Fabrication of long lengths of low-loss IR transmitting As40S(60-x)Sex glass fibers

Teflon clad and As₄₀S₆₀ glass clad As₄₀ S₅₅Se₅ fibers transmitting in the 1-6 μm wavelength region have been fabricated in lengths of about 50 m and with minimum losses of 0.098 and 0.65 dB/m, respectively. Short lengths of the Teflon clad fiber possessed a minimum loss of 0.047 dB/m. While current fiber losses are dominated by extrinsic scattering and absorption, the calculated theoretical minimum loss is estimated to be 3.6 dB/km at 5.3 μm and is limited by the contribution from the weak absorption tail. Improvements in the purification and processing of the glasses into the optical fibers are required to reduce the losses further     

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     

Transmission-loss characteristics of Al2O3-doped silica fibers

Transmission-loss characteristics of Al2O3-doped silica fibers have been investigated to develop an Al2O3alternative dopant for VAD silica-based optical fibers. Optical properties of Al2O3-doped silica bulk glass and fibers were measured in the0.11-30-mum spectral region. From the experimental results, the intrinsic loss due to glass material was estimated for Al2O3-doped silica fibers. The calculated intrinsic loss minima for Al2O3-doped silica fibers with 0.2- and 1.0- percent relative refractive-index differences were 0.17 dB/km at 1.548 μm and 0.28 dB/km at 1.565 μm, respectively.     

Modeling of Dy3+-doped GeAsSe glass 1.3-μm opticalfiber amplifiers

We present a model for optical amplification at 1.3 μm using Dy ³⁺ in fibers made from a low phonon energy glass, based on GeAsSe. This model uses in-band pumping at 1.28 μm, takes into account the spectral distribution of amplified spontaneous emission, and allows for bottlenecking of excited ions into the intermediate states in Dy as well as the excited state absorption (ESA) from those levels. Using data obtained from spectroscopic measurements and Judd-Ofelt calculations, our model shows that very high gain (>30 dB) is possible in short lengths (40-100 cm) of fiber. Given the very high quantum efficiency of the radiative transition in this glass, we show that bottlenecking and ESA should not have a significant impact on device performance. We also predict that devices made from this fiber should have a very high tolerance to the passive loss of the fiber     

Polarisation-independent LiNbO3 4×4 matrix switch

The first polarisation independent LiNbO₃ strictly non-blocking 4×4 matrix switch has been developed. This matrix switch has a 4-6 dB insertion loss at any incident polarisation with 1.3 μm wavelength and about 30 V switching voltage     

Diode-array pumping of Er3+/Yb3+ Co-dopedfiber lasers and amplifiers

Single-mode double-clad Er³⁺/Yb³⁺ co-doped fibers are shown to be suitable for diode array pumping at around 960 nm. A fiber laser with 96-W output power at 1.53 μm and a power amplifier exhibiting a small signal gain of 24 dB and a saturated output power of +17 dBm are reported     

A dual wavelength (1.32-1.56 μm) directional couplerdemultiplexer by ion exchange in glass

A 1.32-1.56-μm demultiplexer using a symmetrical directional coupler consisting of Ag⁺-Na⁺ exchanged channel waveguides in BK7 glass with a total insertion loss of 1.25 dB for a 14.5-mm-long device and a propagation loss of 0.15 dB/cm is demonstrated. The crosstalk at 1.315 and 1.561 μm and the cross power ratio at 1.315 μm were measured to be less than -40 dB for the TE mode     

Low-loss polyimide-Ta2O5-SiO2hybrid ARROW waveguides

A low-loss polyimide-Ta₂O₅-SiO₂ hybrid antiresonant reflecting optical waveguide (ARROW) is presented. The ARROW device was fabricated using both the organic and dielectric thin-film technologies. It consists of the fluorinated polyimide, tantalum pentoxide (Ta₂O₅), and silicon dioxide (SiO₂) hybrid layers deposited on a Si substrate. For transverse electric polarized light, the propagation loss of the waveguide as low as 0.4 dB/cm was obtained at 1.31 μm. The propagation loss for transverse magnetic polarized light is 1.5 dB/cm. An ARROW waveguide fabricated using the polyimide-Ta₂O₅ -polyimide material system is also presented for comparison     

Gain characteristics of an Er3+-doped multicomponentglass single-mode optical fiber

Experimental results on gain characteristics of an Er³⁺-doped multicomponent glass single-mode optical-fiber amplifier are reported. This amplifier shows a gain spectrum with twin gain peaks of 1.535 and 1.543 μm, providing a broadened gain bandwidth. The apparent 6-dB gain bandwidth is 12 nm. Furthermore, the signal gain of 17 dB and 15-mW pump power is realized at a signal wavelength of 1.536 μm, and a signal gain coefficient of 1.4 dB/mW is achieved     

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     

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     

Low-loss proton-exchanged waveguide in MgO-doped LiNbO3fabricated with pyrophosphoric acid using Ta2O5protective mask

The authors describe low-loss proton-exchanged channel waveguides in MgO-doped LiNbO₃. The authors demonstrate the application of a Ta₂O₅ film for the protective mask material in proton-exchanging instead of a Ta film in order to reduce the propagation loss. A Ta₂O₅ sputtered film was applied as a protective mask with pyrophosphoric acid. The propagation loss of the waveguide, measured with laser diode light (λ=0.83 μm) was 0.5 dB/cm. It is shown that the use of a Ta₂O₅ mask reduces the propagation loss compared with the use of a Ta mask (1.5 dB/cm)     

Fiber-compatible K+-Na+ ion-exchanged channelwaveguides: fabrication and characterization

A systematic study of waveguides fabricated by K⁺-Na ⁺ exchange in soda-lime silicate and BK7 glasses is presented. The measured K⁺ concentration profile, the refractive index profile, and the diffusion profile obtained by solving the one-dimensional diffusion equation are correlated to explain the differences in the index profiles in the two glasses. The mobility of the potassium ions was measured by fabricating waveguides using electromigration. Surface waveguides formed by diffusion from a molten KNO₃ salt bath were buried by applying an electric field. Single-mode channel waveguides for operation at a wavelength of 1.3 μm that exhibit excellent mode matching with conventional optical fibers, achieving a fiber-waveguide insertion loss of less than 1 dB for a 20-mm-long waveguide, have been obtained     

7.1 GHz bandwidth monolithically integratedIn0.53Ga0.47As/In0.52Al0.48As PIN-HBT transimpedance photoreceiver

A monolithically integrated photoreceiver using an InAlAs/InGaAs HBT-based transimpedance amplifier has been fabricated and characterized. The p-i-n photodiode is implemented using the base-collector junction of the HBT. The 5 μm×5 μm emitter area transistors have self-aligned base metal and non-alloyed Ti/Pt/Au contacts. Discrete transistors demonstrated f_T and f_max of 54 GHz and 51 GHz, respectively. The amplifier demonstrated a -3 dB transimpedance bandwidth of 10 GHz and a gain of 40 dBΩ. The integrated photoreceiver with a 10 μm×10 μm p-i-n photodiode showed a -3 dB bandwidth of 7.1 GHz     

Chalcogenide glass fibers for mid-infrared transmission

Chalcogenide glass fibers for mid-infrared transmission have been fabricated in As-S, As-Ge-Se, and Ge-S glass systems using high purity materials. The preparation of unclad, Teflon FEP clad, and chalcogenide glass clad fibers and their transmission loss characteristics are reported. It is found that appropriate glass compositions for drawing low-loss fibers are limited to the narrow ranges in the glass-forming regions. The minimum losses obtained are 35 dB/km at 2.44μm for As40S60unclad fiber, 182 dB/km at 2.12 μm for As38Ge5Se57unclad fiber, and 148 dB/km at 1.68 μm for Ge20S80unclad fiber. It is shown that hydrogen impurity absorptions and short-wavelength weak absorption tails seriously enhance loss in the fibers. It is also suggested that ultralow loss cannot be achieved due to the existence of the weak absorption tail. However, it is expected that the chalcogenide glass fibers can be used in short fiber-length applications such as in the remote monitoring and delivery of CO laser radiation. This is due to their wide operating wavelength ranges of0.9-6mum for As-S,1.3-9mum for As-Ge-Se, and0.8-5mum for Ge-S, in which losses can be reduced to below 1 dB/m.     

Fabrication techniques and characteristics of Al-SiO2laminated optical polarizers

Techniques for fabricating laminated polarizers (LAMIPOLs), which consist of alternating laminated layers of aluminum and silica, for the wavelength region λ>1 μm, are investigated. The oxidation of Al films is prevented by a suitable choice of deposition conditions. The surfaces of SiO₂ films are smoothed by bias sputtering. A 10 μm thick LAMIPOL was obtained having an insertion loss of 0.15 dB and an extinction ratio of greater than 60 dB at the wavelength of 1.3 μm. These characteristics can be estimated from the attenuated constants of the fundamental modes even when higher modes are considered     

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     

Er3+-doped fiber amplifier pumped by 0.98 μm laserdiodes

The performance of an Er³⁺-doped fiber amplifier pumped by 0.98 μm InGaAs laser diodes (LDs) is reported. By using a fiber with low Er³⁺ content and optimizing the fiber length, a maximum signal gain of 37.8 dB at 30-mW pump power was realized at a signal wavelength of 1.536 μm. A maximum gain coefficient of 1.9 dB/mW at 14 mW pump power was achieved. It was found that the fiber amplifier pumped by the 0.98-μm LDs is twice as efficient as that pumped by 1.48-μm LDs, from the viewpoint of both required fiber length and the attained gain     

Efficient coupling between annealed K+-Na+ion-exchanged channel waveguides and 10/125 single-mode fibers atλ=1.321 μm

The process of thermal annealing of K⁺-Na⁺ ion-exchanged channel waveguides has been studied with the aim of optimizing their coupling efficiency with commercial single-mode fibers at λ=1.321 μm. Waveguides obtained in soda-lime glass slides, with mask apertures ranging between 13.4 and 2.6 μm, were characterized before the annealing by combining nearfield measurements and an etching procedure. The experimental results were successfully compared with a theoretical model based on the variational principle. The refractive index distribution of K⁺-Na⁺ ion-exchanged channel waveguides supporting one or a low number of modes was given: compared to the corresponding slab case, the refractive index step Δn_o remained constant, while the waveguide depth was lower. The thermal annealing process of the channels was then performed and modeled by means of the standard diffusion theory. As a result, the channel fabrication parameters for optimum guide-fiber coupling could be predicted: 0.23-dB mode mismatch losses were measured between the optimized channel and a commercial 10/125 single-mode fiber, at λ=1.321 μm     

Rayleigh scattering reduction method for silica-based optical fiber

The effect of the thermal treatment of silica-based glasses and glass fibers on their Rayleigh scattering is investigated experimentally. The Rayleigh scattering coefficients of bulk glasses are found to be increased 5-10% by heating them to 1800 °C because the density fluctuation is in proportion to their fictive temperature. Based on these results, we propose a method for reducing the Rayleigh scattering losses of silica-based optical fibers by drawing them slowly at low temperatures. We used this method to obtain a GeO₂ doped silica core single-mode fiber with a minimum loss of 0.16 dB/km at 1.55 μm. As a result, we confirmed that the reduction in the fictive temperature of silica-based glasses and glass fibers reduces their Rayleigh scattering