Microcavity Filters Research Articles

16-channel snapshot multispectral imaging based on integrated Fabry Perot microcavity array

<sec>By designing and fabricating a narrow-band Fabry-Perot multi-beam interference spectroscopic microcavity array, and integrating it with a visible light detector focal plane array, we demonstrate a small compact multispectral imaging detector. The micro-cavity filter array with 4×4 basic repeating units and a total of 2048×2048 pixels is obtained on a quartz substrate by the four-fractal combination lithograph-etching process. Then the micro miniatured multispectral imaging detector is formed by fitting with the detector chip. The depth and precision of the etching will determine the distribution and offset of the central wavelength of the narrowband spectral channel respectively. The results show that the etching rate of reactive ion is (3.6 ± 0.2) Å/s, and the process is stable and controllable. Due to the different etching depths, the basic repeating unit forms 16 different levels of steps, and the process achieves the design expectation well.</sec><sec>The results are obtained as follows: the response spectrum peak of the microcavity array sample varies from 520 to 680 nm, the free spectrum range is 160 nm, the full width at the half-peak is less than 10 nm, the transmittance is about 70%, the relative half-width of the transmittance peak at 590 nm is 1.19%, and the waveform coefficient is 2.78. A 16-channel multispectral camera is constructed by using the optical micro-precision assembly device to realize the precise alignment and the fitting of the micro-cavity filter array and the image sensor. Xenon lamp and monochromator are used as tunable wavelength monochromatic cooperative light source to detect the effect of 16-channel snapshot multispectral imaging on a pixel scale. The results show that the multispectral imaging detector has 16 different narrow-band response spectra. The characteristic spectrum of the target can be clearly distinguished by spectral channel.</sec><sec>When imaging the target with known spectral characteristics, for a certain frame of multi-spectral image, selecting a suitable spectral channel can eliminate the background in the field of view through image subtraction and improve the contrast of the target. In the dark room condition, we take the LED light source with center wavelength varying in a range between 528 and 589 nm as the target (the wavelength coincides with the working wavelength of the spectral channel), and effectively suppress the background through the spectral differential intensity subtraction, which can improve the accuracy and sensitivity of the target capture. The 16-channel snapshot multi-spectral imaging detector based on integrated Fabry-Perot microcavity array has the advantages of small size, high integration and strong environmental adaptability, and is expected to play a role in realizing the real-time detection of weak moving targets, auxiliary diagnosis of skin surface observation, and high dynamic range imaging of target observation under backlight conditions.</sec>

Graphene/Epoxy Composite Based Broadband All-Optical Tunable Fiber Microcavity Filter

A graphene/epoxy composite based broadband all-optical tunable fiber microcavity filter is presented. The graphene/epoxy composite based microcavity shows the excellent all-optical controlability. Since the light acts on the graphene/epoxy composite directly, the microcavity has stronger optical Kerr effect and photothermal effect induced by the optical pump. Experimental results show that its wavelength tuning range and tuning step reach 25.54 nm and −832 pm/mW, respectively. It is expected to be applied in the fields of tunable optical filters, optical communication, optical sensors, fiber lasers, and spectrum scanning.

Porous Si-SiO2 UV Microcavities to Modulate the Responsivity of a Broadband Photodetector.

Porous Si-SiO2 UV microcavities are used to modulate a broad responsivity photodetector (GVGR-T10GD) with a detection range from 300 to 510 nm. The UV microcavity filters modified the responsivity at short wavelengths, while in the visible range the filters only attenuated the responsivity. All microcavities had a localized mode close to 360 nm in the UV-A range, and this meant that porous Si-SiO2 filters cut off the photodetection range of the photodetector from 300 to 350 nm, where microcavities showed low transmission. In the short-wavelength range, the photons were absorbed and did not contribute to the photocurrent. Therefore, the density of recombination centers was very high, and the photodetector sensitivity with a filter was lower than the photodetector without a filter. The maximum transmission measured at the localized mode (between 356 and 364 nm) was dominant in the UV-A range and enabled the flow of high energy photons. Moreover, the filters favored light transmission with a wavelength from 390 nm to 510 nm, where photons contributed to the photocurrent. Our filters made the photodetector more selective inside the specific UV range of wavelengths. This was a novel result to the best of our knowledge.

Cascaded integrated waveguide linear microcavity filters

We experimentally demonstrate cascaded Fabry-Perot microcavity filters fabricated on silicon-on-insulator substrates. The cavities are formed by etching three sets of quarter-wavelength trenches along a rib waveguide, each set forming a Bragg reflector. Various configurations are examined with a view towards maximizing the filter extinction and minimizing the linewidth. We investigate the origin of spurious cavity modes and show how these are minimized. The effect of mode-splitting due to inter-cavity coupling is suppressed by increasing the reflectivity of the center mirror. Experimental results compare well with transfer matrix predictions.

Tunable optofluidic nano-Bragg microcavity filter

An optofluidic nano-Bragg microcavity filter is designed using three-dimensional finite difference time domain technique and fabricated using electron-beam lithography and reactive ion etching techniques on a silicon-on-insulator (SOI) material. Continuous filter tuning is possible via small refractive index changes by introducing different fluids. An index change of 0.03 corresponds to a peak resonance wavelength shift of approximately 1 nm. The SOI chip is also integrated with a polydimethlysiloxane microfluidic chip for the fluid delivery.

Highly efficient phosphor-converted white organic light-emitting diodes with moderate microcavity and light-recycling filters

We demonstrate the combined effects of a microcavity structure and light-recycling filters (LRFs) on the forward electrical efficiency of phosphor-converted white organic light-emitting diodes (pc-WOLEDs). The introduction of a single pair of low- and high-index layers (SiO(2)/TiO(2)) improves the blue emission from blue OLED and the insertion of blue-passing and yellow-reflecting LRFs enhances the forward yellow emission from the YAG:Ce(3+) phosphors layers. The enhancement of the luminous efficacy of the forward white emission is 1.92 times that of a conventional pc-WOLED with color coordinates of (0.34, 0.34) and a correlated color temperature of about 4800 K.

Photonic Bandgap Microcavities With Flat-Top Response

In this paper, the analysis and the design of a photonic bandgap (PBG) microcavity waveguide filter with flat-top spectral characteristics are theoretically presented. The split filter analysis and the bidirectional eigenmode propagation method are applied to the investigation of this waveguide structure to obtain the design parameters of the filter with nearly unity transmittance and a squared passband. It shows that the radiation loss in the PBG mirrors diminishes the transmittance of the filter, and a mirror with anomalous dispersion region in reflection phase could be used to assemble an optical filter with the flat-top passband. A 1-D PBG monorail waveguide microcavity filter centered at 1554 nm with a maximum transmission of -0.55 dB and full-width at half-maximum (FWHM) of 13.6 nm is numerically carried out by using 3-D finite-difference time-domain method

Room temperature operation of epitaxial lead-telluride detectors monolithically integrated on midinfrared filters

Epitaxial PbTe midinfrared photodetectors are monolithically integrated on optical filter structures, like λ∕4 antireflection layers or λ∕2 microcavities. The antireflection layers result in an increased photoresponsivity of the detectors by a factor of 2.2, measured at the target wavelength of 3.1μm. The microcavities, acting as efficient narrow band filters, consist of two PbEuTe∕EuTe Bragg interference mirrors separated by a PbEuTe cavity layer. The photoresponse spectra of the detectors integrated with the microcavity filters exhibit a single resonance at 3.6μm with a relative line width of 2.7%. The narrow photoresponse peak is in coincidence with a molecular absorption line typical for nonaromatic aldehydes. For all devices room temperature operation is demonstrated either in photoconductive or in photovoltaic operation mode.

Compact and integrated 2-D photonic crystal super-prism filter-device for wavelength demultiplexing applications

A two-dimensional photonic crystal (PhC) super-prism integrated with one-dimensional photonic crystal microcavity filters has been designed using the plane wave expansion (PWE) and 2-D Finite Difference Time Domain (FDTD) methods based on Silicon-on-Insulator (SOI) technology. The super-prism operates as a coarse spatial filter with an average response bandwidth of 60 nm, while the 1-D PhC microcavity filters operate as narrow band-pass transmission filters with an average filter response line-width of 10 nm. This work demonstrates the simultaneous operation of two photonic devices for de-multiplexing applications on a single platform that could be useful in future Photonic Crystal Integrated Circuits (PCICs).

Microcavity filters based on hexagonal lattice 2-D photonic crystal structures embedded in ridge waveguides

Two-dimensionally periodic photonic crystal microcavity filters in a ridge waveguide format have been designed and fabricated. Transition mode-matching features were added to increase the optical throughput by more than a factor of two. An increase of Q-factor (more than 100%) was achieved by the addition of two further rows of photonic crystal holes to the microcavity filters. Attempts have also been made to tailor the filter response by applying design concepts used in other Bragg-grating optical filter technologies.

Electrooptic tuning of InP-based microphotonic Fabry-Perot filters

This paper presents the experimental results for compact (20- and 40-/spl mu/m-long) electrooptically tuned deeply etched Fabry-Perot (F-P) filters in InP-based material. Both the quantum-confined Stark effect (QCSE) and carrier-injection (C-I) effects were implemented to achieve tunability of these microcavity filters. Red and blue shifts of the transmission peaks in the order of 1 to 2 nm were observed for both effects, and the limitations on C-I due to thermal effect are clearly demonstrated and discussed. The advantages and disadvantages of both tuning mechanisms are highlighted.

Design of MEMS-tunable novel monolithic optical filters in InP with horizontal bragg mirrors

This paper presents the theoretical design and analysis of a tunable Fabry–Perot resonant microcavity filter realized by movable-waveguide-based integrated optical MEMS technology in InP. Wide-bandwidth, high-reflectivity horizontal InP/air-gap distributed bragg reflector (DBR) mirrors monolithically integrated with the waveguides have been proposed. The filter can be tuned by moving one of the high-reflectivity mirrors axially with on-chip MEMS electrostatic actuation. Spectral performance of the filter is numerically simulated taking into account the diffraction effects. Finite element mechanical modeling of the parallel-plate capacitive microactuator, consisting of a micromachined suspension beam and fixed electrodes, predicts a wide wavelength tuning range (1250–1650 nm) achievable by low actuation voltage (<7 V).

Engineering the filter response of photonic crystal microcavity filters

Compact photonic crystal (PhC) filters will play a vital role in wavelength division multiplexing applications and they could be the stepping stones towards the realisation of dense and multifunctional photonic integrated circuits. Bragg grating concepts are applied to PhC filters to control their response by introducing suitable phase shifts and choosing appropriate locations and magnitudes. Moreover, the variation of the PhC hole size at the input and output regions could offer an extra degree of freedom in tailoring the filter characteristics. The ability to engineer and control the filter response of photonic crystal filters is investigated in this paper.

One-dimensional periodic photonic crystal microcavity filters with transition mode-matching features, embedded in ridge waveguides

The design, fabrication and characterisation of several one-dimensionally periodic photonic crystal microcavity filters in ridge waveguides, with light transmission of more than 90%, are presented. Transition mode-matching features are incorporated both within and outside the cavity region to enhance the quality factor and light throughput.