Fabrication and optical measurements of the microcavities Circular in shape microcavities (54 µm diameter, 62.5 µm height) were fabricated in side surface of standard Corning SMF28 fibers. The micromachining process was performed using an NKT Origami 10XP laser operating at wavelength of 1030 nm. The fiber was irradiated by ca. 400 fs pulses. Fused silica glass shows very low absorption at 1030 nm, and therefore linear absorption of the laser radiation does not occur when the glass is irradiated by the laser beam . The system worked with a repetition rate of 15 kHz. The laser beam was focused on the sample with a suitably designed micromachining setup based on the Newport mFab system. It was equipped with a 20x lens (NA = 0.30). The laser pulse energy was equal to 6 nJ. Fiber transmission was monitored during the process with an NKT Photonics SuperK COMPACT supercontinuum white light source and a Yokogawa AQ6370D optical spectrum analyzer. The fabrication process was controlled with an in-house developed software.