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  1. Free, publicly-accessible full text available August 1, 2025
  2. We design a three-way silicon optical waveguide with the Bloch dispersion relation supporting a stationary inflection point (SIP). The SIP is a third order exceptional point of degeneracy (EPD) where three Bloch modes coalesce forming the frozen mode with greatly enhanced amplitude. The proposed design consists of a coupled resonators optical waveguide (CROW) coupled to a parallel straight waveguide. At any given frequency, this structure supports three pairs of reciprocal Bloch eigenmodes, propagating and/or evanescent. In addition to full-wave simulations, we also employ a so-called “hybrid model” that uses transfer matrices obtained from full-wave simulations of sub-blocks of the unit cell. This allows us to account for radiation losses and enables a design procedure based on minimizing the eigenmodes’ coalescence parameter. The proposed finite-length CROW displays almost unitary transfer function at the SIP resonance, implying a nearly perfect conversion of the input light into the frozen mode. The group delay and the effective quality factor at the SIP resonance show an $N^3$ scaling, where N is the number of unit cells in the cavity. The frozen mode in the CROW can be utilized in various applications like sensors, lasers and optical delay lines. 
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  3. Metallic nanostructures can be used to selectively absorb a specific regime of the infrared (IR) spectrum depending on its constituent materials and geometry. In this paper, we propose and analyze a plasmo-thermomechanical detector that includes a graphene layer on top of metallic nanowires to enhance the absorption and sensitivity. The proposed device converts the free-space IR radiation to mechanical deformation of nanowires that modulates the insertion loss of the waveguide underneath the nanowires and facilitates the on-chip optical readout of the free-space radiation at room temperature. Our design takes advantage of localized surface plasmon resonances to maximize absorption at the desired IR spectrum. We provide a systematic investigation of different material combinations with and without graphene in addition to variations in detector geometry to optimize the designed IR detector. On top of the absorption enhancement, the graphene layer over the nanowires boosts thermal relaxation speed of the nanowires by 3 times due to graphene’s high thermal conductivity, in turn speeding up the response of the IR detection. Moreover, the coated graphene layer enhances the mechanical deformation by a factor of 6 and bends the suspended nanowires downward, enhancing the light–matter interaction between the nanowires and the waveguide evanescent field. Overall, incorporating graphene is beneficial for enhanced spectrum absorption, speed of the IR detection, and optical readout sensitivity.

     
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