We report fabrication of tapered silicon core fibers with nano-spikes enabling efficient optical coupling into the core, as well as their seamless integration with single mode fibers. A proof-of-concept integrated in-fiber silicon device is demonstrated.
Acousto-optic coupling in polyimide-coated single-mode optical fibers using flexural elastic waves is demonstrated. The effect of the polyimide coating on the acoustooptic interaction process is analyzed in detailed. Theoretical and experimental results are in good agreement. Although the elastic attenuation is significant, we show that acousto-optic coupling can be produced with a reasonably good efficiency. To our knowledge, it is the first experimental demonstration of acousto-optic coupling in optical fibers with robust protective coating.
We present the experimental demonstration of in-fiber acousto-optic coupling in a polyimide-coated optical fiber. Although the presence of the polyimide coating increases is significantly the attenuation of the acoustic wave, we show that acousto-optic interaction can still be produced with reasonable efficiency. The effect of the polyimide coating on the acousto-optic interaction process is analyzed in detailed. Theoretical and experimental results are in good agreement. To our knowledge, this is the first experimental demonstration of acousto-optic coupling in optical fibers with robust protective coating.
In this work, we report on a twin-core fiber sensor system that provides improved spectral efficiency, allows for multiplexing and gives low level of crosstalk. Pieces of the referred strongly coupled multicore fiber are used as sensors in a laser cavity incorporating a pulsed semiconductor optical amplifier (SOA). Each sensor has its unique cavity length and can be addressed individually by electrically matching the periodic gating of the SOA to the sensor's cavity roundtrip time. The interrogator acts as a laser and provides a narrow spectrum with high signal-to-noise ratio. Furthermore, it allows distinguishing the response of individual sensors even in the case of overlapping spectra. Potentially, the number of interrogated sensors can be increased significantly, which is an appealing feature for multipoint sensing.
Optofluidic all-fiber devices are used for orientation of Au-nanorods under strongelectric fields. The dynamics is studied on sub-microsecond time-scales. A two-level laser rateequation model allows inferring diffusion rate, rotational mobility and other parameters.
We report on a new longwave infrared optical parametric source, and its implementation for long range or medium range standoff detection of gaseous chemical warfare agents.
We report on a longwave infrared lidar, tailored for detection of chemical warfare agents in the gaseous phase. The emitter is based on single-frequency 2 μm parametric oscillator/amplifier systems followed by a ZnGeP2 downconversion stage.
Laser-induced damage threshold (LIDT) measurements were performed on blank, uncoated Rb:KTiOPO4 (RKTP) samples at 1.03 μm with pulse durations of 330 and 930 fs and a repetition rate of 100 kHz, including temperature dependence.
A laser-induced damage study is performed on blank, uncoated Rb:KTiOPO4 (RKTP) samples at 1.03 mu m with two different pulse durations of similar to 0.3 and similar to 1.0 ps and a repetition rate of 100 kHz. The effect of the sample temperature is also considered.
We report on passive mode-locking of a Ti:sapphire laser employing a single-walled carbon nanotube saturable absorber (SWCNT-SA) specially designed and fabricated for wavelengths near 800 nm. Mode-locked pulses as short as 62 fs were generated at a repetition rate of 99.4 MHz. We achieved output powers from the SWCNT-SA mode-locked laser as high as 600 mW with a slope efficiency of 26%. The characteristics of SWCNT-SA-assisted mode-locking were compared with those of Kerr-lens mode-locking without SWCNT-SA.
The work presented in this thesis shows the development of optically poleddevices for use in electro-optic experiments. In the form of papers published,it describes three optical poling methods: green light poling (Paper I), poling with a UV lamp (Paper II), and corona discharge poling (Paper V).Applications using the poled components are studied in distributed sensingby exploring Rayleigh scattering in poled fibers (Paper III), intermodal interference in poled fibers (Paper IV), and FBG inscribed in poled fibers forvoltage sensing (Paper VI).In thermal poling, heat increases the mobility of added ions to the fiber.An external electric field displaces the charges creating a depletion regionclose to the anode, where the fiber core is usually positioned. The proximityof the metal electrode to the core can cause optical losses, making electrooptic applications less efficient. The need for additional dopant in the preformcan make the production of these devices expensive.Optical poling explores the presence of Ge E’ centers in the fiber core torelease charges after light excitation. These centers are already present in anyfiber with Ge in the core. This enables the development of a fiber for opticalpoling very similar to a standard telecom fiber, making it cheaper and easyto integrate with standard components. Optical poling does not rely on theformation of a depleted region in the cladding, and the core can be positionedfar from the metal electrodes. This advantage allows low-loss electro-opticcomponents to be fabricated.Optical poling is usually thought to have lower induced effects when compared with thermal poling. In this work, experiments with optical polingwere made to study the possibility of increasing the induced second-ordernonlinearities to a level comparable with thermal poling.The fabricated poled fibers were used to investigate their potential usein fiber sensing. The emphasis was to explore new technologies such as CPϕOTDR, few-mode fiber sensing, which gained attention in the latest years,and FBGs, which is a mature technology.The results presented in the Papers I-VI show the advances and potentialapplications explored.
The development of reliable periodic poling methods that allow for sub-µm quasi-phase matched (QPM) gratings and, at the same time, allow for waveguide implementation, is of paramount importance for a large number of applications. For instance, backward-wave optical parametric oscillators [1] are only viable if the QPM period is on the same order of magnitude as the wavelengths of the interacting waves. Furthermore, the integration of such QPM devices in a waveguide format would unveil countless possibilities in quantum optics employing the crystal as an ultrabright bi-photon source with unique spectral characteristics.
We propose and demonstrate a method for quantum-state tomography of qudits encoded in the quantum polarization of N-photon states. This is achieved by distributing N photons nondeterministically into three paths and their subsequent projection, which for N = 1 is equivalent to measuring the Stokes (or Pauli) operators. The statistics of the recorded N-fold coincidences determines the unknown N-photon polarization state uniquely. The proposed, fixed setup manifestly rules out any systematic measurement errors due to moving components and allows for simple switching between tomography of different states, which makes it ideal for adaptive tomography schemes.
We demonstrate wavelength locking of a diode laser at 760 nm with feedback from an elastic transmission grating in the Littrow configuration. The laser was in a single longitudinal mode with a side-mode suppression of 20 dB. By stretching the grating the laser could be tuned over a few nm. The grating was fabricated in a silicone elastomer ( polydimethylsiloxane) by a moulding technique, and coated by a thin layer of Ti and Au to achieve an increased diffraction efficiency needed for efficient locking.
The fluorescence dynamics in Er3+ and Yb3+ doped KGd(WO4)(2) and KY(WO4)(2) has been investigated. Lifetimes have been measured for the Yb(F-2(5/2)), Er(I-4(13/2)), and Er(S-4(3/2)) levels around 1, 1.5, and 0.55 mu m, respectively. The Yb(F-2(5/2)) lifetimes show a decreasing trend toward the limiting Er(I-4(11/2)) lifetime with increasing Er-to-Yb concentration ratio, whereas the Er(I-4(13/2)) lifetimes are mostly unaffected by the doping concentrations. A rate equation analysis has been performed to explain the observed behavior and gain is calculated for a continuous-wave laser at 1.53 mu m to find the optimum doping concentrations for high gain.
High quality Er:Yb:KLu(WO4)2have been grown using TSSG method and spectroscopically investigated . The laser performance is compared with that in Er:Yb:KY(WO4)2. Role of upconversion processes and optimum doping concentrations have been estimated.
Here we show the results we obtained in the fabrication of planar wave guide lasers based on monoclinic double tungstates doped with Er3+ and Tm3+. We have successfully introduced these ions into the lattice matched KY0.59Gd0.19Lu0.22(WO4)(2) epitaxial layers grown on KY(WO4)(2) substrates without loss of optical quality and keeping a high refractive index contrast between the epitaxial layer and the substrate. We characterized the waveguiding properties of these epitaxial layers at lambda = 632.8 nm by dark modes spectroscopy, and we showed that these waveguides can support several TE and TM modes. Spectroscopic characterization of the active lanthanide ions in these crystals is also presented.
An overall quantum conversion efficiency of 7.8% is achieved by intracavity mixing the signal and idler of a 1.064-μm pumped Rb:PPKTP OPO in BaGa4Se7, generating >0.7 mJ pulse energy at ~7 μm and 100 Hz.
We report on a AgGaSe2 optical parametric oscillator (OPO), intracavity pumped by the 1.85-μm signal pulses of a 1.064-μm pumped Rb:PPKTP OPO. It operates at 100 Hz with idler tunability from ~8 to 18 μm.
We report on an AgGaSe2 optical parametric oscillator (OPO), intracavity pumped by the 1.85-μm signal pulses from a 1.064-μm pumped Rb:PPKTP OPO. It operates at 100 Hz with idler tunability from 5.8 to 8.3 μm.
An overall quantum conversion efficiency of 7.8% is achieved by intracavity mixing the signal and idler of a 1.064 mu m pumped Rb: PPKTP optical parametric oscillator in BaGa4Se7. In this way, a pulse energy of similar to 0.71 mJ is generated at similar to 7 mu m for a repetition rate of 100 Hz. Tuning of the mid-IR radiation is demonstrated by heating of the Rb: PPKTP crystal.
A 1.064 mu m pumped Rb:PPKTP optical parametric oscillator (OPO) generates mid-IR radiation by intracavity mixing the resonant signal and idler waves in AgGaSe2. The similar to 6 ns pulses at similar to 7 mu m have an energy of 670 mu J at 100 Hz, equivalent to an average power of 67 mW. The overall quantum conversion efficiency from 1.064 mu m amounts to 8%, and the power conversion efficiency is 1.2%.
We report on a AgGaSe2 optical parametric oscillator (OPO), intracavity pumped by the 1.85-μm signal pulses of a 1.064-μm pumped Rb:PPKTP OPO. It operates at 100 Hz with idler tunability from ∼8 to 18 μm.
We present a narrowband, non-resonant optical parametric oscillator based on 5-mm thick Rb-doped periodically-poled KTiOPO4 (PPKTP) operating in the high-energy/low repetition-rate regime. An uncoated volume Bragg grating (VBG) is employed as one of the cavity mirrors reflecting only the signal whereas the other cavity mirror is reflecting only the idler. Pumping by a Nd:YAG laser at 1.0642 mu m in a double-pass, the signal plus idler output energy reached almost 5 mJ at a repetition rate of 100 Hz corresponding to a conversion efficiency of similar to 26%. Both signal and idler are narrowband with full width at half maximum (FWHM) of 0.5 nm at 1942 nm and 0.76 nm at 2355 nm, respectively.
A Nd:YVO4 laser operating at 1064 nm generating a stable mode-locked train of 10 ps-long dark pulses with a 211 MHz repetition rate is presented. The mode-locking relies on a periodic loss modulation produced by intra-cavity sum-frequency mixing with a synchronous bright-pulse train from a mode-locked femtosecond Yb:KYW laser at 1040 nm. A modulation depth of 9050 was achieved for the dark pulses, confirmed by cross-correlation measurements. The ultrafast loss modulation injects power into the Nd:YVO4 laser cavity modes beyond the laser gain bandwidth. At proper laser cavity length, the detuning interaction of these modes with the lasing modes leads to the generation of periodic ultra-fast transients at frequencies above 1.5 THz.
We demonstrate broadband parametric amplification in GaSe crystal in noncollinear geometry. Seed pulses spanning 1.5-2.6μm are produced by cascaded χ(2) nonlinearity in a periodically poled Rb:KTP crystal. Amplified pulse bandwidths supporting 10-15fs transformlimited pulse durations at ~2μm central wavelength are achieved.
We study the creation and erasure of the linear electrooptical effect in silicate fibers by optical poling. Carriers are released by exposure to green light and displaced with simultaneous application of an internal dc field. The second order nonlinear coefficient induced grows with poling bias. The field recorded (similar to 10(8) V/m) is comparable to that obtained through classical thermal poling of fibers. In the regime studied here, the second-order nonlinearity induced (similar to 0.06 pm/V) is limited by the field applied during poling (1.2 x 10(8) V/m). Optical erasure with high-power green light alone is very efficient. The dynamics of the writing and erasing process is discussed, and the two dimensional (2D) field distribution across the fiber is simulated. (C) 2015 Optical Society of America
Frequency doubling is demonstrated in femtosecond-laser-created single-mode waveguides written in a periodically-poled potassium titanyl phosphate crystal. Conversion efficiencies of 0.22%/W (0.02%/W) were obtained for first (third) order phasematching at 980nm (800nm).
The second-harmonic conversion efficiency within the PPKTP waveguide is investigated using two separate tunable CW Ti:sapphire lasers at 800 nm and 980 nm. Results show strong conversion efficiency which imply that the local damage-induced index modification does not adversely affect the periodic domain structure in the material.
Frequency doubling has been achieved in femtosecond-laser-inscribed single-mode waveguides written in two periodically-poled potassium titanyl phosphate crystals. A conversion efficiency of 0.22 %W-1 was obtained for first-order quasi-phase matching at 980 nm and an efficiency of 0.02 %W-1 for third-order quasi-phase matching at 800 nm.
Precise control of the bandwidth of quasi-phase-matched second-harmonic generation in silica fibers is realized through chirped-period poling. The bandwidth is expanded by a factor of 33 over a uniform-period poled fiber of the same interaction length.