Output beam engineering with 2-step ridge etching

Silicon photonics offers platforms to build mass-producible optical circuits. Extremely small optical components are required for this purpose, so fiber coupled systems are an order of magnitude too large. In order to successfully integrate laser source to the circuits, output beam properties have to be controlled and desired for the purpose. When fabricating single-mode ridge waveguide (RWG) laser diodes, ridge width has to be narrow enough for ensuring single-mode operation. When designing RWG device, one must take also electrical properties and catastrophic optical damage into account – narrow ridges tend to have higher series resistance values and are more prone to COD in low output powers than wide ridges. However, having too wide ridge for a wavelength, RWG starts to support multiple modes. In this work, we have experimentally found a way to utilize 2-step etching to alter the output beam horizontal far-field values of originally nominally identical ridge width devices. By being able to alter the output beam shape, coupling of the laser beams to different photonic integrated circuits can be done based on the circuit, not the laser. Correlation between ridge sidewall angle and horizontal beam width is presented with experimental data. By altering the angle, the ridge can become effectively wider than it physically is, meaning advantages such as low series resistance can be achieved as well as higher COD levels. We present implementing the method for 6XX nm region laser diode source.