Numerical design of high nonlinear coefficient of microstructure optical fibers

This paper presents a theoretical design of highly nonlinear microstructure optical fiber with dispersion-flat characteristics. The APSS™ 2.3 software based on the finite difference method with perfectly matched boundary conditions is used to simulate the properties of the proposed microstructure optical fiber. According to simulation, the proposed fiber warrants a high nonlinear coefficient of the order 41 W⁻¹ km⁻¹ and a low dispersion of 0.25 ps/nm/km at 1550 nm wavelength. It assumes a dispersion-flat characteristic of 0 ± 0.50 ps/nm/km in a 1450-1620 nm wavelength range centering 1550 nm wavelength with a modest number of design parameters.     

A novel double-Brillouin-frequency spaced multi-wavelength Brillouin erbium-doped fiber laser based on non-linear amplified fiber loop mirror

In the paper, a ring double-Brillouin-frequency spaced multi-wavelength Brillouin erbium-doped fiber laser based on non-linear amplified fiber loop mirror filter is demonstrated, in which the non-linear amplified fiber loop mirror (AFLMF) is used as a filter. At the 980 nm pump power of 10.29 dBm, the tunable laser source center wavelength of 1563 nm and power of −3 dBm, up to 12 even output channels with 0.16 nm spacing are achieved. At the same time, we study the influence of 980 nm pump power, the polarization controller and the tunable laser source center wavelength on the number of Stokes light wave.     

Laser-assisted decontamination—A wavelength dependent study

We present here the experimental results on cleaning of radioactive dielectric particulates, loosely deposited on stainless steel, by coherent light of 1064 nm wavelength and its three harmonics occurring at 532 nm, 355 nm and 266 nm, derived from an Nd-YAG laser. For the initial few exposures, the decontamination factor has been found to be highest when exposed to 1064 nm radiation. With increasing number of exposures, however, the radiation with reducing wavelength assumes a more important role as a cleaning agent. The observation of almost no cleaning with 1064 nm and much reduced cleaning with its harmonics when the contamination is deposited on a transparent substrate confirms the dominant role played by metal substrate towards expelling the loose particulates from its surface.     

Design and fabrication of arrayed waveguide grating using fluoropolymer PFS-co-GMA

A 33×33 polymer arrayed waveguide grating (AWG) multiplexer is optimized and fabricated. This device is made of polymeric materials named 2,3,4,5,6-pentafluorostyrene-co-glycidylmethacrylate (PFS-co-GMA). The central wavelength and wavelength spacing are designed to be 1550.918 and 0.8 nm, respectively. The calculated results are: the 3-dB bandwidth is about 0.24 nm, insertion loss is about 8.4 dB and crosstalk is −33.7 dB. The corresponding measured results are: the center wavelength is about 1550.85 nm, wavelength channel spacing is about 0.81 nm, 3-dB bandwidth is about 0.35 nm, crosstalk is about −20 dB, insertion loss is between 10.4 dB for the central port and 11.9 dB for the edge ports.     

Tunable polymer waveguide Bragg filter fabricated by direct patterning of UV-curable polymer

Tunable polymer wavelength filters are demonstrated using a silicon-nitride grating which gives high refractive index contrast with polymers. The polymer waveguides are defined using direct patterning of a liquid-state UV-curable polymer by proximate-contact lithography technique. The wavelength filter exhibits a narrow bandwidth of less than 1.0 nm and a transmission dip of more than −15 dB. The peak wavelength is shifted over 10 nm in the temperature range of 25-70 °C and the thermal tuning efficiency is −0.212 nm/°C.     

Optimization of optical parametric chirped pulse amplification with different pump wavelengths

Optical parametric chirped pulse amplification with different pump wavelengths was investigated using LBO crystal, at signal central wavelength of 800 nm. According to our theoretical simulation, when pump wavelength is 492.5 nm, there is a maximal gain bandwidth of 190 nm centered at 805 nm in optimal noncollinear angle using LBO. Presently, pump wavelength of 492.5 nm can be obtained from second harmonic generation of a Yb:Sr₅(PO₄)₃F laser. The broad gain bandwidth can completely support ∼6 fs with a spectral centre of seed pulse at 800 nm. The deviation from optimal noncollinear angle can be compensated by accurately tuning crystal angle for phase matching. The gain spectrum with pump wavelength of 492.5 nm is much better than those with pump wavelengths of 400, 526.5 and 532 nm, at signal centre of 800 nm.     

The cascaded exponential-tapered multimode interference couplers based triplexer design for FTTH system

A novel compact triplexer, which consists of series cascaded exponential-tapered multimode interference couplers, is introduced in this paper. General self-image properties of the exponential-tapered multimode interference couplers are investigated thoroughly to fulfill the compact integrated triplexer. By combining four exponential-tapered MMI couplers, a novel compact 0.6 cm-long triplexer that is with ITU standard wavelength of 1310 nm, 1490 nm and 1550 nm for FTTH is achieved without requiring complicated design. And it can be fabricated by common planar lightwave circuit (PLC) technology. From the simulation results for wavelength of 1310 nm, 1490 nm and 1550 nm, the insertion losses are 0.34 dB, 0.9 dB and 1.17 dB, with isolations for each output waveguide ranging from 12.74 dB to 37.15 dB. The 3 dB passband widths for 1310 nm, 1490 nm and 1550 nm are 112.39 nm, 29.44 nm and 26.7 nm.     

Characteristic difference between ITO/ZrCu and ITO/Ag bi-layer films as transparent electrodes deposited on PET substrate

The metallic-glass film of ZrCu layer deposited by co-sputtering was utilized as the metallic layer in the bi-layer structure transparent conductive electrode of ITO/ZrCu (IZC) deposited on the PET substrate using magnetron sputtering at room temperature. In addition, the pure Ag metal layer was applied in the same structure of transparent conductive film, ITO/Ag, in comparison with the IZC film. The ZrCu layer could form a continuous and smooth film in thickness lower than 6 nm, compared with the island structure of pure Ag layer of the same thickness. The 30 nm ITO/3 nm ZrCu films could show the optical transmittance of 73% at 550 nm wavelength. The 30 nm ITO/12 nm ZrCu films could show the better sheet resistance of 20 Ω/sq, but it was still worse than that of the ITO/Ag films. It was suggested that an alloy system with lower resistivity and negative mixing heat between atoms might be another way to form a continuous layer in thickness lower than 6 nm for metal film.     

Photoluminescence and electroluminescence studies of polyvinyl carbazole films

Polyvinyl carbazole (PVK) film has been prepared by solution method. Its absorption, photoluminescence (PL) and electroluminescence (EL) have been studied. For PL and absorption studies, film of PVK was prepared by spreading PVK solution on clean glass plate. The dried film was taken out of the glass plate and used for absorption, thickness measurement and PL studies. The film is transparent in the visible region and absorption starts at 340 nm wavelength. The absorption peaks are obtained at 280, 250 and 220 nm, indicating that optical gap of film is 3.65 eV and molecular orbitals exist at 4.43, 4.96 and 5.64 eV. PL studies reveal that excitation by violet light gives luminescence at 430, 480 and 690 nm. For EL studies, cell is prepared by depositing PVK film on a portion of conducting glass plate and taking aluminum foil as second electrode. It is observed from the characteristics that the current varies linearly, where as EL intensity varies non-linearly with increasing voltage. Higher brightness has been observed at higher frequencies. EL spectrum shows a sharp peak at 400 nm and a broad and less intense peak at 700 nm, which are attributed to radiative decay of singlet exciton and defect centers, respectively.     

Broadband Er-Yb co-doped superfluorescent fiber source

In this paper, extensive experimental results on broad-band double cladding Er³⁺-Yb³⁺ co-doped superfluorescent fiber sources (SFSs), characterizing their output power, mean wavelength, and bandwidth (BW) stability with variations of pump power, pump wavelength, and fiber temperature, have been reported. For a 55-cm fiber, SFS power from 3.7755 (maximum BW condition of more than 80 nm) to 9.1837 mW (maximum power condition, BW is about 34 nm) has been achieved. The SFS mean wavelength dependence on pump wavelength is highly pump temperature sensitive, and can be reduced to zero in a chosen pump temperature field. The intrinsic variation of the SFS mean wavelength λ_m with fiber temperature is also measured, and a linear variation from 15 to 45 °C with a slop of −0.053 nm/°C for L_f = 100 cm and −0.04 nm/°C for L_f = 55 cm is found.     

Polymeric arrayed waveguide grating using imprint method incorporating a flexible PDMS stamp

A polymeric arrayed waveguide grating (AWG) has been proposed and demonstrated by employing the nanoimprint method. A flexible PDMS (polydimethylsiloxane) stamp with the device patterns engraved was developed from a rigid master mold made of quartz glass, featuring uniform precision contact with and easy separation from polymer films. The device was fabricated by replicating the pattern on the stamp in a core polymer layer, with no etching process involved. For our device, the number of the output channels is eight and the center wavelength of each output channel is positioned from 1543.7 nm to 1548.3 nm with the spacing of 0.8 nm. The achieved channel crosstalk was about 10 dB and the 3 dB bandwidth approximately 0.8 nm.     

Four-wave mixing in dual wavelength fiber laser utilizing SOA for wavelength conversion

In this paper, a novel configuration of a wavelength converter is set forth by utilizing a semiconductor optical amplifier (SOA) as a nonlinear gain medium to generate a four-wave mixing (FWM) effect by using a dual wavelength bi-erbium-doped fiber laser that uses an Arrayed Waveguide Grating (AWG) together with two optical channel selector (OSC) as selective elements to function as a dual wavelength switchable pump power. The four-wave mixing (FWM) is produced with a wavelength detuning of 7 nm from the pump and signal which used is as the converted signal at wavelength 1532.8 nm or 1534.5 nm for transferring data from the input signal at wavelength 1547.0 nm. Thus, even though the conversion efficiency is as low as −43 dB, it is still possible for applications as a wavelength converter.     

Compact,wide bandwidth,multi-channel power dividers based on one-dimensional photonic crystal waveguides

We propose novel compact multiport power dividers based on one-dimensional photonic crystal omnidirectional reflective waveguides. The proposed power dividers have advantages of wide bandwidth, flexible extended output channel number and compact size. The power dividers are numerical simulations using finite-difference time-domain method. Near-complete transmission and uniform at every branch of output power of multi-port power dividers are observed within wide frequency range. For a 1D PhC 1 × 6 power divider, the six output port achieved nearly 16.5% transmission at each arm from 1545 nm to 1553 nm and the size of 1 × 6 power divider is 14.3 μm × 14.3 μm at 1.55 μm operation wavelength.     

Incorporate, switchable dual-wavelength fiber laser with Bragg gratings written in a polarization-maintaining erbium-doped fiber

A stable, incorporate and switchable dual-wavelength fiber laser with two fiber Bragg gratings written in a photosensitive and polarization-maintaining erbium-doped fiber directly, that is, without splices in the laser cavity, is proposed and demonstrated. Simultaneous dual-wavelength oscillation is achieved at room temperature with a wavelength spacing of 0.343 nm. The power fluctuation and wavelength shift of single-wavelength oscillations are measured to be less than 0.24 dB and 0.013 nm over 2 h. The wavelength switchability between single- and dual-wavelength oscillations is realized by altering the voltage upon the electrostrictive ceramic actuator.     

Preparation and optical properties of barium titanate thin films

Barium titanate (BTO) films were prepared by sol-gel spin-coating technique. The crystal structure and optical properties of BTO films have been investigated. The results indicate that the BTO films are single perovskite phase having tetragonal symmetry. The band gap of the BTO films increases with the increasing of layer number and decreasing of solution concentration. The transmittance and band gap of the BTO films annealed at 900 °C is more than that of the BTO films annealed at 700 °C when wavelength is 200-1000 nm. When wavelength is 400-1000 nm, the absorption coefficient α obtained by experiment is higher than that obtained by calculation (close to zero).     

Design and characterization of single mode circular photonic crystal fiber for broadband dispersion compensation

In this paper, we present a single mode circular photonic crystal fiber (C-PCF) for broadband dispersion compensation covering 1400 to 1610 nm wavelength band over the telecommunication windows. Investigations of guiding properties are carried out using finite element method (FEM) with circular perfectly matched layer boundary condition. Numerical study reveals that a negative dispersion coefficient of about −386.57 to −971.44 ps/(nm km) is possible to obtain over the wavelength ranging from 1400 to 1610 nm with a relative dispersion slope (RDS) of about 0.0036 nm⁻¹ at 1550 nm wavelength. In addition, the single mode behaviour of C-PCF is demonstrated by employing V parameter. According to simulation, it is found that the proposed C-PCF acts as a single mode fiber within 1340 to 1640 nm wavelength. Moreover, effective dispersion, relative dispersion slope, birefringence and confinement loss are also presented and discussed.     

Control of polarization deviation at two separate wavelength by using all dielectric thin film materials

Two separate wavelength 1315 nm and 1550 nm were most widely used in near-infrared spectrum region. Based on a four-layer structure and a symmetry structure, a initial thin film stack system was constructed. Then it was optimized alternately by simplex and conjugate graduate algorithm, a beam splitter with splitting ratio R:T = 50:50 at this two wavelength was gained. The design result showed that the difference between reflectivity of P and S light around wavlength range 1300?1330 nm and 1535?1565 nm at incident angle 40°?50° was all below 2%. That indicated our design controlled the polarization deviation well at two separate wavelength with a reasonable range for both wavelength and incident angle.     

Broadband antireflective structures with hole for highly transparent glasses

Optimal sub-wavelength structures (SWS) with parabolic hole on glass substrate are designed using effective medium theory (EMT), which will reduce the reflectance over wavelength range from 300 to 1200 nm and 0° to 80° angle of incidence. The performance of SWS integrated glass is verified by genetic algorithm. The optimized SWS with the cross-sectional profile of parabolic hole have parameters with ∼120 nm diameter and 300 nm height. The average reflectance over wavelength range from 300 to 1200 nm and 0° to 80° angle of incidence could be reduced to only 0.5% by applying the optimized SWS onto glass.     

Thermally tunable microfiber knot resonator based erbium-doped fiber laser

A compact and tunable erbium-doped fiber laser is demonstrated using a highly doped fiber and a microfiber knot resonator (MKR) structure which is laid on the surface of a small peltier. The MKR functions as both a reflector and a tunable filter where tunability is achieved by varying the temperature of the resonator by heating the peltier. A stable laser output is achieved at the 1533 nm region with an optical signal to noise ratio (OSNR) of 27 dB using a 65 mW of 980 nm pump power. The operating wavelength of the laser can be tuned from 1532.60 nm to 1533.49 nm as the temperature is increased from the room temperature of 24 to 90 °C. It is observed that the operating wavelength shifts to a longer wavelength as the temperature increases with an efficiency of 12.4 pm/°C. This is due to the thermally induced optical phase shift attributable to the changes in effective refractive index and optical path length of the MKR loop.     

Accurate temperature profiling of the atmospheric boundary layer using an ultraviolet rotational Raman lidar

An ultraviolet rotational Raman lidar (RRL) system at an eye-safe wavelength of 354.7 nm is demonstrated for profiling the vertical temperature of the atmospheric layer. Two sets of narrow-band interference filters, which central wavelengths are located at 353.9 and 352.5 nm, respectively, are employed to block the elastic Mie- and Rayleigh-scattering signals and to separate two required rotational Raman signals for temperature retrieval. Experiments were carried out for verifying the feasibility of the prototype of the ultraviolet RRL from May to November in 2008, and the system calibrations were performed with the radiosonde data which were obtain from the local meteorological bureau, and good agreements were got in the experiment results. The observation results show that a statistical temperature error of less then 1 K was obtained up to the heights of 2.5 km for nighttime and 2.0 km for daytime with 300 mJ laser energy and ∼8 min observation time.