WIC Wavelength Independent Coupler

The function of wavelength independent coupler was to couple the light from each channel to the other one. It was applied to distribute suitable optical power in our optical circuits and the ratio of distribution was independent wavelength.

General specifications of couplers could be classed two categories, one was 50% to 50% (3dB) four ports another was 5%/95% and 1%/99% three ports.

The former mainly applied on the distribution of communication system channels, latter one may used to monitor the energy stability of transmission system and the optical characteristic parameters.

It had several kinds to manufacture coupler, what was more common method (fusion) to pulling four ends of two fibers while heating up till suitable coupling ratio.

Theoretically, a good coupler, the total input power should be same with the total output energy, but we known that it was imposable.
So, the Excess Loss was defined as: EL = -10log[summation (Pout)/Pin]. The extra loss value (EL Excess Loss) should reduce as far as possible, generally was 0.2 to 0.5dB about.