Practical realization of a passive coherent population trapping frequency standard

The paper describes the practical realization and characteristics of a small, totally autonomous, passive frequency standard based on the coherent population trapping (CPT) phenomenon. A description of the frequency standard, including physical characteristics, block diagrams of the optical control CPT resonance system and of the digital control electronics is given. The characteristics of the frequency standard relative to general functionality and frequency stability are given, as measured on several units.