Browsing by Subject "Cavity resonators"
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Item Open Access 1.3 μm GaAs based resonant cavity enhanced Schottky barrier internal photoemission photodetector(IEEE, Piscataway, NJ, United States, 2000) Necmi, B.; Kimukin, I.; Özbay, Ekmel; Tuttle, G.GaAs based photodetectors operating at 1.3 μm that depend on internal photoemission as the absorption mechanism were fabricated. Quantum efficiency (QE) was increased using resonant cavity enhancement (RCE) effect.Item Open Access 100-GHz resonant cavity enhanced Schottky photodiodes(Institute of Electrical and Electronics Engineers, 1998) Onat, B. M.; Gökkavas, M.; Özbay, Ekmel; Ata, E. P.; Towe, E.; Ünlü, M. S.Resonant cavity enhanced (RCE) photodiodes are promising candidates for applications in optical communications and interconnects where ultrafast high-efficiency detection is desirable. We have designed and fabricated RCE Schottky photodiodes in the (Al, In) GaAs material system for 900-nm wavelength. The observed temporal response with 10-ps pulsewidth was limited by the measurement setup and a conservative estimation of the bandwidth corresponds to more than 100 GHz. A direct comparison of RCE versus conventional detector performance was performed by high speed measurements under optical excitation at resonant wavelength (895 nm) and at 840 nm where the device functions as a single-pass conventional photodiode. A more than two-fold bandwidth enhancement with the RCE detection scheme was demonstrated.Item Open Access 45 GHz bandwidth-efficiency resonant cavity enhanced ITO-Schottky photodiodes(OSA, 2001) Bıyıklı, Necmi; Kimukin, İbrahim; Aytür, Orhan; Özbay, Ekmel; Gökkavas, M.; Ünlü, M. S.We demonstrated high-performance resonant cavity enhanced ITO-Schottky photodiodes. We achieved a peak efficiency of 75% around 820 nm with a 3-dB bandwidth of 60 GHz resulting in a bandwidth-efficiency product of 45 GHz.Item Open Access 45-GHz bandwidth-efficiency resonant-cavity-enhanced ITO-Schottky photodiodes(IEEE, 2001) Bıyıklı, Necmi; Kimukin, I.; Aytür, O.; Gökkavas, M.; Ünlü, M. S.; Özbay, EkmelHigh-speed Schottky photodiodes suffer from low efficiency mainly due to the thin absorption layers and the semitransparent Schottky-contact metals. We have designed, fabricated and characterized high-speed and high-efficiency AlGaAs-GaAs-based Schottky photodiodes using transparent indium-tin-oxide Schottky contact material and resonant cavity enhanced detector structure. The measured devices displayed resonance peaks around 820 nm with 75% maximum peak efficiency and an experimental setup limited temporal response of 11 ps pulsewidth. The resulting 45-GHz bandwidth-efficiency product obtained from these devices corresponds to the best performance reported to date for vertically illuminated Schottky photodiodes.Item Open Access All-fiber all-normal-dispersion femtosecond laser with nonlinear multimodal interference-based saturable absorber(Institute of Electrical and Electronics Engineers Inc., 2019) Teğin, Uğur; Ortaç, BülendChong et al. demonstrated a stable passively mode-locked all-normal-dispersion fiber laser and pulse generation is attributed to the strong spectral filtering of chirped pulses, dissipative soliton pulses [1]. In the following years, with very-large-mode-area fibers the energy and power scalability of the dissipative soliton pulses is demonstrated. Recently, multimodal interactions are subject to device studies with various configurations. Nazemosadat et al. theoretically proposed a short graded-index multimode fiber segment in between single mode fiber as a saturable absorber [2]. On the other hand, with similar device structure an all-fiber bandpass filter is later presented both numerically and experimentally [3].Item Open Access Directional processing of ultrasonic arc maps and its comparison with existing techniques(IEEE, 2007) Barshan, Billur; Altun, KeremDirectional maximum (DM) technique for processing ultrasonic arc maps (UAMs) is proposed and compared to existing techniques. It employs directional processing in extracting the map of the environment from UAMs. DM aims at overcoming the intrinsic angular uncertainty of ultrasonic sensors in map building, as well as eliminating noise and cross-talk related misreadings. The comparison is based on experiments with a mobile robot which ac-quired ultrasonic range measurements through wall following. Three complementary performance criteria are used. The DM technique offers a very good compromise between mean absolute error and correct detection rate, with a processing time less than one tenth of a second. It is also superior in range accuracy and in eliminating artifacts, resulting in the best overall performance. The results indicate several trade-offs in the choice of UAM processing techniques.Item Open Access Experimental investigation of layer-by-layer metallic photonic crystals(Institution of Electrical Engineers, 1998-12) Temelkuran, B.; Altug, H.; Özbay, EkmelThe authors have investigated the transmission properties and defect characteristics of layer-by-layer metallic photonic crystals. They have demonstrated experimentally that the metallicity gap of these crystals extends to an upper band-edge frequency, and no lower edge was detected down to 2 GHz. The defect structures built around these crystals exhibited high transmission peak amplitudes (100%) and high Q factors (2250). The crystals with low filling ratios (around 1-2%) were tested and were still found to possess metallic photonic crystal properties. These crystals exhibited high reflection rates within the metallicity gap and reasonable defect mode characteristics. A power enhancement factor of 190 was measured for the electromagnetic (EM) wave within planar cavity structures, by placing a monopole antenna inside the defect volume. These measurements show that detectors embedded inside a metallic photonic crystal can be used as frequency selective resonant cavity enhanced (RCE) detectors with increased sensitivity and efficiency when compared to conventional detectors.Item Open Access Experimental study of linear closed-loop control of subsonic cavity flow(2006) Yan P.; Debiasi, M.; Yuan X.; Little J.; Özbay, Hitay; Samimy, M.A study is presented of the modeling and implementation of different concepts for linear feedback control of a single-mode resonance shallow cavity flow. When a physics-based linear model is used for cavity pressure oscillations-, an H∞ controller was designed and tested experimentally. It significantly reduced the main Rossiter mode for which it was designed, while leading to strong oscillations at other Rossiter modes. Other linear control methods such as Smith predictor controller and proportional integral derivative (PID) controller exhibited similar results. The ineffectiveness of using fixed linear models in the design of controllers for the cavity flows is discussed. A modification of the PID design produced a parallel-proportional with time-delay controller that remedied this problem by placing zeros at the frequencies corresponding to other resonance states. Interestingly, it was observed that introducing the same zero to the H∞ controller can also successfully avoid the strong oscillations at other Rossiter modes otherwise observed in the single-mode-based design. The parallel-proportional with time-delay controller was compared to a very effective open-loop method for reducing cavity resonance and exhibited superior robustness with respect to departure of the Mach number from the design conditions. An interpretation is presented for the physical mechanisms by which the open-loop forcing and the parallel-proportional with time-delay controllers reduce the cavity flow noise. The results support the idea that both controls induce in the system a rapid switching between modes competing for the available energy that can be extracted from the mean flow.Item Open Access High-performance 1.55 μm resonant cavity enhanced photodetector(IEEE, 2002) Kimukin, İbrahim; Bıyıklı, Necmi; Özbay, EkmelA high speed and high efficiency resonant cavity enhanced InGaAs based photodetector was demonstrated. A peak quantum efficiency of 66% was measured along with 31 GHz bandwidth with the device. The photoresponse was found to be linear upto 6 mW optical power, where the device 5 mA photocurrent.Item Open Access High-performance ALGaN-based visible-blind resonant cavity enhanced Schottky photodiodes(Materials Research Society, 2003-04) Kimukin, İbrahim; Bıyıklı, Necmi; Kartaloğlu, Tolga; Aytür, Orhan; Özbay, EkmelWe have designed, fabricated and tested resonant cavity enhanced visible-blind AlGaN-based Schottky photodiodes. The bottom mirror of the resonant cavity was formed with a 20 pair AlN/AlGaN Bragg mirror. The devices were fabricated using a microwave compatible fabrication process. Au and indium-tin-oxide (ITO) thin films were used for Schottky contact formation. ITO and Au-Schottky devices exhibited resonant peaks with 0.153 A/W and 0.046 A/W responsivity values at 337 nm and 350 nm respectively. Temporal high-speed measurements at 357 nm resulted in fast pulse responses with pulse widths as short as 77 ps. The fastest UV detector had a 3-dB bandwidth of 780 MHz.Item Open Access High-speed 1.55 μm operation of low-temperature-grown GaAs-based resonant-cavity-enhanced p-i-n photodiodes(American Institute of Physics, 2004) Butun, B.; Bıyıklı, Necmi; Kimukin, I.; Aytur, O.; Özbay, Ekmel; Postigo, P. A.; Silveira, J. P.; Alija, A. R.The 1.55 μm high-speed operation of GaAs-based p-i-n photodiodes was demonstrated and their design, growth and fabrication were discussed. A resonant-cavity-detector structure was used to selectively enhance the photoresponse at 1.55 μm. The bottom mirror of the resonant cavity was formed by a highly reflecting 15-pair GaAs/AlAs Bragg mirror and molecular-beam epitaxy was used for wafer growth. It was found that the fabricated devices exhibited a resonance of around 1548 nm and an enhancement factor of 7.5 was achieved when compared to the efficiency of a single-pass detector.Item Open Access High-speed InGaAs based resonant cavity enhanced p-i-n photodiodes(IEEE, 2001) Kimukin, İbrahim; Bıyıklı, Necmi; Özbay, EkmelHigh-speed InGaAs based resonant cavity enhanced photodiodes were discussed. The responses of the photodiodes was measured under high incident optical powers. Bandwidth-efficiency (BWE) product was used to measure the performance of the photodiode. Transfer matrix method was used to design the epilayer structure and to simulate the optical properties of the photodiode. Photo response measurements were carried out in 1450 nm to 1700 nm range using a tungsten-halogen projection lamp as the light source and a single pass monochromator. The deconvolved Fourier transform of the data was found to have a bandwidth of 31 GHz under conditions of 40 GHz limit.Item Open Access High-speed visible-blind resonant cavity enhanced AlGaN Schottky photodiodes(Materials Research Society, 2003) Bıyıklı, Necmi; Kartaloglu, T.; Aytur, O.; Kimukin, I.; Özbay, EkmelWe have designed, fabricated and tested resonant cavity enhanced visible-blind AlGaN-based Schottky photodiodes. The bottom mirror of the resonant cavity was formed with a 20 pair AlN/Al 0.2Ga 0.8N Bragg mirror. The devices were fabricated using a microwave compatible fabrication process. Au and indium-tin-oxide (ITO) thin films were used for Schottky contact formation. ITO and Au-Schottky devices exhibited resonant peaks with 0.153 A/W and 0.046 A/W responsivity values at 337 nm and 350 nm respectively. Temporal high-speed measurements at 357 nm resulted in fast pulse responses with pulse widths as short as 77 ps. The fastest UV detector had a 3-dB bandwidth of 780 MHz.Item Open Access High-speed widely-tunable >90% quantum-efficiency resonant cavity enhanced p-i-n photodiodes(IEEE, 1998) Bıyıklı, Necmi; Kimukin, İbrahim; Aytür, Orhan; Gökkavas, M.; Ulu, G.; Mirin, R.; Christensen, D. H.; Ünlü, M. S.; Özbay, EkmelWidely-tunable high-speed resonant cavity enhanced p-i-n photodiodes were designed, fabricated and tested for operation around 820 nm. The structure was grown by solid-source MBE on GaAs substrates and features high-reflectivity Bragg mirrors made of quarter-wave Al0.20Ga0.80As/AlAs stacks. Photoresponse and photospectral measurements were carried out. The tuning of the resonance wavelength within the Bragg mirror's upper and lower edges was observed. Quantum efficiency greater than 90% was demonstrated.Item Open Access Microcavity enhanced amorphous silicon photoluminescence(IEEE, 1997) Serpengüzel, Ali; Aydınlı, Atilla; Bek, AlpanA microcavity enhancement of room temperature photoluminescence (PL) of a hydrogenated amorphous silicon (a-Si:h) was performed. A quantum confinement model was developed to describe the occurrence of the PL in the bulk a-Si:H. According to the model, small a-Si clusters are in a matrix of a-Si:H. The regions with Si-H, having larger energy gaps due to strong Si-H bonds, isolate these clusters, and form barrier regions around them. The PL originates from these a-Si clusters.Item Open Access Phase-matched self-doubling optical parametric oscillator(IEEE, 1996) Kartaloğlu, Tolga; Köprülü, Kahraman G.; Aytür, OrhanA new self-doubling optical parametric oscillator (OPO) uses a single nonlinear crystal for both parametric generation and frequency doubling. It is based on a KTiOPO4 (KTP) crystal pumped by a Ti:Sapphire laser operating at a wavelength of 739 nm. The crystal is cut such that the signal wavelength of the OPO is at 1064 nm, corresponding to an idler wavelength of 2420 nm. The OPO cavity resonates only the signal wavelength. The signal beam is also phase-matched for second harmonic generation (SHG) at the same crystal orientation. With proper polarization rotation, an output beam at a wavelength of 532 nm can be obtained.Item Open Access Photonic-crystal-based resonant-cavity-enhanced detectors(IEEE, 1998) Temelkuran, Burak; Özbay, Ekmel; Kavanaugh, J. P.; Tuttle, G.; Ho, K. M.A layer-by-layer three-dimensional photonic crystal, with a full photonic bandgap (PBG) in all directions is proposed. The electrical fields in the cavities of this crystal are usually enhanced, and by placing active devices such as resonant cavity enhanced (RCE) photodetectors and light emitting diodes. The RCE effect is demonstrated by placing microwave detectors within localized modes of photonic crystal, along with a monopole antenna. A network analyzer measured the enhanced field. Such RCE detectors are more sensitive and efficient as compared to conventional detectors, and can be used for various applications where sensitivity and efficiency are important parameters.Item Open Access Reflection properties and defect formation in photonic crystals(A I P Publishing LLC, 1996-08-05) Özbay, Ekmel; Temelkuran, B.We have investigated the surface reflection properties of a layer-by-layer photonic crystal. By using a Fabry-Perot resonant cavity analogy along with the reflection-phase information of the photonic crystal, we predicted defect frequencies of planar defect structures. Our predictions were in good agreement with the measured defect frequencies. Our simple model can also predict and explain double defect formation within the photonic band gap.Item Open Access Reflection properties of metallic photonic crystals(1998) Temelkuran, B.; Özbay, Ekmel; Sigalas, M.; Tuttle, G.; Soukoulis, C. M.; Ho, K. M.We measured reflection-magnitude and reflection-phase properties of metallic photonic crystals. The experimental results are in good agreement with the theoretical calculations. We converted the reflection-phase information to an effective penetration depth of the electromagnetic waves into the photonic crystal. This information was then used to predict resonance frequencies of defect structures. A symmetric resonant cavity was built, and an experimental set-up limited reflection magnitude of 80 dB below the incident signal was observed at resonance frequency.Item Open Access Resonant cavity-enhanced detectors embedded in photonic crystals(IEEE, 1996) Temelkuran, Burak; Özbay, EkmelSummary form only given. We demonstrate the resonant-cavity-enhanced effect by placing microwave detectors in a layer-by-layer photonic crystal. We used the output of a network analyzer as the microwave source, and fed the output to a horn antenna to obtain EM waves. The crystal was then replaced in the beam-path of the EM wave, and the electric field inside the cavity was measured by a probe that consisted of a monopole antenna. The output of the antenna was measured by use of two different techniques: network analyzer and microwave detector within the cavity. The first cavity structure was similar to a one-dimensional Fabry-Perot resonator made of two mirrors separated by a distance.