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     

1.5-μm-band optical time domain reflectometer for single-modeoptical fiber using a P2O5-highly-doped fiberRaman laser

A wide-dynamic-range 1.5-μm-band optical time-domain reflectometer (OTDR) for single-mode optical fibers using a P₂O₅-highly-doped fiber Raman laser light source and a cooled Ge-p-i-n photodiode is realized for the first time. The stimulated-Raman-scattering properties of P₂O₅-doped single-mode fiber are investigated. Using this fiber and an Nd:YAG laser operating at 1.32 μm, a high-power light pulse at 1.59 μm is generated with high efficiency. Using the stimulated-Raman-scattering light as the light source and a high-sensitivity optical receiver, a 1.5-μm-band OTDR having a one-way dynamic range of 35 dB is realized     

Optimal pump wavelength in the4I15/2-4I13/2 absorption band for efficient Er3+-doped fiberamplifiers

The authors report the measured gain of a highly efficient erbium-doped fiber amplifier pumped at wavelengths between 1.46 and 1.51 μm. The optimal pump wavelength, λ_opt, was determined to be 1.475 μm. At this wavelength, the maximum gain coefficients for signals at 1.531 and 1.544 μm were 2.3 and 2.6 dB/mW, respectively. At λ_opt, high gains ranging from 32 dB at pump power P_p=20 mW up to 40 dB at P _p=80 mW were obtained. These modest pump powers are within the capabilities of currently available 1.48-μm diode lasers. The width about λ_opt for 3-dB gain variation exceeded 27 nm for P_p=10 mW and 40 nm for P_p >20 mW. With this weak dependence on pump wavelength, single-longitudinal-mode lasers do not have a significant advantage over practical Fabry-Perot multimode pump lasers     

Doubly strainedIn0.41Al0.59As/n+-In0.65Ga0.35As HFET with high breakdown voltage

An In_0.41Al_0.59As/n⁺-In_0.65 Ga_0.35As HFET on InP was designed and fabricated, using the following methodology to enhance device breakdown: a quantum-well channel to introduce electron quantization and increase the effective channel bandgap, a strained In_0.41Al_0.59As insulator, and the elimination of parasitic mesa-sidewall gate leakage. The In_0.65Ga_0.35As channel is optimally doped to N_D=6×10¹⁸ cm^-3. The resulting device (L_g=1.9 μm, W_g =200 μm) has f_t=14.9 GHz, f_max in the range of 85 to 101 GHz, MSG=17.6 dB at 12 GHz V_B=12.8 V, and I_D(max)=302 mA/mm. This structure offers the promise of high-voltage applications at high frequencies on InP     

Short-pulse, high-power Q-switched fiber laser

A high-power, laser-diode-pumped, Q-switched fiber laser operating at 1.053 μm which is suitable for use in time-multiplexed fiber sensor applications is described. The laser emits >1-kW pulses at 1.053 μm with 2-ns duration at up to 1-kHz repetition rates for an adsorbed pump power of only 22 mW at 810 nm. Tunable Q-switched operation over a 40-nm wavelength range has also been demonstrated     

Gain characteristics of ER3+ doped fiber with aquasi-confined structure

The fiber-structure dependence of the gain characteristics of Er ³⁺ doped fibers pumped at 1.48 μm is analyzed. The optimum V value is derived theoretically and experimentally. For step-index fibers, the optimum V value is 1.6, which is smaller than that needed to minimize spot size. The fiber with a small V value enjoys a large Er³⁺ confinement effect. For laser diode pumping, an efficiency of 1.7 dB/mW is achieved at 1.536 μm. The bending characteristics are also described     

Simplified Z-propagating DC bias stable TE-TM modeconvertor fabricated in Y-cut lithium niobate

A TE-TM mode converter, useful at either 0.632 or 0.840 μm, has been fabricated on y-cut LiNbO₃ by Ti indiffusion with the channel waveguide placed parallel to the z-axis. For TE polarized input, the maximum TM modulation depth is 97 percent at 0.632 μm with a 5-V (pp) drive and 99 percent at 0.840 μm with a 12-V (pp) drive. A similar device operating at 1.3 μm displays 98-percent TE-TM switching at 68 V. Operation involves only coplanar electrodes placed alongside the channel acting on the r₆₁ electrooptic coefficient. A separately deposited buffer layer is unnecessary. Testing indicates a substantially greater tolerance to electrode misalignment than afforded by similar structures formed in x-cut substrates. Data illustrating immunity to photorefractive drift in the presence of a DC bias voltage is presented for 0.840-μm wavelength operation     

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     

An EMQ-switched CO2 laser as a pump source for afar-infrared laser with a high peak power and a high repetitionrate

A modified current pulsed Q (EMQ)-switched CO₂ laser which is Q-switched by a mechanical beam chopper in combination with a pulsed discharge current is discussed. The laser produces a very stable output with a peak power greater than 1 kW at a repetition rate of 1000 p.p.s. for all transitions in the P and R branches of the CO₂ spectrum. A CH₃F laser pumped by the EMQ-switched laser produces 496 μm radiation in a 6.5 W peak, 100 ns pulses at 500 p.p.s. in the lowest loss EH₁₁ mode     

Highly reliable, high-C DRAM storage capacitors with CVD TA2O5 films on rugged polysilicon

The authors report on a highly reliable stacked storage capacitor with ultrahigh capacitance using rapid-thermal-annealed low-pressure chemical vapor deposited (LPCVD) Ta₂O₅ films (~100 Å) deposited on NH₃-nitrided rugged poly-Si electrodes. Capacitances as high as 20.4 fF/μ² (corresponding to the thinnest t_ox.eff (16.9 Å) ever reported using LPCVD-Ta₂O₅ and poly-Si technologies) have been achieved with excellent leakage current and time-dependent dielectric breakdown (TDDB) characteristics. Extensive electrical characterization over a wide temperature range (~25-300°C) shows that Ta₂O ₅ films on rugged poly-Si electrodes have a better temperature stability in dielectric leakage and breakdown compared to the films on smooth poly-Si electrodes     

Gate-length dependence of DC and microwave properties ofsubmicrometer In0.53Ga0.47As HIGFETs

In_0.52Al_0.48As/In_0.53Ga_0.47 As/InP heterostructure insulated-gate field-effect transistors (HIGFETs) with gate lengths from 1.1 and 0.3 μm have been fabricated, and their electrical performance is characterized at DC and microwave frequencies. The refractory-gate self-aligned process, applied to devices with In_0.53Ga_0.47As channels, yields an unprecedented combination of very-high speed and excellent uniformity. HIGFETs with L_g=0.6 μm showed average peak transconductance g_m of 528 mS/mm and unity-current-gain cutoff frequency f_t of 50 GHz. The uniformity of g_m was better than 1%, and the voltage of the g_m peak was uniform to ±30 mV. HIGFETs with L_g=0.3 μm showed f₁ up to 63 GHz, but suffered from serious short-channel effect, due to excessive thickness of the InGaAs channel layer. A self-aligned technique for gate resistance reduction is shown to substantially improve microwave power gain     

Absolute and relative nonlinear optical coefficients of KDP, KD*P,BaB2O4, LiIO3, MgO:LiNbO3,and KTP measured by phase-matched second-harmonic generation

Both absolute and relative nonlinear optical coefficients of six nonlinear materials measured by second-harmonic generation are discussed. A single-mode, injection-seeded, Q-switched Nd:YAG laser with spatially filtered output was used to generate the 1.064-μm fundamental radiation. The following results were obtained: d₃₆(KD*P)=0.38 pm/V, d₃₆(KD*P)=0.37 pm/V, |d₂₂(BaB ₂O₄)|=2.2 pm/V, d₃₁(LiIO₃ )=-4.1 pm/V, d₃₁(5%MgO:MgO LiNbO₃)=-4.7 pm/V, and d_eff(KTP)=3.2 pm/V. The accuracy of these measurements is estimated to be better than 10%     

High-transconductance heterostructure Ga0.47In0.53As/InP metal-insulator-semiconductor field-effect transistorsgrown by chemical beam epitaxy

SiO₂ insulator is on top of an InP layer; current transport occurs, however, an in adjacent n-type Ga_0.47In_0.53As:Sn layer. A transconductance of g_m=300 mS/mm is obtained from depletion-mode MISFETs with a gate length of 1.2 μm. This MIS (metal-insulator-semiconductor) junction has a symmetric current-voltage characteristic and a low-leakage current of ~1 nA at ±2 V. High-frequency S-parameter measurements performed b probing devices on the wafers yield a unity current gain frequency of F _t=22.2 GHz and a maximum frequency of oscillation f _max=27 GHz     

Method for calculating coupling length of Ti:LiNbO3waveguide directional couplers

Reports a theory for calculating the coupling length L _c of Ti:LiNbO₃ single-mode waveguide directional couplers from process parameters and operating wavelength. Estimates are accurate to within a factor of 2 compared with published experimental results for z-cut y-propagating LiNbO₃ devices for 0.63 μm⩽λ⩽1.56 μm. Use of this formalism to assess acceptable process parameter and wavelength tolerances is demonstrated     

Observation of a large number of new laser lines from12CD3F gas optically pumped with a continuouslytunable high-pressure pulsed CO2 laser

An observation is reported of a large number of new laser lines from ¹²CD₃F gas optically pumped with a continuously tunable high-pressure pulsed CO₂ laser. Making use of the coincidence of the 10 μm P and R branches of CO₂ with the v₃ and v₆ vibrational-rotational absorption bands of ¹²CD₃F, 180 laser lines were found in the wavenumber range between 8 and 55 cm^-1, all of them yet unknown; these lines are studied for characteristic properties of laser action. All laser lines are assigned as pure rotational transitions in the vibrational excited or ground states     

High-performance highly strainedGa0.23In0.77As/Al0.48In0.52As MODFET's obtained by selective and shallow etch guide recesstechniques

Record high f_TL_g products of 57 and 46 GHz-μm have been achieved in Ga_1-x In_x As/AlInAs MODFETs with a strain compensated channel of x=0.77 and a lattice-matched channel of x=0.53, respectively. Although g_m as high as 950 mS/mm has been obtained by conventional deep recess for the gate, these latter devices show a prominent kink effect which lowers f_T and the voltage gain. By limiting the depth of final nonselective recess etch to 3 nm with the help of selective step etches, f_T as high as 47 GHz and g_m as high as 843 mS/mm have been achieved for MODFETs with x=0.77 and L_g=1.1 μm     

Ga1-yInyAs/InAsxP1-1 (y>0.53, x>0) pin photodiodes for long wavelengthregions (λ>2 μm) grown by hydride vapour phase epitaxy

pin photodiodes with a 2.3 μm absorption edge are presented, using hydride vapour phase epitaxy. A Ga₁-_yIn_yAs (y=0.72) absorption layer, lattice-mismatched to the InP substrate, was grown on an InAs_xP_1-x (x=0-0.33) graded composition buffer layer. Typical dark current was 5 μA (0.03 A/cm²) at -6 V. Effective carrier lifetime of 0.05 μs was estimated from I/V characteristics     

Guided wave modulators in Ti ion implanted LiNbO3waveguides

Electrooptic modulators in Ti-ion-implanted LiNbO₃ waveguides are discussed. Low loss (<1-dB/cm) planar and channel waveguides were fabricated and compared to indiffused waveguides. Higher Δn values are obtained, allowing smaller waveguide geometries and tighter mode confinement. Wavelengths of 0.85 and 1.3 μm are used. The small mode profiles resulting from the Ti doses up to 4×10¹⁷ Ti/cm² resulted in V-L products of 8.8 V-mm at 0.85 μm and 20 V-mm at 1.3 μm. These values are lower than any previously reported for a Mach-Zehnder modulator using a buffer layer. Comparison of diffused and implanted waveguide modulators indicated that modular efficiency can be optimized by electrode gap spacing and enhanced with smaller mode profiles achievable in implanted guides     

Second harmonic generation and sum frequency mixing of dualwavelength Nd:YAlO3 laser in flux grown KTiOPO4crystal

On the basis of accurately measured refractive indexes, the authors have obtained the Sellmeier's equations for flux grown KTiOPO ₄ (KTP) crystal and used them to calculate the phase matched angles (&thetas;_m, φ_m) and effective nonlinear coefficients (d_eff) for type I and III second harmonic generation (SHG) and sum frequency mixing (SFM) of radiations at 1.0795 and 1.3414 μm. The optimum phase matching conditions for 1.0795 and 1.3414 μm SHG are that &thetas;_m=86.88 and 58.88°, respectively, in an XZ plane (φ=0) and for SMF of 1.0795 and 1.3414 μm in the same plane 76.02°. The corresponding d_eff values calculated from &thetas; _ms are 18.07×10^-9 and 17.42×10^-9 esu     

High vibrational temperatures in optically-pumped CO2

A pulsed 4.3-μm CO₂ laser was used to optically pump mixtures of CO₂ and He, and create transient gain at 9 and 10 μm. A conventional continuous-wave CO₂ laser operating on both regular and sequence bands measures this transient gain, and determined the ν₃ (asymmetric stretching)-mode vibrational temperature T₃. The measured values of T ₃ are generally much higher than those attained in discharge-excited CO₂. It is shown that a Treanor distribution must be used to describe the populations in the ν₃ -mode when dilute mixtures of CO₂ in He are optically pumped to ν₃-mode temperatures of 3000 to 4000 K. Under these conditions the sequence-band gain coefficients are almost equal to those on the regular bands. The collisional relaxation of energy from the ν₃ mode shows evidence of fast V-T relaxation at high values of T₃, followed by a slower relaxation rate characteristic of the 00⁰1 population lifetime