Optical fiber for laser beam guiding for cure

Details Optical fiber for laser beam guiding for cure Optical fiber for laser beam guiding for cure

1990-02-06

1993-06-22

Ullah, Akm E.

Optical waveguides

Having nonlinear property

359326, 385 31, 385123, G02B 600, G02B 636

Patent

active

052221822

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to an optical fiber for laser beam guiding. In particular, the present invention relates to an optical fiber for laser beam guiding comprising a secondary non-linear optical element, which fiber can be used in, for example, a catheter for lasing in which laser beam irradiation cures a lesion portion.


BACKGROUND OF THE INVENTION

An optical fiber for laser beam guiding is used in a catheter for the use of lasing which removes a lesion portion such as a thrombus in a blood vessel, which a practitioner cannot directly approach, by means of irradiating with a laser beam and vaporizing the portion. In such the lasing catheter, the optical fiber is used to transmit the laser beam to a tip of the catheter with a low beam loss.
In the meantime, in the lasing, it is required for the cure to use a beam having a short wavelength which has a large amount of energy and is sufficiently absorbed in a tissue in vivo.
However, a threshold value of destruction of the optical fiber for laser beam guiding is sharply reduced as the wavelength of the laser beam injected therein becomes short. For example, in the case of quartz, it is said that while the threshold value of destruction for the fundamental wave (1.064 .mu.m) of YAG laser beam is 130 GW/cm.sup.2, the triple-frequency wave (0.355 .mu.m) is reduced to one fifth of that for the fundamental wave.
Thus, even though lasing with a beam having the short wavelength such as an ultraviolet light (UV light) is effective for the cure, it has not been sufficiently utilized since the threshold value of destruction for the laser beam having the short wavelength is low.


OBJECT OF THE INVENTION

It is an object of the present invention to provide an optical fiber for laser beam guiding which makes it possible to irradiate with a beam having a short wavelength which has not been conventionally used due to a low threshold value of destruction for the short wavelength laser beam.


DISCLOSURE OF THE INVENTION

An optical fiber for laser beam guiding according to the present invention is characterized in that it comprises a secondary non-linear optical element at its one tip.
Any known secondary non-linear optical material can be used to form said secondary non-linear optical element. For example, an inorganic material such as LiNbO.sub.3, LiIO.sub.3, KH.sub.2 PO.sub.4 (KDP), KTiOPO.sub.4 (KTP), Ba.sub.2 NaNb.sub.5 O.sub.15 or an organic material such as 2-methyl-4-nitroaniline (MNA), urea, m-nitroaniline can be used. When an ultraviolet light is generated with wavelength conversion, desired is the material such as KDP which shows an absorption on the shorter wavelength side.
The non-linear optical material is not limited to one of a crystal form but a polymer material in which the non-linear optical material is dispersed may be used. In addition, the non-linear optical element may be in the form of a bulk crystal which automatically phase-matches or in the form which phase-matches by means of a waveguide configuration.
The optical fiber may be a multi-mode fiber or a single-mode fiber. In order to transmit a wavelength converted beam with a high efficiency, the single-mode fiber is preferred. The wavelength resulted from the wavelength conversion may be one of any wave such as a double-frequency wave, a triple-frequency wave and a quadruple-frequency wave. For example, when YAG laser is used, the combinations shown in the below table are possible, and any suitable combination can be optionally selected depending on curing effects. In particular, the fiber has not been known which can transmit an ultraviolet light such as the quadruple-frequency wave.


TABLE ______________________________________ Injected laser beam Converted beam ______________________________________ Fundamental wave Double-frequency wave (1.06 .mu.m) (0.53 .mu.m) Fundamental wave + Triple-frequency wave double-frequency wave (0.355 .mu.m) Double-frequency wave Quadruple-frequency wave (0.266 .mu.m) ___________________________________

REFERENCES:
patent: 4538278 (1985-08-01), Gergely
patent: 4612456 (1986-09-01), Gergely
patent: 4867510 (1989-09-01), Dobson
patent: 4909595 (1990-03-01), Okazaki et al.
patent: 4909609 (1990-03-01), McDowell
patent: 4923277 (1990-05-01), Okazaki et al.
patent: 4973125 (1990-11-01), Normandin
N. Uesugi et al, "Efficient second-harmonic generation in three-dimensional LiNbO3 optical waveguide", APPLIED PHYSICS LETTERS, vol. 29, No. 9, Nov. 1, 1976, New York US, pp. 572-574.

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