1. Field of the Invention
This invention pertains generally to optical delay lines and more particularly to an optical delay line where electro-optical control of microwave amplitude and phase is applied to each individual tap in a fiber optic multi-tap delay line.
2. Description of the Related Art
Fiber optic multi-tap delay lines are in a developmental stage for electronic applications. Multi-tap delay lines split a optical signal into many paths which are delayed relative to each other, modulated in amplitude and phase, and then recombined. The term multi-tap delay lines can also refer to transversal filters since they can be used to implement finite impulse response (FIR) filter designs. Compared to other technologies, such as micro-strip delay lines, fiber optics offers some distinct advantages such as lower loss and significantly higher bandwidths.
Current fiber optic delay lines use a radio frequency (RF) signal to amplitude modulate an optical carrier, typically using a directly modulated laser. The optical carrier is then split into multiple fiber path lengths (taps), each tap is then separately detected and recombined. Single sideband or vector modulators may then be used to modify the RF spectrum of each tap before it is recombined. The electrical components to detect, modulate and combine the taps is fairly large in size and high in power consumption.