A lossless optical coupler includes at least one input waveguide, at least two output waveguides and an intermediate optical splitter. The instrument is further provided with interchangeable handle inserts that provide additional weight at the back end of the instrument. The virtual machines may retrieve stored state information to recover from a fault. The proximal side probe component is bent relative to the probe body at a bending position so that a center of gravity of the proximal side component is deviated from the X-axis and a second lateral vibration of the proximal side component is superposed on the longitudinal vibration of the ultrasonic probe.