Browsing by Subject "Subsurface"
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Item Open Access In-chip devices fabricated with nonlinear laser lithography deep inside silicon(Bilkent University, 2019-05) Turnalı, AhmetThe integration of photonic elements with electronic elements on the same chip is highly desirable, since it may lead to new generation of devices. One constraint in this direction is the limited space available on the wafer surface. Currently, conventional fabrication methods use only the top thin layer of the silicon platforms for device fabrication. Therefore, new architectural designs are necessary. Creating functional elements deep inside silicon without damaging the surfaces is a promising approach to overcome space bottleneck in electronicphotonic integration, since the bulk of the wafer can be utilized with this method. Laser-written devices have been demonstrated in various transparent materials, such as glasses and polymers. When focused, high-energy laser pulses can induce nonlinear breakdown and change the morphology of the interaction region enclosed by the material. This process enables the fabrication of a diverse set of devices, including interconnects, optical waveguides and quantum photonic devices. However, so far, similar approaches did not succeed in silicon. We demonstrated a similar enabling method inside silicon, where nonlinear e ects were exploited to generate highly controllable modi cations deep inside silicon. We used these modi cations as building blocks to create in-chip elements. We developed a simple, intuitive model to understand the structure formation in more detail, which indicated that nonlinear interaction between counterpropagating beams causes the self-focusing of the beam, resulting in disruption in crystal structure. Propagation of the pulses are recon gured by the previously modi ed region. The focal point of the pulse shifts, elongating the structure. These elongated structures can provide the necessary phase shift to build di ractive optical elements embedded in Si, among other optical elements. We demonstrated this concept by fabricating binary and grayscale Fourier holograms and a binary Fresnel hologram projecting four layers forming a 3D image. In an extension of this work, the algorithm is developed for greyscale Fresnel holograms and increased the possible numbers of projections layers three orders of magnitude. Moreover, we used in-chip modi cations for creating optical waveguides inside silicon with the lowest losses reported so far. By selectively etching the modi- cations, we showed a second set of applications. We sculpted the silicon with this method to fabricate micropillars, through-Si vias and micro uidic channels. Further, we extended the method to other semiconductors and nanostructured the bulk GaAs. We also investigated the possibility of new processing regimes by using Bessel beams and 2 m laser pulses.Item Open Access Three dimensional processing of silicon with pulsed lasers for optical applications(Bilkent University, 2015-05) Turnalı, AhmetMicromachining of silicon with lasers is being investigated for the last three decades. Until now, interior silicon modification without inscribing the surface has not resulted in success. Such an ability could enable disruptive technologies in nanophotonics by paving the way for producing monolithic optoelectronic chips. Here, we report a maskless, one step photo-induced method to generate subsurface modifications in silicon with pulsed infrared lasers for indefinitely large areas. We demonstrate continuous, highly controllable structures buried in the bulk of silicon wafers and investigate the underlying mechanism. Further, we utilize the method for spatial information encoding and fabrication of optical components in the infrared regime in silicon. This silicon processing technology can be useful in various applications, including multilayer silicon chips, solar cells and opto uidics.