Applications for Quantum Amplifiers in Simple Digital Optical Communication Systems

Q u a n t u m amplifiers can be used in optical c o m m u n i c a t i o n s y s t e m s even if t h e optical sources are only p a r t i a l l y coherent. T h e y can serve as optical analog r e p e a t e r s between r e g e n e r a t i n g r e p e a t e r s in a h y b r i d digital s y s t e m to c o m p e n s a t e for t r a n s m i s s i o n loss (see Fig. 1), a n d also as t h e f r o n t e n d s of regenerating r e p e a t e r s which d e m o d u l a t e back to baseband. T h i s p a p e r investigates t h e a p p l i c a t i o n s for q u a n t u m amplifiers in simple digital c o m m u n i c a t i o n s y s t e m s e m p l o y i n g " o n - o f f " i n t e n s i t y m o d u l a t i o n . It will be a s s u m e d t h a t d u e to source instability, t h e optical s y s t e m b a n d w i d t h m a y be orders of m a g n i t u d e g r e a t e r t h a n t h e b a n d w i d t h o f t h e m o d u l a t i o n , a n d t h a t t h e q u a n t u m amplifiers h a v e limited gain. We shall calculate C h e r n o v b o u n d s on t h e required signal energy per pulse at t h e d e t e c t o r of a digital r e p e a t e r (to be described in detail below) to achieve a 10~9 error r a t e as a f u n c t i o n of t h e received s p o n t a 117