Temperature-dependent Sellmeier coefficients and chromaticdispersions for some optical fiber glasses

Temperature-dependent Sellmeier coefficients are necessary to optimize optical design parameters of the optical fiber transmission system. These coefficients are calculated for fused silica (SiO₂ ), aluminosilicate, and Vycor glasses for the first time to find the temperature dependence of chromatic dispersion at any wavelength from UV to 1.7 μm. The zero dispersion wavelength λ₀ (1.273 μm for SiO₂, 1.393 μm for aluminosilicate, and 1.265 μm for Vycor glasses at 26°C) varies linearly with temperature, and dλ₀/dT is 0.03 nm/K for aluminosilicate and Vycor glasses, whereas for SiO₂ it is 0.025 nm/K. This study interprets the recently observed experimental value of dλ₀/dT for two dispersion shifted optical fibers; and the dominantly material origin of dλ₀/dT is confirmed here as a fundamental property of the optical fiber glasses     

Grating compensation of third-order fiber dispersion

Subpicosecond optical pulses propagating in single-mode fibers are severely distorted by third-order dispersion even at the fiber's zero-dispersion wavelength (λ₀). Using cross-correlation techniques, the authors measured the broadening of a 100-fs pulse to more than 5 ps after passing through 400 m of fiber near λ₀. The measured asymmetric and oscillatory pulse shape is in agreement with calculations. A grating and telescope apparatus was configured to simultaneously equalize both third- and second-order dispersion for wavelengths slightly longer than λ ₀. Nearly complete compensation has been demonstrated for fiber lengths of 400 m and 3 km of dispersion-shifted fiber at wavelengths of 1560-1580 nm. For the longer fibers, fourth-order dispersion due to the grating becomes important     

Leaky mode propagation in planar multilayer birefringentwaveguides: longitudinal dielectric tensor configuration

In this paper we examine leaky mode propagation in a general five-layered c-rotated optical structure with longitudinal dielectric tenser configuration that can be considered a useful pattern for many actual waveguides. The dependence of the leaky mode propagation on the longitudinal angle φ (between the optical c-axis and laboratory axis) is shown and the dispersion characteristics for different types and thicknesses of buffer and metal layer are reported. The guided mode losses at the wavelength λ=0.633 μm assume the lowest values (about 1 dB/cm) for an Ag layer and for φ=0°. Furthermore, we investigate the variation in the propagation characteristics of the leaky and guided modes with respect to the source wavelength. We obtain the transition wavelength from (G) guided modes to lowest order (L¹ ) leaky mode, having the ordinary component that leaks into the substrate; the transition wavelength to a higher order (L²) leaky mode, which has both ordinary and extraordinary leaky components and the leaky cutoff wavelength. As an example, for φ=10° and an Ag metal layer, the first-order G₁₁ mode transforms from guided to leaky L₁₁¹ at λ_gl≃0.9 μm. The losses exhibit a change of several dB near the wavelength transition from guided to leaky mode (e.g. The attenuation constant of the G₁₁ mode changes from 0.26×10² dB/cm at λ=0.633 μm to 0.18×10 ⁵ dB/cm at λ=0.95 μm where its ordinary component is a leaky one). A similar change is found near the transition wavelength from a lowest-order mode to the highest-order leaky mode     

High-nonlinearity fiber optical parametric amplifier with periodicdispersion compensation

Theory shows that the maximum gain and bandwidth of one-pump fiber optical parametric amplifiers made from high-nonlinearity fiber, operated with a pump wavelength λ_p far from the fiber zero-dispersion wavelength λ₀ can greatly be improved by periodic dispersion compensation. We have performed experiments and obtained good agreement with theory: for λ_p=1542 and λ₀=1591 nm, we have increased the bandwidth from 7 to 28 nm, and the maximum gain from 15 to 20 dB, by splicing three pieces of standard fiber at regular intervals in a 40-m long nonlinear fiber     

Spectral gain hole-burning at 1.53 μm in erbium-doped fiberamplifiers

Spectral gain hole-burning at λ₀=1.53 μm was observed in an erbium-doped fiber amplifier at temperatures between 4.2 and 77 K. The hole width was found to broaden with temperature for T ⩾20 K according to a T^1.73 law. From the data, the room-temperature homogeneous linewidth associated with the 1.531-μm transition in the ⁴I_13/2-⁴I_15/2 laser system was determined to be Δλ_h=11.5 nm for aluminosilicate fibers     

InGaAsPN-InP-based photodetectors for long wavelength(λ>1.65 μm) applications

We demonstrate InGaAsPN p-i-n photodetectors lattice-matched to InP substrates with cutoff wavelengths larger than 1.65 μm. The narrow bandgap InGaAsPN absorption layers were grown by gas source molecular beam epitaxy using an RF plasma nitrogen source. Optical absorption spectra reveal that InGaAsPN with 5% P and 2.8% N has a cutoff wavelength λ_CO=1.90 μm Background doping in the absorption layer for a detector with 1.5% N and 5% P is reduced from (1.5±0.5)×10¹⁷ cm^-3 for the as-grown device, to (5±0.5)×10¹⁶ cm^-3 for a thermally annealed device. The unintentional high background doping is due to N-H bond formation or local strain induced defects. Spectral response measurements indicate that λ_CO=1.85 μm is achieved for detectors annealed at 800°C with 2% N and 5% P in the InGaAsPN absorption layer, suggesting that annealed InGaAsPN alloys are promising for use in detectors with response in the near and mid-IR wavelength spectral range     

The performances of (InAs)1/(GaAs)2short-period superlattice strained single-quantum-well laser on GaAssubstrate

We fabricated an (InAs)₁/(GaAs)₂ short-period superlattice (SPS) strained quantum-well laser at 1.07 μm by MOVPE. The SPS active layer has 10 periods of (InAs)₁/(_GaAs)₂ and an average mismatch of over 2.2%. In highly strained conditions the device showed a lasing wavelength of 1.07 μm, a threshold of 130 A/cm², and a characteristic temperature T₀ of 175 K. We measured the gain characteristic by the Hakki and Paoli method at LED conditions and obtained a high differential gain of 2.0×10^-15 cm² at the threshold current     

Low Rayleigh scatteringP2O5-F-SiO2 glasses

The Rayleigh scattering and infrared absorption losses of P₂ O₅-F-doped silica glass, which is a candidate material for ultra-low-loss optical fiber, were investigated experimentally. The Rayleigh scattering loss of 8.5 wt.% P₂O₅ and 0.3 wt.% F-doped SiO₂ glass is found to be 0.8 times that of pure silica glass. It is also found that the infrared absorption property of P₂O₅-F-SiO₂ glass is almost the same as that of pure silica glass. The minimum loss for the proposed composition is estimated to be 0.11 dB/km at 1.55 μm wavelength, and 0.21 dB/km at 1.3 μm wavelength     

Gain and saturation intensity of the green Ho:ZBLAN upconversionfiber amplifier and laser

The gain and saturation intensity of the green Ho-doped fluorozirconate (ZBLAN) glass fiber amplifier and laser, pumped in the red (643 ⩽ λ_p ⩽ 649 nm; ⁵F₅ ← ⁵I₈), have been measured. For a 2.4-μm core diameter fiber 45 cm in length, the single-pass gain at 543.4 nm exceeds 12 dB for 90 mW of pump power at 643.5 nm. The saturation power for the ⁵F₄, ⁵S₂ → ⁵I₈ lasing transition was determined from gain measurements to be 970 ± 175 μW, which corresponds to a saturation intensity of 19.8 ± 3.5 kW · cm^-2 , and a stimulated emission cross section approximately one order of magnitude larger than theoretical estimates     

Emission cross sections and spectroscopy of Ho3+ laserchannels in KGd(WO4)2 single crystal

The spectroscopic properties of Ho³⁺ laser channels in KGd(WO₄)₂ crystals have been investigated using optical absorption, photoluminescence, and lifetime measurements. The radiative lifetimes of Ho³⁺ have been calculated through a Judd-Ofelt (JO) formalism using 300-K optical absorption results. The JO parameters obtained were Ω₂=15.35×10^-20 cm², Ω ₄=3.79×10^-20 cm², Ω₆ =1.69×10^-20 cm². The 7-300-K lifetimes obtained in diluted (8·10¹⁸ cm^-3) KGW:0.1% Ho samples are: τ(⁵F₃)≈0.9 μs, τ( ⁵S₂)=19-3.6 μs, and τ(⁵F₅ )≈1.1 μs. For Ho concentrations below 1.5×10²⁰ cm^-3, multiphonon emission is the main source of non radiative losses, and the temperature independent multiphonon probability in KGW is found to follow the energy gap law τ_ph ^-1(0)=βexp(-αΔE), where β=1.4×10^-7 s^-1, and α=1.4×10³ cm. Above this holmium concentration, energy transfer between Ho impurities also contributes to the losses. The spectral distributions of the Ho³⁺ emission cross section σ_EM for several laser channels are calculated in σ- and π-polarized configurations. The peak a σ_EM values achieved for transitions to the ⁵I₈ level are ≈2×10^-20 cm² in the σ-polarized configuration, and three main lasing peaks at 2.02, 2.05, and 2.07 μm are envisaged inside the ⁵I₇→⁵I₈ channel     

Fabrication of planar optical waveguides in LiB3O5 by 2 MeV He+ ion implantation

The fabrication of planar optical waveguides in LiB₃O ₅ is discussed. Using 2-MeV ⁴He⁺ implantation with a dose of 1.5×10¹⁶ ions/cm² at 300 K, the refractive indexes of a 0.2-μm-thick layer 5.1 μm below the crystal surface are reduced to form optical barrier guides. For this ion dose the maximum change from the bulk values of refractive index at a wavelength of 0.488 μm are 1.5%, 5.25%, and 4% for n_x, n_y, and n_z, respectively. The refractive indexes of the guiding region change by less than 0.02% from the bulk values. The dose dependence of the optical barrier height has been measured. A threshold ion dose of about 0.75×10¹⁶ ions/cm² is required to form a refractive index barrier and ion doses higher than about 2.5×10¹⁶ ions/cm². saturate the refractive index decrease. Waveguide propagation losses for annealed single energy implants of dose 1.5×10¹⁶ ions/cm² are dominated by tunneling and are estimated to be ~8.9 dB/cm for the z-cut waveguides used. Multiple energy implants broaden the optical barrier, and losses of <4 dB/cm have been observed     

Merged Sagnac-Michelson interferometer for distributed disturbancedetection

An interferometric technique is described to detect and locate perturbations along an optical fiber. This distributed sensor has a position dependent response to time-varying disturbances such as strain or temperature. These disturbances cause a phase shift which is detected and converted to spatial information, The sensor consists of a Sagnac interferometer merged with a Michelson interferometer. This is achieved by a frequency selective mirror in the center of the Sagnac-loop. The sensor is illuminated by two light sources with wavelengths λ₁ and λ₂, respectively. The mirror reflects λ₁ and transmits λ₂, causing the interferometer to operate as a Michelson at wavelength λ₁ and as a Sagnac at wavelength λ₂. Any time-varying perturbation on, the fiber will, result in a signal at λ₂ proportional to the product of the rate of phase change caused by the perturbation and the distance of the perturbation relative to the position of the mirror. The output of the Michelson interferometer at wavelength λ₁ is proportional to the phase change caused by the unknown perturbation. By dividing the output of the Sagnac interferometer by the time rate of change of the Michelson interferometer signal, the position of the disturbance relative to the mirror is located. Results obtained with a 200 m-distributed fiber sensor are discussed     

Self-phase modulation and dispersion in high data rate fiber-optictransmission systems

The theoretical transmission limits imposed by the interaction of first- and second-order group velocity dispersion and intensity-dependent self-phase modulation (SPM) effects for a range of wavelengths around the zero dispersion wavelength (λ₀) for fibers in which polarization dispersion is negligible are investigated. It is found that increasing the peak input power to 30 mW reduces the transmission distance for data rates greater than 50 Gb/s, if operating at wavelengths shorter than λ₀. Operating at wavelengths longer than λ₀ improves the performance due to the cancellation of first-order dispersion by self-phase modulation. For example, at 50 Gb/s and 30 mW peak input power, the maximum transmission distance is 255 and 162 km, if operating at wavelengths 1 nm longer or shorter than λ₀, respectively. Above 100 Gb/s, higher-order dispersion limits the transmission distance even at wavelengths equal to, or longer than, λ₀. Linear dispersion compensation using a grating-telescope combination can significantly improve system performance for wavelengths where first-order dispersion dominates     

InGaAlAs-InP quantum-well infrared photodetectors for 8-20-μmwavelengths

We demonstrate the first long-wavelength quantum-well infrared photodetectors using the lattice-matched n-doped InGaAlAs-InP materials system. Samples with AlAs mole fractions of 0.0, 0.1, and 0.15 result in cutoff wavelengths of 8.5, 13.3, and 19.4 μm, respectively, a 45° facet coupled illumination responsivity of R=0.37 μm and detectivity of D_λ*=3×10⁸ cm·√(Hz)· at T=77 K, for a cutoff wavelength λ_c=13.3 μm have been achieved. Based on the measured intersubband photoresponse wavelength, a null conduction band offset is expected for In_0.52Ga_0.21Al_0.27 As-InP heterojunctions     

Laser diode-pumped holmium-doped fluorozirconate glass fiber laserin the green (λ~544-549 nm): power conversion efficiency, pumpacceptance bandwidth, and excited-state kinetics

The green (544-549 nm) Ho-doped fluorozirconate (ZBLAN) glass fiber laser, pumped in the red (λ~6;15 nm) by a high-power (~30 mW) InGaAlP laser diode or a ring dye-laser, has been characterized with regard to power conversion efficiency, fiber core-diameter and length, cavity output coupling, and pump acceptance bandwidth. Fibers doped with ~1200 ppm (by weight) of Ho and having core diameters of 1.7, 3, and 11 μm, and lengths ranging from 12.5 to 86 cm, have been studied in Fabry-Perot resonators having output couplings ranging from 1.545 to 96%. For a 1.7-μm core-diameter fiber, 21 cm in length, the threshold-launched pump power for the diode-pumped fiber laser is 1.9 and 3.5 mW for cavity output couplings of 1.5% and 24%, respectively. These values are the lowest for any upconversion-pumped fiber laser reported to date. Also, the noise and threshold-pumping power properties of the diode-pumped fiber laser are superior to those for its dye-laser-pumped counterpart. The highest laser slope efficiency (>22% with respect to launched pump power) was measured for a 3-μm core-diameter fiber and a cavity output coupling of 24%. The spectral interval over which the launched threshold pump power for this laser is <10 mW is almost 20 nm (637-656 nm). Studies of the fiber laser waveform as a function of pump power reveal competition for population between the ⁵S² and ⁵F₄ states and among the Stark sublevels of the ⁵F₄ manifold. Also, measurements of the output power on individual laser lines of the ⁵F₄, ⁵S₂→ ⁵I₈ (ground) transitions of Ho³⁺:ZBLAN as a function of pump power demonstrate the existence of a loss mechanism at the fiber laser wavelength, presumably due to absorption from ground or the ⁵I_y, ⁶S₂ or ⁵F₄ excited states of the ion     

High-performance long-wavelength (λ~1.3 μm) InGaAsPNquantum-well lasers

We demonstrate high-performance InGaAsPN quantum well based long-wavelength lasers grown on GaAs substrates, nitrogen containing lasers emitting in the λ=1.2- to 1.3-μm wavelength range were grown by gas source molecular beam epitaxy using a RF plasma nitrogen source. Under pulsed excitation, lasers emitting at λ=1.295 μm exhibited a record low threshold current density (J_TH) of 2. 5 kA/cm². Lasers grown with less nitrogen in the quantum well exhibited significantly lower threshold current densities of J_TH =1.9 kA/cm² at λ=1.27 μm and J_TH=1.27 kA/cm² at λ=1.2 μm. We also report a slope efficiency of 0.4 W/A and an output power of 450 mW under pulsed operation for nitrogen containing lasers emitting at 1.2 μm     

Low-temperature sensitive, compressively strained InGaAsP active(λ=0.78-0.85 μm) region diode lasers

This letter reports comparative studies between (Al)GaAs versus InGaAsP active region edge-emitting semiconductor lasers for emission wavelength in the IR regime (λ=0.78-0.85 μm). High characteristic temperature T₀(200 K) and T₁ (450 K) edge-emitting diode lasers have been demonstrated by using the compressively strained (Δa/a=0,6%) Al-free (InGaAsP) active region with an emission wavelength of 0.85 μm. The high T₀ and T ₁ a result of low active-layer carrier leakage, will be beneficial for high-temperature and high-power operation. Implementation for InGaAsP-active VCSEL's with compressively strained InGaAsP-active layers and conventional DBR's is also discussed     

Low frequency noise in 6H-SiC MOSFET's

The noise spectra for n-channel, depletion-mode MOSFETs fabricated in 6H-SiC material were measured from 1-10⁵ Hz at room temperature. Devices were biased in the linear regime, where the noise spectra was found to be dependent upon the drain-to-source bias current density. At a drain-to-source current of 50 μA for MOSFETs with a W/L of 400 μm/4 μm, the measured drain-to-source noise power spectral density was found to be A/(f^λ), with A being 2.6×10^-12 V², and λ being between 0.73 and 0.85, indicating a nonuniform spatial trap density skewed towards the oxide-semiconductor interface. The measured Hooge parameter (α_H) was 2×10^-5. This letter represents the first reported noise characterization of 6H-SiC MOSFET's     

Design optimization of ARROW-type diode lasers

Antiresonant reflecting optical wavelength (ARROW)-type diode lasers have been optimized for high-power, single-spatial-mode operation. Calculated modal behavior predicts strong intermodal discrimination with low loss for the fundamental ARROW mode. Single-lobe far-field operation is obtained only when the high-index reflecting (antiresonant) cladding layers correspond to an optical thickness of λ₁ (m+3/4), where λ is the lateral (projected) wavelength of the leaky wave in the high-index layers, and m is an integer (m=0, 1,. . .). Experimental results include stable, single-spatial mode operation to 500-mW peak pulsed power and 300-mW CW power at an emission wavelength of 0.98 μm     

Upconversion pumped thulium-doped fluoride fiber amplifier andlaser operating at 1.47 μm

A 1.064-μm band upconversion pumped Tm³⁺-doped fluoride fiber amplifier and a laser both operating at 1.47 μm are investigated in detail. The two devices are based on the ³F ₄→³H₄ transition in a trivalent thulium ion, which is a self-terminating system. When pumped at 1.064 μm, the amplifier has a gain of over 10 dB from 1.44 to 1.51 μm and a low-noise characteristic. Also, the fiber laser generates a high-output power of over 100 mW with a slope efficiency of 59% at around 1.47 μm. These levels of performance will be important for optical communication systems