Reconfigurable metasurfaces have been pursued intensively in recent years for the ability to modulate the light after fabrication. However, the optical performances of these devices are limited by the efficiency, actuation response speed and mechanical control for reconfigurability. In this paper, we propose a fast tunable optical absorber based on the critical coupling of resonance mode to absorptive medium and the plasma dispersion effect of free carriers in semiconductor. The tunable absorber structure includes a single-layer or bi-layer silicon photonic crystal slab (PCS) to induce a high-Q optical resonance, a monolayer graphene as the absorption material, and bottom reflector to remove transmission. By modulating the refractive index of PCS via the plasma dispersion of the free carrier, the critical coupling condition is shifted in spectrum, and the device acquires tuning capability between perfect absorption and total reflection of the incident monochromatic light beam. Simulation results show that, with silicon index change of 0.015, the tunable absorption of light can achieve the reflection/absorption switching, and full range of reflection phase control is feasible in the over coupling region. The proposed reconfigurable structure has potential applications in remote sensing, free-space communications, LiDAR, and imaging.
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Graphene-incorporated plasmo-thermomechanical infrared radiation detection
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.
more » « less- NSF-PAR ID:
- 10135174
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Journal of the Optical Society of America B
- Volume:
- 37
- Issue:
- 3
- ISSN:
- 0740-3224; JOBPDE
- Page Range / eLocation ID:
- Article No. 774
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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