The small dimensions of laser diode emitting areas, single-mode fiber cores, and some detector active areas make their mutual alignment difficult requiring precision positioning devices. This difficulty can be attributed to the high spatial sensitivity of the coupling efficiency between the two small optical components. However, the high spatial sensitivity can be utilized to cause a small fluctuation in the coupled light by imposing a small vibration (e.g., 10 nm) on one of the components. The amplitude of the coupled light fluctuation and its phase contain information about the relative offset of the components. This information is easily extracted with a phase sensitive detector. By providing feedback of the dc output of the phase sensitive detector to the transducer which is vibrating one of the optical components, that component will lock onto the optimum coupling position, where the optical fluctuations are minimal. Figure 1 is a schematic diagram of the real-time alignment setup. Alignment of an orthogonal axis has been incorporated simply by having the dither in this axis take place at a different frequency, with another phase-sensitive detector used to produce the dc error signal for the orthogonal driving transducer.
© 1986 Optical Society of AmericaPDF Article