Abstract: A method for producing a glass filament, the method including: irradiating a raw yarn containing 70 wt % or more of SiO2 and having a raw yarn diameter of 100 to 2,000 ?m with laser light having a wavelength of 0.7 to 100 ?m to heat the raw yarn; and stretching the raw yarn to obtain the glass filament having a hydroxyl group (Si—OH) content of 300 ppm or less and a diameter of 1 to 20 ?m.

Abstract: A high-strength synthetic fiber is fabricated in such a way that a fiber, such as a polyester fiber, nylon fiber, or polyether ketone fiber, is irradiated with an infrared beam and is drawn while its thread is heated and softened at temperatures higher than a glass transition temperature. An apparatus for fabricating a fiber is provided with a means (10) for continuously feeding a thread (1) at a constant feed rate (v) and an infrared irradiation means (13) including a laser for irradiating the thread (1) with an infrared beam, interposed between the means (10) for feeding the thread and a fiber winding means (11) for winding the thread (1) at a winding rate (V) higher than the constant feed rate (v), in order to soften the thread (1) traveling to be fed and wound.