Broadband photoluminescence from pulsed laser deposited Er2O3 films

Photoluminescence (PL) with the bandwidth of 45 nm (1523-1568 nm at the level of 3 dB) was observed in amorphous Er₂O₃ films grown on to the quartz substrate by pulsed laser ablation of erbium oxide stoichiometric target. Optical transmission spectrum has been fitted to Swanepoel formula to determine the dispersion of refractive index and to extract resonance absorption peaks at 980 and 1535 nm. The maximum gain coefficient of 800 dB/cm at 1535 nm was estimated using McCumber theory and experimental spectrum of the resonance absorption. In 5.7 mm-long waveguide amplifier a theory predicts the spectral gain of 20 dB with 1.4 dB peak-to-peak flatness in the bandwidth of 31 nm (1532-1563 nm) when 73% of Er³⁺ ions are excited from the ground state to the ⁴I_13/2 laser level. Strong broadband PL at room temperature and inherently flat spectral gain promise Er₂O₃ films for ultra-short high-gain optical waveguide amplifiers and integrated light circuits.     

Boson peak of AsxS1−x glasses and theoretical calculations of low frequencies clusters vibrations

The results of comparison of spectral position of the LF bands of g-As₂S₃ and g-As₂₂S₇₈ with theoretical calculations of vibrational spectra of different clusters (As₂S₄, As₂S₅, As₂S₆, AsS₃-As₃) in the LF region (10-85 cm⁻¹) are given. The torsion type vibrations of the small chain-like clusters are located in the same spectral region as Boson peak of As-S glasses system. They can make several contributions to the LF spectrum. The cluster lengths by weight distribution functions f(L)*L are from 5.5 to 10.1 Å and from 4.5 to 7.5 Å for g-As₂S₃ and g-As₂₂S₇₈, respectively. The lognormal fittings of the f(L)*L functions give the most probably values about the 7.6 Å (for g-As₂S₃) and 6.2 Å (for g-As₂₂S₇₈).     

The rotationally-resolved absorption spectrum of formaldehyde from 6547 to 6804 cm

The room temperature absorption spectrum of formaldehyde, H₂CO, from 6547 to 6804 cm⁻¹ (1527-1470 nm) is reported with a spectral resolution of 0.001 cm⁻¹. The spectrum was measured using cavity-enhanced absorption spectroscopy (CEAS) and absorption cross-sections were calculated after calibrating the system using known absorption lines of H₂O and CO₂. Several vibrational combination bands occur in this region and give rise to a congested spectrum with over 8000 lines observed. Pressure broadening coefficients in N₂, O₂, and H₂CO are reported for an absorption line at 6780.871 cm⁻¹, and in N₂ for an absorption line at 6684.053 cm⁻¹.     

Study of Be δ-doped GaAs/AlAs multiple quantum wells by the surface photovoltage spectroscopy

We report a surface photovoltage and differential surface photovoltage (DSPV) study of Be δ-doped GaAs/AlAs multiple quantum wells (QWs) with widths ranging from 3 to 20 nm and sheet doping densities from 2 × 10¹⁰ to 2.5 × 10¹² cm⁻² per well aiming to characterize their electronic properties and structural quality. From a line shape analysis of room temperature DSPV spectra the interband excitonic transition energies and broadening parameters for a large number of QW-related subbands have been established. A study of well-width and quantum number dependencies of the excitonic linewidths allowed us to evaluate the various broadening contributions to the spectral line shapes in QWs of different design. It was found that an average half monolayer well-width fluctuations are the dominant broadening mechanism of the excitonic line for QWs thinner than 10 nm. In QWs thicker than 10 nm, the spectral line broadening originates mainly from thermal broadening as well as Stark broadening due to random electric fields of ionized impurities and exciton scattering by free holes.     

Femtosecond optical Kerr effect study of Ge10As40S30Se20 film

The results of the femtosecond optical heterodyne detection of optical Kerr effect at 805 nm with the 80 fs ultrafast pulses in amorphous Ge₁₀As₄₀S₃₀Se₂₀ film is reported in this paper. The film shows an optical non-linear response of 200 fs under ultrafast 80 fs-pulse excitation, and the values of real and imaginary parts of non-linear susceptibility χ⁽³⁾ were 9.0×10⁻¹² and −4.0×10⁻¹² esu, respectively. The large third-order non-linearity and ultrafast response are attributed to the ultrafast distortion of the electron orbits surrounding the average positions of the nucleus of Ge, As, S and Se atoms. This Ge₁₀As₄₀S₃₀Se₂₀ chalcogenide glass would be expected as a promising material for optical switching technique.     

光折变法制备的As2S8条形波导的光阻断效应

实验研究了As₂S₈薄膜光折变现象.提出并采用紫外光激励的方法试制了As₂S₈条形波导，导模激励显示该波导具有良好的导波特性.在此基础上，考察了As₂S₈条波导的光阻断效应，实现了光-光效应的开关功能. 关键词： 光波导技术 2S₈条形波导')" href="#">As₂S₈条形波导 光阻断效应 光激励法     

Photosensitive post tuning of chalcogenide Te20As30Se50 narrow bandpass filters

We present an experimental study on the photosensitive properties of narrow bandpass filters based on a chalcogenide Te₂₀As₃₀Se₅₀ (TAS) spacer. The transmittance curve of single TAS layer was shifted towards long wavelength direction after 2 h exposure by Xenon arc lamp. The refractive index and extinction coefficient were both increased together with a red shift of optical gap. A maximum 1.7% photo-induced effect was observed. Narrow band filters constituted by TAS and cryolite were manufactured by electron beam deposition. The transmittance spectrum of the filter during the exposure by a wide band source was in situ measured and the resonant wavelength was observed to turn longer gradually till saturation. A spatially localized central wavelength change up to 5.7 nm was finally obtained. The stability of the photo-induced effect was studied and some comments were given at the end of this paper.     

Second-harmonic generation in transparent surface crystallized GeS2-Ga2S3-CdS chalcogenide glasses

Transparent surface crystallized glasses containing CdGa₂S₄ nonlinear optical crystal were prepared by the 70GeS₂ · 15Ga₂S₃ · 15CdS (GGC15) chalcogenide glass. Average diameters of crystallites are about 150 nm and 600 nm for heating at 405 °C for 48 and 108 h (named GGC15-48 and GGC15-108), respectively, and the thickness of the surface crystallized layer was approximately 15 μm. By using the Maker fringe measurement, prominent second-harmonic generation was observed from these crystallized glasses, and the χ⁽²⁾ of the GGC15-48 sample is calculated to be as well as 38.85 pm/V, and the value is 13.7 pm/V for the GGC15-108. They are promising to be applied in photoelectric and all-optical field in the future.     

Numerical investigation on buffer performance based on acoustic excitation by stimulated Brillouin scattering in an As2Se3 fiber

Buffer performance of a 2.5 Gb/s bit stream with non-return-to-zero format is investigated based on acoustic excitation by stimulated Brillouin scattering in an As₂Se₃ fiber. The storage process and the retrieval process of the bit stream are separately controlled by a “Write” pulse and a “Read” pulse. The research results show that the output signal-to-noise ratio and the readout efficiency of the buffer are agreeable, and the pulse distortion is low, if both the “Write” and the “Read” pulses are with high enough peak power and spectrum wider than that of the signal pulse. Buffering of a consecutive 10-bit-long 2.5 Gb/s NRZ bit stream has also been demonstrated in the As₂Se₃ fiber with length of only 0.5 m. The storage of a long bit stream, such as the data packet containing about 1000 bits in the telecommunications, is limited by the high loss in the As₂Se₃ fiber. However, the development of the special optical fiber with high Brillouin gain coefficient, long acoustic lifetime and low loss can make this technology applicable for all-optical buffering in high speed optical networks.     

All-optical RZ-to-NRZ data format conversion using spectral broadening effect in a dispersion-shifted fiber

We propose a simple and efficient approach to obtain all-optical RZ-to-NRZ data format conversion using self-phase modulation (SPM) in a dispersion-shifted fiber. By exploiting SPM induced spectral broadening together with group velocity dispersion in the normal regime, a 10 Gb/s return-to-zero data signal has been converted to the non-return-to-zero format. The proposed scheme can work with different signal bit rates and does not require any external pulse duplicator. The 10 Gb/s bit-error-rate (BER) measurement shows a power penalty of less than 1.5 dB at 10⁻⁹ BER level.     

Strip silicon waveguide for code synchronization in all-optical analog-to-digital conversion based on a lumped time-delay compensation scheme

An all-optical analog-to-digital converter(ADC) based on the nonlinear effect in a silicon waveguide is a promising candidate for overcoming the limitation of electronic devices and is suitable for photonic integration. In this paper, a lumped time-delay compensation scheme with 2-bit quantization resolution is proposed. A strip silicon waveguide is designed and used to compensate for the entire time-delays of the optical pulses after a soliton self-frequency shift(SSFS) module within a wavelength range of 1550 nm–1580 nm. A dispersion coefficient as high as-19800 ps/(km·nm) with ±0.5 ps/(km·nm)variation is predicted for the strip waveguide. The simulation results show that the maximum supportable sampling rate(MSSR) is 50.45 GSa/s with full width at half maximum(FWHM) variation less than 2.52 ps, along with the 2-bit effectivenumber-of-bit and Gray code output.     

Studies on electrodeposited As2S3 thin films by double exposure holographic interferometry technique

Arsenic trisulphide (As₂S₃) thin films have been deposited onto stainless steel and fluorine doped tin oxide (FTO) coated glass substrates by electrodeposition technique using arsenic trioxide (As₂O₃) and sodium thiosulphate (Na₂S₂O₃) as precursors and ethylene diamine tetracetic acid (EDTA) as a complexing agent. Double exposure holographic interferometry (DEHI) technique was used to determine the thickness and stress of As₂S₃ thin films. It was observed that the thickness of the thin film increases whereas film stress to the substrate decreases with an increase in the deposition time. X-ray diffraction and water contact angle measurements showed polycrystalline and hydrophilic surface respectively. The bandgap energy increases from 1.82 to 2.45 eV with decrease in the film thickness from 2.2148 to 0.9492 μm.     

In situ high-pressure X-ray diffraction study of densification of a molecular chalcogenide glass

Structural mechanisms of densification of a molecular chalcogenide glass of composition Ge_2.5As_51.25S_46.25 have been studied in situ at pressures ranging from 1 atm to 11 GPa at ambient temperature as well as ex situ on a sample quenched from 12 GPa and ambient temperature using high-energy X-ray diffraction. The X-ray structure factors display a reduction in height of the first sharp diffraction peak and a growth of the principal diffraction peak with a concomitant shift to higher Q-values with increasing pressure. At low pressures of at least up to 5 GPa the densification of the structure primarily involves an increase in the packing of the As₄S₃ molecules. At higher pressures the As₄S₃ molecules break up and reconnect to form a high-density network with increased extended-range ordering at the highest pressure of 11 GPa indicating a structural transition. This high-density network structure relaxes only slightly on decompression indicating that the pressure-induced structural changes are quenchable.     

Controlled Stark shifts in Er-doped crystalline and amorphous waveguides for quantum state storage

We present measurements of the linear Stark effect on the ⁴I_15/2 → ⁴I_13/2 transition in an Er³⁺-doped proton-exchanged LiNbO₃ crystalline waveguide and an Er³⁺-doped silicate fiber. The measurements were made using spectral hole burning techniques at temperatures below 4 K. We measured an effective Stark coefficient (Δμ_eχ)/(h) = 25 ± 1 kHz/V cm⁻¹ in the crystalline waveguide and  kHz/V cm⁻¹ in the silicate fiber. These results confirm the potential of erbium-doped waveguides for quantum state storage based on controlled reversible inhomogeneous broadening.     

Optical and photophysical investigation of Meso, Proto and Hematoporphyrin(IX)dimethylester doped hybrid borate glasses

Hybrid borate glasses containing different concentrations (0.5-2.0 mg in 12 g of boric acid) of Mesoporphyrin(IX)dimethylester, Protoporphyrin(IX)dimethylester and Hematoporphyrin(IX)dimethylester were prepared by rapid melt quench technique at 230 °C. The hybrid glass samples were characterized by X-ray diffraction, optical absorption, steady state and time-resolved fluorescence emission. The optical absorption spectrum shows red-shift in Soret band along with change in Q-band pattern. The intensity of Q-band was found to increase with increase in the concentration of porphyrin in the glass. Steady state emission spectrum shows strong S₂→S₀ emission in the range 462-495 nm and blue shift in S₁→S₀ emission. Time-resolved fluorescence emission and fluorescence excitation spectra showed that different structures of porphyrins were exist in the glass samples. The variation in the spectral behaviour in the glass was correlated with those in solution medium and possible structures of porphyrin in borate glass were explored.     

Pulsed laser deposition of fluoride glass thin films

The development of integrated waveguide lasers for different applications such as marking, illumination or medical technology has become highly desirable. Diode pumped planar waveguide lasers emitting in the green visible spectral range, e.g. thin films from praseodymium doped fluorozirconate glass matrix (called ZBLAN, owing to the main components ZrF₄, BaF₂, LaF₃, AlF₃ and NaF) as the active material pumped by a blue laser diode, have aroused great interest. In this work we have investigated the deposition of Pr:ZBLAN thin films using pulsed laser radiation of λ = 193 and λ = 248 nm. The deposition has been carried out on MgF₂ single crystal substrates in a vacuum chamber by varying both processing gas pressure and energy fluence. The existence of an absorption line at 210 nm in Pr:ZBLAN leads to absorption and radiative relaxation of the absorbed laser energy of λ = 193 nm preventing the evaporation of target material. The deposited thin films consist of solidified and molten droplets and irregular particulates only. Furthermore, X-ray radiation has been applied to fluoride glass targets to enhance the absorption in the UV spectral region and to investigate the deposition of X-ray treated targets applying laser radiation of λ = 248 nm. It has been shown that induced F-centres near the target surface are not thermally stable and can be easily ablated. Therefore, λ = 248 nm is not suitable for evaporation of Pr:ZBLAN.     

Ring resonator with multimode waveguide turning-mirror couplers in InGaAsP-InP

Compact In_0.67Ga_0.33As_0.6P_0.4/In_0.71Ga_0.29As_0.74P_0.26 on InP single ring resonators incorporating 2 × 2 multimode interference (MMI) turning-mirror couplers with cross coupling factor of 0.15 have been demonstrated. The form of race tracks is a 15-degree arc of 260 μm radius joined with a 60-degree arc of 110 μm radius, and finished with another 15-degree arc of 260 μm radius. The MMI turning-mirror coupler of 128 μm in length is used in the single ring resonators, which correspond to free spectral ranges of 82 GHz. A contrast of 4 dB, a finesse of nearly 3 and full-width at half-maximum (FWHM) of 0.24 nm for the drop port have been achieved in this single ring resonator. From the experimental value T_max/T_min of 21 dB, the experiment coupling factor coincides with the simulation.     

High-contrast all-optical switching with Pt:ethynyl complex

We have theoretically analyzed all-optical switching in Pt:ethynyl complex based on nonlinear excited-state absorption. A detailed analysis for Pt:ethynyl complex has been presented based on rate equation approach. It is shown that a pulsed pump laser beam at 355 nm switches the transmission of a cw probe laser beam at 633 nm through a Pt:ethynyl sample. The effect of various parameters, such as pump pulse width, peak pumping intensity, normalized parameter , transition times of S₁→S₀ and S₁→T₁ states and lifetime of triplet state, on switching characteristics has been analyzed in detail. It has been shown that the probe beam can be completely switched off (i.e. 100% modulation) by a pulsed pump laser beam at 50 kW/cm². These results have been used to design all-optical NOT and the universal NOR and NAND logic gates with multiple pump laser pulses.     

Preparation and characterization of SnO2 nanoparticles using high power pulsed laser

Tin dioxide (SnO₂) nanoparticles having 3 nm size were synthesized by irradiating pure tin metal using high power Nd:YAG laser in deionized water. Formation of nano-SnO₂ crystallites was confirmed by X-ray diffraction (XRD) and AFM study. UV-vis absorption spectral studies showed a peak at 240 nm. FTIR spectrum showed a band in the range of 400-700 cm⁻¹ which was assigned to Sn-O antisymmetric vibrations. Photoluminescence spectrum of synthesized SnO₂ nanoparticles showed peak corresponding to 3.175, 2.901 and 2.613 eV respectively.     

Configurable coarse wavelength division demultiplexers based on planar reflective gratings

Configurable coarse wavelength division multiplexing filters were realized using a planar reflective grating architecture utilizing small diffraction angles. The novel architecture yielded a 10-fold reduction in the chip size compared to previously reported filter configurations. The proposed design was manufactured using a standard silica-on-silicon process with a waveguide refractive index contrast of 0.82%. Polarization dependent losses of less than 0.2 dB were achieved without any post-processing steps. Fabricated filters showed insertion losses of 2.4 dB and remarkably broad free spectral ranges of more than 500 nm. The combination of single-mode input and multi-mode output guides resulted in box-like passband responses with bandwidth of 14.2 nm. Applications of the filters for integrated coarse wavelength division receivers and monitors are discussed.