Multiwavelength erbium-doped fiber laser using twin-core photonic crystal fiber

Laser Physics - We propose a novel multiwavelength erbium-doped fiber laser incorporating a twin-core photonic crystal fiber (TC-PCF) based Mach-Zehnder interferometer (MZI). TC-PCF based...     

Fabrication of polaritonic structures in LiNbO<Subscript>3</Subscript> and LiTaO<Subscript>3</Subscript> using femtosecond laser machining

Fabrication of patterned materials in ferroelectric LiNbO₃ and LiTaO₃ crystals using femtosecond laser micromachining is presented and discussed. Damage feature sizes in the 10–100 μm range were achieved using 800-nm, 50-fs (FWHM) ultra-fast laser pulses with energies ranging from 10 μJ up to 350 μJ. Fabrication of polaritonic devices such as waveguides, resonators, focusing reflectors, diffractive and dispersive elements, photonic band gap materials, and other microstructures is demonstrated. PACS 77.84.Dy; 42.62.Cf; 71.36.+c     

Optical waveguides in LiNbO<Subscript>3</Subscript> and stoichiometric LiNbO<Subscript>3</Subscript> crystals by proton exchange

The formation of optical planar waveguides in LiNbO₃ and stoichiometric LiNbO₃ crystals by proton exchange was reported. The prism-coupling method was used to characterize the dark-line spectroscopy at the wavelength of 633 and 1539 nm, respectively. The mode optical near-field outputs from proton-exchanged LiNbO₃ and SLN waveguides at 633 nm were presented. The mode field from stoichiometric LiNbO₃ (SLN) waveguide is lighter and more uniform than that from LiNbO₃ waveguide, which means the quality of the waveguide in SLN crystal is better than that of the LiNbO₃ waveguide. For proton-exchanged LiNbO₃ waveguides, the evolution of the refractive index profile with annealing was presented. The disorder profiles of Nb atoms in proton-exchanged LiNbO₃ waveguides were obtained by Rutherford backscattering/channeling technique. It is shown that the longer the exchange time, the larger the displacement of Nb atoms. Supported by the National Natural Science Foundation of China (Grant No. 10475052) and the Scientific Research Start-up Financing of Qufu Normal University     

Light scattering in single crystals of nonlinear-optical photorefractive LiNbO<Subscript>3</Subscript>:Cu and LiNbO<Subscript>3</Subscript>:Zn

Comparative studies are made of the photorefractive scattering of light in nonlinear single crystals of lithium niobate with congruent compositions (LiNbO₃) doped with "photorefractive" Cu [0.015 mass %] and "nonphotorefractive" Zn [0.5 mass %] cations. For the first time it is found that single crystals doped with "photorefractive" and "nonphotorefractive" cations have different indicatrices for photorefractive light scattering. The aperture angle for photorefractive scattering reaches its steady state value more rapidly with high laser powers than with low. However, at high powers laser induced heating of the crystal is greater, and this leads to a narrowing of the scattering indicatrix. It is also found that photorefractive scattering in these single crystals depends on the region of the boule from which a sample has been cut. This indicates that there is a nonuniform distribution over the boule of the imperfections with localized electrons which determine the magnitude of the photorefractive effect.     

Multiwavelength fiber laser using S-band erbium-doped fiber amplifier and semiconductor optical amplifier

A multiwavelength fiber ring laser that is based on an S-band erbium-doped fiber amplifier (EDFA) and a semiconductor optical amplifier (SOA) is developed. An optical switch is used to switch the multiwavelength fiber laser between S-band and L-band. This fiber laser can stably lase seven wavelengths in the S-band or 28 wavelengths in the L-band. Additionally, the lasing wavelengths with a signal-to-noise ratio of over 33 dB and a wavelength spacing of 100 GHz are demonstrated experimentally. The average powers of the lasing wavelength in the S-band and the L-band are −7.53 and −12.15 dBm, respectively.     

Mode-selective coupler for wavelength multiplexing using LiNbO<Subscript>3</Subscript>:Ti optical waveguides

A mode-selective directional coupler based on titanium in-diffused channel waveguides in lithium niobate is investigated. This coupler may be utilized as a key part of an add-drop multiplexer for dense wavelength division multiplexing in optical network nodes. The proposed coupler is based on evanescent coupling of the fundamental mode of a single-mode channel to the first higher mode of a parallel bi-modal waveguide. Our experimental results show that a compact directional coupler with coupling efficiencies larger than 90%, large bandwidth around 1550 nm, and with negligible polarization dependence can be realized using electro-optic lithium niobate substrates. Presented at 9-th International Workshop on Nonlinear Optics Applications, NOA 2007, May 17–20, 2007, Świnoujście, Poland     

Compact passively Q-switched green laser with periodically poled MgO:LiNbO<Subscript>3</Subscript>

Passively Q-switched green output with Cr⁴⁺:YAG as saturable absorber and PPMgLN as the frequency doubling crystal was realized in a compact diode end-pumped Nd:YVO₄ laser. The green light output power, pulse width, pulse repetition rate, pulse energy and peak power with three Cr⁴⁺:YAG of different initial transmissions were investigated. The maximum average output power was 1.2 W at the pump power of 4.0 W and the maximum conversion efficiency was 30% with the Cr⁴⁺:YAG of 90% initial transmission. The maximum pulse energy and minimum pulse width were 10.9 μJ and 12 ns with the Cr⁴⁺:YAG of 75% initial transmission.     

Broadband and low-driving-power LiNbO<Subscript>3</Subscript>electrooptic modulators

Microwave and optical properties of lithium niobate electrooptic modulators are investigated in this paper. The effect of simultaneous matching of optical and microwave velocities and impedance matching, conductor loss, dielectric loss on the optical bandwidth of an ultra-high-speed lithium niobate modulator are presented here. The metal electrode design, buffer thickness, ridge depth, and the gap between electrodes at different operating frequencies on device performance are thoroughly investigated by using the finite element method.     

Photoconductivity in LiNbO<Subscript>3</Subscript> crystals codoped with MgO and Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>

Polymer stabilized cholesteric texture cells with various chiral and monomer concentrations were fabricated. Electro-optical measurement indicates that the chiral concentration and the monomer concentration significantly influence the hysteresis, threshold voltage and field-on and field-off response times of the cell. The chiral dopant is found to increase the hysteresis width and to decrease the field-off response time of the cell. The monomer is found to decrease the hysteresis width and to increase the field-off response time of the cell. The field-on response time is independent of the monomer concentration and the chiral concentration of the cell. A thinner cell has a smaller hysteresis width. PACS 61.30.-v; 42.70.Df; 42.79.Kr     

Superlinear photovoltaic currents in proton-exchanged LiNbO<Subscript>3</Subscript> waveguides

Photovoltaic currents along the c axis have been measured in α-phase LiNbO₃ proton-exchanged waveguides at several visible wavelengths for a guided-beam configuration. The light-intensity dependence is superlinear and all experimental curves are very well fitted by computer simulations using a two-centre model, with Fe²⁺/Fe³⁺ as primary and Nb_Li ⁴⁺/Nb_Li ⁵⁺ as secondary photovoltaic centres. The superlinear behaviour arises from a much higher effective photovoltaic length of Nb_Li ⁴⁺ (small polaron) compared with that of Fe²⁺. In β₁-phase guides, the photocurrents are much smaller than in α-phase guides and apparently do not show superlinear behaviour. Received: 22 October 2002 / Revised version: 6 January 2003 / Published online: 12 May 2003 RID="*" ID="*"Corresponding author. Fax: +34-91/3978-579, E-mail: m.carrascosa@uam.es     

Origins of waveguiding in femtosecond laser-structured LiNbO<Subscript>3</Subscript>

Femtosecond laser-induced structural changes in LiNbO₃ are studied. Depending on the laser processing parameters two different types of modification are identified and their origin is discussed. Both types of modification can be described within the framework of induced lattice defects. For strong material damage a refractive index increase can be obtained due to the induced stress field. By appropriate tailoring of this stress field thermally stable and highly symmetric waveguides can be obtained well suited for nonlinear integrated-optical applications. PACS 61.80.Ba; 77.84.Dy; 42.65.Re; 42.82.Et     

Yellow nanosecond sum-frequency generating optical parametric oscillator using periodically poled LiNbO<Subscript>3</Subscript>

Nanosecond yellow light has been generated through simultaneously phase matched sum-frequency generation and optical parametric oscillation in a periodically poled LiNbO₃ crystal. 300 mW of yellow light at a wavelength of 586 nm has been generated from 1.3 W of laser power from a Q-switched Yb:YAG laser operating at 1031 nm. The conversion efficiency of the device is 23%. PACS 42.65.Ky; 42.65.Yj     

Multiwavelength erbium-doped fiber laser employing a nonlinear optical loop mirror

A stable and broad bandwidth multiwavelength erbium-doped fiber laser is proposed and demonstrated successfully. A nonlinear optical loop mirror which induces wavelength-dependent cavity loss and behaves as an amplitude equalizer is employed to ensure stable room-temperature multiwavelength operation. Up to 50 wavelengths lasing oscillations with wavelength spacing of 0.8 nm within a 3-dB spectral range of 1562-1605 nm has been achieved. The measured power fluctuation of each wavelength is about 0.1 dB within a 2-h period.     

LiNbO<Subscript>3</Subscript>:Yb<Superscript>3+</Superscript> crystals for optical temperature sensors

Possibilities of using lithium niobate crystals, doped with ytterbium (LN:Yb³⁺) as materials for optical temperature sensor (OTS), are discussed. We consider both the radiative and absorptive characteristics of the crystals, assuming that their temperature dependences are caused by the Boltzmann factor of the initial population of Stark sublevels of the ion. It is shown that the crystals can be used as materials for OTS in the temperature range 150–400 K.     

Crystal LiNbO<Subscript>3</Subscript>-Ho<Superscript>3+</Superscript>: Material for optical cooling

The possibilities of LiNbO₃-Ho³⁺ crystals for optical cooling based on the anti-Stokes luminescence in the wavelength range 2000-2200 nm are investigated. The efficiency and cooling temperature under the continuous wave (CW) excitation at the wavelengths 2035-2071 nm by ~100 W power are estimated. It is shown that under the CW excitation at 2035 nm wavelength the maximum cooling temperature is equal to 2.5 K, and at 2071 nm wavelength is equal to 10.9 K.     

Temperature effects in proton exchanged LiNbO<Subscript>3</Subscript> waveguides

Temperature effects on single, homogeneous phases of proton exchanged LiNbO₃ waveguides have been studied. The refractive index of -phase guides on z-cut and x-cut congruent substrates monotonically increases with temperature, the thermo-optical coefficient being similar to that of the substrate. In ₂-phases on z-cut congruent substrates and in ₁-phases on z-cut and x-cut congruent and quasi-stoichiometric substrates, the thermo-optical coefficient is smaller than that of the substrate below 60 °C and higher above this temperature. A rather similar effect has been observed in ₁-phases on z-cut and x-cut congruent substrates in the linear expansion coefficient. The microscopic origin of the phase transition is not known for the moment. PACS Provide PACS codes please.     

Multiwavelength fiber ring laser using a gain clamped semiconductor optical amplifier

We demonstrate a novel multi-wavelength fiber ring laser based on a gain clamped semiconductor optical amplifier. The number of lasing lines can be tuned by adjusting the loss inside the cavity. The wavelength interval between the wavelengths is 100 GHz. The proposed laser shows a stable operation with total intensity fluctuation for a single laser line within ±0.02 dB at room temperature for a period of 30-minutes.     

Controlling optical inhomogeneity of LiNbO<Subscript>3</Subscript> single crystals

Different ways of inducing changes in the optical inhomogeneity of single crystals of lithium niobate are described. These include the application of a conductive coating in combination with the heating of samples and exposure to the field of a corona discharge, to UV radiation from a Nd:YAG laser, and to the electron beam of an electron microscope. All such effects can be used to record images.     

Selective photorefractive scattering in LiNbO<Subscript>3</Subscript>:Rh crystals

Photorefractive scattering occurs in rhodium-doped lithium niobate crystals irradiated by coherent light. The photorefractive scattering has both wide-angle and selective components. The results of experimental investigation of selective photorefractive scattering in LiNbO₃:Rh crystals and calculation of the spatial structure of scattering are reported. The selective scattering is regarded as a kind of a frequency-degenerate fourwave vector interaction.