In-situ investigation of coupling between a fibre and a slab waveguide

The mode coupling between a fibre and a slab waveguide was experimentally investigated during the formation of the slab. A thin film has been deposited on a polished fibre close to the core-clad interface. By monitoring the optical transmittance of the fibre during the film deposition the coupling efficiency between the formed slab and the fibre has been studied as a function of the film thickness. Strong attenuation in the fibre output has been observed for thickness values at which the propagation constants of the optical mode in the fibre match those of the slab waveguide.<>     

Effectively nonreciprocal evanescent-wave optical-fibre directional coupler

An effectively nonreciprocal directional coupler has been demonstrated using evanescent coupling between a single-mode and a multimode optical fibre. At least 17 dB difference in coupling efficiency between transmit and receive branches has been measured. The near-field mode patterns show coupling between the single-mode fibre and a few high-order modes of the multimode fibre.     

Fused single mode fibre access couplers

Single mode fibre access couplers have been fabricated by chemically etching most of the glass cladding material surrounding the fibre core, and thermally fusing the fibres together in the etched region. The resulting couplers have low loss and are both durable and insensitive to ambient temperature variations.     

Cascaded multipole switches for single-mode and multimode optical fibres

Multistage moving-fibre array switches which use preferentially etched silicon chips for the precise alignment of the optical fibres have been developed. In particular, a 1×4 single mode, and a 1×8 multimode fibre switch are described, with which average insertion losses of 0.8 and 0.2 dB were achieved, respectively.     

An etched two-mode fiber modal coupling element

When a fiber with topological structures built directly on the cladding is compressed longitudinally, lateral bends are induced. The lateral bends lead to mode coupling. We have built several etched two-mode fiber modal coupling elements to take advantage of this effect of bending. The resulting modal coupling elements are compact. More importantly, the percentage of power converting from one mode to another is variable by varying the axial compression. In this paper, we present a theoretical model describing the mode conversion in the etched fiber elements. Also discussed are the fabrication and testing of the modal coupling elements and the experimental confirmation of the theoretical model     

光纤锥模场传输特性及光纤微透镜最佳位置研究

分析了两类光纤维（熔拉锥和腐蚀锥）的模场传输特性,引入了特征转换点,为降低模式耦合损失和增强聚焦效果,光纤锥微透镜制作的最佳位置,熔拉锥在靠近特征转换点处,腐蚀锥在锥端至特征转换点之间,并讨论光纤微透镜对高斯光束的聚焦。     

Improved coupling between laser diode and single-mode fibre tipped with a chemically etched self-centred diffracting element

Coupling efficiency between a laser diode and single-mode fibre can be highly increased by using an appropriate intermediate optical element. A simple new method is intended to improve the mode matching of the two elements by chemically etching the fibre end into a self-centred diffracting element. A gain by a factor of 3.5 over classical butt coupling has been obtained.     

Bend loss in buffered over-moded optical fibre: LP11mode and `whispering gallery' mode interaction

Bend loss in over-moded fibre has been measured as a function of temperature. For the LP₁₁ mode, an oscillatory loss dependence on temperature was observed, caused by coupling between the LP₁₁ mode and a `whispering gallery' mode. These interactions could have a significant effect on singlemode cutoff wavelength measurements     

Two-dimensional optical power distribution of side-out-coupled radiation from tilted FBGs in multimode fibre

Two-dimensional optical power distribution of the out-coupled radiation from UV-inscribed tilted fibre Bragg gratings (TFBGs) in multimode fibre (MMF) has been side-detected with high spatial/spectral resolution, showing a near-identical radiation mode profile to that measured from the fibre-end detection method. A comparative investigation of the radiation characteristics of TFBGs fabricated in singlemode fibre (SMF) and MMF clearly indicates that the radiation out-coupling is stronger and spatially more confined in MMF. The unique spatial-to-spectral encoding property of the coupling mechanism offers potential application in low-cost WDM devices.     

Single-mode-fibre passive components made in the fused-head-end technique

The fused-head-end technique, used successfully until now for producing passive fibre components in multimode fibre, can also be applied to produce single-mode fibre couplers and splitters. The device is based on evanescent mode coupling and has no pigtail problem. The first experimental results are presented, together with the theoretical interpretation. Some expected system applications and further improvements are indicated.     

Analysis of ring launching scheme using hollow optical fibre mode converter for 10 Gbps multimode fibre communication

A ring launching scheme using a mode converter based on hollow optical fibre (HOF) is theoretically investigated for the purpose of increasing bandwidth for multimode Gigabit Ethernet communication. The mode converter based on HOF transforms the fundamental mode of a single-mode fibre (SMF) to a ring-shaped mode. It has the characteristic to improve the bandwidth by exciting higher-order modes of the multimode fibre (MMF) selectively. The HOF launch is studied under various aspects such as induced coupling efficiency, mode power distribution, and bandwidth-length product and is compared to centre and offset launching schemes. It is shown that the ring launching scheme is expected to support 10-Gb Ethernet applications using conventional multimode fibres.     

Optical frequency shifter using linearly birefringent monomode fibre

An optical frequency shifter has been constructed which uses travelling acoustic flexure waves induced on a single linearly birefringent monomode fibre to produce mode coupling between the two orthogonal polarisation eigenmodes. The output of the frequency shifter is examined using a heterodyne interferometer. The measured efficiency was ?2% at a shift frequency of 491 kHz.     

Engineering of InGaAsP layer structures for low divergent longwavelength lasers

The epitaxial layers of an lnGaAsP laser structure have been engineered to obtain a transverse mode size of 3.1 μm and a FWHM transverse divergence to 22° while still retaining single mode operation. Ridge lasers based on this structure demonstrate 32% butt coupling efficiency to single mode fibre     

Novel mass-fabrication of fibre couplers using arrayed fibreribbons

To achieve high productivity and high density packaging of fibre couplers for practical systems, a novel mass-fabrication process using arrayed fibre ribbons has been developed. The fabricated arrayed-fibre coupler consists of four couplers which are all fabricated together from four-fibre ribbons. Each fibre coupler had 3 dB coupling ratio to within 49.3±2.1%. It has been confirmed that plural fibre couplers with equal coupling ratio can be simultaneously fabricated by the mass-fabrication process     

Self-adjusted permanent attachment of fibres to GaAs waveguide components

We present a self-aligned flip-chip mounting technique for permanent coupling of single-mode fibres to rib waveguides By help of reactive-ion-etched alignment ribs and preferentially etched silicon V-grooves, self-adjusted alignment with excess coupling loss as low as 0.3 dB has been achieved.     

Enhancement of bandwidth and additional loss caused by controlled mode coupling in quartz fibres

Controlled mode coupling is applied to a 1 km quartz multimode fibre. Bandwidth and associated increase in loss, and the time relation between pulses with and without mode coupling, are reported.     

Monolithically integrated laser/rear-facet monitor arrays withV-groove for passive optical fiber alignment

An InGaAsP/InP laser monolithically integrated with a rear facet monitor and a fiber V-groove has been demonstrated for the first time. The integrated device incorporates an etched-facet laser fabricated using an in situ, multistep, reactive ion etch process. The integrated V-groove, which is etched directly into the InP substrate, is designed to enable passive alignment of an optical fiber to the active region of the laser. Passive coupling efficiencies of 18% and 8% have been obtained using cleaved multimode and single mode fibers, respectively. Responsivities of the rear facet monitor were as high as 0.49 A/W     

Wavelength-switching fibre laser based on multimode fibre Bragg gratings

A multimode fibre Bragg grating (MMFBG) based wavelength-switching erbium-doped fibre laser is reported. With a simple singlemode fibre to MMFBG structure, a novel wavelength-selection technique is developed to achieve the wavelength-switching by changing the mode coupling condition in the multimode fibre. 31 discrete lasing wavelengths are obtained over a wide wavelength range.     

Bandwidth of long monomode fibre links in the presence of weak mode coupling

The bandwidth of long monomode fibre links may be reduced in the presence of weak mode coupling such as that introduced by cabling. This is in contrast to the single fibre case.     

High optical coupling efficiency using 45 °-ended fibre for low-height and low-cost optical interconnect modules

High optical coupling efficiency of more than 80% between an optical fibre and a vertical-cavity surface-emitting laser (VCSEL) has been achieved without use of a lens. A 45deg-ended fine-drawn optical fibre can be positioned closer to a VCSEL than a conventional multimode fibre. 12.5 Gbit/s/ch optical signal transmissions using a low-height optical coupling structure have been demonstrated with optical output power as high as +2.0 dBm without use of a lens.