High-power 1.02 mu m InGaAs/AlGaAs strained quantum well lasers with GaInP buried waveguides for pumping Pr/sup 3+/-doped optical fibre amplifier

High power 1.02 mu m single spatial mode laser diodes with low-loss (3.3 cm/sup -1/) GaInP buried waveguides have been developed for pumping Pr/sup 3+/-doped optical fibre amplifiers. A maximum CW light output power of 415 mW and an optical fibre output of 71 mW at 200 mA have been achieved. A preliminary lifetest showed stable operation for over 2300 h under 100 mW CW conditions at 50 degrees C.<>     

Simple and low-loss fibre-to-chip coupling by integrated field-matching waveguide in InP

A nested taper structure in InGaAsP/InP, using only horizontally tapered waveguides, transforms the fundamental mode of an integrated waveguide to the mode profile of a singlemode fibre. Taper tips below 300 nm width have been achieved with standard technology. Very first measurement results show an insertion loss of only 4 dB for a 1 mm long device without any antireflective coating or immersion fluid.<>     

Rectangular mode transformers in tapered single-mode fibres

A single-mode fibre, polished on both sides and subsequently tapered, yields a low-loss circular-to-rectangular mode transformer. This device should permit more efficient interconnection of circular fibres to rectangular integrated-optic and semiconductor waveguides.<>     

New single-mode single-polarisation optical fibre

The theory for understanding fibres composed of `highly? birefringent material is presented. One of the two possible polarisation states of the fundamental mode can be made leaky, suggesting a novel single-mode single-polarisation fibre design. No leakage occurs in planar waveguides constructed similarly from the identical material.     

Spot-size converter using vertical ridge taper for low fibre-coupling loss in 2.5%-/spl Delta/ silica waveguides

A novel spot-size converter based on a vertical ridge waveguide taper for super-high-/spl Delta/ silica waveguides is demonstrated. This structure can be formed with a simple fabrication process. The coupling loss between a singlemode fibre and a 2.5%-/spl Delta/ silica waveguide was reduced to 0.31 dB/point compared to 2.7 dB/point for conventional straight waveguides.     

Low-insertion-loss channel waveguides in LiNbO3 fabricated by proton exchange

We describe single-mode proton exchange waveguides in Z-cut LiNbO3 at the 1.32 ?m wavelength having low fibre/waveguide/fibre insertion loss.     

Polarisation insensitive 1.55 mu m semiconductor integrated optical amplifier with access waveguides grown by LP-MOCVD

A 1.55 mu m GaInAsP/InP optical amplifier integrated with access waveguides provides 0 dB fibre to fibre gain at only 47 mA bias current and a 5 dB saturation gain already high enough to design 0 dB integrated complex circuits. Polarisation gain dependence and gain ripple are less than 0.5 dB and 0.7 dB, respectively.<>     

Symmetry-Induced Modal Characteristics of Uniform Waveguides --- I: Summary of Results

The application of symmetry analysis to uniform waveguides is discussed. Symmetry analysis provides exact information concerning mode classification, mode degeneracy, modal electromagnetic-field symmetries, and the minimum waveguide sectors which completely determine the modes in each mode class. Tables are presented which list the possible mode classes and their degeneracies for the two general symmetry families, C/sub n/ and C/sub nv/, of uniform waveguides. Tables showing the azimuthal dependence of the longitudinal components of the electric and magnetic fields for each mode class are given. Based on this azimuthal dependence, figures showing the minimum waveguide sectors which are necessary and sufficient to completely determine the modes of the various mode classes are presented. The application of symmetry analysis is illustrated by considering uniform waveguides with C/sub 4/ and C/sub 6v/ symmetry.     

Microstructure fibre array for RF photonic signal processing applications

A novel microstructure fibre array (MFA), comprising multiple singlemode fibre waveguides reduced to an overall diameter of approximately 30 /spl mu/m is reported. When used in conjunction with a single photodetector, the array facilitates the efficient and stable electrical summation of a number of RF-modulated optical signals with minimal optical interference effects. The reported MFA has optical insertion loss less than 0.1 dB. An RF filter based on the array exhibits less than 0.4 dB optical insertion loss and excellent temporal stability.     

Leaky Waveguide: TE/sup cir//sub 01/ Circular Waveguide Periodic Array of Circular Apertures

This paper describes propagation characteristics of periodic leaky waveguides for helix waveguides and solid metal waveguides carrying a TE/sup cir//sub 01/ mode based primarily on experimental studies. For low-loss leaky waveguides, this type has not been considered feasible, because of the critical problem encountered in mode conversion-reconversion at the circular apertures. Additional loss due to the periodic array of the circular apertures and TE/sup cir//sub 01/ loss/frequency characteristics of the periodic leaky waveguide using helix waveguides and solid metal waveguides are measured by the shuffle-pulse method in the X-band. The periodic leaky waveguides using solid metal waveguides are seen to be acceptable for practical use as a low-loss leaky waveguide system, according to these measurements.     

Silicon raised strip waveguides based on silicon and silicon dioxide thermal bonding

Si raised strip waveguides on SiO/sub 2/ have been proposed and fabricated, which are based on silicon-on-insulator (SOI) material. In the waveguides, the SOI technique utilizes silicon and silicon dioxide thermal bonding and back-polishing. An anisotropic etchant is used to produce the trapezoidal Si raised strip waveguides by etching the Si film down to the SiO/sub 2/ etch-stop buried layer. The transmission losses of the Si waveguides are measured to be less than 0.2 dB/cm at the 1.3 /spl mu/m wavelength for the lowest mode TE-like mode.     

Optical-fibre end preparation by spark erosion

Before splicing two optical-fibre waveguides, endfaces have to be prepared which are plane and perpendicular to the fibre axis A new method for preparing endfaces is proposed which is simple and reliable. The fibre surface is eroded by sparks and the fibre is then broken by hand.     

Mode Conversion in Tapered Waveguides At and Near Cutoff

The coupling coefficient between the TE/sub 11/ mode and the TM/sub 11/ mode in tapered circular waveguides is derived, and at cutoff frequency it tends to approach an infinity of the order of 0/sup -1/4/. It is surprising to discover that the corresponding coupling coefficient between the TE/sub 10/ mode and the TM/sub 12/ mode in tapered rectangular waveguides approaches instead a zero of the order of 0/sup 1/4/ at cutoff frequency. Accordingly, for the modes concerned, the choice of using circular or square waveguides as tapers for transition at and near cutoff frequency is significant in reducing mode conversion level. At and near cutoff frequency a "synthesized" square taper is better in that it is shorter than a "synthesized" circular taper for the same mode conversion levels. On the other hand, for frequencies far away from cutoff the choice is insignificant. Design procedures for "synthesized" waveguide tapers at and near cutoff are presented, and the results of measurements are in agreement with the theoretical calculations.     

Higher order mode coupling effects in the feeding waveguide of a planar slot array

The effect of internal higher order modes in the feeding waveguide of a planar slot array is investigated. Both the centered-inclined coupling slot and the longitudinal-transverse coupling slot are considered. Method of moments solutions to pertinent coupled integral equations are investigated for arrays of coupling slots of the centered-inclined and longitudinal-transverse types between a main waveguide and crossed branch waveguides. It is demonstrated that, by including the TE/sub 20/ mode coupling in the analysis, most of the higher order mode effects can be accounted for in reduced height waveguides, whereas in waveguides of standard height there may be a small additional effect arising from the TE/sub 01/ mode coupling.<>     

Optical coupling between thin films and circular fibres

Techniques are proposed for launching light into circular glass-fibre waveguides from prism couplers and thin-film optical waveguides. To make the evanescent field of core modes available, the fibre cladding is etched away, or its refractive index modified by ion exchange.     

Coupled mode theory of parallel waveguides

A new coupled mode formulation for parallel dielectric waveguides is described. The results apply to any guided modes (TE, TM, or hybrid) in waveguides of arbitrary cross-section, dissimilar index, and nonidentical shape. Additional index perturbations not included within the waveguides are encompassed by the theory. Propagation constants and mode patterns for the coupled modes computed according to this theory are shown to agree very well with numerical solutions for the system modes when the latter can be determined. Moreover, the new results are more accurate than those obtained from prior coupled mode formulations. It is shown that even for Iossless guides the coupling coefficients from waveguide"b"to"a"and from"a"to"b,"described by kaband kbarespectively, are not related by their complex conjugates if the guides are not identical.     

Sol-gel glass waveguide and grating on silicon

This paper reports on the fabrication and characterization of hybrid organic-inorganic glass sol-gel slab and channel waveguides by ultraviolet light imprinting in thin films deposited by a one-step dip-coating process. The adjustment of chemical composition of the materials provides precise selection of refractive index from 1.48 to 1.52 at the wavelength of 632.8 mn. The refractive index of the waveguides at 1.55 μm is similar to that of optical fiber, thus reducing the reflection loss between the two to less than 0.01 dB. The effect of ultraviolet light exposure and heat treatment on waveguide refractive index is studied. Fabrication parameters to produce ridge waveguides are optimized to achieve very smooth side walls. Propagation losses in these waveguides are ~0.1 dB/cm. Single mode buried waveguides, at 1.55 μm wavelength, with circular mode profile are demonstrated     

Optical surface wave mode converters and modulators utilizing static strain-optic effects

Periodic perturbations of dielectric waveguides can be obtained by an evaporated SiO2thin film grating through the static strain-optic effect. These waveguides are applied to TE-TM mode converters and modulators in Ti-diffused LiNbO3waveguides. Using a coupling length of 3 mm in an optical surface waveguide, we have demonstrated a TE-TM mode conversion efficiency of 80 percent and a TE-TM mode modulator with 100 percent modulation with an applied field of 2 V/μm. A theoretical analysis of a reflector for a semiconductor laser waveguide is also described.     

Microstructured optical fibre with tunable birefringence

An approach is presented for manipulating and tuning birefringence in a microstructured photonic crystal optical fibre. This is accomplished by filling certain airholes with an index tunable polymer which creates a tunable asymmetry in the index profile of the cladding. It is also demonstrated that fibre waveguides with three- and sixfold symmetry exhibit minimal birefringence     

Optimization of novel high-power millimeter-wave TM01-TE11 mode converters

In this paper, a numerical study of direct TM₀₁-TE₁₁ mode converters in highly overmoded, bent smooth, circular waveguides is presented for high-power millimeter waves. The various shapes of bent waveguides are elaborately chosen, and their optimized geometrical dimensions have been achieved with a general optimization code employing the coupled mode theory. The mode converters designed can have high conversion efficiencies over 98% and wide bandwidths of 28%