Optical Filtering Effect Research Articles

Optical filter effect of the metal–dielectric–metal waveguide with stub structure

Abstract The optical filter effect of the metal–dielectric–metal (MDM) waveguide with stub structure is investigated with surface plasmons (SPs) interference theory and simulated using finite difference time domain (FDTD) method. The transmission process of the surface plasmons propagating through the stub structure is discussed in detail, and testified by different time step field intensity images of FDTD simulation. It is verified by the FDTD simulation that the oscillation periods of the transmission curves are proportional to the wavelengths, and the number of the wavelength of the standing wave in the stub is linear to the stub length d. When the monochromatic continuous waves are incident, the transmissions are also periodically changed with the length of the stub. The shorter wavelengths present better filter sensitivity than longer wavelengths. The above optical filter effect implies that the MDM waveguide with stub structure can be applied in the fields of photonic integration devices and sensors.

Back-Illuminated GaN/AlGaN Solar-Blind Avalanche Photodiodes

The separate absorption and multiplication (SAM) GaN/AlGaN solar-blind avalanche photodiodes (APDs) integrated with the specific design of 1-D dual-periodic photonic crystal on the back of the sapphire substrate are investigated numerically. The calculated results show that the proposed APDs can increase significantly the avalanche gain compared with the conventional SAM AlGaN solar-blind APDs using GaN instead of AlGaN as the multiplication layer. The enhanced performance can be explained by the larger hole ionization coefficient in the multiplication layer, the higher hole injection efficiency, and the reduced total dark current in this APDs. Meanwhile, the cutoff wavelength of 282 nm is achieved due to the optical filter effect of 1-D dual-periodic photonic crystal.

Effect of Optical Filtering for Wavelength Division Multiplexing Systems

Effect of Optical Filtering for Wavelength Division Multiplexing Systems

Influence of optical filtering on transmission capacity in single mode fiber communications

This paper presents the design and analysis of optical filters that are placed at the output of directly modulated vertical cavity surface emitting laser (VCSEL) in the process of inexpensive transmitter’s implementation for upcoming generation optical access network. Generation of non return to zero (NRZ) optical signal from the transmitter for 110 km error-free single mode fiber (SMF) transmission at 10 Gb/s with bit error rate (BER) of 10−30 in the absence of the external modulator and encoder was proposed. Effects of super-Gaussian and Butterworth optical filters at VCSEL output were demonstrated to maximize performance of SMF optical systems without need of any dispersion compensation technique.

Factors Affecting the Performance of Bifacial Inverted Polymer Solar Cells with a Thick Photoactive Layer

Photocurrent voltage curves and photocurrent action spectra of bifacial inverted polymer solar cells with a structure of ITO/ZnO/[6,6]-phenyl C61 butyric acid methyl ester (PCBM):regioregular poly(3-hexylthiophene) (P3HT)/poly(3,4-ethylenedioxylenethiophene):poly(4-styrene sulfonic acid) (PEDOT:PSS)/Au were measured. High performance was obtained when light was irradiated from each side of the devices, even for those with a 500 nm thick PCBM:P3HT layer, but an optical filter effect of the photocurrent was somewhat larger for irradiation from the Au side than that for the ITO side. These results suggested that the efficiency of photocharge separation near the ZnO/PCBM:P3HT interface was higher than that near the PCBM:P3HT/PEDOT:PSS interface, although the photocharge separation and the charge transport were smooth in the whole PCBM:P3HT layer. Further, we found that the fill factor of the photocurrent voltage curves of these devices depended on the migration distance of holes with lower mobility in the PCB...

Band-stop filters based on a coupled circular ring metal–insulator–metal resonator containing nonlinear material

An all-optical plasmonic filter based on a metal–insulator–metal (MIM) waveguide coupled with a circular ring resonator containing a Kerr nonlinear medium is proposed and numerically investigated. The optical filtering effect is verified by the finite difference time-domain (FDTD) method and the simulation results reveal that the increase in the refractive index induced by enhancing the incident intensity can cause a red-shift for the resonance wavelengths. Thus the resonant wavelengths can be tuned without changing the outer size of the structure. The proposed band-stop plasmonic filter is of a compact size that has potential application for integrated optics in which we have limitations on the outer dimensions and it is not possible to enlarge the dimension of the ring resonator to reach longer resonant wavelengths.

DRUSEN CHARACTERIZATION WITH MULTIMODAL IMAGING

To characterize the known appearance of cuticular drusen, subretinal drusenoid deposits (reticular pseudodrusen), and soft drusen as revealed by multimodal fundus imaging and to create an explanatory model that accounts for these observations. Reported color, fluorescein angiographic, autofluorescence, and spectral domain optical coherence tomography images of patients with cuticular drusen, soft drusen, and subretinal drusenoid deposits were reviewed, as were actual images from affected eyes. Representative histological sections were examined. The geometry, location, and imaging characteristics of these lesions were evaluated. A hypothesis based on the Beer-Lambert law of light absorption was generated to fit these observations. Cuticular drusen appear as numerous, uniform, round, yellow-white punctate accumulations under the retinal pigment epithelium (RPE). Soft drusen are larger, yellow-white dome-shaped mounds of deposit under the RPE. Subretinal drusenoid deposits are polymorphous light-gray interconnected accumulations above the RPE. Based on the model, both cuticular and soft drusen appear yellow because of the removal of shorter wavelength light by a double pass through the RPE. Subretinal drusenoid deposits, which are located on the RPE, are not subjected to short-wavelength attenuation and therefore are more prominent when viewed with blue light. The location and morphology of extracellular material in relationship to the RPE, and associated changes to RPE morphology and pigmentation, appeared to be the primary determinants of druse appearance in different imaging modalities. Although cuticular drusen, subretinal drusenoid deposits, and soft drusen are composed of common components, they are distinguishable by multimodal imaging because of differences in location, morphology, and optical filtering effects by drusenoid material and the RPE.

Optical Filter Effects on Night Vision Goggle Acuity and Preservation of Dark Adaptation

The high output of night vision goggles (NVGs) can cause a loss of dark adaptation, resulting in suboptimal unaided vision. Optical filters have been designed to mitigate this problem by changing the overall output characteristics of the NVGs. Several aspects of visual performance related to NVG use were studied in a repeated measures design, filters versus no filters. NVG acuity was assessed using a 25% contrast chart, while preservation of dark adaptation after NVG use was measured with a scotopic sensitivity tester (SST) and a low luminance acuity chart. Testing was accomplished at two light levels, roughly corresponding to starlight and quarter moon conditions. Use of the filters resulted in a statistically significant loss of acuity of about a 1/2 line (approximately 2.5 letters) at both light levels. The second part of the study identified a 47% improvement in preservation of dark adaptation under simulated starlight conditions and a 31% improvement under simulated quarter moon conditions with filter use; however, only the starlight finding was statistically significant. No significant differences in performance were seen with the low luminance chart. Despite a small loss of visual acuity with filter use, the improvement in retention of dark adaptation may be beneficial in certain operational environments. Aviators, airmen, and commanders should evaluate how the potential for slightly poorer visual acuity and improved recovery of dark adapted vision relates to their mission specific requirements prior to implementing use of NVG filters.

Simultaneous demodulation and slow light of differential phase-shift keying signals using stimulated-Brillouin-scattering-based optical filtering in fiber

For the first time to our knowledge, we demonstrate simultaneous demodulation and slow-light delay of differential phase-shift keying (DPSK) signals at flexible bit rates using the stimulated-Brillouin-scattering-based optical filtering effect in optical fiber. Both 10 and 2.5 Gbit/s DPSK signals have been demodulated and delayed with excellent performances. In the case of the 10 Gbit/s DPSK signal, after demodulation the tunable delay range with error-free operation is about 50 ps, which we believe is the best result obtained for 10 Gbit/s slow-light demonstrations. For the 2.5 Gbit/s DPSK signal, the optimal sensitivity after demodulation is -36.5 dBm, which is comparable with the back-to-back sensitivity of a 2.5 Gbit/s nonreturn-to-zero signal.

EFFECT OF TINTED OPTICAL FILTERS ON VISUAL ACUITY AND CONTRAST SENSITIVITY IN PATIENTS WITH INFLAMMATORY CYSTOID MACULAR EDEMA

To ascertain the effect of tinted optical filters (TFs) on visual function in patients with inflammatory cystoid macular edema (CME). A prospective study included 14 patients with inflammatory CME and best-corrected visual acuity between 0.1 and 0.8 (CME group) and 16 sex-, age-, and best-corrected visual acuity-matched patients with macular disorders but no CME (non-CME group). All patients from both groups underwent the following tests: determination of visual acuity at distance, contrast sensitivity (CS) testing; and subjective grading of each TF for best-corrected visual acuity and CS compared with no TFs. All tests were performed with the following TFs: Corning photochromic filter with a cutoff at 450 nm; Zeiss filter with a cutoff at 560 nm; and cheap widely available yellow filter with a cutoff at 489 nm. Without TFs, the CME and non-CME groups did not differ in best-corrected visual acuity (P = 0.79). Using the TFs, a clinically significant improvement was not achieved by any patient. However, using the definition of any improvement, best-corrected visual acuity with all TFs showed a significant improvement in the CME group compared with no TFs (P < 0.01). The CME group rated the Corning photochromic filter with a cutoff of 450 nm significantly higher than the other TFs when determining visual acuity (P = 0.05) and CS (P = 0.01) in contrast to no improvement in the non-CME group. Although the use of TFs for the CME patients was not associated with criteria of clinically significant improvement, our results indicate that visual acuity and CS in patients with inflammatory CME might benefit from the use of TFs.

Feasibility Study of SOA-Based Noise Suppression for Spectral Amplitude Coded OCDMA

We investigate the benefits of employing a saturated semiconductor optical amplifier (SOA) to reduce the optical noise in an incoherent light optical code division multiple access (OCDMA) system. In the context of spectrum slicing, SOA-based noise suppression has shown significant potential in enhancing the signal quality of noisy light. In this paper, we evaluate the viability of the technique for spectral amplitude coded OCDMA and show that the benefits of SOA-based noise suppression do not extend readily to this application due to post-SOA optical-filtering effects at the receiver. However, appreciable performance improvements can in principle be realized through optimized system and decoder design

Consideration and compensation for precision optical flying height measurement

It is a big challenge to determine ultra-low slider flying height accurately. The intensity interferometry flying height testing method is widely used to determine slider flying height. However, the intrinsic measurement errors of the method are becoming non-negligible with the decrease in slider flying height. Strategies have to be developed to minimize the errors. To measure flying height with a normal incidence optical flying height tester, a calibration process is required to determine several constants used in flying height calculation. In practice, the calibration is usually done simply by retracting the slider from the disk and measuring the intensity minima and maxima of the interferogram during the retracting process. It has been demonstrated that the single most important source of error in the flying height measurement is associated with errors in the determination of the intensity maxima and minima. In this work, the effects of optical filter, the responding frequency of photodetector, and the lack of the first order intensity minimum on the determination of the intensity maxima and minima are studied. Methodologies to minimize the errors in flying height measurement caused by the above factors are developed.

Performance evaluation of optical DQPSK using saddle point approximation

In this paper, the authors derive the moment generating function (MGF) of the decision variable for a practical optical differential quadrature phase shift keying (DQPSK) receiver affected by phase noise and the amplifier spontaneous emission noise. The effect of the different optical filters, Gaussian, Fabry-Peacuterot (FP), and optical integrator, on the phase noise is examined. Using the saddle point approximation, the authors obtain numerically the bit error rate (BER) for the above system, as a function of the optical-signal-to-noise ratio (OSNR) and the source linewidth. The model is found to agree with previous published simulation results and the Monte Carlo simulations presented in this paper. The authors also calculate the BER floors for DQPSK inflicted by the phase noise and compare its performance with differential phase shift keying (DPSK). Finally, the authors examine the effect of interferometric demodulation on the relative intensity noise (RIN) spectra and the impact on the DQPSK system performance. In particular, the authors examine the influence of system dispersion on the receiver sensitivity

Optical filters inhibiting television-induced photosensitive seizures.

Televised images are the most common stimulus for provoking photosensitive seizures in photosensitive persons. To inhibit photosensitive seizures in photosensitive persons who do or do not have epilepsy, the authors sought nonpharmacologic methods for reducing the levels of photic stimulation of televised images. The authors found two types of pathophysiologic mechanisms (wavelength-dependent and quantity of light-dependent mechanisms) for photoparoxysmal responses (PPR). The authors tested two different types of optical filters, one reflecting long-wavelength red light selectively, which stimulates a wavelength-dependent mechanism, and the other absorbing light in the visible spectrum evenly (neutral density filters). Inhibiting effects of optical filters were studied by conventional intermittent photic stimulation (IPS) using strobe light and novel photic stimulation using flashing cathode ray tubes (CRT). Both filters individually inhibited PPR insufficiently (less than 50%). Compound optical filters, composed of both types of filters, can inhibit the PPR, approximately 90% for IPS and 95% for photic stimulation with CRT. These compound optical filters do not destroy chromaticity of emissions from the television's CRT. These compound filters may be useful to prevent seizures induced by television in photosensitive persons.

Improving the analytical performance of hydride generation non-dispersive atomic fluorescence spectrometry. Combined effect of additives and optical filters

The effects of tetrahydroborate and acid concentration and the presence of l-cysteine and thiourea were investigated in the determination of As, Bi and Sn using continuous flow hydride generation atomic fluorescence spectrometry (HG AFS). The aim was to find conditions allowing the control of those effects exerting negative influence on the analytical performance of the HG AFS apparatus. The effects taken into account were: (i) the radiation scattering generated by carryover of solution from the gas–liquid separator to the atomizer; (ii) the introduction of molecular species generated by tetrahydroborate decomposition into the atomizer; and (iii) interference effects arising from other elements in the sample matrix and from different acids. The effects (i) and (ii) could be controlled using mild reaction conditions in the HG stage. The effect of HG conditions on carryover was studied by radiation scattering experiments without hydride atomization. Compromised HG conditions were found by studying the effects of tetrahydroborate (0.1–20 g l −1) and acid (0.01–7 mol l −1) concentration, and the addition of l-cysteine (10 g l −1) and thiourea (0.1 mol l −1) on the HG AFS signals. The effect of optical filters was investigated with the aim of improving the signal-to-noise ratio. Optical filters with peak wavelengths of 190 and 220 nm provided an improvement of detection limits by factors of approximately 4 and 2 for As and Te, respectively. Under optimized conditions the detection limits were 6, 5, 3, 2, 2 and 9 ng l −1 for As, Sb, Bi, Sn, Se and Te, respectively. Good tolerance to various acid compositions and sample matrices was obtained by using l-cysteine or thiourea as masking agents. Determination of arsenic in sediment and copper certified reference materials, and of bismuth in steel, sediment, soil and ore certified reference material is reported.

Effect of optical filtering on pulses generated with a gain-switched DFB laser

Gain-switched laser diodes are widely used to generate short optical pulses, which find several applications in optical fiber measurements and high-speed optical communication systems. Temporal and spectral properties of the gain-switched pulses can be tailored by filtering their optical spectrum. Optical filtering leads to suppression of frequency chirp and generation of transform-limited pulses. We show that tuning of the center frequency of an optical bandpass filter can result in not only pulse compression, but also in the generation of a series of secondary oscillations after the primary pulse. The origin of these secondary oscillations is investigated both experimentally and analytically.

Simultaneous counting of radiation emitted from actinides with improved phoswich detectors by applying an optical filter

The effects of optical filters on rise times of output signals from a ZnS(Ag) scintillator have been examined, and phoswich detectors applying them were devised for more effective simultaneous counting of α and β (including γ) rays emitted from actinides. The optical sharpcut filters made the rise times slower and optical bandpass filters made them faster. In this paper, two improved phoswich detectors, ZnS(Ag)/sharpcut-filter/NaI(Tl) and ZnS(Ag)/bandpass-filter/CsI(Tl), are demonstrated.

The interaction of melanin with 8-methoxypsoralen: effect on radiative and nonradiative transitions. A fluorescence and pulsed photoacoustic study.

The interaction of 8-methoxypsoralen (8-MOP) with synthetic eumelanin was investigated using static and time-resolved fluorescence and pulsed photoacoustic calorimetry. Due to the strong overlap of the absorption bands of melanin and 8-MOP, a method is presented to account for the systematic errors introduced by the optical filter effect exerted by each absorbing species in the fluorescence and the photoacoustic measurements. As a preliminary step to the understanding of the nonradiative behavior of the psoralen-melanin complexes, the photoacoustic parameters of 8-MOP in various solvents were determined. Spectroscopic data indicate the absence of interaction at the ground-state level, whereas the singlet excited state of 8-MOP is quenched by the pigment; the average fluorescence lifetimes are independent of the melanin concentration, thus indicating a static quenching mechanism. The photoacoustic data show that the quenching process involves an increased intersystem crossing probability, which is almost unaffected by the presence of oxygen, as expected for a molecule essentially acting as a type I photosensitizing agent.

THE INTERACTION OF MELANIN WITH 8‐METHOXYPSORALEN: EFFECT ON RADIATIVE and NONRADIATIVE TRANSITIONS. A FLUORESCENCE and PULSED PHOTOACOUSTIC STUDY

Abstract –The interaction of 8‐methoxypsoralen (8‐MOP) with synthetic eumelanin was investigated using static and time‐resolved fluorescence and pulsed photoacoustic calorimetry. Due to the strong overlap of the absorption bands of melanin and 8‐MOP, a method is presented to account for the systematic errors introduced by the optical filter effect exerted by each absorbing species in the fluorescence and the photoacoustic measurements. As a preliminary step to the understanding of the nonradiative behavior of the psoralen‐melanin complexes, the photoacoustic parameters of 8‐MOP in various solvents were determined. Spectroscopic data indicate the absence of interaction at the ground‐state level, whereas the singlet excited state of 8‐MOP is quenched by the pigment; the average fluorescence lifetimes are independent of the melanin concentration, thus indicating a static quenching mechanism. The photoacoustic data show that the quenching process involves an increased intersystem crossing probability, which is almost unaffected by the presence of oxygen, as expected for a molecule essentially acting as a type I photosensitizing agent.

Transmission-line laser modelling of semiconductor laser amplified optical communications systems

Previously, the transmission-line laser model (TLLM) has been used to simulate the optical noise characteristics of semiconductor lasers and semiconductor laser amplifiers in the time-domain. The paper shows that, with the addition of a suitable photodiode model, the base-band electrical noise characteristics of amplified optical systems can also be simulated with the TLLM. A simple theory of the baseband noise properties of a detected optical signal is presented and photodiode model for the TLLM is developed. The baseband electrical noise spectra of travelling-wave, Fabry–Perot and DFB laser amplifiers are numerically simulated, and the travelling-wave laser amplifier spectrum is in excellent agreement with simple theory. This new approach to amplified optical communications system modelling allows the effects of different optical and electrical filters on the signal and the noise to be studied simultaneously over a wide bandwidth. As an example, a 10 Gbit/s system is simulated, and the effects of the optical filter on the signal and the noise are investigated.