An incident optical signal is captured by an array of apertures and directed to pairs of fibers, each pair having a delay fiber with a unique length and a no-delay fiber. Each pair of fibers further has a unique transmission characteristic. Time interpolation is then performed using the transmission characteristic curve for each delay fiber and the duration from the time the optical signal arrives over the no-delay fibers and the time the signal arrives over the delay fibers to determine the wavelength. In a second embodiment, each pair of delay and no-delay fibers is replaced by a fiber splitter which directs light into a no-delay fiber and a delay fiber that have been split from the input of the splitter. In a third embodiment, two fiber splitters are used in place of the pairs of fibers. Each splitter has a number of branches for receiving light and an output end for guiding light onto the photodetectors. The propagation time of the delay optical signal, as compared against the no-delay signal, and other factors such as the length of the individual fiber and the transmission characteristics, are used to determine the wavelength.