Fano Filters Research Articles

Design and Analysis of Femtosecond Laser-Generated Metasurface for Optical Filter Application

This work investigates a Fano filter design based on a nano-hole array, patterned in fused silica using high-energy ultrafast femtosecond laser pulses. After carefully observing the experimental results, the structural profile of the nano-holes is numerically modeled in a 3D finite-difference time-domain-based software platform. The metasurface design consists of conical shaped air holes structured in the substrate, and a later deposited waveguide layer which leaves craters on the surface as the material fills inside the nano-holes. The spectral properties of the device are studied against variations in the structural parameters, such as the depth of the nano-holes, its surface diameter, and the depth of the craters on the surface of the waveguide. The proposed Fano filter device is designed to operate in the near-infrared (NIR) wavelength range around a telecommunication window of 1550 nm. Multiple narrowband resonances are observed with a linewidth in the range of 1.4 to 24.2 nm and a quality factor of 66.51 to 1090.12. The device shows good spectral tunability over a wide range from 1380 to 1650 nm comprising multiple narrowband resonances and variations in the structural parameters. Since the device can be implemented using a cost-effective and rapid fabrication method, it can be proposed for use in various optical filtering and sensing applications.

Resonance of Different Waveguide Structures with Various Vertical Indirect Coupled Cavities

In the paper, resonances of different waveguide structures with various vertical indirect coupled cavities were investigated by FDTD (finite difference-time domain). In the silicon cavity, Fano resonance could be observed at about 1430 nm. The coupling distance for the gold cavity/air cavity had less effect on the transmittance of the main waveguide but had a great influence on the transmission for water cavity in the visible region, which showed that water cavity could adjust resonance of waveguide structures. In addition, with the increment of refractive index n, the resonance peak at about 850 nm moved to the long wavelength (redshift). Dispersion rate about 2 × 10–3/nm indicated that the transparent dielectric selectively absorbed the surface plasmon polariton wave and the sensitivity of the waveguide structure designed in this paper has high stability for the refractive index of the main waveguide cavity. Obvious Fano resonance could be observed with the increase of refractive index for silicon cavity. Among the four dielectrics, silicon and water are suitable for studying Fano resonance and filter dielectrics.

Continuously tunable fiber laser based on Fano resonance filter of thin-fiber-taper-coupled conical microresonator

Through Fano resonance, the resonant modes exhibiting peak-like shapes on the bandpass spectrum of the thin-fiber-taper-coupled conical microresonator are generated. For the first time, this thin-fiber-taper-coupled conical microresonator functions as a Fano filter, and is applied as a tunable internal-cavity bandpass filter for an Erbium-doped fiber ring laser. If the size of the conical microresonator in the coupling junction is adjusted by displacing the fiber taper along the resonator axis, the wavelength of the output laser is able to be tuned linearly and continuously with a coefficient of 0.225 nm/mm.

Meandering Waveguide Distributed Feedback Lightwave Circuits

Meandering waveguide distributed feedback structures are introduced as novel integrated photonic lightwave circuit elements, and analyzed in the frequency domain by the transfer matrix method. The directional coupling of the electromagnetic field occurs at the meander coupling points. The meandering loop mirror is the building block of all meandering waveguide-based lightwave circuit elements. The simplest uncoupled meandering distributed feedback structure exhibits Rabi splitting in the transmittance spectrum. The symmetric and antisymmetric coupled meandering distributed feedback geometries can be utilized as bandpass, Fano, or Lorentzian filters or Rabi splitters. Meandering waveguide distributed feedback structures with a variety of spectral responses can be designed for a variety of lightwave circuit element functions.

Fano Resonance Photonic Crystal Membrane Lasers and Filters for Integrated Silicon Photonics

Fano resonance, known from atomic physics, has been employed for a wide variety of nanophotonic structures, such as quantum dots, photonic crystal, plasmonics, and metamaterials, and so on. With modal dispersion engineering, Fano filters and reflectors can all be realized in single layer dielectric photonic crystal structures. Based on Fano resonance principle in 2D air hole photonic crystal slabs, combined with crystalline semiconductor nanomembrane transfer printing techniques, we have demonstrated a range of ultra-compact high performacne photonic and electronic devices on silicon and on flexible substrates.By sandwiching InGaAsP quantum well cavity in between two single –layer silicon Fano resonance photonic crystal membrane reflectors (MR), membrane reflector vertical-cavity surface- emitting lasers (MR-VCSELs) were proposed and demonstrated. We will report our recent progresses on this new type of membrane lasers, which can be built on silicon, and on flexible substrates.Ultra-compact high quality factor optical filters have also been realized experimentally, based on Fano resonances in single or coupled bi-layer photonic crystal slabs, without or with lattice displacements. Theoretically, with the control of lattice displacement between two coupled photonic crystal slabs layers, optical filter Q factors can approach 211,000,000 or infinite. Experimentally optical filters with quality factors up to 80,000 have been demonstrated. Finally, we will review other type of Fano resonance based optical structures, such as vertical to in-plane couplers, and beam routing structures, for integrated silicon photonics. The convergence of nanomembranes and Fano resonance photonic crystals offer unprecedented opportunities for unique electronic and photonic devices for 3D multi-functional Si CMOS photonics, flexible, bio-inspired/integrated photonic/electronic systems, and multi-spectral multi-color infrared imaging and sensing systems, etc. The work was supported by US AFOSR, ARO and NSF.

Colloidal quantum dot absorption enhancement in flexible Fano filters

We report here modified absorption property of colloidal quantum dots (CQDs) inside flexible Fano filters—made of patterned single crystalline silicon nanomembrane transferred onto flexible plastic substrates. Enhanced optical absorption was obtained both experimentally and theoretically, when the CQD absorption peak spectrally overlaps with Fano resonance peak. On the other hand, suppressed absorption was observed when the Fano resonance has no spectral overlap with the CQD absorption bands.

Flexible photonic-crystal Fano filters based on transferred semiconductor nanomembranes

Crystalline semiconductor nanomembranes (NMs), which are transferable, stackable, bondable and manufacturable, offer unprecedented opportunities for unique and novel device applications. We report and review here nanophotonic devices based on stacked semiconductor NMs that were built on Si, glass and flexible PET substrates. Photonic-crystal Fano resonance based surface-normal optical filters and broadband reflectors have been demonstrated with unique angle and polarization properties. Such a low temperature NM stacking process can lead to a paradigm shift on silicon photonic integration and inorganic flexible photonics.

Study of 2-D photon crystal Fano slab filters for biological sensing

A new compact optical Fano filter suitable for biological sensing is proposed, which patterns photon crystal in single crystalline silicon nanomembranes (SiNMs) and transferring onto transparent glass substrates. The effects of air hole size and silicon thickness on the transmission characteristics of new filter are numerically investigated by using three-dimensional finite-difference time-domain (FDTD) technique, the spectral response is also studied by back-filling bio-liquid. The results show that the dip wavelength will shift toward longer wavelength by either reducing air hole radius or filling bioliquid. The number of dips will increase with the increase of silicon thickness. The size of proposed filter can be less than 1 mm2.

Polarization and angular dependent transmissions on transferred nanomembrane Fano filters

We report angular and polarization dependent transmission properties of Fano resonance optical filters with transferred silicon nanomembrane on glass substrate. The transmission spectra of the filters can have either weak or strong polarization and angular dependence, depending on properties of individual Fano resonance modal dispersion. Measurement results agree very well with simulations based on a rigorous coupled-wave analysis for the transmission spectra, on planewave expansion wave-vector technique for the dispersion property analysis, and on a three-dimensional finite-difference time-domain technique for the propagating modal study. These results will provide importance guidance for the design of a new class of ultra-compact surface-normal frequency selective components with preferred polarization and angular properties. These components are highly desirable for silicon photonic integration.

Fano filters based on transferred silicon nanomembranes on plastic substrates

We report here the characteristics of surface-normal optical filters based on Fano resonances on patterned single crystalline silicon nanomembranes (SiNMs), which were fabricated and transferred onto transparent plastic substrates using a SiNM wet transfer process. Detailed experimental and theoretical analyses were carried out on the angular- and polarization-dependent transmission properties. The filter transmission is independent of the incident beam polarization under surface-normal conditions. Angle-independent transmission was observed for specific Fano resonances with certain polarizations. The measured angle-dependent transmission agrees well with the simulated transmission and dispersion properties based on the propagation wave-vector analysis.

Surface-normal Fano filters based on transferred silicon nanomembranes on glass substrates

Surface-normal optical filters are reported based on Fano resonances in patterned single crystalline silicon nanomembranes (SiNM), which were fabricated and transferred onto transparent glass substrates using a disruptive wet transfer process. The measured filter transmission results agree well with the design using a three-dimensional finite-difference time-domain technique. Using the SiNM wet transfer and stacking process, vertically stacked ultra-compact surface normal filters, switches, modulators and spectrally-selective photodetectors will become feasible.