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  • 251.
    Jelger, Pär
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Increased spectral density in an Yb-doped fiber laser using two identical volume Bragg gratings2009Konferansepaper (Fagfellevurdert)
  • 252.
    Jelger, Pär
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Narrow linewidth dual volume-bragg-grating locked ytterbium-doped fiber-laser2009Inngår i: Advanced Solid-State Photonics (ASSP) 2009, Optical Society of America, 2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Two identical highly reflective volume Bragg gratings are used in tandem to lock an ytterbium doped fiber laser. A narrow linewidth (<2GHz) and high efficiency (>70%) is achieved with output powers above 7W.

  • 253.
    Jelger, Pär
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Narrow linewidth high output-coupling dual VBG-locked Yb-doped fiber laser2010Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, nr 5, s. 4980-4985Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two equal highly reflective volume Bragg gratings (VBGs) were used to lock an Yb-doped fiber laser. By heating one of the VBGs, its center wavelength was shifted and the laser was locked on the overlap between the main peak of one grating and the side-lobe of the other creating a large outcoupling with high spectral selectivity. With this simple arrangement, unidirectional output is achieved with a narrow linewidth (2.5GHz), high efficiency (>70%) and with an output power above 7W.

  • 254.
    Jelger, Pär
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Seger, Kai
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Cryogenic cooling of Ytterbium fiber lasers for increased efficiency and stability2009Konferansepaper (Fagfellevurdert)
  • 255.
    Jelger, Pär
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Seger, Kai
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Highly efficient temporally stable narrow linewidth cryogenically cooled Yb-fiber laser2009Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 17, nr 10, s. 8433-8438Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cryogenic cooling is an effective way of increasing the efficiency in many solid-state lasers. In fiber lasers however, while the efficiency is increased, a reduced reabsorption in combination with reduced homogeneous broadening tends to broaden the linewidth, yielding a low spectral power density of the laser emission. In this work we lock a cryogenically-cooled Yb-doped fiber laser with a volume Bragg grating to overcome this problem and achieve a temporally stable narrow linewidth highly efficient laser. We extract 11.4-W of output power in spectral window of less than 0.4-nm with 14.5-W of launched pump light.

  • 256.
    Jelger, Pär
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Seger, Kai
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Spectral Narrowing of Highly Efficient Cryogenically Cooled Ytterbium Doped Fiber Lasers2009Inngår i: 2009 Conference on Lasers and Electro-Optics and 2009 Conference on Quantum Electronics and Laser Science Conference, CLEO/QELS 2009, IEEE , 2009, s. 994-995Konferansepaper (Fagfellevurdert)
    Abstract [en]

    VBGs can efficiently be used to mitigate the spectrally broad output from cryogenically cooled Yb-fiber lasers. We extract 11.5-W of output power in spectral window of less than 0.4-nm with 14.5-W of launched pump light.

  • 257. Johansson, S.
    et al.
    Spiekermann, S.
    Wang, S.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Karlsson, H.
    Ekvall, K.
    Coherent light source based on sum-frequency mixing2005Patent (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    A method and a device for generating visible coherent radiation is disclosed. The visible coherent radiation is generated by sum-frequency mixing of a first fundamental beam from a diode laser and a second fundamental beam from a diode-pumped solid-state laser. The mixing is performed by means of a quasi-phasematching element provided within the resonant cavity of the solid-state laser. The first fundamental beam is stabilized by providing feedback to the diode laser.

  • 258.
    Johansson, S.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Spiekermann, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Ekvall, K.
    Wang, S.
    Generation of turquoise light by SFM a DPSSL and a laser diode in a single-pass configuration2004Konferansepaper (Fagfellevurdert)
  • 259.
    Johansson, Sandra
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Bjurshagen, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Koch, Ralf
    An all solid-state UV source based on a frequency-quadrupled, passively Q-switched 946 nm laser2007Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, nr 2, s. 449-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report a 236 nm light source with 20 mW of average power based on critically phase-matched second-harmonic generation in a beta-barium borate crystal at room temperature. The fundamental light source was a passively Q-switched 946 nm Nd: YAG laser tunable from 10-38 kHz and with a pulse length of 16 ns. In the generation of 473 nm light, periodically poled KTP and BiBO was compared in terms of conversion efficiency and stability.

  • 260.
    Johansson, Sandra
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Hansson, Renee
    Ekvall, Katrin
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laser diode beam shaping with GRIN lenses using the twisted beam approach and its application in pumping of a solid-state laser2007Inngår i: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 274, nr 2, s. 403-406Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report a novel beam shaping method for laser diodes based on the concept of twisted Gaussian Schell-model beams using GRIN lenses. This method enables a more symmetric pump as well as a compact setup for pumping of solid-state lasers. In the experiment with a standard 2 W diode, the beam quality factors in the two orthogonal directions were equalized to M-x(2) approximate to 24 and M-y(2) approximate to 18, respectively, which pumped an intra-cavity frequency-doubled Nd:YAG laser at 946 run with an output of 28 mW at 473 nm.

  • 261. Jonsson, P.
    et al.
    Kullander, F.
    Vahlberg, C.
    Jelger, Pär
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Tiihonen, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Wästerby, P.
    Tjärnhage, T.
    Lindgren, M.
    Spectral detection of ultraviolet laser induced fluorescence from individual bioaerosol particles2006Inngår i: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 6398Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present results of a measurement system designed for detecting the fluorescence spectrum of individual aerosol particles of biological warfare agents excited with laser pulses at wavelengths around 290 or 340 nm. The biological aerosol is prepared and directed into a narrow air beam. A red laser is focused on the aerosol beam and a trigger photomultiplier tube monitor the presence of individual particles by measuring the scattered light. When a particle is present in the detection volume, a laser pulse is triggered from an ultraviolet laser and the fluorescence spectrum is acquired with a spectrometer based on a diffraction grating and a 32 channels photomultiplier tube array with single-photon sensitivity. The spectrometer measures the fluorescence spectra in the wavelength region from 300 to 800 nm. In the experiment we used different simulants of biological warfare agents. These bioaerosol particles were excited by a commercial available gas laser (337 nm), or a laser (290 nm) that we have developed based on an optical parametric oscillator with intracavity sum-frequency mixing. In the analysis of the experiments we compare the measured signals (fluorescence spectra, total fluorescence energy and the scattered energy) from the individual bioaerosol particles excited with the two different ultraviolet wavelengths.

  • 262. Kabakova, Irina V.
    et al.
    Yu, Zhangwei
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Halliwell, David
    Fonjallaz, Pierre-Yves
    Tarasenko, Oleksandr
    de Sterke, C. Martijn
    Margulis, Walter
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Switching and dynamic wavelength conversion in a fiber grating cavity2012Inngår i: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 29, nr 1, s. 155-160Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Switching and dynamic wavelength conversion of light are demonstrated in a fiber grating cavity detuned by high-voltage electrical pulses. The cavity dynamics is studied using a heterodyne technique in which the frequency-shifted light, trapped by the cavity, mixes with the backreflected light at the incident frequency. We find that the frequency shift scales linearly with the energy of the electric driving pulses.

  • 263. Karlsson, G.
    et al.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Fragemann, A.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Generationof 100kW level pulses at 1.53 µm un the diode pumped Er-Yb:glass laser-PPKTPoptical parametric amplifier system2002Konferansepaper (Fagfellevurdert)
  • 264. Karlsson, G.
    et al.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Tellefsen, Jens Aage
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Denker, B. I.
    Osiko, V.
    Sverchkov, S.
    Co2+: MgAl2O4 Crystalas saturable absorbers for diode-pumped Q-switched Er:Yb glass lasers2000Konferansepaper (Fagfellevurdert)
  • 265. Karlsson, G.
    et al.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Tellefsen, Jens Aage
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Denker, B.
    Osiko, V.
    Sverchkov, S.
    Co2+: MgAl2O4Crystal as saturable absorbers in diode-pumped Q-switched Er:Yb glass lasers2001Konferansepaper (Fagfellevurdert)
  • 266. Karlsson, H.
    et al.
    Arvidsson, G.
    Olsson, M.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Periodically poled materials from the KTP family for usein optical parametric oscillators1998Konferansepaper (Fagfellevurdert)
  • 267. Karlsson, H.
    et al.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Diode laser frequency doubling in periodically poledRbTiOPO41996Konferansepaper (Fagfellevurdert)
  • 268. Karlsson, H.
    et al.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Electric field poling of chemically processed flux grownKTiOPO41997Konferansepaper (Fagfellevurdert)
  • 269. Karlsson, H.
    et al.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Hansson, G.
    Henriksson, P.
    Arvidsson, G.
    Periodically poled RbTiOAsO4 fornonlinear frequency conversion1996Konferansepaper (Fagfellevurdert)
  • 270. Karlsson, H.
    et al.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Henriksson, P.
    Arvidsson, G.
    Nonlinear interactions in periodically poled RbTiOAsO41996Konferansepaper (Fagfellevurdert)
  • 271. Karlsson, H.
    et al.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Henriksson, P.
    Arvidsson, G.
    Second-Harmonic Generation in Periodically PoledRbTiOAsO41996Konferansepaper (Fagfellevurdert)
  • 272. Karlsson, H.
    et al.
    Olsson, M.
    Arvidsson, G.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Bäder, U.
    Borsutzky, A.
    Wallenstein, R.
    Wickström, S.
    Gustafsson, M.
    High power nanosecond optical parametric oscillator at1.6 μm based on periodically poled RbTiOAsO41998Konferansepaper (Fagfellevurdert)
  • 273. Karlsson, H.
    et al.
    Pierrou, M.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    A quasi-phasematched intracavity frequency doubledminiature laser1996Konferansepaper (Fagfellevurdert)
  • 274. Kellner, T.
    et al.
    Czeranowsky, C.
    Huber, G.
    Pierrou, M.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Karlsson, H.
    High power blue light generation by intracavityfrequency doubling with a first order quasi-phasematched KTiOPO4crystal1998Konferansepaper (Fagfellevurdert)
  • 275. Kennedy, G. T.
    et al.
    Reid, D. T.
    Miller, A.
    Ebrahimzadeh, M.
    Karlsson, H.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    A picosecond optical parametric oscillator based onperiodically poled RbTiOAsO41998Konferansepaper (Fagfellevurdert)
  • 276. Kennedy, G. T.
    et al.
    Reid, D. T.
    Miller, A.
    Ebrahimzadeh, M.
    Karlsson, H.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    "Mid-infrared picosecond optical parametricoscillator based on periodically poled RbTiOAsO41998Konferansepaper (Fagfellevurdert)
  • 277. Kennedy, G.T.
    et al.
    Reid, D. T.
    Miller, A.
    Ebrahimzadeh, M.
    Karlsson, H.
    Arvidsson, G.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Mid-infrared picosecond optical parametric oscillatorbased on periodically poled RbTiOAsO41998Konferansepaper (Fagfellevurdert)
  • 278.
    Kianirad, Hoda
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Studies on Domain Dynamics in Nonlinear Optical Ferroelectric Oxide Crystals2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Nonlinear optical frequency conversion is the key technology for modifying laser output radiation, in order to target specific applications. The most powerful technique to obtain tailored second-order nonlinear interactions is the quasi-phasematching (QPM) approach. QPM is based on periodic modulation of the medium’s nonlinearity and allows versatile and efficient frequency conversion in the whole transparency region of the material. QPM is commonly implemented in ferroelectric oxide crystals by periodically inverting the spontaneous polarization, so-called, periodic poling. However, in order to achieve QPM structures of practical relevance, both the optical properties of the material and the domain engineering techniques have to be suitable for the targeted nonlinear interaction.

    Rb-doped KTiOPO4 (RKTP) and vapor-transport-equilibrated stoichiometric LiTaO3 (VTE-SLT) are two of the most promising ferroelectric oxides used for nonlinear optics. The former is suitable for high peak-power applications and for engineering of QPM devices with sub-µm periodicity. The latter shows a short cut-off wavelength with low linear absorption, which makes it very attractive for UV-light generation. However, in order to fully exploit the potential of these two materials, it is of utmost importance to understand the domain dynamics and stability from a fundamental point of view, as well as to investigate ways to overcome their limitations.

    This thesis presents studies on domain dynamics and stability in these two materials. A novel method for periodic poling of RKTP has been investigated. The method, based on using a micro-structured silicon chip as the contact electrode, has been used to fabricate periodically poled RKTP crystals with 9.01 µm period. The samples became well-poled and showed high conversion efficiency for second harmonic generation. The domain dynamics, when the silicon stamp was used as an electrode were studied, showing potential for short-pitch poling and complex patterning.

    Furthermore, the domain stability in RKTP during thermal annealing at high temperatures was investigated. The results show anisotropic domain wall motion, with severe domain contraction along the crystallographic b-axis when the periodicity was reduced. A technique to suppress this domain contraction was developed based on dicing away the edges of the QPM grating so that the domain b-faces terminate in air. This gave excellent results for a broad range of periodicities.

    Studies of the domain stability of periodically poled VTE-SLT during chemical etching were performed by on-line second harmonic generation, and optical microscopy. The results show that wet etching directly after poling leads to domain-wall motion, resulting in back-switching or domain merging. 

    Furthermore, the domain wall motion induced by electron beam irradiation was investigated using a scanning electron microscope. It was found that domain switching strongly depends on the ratio of secondary electrons to incident electrons. These results are discussed in terms of electron beam and screening charges interaction.

  • 279.
    Kianirad, Hoda
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Domain wall motion in stoichiometric LiTaO3 induced by low-energy electron beam2019Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Scanning electron microscopy was used to study the mobility of domain walls in vapor-transport equilibrated stoichiometric LiTaO3. By using low-acceleration voltage, switching occurs solely for polarization pointing-up domains, resulting in fast domain-wall motion. When the incoming electron beam was more energetic with larger penetration depth, the switching instead occurred for polarization pointing down domains. Our results are discussed in terms of the interaction of the scanning electron beam with the polarization-screening charges at the crystal surface.

  • 280.
    Kianirad, Hoda
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Domain wall motion in stoichiometric LiTaO3 induced by low-energy electron beam2019Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 115, nr 5, artikkel-id 052901Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Scanning electron microscopy was used to study the mobility of domain walls in vapor-transport equilibrated stoichiometric LiTaO3. By using low-acceleration voltage, switching occurs solely for polarization pointing up domains, resulting in fast domain-wall motion. When the incoming electron beam was more energetic with larger penetration depth, the switching instead occurred for polarization pointing down domains. Our results are discussed in terms of the interaction of the scanning electron beam with the polarization-screening charges at the crystal surface.

  • 281.
    Kianirad, Hoda
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Lindgren, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Peña, A.
    Zukauskas, Andrius
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Ménaert, B.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Boulanger, B.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Stabilization of domain structures in Rb-doped KTiOPO 4 for high-temperature processes2019Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 114, nr 5, artikkel-id 052904Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A way to stabilize the domain structure in periodically poled Rb-doped KTiOPO 4 samples at high-temperatures is presented. The domain contraction along the b-crystallographic axis that is observed when crystals are annealed at high temperatures is suppressed when the ends of the domains along the b-axis are diced away. Additionally, the thermal stability of self-assembled domain gratings with a sub-μm average periodicity of 650 ± 200 nm and a domain-width of 225 ± 75 nm in mm-thick samples is investigated, and it is shown that the key factor for the domain stability is the domain width rather than the interdomain distance.

  • 282.
    Kianirad, Hoda
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Zakauskas, Andrius
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Domain dynamics in Stoichiometric Lithium Tantalate revealed by etching and on-line Second Harmonic Generation2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Periodically poled LiTaO3 has a shorter cut-off wavelength than KTP and LiNbO3, which makes this material attractive for UV generation. However, the standard congruent material suffers strongly from photorefractive damage which has limited its use in the UV. It is expected that stoichiometric LiTaO3 (SLT) would make a superior material in this context, as the defect concentration, which directly relates to the damage, is strongly reduced. Close to perfectly stoichiometric crystals can be obtained by post growth diffusion of Li2O into the crystal at high temperatures to compensate the Li2O deficiency, so called vapour transport equilibrated (VTE) SLT [1]. The coercive field is drastically reduced for SLT which facilitates the way for fabricating QPM devices [2]. However lower defects and reduced coercive field might cause instability for charged domain walls (DW) or walls that are not in their lowest energy state. Since the stability mechanism for VTE SLT is not very well known, its investigation would lead to improvement in device fabrication with short period and also helps to understand the DW dynamics.

     

    In this work, we study the impact of chemical etching after poling on domain stability of SLT. We show that chemical etching right after poling induced DW movement without any external field. We demonstrate that when the original DW configuration is head-to-head (HH) or tail-to-tail (TT), the DW movement results in backswitching or merging with neighboring domians, respectively. Our finding are monitored by in situ SHG during etching followed by characterization of the domain structure with optical microscopy. We also show that this behavior is independent of the domain orientation with respect the crystallographic axes.

  • 283.
    Kianirad, Hoda
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Zukauskas, Andrius
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Domain dynamics in stoichiometric lithium tantalate revealed by wet etching and on-line second harmonic generation2017Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, nr 18, artikkel-id 184103Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of chemical etching on the stability of domains in periodically poled stoichiometric lithium tantalate is studied by on-line second harmonic generation and microscopy. It is found that wet etching directly after poling leads to domain-wall movement, resulting in back-switching or domain merging. Head-to-head domains tend to backswitch, while tail-to-tail domains merge. For samples where the domain structure stabilized for longer time, no domain motion is observed when etched.

  • 284.
    Kianirad, Hoda
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Zukauskas, Andrius
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Domain engineering using Si-electrode stamp2016Konferansepaper (Fagfellevurdert)
  • 285.
    Kianirad, Hoda
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Zukauskas, Andrius
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    On the stability of periodically poled Lithium Tantalate2014Konferansepaper (Fagfellevurdert)
  • 286.
    Kianirad, Hoda
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Zukauskas, Andrius
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Frisk, Thomas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Cellens fysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Contact poling of Rb:KTiOPO4 using a micro-structured silicon electrode2015Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, nr 2, s. 636-641Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A contact poling technique for domain engineering of ferroelectrics using a micro-structured silicon electrode is demonstrated on Rb:KTiOPO4. High quality QPM gratings were reproducibly fabricated. The silicon electrode is reusable and the technique potentially suitable when complex structures with sub-mu m features are to be domain engineered, which otherwise is incompatible with conventional photolithography. A non-negligible domain broadening was seen and attributed to a low nucleation rate using this type of electrode. However, under the appropriate poling conditions, this could be exploited to obtain a QPM grating with a short pitch (2 mu m), equal to half of the electrode period.

  • 287.
    Kianirad, Hoda
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Zukauskas, Andrius
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Frisk, Thomas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Cellens fysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Contact poling of RKTP using a micro-structured silicon electrode2014Konferansepaper (Annet vitenskapelig)
  • 288.
    Kianirad, Hoda
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Zukauskas, Andrius
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Frisk, Thomas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Cellens fysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Contact poling of RKTP with silicon pillars2013Inngår i: 2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference, CLEO/Europe-IQEC 2013, IEEE Computer Society, 2013, s. 6800873-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Quasi-phase-matching (QPM) is a method to get tailored efficient second order nonlinear interactions [1]. Several techniques exist for fabrication of periodic domain structures in ferroelectric crystals for QPM frequency conversion. By far, electric field poling using lithographically patterned electrodes on the z-face of the crystal is the most common one [2]. High-quality periodically inverted ferroelectric domain structures in flux grown KTiOP 4 (KTP) crystals were fabricated already in the late 90's using this technique [3], and recently periodic domain sizes of few hundred nanometers were fabricated in 1 mm thick samples thanks to the quasi-one dimensional structure of KTP. It has recently also been shown that a slight Rb doping of the KTP crystal (RKTP) facilitates the periodic poling [4]. However, fabrication of two-dimensional (2D) domain structures in RKTP has not yet been investigated. A disadvantage with the lithographic patterning is that each sample needs to be patterned individually, which is tedious and time consuming. Moreover, when it comes to the small domain features, which are required by the next generation of nonlinear optical devices, a more versatile poling technique has to be developed due to the limitations of conventional photolithography. Structured silicon has been investigated as an alternative electrode for formation of 1D domains by contact poling in LiNb3 [5]. However, these electrodes were fabricated by wet etching and the sample thickness was limited to ∼200 μm.

  • 289.
    Kim, Hwi-Min
    et al.
    Korea Adv Inst Sci & Technol, Dept Phys, Daejeon 34141, South Korea..
    Jang, Hoon
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik. Korea Adv Inst Sci & Technol, Dept Phys, Daejeon 34141, South Korea.
    Pramudita, Putu
    Korea Adv Inst Sci & Technol, Dept Phys, Daejeon 34141, South Korea..
    Kim, Myung-Ki
    Korea Univ, KU KIST Grad Sch Converging Sci & Technol, Seoul 02841, South Korea..
    Lee, Yong-Hee
    Korea Adv Inst Sci & Technol, Dept Phys, Daejeon 34141, South Korea..
    Monolithic integration of self-aligned nanoisland laser with shifted-air-hole waveguide2018Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, nr 10, s. 12569-12578Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report a novel scheme for monolithic integration of a nanoisland laser with a shifted-air-hole waveguide by employing selective etching techniques. An active L3 laser cavity and passive shifted-air-hole waveguide are simultaneously formed through a single fabrication step. In the shifted-air-hole waveguide, the air-hole position is adjusted to be compatible with selective etching. The spectral overlap between the L3 laser resonance and guided mode is achieved by introducing small air holes at the nodes of the shifted-air-hole waveguide. Experiments show that >60% of the light is coupled from the nanoisland laser to the end of the 12-mu m-long waveguide.

  • 290. Kim, J. W.
    et al.
    Jelger, Pär
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Sahu, J. K.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Clarkson, W. A.
    High-power and wavelength-tunable operation of an Er, Yb fiber laser using a volume Bragg grating2008Inngår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 33, nr 11, s. 1204-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Efficient high-power operation of double-clad Er,Yb-doped fiber lasers with fixed-wavelength and wavelength-tunable resonator configurations using volume Bragg gratings for wavelength selection are reported. The fixed-wavelength laser yielded a maximum output power of 103 W at 1552.6 nm with a linewidth of ∼0.4 nm (FWHM) for a launched pump power of 290 W at 976 nm. The wavelength-tunable laser could be tuned from 1528 to 1550 nm with a linewidth of 0.2 nm (FWHM) and with output power in the range 30-38 W for a launched pump power of 120 W. The prospects for further improvement in performance are considered.

  • 291.
    Klemming Eklöf, Finn
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Yu, Zangwei
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Rugeland, Patrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Zeil, Peter
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Tjörnhammar, Staffan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Compact Three-wavelength Fiber Laser for Multi-wavelength Digital Holography2013Inngår i: Workshop on Specialty Optical Fiber and Their Applications, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A compact three‐wavelength narrow‐linewidth fiber laser with single pump is demonstrated. The multiple‐wavelength output signal can be effectively employed to synthesize large effective probing wavelength of up to 1.16mm for high depth resolution digital holography.

  • 292.
    Kores, Cristine C.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Geskus, Dimitri
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Ismail, Nur
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Dijkstra, Meindert
    Bernhardi, Edward H.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Pollnau, Markus
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    The linewidth of distributed feedback resonators: the combined effect of thermally induced chirp and gain narrowing2017Inngår i: Laser Resonators, Microresonators, and Beam Control XIX / [ed] Kudryashov, AV Paxton, AH Ilchenko, VS, SPIE - International Society for Optical Engineering, 2017, artikkel-id UNSP 1009014-1Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Distributed-feedback (DFB) laser resonators are widely recognized for their advantage of generating laser emission with extremely narrow linewidth. Our investigation concerns ytterbium-doped amorphous Al2O3 channel waveguides with a corrugated homogeneous Bragg grating inscribed into its SiO2 top cladding, in which lambda/4 phase-shift provides a resonance and allows for laser emission with a linewidth as narrow as a few kHz. Pump absorption imposes a thermal chirp of the grating period, which has implications for the spectral characteristics of the resonator. Thermal effects on the spectral response of a DFB passive resonator were investigated via simulations using Coupled Mode Theory by considering (i) a constant deviation of the grating period or (ii) a chirp with a linear profile. We report an increase of the resonance linewidth up to 15%. This result is due to two factors, namely changes of the grating reflectivity at the resonance frequency up to 2.4% and of the shift of resonance frequency up to 61 pm due to an accumulated phase shift imposed on the grating by the chirp profile. The linewidth decrease due to gain is on the order of 106, which is a much larger value. Nevertheless, according to the Schawlow-Townes equation the linewidth increase of the passive resonator due to a thermal chirp quadratically increases the laser linewidth.

  • 293.
    Kores, Cristine Calil
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Geskus, Dimitri
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Ismail, Nur
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Dijkstra, M.
    Bernhardi, E. H.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Pollnau, Markus
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Characterization of Ultranarrow-Linewidth Distributed-Feedback Resonators Below Laser Threshold2016Konferansepaper (Fagfellevurdert)
  • 294.
    Kores, Cristine Calil
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Ismail, N.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Geskus, D.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Dijkstra, M.
    Univ Twente, MESA Inst, Opt Sci, NL-7500 AE Enschede, Netherlands..
    Bernhardi, E. H.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Pollnau, Markus
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. Univ Surrey, Adv Technol Inst, Guildford GU2 7XH, Surrey, England..
    Temperature Dependence of Spectral Characteristics of Distributed-Feedback Resonators2018Inngår i: FIBER LASERS AND GLASS PHOTONICS: MATERIALS THROUGH APPLICATIONS / [ed] Taccheo, S Mackenzie, JI Ferrari, M, SPIE-INT SOC OPTICAL ENGINEERING , 2018, artikkel-id 106830BKonferansepaper (Fagfellevurdert)
    Abstract [en]

    The spectral response of a distributed-feedback resonator with a thermal chirp is investigated. An Al2O3 channel waveguide with a surface Bragg grating inscribed into its SiO2 top cladding is studied. A linear temperature gradient along the resonator leads to a corresponding variation of the grating period. We characterize its spectral response with respect to wavelength and linewidth changes of the resonance peak. Simulated results show good agreement with the experimental data, indicating that the resonance wavelength is determined by the total accumulated phase shift. The calculated grating reflectivities at the resonance wavelength largely explain the observed changes of the resonance linewidth. This agreement demonstrates that the linewidth increase is caused by the increase of resonator outcoupling losses.

  • 295.
    Kores, Cristine Calil
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Ismail, Nur
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Bernhardi, E. H.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pollnau, Markus
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Distributed phase shift and lasing wavelength in distributed-feedback resonators2019Konferansepaper (Fagfellevurdert)
  • 296.
    Kores, Cristine Calil
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Ismail, Nur
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Bernhardi, E. H.
    KTH.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pollnau, Markus
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. Univ. of Surrey (United Kingdom) .
    Lasing wavelength in dielectric distributed-feedback lasers with a distributed phase shift2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Distributed-feedback waveguide lasers based on Bragg-grating resonators generate ultranarrow-linewidth emission. Oscillation at the center of the reflection band ensures maximum reflectivity, hence minimum laser linewidth. The required μ/2 phase shift is often introduced by a distributed change in effective refractive index, e.g. by adiabatically widening the waveguide. Despite careful design and fabrication, the experimentally observed resonance wavelength deviates, thereby placing the resonance and laser emission at a position with lower reflectivity inside the reflection band. This effect is usually incorrectly attributed to fabrication errors. Here we show theoretically and experimentally that the decay of light intensity during propagation from the phase-shift center into both sides of the Bragg grating due to (i) reflection by the periodic grating and (ii) the adiabatic refractive-index change causes an incomplete accumulation of designed phase shift, thereby systematically shifting the resonance to a shorter wavelength. Calculations are performed based on the characteristic-matrix approach. Experimental studies are carried out in a distributed-feedback channel-waveguide resonator in amorphous Al2O3 on silicon with a distributed phase shift introduced by adiabatic widening of the waveguide according to a sin2 function. Calculations and experiments show good agreement. Considering in the design the overlap integral between distributed phase shift and light intensity provides the desired performance.

  • 297.
    Kores, Cristine Calil
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Ismail, Nur
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Bernhardi, E. H.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pollnau, Markus
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. Univ. of Surrey (United Kingdom).
    Spectral behavior of integrated distributed-feedback resonators utilizing a distributed phase shift2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Bragg-grating-based distributed-feedback waveguide resonators, with a discrete phase shift introduced inside the Bragg grating, exhibit within their grating reflection band a Lorentzian-shaped resonance line with an ultranarrow linewidth. If the phase shift is π/2, the resonance is located at the center of the reflection band, i.e., at the Bragg wavelength, where the grating reflectivity is maximum, hence the resonance linewidth is minimum. Alternatively, the required π/2 phase shift is often introduced by a distributed change in effective refractive index, e.g. by adiabatically widening the waveguide. Despite careful design and fabrication, the experimentally observed resonance wavelength deviates from the designed one. Besides deviations owing to fabrication errors, a fundamental, systematic shift towards shorter wavelengths occurs. We show theoretically and experimentally that the decay of light intensity during propagation from the phase-shift center into both sides of the Bragg grating due to (i) reflection by the periodic grating and (ii) the adiabatic refractive-index change causes an incomplete accumulation of designed phase shift by the oscillating light, thereby systematically shifting the resonance to a shorter wavelength. Calculations are performed based on the characteristic-matrix approach. Experimental studies are carried out in distributed-feedback channel-waveguide resonators in an amorphous aluminum oxide thin film on silicon with a distributed phase shift introduced by adiabatic widening of the waveguide according to a sin2 function. Calculations and experiments show good agreement. Considering in the design the overlap integral between distributed phase shift and light intensity provides a performance that is much closer to the desired value.

  • 298.
    Kores, Cristine Calil
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Ismail, Nur
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Bernhardi, Edward H.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Pollnau, Markus
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Accumulation of distributed phase shift in distributed-feedback lasers2018Inngår i: Optics InfoBase Conference Papers, OSA - The Optical Society , 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In distributed-feedback lasers, a distributed phase shift of /2, seemingly placing the resonance at the Bragg wavelength, is not accumulated because of light confinement and asymmetry, leading to a systematic resonance shift to shorter wavelengths.

  • 299.
    Kores, Cristine Calil
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Ismail, Nur
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Bernhardi, Edward H.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pollnau, Markus
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Accumulation of Distributed Phase Shift in Distributed-Feedback Resonators2019Inngår i: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 11, nr 1, artikkel-id 1500109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Distributed-feedback waveguide lasers based on Bragg-grating resonators generate ultranarrow-linewidth emission. Oscillation at the center of the reflection band ensures maximum reflectivity, hence minimum linewidth. The required pi/2 phase shift is often introduced by a distributed change in effective refractive index, e.g., by widening the waveguide. Despite careful design and fabrication, the experimentally observed resonance wavelength deviates from the designed wavelength. Even when thermally induced chirp or fabrication errors are negligible, this deviation is still present. Here, we show theoretically and experimentally that this deviation is of fundamental nature. The decay of light intensity during propagation from the phase-shift center into both sides of the Bragg grating due to reflection by the periodic grating and the refractive index change causes an incomplete accumulation of designed phase shift, thereby systematically shifting the resonance to a shorter wavelength. Considering the overlap integral between the distributed phase shift and light intensity in the design provides the desired performance.

  • 300.
    Kores, Cristine Calil
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Ismail, Nur
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Geskus, Dimitri
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Dijkstra, M.
    Bernhardi, Edward H.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Pollnau, Markus
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Frequency and linewidth dependence of distributed-feedback resonators on thermal chirp2017Inngår i: 2017 19th International Conference on Transparent Optical Networks (ICTON), IEEE Computer Society, 2017, artikkel-id 8025100Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We present an analysis of the spectral characteristics of distributed-feedback (DFB) laser resonators with thermally chirped distributed mirrors. Such DFB resonators have the interesting capability of producing a linewidth as narrow as a few kHz. The investigated devices are ytterbium-doped amorphous Al2O3 channel waveguides with a periodic Bragg grating inscribed into its SiO2 top cladding. The resonance in the spectral response of the resonator results from a distributed λ/4 phase-shift produced by increasing the waveguide width. Its frequency is determined by the period of the Bragg grating, whereas its linewidth is determined by the intrinsic losses and the outcoupling losses of the resonator. When such a device is optically pumped to achieve gain and eventually lasing, the grating period becomes thermally chirped, thereby influencing the spectral characteristics of the resonator. We investigate experimentally and via simulations the frequency and linewidth of the resonance in the presence of a thermally induced linear chirp on the grating profile. Experiments and simulations show good quantitative agreement.

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