A photonic crystal fibre including a plurality of longitudinal holes (220), in which at least some of the holes have a different cross-sectional area in a first region (200) of the fibre, that region having been heat-treated after fabrication of the fibre, from their cross-sectional area in a second region of the fibre (190), wherein the optical properties of the fibre in the heat-treated region (200) are altered by virture of the change in cross-sectional area of holes (230) in that region (200).

Photonic crystal fibres

Ultra-small optical probes comprising a single-mode optical fiber and a lens which has substantially the same diameter as the optical fiber. The optical fiber and lens are positioned in a probe housing which is in the form of an insertional medical device such as a guidewire. Connector elements are provided to facilitate the attachment of the probe to an optical system and the quick disconnection of the probe from the optical system. The probe is used to obtain optical measurements in situ in the body of an organism and can be used to guide interventional procedures by a surgeon.

Ultra-small optical probes, imaging optics, and methods for using same

Visual-assisted guidance of an ultra-thin flexible endoscope to a predetermined region of interest within a lung during a bronchoscopy procedure. The region may be an opacity-identified by non-invasive imaging methods, such as high-resolution computed tomography (HRCT) or as a malignant lung mass that was diagnosed in a previous examination. An embedded position sensor on the flexible endoscope indicates the position of the distal tip of the probe in a Cartesian coordinate system during the procedure. A visual display is continually updated, showing the present position and orientation of the marker in a 3-D graphical airway model generated from image reconstruction. The visual display also includes windows depicting a virtual fly-through perspective and real-time video images acquired at the head of the endoscope, which can be stored as data, with an audio or textual account.

Catheterscope 3D Guidance and Interface System

Researchers show that optical isolators based on nonlinearity cannot provide complete isolation for arbitrary backwards propagating noise, revealing limitations for their practical application.

Limitations of nonlinear optical isolators due to dynamic reciprocity

This paper presents two dimensional (2-D) finite difference time domain (FDTD) simulations of low-loss right-angle waveguide bends, T-junctions and crossings, based on high index-contrast waveguides. Such structures are essential for the dense integration of optical components. Excellent performance characteristics are obtained by designing the waveguide intersection regions as low-Q resonant cavities with certain symmetries and small radiation loss. A simple analysis, based on coupled mode theory in time, is used to explain the operation principles and agrees qualitatively with the numerical results.

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High-density integrated optics

A beam-expanding fiber (BEF) for embedding optical devices has been fabricated by utilizing thermally induced Ge diffusion in silica single-mode fibers (SMFs). The preparation of fiber samples and their heat treatment is described, and the effect of heat on Ge dopant distribution and diffusion is discussed. Modal-intensity distributions were studied and found to confirm the broadening of the modal field distribution after heat treatment of the fiber. Localized heat treatment to obtain BEFs is considered, and device characteristics are discussed. The BEF can arbitrarily change the spot size of a propagating mode without changing the normalized frequency. >

Beam expanding fiber using thermal diffusion of the dopant

Characteristics of light propagation in thermally diffused expanded-core (TEC) fibers are analyzed. Changes in the modal-field distributions along fibers and transition losses are obtained by use of the propagating-beam method. It is found that a transition length sufficiently longer than the characteristic length is necessary to expand or reduce the field diameter with low losses. A simplified model for understanding the mechanism of light propagation in TEC fibers is presented. Transmission losses between TEC fibers having imperfect splices are measured, the results are compared with those obtained by a simple theory and an exact theory. >

Light-propagation characteristics in thermally diffused expanded core fibers

Theoretical and experimental performances of a robust Si-based spot-size converter (SSC) for efficient coupling between a single-mode fiber and a photonic Si-wire waveguide are reported. The SSC is comprised of cascaded horizontal linear and vertical nonlinear up tapers measured 2.0mm and 86μm in length, respectively, in a silicon-on-insulator substrate. The fine modal field of a Si-wire waveguide, 0.54×0.38μm2 in diameters, was expanded to diameters of 5.1×9.2μm2 with measured net transmission loss of 0.5dB at the wavelength of 1.55μm by the miniature SSC.

A silicon-based spot-size converter between single-mode fibers and Si-wire waveguides using cascaded tapers

A new scheme is proposed for lensed fibers with a long working distance, as used in the coupling between laser diodes and single-mode fibers. The scheme consists of the combination of a hemispherically-ended coreless-fiber tip and an expanded-core fiber. The working distance is measured as 169 /spl mu/m with a relatively low coupling-loss of 4.2 dB at a wavelength of 1.49 /spl mu/m. Tolerances for a 1-dB loss increment for axial-, lateral-, and angular-misalignment are 35, 2.6 /spl mu/m, and 0.8 degrees, respectively. The new configuration is suitable for alignment-free coupling between arrayed laser diodes and an array of single-mode fibers. >

A fiber lens with a long working distance for integrated coupling between laser diodes and single-mode fibers

A structure that tan reduce abrupt-bend losses in dielectric optical waveguides is proposed. The structure has a relatively low refractive-index region at the outside of the corner; the region operates as a phase-front accelerator of the propagating mode. It has been ascertained by basic experiments that the bending loss of this structure can be significantly reduced from that of the conventional one.

Kazuo Shiraishi

Papers

Beam expanding fiber using thermal diffusion of the dopant

Light-propagation characteristics in thermally diffused expanded core fibers

A silicon-based spot-size converter between single-mode fibers and Si-wire waveguides using cascaded tapers

A fiber lens with a long working distance for integrated coupling between laser diodes and single-mode fibers

Waveguide-bend configuration with low-loss characteristics