Fabry-Perot Cavity Modes Research Articles

Incorporation of nanovoids into metallic gratings for broadband plasmonic organic solar cells

We present investigation and optimization of a newly proposed plasmonic organic solar cell geometry based on the incorporation of nanovoids into conventional rectangular backplane gratings. Hybridization of strongly localized plasmonic modes of the nanovoids with Fabry-Perot cavity modes originating from surface plasmon reflection at the grating elements is shown to significantly boost performance in the long wavelength regime. This constitutes improved broadband operation while maintaining absorption enhancements at short wavelengths derived from conventional rectangular grating. Our calculations predict a figure of merit enhancement of up to 41% compared to when the nanovoid indented grating is absent. This is a significant improvement over the previously considered rectangular grating structures, which is further shown to be maintained over the entire angular range.

Study of luminescence and optical resonances in Sb2O3 micro- and nanotriangles

Luminescence of micro-and nanotriangles of cubic antimony oxide, Sb_2O_3 has been investigated by cathodoluminescence (CL) in scanning electron microscope and by photoluminescence (PL) in a laser confocal microscope. The triangles were grown by a thermal evaporation-deposition process with pure antimony powders as precursor, and present a self assembled arrangement covering extended areas of the samples. CL spectra of the triangles show bands at 2-2.5 and 3.1 eV, the latter is not observed in the Sb_2O_3 initial powder. PL excited by 325 nm laser shows a band at 2.4 eV with a shoulder at 2.75 eV, as well as resonance modes suggesting optical cavity behavior of the triangles. The separation between resonant peaks from different triangles has been correlated with the triangle side length and possible optical paths were obtained according to the Fabry-Perot relationship. These results along with the optical images suggest that not only Fabry-Perot cavity modes, but also whispering gallery modes may occur inside the micro-and nanotriangle structures.

Tuning the scale factor and sensitivity of a passive cavity with optical pumping

The pushing of the Fabry-Perot cavity modes by an intracavity medium of Rb vapor may be tuned with optical pumping. A second laser, propagating through the Rb vapor orthogonal to the intracavity beam, is used to modify the optical transmission of the Rb vapor. We demonstrate that the cavity scale factor may be switched from $S>1$, on one side of its pole along the gain axis, to the other side of the pole, where mode splitting occurs, simply by changing the pumping transition. Continuous tuning of the cavity scale factor and sensitivity may be realized by varying the intensity and/or frequency of the pump beam.

Polarization-Insensitive Metal–Semiconductor–Metal Nanoplasmonic Structures for Ultrafast Ultraviolet Detectors

We propose a theoretical design principle of polarization-insensitive metal–semiconductor–metal (MSM) structure for ultraviolet photodetectors based on one-dimensional nanogratings. Because the Fabry–Perot cavity modes supported by a 100-nm-thick ZnO layer with nanostructures for transverse electric and transverse magnetic polarized incidence overlap with each other, a polarization-insensitive absorption enhancement for the ZnO layer at UV wavelengths is achieved, which can be implemented as a nano-interdigitated electrode to address a long-existing limitation between the speed and the responsivity for conventional MSM photodetectors.

Enhanced spontaneous emission from quantum dots in short photonic crystal waveguides

We report a study of the quantum dot (QD) emission in short photonic crystal waveguides. We observe that the quantum dot photoluminescence intensity and decay rate are strongly enhanced when the emission energy is in resonance with Fabry-Perot (FP) cavity modes in the slow-light regime of the dispersion curve. The experimental results are in agreement with previous theoretical predictions and are further supported by three-dimensional finite element simulations. Our results show that the combination of slow group velocity and Fabry-Perot cavity resonance provide an avenue to efficiently channel photons from quantum dots into waveguides for integrated quantum photonic applications.

Frequency domain analysis of modes in a photonic crystal micro-opto-electro-mechanical system with periodically arranged circular holes

In the present work we investigate the electromagnetic properties of a photonic crystal micro-opto-electro-mechanical system. It consists of vertically arranged semiconductor membranes with air gaps forming a Fabry–Perot cavity with distributed Bragg reflectors on each side. In the top membrane, circular holes are etched introducing a photonic crystal. We investigate the optical transmission behavior of this system by detailed simulation. It includes an analysis of the three-dimensional eigenmodes and calculation of the transmittivity from the source problem. We find that in addition to the vertical Fabry–Perot cavity modes additional modes exist. The origin of these modes can be traced to resonances occurring in the top photonic crystal membrane. It is shown that the photonic crystal modes have a strong impact on the transmittivity of the filter system.

Coaxial multishell nanowires with high-quality electronic interfaces and tunable optical cavities for ultrathin photovoltaics

Silicon nanowires (NWs) could enable low-cost and efficient photovoltaics, though their performance has been limited by nonideal electrical characteristics and an inability to tune absorption properties. We overcome these limitations through controlled synthesis of a series of polymorphic core/multishell NWs with highly crystalline, hexagonally-faceted shells, and well-defined coaxial (p/n) and p/intrinsic/n (p/i/n) diode junctions. Designed 200-300 nm diameter p/i/n NW diodes exhibit ultralow leakage currents of approximately 1 fA, and open-circuit voltages and fill-factors up to 0.5 V and 73%, respectively, under one-sun illumination. Single-NW wavelength-dependent photocurrent measurements reveal size-tunable optical resonances, external quantum efficiencies greater than unity, and current densities double those for silicon films of comparable thickness. In addition, finite-difference-time-domain simulations for the measured NW structures agree quantitatively with the photocurrent measurements, and demonstrate that the optical resonances are due to Fabry-Perot and whispering-gallery cavity modes supported in the high-quality faceted nanostructures. Synthetically optimized NW devices achieve current densities of 17 mA/cm(2) and power-conversion efficiencies of 6%. Horizontal integration of multiple NWs demonstrates linear scaling of the absolute photocurrent with number of NWs, as well as retention of the high open-circuit voltages and short-circuit current densities measured for single NW devices. Notably, assembly of 2 NW elements into vertical stacks yields short-circuit current densities of 25 mA/cm(2) with a backside reflector, and simulations further show that such stacking represents an attractive approach for further enhancing performance with projected efficiencies of > 15% for 1.2 μm thick 5 NW stacks.

Photonic crystal refractive index sensing based on sandwich structure

An ultracompact refractive index sensing based on the sandwich structure of photonic crystal is presented and demonstrated with solutions of water, methylsilicone and silicone. The performances of the sensor are analyzed theoretically by using Fabry–Perot cavity mode, the change in opposite direction between the transmission of the refractive index sensing and its quality factor is derived. The experimental results are consistent with the results of theoretical analysis.

Mode coupling and interaction in a plasmonic microcavity with resonant mirrors

We study mode interaction mechanisms in a plasmonic microcavity which consists of two periodically corrugated metallic mirrors. In this system it can be observed that not only does mode hybridization between surface plasmons on the two mirrors occur, but also an anticrossing due to the interaction between plasmons and the Fabry-Perot cavity modes. This behavior is interpreted from the viewpoint of mode symmetry. By controlling the mode interaction strength via structural parameters of the resonant mirrors, the mode dispersion of both the Fabry-Perot cavity mode and the surface plasmons can be modified. This can be applied to control light-matter interaction, subwavelength imaging, or other functional devices.

Plasmonic band edge effects on the transmission properties of metal gratings

We present a detailed analysis of the optical properties of one-dimensional arrays of slits in metal films. Although enhanced transmission windows are dominated by Fabry-Perot cavity modes localized inside the slits, the periodicity introduces surface modes that can either enhance or inhibit light transmission. We thus illustrate the interaction between cavity modes and surface modes in both finite and infinite arrays of slits. In particular we study a grating that clearly separates surface plasmon effects from Wood-Rayleigh anomalies. The periodicity of the grating induces a strong plasmonic band gap that inhibits coupling to the cavity modes for frequencies near the center of the band gap, thereby reducing the transmission of the grating. Strong field localization at the high energy plasmonic band edge enhances coupling to the cavity modes while field localization at the low energy band edge leads to weak cavity coupling and reduced transmission.

Slope Efficiency Improvement in Mode-Hop Driven Tunable Single-Mode Cholesteric Liquid Crystal Laser

We report the improvement in the slope efficiency of tunable single-mode cholesteric liquid crystal (ChLC) lasers with a three-layered structure. The device consists of one photopolymerized ChLC layer with a wide reflection band, another ChLC layer with a notch reflection band, and a rhodamine-6G-doped ionic liquid layer acting as the gain medium. Single-mode lasing is obtained from this device structure because the ChLC layer with the notch reflection band strongly reflects only one of the Fabry–Perot cavity modes, and the mode-hop-driven tuning of the lasing wavelength is possible because the reflection band of the notch ChLC can be tuned using external stimuli, such as heat. Our device showed a maximum slope efficiency of 16% (considering emission only in the forward direction), and was found to be approximately 1.5 times larger than that of ordinary ChLC lasers doped with the pyrromethene 597 laser dye. The improvement in the slope efficiency is believed to be attributed to the high quantum efficiency of the rhodamine 6G dye, which cannot be used in conventional ChLC lasers because of its low solubility, but can be used in our device because of the isotropic gain medium employed.

Slope Efficiency Improvement in Mode-Hop Driven Tunable Single-Mode Cholesteric Liquid Crystal Laser

We report the improvement in the slope efficiency of tunable single-mode cholesteric liquid crystal (ChLC) lasers with a three-layered structure. The device consists of one photopolymerized ChLC layer with a wide reflection band, another ChLC layer with a notch reflection band, and a rhodamine-6G-doped ionic liquid layer acting as the gain medium. Single-mode lasing is obtained from this device structure because the ChLC layer with the notch reflection band strongly reflects only one of the Fabry–Perot cavity modes, and the mode-hop-driven tuning of the lasing wavelength is possible because the reflection band of the notch ChLC can be tuned using external stimuli, such as heat. Our device showed a maximum slope efficiency of 16% (considering emission only in the forward direction), and was found to be approximately 1.5 times larger than that of ordinary ChLC lasers doped with the pyrromethene 597 laser dye. The improvement in the slope efficiency is believed to be attributed to the high quantum efficiency of the rhodamine 6G dye, which cannot be used in conventional ChLC lasers because of its low solubility, but can be used in our device because of the isotropic gain medium employed.

Analysis of threshold conditions for generation of a closed mode in a Fabry-Perot semiconductor laser

Threshold conditions for generation of a closed mode in the crystal of the Fabry-Perot semiconductor laser with a quantum-well active region are analyzed. It is found that main parameters affecting the closed mode lasing threshold for the chosen laser heterostructure are as follows: the optical loss in the passive region, the optical confinement factor of the closed mode in the gain region, and material gain detuning. The relations defining the threshold conditions for closed mode lasing in terms of optical and geometrical characteristics of the semiconductor laser are derived. It is shown that the threshold conditions can be satisfied at a lower material gain in comparison with the Fabry-Perot cavity mode due to zero output loss for the closed mode.

Single-mode quantum cascade lasers based on a folded Fabry-Perot cavity

We demonstrate single-mode quantum cascade lasers employing a folded Fabry-Perot cavity consisting of two straight sections connected by a semicircular section in a “hairpin” shape. These folded cavity lasers emitting at ∼4.5 μm are fabricated with identical processes as those for plain Fabry-Perot ridge lasers, and show a strong suppression of the comb of Fabry-Perot cavity modes, leading to tunable single-mode emission with up to 27 dB side mode suppression ratio and a single-mode operating current range of up to 60% above the threshold current when operated in pulsed mode; single-mode emission is achieved from 80 to ∼240 K.

Broadband Cavity‐Mode Lasing from Dye‐Doped Nematic Liquid Crystals Sandwiched by Broadband Cholesteric Liquid Crystal Bragg Reflectors

Multiple polymer cholesteric liquid crystal (PCLC) layers with different pitches and a sandwich structure of nematic liquid crystal by these PCLC films are presented. The former serves as broadband-distributed Bragg reflectors and the latter as multiple-band electrotunable filters. Using the latter dye-doped hybrid film red–green–blue simultaneous lasing due to Fabry–Perot cavity modes is achieved (see figure).

Transmission of light through coaxial and non-coaxial double-layer gold slit arrays

Abstract We investigate numerically the transmittance of light through gold double-layer structures with periodic coaxial and non-coaxial slits. We attribute the enhanced optical transmission to the surface plasmon resonance collaborating with the localized waveguide resonance. The transmission spectra and the surface electric fields are used to characterize the resonances of both types. For the coaxial system, with the increase of the slit width of the second layer, the resonance peak values of both types increase sharply at first until the two layers have the same slit width and then decrease dramatically; additionally, the center of the localized waveguide resonance peak shifts to shorter wavelength noticeably, but the surface plasmon peak center moves negligibly. As regards the non-coaxial structure, it shows a similar behavior of the localized waveguide resonance peak to that of the coaxial one; however, the surface plasmon resonance peak behaves in a different way. These results may be associated with the surface plasmon coupling modes and the Fabry–Perot cavity modes in the double-layer structure.

Large and dynamical tuning of a chalcogenide Fabry-Perot cavity mode by temperature modulation

Te-enriched chalcogenide glass Ge(15)As(25)Se(15)Te(45) (GAST) is synthesized, thermo-optically characterized and used to fabricate a one dimensional photonic crystal cavity mode that is dynamically and reversibly tuned by temperature modulation. The optical cavity mode is designed using GAST and As(2)S(3) glasses after fully determining their temperature dependence of the complex refractive indices in the visible and near infrared spectrum using spectroscopic ellipsometry. By making use of the very large thermo-optic coefficient (dn/dT = 4 x 10(-4)/ degrees C) of GAST glass at 1.2 mum, the cavity mode of the multilayer was tuned reversibly more than 16 nm, which is, to the best of our knowledge, an order of magnitude larger for this kind of cavity modulation. Wide and dynamical spectral tuning of low bandgap chalcogenide glasses via temperature modulation can be utilized in photonic crystal based integrated optics, quantum dot resonance matching, solid state and gas laser components, and infrared photonic crystal fibers.

High speed phase shifting interferometry using injection locking of the laser frequency to the resonant modes of a confocal Fabry-Perot cavity

We present a high speed phase shifting interferometer which utilizes the self injection locking of a frequency tunable laser diode. By using a confocal Fabry-Perot cavity made of ultra low expansion glass, and linearly modulating the laser diode current, the laser frequency could be injection locked to the resonant modes of the Fabry-Perot cavity consecutively. It provided equal phase steps to the interferograms which are ideal to be analyzed by the Carré algorithm. The phase step error was evaluated to be about 3 MHz which corresponds to 0.2 nm in length measurement. With this technique, profile measurements are insensitive to external vibration since four 640x480 pixels images can be acquired within 4 ms. Difference of two profile measurements, each made with and without vibration isolation, respectively, was evaluated to be 0.5 nm (rms).

A study on the interval between longitudinal modes of Fabry-Perot cavity composed of fiber Bragg gratings

The characteristics of transmission spectrum of the Fabry-Perot (F-P) cavity composed of two fiber Bragg gratings (FBG) are analyzed detailedly in this paper. The influencing factors of the position of the longitudinal mode are pointedout. The relationship and difference between the FBG F-P cavity and normal F-P cavity are discussed. The phase factor of the amplitude reflection coefficient in the range of the FBG main lobe is simulated linearly using the effective mirror surface model. The effective length of the FBG is defined and the expression of the effective length is obtained. Furthermore， the effective length of the FBG is brought into the equivalent cavity length of the FBG F-P cavity. The interval between longitudinal modes of the FBG F-P cavity is calculated using the equivalent cavity length. Both the numerical simulation and experimental results show that the interval calculated using the equivalent cavity length accords well with the true interval between longitudinal modes of the FBG F-P cavity.

Dependence of self-pulsation characteristics of multisection index-coupled distributed feedback lasers on section lengths

We investigate the effect of section lengths on the self-pulsation (SP) characteristics of a multisection index-coupled distributed feedback (DFB) laser that is composed of two spectrally detuned DFB sections and a phase-tuning section between them. Compound-cavity modes in multisection DFB lasers can be obtained by the concept of Fabry-Perot cavity modes. The simple equation for a CS number, which represents the number of compound-cavity modes within the stop-band width of a DFB section, is derived. By using the CS number, we were able to predict the SP characteristics such as abrupt changes of SP frequency due to mode hopping. Stable SP characteristics without abrupt changes of SP frequency for the variation of the spectral detuning and the phase shift in a phase-tuning section were obtained in cases with small CS numbers, which can be obtained by adjustment of section lengths.