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This study reports design, fabrication, and characterization of high-performance guided-mode resonance (GMR) infrared filters based on germanium (Ge) operating in the 7 to 15 µm spectral region. The single-layer GMR filters exhibit deep transmittance nulls and high sideband efficiency functioning as band-stop filters. There is reasonable agreement between experimental and theoretical spectral results. By modifying design parameters and incorporating an anti-reflection (AR) layer on the substrate backside, the functionality of the filter is significantly enhanced. The measured low transmittance value of the fabricated filters is found to be as low as 0.021% corresponding to an optical density of OD = 3.68. The results highlight the potential of GMR technology operating at long infrared wavelengths to enable high performance filters with tunable spectral characteristics. Anticipated application domains include the fields of sensing, imaging, and spectroscopy.

Fundamental effects in nanophotonic resonance systems focused on singular states and their properties are presented. Strongly related to lattice geometry and material composition, there appear resonant bright channels and non-resonant dark channels in the spectra. The bright state corresponds to high reflectivity guided-mode resonance (GMR) whereas the dark channel represents a bound state in the continuum (BIC). Even in simple systems, singular states with tunable bandwidth appear as isolated spectral lines that are widely separated from other resonance features. Under moderate lattice modulation, there ensues leaky-band metamorphosis, merging modal bands and resulting in offset dark states and reflective BICs along with transmissive BICs within a high-reflectance wideband. Rytov-type effective medium theory (EMT) is shown to be a powerful means to describe, formulate, and understand the collective GMR/BIC fundamentals in resonant photonic systems. Particularly, the discarded Rytov analytical solution for asymmetric fields is shown here to predict the dark BIC states essentially exactly for considerable modulation levels. The propagation constant of an equivalent EMT homogeneous film provides a quantitative evaluation of the eminent, oft-cited embedded BIC eigenvalue. The work concludes with experimental verification of key effects.

A dynamic spectroscopic imaging ellipsometer (DSIE) employing a monolithic polarizing interferometer is described. The proposed DSIE system can provide spatio-spectral ellipsometric phase map data Δ(λ, x) dynamically at a speed of 30?Hz. We demonstrate the ultrafast mapping capability of the spectroscopic ellipsometer by measuring a patterned 8-inch full wafer with a spatial resolution of less than 50?×?50 µm^2 in an hour.

Polarizers are universal components deployed in diverse application fields including imaging, display, microscopy, interferometry, ellipsometry, and instrumentation. Here, we demonstrate design and fabrication of a new class of polarizers that are extremely compact and efficient. Based on an elemental low-loss single-resonant grating, we develop multilayer modules providing ultrahigh extinction ratio polarizers. The elemental polarizer contains a subwavelength periodic pattern of crystalline silicon on a quartz substrate. A stack of two dual-grating modules exhibits a measured extinction ratio (ER) of ∼100,000 in a sparse 2-mm-thick device across a bandwidth of ∼50  nm in the telecommunications spectral region. Theoretical computations indicate that extreme values of extinction are possible. Further development of the basic concepts explored herein may lead to a new class of practical polarizers with excellent attributes.

In photonic lattices with thin-film geometry, TE modes possess an in-plane electric field component parallel to the film surface, whereas TM modes have a magnetic field component similarly oriented. This study reports the essential properties of, and differences between, TE and TM band gaps induced by laterally periodic thin-film photonic lattices at the first Bragg condition. Because TE and TM guided waves obey different wave equations, TE and TM band gaps exhibit different evolution as the film thickness varies. The first TM band exhibits both band gap closure and band flips wherein the symmetry properties of the band-edge modes are reversed by variation of film thickness. In the first TE band, in contrast, there is neither band gap closure nor band flip. The work provides an insightful semianalytical formulation whose results are verified by rigorous computations.

A guided-mode resonance filter (GMRF) consists of a subwavelength grating on a thin-film waveguide and can provide narrowband filtering with fewer layers in contrast to a multilayer dielectric mirror. A GMRF normally shows a peaky reflection spectrum and polarization dependency. In this Letter, two GMRFs are orthogonally stacked to give polarization-independent narrowband flat-top filtering. The GMRFs are designed by numerical methods and then fabricated and stacked. Each GMRF is formed by corrugation of a ${{\rm TiO}_2}$TiO_2 grating layer on a SiN guiding core layer on a ${{\rm SiO}_2}$SiO_2 substrate. A narrowband flat-top filter is demonstrated with a 7 nm full-width at half-maximum.

Metamaterials are important, as they possess properties not found in simple materials. Photonic device technology applying metamaterials supports many new and useful applications. Here, we address the fundamental physics of wideband metamaterial reflectors. We show that these devices operate because of resonant leaky Bloch modes propagating in the periodic lattice. Moreover, in contrast to published literature, we demonstrate that Mie scattering in individual array particles is not a causal effect. In particular, by connecting the constituent particles by a matched sublayer and thereby destroying the Mie cavity, we find that the resonance bandwidth actually expands even though localized Mie resonances have been extinguished. There is no abrupt change in the reflection characteristics on addition of a sublayer to any metamaterial array consisting of discrete particles. Thus, the physics of the discrete and connected arrays is the same. The resonant Bloch mode picture is supported by numerous additional examples and analyses presented herein.

Guided-mode resonant (GMR) thin films integrated on fiber tips are known to realize compact filters and sensors. However, limited progress in experimental realization has been reported to date. Here we provide a considerable advance in this technology, as we experimentally demonstrate efficient fiber-facet mounted device prototypes. To retain a large aperture for convenient coupling, we design and fabricate silicon nitride-based resonators on the tip of a multimode fiber. We account for light propagation along the multimode fiber with exact numerical methods. This establishes the correct amplitude and phase distribution of the beam incident on the tip-mounted GMR element, thus enabling us to properly predict the resonance response. To fabricate the integrated GMR structures on the tips of fibers, we employ standard microfabrication processes, including holographic interference lithography and reactive-ion etching. The experimental results agree with simulation with an example device achieving high efficiency of ∼77% in transmission. To investigate fiber sensor operation, an etched silicon nitride fiber tip filter is surrounded with solutions of various refractive indices, yielding an approximate sensitivity of 200 nm/RIU.

Resonant nanogratings and periodic metasurfaces express diverse spectral and polarization properties on broadside illumination by incident light. Cooperative resonance interactions may yield shaped spectra for particular applications, in contrast to a multilayer dielectric mirror. Here, we provide guided-mode resonance filters with flat-top spectra suitable for wavelength division multiplexing systems. Applying a single one-dimensional grating layer sandwiched by two waveguides, we theoretically achieve high-efficiency flat-top spectra in the near-infrared region. This result is obtained by inducing simultaneous nearly degenerate resonant modes. The resonance separation under this condition controls the width of the flat-top spectrum. This means we can implement spectral widths ranging from a sub-nanometer to several nanometers applying fundamentally the same device architecture.

Narrow bandpass filters are applied in laser systems, imaging, telecommunications, and astronomy. Traditionally implemented with thin-film stacks, there is recent interest in alternative means incorporating photonic resonance effects. Here, we demonstrate a new approach to bandpass filters that engages the guided-mode resonance effect working with a cavity-based Fabry–Perot resonance to flatten and steepen the pass band. Both of these resonance mechanisms are native to simple resonant bandpass filters placed in a cascade. Numerical examples provide quantitative spectral properties including pass-band shape and sideband levels. Thus, we compare the spectra of single-layer 1D and 2D resonant gratings with the dual-cascade design incorporating identical gratings. Two- and three-cavity designs are measured against a classic multi-cavity thin-film filter with 151 layers. Whereas these initial results show comparable and improved results achieved with sparse structures, the challenge remains of developing a suitable fabrication technology to capitalize on this promise.

Bandpass filters based on subwavelength dielectric gratings are grounded in physical principles that are totally distinct from their thin-film counterparts. Ease in fabrication, design scalability, material sparsity, and on-chip integration compatibility makes them a promising alternative especially for long-wavelength applications. Here we demonstrate the interesting attribute of resonant bandpass filters of high angular stability for fully conical light incidence. Fashioning an experimental bandpass filter with a subwavelength silicon grating on a quartz substrate, we show that fully conical incidence provides an angular full width at half-maximum linewidth of ∼9.5° compared to a linewidth of ∼0.1° for classical incidence. Slow angular variation of the central wavelength with full conical incidence arises via a corresponding slow angular variation of the resonant second diffraction orders driving the pertinent leaky modes. Moreover, full conical incidence maintains a profile with a single passband as opposed to the formation of two passbands characteristic of resonant subwavelength gratings under classical incidence. Our experimental results demonstrate excellent stability in angle, spectral profile, linewidth, and efficiency.

There is immense scientific interest in the properties of resonant thin films embroidered with periodic nanoscale features. This device class possesses considerable innovation potential. Accordingly, we report unpolarized broadband reflectors enabled by a serial arrangement of a pair of polarized subwavelength gratings. Optimized with numerical methods, our elemental gratings consist of a partially etched crystalline-silicon film on a quartz substrate. The resulting reflectors exhibit extremely wide spectral reflection bands in one polarization. By arranging two such reflectors sequentially with orthogonal periodicities, there results an unpolarized spectral band that exceeds those of the individual polarized bands. In the experiments reported herein, we achieve zero-order reflectance exceeding 97% under unpolarized light incidence over a 500 nm wide wavelength band. This wideband represents a ∼44% fractional band in the near infrared. Moreover, the resonant unpolarized broadband accommodates an ultra-high reflection band spanning ∼85  nm and exceeding 99.9% in efficiency. The elemental polarization-sensitive reflectors based on one-dimensional (1D) resonant gratings have a simple design and robust performance, and are straightforward to fabricate. Hence, this technology is a promising alternative to traditional multilayer thin-film reflectors, especially at longer wavelengths of light where multilayer deposition may be infeasible or impractical.

This Letter describes a Stokes vector measurement method based on a snapshot interferometric common-path spectropolarimeter. The proposed scheme, which employs an interferometric polarization-modulation module, can extract the spectral polarimetric parameters Ψ(k) and Δ(k) of a transmissive anisotropic object by which an accurate Stokes vector can be calculated in the spectral domain. It is inherently strongly robust to the object 3D pose variation, since it is designed distinctly so that the measured object can be placed outside of the interferometric module. Experiments are conducted to verify the feasibility of the proposed system. The proposed snapshot scheme enables us to extract the spectral Stokes vector of a transmissive anisotropic object within tens of msec with high accuracy.

Resonant periodic surfaces and films enable new functionalities with wide applicability in practical optical systems. Their material sparsity, ease of fabrication, and minimal interface count provide environmental and thermal stability and robustness in applications. Here, we report an experimental bandpass filter fashioned in a single patterned silicon layer on a quartz substrate. Its performance corresponds to bandpass filters requiring 15 traditional Si/SiO_2 thin-film layers. The feasibility of sparse narrowband high-efficiency bandpass filters with extremely wide, flat, and low sidebands is thereby demonstrated. This class of devices is designed with rigorous solutions of Maxwell’s equations while engaging the physical principles of resonant waveguide gratings. An experimental filter presented exhibits a transmittance of ∼72%, bandwidth of ∼0.5  nm, and low sidebands spanning ∼100  nm. The proposed technology is integration-friendly and opens doors for further development in various disciplines and spectral regions where thin-film solutions are traditionally applied.

A guided-mode resonance mirror (GMRM) consists of a waveguide grating integrated on an optical buffer layer on a high-reflection substrate. An incident free-space wave at the resonance wavelength is once coupled by the grating to a guided mode and coupled again by the same grating back to free space. The reflection characteristics of a GMRM are numerically calculated and theoretically analyzed. It is predicted that notch filtering or flat reflection spectra are obtained depending on the optical buffer layer thickness. Design of short cavities using a GMRM is discussed for potential application in surface-mount packaging of diode lasers onto a photonic circuit board.

The spectral properties of high-reflection mirrors imbued with two-dimensional (2D) subwavelength periodicity are investigated. The reflectors are designed in a silicon-on-glass film that is partially etched to implement a zero-contrast interface between the grating pillars and the sublayer, thereby annulling the local reflections and phase changes associated with hard interfaces. This approach has shown impressive results for 1D polarized reflectors; here we strive to discover analogous wideband unpolarized reflectors. Using particle swarm optimization, we report wideband unpolarized reflectors in the 1.4–2.0 μm wavelength band. A 2D reflector with square pillars exhibits 99% reflectance across a bandwidth exceeding 350 nm and possesses tolerance against angular deviations. The complementary structure with rectangular periodic voids achieves a bandwidth of 370 nm. A comparable, optimized 2D high-contrast grating reflector with grating pillars residing directly on the substrate yields a 99% bandwidth of 240 nm.

We present wideband resonant reflectors designed with gratings in which the grating ridges are matched to an identical material, thereby eliminating local reflections and phase changes. This critical interface thus possesses zero refractive-index contrast; hence “zero-contrast gratings.” We design reflectors with zero-contrast gratings and high-contrast gratings and compare the results. For simple gratings with two-part periods, we show that zero-contrast grating reflectors outperform comparable high-contrast grating reflectors. An example silicon-on-glass reflector exhibits a 99% reflectance bandwidth of ∼700  nm for zero refractive-index contrast Δn=0, whereas a high-contrast device with Δn=2 yields a bandwidth of ∼600  nm. It follows that local Fabry–Perot modes residing in the grating ridges and reflecting off a high-contrast interface are not the root cause of wideband reflection.

This Letter describes a universal calibration theory by which conventional interferometry can be extended to vibration robust snapshot polarization-sensitive spectral reflectometry without any complicated optical components or active devices. Experiments for verifying the proposed calibration theory have been conducted by using a Michelson-interferometer-based normal incidence spectroellipsometric system, and also some key system design considerations for object 3D pose tolerant measurement capability have been drawn. The proposed solution enables us to extract the spectroscopic ellipsometric parameter Δ(k) of an anisotropic object within 10 ms with high accuracy.

We describe what we believe to be a new digital holographic configuration that can be utilized for both single-shot, dual-wavelength, off-axis geometry and imaging polarimetry. To get the feasibility of the single-shot, dual-wavelength, off-axis geometry, a sample with a nominal step height of 1.34?μm is used. Undesirable noises that strongly affect the measurement have been suppressed successfully by using a modified flat fielding method for the dual-wavelength scheme. And also, the experiment is conducted on a nanopattern sample on the basis of a single image acquisition to show the imaging polarimetry capability. The proposed scheme can provide a real-time solution for measuring three-dimensional objects having a high abrupt height difference with moderate accuracy. Furthermore, it can be used as a fast polarization imaging measurement tool.

A high-accuracy biosensor system has been developed to provide rapid detection of biomarker proteins as indicators of ovarian cancer. This photonic detection system is based upon guided-mode resonance sensor technology. The buildup of the attaching biolayer can be monitored directly, without use of chemical tags, by following the corresponding resonance shift with a spectrometer or detector array. Additionally, these high-resolution sensors employ multiple resonance peaks at identical physical location on the sensor surface. Each of these resonance peaks responds uniquely to the detection event, thereby enriching the data set available for quantification. The peaks result from individual, polarization-dependent resonant leaky modes that are the foundation of this technology. Examples are presented for detection of ovarian cancer biomarkers (fibronectin and apoliprotein A-1) in serum and cell culture supernatant, with detection sensitivities to ~20 ng/ml. Minimal nonspecific binding was measured in cell media and serum backgrounds. We also present an example dual-polarization resonance response with corresponding backfitting results that illustrate the capability to distinguish between changes at the sensor surface due to biolayer adhesion and those due to sample background changes.

In this paper, we review the basic properties of resonant leaky mode elements implemented with periodic waveguide layers and consider their applicability in photonic devices and systems. Leaky waveguide modes can be exited when an incident light beam is coupled into the waveguide structure through an inscribed periodicity under phase-matching conditions. This results in generation of a guided-mode resonance field response in the spectrum. Device operation can be explained in terms of the photonic band structure and associated leaky-wave effects near the second stop band. Resonant devices such as bandpass/bandstop filters, polarizers, wideband reflectors, biosensors, tunable filters, and display pixels can be designed using this operational principle.

In this paper, we review the basic properties of resonant leaky mode elements implemented with periodic waveguide layers and consider their applicability in photonic devices and systems. Leaky waveguide modes can be exited when an incident light beam is coupled into the waveguide structure through an inscribed periodicity under phase-matching conditions. This results in generation of a guided-mode resonance field response in the spectrum. Device operation can be explained in terms of the photonic band structure and associated leaky-wave effects near the second stop band. Resonant devices such as bandpass/bandstop filters, polarizers, wideband reflectors, biosensors, tunable filters, and display pixels can be designed using this operational principle.

A method for producing stabilized interference patterns for ultraviolet interference lithography using a CCD camera as the detector element is described. Intensity data obtained from the CCD element are filtered in software to minimize speckle and detector noise effects as well as to determine the relative phase of the interfering beams. A control signal is then issued to correct the fringe drift. The system allows rapid reconfiguration of the lithography setup with minimum realignment of optical components.