35-dB gain Tm-doped ZBLYAN fiber amplifier operating at 1.65 /spl mu/m

We demonstrate the first high gain rare-earth-doped fiber amplifier operating at 1.65 /spl mu/m. It consists of ZBLYAN fiber with a Tm/sup 3+/-doped core and Tb/sup 3+/-doped cladding, pumped by 1.22 /spl mu/m laser diodes. It is possible to achieve efficient amplification with Tm/sup 3+/ ions if their amplified spontaneous emission (ASE) in the 1.75 to 2.0 /spl mu/m wavelength region is suppressed by doping Tb/sup 3+/ ions in the cladding. A two-stage-type fiber amplifier is constructed and a signal gain of 35 dB is achieved for a pump power of 140 mW. A gain over 25 dB is realized in the 1.65 /spl mu/m to 1.67 /spl mu/m wavelength region.     

Fabrication of light-induced self-written waveguides with a W-shaped refractive index profile

This paper proposes a novel technique for automatic waveguide formation by means of the self-trapping effect of optical fiber irradiation into a photopolymerizing resin. We investigate experimentally the phenomenon of thin cladding layer formation surrounding the core following the core creation. In the proposed technique, a counterdiffusion effect involving polymerizing monomers via the core/cladding interface causes enrichment of a low refractive index monomer, and a resultant "W-shaped" refractive index profile is realized. The measured propagation loss of the fabricated waveguide is 1.7 dB/cm at 0.68 /spl mu/m wavelength. This technology is appropriate for the fabrication of large-core optical waveguides of greater than 0.5 mm in diameter and is useful for automating the optical fiber connection and packaging process by virtue of being an all-passive optically induced process.     

Neodymium-doped cladding-pumped aluminosilicate fiber laser tunable in the 0.9-/spl mu/m wavelength range

A tunable high-power cladding-pumped neodymium-doped aluminosilicate fiber laser is demonstrated. The maximum power reached was 2.4 W with a slope efficiency of 41% and a threshold pump power of 1.68 W, both with respect to launched pump power, when cladding pumped by two 808-nm diode pump sources at both fiber ends. The dependence of the tuning range on the fiber length is investigated. The tuning range changed from 922 to 942 nm for a 25-m-long fiber to 908-938 nm with a 14-m-long fiber, because of reabsorption effects. The output linewidth was 0.26 nm in a diffraction-limited beam. Operation on the challenging 0.9-/spl mu/m three-level transition in neodymium-doped double-clad fiber laser was facilitated by a W-type core refractive index profile. This filtered out the unwanted and competing strong transition at 1.06 /spl mu/m while guidance of 0.9 /spl mu/m remained intact.     

Stress-induced polymer waveguides operating at both 1.31 and 1.55 /spl mu/m wavelengths

Metal-defined polymer optical waveguides have been demonstrated for the first time. A metal strip patterned on top of a polymer slab waveguide causes a stress-induced refractive index change, providing lateral optical mode confinement within the core layer. Fabricated waveguides exhibit low propagation loss values of 1.1 dB/cm at 1.31 /spl mu/m and 1.3 dB/cm at 1.55 /spl mu/m for both TE and TM polarisations.     

Metal-defined polymeric variable optical attenuator

A variable optical attenuator (VOA) based on a metal-defined polymeric optical waveguide has been demonstrated for the first time. The metal film stressor deposited on top of the upper cladding layer not only produces the refractive index change within the core layer, but also acts as a thin-film heater allowing thermal tuning of the optical power within a metal-defined optical waveguide. Fabricated devices exhibit greater than 25 dB of optical attenuation with an applied electrical current of /spl sim/40 mA at 1550-nm wavelength. The switching speed of the VOA exhibits 800 /spl mu/s of rising and 720 /spl mu/s of falling time.     

Very large effective area singlemode photonic bandgap fibre

A photonic bandgap fibre consisting of a 34 /spl mu/m diameter pure silica core surrounded by a periodic cladding has been modelled and characterised. It guides a robust HE/sub 11/ mode at 1.55 /spl mu/m with a 517 /spl mu/m/sup 2/ effective area and 0.4 dB/m propagation losses.     

一种新型折射率掺镱双包层光纤

为了提高光纤放大器单纤输出功率,设计了一种新型折射率掺镱双包层光纤,纤芯直径30μm,包层直径125μm。采用一种改良的高温气相掺杂技术和改进的化学气相沉积法制作,纤芯折射率分布为凹陷型结构,掺杂区为低折射率区。对光纤的荧光特性、模场特性以及放大特性进行了测试。试验结果表明,该新型折射率分布设计有利于纤芯对抽运光吸收,荧光输出平坦,对光纤进行弯曲处理可实现平坦模场的能量输出,5m光纤实现了40dB 高功率飞秒信号光放大,输出功率30kW。     

Directional light output from photonic-wire microcavity semiconductor lasers

We have obtained directional light output from a recently realized InGaAsP photonic-wire microcavity ring lasers. The output was achieved by fabricating a 0.45-/spl mu/m-wide U-shape waveguide next to a 10-/spl mu/m diameter microcavity ring laser. The laser has a threshold pump power of around 124 /spl mu/W when optically pumped at 514 nm. It is comparable to the former structure without output coupling. The output coupling efficiency can be controlled carefully by choosing the spacing between the laser cavity and the waveguide.     

A new integrated optical-mode stripper configuration: Numerical analysis and design

A novel integrated-optical mode stripper configuration is proposed and analyzed numerically by the BPM. Its operation is based on the coupling of all higher order modes into regions with higher refractive index adjacent to the optical waveguide. It is shown that a high transmission of the fundamental mode and a high suppression of higher order modes can be realized at /spl lambda/=1.3 /spl mu/m and /spl lambda/=1.5 /spl mu/m.     

Two-step laterally tapered spot-size converter 1.55-/spl mu/m DFB laser diode having a high slope efficiency

We demonstrate a two-step lateral tapered 1.55-/spl mu/m spot-size converter distributed feedback laser diode (SSC DFB LD) having slope efficiencies as high as 0.457 and 0.319 mW/mA measured at 25 /spl deg/C and 85 /spl deg/C, respectively. The SSC DFB LD fabricated by using a nonselective grating process has a double core waveguide structure including a planar buried heterostructure type active waveguide and a ridge type passive waveguide. The fabricated SSC DFB LD operates at 1.553-/spl mu/m wavelength and shows a far-field pattern in horizontal and vertical directions of 7.3/spl deg/ and 11.6/spl deg/, respectively.     

Design and performance of an erbium-doped silicon waveguide detector operating at 1.5 /spl mu/m

A new concept for an infrared waveguide detector based on silicon is introduced. It is fabricated using silicon-on-insulator material, and consists of an erbium-doped p-n junction located in the core of a silicon ridge waveguide. The detection scheme relies on the optical absorption of 1.5-/spl mu/m light by Er/sup 3+/ ions in the waveguide core, followed by electron-hole pair generation by the excited Er and subsequent carrier separation by the electric field of the p-n junction. By performing optical mode calculations and including realistic doping profiles, we show that an external quantum efficiency of 10/sup -3/ can be achieved in a 4-cm-long waveguide detector fabricated using standard silicon processing. It is found that the quantum efficiency of the detector is mainly limited by free carrier absorption in the waveguide core, and may be further enhanced by optimizing the electrical doping profiles. Preliminary photocurrent measurements on an erbium-doped Si waveguide detector at room temperature show a clear erbium related photocurrent at 1.5 /spl mu/m.     

Continuous room-temperature operation of optically pumped two-dimensional photonic crystal lasers at 1.6 /spl mu/m

In this letter continuous operation is realized from two-dimensional slab photonic crystal lasers at room temperature. The laser structure is prepared by wafer fusion of an InGaAsP MQW active layer with an AlAs layer that is wet oxidized into an Al/sub 2/O/sub 3/ layer subsequently. The incident threshold pump power at 0.98 /spl mu/m is 9.2 mW for a /spl sim/10-/spl mu/m-diameter hexagonal cavity lasing at 1.6 /spl mu/m.     

Polarization-independent, thickness-insensitive, and refractive-index-difference-independent broad-band fluorinated polyimide waveguide coupler

A statistically optimized design method is proposed for the construction of polarization-independent, thickness-insensitive, and refractive-index-difference-independent broad-band waveguide couplers. Using this method, a fluorinated polyimide waveguide 3-dB coupler for a 1490-1610-nm operation is designed through optimization of the polarization, variation in thickness of the waveguide core, and variation in refractive-index difference of the waveguide core and cladding. The performance of the design is verified through simulation based on the three-dimensional beam-propagation method (3-D-BPM). The two orthogonal polarizations of the final design have a coupling ratio of (50/spl plusmn/2.0)% for a bandwidth of 120 nm, a thickness fluctuation of 7-8 /spl mu/m, and a refractive-index-difference fluctuation of 0.24-0.30%.     

Electroabsorption modulator using intersubband transitions in GaN-AlGaN-AlN step quantum wells

We calculate the high-speed modulation properties of an electroabsorption modulator for /spl lambda/=1.55 /spl mu/m based on Stark shifting an intersubband resonance in GaN-AlGaN-AlN step quantum wells. In a realistic simulation assuming an absorption linewidth /spl Gamma/=100 meV we obtain an RC-limited electrical f/sub 3dB//spl sim/60 GHz at an applied voltage swing V/sub pp/=2.8 V. We also show that a small negative effective chirp parameter suitable for standard single-mode fiber is obtained and that the absorption is virtually unsaturable. The waveguide is proposed to be based on the plasma effect in order to simultaneously achieve a strong confinement of the optical mode, a low series resistance, and lattice-matched cladding and core waveguide layers. Extrapolated results reflecting the decisive dependence of the high-speed performance on the intersubband absorption linewidth /spl Gamma/ are also given. At the assumed linewidth the modulation speed versus signal power ratio is on a par with existing lumped interband modulators based on the quantum confined Stark effect.     

Asymmetric waveguide devices with buried AlO/sub x/ cladding layers

We demonstrate a highly asymmetric waveguide filter for wavelength division multiplexing applications using wet oxidation of AlAs to form low-index cladding layers. The dual waveguide structure consists of a low-index polymer waveguide coupled to a lossy high-index AlGaAs waveguide. The high asymmetry between the polymer and AlGaAs yields high resolution at small device lengths. The light is coupled in and out of the polymer guide and exhibits Fabry-Perot-like resonances as the light couples to different modes of the AlGaAs. With a device length of 400 /spl mu/m, we observe resonances with a width of about 1 nm at 800 nm, agreeing with theoretical expectations. In addition to the simple filter demonstrated here, such a structure could be used to form active light emitting or detector devices.     

Efficient laser diode side pumped neodymium glass slab laser

The authors report efficient pulse operation of an Nd:glass slab laser-side-pumped by laser diode arrays. 7.5 mJ output and a slope efficiency of 29% were obtained with 35 nJ pump energy at 0.8 μm in 200 μs pulses. The wide absorption band at 0.8 and low laser loss in this phosphate glass allow for efficient pump light absorption and straightforward scalability to high power. The authors demonstrate 22% optical efficiency in a long pulse, multimode diode pumped laser oscillator based on a phosphate laser glass, LHG-8, highly doped with Nd ₂O₃. The strong and wide absorption bands in such phosphate glasses allow efficient pumping while somewhat relaxing the expensive wavelength selection requirements for laser arrays compared with crystal line host materials. With such materials, smaller slab thickness or rod diameters that are feasible with Nd:YAG can be used in the side-pumping geometry     

120/spl deg/C 10-gb/s uncooled direct Modulated 1.3-/spl mu/m AlGaInAs MQW DFB laser diodes

A 1.3-/spl mu/m AlGaInAs multiquantum well ridge waveguide distributed feedback laser diode was developed. By forming n-InGaAsP grating in the n-InP cladding layer close to the active region, accumulation of the holes in the grating layer was reduced and over 5 mW of output power was obtained at 120/spl deg/C. Clear eye opening was confirmed with no mask hits for OC-192 under 10-Gb/s direct modulation at the temperature up to 120/spl deg/C.     

Germania-based core optical fibers

Germania-glass-based core silica glass cladding single-mode fibers (/spl Delta/n up to 0.143) with a minimum loss of 20 dB/km at 1.9 /spl mu/m were fabricated by the modified chemical vapor deposition (MCVD) method. The fibers exhibit strong photorefractivity with the type-IIa-induced refractive-index modulation of 2/spl times/10/sup -3/. The Raman gain of 300 to 59 dB/(km/spl middot/W) was determined at 1.07 to 1.6 /spl mu/m, respectively, in a 75 mol.% GeO/sub 2/ core fiber. Only 3 m of such fibers are enough for the creation of a 10-W Raman laser at 1.12 /spl mu/m with a 13-W pump at 1.07 /spl mu/m. Raman generation in optical fiber at a wavelength of 2.2 /spl mu/m was obtained for the first time.     

Optimum core design for erbium-doped integrated optical amplifiers in silica-on-silicon

The gain an Er/P-doped integrated optical waveguide amplifier has been calculated as a function of waveguide core design, pump power, and background loss. The optimum core width varies from 2 to 3 mu m for pump powers close to the threshold for amplification up to 3-5 mu m for high gain operation.<>     

Fiber-device-fiber gain from a sol-gel erbium-doped waveguideamplifier

An erbium-doped silica-on-silicon planar waveguide optical amplifier is described. The active core is a topographic guide formed from aluminophosphosilicate glass doped with erbium and ytterbium. The buffer is formed from silica deposited by thermal oxidation and the cladding from borophosphosilicate glass obtained by plasma-enhanced chemical vapor deposition. The use of low process temperatures allows relatively heavy doping and careful control of the core etching allows low background insertion losses to be obtained. Spontaneous emission and gain measurements are given and 5.4-dB fiber-device-fiber gain is demonstrated using a 5-cm-long chip pumped using a 980-nm laser diode at 175-mW pump power