Design of a Temperature Insensitive Fiber Interferometer for Long-Term Laser Frequency Stabilization using Metal Coated Fibers

Abstract: This work presents the design for a temperature drift-free path imbalanced ber interferometer for long-term laser frequency stabilization using coated bers with different thermal drift. For this purpose, single acrylate, dual acrylate, copper and aluminum coated bers are analyzed theoretically and experimentally regarding the thermal sensitivity of their optical path length. Experimental results were obtained by using few meter sample fibers as low-finesse cavities and measuring the phase of the cavity modes drifting by as a function of temperature. Measurements yield temperature sensitivities of 9.51'10^-6 K^-1, 10.85'10^-6 K^-1, 14.59'10^-6 K^-1 and 17.86'10^-6 K^-1 for the single acrylate, dual acrylate, copper and aluminum fiber respectively and are in general in good agreement with theoretical results. A suggestion for a custom-made aluminum fiber derived from the presented model with an increased thermal sensitivity of 28.6'10^-6 K^-1 is further presented. Choosing aluminum coating for the short arm and single acrylate for the long arm of the fiber interferometer with their length ratio corresponding to the ratio of their thermal sensitivity makes the path difference constant with temperature and the interferometerthus drift-free. A trade-off is to be made between the introduced additional delay of the short arm and the obtained path difference. An additional delay puts demands on the pre-stabilized linewidth of the laser while the latter improves short-term linewidth reduction.