.6 W som diodpumpades vid 982 nm och med en bandbredd på 10 GHz, samt en laser vid 990 nm på 70 mW som pumpades av en Ti:safir-laser vid 980 nm. Om volymbraggittret används vid snett infall kan den reflekterade våglängden avstämmas genom att gittret roteras. Denna princip användes i en diodpumpad Yb:KYW-laser till att erhålla en brett avstämbar laservåglängd mellan 996 nm och 1048 nm med en maximal effekt på 3 W och med 10 GHz bandbredd. Genom att placera gittret i en retroreflektor kunde avstämningen göras utan att kaviteten behövde linjeras om. En laser som denna kan exempelvis användas för olika typer av materialkarakterisering och spektroskopi. Med optiska parametriska oscillatorer (OPO:er) kan laserljus omvandlas till nya våglängder. Därmed kan OPO:er användas som koherenta ljuskällor där inga effektiva lasrar existerar. OPO-processen kan göras effektiv om en pulsad pump används, och den genererade våglängden kan enkelt styras med hjälp av periodiskt polade (PP) icke-linjära kristaller, såsom PP-KTiOPO4, som användes i detta arbete. En nackdel med OPO:er är att i allmänhet är den genererade signalen tämligen spektralt bredbandig. Signalens bandbredd kan dock avsmalnas betydligt om ett spektralt filter såsom ett volymbraggitter används. Genom att byta ut en av speglarna i OPO-kaviteten mot gittret kan utformningen av OPO:n göras väldigt enkel. I en OPO med en signalvåglängd på 975 nm kunde en avsmalning av bandbredden till 50 GHz påvisas med hjälp av ett braggitter. Detta motsvarar 20 gångers minskning jämfört med om en konventionell spegel används. Som mest erhölls en pulsenergi på 0.34 mJ i signalen. Genom att rotera gittret kunde våglängden avstämmas 21 THz. För att förenkla avstämningen konstruerades även en OPO med gittret i en retroreflektor, samtidigt som kaviteten var av ringtyp. I denna OPO vid en våglängd på 760 nm och med en pulsenergi i signalen på upp till 0.42 mJ erhölls en bandbredd på 130 GHz och ett avstämningsområde på 2.6 THz. Slutligen har en OPO vid 1 µm konstruerats med ett gitter med en transversellt varierande period, s.k. chirp. Därigenom kan våglängden avstämmas väldigt enkelt genom att bara flytta gittret transversellt. En tillämpning av dessa OPO:er är såsom ljuskällor i olika typer av laserbaserade sensorer, i vilka en specifik och stabil våglängd erfordras. Dessutom kan de smalbandiga OPO:erna användas som första steg i ickelinjära processer i flera steg. Smal bandbredd är då viktig för effektiviteten i den påföljande ickelinjära omvandlingen i nästa steg. / The object of this thesis is to explore the usage of reflective volume Bragg gratings in photo-thermo-refractive glass for spectral control of solid-state lasers and optical parametric oscillators, to build tunable and narrowband coherent light-sources. In order to provide a design tool for use of reflective volume Bragg gratings in laser cavities, a theory was developed that describes the performance of the gratings if the incident beam has finite width with an angular spectrum that is comparable to the grating's angular acceptance bandwidth. Spectral control was demonstrated in a number of cw solid-state lasers, in terms of narrow bandwidth and tunable wavelength, by use of a volume Bragg grating. The design could be made very simple by replacing one of the cavity mirrors with the grating. Thanks to the grating's strong spectral selectivity, the lasers could be locked anywhere in the gain spectrum, while the laser bandwidth was substantially narrowed. In particular, the following lasers were demonstrated: Single-longitudinal-mode lasing in ErYb:glass at 1553 nm with 90 kHz linewidth and in Nd:GdVO4 at 1066 nm with a linewidth below 40 MHz. Very low quantum defect in Yb:KYW lasers, diode-pumped at 982 nm and lasing at 998 nm with 10 GHz bandwidth, as well as Ti:sapphire-pumped at 980 nm and lasing at 990 nm. An Yb:KYW laser that was widely tunable from 996 nm to 1048 nm with 10 GHz bandwidth. In nanosecond pulsed optical parametric oscillators (OPOs) based on periodically poled KTiOPO4, narrowband operation and a tunable wavelength were demonstrated with a volume Bragg grating as a cavity mirror. At a signal wavelength of 975 nm, the bandwidth was 50 GHz, a reduction by 20 times compared to using a conventional mirror. A tuning range of 21 THz was also demonstrated. In another OPO at a signal wavelength of 760 nm, a ring-cavity design was demonstrated to provide convenient tuning. A tuning range of 2.6 THz and a bandwidth of 130 GHz was shown. Also, narrowband operation and tuning in an OPO around 1 µm was demonstrated by use of a transversely chirped Bragg grating. / QC 20100813