The TCBOC is a natural extension to Cycle’s well-known and patented (one-color) BOC and is used for sub-femtosecond fiber link stabilization over kilometer distances. Due to a balanced optical detection scheme, the TCBOC provides exceptionally high timing sensitivity, attosecond timing resolution, amplitude invariance and robustness against environmental fluctuations. The output of the TCBOC is a baseband voltage signal that is proportional to the relative time delay between the two sources. This output can in turn be used in a phase-locked loop to synchronize the two optical sources (e.g. locking a Ti:Sapphire laser to a low-noise fiber oscillator). Standard wavelengths are 800 nm, 1030 nm and/or 1550 nm.