A highly integrable, compact, reliable, and Low-WDL fiber-optic tap coupler

In this paper, a highly integrable, compact, reliable, and low wavelength dependent loss (WDL) fiber-optic tap coupler is presented. The coupler includes a single-fiber collimator at the input end, a grating beam deflector, a housing, and a specially designed dual-fiber collimator at the output end. One fiber of the dual-fiber collimator serves as the output channel and the other fiber serves as the tap channel. To minimize WDL induced by the wavelength-dependent diffraction efficiency of the phase grating, this dual-fiber collimator is carefully designed so that wavelength-dependent diffraction efficiency is largely compensated by the wavelength-dependent coupling efficiency of the dual-fiber collimator. A low WDL as small as 0.05 dB is achieved within the whole c-band region. The tap ratio can also be adjusted by controlling the modulation depth of the diffraction grating. Since this unique coupler can be easily integrated with other fiber-optic elements, such as variable optic attenuators (VOAs), it can be used to build a variety of fiber-optic modulates with integrated power monitoring capability.