Micro-optical 3-dB mode converters

We present a detailed design of a 3-dB TE₀-TE₁ micro-optical mode converter using a chirped grating to phase-match the two propagation modes in an optical waveguide. Devices were fabricated in titanium in-diffused lithium niobate by ion-beam etching the tapered grating pattern into the waveguide surface. The power transfer between the two coupled modes was observed experimentally by varying the angle between the light beam and the normal grating wave-vector. Insertion loss of the TE₀-TE₁ mode converter due to spurious scattering was estimated at 1.5 dB.