Ultra-compact three-port trench-based photonic couplers in ion-exchanged glass waveguides

An ultra-compact three-port photonic coupler is proposed on a glass substrate based upon a principle of frustrated total internal reflection. A single slash shape narrow trench at the “T” intersection of two ion-exchanged waveguides forms the coupler and is aligned 45° to the waveguides. The three-dimensional finite difference time domain (FDTD) theory is used to simulate the parameterization of the coupler, such as splitting ratios and efficiency versus trench widths, trench lengths, trench locations, and trench angles. The waveguide model used in FDTD is based on an experimental condition of the K+-Na+ ion-exchange process. A single-mode 6 μm wide glass waveguide at 1550 nm wavelength is fabricated through the analysis of the effective index method. The numerical results show that the arbitrary splitting ratios may be controlled by trench widths and trench angles. Comparing to Si, InP and GaAs materials, trench-based coupler on glasses may readily achieve the manufacturability since the low index of glass waveguides results in a wider trench opening. Taking advantage of low loss ion-exchanged waveguides, the high efficiency and short interaction length photonic couplers have a great potential to be integrated for large scale glass-based photonic circuits.