Abstract

In this paper a high precision measurement technique based on measuring the contrast of a Fabry-Perot cavity containing the optical waveguide is demonstrated. A similar approach has been employed for high index waveguides,^1,2 but in the technique described here, the cavity has been extended by two optical fibers with a dielectric coated mirror on one end of each fiber and the other end coupled to the waveguide as shown in Fig. 1. The dielectric mirrors enhance the cavity finesse, leading to improved measurement accuracy. By changing the length of one of the fibers; either by heating a section of the fiber or by stretching it using a piezo-electric element, the optical length of the cavity is changed and the transmission characteristic exhibits Fabry-Perot resonances with maxima and minima as predicted by the Fabry-Perot intensity transmission equation.³ The modified reflection coefficient, R' = R exp(–α_tot) can be calculated from the measured contrast K = (I_max – I_min)/(I_max + I_min), I_max and I_min being the maximum and minimum transmitted optical intensity, respectively. As the mirror reflection coefficient, R, is known, the total propagation loss α_tot can be determined in this way.

© 1994 IEEE