Optical waveguides – Optical fiber bundle – Imaging
Patent
1992-08-17
1994-01-04
Gonzalez, Frank
Optical waveguides
Optical fiber bundle
Imaging
385119, 385122, G02B 604
Patent
active
052767582
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a system for shifting the frequency and wavelength of a laser beam consisting of a scaleable, phase-locked array of non-linear optical fibers each of the said fibers being embedded in an optically transparent medium, which, collectively form a coherently packed bundle, with the opposite faces of said bundle formed by the ends of said fibers, being optically polished, with a micro lens array positioned near to each of the said optically polished faces such that a laser beam incident on one of the micro lens array is split into an array of focussed micro laser beams each one of which matches into a particular optical fiber in the array of said fibers forming the said invention. On being focussed into said fibers within said fiber bundle of said system, the laser light propagating through said fibers is partially frequency shifted to a frequency which depends on the properties of said non-linear optical medium forming said fiber cores and on the frequency of the input laser beam propagating through the said system.
The invention has application for the frequency and wavelength shifting of laser beams used in materials processing, medical, research, defence applications and isotope separation.
SUMMARY OF THE PRIOR ART
Prior art laser beam frequency shifting systems consisted either of a single crystal block of non-linear optical media or a single optical fiber whose core consisted of a non-linear optical medium.
These prior art frequency shifting systems were ineffective in providing scaleable output power under continuous wave operation which demands that the laser beam intensities within the non-linear optical medium be very high, exceeding about 100,000 watts per square centimeter, power levels which would melt known bulk media at such high beam intensities.
Prior art frequency shifting systems which utilised single fiber cores did achieve high beam intensities over extended lengths, a process which led to the efficient conversion (over 50%) of the primary laser beam propagating through said non-linear fiber, but at very low power levels of only a few milliwatts.
The present invention overcomes the defects of prior art frequency and wavelength shifting systems in that it provides high beam intensities within a phase-locked array of fibers of non-linear media so that scalable laser beams of high, continuous wave power is achieved for the first time.
The present invention also differs from the frequency shifters of the prior art because it utilises a phase-locked array of laser beams whose relative phases can be varied to produce scannable output beams at the shifted frequency.
BACKGROUND OF THE INVENTION
As scaleable, high power, continuous wave lasers have become available, their available wavelengths have tended to be in the near and mid infra-red regions of the electro-magnetic spectrum rather than in the visible and ultra violet regions where an increasing number of applications are emerging.
In order effectively shift the infra-red laser wavelengths into the visible and ultra violet regions under continuous wave conditions, it is necessary to pass the said infra-red laser beams at high intensities over relatively long lengths of non-linear optical media. This requirement eliminates the use of bulky non-linear crystals, which are effective under pulsed conditions, because the enormous laser beam intensities would heat up the crystal, initially causing thermally induced self-focussing effects and finally simply destroying the said bulk crystal.
It was known since the early 1960s that laser beams traversing the cores of multimode optical fibers gave rise to very high flux densities of many hundreds of watts per square centimeter. With the subsequent advent of single mode fibers, it was possible to inject a laser beam into a core only a few microns in diameter, that is, with a cross-sectional area of less than a millionth of a square centimeter so that less than a watt of continuous wave power was needed to achieve the enormous laser beam intensities e
REFERENCES:
patent: 4909609 (1990-03-01), McDowell
patent: 4983014 (1991-01-01), Nattermann
patent: 5009483 (1991-04-01), Rockwell, III
patent: 5022043 (1991-06-01), Jacobs
patent: 5032718 (1991-07-01), Murakami
Patent Extracts of Japan, P-12, p. 137, JP, A, 55-003,857, (Mitsubishi Denki K.K) Mar. 18, 1980 (18.03.80), Mutoo et al.
Bednarek Michael D.
Gonzalez Frank
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