Optical waveguides – Optical fiber waveguide with cladding – Utilizing nonsolid core or cladding
Patent
1998-07-01
2000-12-19
Henry, Jon
Optical waveguides
Optical fiber waveguide with cladding
Utilizing nonsolid core or cladding
385142, G02B 620
Patent
active
06163641&
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to optical waveguides generally and to liquid core optical waveguides for the transmission of ultra-violet (UV) radiation in particular.
In the prior art waveguides have been used for a variety of medical, dental and industrial applications to transmit both coherent and incoherent radiation at relatively high energy levels and at ultraviolet, visible and infrared wavelengths.
One type of waveguide which is known in the prior art consists of a series of mirrors arranged along an articulated arm, the laser beam being reflected from mirror to mirror along the arm. However, it will be apparent that such an arrangement has only limited flexibility, and is sensitive to errors in alignment, as well as being bulky and relatively expensive to manufacture and maintain.
Another general type of light waveguide which is known in the prior art employs the principle of total internal reflection to transmit light along a column or core of material, usually quartz or glass. The step-index fibres consist of a central core of glass or quartz surrounded by an optical cladding layer which has a refractive index lower than that of the core material. Light incident on the junction between core and cladding will be almost totally reflected if the angle of incidence, measured from a line normal to the junction, is greater than a critical value. Thus, light can be transmitted along the fibre and around bends, provided that the radius is not too small. In the gradient-index fibres, the refractive index of the core material is highest at the axis of the fibre and decreases gradually towards the cladding, so that the light follows a smooth curved path inside the core instead of a sharp zigzag path as in the step-index fibres.
Glass core fibre optics will transmit wavelengths limited mainly to the visible and are thus not suitable for UV transmission. Quartz will transmit a wide range of wavelengths from the ultraviolet to the near infrared, but quartz waveguides, as well as being fragile, are very expensive and difficult to produce.
Although ideal for communications purposes, which require the transmission of low energy radiation over long distances, fibres of the previous type present great difficulties for the transmission of relatively large amounts of power over shorter distances.
The principal problem with these fibres is that they must be very thin (2-150 microns) to provide the required flexibility. Single fibres of quartz or the like are necessarily quite fragile, especially in applications where repeated flexing is required. Particularly in laser applications, the power densities in thin fibres can be high enough to cause breakdown of the core material due to non-linear and other effects. In addition, it is very difficult to successfully launch incoherent light beams that may be 50 mm or more in diameter, or large diameter laser beams, into fibres of this type without high losses.
Some optical fibres of this type have been formed from finely drawn quartz capillary tubes filled with a liquid, but the same problems of fragility, alignment, and breakdown of the material, prevent their use in any of the aforementioned applications requiring high power levels.
Bonding large numbers of single glass fibres together to form flexible fibre optic bundles of much greater diameter than single fibres has been useful for a number of applications. However, with use, the individual fibres begin to fracture, leading to increasing numbers of "dead spots" and decreasing efficiency of the bundle. Also, because only the cores of individual fibres transmit light and these make up only a percentage of the cross-sectional area of a fibre optic bundle, light falling on the material between the fibres is not transmitted, but absorbed. This causes initial losses proportional to the non-transmitting area of the bundle, and, if the energy of the incident light beam is high enough, destruction of the bundle. Thus, waveguides of this type cannot usually be used for transmission of high energy radiation.
Optical fibres with pla
REFERENCES:
patent: 5412750 (1995-05-01), Nath
patent: 5675689 (1997-10-01), Nath
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