Background: As an important optical element, concave microlens arrays are utilized in many applications. How to fabricate a mass of concave microlens arrays efficiently at a low cost is a key problem to be solved.
Aim: We propose a method of fabricating a concave microlens array based on single mask ultraviolet (UV)-photolithography and dual-step potassium hydroxide (KOH) etching, which has proven to be efficient.
Approach: An arrayed silicon-based concave microlens utilized in the infrared wavelength range was designed and fabricated based on single mask UV-photolithography and dual-step KOH etching. Combining the computation simulation and the evolving microstructural mechanism based on the silicon anisotropic corrosion characteristics in a common KOH solution with several control factors such as the solution concentration, temperature, and corrosion period, an arrayed concave microlens with a spherical profile over a silicon wafer with the required crystal orientation was simulated, designed, and fabricated effectively.
Results: Both the scanning electron microscopy and the surface profile measurements indicate that the fabricated concave microlens arrays present a high filling-factor of more than 80% and a small surface roughness with a root mean square value in several tens of nanometer scale. The common optical measurements demonstrate that the fabricated silicon-based concave microlens presents a good infrared beam divergence performance.
Conclusions: The method highlights the prospect of the industrial production of large-area silicon-based concave microlens arrays for infrared beam shaping and control light applications.
As demonstrated, surface plasmons (SPs) stimulated by incident lightwaves are one of the most popular research fields, currently. The researches about the remarkable generation and efficient transmission and effective manipulation of relatively strong SPs are generally limited by a range constraint of wavelength or sub-wavelength-scaled structures. So far, the interaction between the electromagnetic field and the free electrons over the metal and medium interface or special metal micro-nano-structure has been mainly studied. In reality, a type of adjustable ionic exciter device is needed, which lead to a new focus about the adjustable ionic exciter materials. At present, two-dimensional graphene materials already demonstrate several excellent optical and electrical properties, and their conductivity and dielectric constant can be easily affected by external bias electric field, so as to exhibit a prospect as a kind of basic materials for adjustable and other excitation components. In this paper, the adjustable properties of single crystal graphene are studied. The effects based on the factors including the temperature and the scattering rate and the chemical potential corresponding to some parameters such as the conductivity and dielectric constant of graphene are analyzed carefully. In addition, the composite structure of the graphene grating nano-apexes is designed, which is characterized based on the multi-frequency points resonance according to incident light at the waveband of 4~11μm. The key graphene-based structure is modeled and simulated by the FDTD solution based on a finite difference time domain method under the different chemical potential. Then, the transmission and reflection and absorption behaviors of the graphene-based structure were analyzed according to the near electric field intensity distribution curves.
Currently, optical antenna has already become a research hotspot because of its remarkable local field enhancement effect and resonance propagation characteristics. Optical antennas are usually designed as a type of sub-wavelength-scaled metal structures. By transmitting the field enhancement signal of the optical antenna to the infrared detector, the weak signal detection ability of the infrared detector can be improved. As demonstrated, the resonant wavelength of the local surface plasmons is determined by the structure and material of the antenna and also the material properties of the surrounding medium. By changing the geometry of the antenna or the dielectric characteristics of the circumstance medium, the response frequency of the optical antenna can be regulated. As a two-dimensional material with unique electrical and optical properties, the dielectric properties of graphene can be regulated by applied bias voltage. By selecting the geometry of the antenna and applying bias voltage, the optical antenna with unique characteristics can be obtained. In this paper, an optical antenna with a graphene-silica-silicon trilayer structure is designed and a planar-tip array is fabricated over the graphene layer. The influence of the geometry of the planar-apex array and the thickness of the silica dielectric layer corresponding to the optical properties of the graphene antenna are analyzed. Simulation results show that by changing the shape of the planar-tip and the thickness of the silica dielectric layer, the position and intensity of the absorption peak of the graphene optical antenna can be controlled effectively. At the same time, under the control of external bias voltage, the resonance peak also appears an obvious movement of a maximum range of about three microns.
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