We describe a low-latency optical process-level network (OPLN) scheme based on all-optical edge nodes for sample value (SV) service in substations. The edge nodes we present and demonstrate consist of optical splitters and a wavelength division multiplexer, enabling the proposed scheme to realize optical intrabay physical-layer multicasting and interbay signal gathering. A scalability model for the OPLN and a latency model of the intrabay transmission subsystem are established. Simulation results show that 1 × 32 optical splitters can be used in the all-optical edge nodes with error-free transmission and that the end-to-end latency for the intrabay transmission of SV flows can be reduced by 46.6% compared with an Ethernet switch under the 100BASE protocol. A prototype of the all-optical edge node is developed and tested, achieving ultralow latency (less than 500 ns) and good compatibility with terminals using an Ethernet interface in a substation. A field-experiment system for SV service, covering eight bays with four all-optical edge nodes, is constructed in a 220-kV substation in Sichuan Province, China. This system achieves low-latency transmission of SV flows without frame loss for more than 10 h of continuous operation.