Widely tunable difference frequency generation around 3.4 μm using index dispersion property of PPLN

In this paper, the wide difference frequency generation (DFG) tuning characteristics around 3.4 μm are investigated by using the index dispersion property of PPLN. With a ytterbium doped fiber laser (YDFL) and an erbium doped fiber laser (EDFL) as the fundamental light sources, our simulation results show that the quasi-phase matching (QPM) wavelength acceptance bandwidth (BW) for the pump is much larger than that for the signal. Although the positions of the broadened QPM pump bands vary with the poling period and the signal wavelength, the corresponding idler tuning ranges center around 3.4 μm. With a signal wavelength of 1.57 μm, an idler tuning range of greater than 170 nm is experimentally obtained in the 30 uniform grating PPLN. When the signal wavelength and the poling period are respectively changed to 1.55 and 29.50 μm, wide DFG tuning operations around 3.4 μm are also achieved with the crystal temperature adjusted to adapt the change.     

Excitation of erbium in the heterogeneous nanocrystalline matrix of amorphous silicon

The erbium photoluminescence decay kinetics at a wavelength of 1.54 μm in amorphous hydrogenated silicon films obtained at high oxygen concentrations in a magnetron gas discharge is investigated. Optically active erbium is found to exist both in the semiconducting matrix of amorphous silicon and in dielectric nanocrystals of erbium silicate, which are formed in this case. The concentration ratio of excited erbium in amorphous silicon and in the nanocrystals is determined, as well as the time of excitation transfer from erbium in amorphous silicon to erbium in the nanocrystals. The mechanism of erbium excitation in this heterogeneous system is considered. The external quantum yield of erbium photoluminescence measured at a wavelength of 1.54 μm and room temperature is found to be 0.3–0.4%.     

Interrelation between microstructure and optical properties of erbium-doped nanocrystalline thin films

Nanocrystalline silicon thin films codoped with erbium, oxygen and hydrogen have been deposited by co-sputtering of Er and Si. Films with different crystallinity, crystallite size and oxygen content have been obtained in order to investigate the effect of the microstructure on the photoluminescence properties. The correlation between the optical properties and microstructural parameters of the films is investigated by spectroscopic ellipsometry. PL response of the discussed structures covers both the visible wavelength range (a crystallite size-dependent photoluminescence detected for 5–6 nm sized nanocrystals embedded in a SiO matrix) and near IR range at 1.54 μm (Er-related PL dominating in the films with 1–3 nm sized Si nanocrystals embedded in a-Si:H). It is demonstrated that the different PL properties can be also discriminated on the basis of ellipsometric spectra.     

Photoluminescence of Er<Superscript>3+</Superscript> ions in layers of quasi-ordered silicon nanocrystals in a silicon dioxide matrix

The spectra and kinetics of photoluminescence from multilayered structures of quasi-ordered silicon nanocrystals in a silica matrix were studied for undoped samples and samples doped with erbium. It was shown that the optical excitation energy of silicon nanocrystals could be effectively transferred to Er³⁺ ions, which was followed by luminescence at a wavelength of 1.5 µm. The effectiveness of energy transfer increased as the size of silicon nanocrystals decreased and the energy of exciting light quanta increased. The excitation of erbium luminescence in the structures was explained based on dipole-dipole interaction (the Förster mechanism) between excitons in silicon nanocrystals and Er³⁺ ions in silica surrounding them.     

Erbium photoluminescence excitation spectroscopy in Si: Er epitaxial structures

Excitation spectra of erbium photoluminescence in Si: Er epitaxial structures are studied within a broad pump wavelength range (λ_ex = 780–1500 nm). All the structures studied reveal a fairly strong erbium photoluminescence signal at photon energies substantially smaller than the silicon band-gap width (λ = 1060 nm) with no exciton generation. A possible mechanism of erbium ion excitation in silicon without exciton involvement is discussed.     

Study of the dynamics of the absorption spectra of human tooth enamel and dentine under heating and ablation by submillisecond pulse radiation of an erbium laser with a generation wavelength of 2.79 μm

We studied the absorption spectrum of intact human tooth enamel and dentine in the range of 0.26–10 μm. We present the infrared absorption spectra of destruction products of human tooth enamel and dentine by submillisecond laser pulses on a crystal of yttrium-scandium-gallium garnet, activated by chrome and erbium ions with a wavelength of 2.79 μm. We discuss the effect of water spraying on the mechanism of laser ablation and the infrared absorption spectra. We report for the first time transformations observed in the absorption spectra of human tooth enamel in the wavelength range of 2.5–3.5 μm under its heating to +700°C.     

1.54 μm room temperature emission from Er-doped Si nanocrystals deposited by ECR-PECVD

In this work, silicon nanocrystals (Si-nc) embedded in a silicon-rich silicon oxide (SRSO) matrix doped with Er³⁺ ions for different erbium and silicon concentrations have been deposited by electron-cyclotron resonance plasma-enhanced chemical-vapor-deposition (ECR-PECVD) technique. Their optical properties have been investigated by photoluminescence (PL) and reflectance spectroscopy.Room temperature emission bands centered at ∼1.54 and at 0.75 μm have been obtained for all samples. The most intense emission band at ∼1.54 μm was obtained for samples with concentrations of 0.45% and 39% for erbium and silicon, respectively. Moreover, it has been found that the broad emission band centered at ∼0.75 μm for all samples shows a very strong interference pattern related to the a specific sample structure and a high sample quality.     

Simultaneous broadening and enhancement of the 1.5 μm photoluminescence peak of Er3+ ions embedded in a 1-D photonic crystal microcavity

It is proposed for the first time that the 1.5 μm Er³⁺ photoluminescence peak may be significantly broadened by a photonic crystal microcavity structure. Two coupled microcavities have been designed and prepared by sol-gel processing based on alternating layers of silicate glass and titania materials. The 1.5 μm emission spectra of the Er³⁺ ions embedded in these microcavity structures are measured and discussed. It is found that the spontaneous emission spectra are effectively broadened to a point where they become approximately square in shape. The full width at half maximum (FWHM) reached a value as large as 183 nm, which is the best result reported so far. The measured photoluminescence profiles agree well with simulated curves and an intensity enhancement by the microcavities has also been observed. These results may be of significance for applications requiring broadened or otherwise modified spontaneous emission spectra, such as application-specific LEDs and other non-coherent light sources. The present technique can easily be applied to other active materials.     

Theoretical and experimental investigations of the Mid-IR DFG tuning property based on fiber laser fundamental lights

The tuning properties for the mid-IR DFG laser based on uniform grating PPLN have been investigated with tunable YDFL and EDFL fundamental lights. Our results show that, for a fixed crystal temperature, the idler tunable range is less than 10 nm when the EDFL is tuned. Although the pump may be allowed to be tuned in its two QPM acceptance bands, the idler tunable range is still narrow for a fixed temperature. By optimizing the crystal temperature, however, the two pump QPM acceptance bands may be overlapped to form one broadband QPM band, which may be used to increase the idler tunable range to 175 nm near 3.4 μm region. The positions of the single signal and the two separate pump QPM acceptance bands can be continuously moved by adjusting the temperature, which may also be used for enhancing the idler tuning range. By tuning the EDFL while adjusting the temperature, a whole combined idler tuning range between 2.98 and 3.78 μm was experimentally obtained with three fixed pump wavelengths of 1.05, 1.08 and 1.11 μm. By tuning the YDFL in the two separate QPM acceptance bands, a tuning range of 690 nm has been demonstrated with only one fixed signal wavelength of 1.58 μm.     

Properties of erbium silicate doped with chromium in porous silicon

The possible formation of chromium-doped erbium silicate Er₂SiO₅: Cr in thin layers of porous silicon is demonstrated. This paper reports on studies of the photoluminescence, electron paramagnetic resonance, and transverse current transport in porous silicon layers (with different chromium and erbium contents) grown on n-and p-silicon single crystals heavily doped with shallow impurities. The Er₂SiO₅: Cr phase with the photoluminescence maxima at approximately 1.3 and 1.5 μm manifests itself after high-temperature annealing at 1000°C. The introduction of erbium and annealing at 700°C increase the intensity of the red photoluminescence of porous silicon by several factors. The decrease in the electrical conductivity of porous silicon suggests the onset of the formation of erbium silicate. The current-voltage characteristics exhibit a nonlinear behavior with an exponential dependence of the current on the voltage due to the discrete electron tunneling. An electron paramagnetic resonance spectrum of P _b centers in p-type heavily doped silicon is observed for the first time.     

Luminescence of transparent glass ceramics containing Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> zirconate-titanate nanocrystals

Luminescence regularities have been studied in new erbium/ytterbium materials based on glasses and glass ceramics of a magnesium-aluminosilicate system containing nanoscale erbium/ytterbium zirconate titanate crystals with the pyrochlore structure. Lifetimes of Yb³⁺ and Er³⁺ ions in the ² F_5/2 state and in the ⁴I_11/2 and ⁴I_13/2 states, respectively, and the efficiency of Yb³⁺ → Er³⁺ energy transfer have been evaluated. The identified spectral-luminescent characteristics of the studied glasses and glass ceramics co-doped with erbium and ytterbium ions show that these materials are promising media for producing laser generation in the spectral range around 1.5 μm.     

Synthesis and Optical Properties of Films Formed by the Sol‐Gel Method in Mesoporous Matrices

The main laws governing the formation of films by the solgel method in the mesopores of anodic aluminum oxide, porous silicon, and synthetic opals have been considered. Investigations of the luminescence at 1.5 m in the structure porous silicon–gel, doped with erbium, have been analyzed. Special features of the synthesis of the film structure microporous xerogel–mesoporous anodic aluminum oxide, doped with erbium, terbium, and europium, and the possible factors that enhance the photoluminescence of lanthanides in the structure are shown.     

Vibronic and electric properties of semiconductor structures based on butyl-substituted mono-and triphthalocyanine containing erbium ions

The Raman spectra have been obtained and the temperature dependence of the conductivity of organic semiconductor structures based on butyl-substituted erbium monophthalocyanine and erbium triphthalocyanine has been studied. It has been found experimentally that the activation energy decreases dramatically and the Raman spectra exhibits four new peaks in the region of large Raman shifts as the molecular structure of the samples becomes more complicated.     

Modification of erbium photoluminescence excitation spectra for the emission wavelength 1.54 μm in mesoscopic structures

Photoluminescence excitation (PLE) spectra for the emission wavelength 1.54 μm were studied for erbium-doped xerogels embedded in artificial opals and porous anodic alumina films. Opals were chosen with photonic stop-band in green spectral range, where excitation of 1.54 μm occurs most efficiently. In comparison to the structure erbium-doped titania xerogel/porous anodic alumina/silicon the photoluminescence excitation spectra for 1.54 μm emission wavelength significantly changes for the same xerogels embedded in artificial opals. Enhancement of erbium-related 1.54 μm emission was observed from the structure Fe₂O₃ xerogel/porous anodic alumina fabricated on silicon, having some incompletely anodized aluminium, under excitation with either the lasing source at 532 nm or xenon lamp. Evident difference in PLE spectra for erbium doped TiO₂ and Fe₂O₃ xerogels in porous anodic alumina is observed.     

Si-based erbium-doped light-emitting devices

We report on the fabrication and performance of Si-based light sources. The devices consist of MOS structures with erbium (Er)-doped silicon rich oxide (SRO) film as gate dielectric. The devices exhibit electroluminescence (EL) at 1.54 μm at room temperature with a 0.2% external quantum efficiency. These devices show a high stability due to the silicon excess in the film. The Er-doped SRO films have been introduced in a Si/SiO₂ Fabry-Perot Microcavity in order to increase the spontaneous emission rate, the extraction efficiency and the spectral purity at the resonant wavelength. The active medium in the cavity has been electrically pumped and the conduction mechanisms have been analyzed. The EL spectra have also been acquired and compared with photoluminescence (PL) ones for the same resonant cavity light-emitting device (RCLED). The EL and PL peak intensities of the on-axis emission at the resonant wavelength are over 20 times above that of the similar Er-doped SRO film without a cavity. The Si-based RCLEDs exhibit different quality factors, ranging from 60 to 170. The spectra shape and intensity have been correlated with the quality factor. A high directionality of the emitted light, due to the presence of the resonant cavity, has also been observed: the overall luminescence is confined within 10° cone from the sample normal.     

Picosecond optical switching of a 1.5 μm active birefringent optical fiber loop filter using 1.3 μm control optical pulses and a 1.3 μm semiconductor optical amplifier

Less than 100ps, polarization-independent switching operation of an active birefringent optical fiber loop filter using 1.3 μm control optical pulses as well as a 1.3 μm semiconductor optical amplifier (SOA) has been demonstrated. In the proposed SOA-based active birefringent filter operating at 1.55 μm wavelength, 1.3 μm SOA is employed to control the polarization-mode dispersion in the loop part. By injecting 1.3 μm ps gain-switched optical control pulses into the SOA, 1.5 μm input signals can be switched from the transmission port to the reflection port with less than 100 ps rise time.     

High-efficiency,high-repetition-rate,temperature-tuning optical parametric oscillator based on periodically poled MgO-doped lithium niobate

We report a compact and viable source of high-efficiency, high-repetition-rate, temperature-tuning, mid-IR optical parametric oscillator (OPO) based on periodically poled MgO-doped lithium niobate (PPMgOLN) pumped by a homemade high power AOM Q-switched Nd:YVO₄ laser centered at 1.064 μm. With an optimal plane-concave resonator configuration, average output power of 5.7 W at 2.73 μm was obtained when the pump power was 25 W at the repetition rate of 80 kHz. The conversion efficiency from the 1.064 μm laser to the 2.73 μm laser was 22.8%. Temperature tuning of the OPO yielded a signal wavelength range from 1.67 to 1.75 μm and an idler wavelength in the range of 2.72 to 2.92 μm.     

Effect of ion irradiation on the structure and luminescence characteristics of porous silicon impregnated with tungsten-telluride glass doped by Er and Yb impurities

Using transmission electron microscopy and elemental analysis, it has been shown that tungsten telluride glass (TTG) containing erbium and ytterbium as impurities penetrates into pores of porous silicon (PS) when melted in vacuum at 500°C. It has been found that the intensity of photoluminescence (PL) of erbium at the wavelength of 1.54 μm in PS: TTG layers increases by a factor of up to 5 in the layers irradiated by P⁺ and Ar⁺ ions. This is assigned to ion mixing which favors interaction among the Er ions and PS-embedded Si nanocrystals initiating sensitization of the PL, as well as to broadening of the glass-impregnated PS region. Implantation of the lighter Ne⁺ ions affects only weakly the PL of erbium ions.     

Er<Superscript>3+</Superscript> photoluminescence excitation spectra in erbium-doped epitaxial silicon structures

Excitation spectra of erbium photoluminescence (λ=1540 nm) in Si: Er epitaxial structures were studied within a broad pump wavelength range (λ=780–1500 nm). Erbium photoluminescence was observed to occur at pump energies substantially less than the silicon band-gap width. Possible mechanisms of erbium ion excitation in this pump radiation energy region are discussed.     

Design and Fabrication of GaInAsP/InP VCSEL with Two a-Si/a-SiN x Bragg Reflectors

We report on the design and fabrication of a 1.55 μm wavelength Vertical Cavity Surface Emitting Lasers (VCSELs) which consists of two dielectric Bragg mirrors and a InGaAsP-based active region. The dielectric materials are amorphous silicon and amorphous silicon nitride. Layers of such materials have been deposited by magnetron sputtering and analyzed in order to determine their optical properties. A large refractive index difference of 1.9 is found between these materials. Distributed Bragg Reflectors (DBRs) based on these dielectric materials quarter wave layers have been studied by optical measurements and confronted to theoretical calculations based on the transfer matrix method. A maximum reflectivity of 99.5% at 1.55 μm and a large spectral bandwidth of 800 nm are reached with only four and a half periods of a-Si/a-SiN_x. The VCSEL was fabricated by metallic bonding process. This method allows to bond an InP-based active region as the gain medium on a Si substrate thanks to the formation of a Au–In alloy. This process is performed at a low temperature of 240°C without damaging the optical properties of the microcavity. This VCSEL has been characterized by an optical pumping experiment with a low and a high-density optical power and a laser emission has been obtained at room-temperature.