Volume 8,Issue 6,2012 Table of Contents
2012, 8(6):401-404.
Abstract:
Silver nanoparticles (Ag NPs) are synthesized with chemical method, which are introduced into the traditional organic photovoltaic (OPV) structure. The experimental results show that both the optical and photoelectric properties are enhanced because of localized surface plasmon (LSP) effects of Ag NPs. The advantage of adding Ag NPs behind active layer in incident direction is discussed. We believe this route can avoid absorption shadow and enhance the reusing of transmitted light of active layer. The average short-circuit current (J SC) of the optimum device can be raised from 9.23 mA/cm2 to 10.84 mA/cm2, and the energy converting efficiency (PCE) can be raised from 3.22% to 3.85%.
Silver nanoparticles (Ag NPs) are synthesized with chemical method, which are introduced into the traditional organic photovoltaic (OPV) structure. The experimental results show that both the optical and photoelectric properties are enhanced because of localized surface plasmon (LSP) effects of Ag NPs. The advantage of adding Ag NPs behind active layer in incident direction is discussed. We believe this route can avoid absorption shadow and enhance the reusing of transmitted light of active layer. The average short-circuit current (J SC) of the optimum device can be raised from 9.23 mA/cm2 to 10.84 mA/cm2, and the energy converting efficiency (PCE) can be raised from 3.22% to 3.85%.
2012, 8(6):405-408.
Abstract:
We propose a vertical cavity semiconductor emitting laser (VCSEL) using a coupled-cavity (CC) design to broaden the bandwidths of gain and delay spectra. The structure is formed by constructing a passive cavity coupled with the active cavity. By rendering the strength of the two resonant cavities, the increased gain bandwidth by 340% and the increased delay bandwidth by 800% are achieved as compared with the signal-cavity (SC) VCSEL. The wideband spectra present more square-like passband which is expected for slow light system. By using it, a 20 Gbit/s super Gaussian signal is delayed by about 13 ps with high quality.
We propose a vertical cavity semiconductor emitting laser (VCSEL) using a coupled-cavity (CC) design to broaden the bandwidths of gain and delay spectra. The structure is formed by constructing a passive cavity coupled with the active cavity. By rendering the strength of the two resonant cavities, the increased gain bandwidth by 340% and the increased delay bandwidth by 800% are achieved as compared with the signal-cavity (SC) VCSEL. The wideband spectra present more square-like passband which is expected for slow light system. By using it, a 20 Gbit/s super Gaussian signal is delayed by about 13 ps with high quality.
2012, 8(6):409-413.
Abstract:
A calibration board composed of 8 × 8 near-infrared surface-mounted diodes (NIR-SMDs) (940 nm) is designed. Meanwhile, a common binocular measurement system with the average error less than 0.1320 mm is used to obtain the geometric information of this board. A calibration method with the designed pattern is performed to obtain the parameters of the nearinfrared camera (NIRC). In the experiment, the average relative errors of focal length and principal point are 0.244% and 0.735%, respectively. The mean of image residuals is less than 0.01 pixel. The error of three-dimensional (3D) measurement is less than 0.3 mm. All those results indicate that the designed calibration board is suitable and accurate for calibrating NIRC.
A calibration board composed of 8 × 8 near-infrared surface-mounted diodes (NIR-SMDs) (940 nm) is designed. Meanwhile, a common binocular measurement system with the average error less than 0.1320 mm is used to obtain the geometric information of this board. A calibration method with the designed pattern is performed to obtain the parameters of the nearinfrared camera (NIRC). In the experiment, the average relative errors of focal length and principal point are 0.244% and 0.735%, respectively. The mean of image residuals is less than 0.01 pixel. The error of three-dimensional (3D) measurement is less than 0.3 mm. All those results indicate that the designed calibration board is suitable and accurate for calibrating NIRC.
2012, 8(6):414-417.
Abstract:
A fiber Bragg grating strain sensor, whose reflection bandwidth is insensitive to temperature, is presented. The cross-sectional area is designed to change linearly. Under axial stress, there is a linear relationship between stress and average strain. Experimental results show that when temperature increases, reflection center wavelength shifts to longer wavelength, and there is a good linear relationship between center wavelength and temperature. When stress increases, reflection center wavelength shifts to longer wavelength, and reflection bandwidth increases. There are good linear relationships between reflection center wavelength and stress as well as reflection bandwidth and stress.
A fiber Bragg grating strain sensor, whose reflection bandwidth is insensitive to temperature, is presented. The cross-sectional area is designed to change linearly. Under axial stress, there is a linear relationship between stress and average strain. Experimental results show that when temperature increases, reflection center wavelength shifts to longer wavelength, and there is a good linear relationship between center wavelength and temperature. When stress increases, reflection center wavelength shifts to longer wavelength, and reflection bandwidth increases. There are good linear relationships between reflection center wavelength and stress as well as reflection bandwidth and stress.
2012, 8(6):418-421.
Abstract:
We propose a novel all-optical buffer and shaper based on the adjustable power transferring characteristics of the complex-modulated long-period-grating coupler (CM-LPGC) and the multiple circulations of the self-closed fiber loop. By turning on the external optical pumps, the signals can be stored by utilizing the nonreciprocal power transferring of the CM-LPGC. When the buffer time is satisfied, the signals can be extracted discretionarily by turning off the external optical pumps. In addition, by controlling the spectral bandwidth of the CM-LPGC, the temporal rectangular pulse can be obtained by reshaping the Gaussian input signal.
We propose a novel all-optical buffer and shaper based on the adjustable power transferring characteristics of the complex-modulated long-period-grating coupler (CM-LPGC) and the multiple circulations of the self-closed fiber loop. By turning on the external optical pumps, the signals can be stored by utilizing the nonreciprocal power transferring of the CM-LPGC. When the buffer time is satisfied, the signals can be extracted discretionarily by turning off the external optical pumps. In addition, by controlling the spectral bandwidth of the CM-LPGC, the temporal rectangular pulse can be obtained by reshaping the Gaussian input signal.
2012, 8(6):422-425.
Abstract:
We investigate the spatial coherence of the light generated from high-power multi-chip red LEDs by using the van Cittert-Zernike theorem. It is theoretically demonstrated that the light generated from multi-chip LEDs evolves into partially coherent light after propagation, and the spatial coherence is increased with the increase of propagation distance. Moreover, the spatial coherence of the light is found to be closely related to the chip distribution of multi-chip LEDs. The distribution of the spatial coherence of the light is experimentally examined by Young’s double-slit interference. It is found that the experimental results are consistent with the theoretical ones.
We investigate the spatial coherence of the light generated from high-power multi-chip red LEDs by using the van Cittert-Zernike theorem. It is theoretically demonstrated that the light generated from multi-chip LEDs evolves into partially coherent light after propagation, and the spatial coherence is increased with the increase of propagation distance. Moreover, the spatial coherence of the light is found to be closely related to the chip distribution of multi-chip LEDs. The distribution of the spatial coherence of the light is experimentally examined by Young’s double-slit interference. It is found that the experimental results are consistent with the theoretical ones.
2012, 8(6):426-429.
Abstract:
A model based on propagation rate equations is built up for analyzing the multicore transverse mode gain distribution in an 18-core photonic crystal fiber (PCF) laser. The two kinds of feedback cavities are used for the fiber laser, which are the buttcontact mirror and the Talbot cavity. According to the model, the transverse mode competitions in different feedback cavities are simulated numerically. The results show that the Talbot cavity can improve in-phase supermode gain, while suppress other supermodes.
A model based on propagation rate equations is built up for analyzing the multicore transverse mode gain distribution in an 18-core photonic crystal fiber (PCF) laser. The two kinds of feedback cavities are used for the fiber laser, which are the buttcontact mirror and the Talbot cavity. According to the model, the transverse mode competitions in different feedback cavities are simulated numerically. The results show that the Talbot cavity can improve in-phase supermode gain, while suppress other supermodes.
2012, 8(6):430-432.
Abstract:
A tunable thermo-optic intensity-modulated switch is investigated theoretically and numerically. It is based on the infiltration of temperature-sensitive mixture liquids into index-guiding photonic crystal fibers (PCFs). The switching function attributes to the thermo-optic effect of the effective refractive index of the cladding. The simulation illustrates that the switch presents a tunable transition point according to the concentration of the mixture liquids, and the on-off switching functionality can be realized within a narrow temperature range of 2 °C. The switches have wide application for innovative all-in-fiber optical communication and logic devices.
A tunable thermo-optic intensity-modulated switch is investigated theoretically and numerically. It is based on the infiltration of temperature-sensitive mixture liquids into index-guiding photonic crystal fibers (PCFs). The switching function attributes to the thermo-optic effect of the effective refractive index of the cladding. The simulation illustrates that the switch presents a tunable transition point according to the concentration of the mixture liquids, and the on-off switching functionality can be realized within a narrow temperature range of 2 °C. The switches have wide application for innovative all-in-fiber optical communication and logic devices.
2012, 8(6):433-436.
Abstract:
Slowing down velocity and controlling time delay of optical pulses in fiber have many potential applications in optical communication systems, and a number of theoretical and experimental studies have been done. In this paper, the transmission spectrum and reflective spectrum of active fiber Bragg grating (FBG) couplers are studied, and the analytic expressions of dispersion and time delay are obtained. By changing the detuning and gain coefficient, different dispersions and time delays in active fiber Bragg grating coupler are obtained. The results show that different detunings and gain coefficients can result in various time delays, and thus tunable time delay could be achieved by changing signal frequency or gain coefficient.
Slowing down velocity and controlling time delay of optical pulses in fiber have many potential applications in optical communication systems, and a number of theoretical and experimental studies have been done. In this paper, the transmission spectrum and reflective spectrum of active fiber Bragg grating (FBG) couplers are studied, and the analytic expressions of dispersion and time delay are obtained. By changing the detuning and gain coefficient, different dispersions and time delays in active fiber Bragg grating coupler are obtained. The results show that different detunings and gain coefficients can result in various time delays, and thus tunable time delay could be achieved by changing signal frequency or gain coefficient.
2012, 8(6):437-440.
Abstract:
The performance of all-optical logic NXOR gate based on semiconductor optical amplifiers Mach-Zehnder interferometer (SOAs-MZI) is simulated. The effects of amplified spontaneous emission (ASE) and the input pulse energy on the system’s quality factor are studied. For the parameters used, the all-optical logic gates using SOAs are capable of operating at speed of 80 Gbit/s.
The performance of all-optical logic NXOR gate based on semiconductor optical amplifiers Mach-Zehnder interferometer (SOAs-MZI) is simulated. The effects of amplified spontaneous emission (ASE) and the input pulse energy on the system’s quality factor are studied. For the parameters used, the all-optical logic gates using SOAs are capable of operating at speed of 80 Gbit/s.
Zi-hang Zhu
,
Shang-hong Zhao
,
Zhou-shi Yao
,
Qing-gui Tan
,
Yong-jun Li
,
Xing-chun Chu
,
Xiang Wang
,
Gu-hao Zhao
2012, 8(6):441-444.
Abstract:
For the nonlinearity distortion problem of Mach-Zehnder modulator (MZM) applied in the on-board microwave photonics system, the situation for two input radio frequency (RF) signals with different frequencies and phases is discussed, and an exact analytical solution is derived with the method of expanding Bessel series and Graf addition theory. According to the analytical expression, the nonlinearity characteristics of the modulator can be precisely predicted, and the system performance can be optimized. The correctness of the analytical solution is approved by simulation results. Analytical results indicate that the nonlinearity distortion is suppressed as the decrease of modulation index, the increase of direct current bias phase shift and phase difference between two input RF signals. When the phase difference equals zero or π and the direct current bias phase shift is π/2, there are only odd-order distortion terms. When the phase difference equals zero or π and the direct current bias phase shift is π, there are only even-order distortion terms.
For the nonlinearity distortion problem of Mach-Zehnder modulator (MZM) applied in the on-board microwave photonics system, the situation for two input radio frequency (RF) signals with different frequencies and phases is discussed, and an exact analytical solution is derived with the method of expanding Bessel series and Graf addition theory. According to the analytical expression, the nonlinearity characteristics of the modulator can be precisely predicted, and the system performance can be optimized. The correctness of the analytical solution is approved by simulation results. Analytical results indicate that the nonlinearity distortion is suppressed as the decrease of modulation index, the increase of direct current bias phase shift and phase difference between two input RF signals. When the phase difference equals zero or π and the direct current bias phase shift is π/2, there are only odd-order distortion terms. When the phase difference equals zero or π and the direct current bias phase shift is π, there are only even-order distortion terms.
2012, 8(6):445-448.
Abstract:
ZnO/diamond-like carbon (DLC) thin films are deposited by pulsed laser deposition (PLD), and the room-temperature photoluminescence (PL) is investigated. Using a fluorescence spectrophotometer, we obtain the PL spectra of DLC/Si and ZnO/Si thin films deposited at different substrate temperatures. The ZnO/DLC thin films show a broadband emission almost containing the entire visible spectrum. The Gaussian fitting curves of PL spectra reveal that the visible emission of ZnO/DLC thin films consists of three peaks centered at 381 nm, 526 nm and 682 nm, which are attributed to the radiative recombination of ZnO and DLC, respectively. The Commission International de l’Eclairage (CIE) 1931 (x, y) chromaticity space of ZnO/DLC thin films indicates that the visible PL spectrum is very close to the standard white-light region.
ZnO/diamond-like carbon (DLC) thin films are deposited by pulsed laser deposition (PLD), and the room-temperature photoluminescence (PL) is investigated. Using a fluorescence spectrophotometer, we obtain the PL spectra of DLC/Si and ZnO/Si thin films deposited at different substrate temperatures. The ZnO/DLC thin films show a broadband emission almost containing the entire visible spectrum. The Gaussian fitting curves of PL spectra reveal that the visible emission of ZnO/DLC thin films consists of three peaks centered at 381 nm, 526 nm and 682 nm, which are attributed to the radiative recombination of ZnO and DLC, respectively. The Commission International de l’Eclairage (CIE) 1931 (x, y) chromaticity space of ZnO/DLC thin films indicates that the visible PL spectrum is very close to the standard white-light region.
2012, 8(6):449-452.
Abstract:
Based on the ion beam sputtering deposition technology, ZnO thin films are deposited on the glass substrate. The four-factor and three-level L9(34) orthogonal experiment is used to obtain the best technological parameters of the deposited ZnO thin films, which are the discharge voltage of 3.5 kV, the oxygen current capacity of 8 sccm, the coil current of 8 A and the distance between target and substrate of 140 mm. The purity of the deposited ZnO thin film is 85.77%, and it has good crystallization in orientation. The experimental results show that research and development of the ion beam sputtering source are advanced, and the ion beam sputtering deposition technology can be used to deposit the orientation preferred thin films with good performance.
Based on the ion beam sputtering deposition technology, ZnO thin films are deposited on the glass substrate. The four-factor and three-level L9(34) orthogonal experiment is used to obtain the best technological parameters of the deposited ZnO thin films, which are the discharge voltage of 3.5 kV, the oxygen current capacity of 8 sccm, the coil current of 8 A and the distance between target and substrate of 140 mm. The purity of the deposited ZnO thin film is 85.77%, and it has good crystallization in orientation. The experimental results show that research and development of the ion beam sputtering source are advanced, and the ion beam sputtering deposition technology can be used to deposit the orientation preferred thin films with good performance.
2012, 8(6):453-455.
Abstract:
Pr3+ and Yb3+ co-doped phosphate glasses are prepared to study their optical properties. Excitation and emission spectra and decay curves are used to characterize their luminescence. We demonstrate that upon excitation of Pr3+ ion with one high energy photon at 470 nm, two near-infrared (NIR) photons are emitted at 950 1100 nm (Yb3+:2F5/2→2F7/2) through an efficient cooperative energy transfer (CET) from Pr3+ to Yb3+. The maximum energy transfer efficiency (ETE) and the corresponding quantum efficiency approach up to 90.17% and 190.17%, respectively. The glass materials might find potential application for improving the efficiency of silicon-based solar cells.
Pr3+ and Yb3+ co-doped phosphate glasses are prepared to study their optical properties. Excitation and emission spectra and decay curves are used to characterize their luminescence. We demonstrate that upon excitation of Pr3+ ion with one high energy photon at 470 nm, two near-infrared (NIR) photons are emitted at 950 1100 nm (Yb3+:2F5/2→2F7/2) through an efficient cooperative energy transfer (CET) from Pr3+ to Yb3+. The maximum energy transfer efficiency (ETE) and the corresponding quantum efficiency approach up to 90.17% and 190.17%, respectively. The glass materials might find potential application for improving the efficiency of silicon-based solar cells.
2012, 8(6):456-459.
Abstract:
Super-broadband near-infrared (NIR) emission from 1100 nm to 1600 nm is observed in Bi-doped titanate glasses at the excitation of 808 nm laser diode (LD). The effects of Bi content on the optical spectra are investigated. It is also found that the Bi-related emission intensity can be enhanced by Yb3+ co-doping at the excitation of 980 nm LD. It should be ascribed to the energy transfer from Yb3+ to active Bi ions. The energy transfer processes are studied based on the Inokuti-Hirayama (I-H) model, and the energy transfer of electric dipole-dipole interaction is confirmed to be dominant in Bi/Yb co-doped glasses.
Super-broadband near-infrared (NIR) emission from 1100 nm to 1600 nm is observed in Bi-doped titanate glasses at the excitation of 808 nm laser diode (LD). The effects of Bi content on the optical spectra are investigated. It is also found that the Bi-related emission intensity can be enhanced by Yb3+ co-doping at the excitation of 980 nm LD. It should be ascribed to the energy transfer from Yb3+ to active Bi ions. The energy transfer processes are studied based on the Inokuti-Hirayama (I-H) model, and the energy transfer of electric dipole-dipole interaction is confirmed to be dominant in Bi/Yb co-doped glasses.
16 Preparation and characteristics of Nb-doped indium tin oxide thin films by RF magnetron sputtering
2012, 8(6):460-463.
Abstract:
Niobium-doped indium tin oxide (ITO:Nb) thin films are fabricated on glass substrates by radio frequency (RF) magnetron sputtering at different temperatures. Structural, electrical and optical properties of the films are investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), ultraviolet-visible (UV-VIS) spectroscopy and electrical measurements. XRD patterns show that the preferential orientation of polycrystalline structure changes from (400) to (222) crystal plane, and the crystallite size increases with the increase of substrate temperature. AFM analyses reveal that the film is very smooth at low temperature. The root mean square (RMS) roughness and the average roughness are 2.16 nm and 1.64 nm, respectively. The obtained lowest resistivity of the films is 1.2×10?4Ω·cm, and the resistivity decreases with the increase of substrate temperature. The highest Hall mobility and carrier concentration are 16.5 cm2/V·s and 1.88×1021cm?3, respectively. Band gap energy of the films depends on substrate temperature, which is varied from 3.49 eV to 3.63 eV.
Niobium-doped indium tin oxide (ITO:Nb) thin films are fabricated on glass substrates by radio frequency (RF) magnetron sputtering at different temperatures. Structural, electrical and optical properties of the films are investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), ultraviolet-visible (UV-VIS) spectroscopy and electrical measurements. XRD patterns show that the preferential orientation of polycrystalline structure changes from (400) to (222) crystal plane, and the crystallite size increases with the increase of substrate temperature. AFM analyses reveal that the film is very smooth at low temperature. The root mean square (RMS) roughness and the average roughness are 2.16 nm and 1.64 nm, respectively. The obtained lowest resistivity of the films is 1.2×10?4Ω·cm, and the resistivity decreases with the increase of substrate temperature. The highest Hall mobility and carrier concentration are 16.5 cm2/V·s and 1.88×1021cm?3, respectively. Band gap energy of the films depends on substrate temperature, which is varied from 3.49 eV to 3.63 eV.
2012, 8(6):464-467.
Abstract:
An approach of multiple-frequency millimeter-wave (mm-wave) signal generation is proposed for radio-over-fiber (RoF) system with multiple-frequency basestations (MFBSs). Two groups of orthogonally polarized signals are injected into a semiconductor optical amplifier (SOA), and subsequently ten new different wavelengths are generated via four-wave mixing (FWM) effect. At each MFBS, different wavelengths are filtered out using demultiplexer and then input to a photodiode (PD) to generate the mm-wave signals with the frequencies from 52 GHz to 68 GHz at the interval of 2 GHz. Simulation results verify that the proposed multiple-frequency generation for MFBS RoF system can work properly.
An approach of multiple-frequency millimeter-wave (mm-wave) signal generation is proposed for radio-over-fiber (RoF) system with multiple-frequency basestations (MFBSs). Two groups of orthogonally polarized signals are injected into a semiconductor optical amplifier (SOA), and subsequently ten new different wavelengths are generated via four-wave mixing (FWM) effect. At each MFBS, different wavelengths are filtered out using demultiplexer and then input to a photodiode (PD) to generate the mm-wave signals with the frequencies from 52 GHz to 68 GHz at the interval of 2 GHz. Simulation results verify that the proposed multiple-frequency generation for MFBS RoF system can work properly.
Aftab Hussain
,
Xiang-jun Xin
,
Abdul Latif
,
Ashiq Hussain
,
Chong-xiu Yu
,
Abid Munir
,
Yousaf Khan
,
Muhammad Idrees Afridi
2012, 8(6):468-472.
Abstract:
We propose the single feeder fiber architecture for wavelength division multiplexing passive optical network (WDM-PON) based on directly modulated chirp managed laser (CML). The downlink (DL) signal output from the laser is converted to return-to-zero (RZ) differential phase shift signal using a pulse carver. The downstream signal is reused as a carrier for the upstream using intensity modulation technique. Simulation results show the error-free performance at symmetric data rate of 10 Gbit/s per channel with negligible power penalty and improved receiver sensitivity for the uplink (UL), over 25 km standard single-mode fiber (SSMF). A low-cost and reduced circuitry network design is implemented on a single feeder fiber with the elimination of differential encoder and one external modulator.
We propose the single feeder fiber architecture for wavelength division multiplexing passive optical network (WDM-PON) based on directly modulated chirp managed laser (CML). The downlink (DL) signal output from the laser is converted to return-to-zero (RZ) differential phase shift signal using a pulse carver. The downstream signal is reused as a carrier for the upstream using intensity modulation technique. Simulation results show the error-free performance at symmetric data rate of 10 Gbit/s per channel with negligible power penalty and improved receiver sensitivity for the uplink (UL), over 25 km standard single-mode fiber (SSMF). A low-cost and reduced circuitry network design is implemented on a single feeder fiber with the elimination of differential encoder and one external modulator.
2012, 8(6):473-476.
Abstract:
2012, 8(6):477-480.
Abstract:
The temperature and LO phonon effects of the bipolaron in polar semiconductor quantum dots (QDs) are studied by using the Tokuda modified linear-combination operator method and the Lee-Low-Pines variational method. The expressions for the mean number of LO phonons and the effective mass of the bipolaron are derived. Numerical results show that the mean number of LO phonons of the bipolaron decreases with increasing the temperature and the relative distance r between two electrons, but increases with increasing the electron-phonon coupling strength α. The effective mass of the bipolaron M* increases rapidly with increasing the relative distance r between two electrons when r is smaller, and it reaches a maximum at r ≈ 4.05r p, while after that, M* decreases slowly with increasing r. The effective mass of the bipolaron M* decreases with increasing the temperature. The electron-phonon coupling strength markedly influences the changes of mean number of LO phonons and the effective mass M* with the relative distance r and the temperature parameter γ.
The temperature and LO phonon effects of the bipolaron in polar semiconductor quantum dots (QDs) are studied by using the Tokuda modified linear-combination operator method and the Lee-Low-Pines variational method. The expressions for the mean number of LO phonons and the effective mass of the bipolaron are derived. Numerical results show that the mean number of LO phonons of the bipolaron decreases with increasing the temperature and the relative distance r between two electrons, but increases with increasing the electron-phonon coupling strength α. The effective mass of the bipolaron M* increases rapidly with increasing the relative distance r between two electrons when r is smaller, and it reaches a maximum at r ≈ 4.05r p, while after that, M* decreases slowly with increasing r. The effective mass of the bipolaron M* decreases with increasing the temperature. The electron-phonon coupling strength markedly influences the changes of mean number of LO phonons and the effective mass M* with the relative distance r and the temperature parameter γ.
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