Y-branch couplers are the simplest type optical splitting device used in these applications.
In addition, a low cost metal-based symmetrical coupling-ratio Y-branch POF coupler constructed using hollow waveguide taper structure has also been developed by us which provided an excess loss of 5 dB .
 is a single mode Y-branch coupler with the center axis of the branching output waveguide and the center axis of the waveguide taper shifted from each other.
The work demonstrated in this paper showed how a low cost acrylic-based variable coupling ratio Y-branch POF coupler can be implemented using a single structure Y-branch.
The design of the variable coupling ratio coupler is based on a simple Y-branch structure.
Figure 4 shows a generic design structure for the proposed variable Y-branch POF coupler.
The use of a symmetrical Y-branch coupler will ensure that the output power is divide equally by the waveguide taper in the middle.
In this device, amplitude modulation is effectuated by splitting the optical signal equally at the first Y-branch, and phase modulating the light in either or both of the two interferometer arms by applying a voltage across the electrodes.
Optical insertion loss is determined by the spatial mis-match in the optical fields at the fiber/waveguide coupling interfaces, Fresnel reflection losses at the fiber/waveguide interfaces, attenuation due to absorption and scattering within the waveguide material, and scattering losses at each of the two Y-branches. Careful design of the waveguide can ensure a mode profile that closely matches that of the pigtailed optical fibers.