Broadband amplifier and high performance tunable laser with an extinction ratio of higher than 60 dB using bismuth oxide-based erbium-doped fiber

A Bi₂O₃-based erbium-doped fiber (Bi-EDF) ring laser with a 70?nm tunable range is demonstrated with a 49?cm long Bi-EDF in which tuning range can be extended to larger than 100?nm using an optical switch to alter the length of Bi-EDF in the laser cavity. With an extinction ratio of better than 60?dB throughout the entire tuning range, the measured FWHM of laser lines are measured to be 0.09?nm. In addition, the common amplification parameters are measured and studied in detail for various pumping configurations.     

Wideband tunable Q-switched fiber laser using graphene as a saturable absorber

An ultra-wide wavelength tuning range, which covers three different band regions consisting of the S-, C-, and L-bands, is proposed and demonstrated for a graphene-based Q-switched erbium-doped fiber laser using a tunable bandpass filter as the wavelength tuning and filtering mechanism. A 3?m length of erbium-doped fiber is used as the gain medium in a ring laser cavity configuration, with absorption coefficients of between 11 and 13 dB?m^?1 at 980?nm and about 18?dB?m^?1 at 1550?nm. The tuning range of the Q-switching pulses covers a wide wavelength range of 58?nm, which spans from 1512.5?nm to 1570.5?nm. In addition, the lasing and Q-switching thresholds are considerably low, with respective values of ～11.0?mW and ～18.4?mW. A repetition rate of 55.3?kHz is obtained at the maximum pump power of 100.4?mW, together with pulse width and pulse energy of 1.6?μs and 25.8?nJ, respectively.     

Travelling-wave Brewster-angled Stripe InGaAsP Laser Amplifier at 1·3 µm

Abstract

Optical amplification of a Brewster-angled stripe travelling-wave laser amplifier operating at 1·3 µm is described. An actively mode-locked external cavity semiconductor laser generating pulses of duration from 11 to 30 ps was used as a signal source. Maximum single-pass gain of 32 dB was attained for an input of ?24 dB m and a maximum output peak power of 25 dB m was measured for an input power of 8 dB m. Narrowing in the amplified pulse was observed on a synchroscan streak camera when the amplifier gain is too weak to sustain constant temporal amplification across the whole pulse     

Characteristics and plasma parameters of a short-wavelength low-pressure discharge lamp

We have studied the working optical characteristics and electron kinetic coefficients of a short-wavelength, electric discharge exciplex-halogen UV-VUV lamp employing a mixture of argon and chlorine with a total pressure of P = 0.5–10 kPa. The lamp operates on a system of broadened electron-vibrational bands of ArCl (175 nm) and chlorine (200, 258 nm) molecules, which overlap to form a continuum in the spectral range of 160–260 nm. It is established that the optimum mixtures are those with p(Ar) − p(Cl₂) = (2–4)−(0.15–0.30) kPa. The average output power of the short-wavelength radiation is 1–2 W at an efficiency of ∼5%. The electron energy distribution functions (EDFs) and the discharge plasma parameters have been calculated by solving the Boltzmann equation for a gas mixture with the experimentally determined optimum composition in the range of E/P values from 1 to 200 V/(cm Torr), where E is the electric field strength and P is the total gas pressure. Using the obtained EDFs, the electron transport characteristics, specific discharge power losses for the main elementary processes, and rate constants of electron processes are determined.     

Frequency modulation response due to the intensity modulation of fiber-grating Fabry–Perot lasers

A comprehensive study on the small-signal frequency modulation (FM) characteristics of a fiber-grating Fabry–Perot (FGFP) laser is numerically conducted. Fiber Bragg grating (FBG) is used as a wavelength selective element to control the properties of the laser output by controlling the external optical feedback (OFB) level. In addition to the external OFB level, the effect of other parameters such as temperature, injection current, cavity volume, nonlinear gain compression factor, linewidth enhancement factor, and fiber-grating (FG) parameters on FM characteristics of the laser are investigated. The study is performed by modifying a set of rate equations that are solved by considering the effects of external OFB and ambient temperature (T) variations. The temperature dependence (TD) of FM characteristics is calculated according to TD of laser parameters instead of using well-known Pankove relationship. Results show that the optimum external fiber length (L_ext) is 3.1?cm and the optimum range of working temperature for FGFP laser is within?±?2?°C from the FBG reference temperature (T_o). Also, it is shown that antireflection (AR) coating reflectivity and the linewidth enhancement factor have no significant effect on the FM response. The FM spectra peak amplitude is less than 5?dB with 5?mW output power. Good temperature stability is also obtained.     

Second-order optical effects in seed-mediated grown palladium nanoparticles

Palladium nanoparticles deposited on SnO₂-doped In₂O₃ substrate show substantial optical second harmonic generation (SHG) in the spectral range (λ?=?120–160?nm) which is a part of the vacuum ultraviolet (VUV) spectrum. A single crystalline Li₂ B₄ O₇ optical parametric generator (OPG) pumped by nanosecond xenon–fluorine excimer laser (EMG 500/218 (Lambda Physics)) with the wavelength 218?nm, pulse duration about 6–8?ns; pulse rate about 80?hz, average pulse power about 0.2?MW and beam diameter varying within the 1.3–7.5?nm was used to form the fundamental beam. The OPG Li₂ B₄ O₇ single crystal was cut in the XZ optical plane. We have tuned the fundamental wavelengths within the 250–320?nm spectral range varying the angle of the plane with respect to the incident pumping beam. Maximal SHG output (in the reflected SHG geometry) is observed for the incident angles 75^○–80^○ with respect to the surface normal and p-polarized incident fundamental ultraviolet beams. Spectral separation between the vacuum ultraviolet (VUV) SHG intensities and the fundamental beams was performed using a VUV Seya-Numioka vacuum monochromator with spectral resolution 6?nm in the investigated spectral range. We have found that decreasing mean average palladium nanoparticle sizes favour substantial enhancement of the output SHG within the 120–160?nm spectral range. A layer of platinum nanoparticles coated on a layer of palladium nanoparticles suppresses the SHG effect indicating a quenching of the surface plasmon excitation originating from the palladium nanoparticles. The observed effect allows utilizing the palladium nanoparticles as an efficient material for frequency transformation of the UV nanosecond pulses (spectral range 240–310?nm) into the nanosecond laser pulses with wavelengths 120–160?nm.     

Solar-blind UV photocathodes based on AlGaN heterostructures with a 300- to 330-nm spectral sensitivity threshold

Solar-blind UV photodetectors based on photocathodes are among the important applications of heterostructures based on group III metal nitride semiconductors. Related investigations are most frequently devoted to photocathodes with p-GaN active regions characterized by a long-wavelength sensitivity threshold at 360 nm. Since the detected radiation is mostly concentrated in the spectral range below 240?C290 nm, corresponding displacement of the long-wavelength sensitivity threshold of photodetectors by using photocathodes with p-AlGaN active regions is a topical task. We present preliminary results on manufacturing photocathodes with a p-Al _x Ga_{1 ? x} N (x = 0.1 and 0.3) active region (possessing a long-wavelength sensitivity threshold at 330 and 300 nm, respectively).     

A high-frequency UV-VUV radiation source operating on a mixture of argon with chlorine molecules

We present the working optical characteristics of a short-wavelength electric-discharge lamp operating at 150–270 nm (UV-VUV spectral range). The working medium is a mixture of argon with chlorine molecules (Ar-Cl₂) excited in a high-frequency transverse discharge between a metal electrode and a semitransparent nickel grid with an interelectrode distance of 2.2 cm. The proposed UV-VUV radiation source operates on the broadened emission lines of chlorine (Cl₂) and argon chloride (ArCl) molecules, which form a continuum in the 150–270 nm wavelength range. The source operation was optimized depending on the pumping power and the pressure and composition of the Ar-Cl₂ mixture. For a discharge excitation power within 50–300 W, the optimum working media were Ar-Cl₂ mixtures with the partial pressures P(Ar) = 300?400 Pa and P(Cl₂) = 30?40 Pa. The average total output power of the UV-VUV radiation extracted from the optimized source amounted to 15 W.     

Preparation,characterisation and antimicrobial activities of polymer/realgar nanocomposites

Preparation and study of homogeneous nanoparticles (NPs) have been an important area of research in recent years. In this work, we describe a polymer-protected method for the preparation and formation of realgar nanocomposites with various average diameters. Two types of macromolecules were selected and their interactions with nanorealgar were studied by spectrometric methods. It is found that the starch has a significant effect on the formation and growth of homogeneous nanorealgar with an average diameter of 30?nm. In the case of using polyvinylpyrrolidone (PVP) as a protecting polymer, the realgar NP size is in the range of 20–80?nm, with an average value of 55?nm. The polymer-protected nanorealgar shows superior antimicrobial activity against Escherichia coli and Staphylococcus aureus, whereas the bulky realgar colloid formed in aqueous solution has much less antimicrobial activity. The antimicrobial activity followed the order As₄S₄–starch NPs?>?As₄S₄–PVP NPs?>?As₄S₄ NPs, which suggests small realgar NPs are more favourable.     

Er doped waveguide amplifiers written with femtosecond laser in germanate glasses

The authors report the fabrication and characterization of active waveguides in GeO₂–PbO–Ga₂O₃ glass samples doped with Er³⁺, written with a femtosecond laser delivering pulses of 150 fs duration at 1 kHz repetition rate. Permanent refractive index change was obtained and waveguides were formed under different laser pulse energies and scan velocities. The passive and active optical properties of the waveguides were investigated. The minimum value of propagation loss was of 4.8 dB/cm. Optical amplification at 1.5 μm under 980 nm excitation was observed showing a maximal internal gain of 2.7 dB/cm.     

Hybrid integrated photodetector with flat-top steep-edge spectral response

Hybrid integrated photodetectors with flat-top steep-edge spectral responses that consist of an Si-based multicavity Fabry-Perot (F-P) filter and an InP-based p-i-n absorption structure (with a 0.2?μm In_0.53Ga_0.47As absorption layer), have been designed and fabricated. The performance of the hybrid integrated photodetectors is theoretically investigated by including key factors such as the thickness of each cavity, the pairs of each reflecting mirror, and the thickness of the benzocyclobutene bonding layer. The device is fabricated by bonding an Si-based multicavity F-P filter with an InP-based p-i-n absorption structure. A hybrid integrated photodetector with a peak quantum efficiency of 55% around 1549.2?nm, the -0.5 dB band of 0.43?nm, the 25?dB band of 1.06?nm, and 3?dB bandwidth more than 16?GHz, is simultaneously obtained. Based on multicavity F-P structure, this device has good flat-top steep-edge spectral response.     

Wide-band flat-gain optical amplifier using Hafnia and zirconia erbium co-doped fibres in double-pass parallel configuration

ABSTRACT

A new compact and wide-band erbium-doped fibre amplifier (EDFA) was demonstrated by combining Hafnia-bismuth Erbium co-doped fibre (HB-EDF) and zirconia–yttria–aluminum Erbium co-doped fibre (Zr-EDF) as a hybrid gain medium, in parallel double-pass configuration. The proposed amplifier comprises a 0.5?m long HB-EDF and 4?m long Zr-EDF optimized for C- and L-band operations, respectively. The HB-EDF and Zr-EDF has erbium ion concentration of 12,500?ppm and 2800?ppm, respectively. At -10 dBm input signal, a wide-band flat gain of 15.7?dB is achieved with gain fluctuation of less than 1.5?dB within a wavelength region from 1525 to 1600?nm. Compared to same configuration of HB-EDF and Zr-EDF amplifiers which are using two pieces of HB-EDF and Zr-EDF, respectively with the same total amount of erbium ions, the proposed EDFA with hybrid gain medium provides even better performances in term of flat gain, bandwidth and noise figure.     

The effect of water vapor on the characteristics of a pulsed-periodic ultraviolet radiation source

The effect of a small admixture of water vapor on the optical characteristics of an UV radiation source using a He-air-H₂O mixture as the working medium was studied. The gas mixture was excited in a short-pulse transverse volume discharge operating at a charging voltage of U _ch ≤10 kV. As the partial pressure of helium was varied in the 10–45 kPa range at an air pressure of P(air)=130 Pa and the water vapor pressure within P(H₂O)=50–100 Pa, the main optical emission from plasma in the UV wavelength range was concentrated in a broad band peaked at λ_max=309.7 nm and was two times greater than the intensity of the base emission bands of the nitrogen molecule in this spectral range (λ=337.1 and 315.9 nm, N₂(C-B)). Adding water vapor to the He-air mixture increases the spectral range of the UV source toward shortwave region, which is related to a spontaneous decay of the products of dissociation of water molecules.     

Polymeric waveguides using oxidized porous silicon cladding for optical amplification

We report on a new hybrid approach to realize optical slab waveguides for optical amplification purposes. The structure consists of a dye-doped polymer core (PMMA) deposited over an oxidized porous silicon (PS) cladding layer formed on a silicon wafer. The very low refractive index (n = 1.16) achievable in the cladding allows obtaining monomodal behavior with high confinement factors (Γ_TE = 96%) even for very thin cores (400 nm). Optically excited guided luminescence shows stimulated emission, strong line narrowing and a clear threshold and superlinear behavior with pump energy. By means of the variable stripe length (VSL) technique, values of net optical gain up to 113 dB/cm (constant over 3 mm) and absolute amplification values up to 34 dB have been measured at 694 nm when pumping with 80 mJ/cm² energy pulses. These results validate the use of oxidized PS as a cladding layer in silicon photonics.     

Influence of drug physicochemical characteristics on in vitro transdermal absorption of hydrophobic drug nanosuspensions

Abstract

The purpose of this paper was to study the influence of drug physicochemical characteristics on in vitro transdermal absorption of hydrophobic drug nanosuspensions. Four drug nanosuspensions were produced by high-pressure homogenization technique, which were the same in stabilizer and similar in particle size. Differential scanning calorimetry and powder X-ray diffraction analysis showed that the crystalline state of the nanocrystals did not change. In vitro permeation study demonstrated that the drug nanosuspensions have a higher rate of permeation that ranged from 1.69- to 3.74-fold compared to drug microsuspensions. Correlation analysis between drug physicochemical properties and J_ss revealed that log P and pKa were factors that influenced the in vitro transdermal absorption of hydrophobic drug nanosuspensions, and drugs with a log P value around 3 and a higher pKa value (when pKa?<?pH+2) would gain higher J_ss in this paper.     

Tunable S-band output based on Raman shift in dispersion shifted fiber

A tunable short-wavelength band Raman fiber laser using a dispersion shifted fiber as the nonlinear medium is proposed and demonstrated. This approach provides an alternative to the common method of using depressed-cladding, erbium-doped fibers as the gain medium in S-band fiber lasers. The proposed laser has a tuning range of 1508 to 1534?nm as well as an average peak power of about ?11.3?dBm within the range 1518–1530?nm. A high signal-to-noise ratio of approximately 70 dB is obtained from the system at this range.     

Spectra and broad-spectral laser operation of a disordered Nd:LiLa(MoO4)2 crystal

The crystal characteristics of a disordered Nd:LiLa(MoO₄)₂ laser crystal were investigated in detail, including its structure, absorption, emission and Raman scattering spectra. Laser operation, end-pumped by an 808?nm diode laser, has been demonstrated in both a concave-plano and plane-parallel resonator cavity. A broad-spectral dual-peak laser emission at 1061?nm and 1060?nm with a full width at half maximum of 2?nm was obtained in the experiment. A maximum output power of 267?mW was obtained in the concave-plano cavity. However, in the plane-parallel cavity, laser output of 381?mW was obtained, giving a slope efficiency of 14.5%. The results lay the groundwork for Raman, mode-locked and tunable laser applications generated by a Nd:LiLa(MoO₄)₂ laser crystal.     

Tm3+-doped fiber master oscillator power amplifier with broad tunability in pulse duration using an acousto-optic external modulator

ABSTRACT

We demonstrate a pulse-duration tunable Tm³⁺-doped pulsed all-fiber master oscillator power amplifier (MOPA) operating at a central wavelength of 1908 nm. By using acousto-optic(AO) external modulation, the amplified laser pulse shows a tuning range having pulse durations from 66.5 ns to 8.0 μs and a repetition rate of 100 kHz-2 MHz. The laser achieved a maximum average power of 28.1 W and a corresponding energy of 28.1 μJ at 1MHz with a 3 dB linewidth of 0.63 nm and a beam quality factor of M_x²=1.25 and M_y²=1.32. The ASE suppression ratio is 50 dB and the corresponding total amplifier gain is 27.5 dB. To the best of our knowledge, it is the highest average output power and slope efficiency (～51.0%) achieved using AO external modulation in a Tm³⁺-doped pulsed fiber amplifier.     

Tunable Brillouin-erbium fiber laser incorporating a low-cost biconic tapered fiber

A new method of tuning a multi-wavelength Brillouin-erbium fiber laser (BEFL) within a Fabry–Perot cavity by incorporating a low-cost biconic tapered fiber is reported. The biconic tapered fiber was fabricated using a flame elongation technique and it was incorporated into the BEFL system to position the self-lasing cavity modes over a tuning range of 5.5 nm within the erbium-doped fiber gain profile. By injecting the Brillouin pump near to the tunable self-lasing cavity modes, it suppresses the modes and generates stable cascaded Brillouin–Stokes lines with more than 20 dB signal-to-noise ratio.     

The Effect of Parameter Estimation on Upper‐sided Bernoulli Cumulative Sum Charts

The Bernoulli cumulative sum (CUSUM) chart has been shown to be effective for monitoring the rate of nonconforming items in high‐quality processes where the in‐control proportion of nonconforming items (p₀) is low. The implementation of the Bernoulli CUSUM chart is often based on the assumption that the in‐control value p₀ is known; therefore, when p₀ is unknown, accurate estimation is necessary. We recommend using a Bayes estimator to estimate the value of p₀ to incorporate practitioner knowledge and to avoid estimation issues when no nonconforming items are observed in phase I. We also investigate the effects of parameter estimation in phase I on the upper‐sided Bernoulli CUSUM chart by using the expected value of the average number of observations to signal (ANOS) and the standard deviation of the ANOS. It is found that the effects of parameter estimation on the Bernoulli CUSUM chart are more significant than those on the Shewhart‐type geometric chart. The low p₀ values inherent to high‐quality processes imply that a very large, and often unrealistic, sample size may be needed to accurately estimate p₀. A methodology to identify a continuous variable to monitor is highly recommended when the value of p₀ is low and the required phase I sample size is impractically large. Copyright © 2012 John Wiley & Sons, Ltd.