Three dimensional fabrication of optical waveguiding elements for on-chip integration

Abstract

We present micro polymer optical waveguide elements fabricated using femtosecond laser and two-photon absorption (TPA) process. The POWs are constructed by tightly focusing a laser beam in SU-8 based resists transparent to the laser wavelength for single-photon absorption. The TPA process enables the patterning of the resist in three dimensions at a resolution of 100-200 nm, which provides a high degree of freedom for POW designs. Using this technology, we provide a novel approach to fabricate Three dimensional Polymer Optical Waveguides (3D-POW) and coupling with single mode fibers in the visible wavelength regions. Our research is also focused on fabricating passive micro optical elements such as splitters, combiners and simple logical gates. For this reason we are aiming to achieve optimum coupling efficiency between the 3D-POW and fibers. The technology also facilitates 3D-POW fabrication independent of the substrate material. We present these fabrication techniques and designs, along with supporting numerical simulations and its transmission properties. With a length of 270 µm and polymer core diameter of 9 µm with air cladding, the waveguides possess a total loss of 12 dB. This value also includes the external in and out mode coupling and in continuously being improved upon by design optimization and simulations. We verify the overall feasibility of the design and coupling mechanisms that can be exploited to execute waveguide based optical functions such as filtering and logical operations.

Ultrafast Laser Welding of Silicon

“…In contrast, ultrashort pulses (<10 ps) lead to limited heat‐affected zone. However, permanent modifications are extremely challenging to produce in the bulk and the exit surface of silicon with ultrashort laser pulses, [ 12 ] unless complex approaches are implemented for optimizing the spatial, [ 26–28 ] spectral, [ 29,30 ] or temporal [ 31–33 ] properties of the irradiation. These limitations originate from the high nonlinear refractive index of silicon (on the order of 10 −14 cm 2 W −1 [ 34,35 ] ), which causes micro‐filamentation at modest peak powers—and thus, an intensity clamping similar to that described for transparent media.…”

Crystal structure of laser-induced subsurface modifications in Si

“…Several femtosecond studies were based on line scans. These resulted in a combination of surface damage and modifications at a shallow depth (k ¼ 0:8 lm) [26,27], modifications just below an oxide overcoat (k ¼ 2:4 lm) [20], a combination of surface damage and subsurface modifications at an unknown depth (k ¼ 1:55 lm) [28] and modifications near the back surface of a substrate (k ¼ 1:55 lm) [29]. In other femtosecond studies, single or multiple laser pulses were applied to a single location.…”