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Halcyon Optical Services has many years of optical design expertise, using a variety of optical design tools, including WinLens, Zemax, MathCad and proprietary software packages.

A few examples of projects are given below:

The problem was to measure the diameter of the transparent protective coatings on an optical fibre. The novel wedge-shaped prism, shown above, was designed to provide dark-field illumination across the fibre. The coating boundaries, acting like negative cylindrical lenses, caused light to enter the collection optics and form an image on the camera consisting of a series of bright lines on a dark background. The figure, right, shows an intensity plot across the fibre diameter. The diameter and concentricity of the cladding and the two coating layers were then readily computed from measurements made at different angular positions of the fibre.

For more details see:

'Measurement and Calibration of Fiber Coating Geometry by Grey-Scale Analysis', Journal of Lightwave Technology, vol 13, no. 8, Aug 1995. (patent no.US5335057).

The challenge here was to provide a high quality image of a cleaved fibre end that could be accurately positioned in side a software alignment box. A careful balance between optical resolution and the depth of focus had to be made so that both the end and the sides of the fibre were in focus.

For more details on this project click here.

The Michelson interferometer is a powerful tool for measuring surface flatness and has been used to great effect in the VF-20 Fiber Inspection System. In the interferometer the object is viewed via a beamsplitter cube and the design had to take account of aberrations caused by the presence of the cube. Using ray-tracing software it was possible to design a diffraction-limited optical system that had a 0.32 numerical aperture and gave x20 magnification.

An image of the near-field light distribution in a multimode optical fibre was required so that the 'Mode Profile Distribution' of the fibre could be determined. A high quality machine-vision CCD camera was chosen having 768 x 574 picture elements, or pixels. An imaging system was then designed to give (a) a field-of-view commensurate with the fibre sizes to be measured, and (b) an optical resolution commensurate with the physical pixel size in the camera.

Increasing the numerical aperture of the optics in this type of application does not always lead to a better image quality if the pixel size is not sufficiently small to make use of the extra resolution.

For more details on camera-based systems click here.

Halcyon Optical Services, 'Sandridge', Winchester Road , Waltham Chase, Hants, SO32 2LG. UK

Tel: +44 (0)1489 890149

info@halcyon-optical.co.uk

The requirement was to form an image of a 1mm plastic optical fibre with a magnification of x4 onto a CCD camera. Sounds quite easy, but there were constraints. Firstly, for mechanical reasons, the image plane had to be 155 mm from the fibre end and, secondly, near diffraction-limited performance was required for a minimum fibre NA of 0.2. Thirdly, for reasons of time and cost, the components had to be off-the-shelf. As the application was for modal-profiling it was not possible to use stops as all the light from the fibre had to reach the camera. Fortunately, chromatic aberrations were not an issue as the light source was virtually

The final system consisted of a first achromat with the fibre at its front focus, and a second group consisting of an achromat, a negative field-flattener lens and a plano convex lens. The through-focus spot diagrams show that the aberrations are well balanced. The small residual field curvature is within the depth of focus of the system.

A 0.8NA microscope objective with diffraction-limited performance at 633nm was required for focussing a laser beam to a tiny spot for an optical profiling application. The image plane was to be formed through a 170um coverslip glass. Using ZEMAX ray trace software the through-focus spot diagrams, below, show the excellent on-axis performance of the design.

The requirement was to produce low divergence optical beams from each of the three LEDs, such that they overlapped at a distance of 2m to give a white illumination area. A prototype was built which consisted of three Fresnel wedge lenses fitted together