Progress in tunable longwave infrared notch filters

We describe recent progress in the development of spectrally tunable micro-engineered notch filters operating in the longwave infrared (LWIR) region from 8 to 12 µm based on using the guided-mode resonance (GMR) effect. The device structure consists of a subwavelength dielectric grating on top of a homogeneous waveguide using high-index dielectric transparent materials, i.e., germanium (Ge) with a refractive index of 4.0 and zinc selenide (ZnSe) with a refractive index of 2.4. We design the filters to reflect the incident broadband light at one (or more) narrow spectral band while fully transmitting the rest of the light. Filters based on one-dimensional (1-D) gratings are polarization-dependent and those based on two-dimensional (2-D) gratings are less polarization-dependent. We designed and characterized both 1-D and 2- D filters. Anti-reflection coatings (ARCs) were applied on the backside of some of the filter substrates to improve transmission over the entire spectral region. We carried out transmission measurements of these filters using two separate experimental setups—an automated tunable room-temperature quantum cascade laser (QCL) system as well as a modified Fourier Transform Infrared (FTIR) spectrometer with normal incidence of light on the sample. We will present filter designs, theoretical simulation, characterization experiments and results.

[1]  R. Magnusson,et al.  Fabrication methods for infrared resonant devices. , 2018, Optics letters.

[2]  Neelam Gupta,et al.  Development of tunable longwave infrared metamaterial notch filters , 2019, Defense + Commercial Sensing.

[3]  Guillaume Huyet,et al.  Realization of high-contrast gratings operating at 10  μm. , 2016, Optics letters.

[4]  R. Magnusson,et al.  New principle for optical filters , 1992 .

[5]  R. Magnusson,et al.  Resonant filters with concurrently tuned central wavelengths and sidebands. , 2020, Optics letters.

[6]  N. Gupta,et al.  High-quality large-scale electron-beam-written resonant filters for the long-wave infrared region. , 2020, Optics letters.

[7]  D. Wasserman,et al.  Mid-wave infrared narrow bandwidth guided mode resonance notch filter. , 2017, Optics letters.

[8]  Thomas K. Gaylord,et al.  Stable implementation of the rigorous coupled-wave analysis for surface-relief gratings: enhanced transmittance matrix approach , 1995 .

[9]  Robert Magnusson,et al.  Wideband reflectors with zero-contrast gratings. , 2014, Optics letters.

[10]  Neelam Gupta,et al.  Development of tunable longwave infrared filters based on guided-mode resonance , 2020, OPTO.

[11]  Brian T. Cunningham,et al.  Optimally designed narrowband guided-mode resonance reflectance filters for mid-infrared spectroscopy , 2011, Optics express.

[12]  A. Friesem,et al.  Resonant grating waveguide structures , 1997 .

[13]  T. Gaylord,et al.  Rigorous coupled-wave analysis of planar-grating diffraction , 1981 .

[14]  S. Selvaraja,et al.  Polarization-independent angle-tolerant mid-infrared spectral resonance using amorphous germanium high contrast gratings for notch filtering application , 2020 .

[15]  S. S. Wang,et al.  Multilayer waveguide-grating filters. , 1995, Applied optics.

[16]  D. Suhre,et al.  Notch filtering using a multiple passband AOTF in the SWIR region. , 2016, Applied optics.

[17]  Jari Turunen,et al.  Eigenmode method for electromagnetic synthesis of diffractive elements with three-dimensional profiles , 1994 .

[18]  Neelam Gupta,et al.  Performance characterization of tunable longwave infrared notch filters using quantum cascade lasers , 2018, Optical Engineering.

[19]  Philippe Lalanne,et al.  Improved formulation of the coupled-wave method for two-dimensional gratings , 1997 .

[20]  T. Gaylord,et al.  Formulation for stable and efficient implementation of the rigorous coupled-wave analysis of binary gratings , 1995 .