UltraFlow: Elastic, flexible and dual-mode long-reach optical access network In this paper, we develop the UltraFlow access network simulation platform to perform numerical simulations on its network performance. We further propose, analyze and simulate flexible grid and elastic spectrum allocation on the reconfigurable long-reach (R-LR) UltraFlow access network, which results in at most 3 times reduction in Flow request waiting time and 20% increase of network throughput. It can also reduce the required feeder fiber to simultaneously support 1024 users from 13 to 3. In addition, the advantages of utilizing dual-mode network comparing to Flow only network are analyzed and simulated in terms of cost, latency, and network throughput. Specifically, numerical simulations show that service time (average file transfer time) can be reduced by a factor of 25 for traffic with large variance. The feasibility of Flow resource sharing scheme with local and external Flow channels is experimentally demonstrated, which can significantly reduce the cost of network equipment, energy consumption, etc.