Electric heating – Metal heating – By arc
Reexamination Certificate
2002-05-10
2004-11-30
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
By arc
C219S121680
Reexamination Certificate
active
06825440
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a laser beam machining method and apparatus for irradiating a work with a laser beam, to melt-evaporate the irradiated region of the work at the irradiation spot. Particularly the present invention provides a laser beam machining method and apparatus that can machine the tip portion of an optical fiber, as an example of the work, into a desired form.
BACKGROUND OF THE INVENTION
Optical fibers, for example, optical fibers mainly composed of quartz glass are used in optical transmission systems and other optical systems, and the tip forms of these optical fibers play an important role irrespective of kinds of fibers such as single mode fibers and multi-mode fibers.
It is desired that the end faces of an optical fiber have an especially smooth surface and an accurate form for minimizing the connection loss in its connection with another optical fiber or an active device. Therefore, it is desired that the method of machining the tip of an optical fiber can achieve accurate machining into a predetermined form at high productivity
Known methods of finely processing the tip of an optical fiber include mechanical methods such as fiber cleaving, chemical methods such as etching and optical methods such as the use of a CO
2
laser, etc.
The mechanical method using a fiber cleaver allows the tip of an optical fiber to be simply and sharply cleaved, but has a problem that it cannot process the tip into a semi-spherical, conical, or wedge-like surface, etc.
The chemical method using etching allows the tip of an optical fiber to be formed as desired, but since it is difficult to control the form and takes a long period of time, the method has a problem in view of productivity.
In the case where the conventional general method of using a CO
2
laser is used to cut an optical fiber to process it at an end, it can happen that the heat generated during machining causes a form error, and since the spatial distribution of light intensities is Gaussian, there is such a problem that the machined edge becomes blunt.
Examples of these cases are described below.
For example, in the optical fiber cutting methods and apparatuses described in the gazettes of JP02-230205A and JP02-238406A, optical fibers are mechanically cut. These methods allow optical fibers to be cut easily and well, but cannot be used for processing the tips of optical fibers.
EP 0987570 discloses a method of cutting an optical fiber using a pulse CO
2
laser. In this method, a circular laser beam with Gaussian-distributed light intensities is merely condensed by a lens for cutting an optical fiber. The method cannot process the tip of the optical fiber into a desired form.
U.S. Pat. No. 5,256,851 discloses a method of melt-evaporating the tip of an optical fiber very little by very little using a pulsed CO
2
laser. This method has such problems that it takes a long period of time for predetermined machining.
In the above-mentioned machining method using a pulsed CO
2
laser, since the tip of an optical fiber to be differently formed depending on the applicable specifications must be processed into a desired form by repeating micro machining, the laser beam must be finely condensed like a point using a lens, for accurate processing into a desired form.
Therefore, the control of the laser beam irradiation position for adaptation to the form to be obtained at the tip of the optical fiber is troublesome, and expensive equipment is necessary for very highly accurate irradiation position control.
In addition, the spatial distribution of light intensities, i.e., profile of the light condensed by a lens becomes conical with the focus as the vertex, machining becomes difficult with the increase in the depth of the machined portion of the optical fiber. Furthermore, there is such a problem that since a thin V-shaped end face is formed in the section of the machined portion, the gas, fume and heat generated during machining are likely to be retained there, to contaminate or curve the machined surface.
Furthermore, if the pulsed CO
2
laser is used, since the tip of an optical fiber is irradiated with a laser beam having high light intensity continuously for a long time, the peripheral portion of the tip portion is also heated to deform the optical fiber, not allowing machining as designed. Moreover, if a pulse laser is used, the thermal effect on the optical fiber can be reduced, but there is another problem that the machining time becomes longer by that.
OBJECTS OF THE INVENTION
One of the objects of this invention is to provide a laser beam machining method and apparatus that can machine the tip of a work such as an optical fiber into a desired form highly accurately within a short period of time.
Another object of this invention is to provide a laser beam machining method and apparatus capable of preventing the vibration of the fiber caused by the ablation during laser beam irradiation and preventing the occurrence of facial sagging, that respectively lower the form accuracy at the cut face when the tip of an optical fiber is cut by means of laser beam machining.
SUMMARY OF THE INVENTION
To solve the above-mentioned problems, the present invention proposes a laser beam machining method, in which a work is irradiated with a laser beam to melt-evaporate the portion irradiated with the laser beam for machining the work, characterized in that
a mask having a light-transmitting section that is predetermined times as large as the laser beam machining spot corresponding to the form of the portion undergoing melt-evaporation of the work, is disposed between a laser beam source and the work, and
the laser beam transmitted from a laser beam source through a beam-shaping optical system is irradiated to said mask in a range larger than said light-transmitting section, and the real image of the light-transmitting section formed by the transmitted light is reduced to the size of said machining spot by means of a reduced image-forming optical system, to form the reduced image on the work, for machining.
According to this method, since the light-transmitting section that is predetermined times as large as the machining spot corresponding to the form of the portion undergoing melt-evaporation of the work is formed in the mask irradiated with a laser beam, the laser beam irradiated in a range larger than the light-transmitting section passes through the light-transmitting section of the mask, to become a beam with a spot form equal to the form of the light-transmitting section.
This beam passes through a reduced image-forming optical system, and as a result, the real image of the light-transmitting section is reduced to the size of said machining spot, to form the reduced image on the work. The portion of the work in the range of the machining spot is melt-evaporated, and the portion not melt-evaporated remains as a desired form.
In this case, if the laser beam passes through the light-transmitting section formed in the mask, the light intensity at the edge portion of the optical beam becomes high due to light interference. So, the portion undergoing melt-evaporation can be well molten also at the area corresponding to the boundary with the portion undergoing no melt-evaporation, and the thermal effect on the portion undergoing no melt-evaporation is small.
As described above, simply by forming the light-transmitting section of the mask with a large area as desired, the real image of the light-transmitting section can be reduced to the size of said machining spot, to form the reduced image on the work. So, when the work is machined, it is not necessary to control the laser beam irradiation position each time.
Furthermore, since the laser beam is not condensed like a point on a work for irradiation as in the conventional method, but is irradiated as said machining spot corresponding to the form of the portion undergoing melt-evaporation, the portion undergoing melt-evaporation can be melt-evaporated generally as a plane not as a point, and the predetermined machining can be accomplished within a short p
Ohta Kazuyoshi
Sasano Naoshige
Elve M. Alexandra
Moritax Corporation
Townsend & Banta
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