We demonstrate a technique for ultrastable optical frequency dissemination in a branching passive optical network using code-division multiple access (CDMA). In our protocol, each network user employs a unique pseudo-random sequence to rapidly change the optical frequency among many distinct frequencies. After transmission through the optical network, each user correlates the received sequence with the transmitted one, thus establishing a frequency-hopping spread spectrum technique that helps reject optical signals transmitted by other users in the network. Our method, which builds on the work by Schediwy et al. [Opt. Lett. {\bf 38}, 2893 (2013)], improves the frequency distribution network's capacity, helps reject phase noise caused by intermediate optical back scattering, and simplifies the operational requirements. Using this protocol, we show that a frequency instability better than ~
10−18 while having more than 100 users operating in the network should be possible. Finally, we theoretically explore the limits of this protocol and show that the demonstrated stability does not suffer from any fundamental limitation. In the future, the CDMA method presented here could be used in complex time-frequency distribution networks, allowing more users while, at the same time, reducing the network's complexity.
The bit error performance of optical synchronous code-division multiple-access (S/CDMA) networks have been evaluated with multiple-user interference (MUI) cancellation technique for PIN+OA (a combination of an optical amplifier and a PIN photodiode) and APD (avalanche photodiode) receivers using perfect difference codes. In addition to shot noise and thermal noise, the PIN+OA receiver analysis incorporates the effects of amplifier spontaneous emission (ASE) noise while the APD receiver analysis includes the excess noise factor and surface- and bulk-leakage currents of APD. Considering typical optical and receiver parameters of the networks, the numerical results of analyses show that PIN+OA receiver requires a received optical power of about 3.7 dBW less compared to APD receiver for reliable communication (P e < 10 -9 ) under full traffic load condition.