In-chip microstructures and photonic devices fabricated by nonlinear laser lithography deep inside silicon

Abstract

Silicon is an excellent material for microelectronics and integrated photonics1–3 with untapped potential for mid-IR optics4. Despite broad recognition of the importance of the third dimension5,6, current lithography methods do not allow fabrication of photonic devices and functional microelements directly inside silicon chips. Even relatively simple curved geometries cannot be realised with techniques like reactive ion etching. Embedded optical elements, like in glass7, electronic devices, and better electronic-photonic integration are lacking8. Here, we demonstrate laser-based fabrication of complex 3D structures deep inside silicon using 1 µm-sized dots and rod-like structures of adjustable length as basic building blocks. The laser-modified Si has a different optical index than unmodified parts, which enables numerous photonic devices. Optionally, these parts are chemically etched to produce desired 3D shapes. We exemplify a plethora of subsurface, i.e., “in-chip” microstructures for microfluidic cooling of chips, vias, MEMS, photovoltaic applications and photonic devices that match or surpass the corresponding state-of-the-art device performances.

Femtosecond laser written waveguides deep inside silicon

“…Using a technique based on the one we have demonstrated in Ref. [22], the possible creation of waveguides using nanosecond pulses have recently been reported [23]. However, no experimental evidence of actual guidance of light was provided, only that the scattered light followed a linear pattern.…”

“…We have first shown the possibility of laser processing deep inside Si using nanosecond pulses at 1.55 μm [21], where Si is transparent. This approach has been subsequently developed into a comprehensive technique that enables creation of arbitrary complex 3D microstructures inside Si with 1-μm resolution [22]. The laserinduced refractive index changes are used to realize functional elements inside Si, in-chip photonic structures and devices, including lenses, gratings, phase-type, high-resolution holograms, as well as waveguides [22].…”

“…This approach has been subsequently developed into a comprehensive technique that enables creation of arbitrary complex 3D microstructures inside Si with 1-μm resolution [22]. The laserinduced refractive index changes are used to realize functional elements inside Si, in-chip photonic structures and devices, including lenses, gratings, phase-type, high-resolution holograms, as well as waveguides [22]. However, the laser-induced index change is negative with nanosecond pulses, which requires tubular or similar waveguide structures.…”

Effective bandwidth approach for the spectral splitting of solar spectrum using diffractive optical elements

“…However, fabrications of these structures with cheap photolithographic processes having less than 1 µm resolution are not possible. Fortunately, with direct laser writing, such a resolution and large scale production is achievable [20].…”

3.5-W, femtosecond chirped pulse amplification fiber laser system at 1560 nm

“…Among them, Er-doped fiber laser is showing more attention in silicon processing and photovoltaic industries [2]. Thermal and nonlinear effects are the main limitation to achieve high power and high energy ultrashort pulses [3,4].…”