Transmission Peak Wavelength Research Articles

Development of Visible Multi−Bandpass Filter Based on F−P Structure

In order to reduce the noise interference of smart wearable devices, spectral filtering technology is used to suppress noise. This technology prevents interference signals from entering the detector from the source, thereby achieving high−precision noise reduction processing. According to the system requirements, a multi−bandpass filter with a wavelength range of 400~1000 nm was designed and prepared on a BK7 substrate. Ta2O5 and SiO2 were selected as the high− and low−refractive−index materials, respectively. By analyzing the −Fabry–Perot narrowband theory, the bandwidth matching coefficient was computed, and the interference order was calculated using the interval of the transmission peak wavelengths. Multiple F−P coating systems were connected through the matching layer to adjust the position of the transmission peak and broaden the bandwidth range. The design was optimized using Macloed film system design software, resulting in the design of a wide half−wave and cutoff multi−bandpass filter. The appropriate preparation process was chosen based on changes in refractive index, surface roughness, and the temperature gradient of the materials. The filter was then produced using Leybold SYRUSpro1110. Sensitivity, filter roughness, and the weak absorption of the film system were tested, and the results met the system requirements.

High‐Performance Colorful Organic Photovoltaics with Microcavity Resonance Color Filter

AbstractMicrocavity resonance is an effective technique for making promising semitransparent organic photovoltaics (ST‐OPVs) even more aesthetically attractive with high color saturation, by tailoring the visible transmittance spectrum to narrow the transmission peak. In this study, a distinctive microcavity resonance color filter (CF) structure of silver/ bismuth(III) fluoride /silver (Ag/BiF3/Ag) is integrated upon the rear transparent electrode, which simultaneously achieves high color purity and high power conversion efficiency (PCE) for colorful OPVs. By precisely regulating the thickness of the BiF3 layer, colorful OPVs with a wide color gamut and high color purity are achieved, including the colors of indigo, blue, bluish‐green, green, orange, and red, as well as compound color devices with dual or multiple transmission peaks in the visible region. A recorded PCE of 16.27% is obtained for the indigo OPV, with the Commission Internationale de l´Eclairage 1931 coordinates of (0.164 and 0.087) and a maximum transmittance of 18.7% at the transmission peak wavelength of 393 nm. Furthermore, colorful OPVs as color reflectors are systematically investigated under different light incident surfaces. The improved stability of colorful OPVs is attributed to the excellent moisture resistance of BiF3. The colorful OPVs with desired transmitted/reflected colors, and wide color gamut show great potential for future energy harvesting solutions.

Quasi-three-dimensional nanopost array integrated Type-II superlattice photodetectors for infrared multispectral filtering

Angle-insensitive and high-transmission infrared spectral filters, comprising periodic quasi-three-dimensional (quasi-3D) nanopost arrays, are fabricated using a nanoimprint lithography technique and directly integrated onto an InAs/GaSb type-II superlattice (T2SL) photodetector. Simulation results of the plasmonic filters reveal that the transmission peak wavelength is linearly adjusted by tuning the filter period as a result of the propagated and localized surface plasmon resonances of the quasi-3D nanopost array structure. Additionally, the transmission peak wavelength of the array structure is measured to increase with decreasing nanopost height owing to stronger field coupling between the Au hole and disk arrays. A tunable bandpass filtering function of the quasi-3D nanopost-integrated T2SL photodetector is successfully demonstrated with narrow bandwidths in the spectral range of 2–6 μm. Our findings offer a significant potential for a scalable low-cost manufacturing method of compact snapshot multispectral infrared imagers for portable-field imaging or airborne-platform-based imaging applications.

Heterogeneously integrated widely tunable laser using lattice filter and ring resonator on Si photonics platform.

We fabricated a tunable laser consisting of a Si lattice filter, a Si ring resonator, and a III-V gain region. The lattice filter, a cascade of interferometers with the same delay length, has periodic transmission peaks with a wide free spectral range (FSR). By connecting the lattice filter to a ring resonator with a narrow FSR, the lasing mode is selected from one of the resonance modes of the ring resonator. The lasing wavelength can be tuned by changing the transmission peak wavelength of the lattice filter, in which an integrated micro heater controls the refractive index of the longer or shorter arm. Since the length of the refractive index control region on both arms of the lattice filter can be extended while maintaining a wide FSR, a wide tuning range can be obtained. This laser facilitates the control of the lasing wavelength because of the simple configuration. The Si lattice filter and the Si ring resonator were fabricated on a Si photonics platform by a Si photonics foundry, and III-V gain region was heterogeneously integrated. The lasing wavelength is shifted to a longer (shorter) one by heating the longer (shorter) arm of the lattice filter, in which the tuning wavelength is 1529 to 1561 nm and side-mode suppression ratio is more than 40 dB. A Lorentzian linewidth for lasing wavelengths narrower than 40 kHz is also demonstrated.

Numerical Simulation of the Self-Imaging at Different Cascaded Optical Fiber Specifications

Cascaded optical fiber single mode-no core-single mode fiber (SNS) attracted attention for being the base of various photonic devices. These devices are used in optical communication, fiber sensors, and fiber laser technology. The effect of variable NCF specifications, length, diameter, external refractive index (ERI), propagating wavelength on the self-imaging position, and the multimode interference (MMI) is studied. The study aims to simulate and analyze cascaded optical fiber by using the finite element beam envelope method (BEM). To the best of our knowledge, this is the first report that studied the self-imaging in cascaded optical fiber longitudinally by using BEM. The NCF length is important in determining the coupled out intensity and peak transmission wavelength. The field in the cascaded fiber is simulated for single and multi-wavelengths to evaluate the maximum transmission and study the structure's tunability. A tunable filter is simulated, where varying the length of the NCF about 0.6 mm produces a wavelength shift of about 40 nm. The BEM is effective in studying the field propagation in large guiding photonic devices

Novel SPR Sensor Based on MIM-based Waveguide and an Asymmetric Cross-shaped Resonator

In recent years, sensing structures based on Fano resonances have become a hot research topic. In this study, a coupled structure, composed of a metal baffle metal-insulator-metal waveguide and an asymmetric cross-shaped resonator, is designed. By changing the coupling distance and asymmetry of the cross-shaped resonator, their influences on the transmission and electromagnetic field distribution were calculated and systematically analyzed. The results showed a good linear relationship between the center wavelength of the Fano transmission peak and the refractive index of the filled material. The sensor sensitivity can reach 795 nm/RIU. The prospective applications of this waveguide structure are promising. The structure can also provide a future reference for the design of a microwave waveguide structure.

Two-Dimensional Tunable and Temperature-Insensitive Lyot Filter for FM-to-AM Compensation

Utilizing polarization maintaining photonic crystal fiber (PM-PCF) with the low temperature coefficient of birefringence, a two-dimensional tunable and temperature-insensitive Lyot filter aiming to compensate the frequency modulation to amplitude modulation (FM-to-AM) conversion in high power laser facility is demonstrated. The Jones matrix is applied to analyze the relationship between optical characteristics of the filter and physical parameters (including amplitude ratio, phase delay, and susceptibility of the birefringence to temperature) of the polarization optical field. Both the transmission peak wavelength and extinction ratio of the spectral transmission are able to be changed simultaneously, hence, it shows more efficient FM-to-AM compensation ability. Besides, the transmission peak shift is about 18pm/°C with the PM-PCF configuration, which is about two orders of magnitude less than the normal polarization maintaining fiber (PMF) configuration. The demonstrated filter presents a practical application potential in large scale laser driven facility.

Two-micron all-fiberized passively mode-locked fiber lasers with high-energy nanosecond pulse

We report on mode-locked thulium-doped fiber lasers with high-energy nanosecond pulses, relying on the transmission in a semiconductor saturable absorber (SESA) and a carbon nanotube (CNTs-PVA) film separately. A section of an SMF–MMF–SMF structure multimode interferometer with a transmission peak wavelength of ∼2003 nm was used as a wavelength selector to fix the laser wavelength. When the SESA acted as a saturable absorber (SA), the mode-locked fiber laser had a maximum output power of ∼461 mW with a pulse energy of ∼0.14 μJ and a pulse duration of ∼9.14 ns. In a CNT-film-based mode-locked fiber laser, stable mode-locked pulses with the maximum output power of ∼46 mW, pulse energy of ∼26.8 nJ and pulse duration of ∼9.3 ns were obtained. To the best of our knowledge, our experiments demonstrated the first 2 μm region ‘real’ SA-based dissipative soliton resonance with the highest mode-locked pulse energy from a ‘real’ SA-based all-fiberized resonator.

Femtosecond Laser Microfabricated Optofluidic Grating Refractometer

A novel femtosecond laser microfabricated optofluidic grating is proposed and demonstrated in this letter, which realizes the measurement of refractive index of liquid. The diffraction grating is fabricated with an epoxy-based negative photoresist (SU-8) on glass substrate by femtosecond laser-induced two-photon polymerization and bonded with a polydimethylsiloxane microchannel, for which the transmission spectrum can be modulated by changing the refractive index of the liquid flowing in the microchannel. Experimental observation on the shift of the transmission peak wavelength indicates that the sensitivity of the diffraction grating is higher for a lower-order mode or a thicker grating, i.e., blue-shifted peak wavelength with a magnitude of 3.586 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> μm per refractive index unit for the second-order mode of the grating with a thickness of 3.60 μm.

Angular Momentum-Dependent Transmission of Circularly Polarized Vortex Beams Through a Plasmonic Coaxial Nanoring

In this paper, we report on the theoretical and numerical study of the transmission of circularly polarized vortex beams through a plasmonic coaxial nanoring. We show that the transmission peak wavelength of an incident circularly polarized vortex beam is dominantly governed by the total angular momentum, which determines the coupling to the plasmonic eigenmode supported by the coaxial nanoring with a given geometry and ultimately the transmitted beam in the far field. In addition, our study shows that the total angular momentum of the incident circularly polarized vortex beam can be conserved, where the far field of the transmitted beam contains both left- and right-handed circular polarization components with correspondingly modulated orbital angular momentum preserving the same total angular momentum. Our work can be potentially useful to advanced nanophotonic devices harnessing light's angular momentum division.

Towards Electrotuneable Nanoplasmonic Fabry\u2013Perot Interferometer

Directed voltage-controlled assembly and disassembly of plasmonic nanoparticles (NPs) at electrified solid–electrolyte interfaces (SEI) offer novel opportunities for the creation of tuneable optical devices. We apply this concept to propose a fast electrotuneable, NP-based Fabry–Perot (FP) interferometer, comprising two parallel transparent electrodes in aqueous electrolyte, which form the polarizable SEI for directed assembly–disassembly of negatively charged NPs. An FP cavity between two reflective NP-monolayers assembled at such interfaces can be formed or deconstructed under positive or negative polarization of the electrodes, respectively. The inter-NP spacing may be tuned via applied potential. Since the intensity, wavelength, and linewidth of the reflectivity peak depend on the NP packing density, the transmission spectrum of the system can thus be varied. A detailed theoretical model of the system’s optical response is presented, which shows excellent agreement with full-wave simulations. The tuning of the peak transmission wavelength and linewidth is investigated in detail. Design guidelines for such NP-based FP systems are established, where transmission characteristics can be electrotuned in-situ, without mechanically altering the cavity length.

Large-Area MEMS Tunable Fabry–Perot Filters for Multi/Hyperspectral Infrared Imaging

This paper reports on a MEMS tunable Fabry–Perot filter technology capable of achieving nanometer-scale optical flatness across a large mirror area of up to square centimeters without any extraneous stress management techniques. The device employs a single-layer tensile silicon or germanium membrane for the suspended top mirror. Optical characterization of the fabricated single-membrane-based tunable filters for the SWIR, MWIR, and LWIR is presented. The fabricated 1000- $\mu$ m dimension Si-membrane-based SWIR and MWIR filters are demonstrated with a wavelength tuning range of 1.77–2.42 and 4.1–4.9 $\mu$ m, respectively, while the fabricated 200- $\mu$ m-dimension Ge-membrane-based LWIR filter is demonstrated with a wavelength tuning range of 8.5–11.46 $\mu$ m. All these filters are shown to achieve transmission characteristics that exceed the optical requirements for multispectral imaging applications. A large-area 1-cm dimension Si membrane-based SWIR tunable Fabry–Perot filter for multispectral imaging is demonstrated as a proof-of-concept, showing an excellent surface flatness in the order of 25 nm and an excellent optical uniformity with transmission peak wavelength variability less than 3% across the entire 1-cm dimension optical imaging area. In addition, the optical transmission behavior of the Fabry–Perot filters based on three-layer Si or Ge-based air-spaced DBRs for SWIR, MWIR, and LWIR is modeled, demonstrating that these filters can achieve a fine spectral resolution of several tens of nanometers suitable for hyperspectral imaging applications.

Performance analysis on cascaded asymmetric photonic crystal Mach–Zehnder tunable filter

A cascaded asymmetric photonic crystal Mach–Zehnder filter structure is proposed to improve the quality factor (Q value) and the sensitivity of the tunable optical filter. The mathematical relationship between the output wavelength of M–Z filter and the voltage applied on the multilayer PZT is established. The simulation results show that the full width at half maximum can be decreased from 17 nm to 9 nm, in addition, the transmission peak wavelength varies by adjusting the applied voltage and the sensitivity can attain to 0.7 nm/V by using the multilayer PZT, which can achieve tunable filtering effectively.

Long-wavelength infrared transmission filters via two-step subwavelength dielectric gratings.

We experimentally demonstrate a long-wavelength infrared narrowband transmission filter using an asymmetric subwavelength dielectric grating. A two-step grating geometry is used to define the asymmetry, which enables resonant narrowband transmission response at normal incidence. Computational modeling is used to show that varying the grating parameter dimensions can shift the transmission peak wavelength. Silicon/air gratings are experimentally demonstrated, with the peak transmission wavelength varying between 10 and 11.3 μm.

Fabrication of a thin plasmonic color sheet embedded with Al subwavelength gratings in parylene

In this study, we developed a thin plasmonic color sheet (TPCS) embedded with Al subwavelength gratings for use in flexible optical transmission filters, and experimentally demonstrated its transmission characteristics. Al subwavelength gratings were formed in a freestanding thin poly-para-xylylene (parylene-N) film less than 1-μm thick by using electron beam (EB) direct writing and sacrificial etching. The fabricated TPCS contained Al subwavelength gratings with periods ranging from 400nm to 600nm, and succeeded in shifting the transmission peak wavelength from 510nm to 650nm in the visible range. The freestanding thin parylene-N film deposited by room-temperature chemical vapor deposition provided enough flatness to the TPCS with a height difference of 900nm in a whole filter area, resulting in uniform transmission spectra. The experimentally obtained peak shift dependent on the grating period agreed well with theoretical calculation results.

Refractive index and temperature nanosensor with plasmonic waveguide system

A surface plasmon polariton sensor consisting of two metal–insulator–metal waveguides and a transverse rectangular resonator is proposed. Both refractive index and temperature sensing characteristics are analyzed by investigating the transmission spectra which demonstrates that the transmission peak wavelength shifting satisfies linear relation with environmental refractive index and temperature, respectively. The proposed design provides high refractive index and temperature sensitivity as 3.38×106%/RIU and 82%/K estimated by integrated response of the sensor, and owns the potentials for high-throughput array sensing. It is believed that the nanoscale sensor can be applied in spot detection for high speed multi-parameter sensing and accurate measurements.

Power-ratio tunable dual-wavelength laser using linearly variable Fabry-Perot filter as output coupler.

For a linearly variable Fabry-Perot filter, the peak transmission wavelengths change linearly with the transverse position shift of the substrate. Such a Fabry-Perot filter is designed and fabricated and used as an output coupler of a c-cut Nd:YVO₄ laser experimentally in this paper to obtain a 1062 and 1083 nm dual-wavelength laser. The peak transmission wavelengths are gradually shifted from 1040.8 to 1070.8 nm. The peak transmission wavelength of the Fabry-Perot filter used as the output coupler for the dual-wavelength laser is 1068 nm and resides between 1062 and 1083 nm, which makes the transmissions of the desired dual wavelengths change in opposite slopes with the transverse shift of the filter. Consequently, powers of the two wavelengths change in opposite directions. A branch power, oppositely tunable 1062 and 1083 nm dual-wavelength laser is successfully demonstrated. Design principles of the linear variable Fabry-Perot filter used as an output coupler are discussed. Advantages of the method are summarized.

MEMS-Based Tunable Fabry–Perot Filters for Adaptive Multispectral Thermal Imaging

This paper reports on a proof-of-concept micro-electromechanical system-based Fabry–Perot filter that is capable of electrically tuning within the long-wave infrared thermal imaging band of 8–12 $\mu \text{m}$ . The device employs a single-layer quarter-wavelength thick tensile germanium membrane for the suspended top mirror in order to achieve nanometer-scale as-released mirror flatness across an area of several hundred square micrometers without any extraneous stress management techniques. Mechanical and optical characterization of the tunable filters of various sizes are presented and compared. A 200- $\mu \text{m}$ dimension square filter is demonstrated with $\mu \text{m}$ , namely, peak transmission above 80%, full-width at half-maximum of spectral passband of approximately 500 nm, and out-of-band rejection greater than 40:1. Optical modeling shows that this filter can achieve a pixel-to-pixel transmission peak wavelength variation of less than 1.2% across the entire $200~\mu \text{m}~ \times200$ - $\mu \text{m}$ optical imaging area. These results exceed the optical performance requirements for passive multispectral thermal imaging applications based on large-area focal plane arrays. In comparison, the 500 and 1000- $\mu \text{m}$ dimension filters are shown to exhibit significant mirror bowing with actuation and, thus, for a pixel-to-pixel transmission peak wavelength non-uniformity of $11.3~\mu \text{m}$ , respectively. [2015-0252]

Angled multimode interferometer for bidirectional wavelength division (de)multiplexing.

We have demonstrated a bidirectional wavelength division (de)multiplexer (WDM) on the silicon-on-insulator platform using two 4-channel angled multimode interferometers (AMMIs) sharing the same multimode interference waveguide. An excellent match of the peak transmission wavelength of each channel between the two AMMIs was achieved. The input and output access waveguides were arranged in a configuration such that the propagation of light of one AMMI in the multimode interference waveguide suffered minimal perturbation by the input and output waveguides of the other AMMI. This type of device is ideal for the WDM system for datacom or telecom applications, e.g. an integrated optical transceiver, where the transmission wavelengths are required to match with the receiving wavelengths. The device also benefits from simple fabrication (as only a single lithography and etching step is required), improved convenience for the transceiver layout design, a reduction in tuning power and circuitry and efficient use of layout space. A low insertion loss of 3–4 dB, and low crosstalk of −15 to −20 dB, was achieved.

Fabrication of metallic hole array metamaterials with 760 nm and 1930 nm lattice constant by interfering femtosecond laser processing

Infrared and ultraviolet femtosecond lasers were used for interfering laser processing of thin gold film on silica glass substrate for the fabrication of MHA (metallic hole array) metamaterial devices. Through single shot processing and step scanning, devices with an area of 10×10mm were successfully fabricated. The lattice constant of the device processed at infrared wavelength was 1930nm, and it was shortened to 760nm by means of ultraviolet wavelength. The transmission spectrum was observed, and the anomalous transmission peak wavelength was approximately 59% shorter in the case of a 760nm lattice constant compared with a 1930nm lattice constant.