At present, there are many problems such as high cost and high pollution in fabrication methods of anti-reflective structures on silicon surfaces. To solve this problem, the utilization of nanosecond pulse infrared laser processing technology is proposed to realize the fabrication of anti-reflective structures on silicon surfaces. Compared with polished silicon, the reflectance of the silicon surface with the anti-reflective structure can be reduced by 89% in the visible light band. In order to unfold the anti-reflection mechanism of the black silicon substrate and optimize the structures, finite difference time domain (FDTD) is adopted to simulate the anti-reflective conical structure with tunable aspect ratios and generate the corresponding reflectance spectrums. To optimize the aspect ratio of silicon surface structure, the processing parameters of nanosecond pulse infrared laser are investigated, which not only realizes the morphology control of the surface structure but also optimizes the anti-reflective performance of the silicon surface. The result shows that the reflectance of the silicon surface is reduced to 3.87% in the visible light band by the anti-reflective structure fabricated by nanosecond pulse infrared laser processing. Also, the variation of aspect ratio of the structure could be monitored and predicted by acoustic signal detection technique. This detection technique provides potential applications in structural integrity monitoring during the fabrication process.
In this work, superwetting alumina coating was coated onto flexible copper mesh by one-step laser cladding treatment. In order to understand the formation mechanism of microstructured coating, the dynamic temperature field distribution during laser cladding is investigated by establishing a three-dimensional finite element simulation model based on the transient thermal analysis method. As the heat source moves, the temperature of the substrate surface increases from room temperature to over 660℃, allowing the aluminum to reach its melting point where melting occurs on the substrate surface. The effect of laser power on the distribution of alumina nanoparticles deposited on copper mesh was further investigated in consideration of temperature field distribution. When the laser power was increased to 1.2 times the initial power, the maximum temperature of the cladding layer increased to about 1930℃, which facilitated the formation of smaller size nanoparticles. It was found that the as-prepared substrate transits from hydrophobicity in air with WCA~125 ° to superhydrophilicity in air with WCA near 0°, while turning oleophobicity with OCA 110°to superoleophobicity with OCA~160°underwater. Oil/water separation was performed on as-prepared superwetting alumina coating coated copper meshes to reveal the enhancement mechanism behind.
Automatic detection of fabric defects is an important process in the textile industry, which is required to locate and classify microdefects from a large fabric image. We propose a learning-based system for automatic detection of microfabric defects. A segmentation algorithm based on fractal and gray features is applied to extract microdefect regions. Gabor fractal network is designed to further improve identification ability of this approach. The proposed network achieves superior performance in terms of detection accuracy with a much smaller model size. The best testing accuracy rates on dark line, hole, broken yarn, and dirt are 96.9%, 98.0%, 92.9%, and 98.8%, respectively. Experimental results demonstrate the effectiveness of the proposed scheme in defect detection for microfabrics. The proposed system has great potential for automatic detection of microfabric defects.
Metal nanoparticles fabricated from chemical methods exhibit various excellent properties with their unique physicochemical properties and structures. To address the problems of the complicated manufacturing process and the side products generation, laser ablation in aqueous environment is proposed as a facile and environment friendly method to fabricate nanoparticles, producing very limited impurities. Ag, TiO2 and Ag/TiO2 composite nanoparticles are fabricated under the irradiation of pulsed laser with surfactant dodecyl trimethyl ammonium bromide (DTAB) as the stabilizer. Assembly shape of surfactants could be tuned by controllable concentrations, resulting in different nanostructures of nanoparticles. The laser processing parameters and the stabilizer showed collaborative effect on the morphology design of metal colloid nanoparticles. SEM images showed different morphologies of Ag nanoparticles and evenly distributed TiO2 nanoparticles are obtained. Typical silver crystals and rutile titanium dioxide crystals was characterized by XRD patterns. The UV-visible spectrum reflected the effects of Ag nanoparticles synthesized under different concentrations of DTAB on the absorption wavelengths of silver and titanium dioxide composites.
We propose a photonic crystal dual-resonant microcavity and waveguide-coupled temperature sensor structure. The resonant characteristics of photonic crystal microcavities are simulated by finite-difference time-domain method. Due to the positive thermo-optic effect of silicon and the negative thermo-optic effect of SU-8 photoresist, a resonant wavelength shift is detected for temperature sensing in the opposite direction, which significantly improves the sensitivity of the sensor. Simulation results highlight that the sensitivity of the temperature sensor is 124.69 pm / ° C, the temperature measuring range is ∼150 ° C, and the limitation of the temperature sensing area is reduced. The sensor can be integrated to lab-on-chip and system-on-chip to achieve real-time temperature measurement in different microregions.
Early detection of knee osteoarthritis (KOA) is meaningful to delay or prevent the onset of osteoarthritis. In consideration of structural complexity of knee joint, position of light incidence and detector appears to be extremely important in optical inspection. In this paper, the propagation of 780-nm near infrared photons in three-dimensional knee joint model is simulated by Monte Carlo (MC) method. Six light incident locations are chosen in total to analyze the influence of incident and detecting location on the number of detected signal photons and signal to noise ratio (SNR). Firstly, a three-dimensional photon propagation model of knee joint is reconstructed based on CT images. Then, MC simulation is performed to study the propagation of photons in three-dimensional knee joint model. Photons which finally migrate out of knee joint surface are numerically analyzed. By analyzing the number of signal photons and SNR from the six given incident locations, the optimal incident and detecting location is defined. Finally, a series of phantom experiments are conducted to verify the simulation results. According to the simulation and phantom experiments results, the best incident location is near the right side of meniscus at the rear end of left knee joint and the detector is supposed to be set near patella, correspondingly.
Low contrast and non-uniform illumination of infrared (IR) meibography images make the detection of meibomian glands challengeable. An improved Mask dodging algorithm is proposed. To overcome the shortage of low contrast using traditional Mask dodging method, a scale factor is used to enhance the image after subtracting background image from an original one. Meibomian glands are detected and the ratio of the meibomian gland area to the measurement area is calculated. The results show that the improved Mask algorithm has ideal dodging effect, which can eliminate non-uniform illumination and improve contrast of meibography images effectively.
A monolithic optical receiver fabricated in standard 0.5μm CMOS process is presented. The fingered doublephotodetector
with structure of P+/N-well and N-well/P-substrate is designed. Some critical characteristics of doublephotodetector
are analyzed in detail. At 2.5V reverse voltage, the maximum dark current is 10 pA. The intrinsic cut-off
frequency is above 100MHz. The measured and simulated responsivity is 0.04A/W and 0.03A/W at 850nm wavelength,
respectively. In the testing of double-photodetector, the minimum and maximum of rise time is 2.67ns and 7.11ns while
the minimum and maximum of fall time is 2.67ns and 31.78ns. A Spice model of DPD is established for the compatibledesign
of OEIC. In simulation of pre-amplifier circuit, the pass-band gain is approximate 18.8 KΩ. The lower cut-off
frequency is 7KHz while the upper cut-off frequency is 700MHz. The simulated eye diagram of OEIC at 100Mbps is
featured of clear trace, wide eye-opening and small zero-crossing distortion. The small signal bandwidth of OEIC is
about 54MHz. The eye diagram at 50Mbps and 250Mbps has some distortion due to direct current malajustment. In the
point-to-point optical interconnection, the transmission bit rate of 72Mbps is achieved. The monolithic optical receiver
can be applied in 10M/100Mbps optical data transmission.
The shape and energy distribution of laser beam directly define its applications in laser processing. In order to cater for
different laser processing requirements, the input beam always needs to be transformed. The transformation between the
solid beam and ring beam can be realized by the axicon-based optical devices. A beam transformation optical system,
which uses a pair of positive axicon and negative axicon is designed and analyzed. The novelty of the optical system is
not only that they can focus the laser beam on a ring pattern or solid beam pattern, but also that they can change the
diameter of patter easily by adjusting the separation of the two conical lenses. The optical system is analyzed based on
the geometry optical theory. By adjusting the separation of the convergent conical lens and the divergent conical lens,
different shapes and the energy distributions are gained. At last, a measurement method of the beam profile is introduced
which based on charge coupled device (CCD) The results show that the axicon-based beam transformations raise the
effectiveness of laser and have a wide application prospect in laser processing field.
A novel scheme is proposed to achieve all-optical SPM-based wavelength conversion in a bismuth oxide-based highly
nonlinear photonic crystal fiber. It consists of erbium-doped fiber amplifier, optical circulator, Fiber Fabry-Perot filters,
photonic crystal fiber and fiber Bragg grating. Owing to SPM, a recirculating configuration is designed to induce the
further spectral broadening and wavelength conversion is achieved with a tunable Fiber Fabry-Perot filter. The
simulation results of bismuth oxide-based photonic crystal fiber indicate that the effective index of the fundamental
mode increases monotonically with the increase in the hole pitch, or the decrease in the ratio of the hole diameter to the
hole pitch. The mode effective area steadily increases with the hole pitch. The nonlinear coefficient, which is beneficial
to shorten the fiber length and reduce the required optical power, is expected to be 1100W-1km-1 by using bismuth
oxide-based glass with high nonlinear refractive index and reducing the effective core area with holey microstructure.
The mode-field diameter of bismuth oxide-based is estimated to be 1.98μm and the predicted small effective core area is
3.3μm2. The propagation loss at 1550nm is about 0.8dB/m. The obtained results show that SPM-based PCF-WC has a
potential of wide conversion bandwidth, high response time, simple configuration and low insertion loss etc.
A simple architecture of all-optical wavelength conversion in a highly nonlinear bismuth oxide-based photonic crystal
fiber (PCF) is proposed, which consists of an erbium-doped fiber amplifier, a polarization controller, a nonlinear medium
PCF, two tunable fiber Fabry-Perot filters and an optical isolator. Self-phase modulation is utilized to induce spectral
broadening for all-optical wavelength conversion. The desired dispersion properties can be tailored by the parameters of
bismuth oxide-based PCF microstructure. The propagation loss at 1550nm is about 0.8dB/m. The nonlinear coefficient is
expected to be 1100W-1km-1 by using bismuth oxide-based glass and reducing the effective core area. The mode-field
diameter of PCF is estimated to be 1.98μm and the predicted effective core area is 3.3μm2. The intermediate high
numerical aperture fibers between bismuth oxide-based PCF and single-mode fibers are considered to reduce the splicing
loss. The obtained results show that the all-optical wavelength converter has a potential of high conversion efficiency,
wide conversion bandwidth, ultrafast response time, compact configuration and low insertion loss etc.
A basic scheme of the polarization insensitive four-wave-mixing all-optical wavelength conversion with a copolarization
dual-pump configuration in a highly nonlinear photonic crystal fiber (PCF) is demonstrated. With two fiber Bragg
Gratings and a Faraday rotator mirror, both the pumps and the signal make a dual pass through a highly nonlinear PCF.
The rotation of the signal polarization by the Faraday rotator mirror guarantees that both orthogonal polarization
components of the signal will efficiently mix with the two pumps to produce a polarization-insensitive multi-wavelength
conversion. The design and simulation of the bismuth oxide-based PCF indicate that the desired dispersion properties can
be tailored by the geometrical parameters of PCF microstructure. The propagation loss at 1550nm is about 0.8dB/m. The
nonlinear coefficient is expected to be 1100W-1km-1 by using bismuth oxide-based glass and reducing the effective core
area. The mode-field diameter of PCF is estimated to be 1.98μm and the predicted effective core area is 3.3μm2. The
polarization insensitive four-wave-mixing wavelength converter with copolarization dual-pump configuration shows the
small polarization sensitivity, the high conversion efficiency and the simultaneous multi-wavelength conversion.
A novel architecture of all-optical wavelength conversion in a highly nonlinear bismuth oxide-based photonic crystal
fiber (PCF) is demonstrated. Self-phase modulation is utilized to induce spectral broadening for the all-optical
wavelength converter. A recirculating configuration is designed to obtain the twice spectral broadening. Therefore,
wavelength conversion is achieved. The design and the simulation of PCF are demonstrated. The desired dispersion
properties can be tailored by the parameters of bismuth oxide (Bi2O3) PCF microstructure. The propagation loss at
1550nm is about 0.8dB/m. The simulation results of PCF indicate the relationship of the effective index of the
fundamental mode, the mode effective area and the holes pitch of PCF. The nonlinear coefficient is expected to be
1100W-1km-1 by using bismuth oxide-based glass and reducing the effective core area. The mode-field diameter of PCF
is estimated to be 1.98μm and the predicted small effective core area is 3.3μm2. The design of Bi2O3-based PCF and the
intermediate high numerical aperture fibers between Bi2O3-based PCF and single-mode fibers are considered to reduce
the splicing loss. The obtained results show that the wavelength converter has a potential of wide conversion bandwidth,
high response time, simple configuration and low insertion loss etc.
A novel high-speed magneto-optic (MO) modulator which consists of an integrated wire grid polarizer (WGP), Bi-YIG
waveguide with cladding layer and conducting micro-strip line is proposed. With the integrated WGP, this MO
modulator is faster, more accurate and more stable because it is not only completely driven by electric signals but also
has no mechanically moving parts. Moreover, it is compact-structured and low-cost. Large Faraday rotation is obtained
with specific arrangement of the directions of the bias magnetic field and the modulation RF magnetic field. Optical
route and optic-electrical detect circuit are also designed and analyzed.
All-optical wavelength converters (AOWCs) are considered to be important components in future wavelength-division-multiplexed
(WDM) networks. Cross gain modulation schemes in semiconductor optical amplifiers (SOA) are promising
candidates for an all-optical wavelength conversion application due to the simple implementation and effective
conversion. However, the slow gain recovery time of SOA limits the maximum operation speed and causes unwanted
pattern effects. This paper provides a novel scheme for wavelength conversion enables ultra-fast conversion speed. On
the one hand, we utilize a three-wavelength-device (TWD) to reduce the recovery time of the SOA. On the other hand,
we use an optical band pass filter (OBF) which central wavelength is blue shifted with respect to the central wavelength
of the probe beam to increase the frequency response. The combination of a reduction of the SOA recovery time and an
increase of the frequency response enables conversion speed potentially to achieve 160 Gb/s or even faster.
In this paper, we demonstrated for the first time variable 1.5μm wavelength conversion through cascaded second order
nonlinear processes "SHG+DFG" by fan-out grating in lithium niobate waveguide. We fabricated the waveguide by
annealed proton exchange in periodically poled LiNbO3 (PPLN). The device used in this experiment is 4 cm long, has a
QPM period from 14.8μm to 15.2μm, waveguide width of 12μm, proton exchange depth of 0.7μm, and was annealed for
32h at 350°C. After proton exchange in pure benzoic acid using a SiO2 mask, the substrate was annealed in an oxygen
atmosphere. The wavelength of signal light was set at 1551.3 nm. The wavelengths of tunable pump lights we used in
experiment were 1543.2 and 1556.2 nm, and the corresponding grating periods were 14.87 μm and 15.03 μm,
respectively. The temperature was set at 100.5°C to avoid photo refractive damage and to match the QPM peaks to the
pump wavelengths. The conversion efficiency was about 10dB to be expected with the pump power 175mW in a similar
device with a slightly different QPM period and operated at 125°C.
KEYWORDS: Waveguides, Signal processing, Wavelength division multiplexing, Modulation, Optical amplifiers, Switching, Signal detection, Signal attenuation, Data conversion, L band
In this paper, we proposed a variable operation of a DC-OFS based on double SFG+DFG (Double-SFG+DFG-OFS)
nonlinearity process for the first time. We studied the principle and configuration of three DC-OFS in detail both
theoretically and experimentally. In order to compare with Double-DFG-OFS and Double-SHG+DFG-OFS, we also
used two four-channel-controlling multiple-quasi-phase-matched LiNbO3 wavelength converters and got ten different
outputs spreading across a wavelength range of as broad as 35 nm by changing the combination of two controlling
wavelengths of the two wavelength converters. And one channel signal was converted to shorter and longer wavelength
and the same wavelength by changing the controlling wavelengths. We got higher conversion efficiency compared with
the other two DC-OFSs mentioned above. We used novel M-QPM-LN wavelength converters having a continuously-phase-
modulated domain structure, which can be operated by multiple pump wavelengths with minimum loss of
efficiency. The periods were 14.8μm. The phase of the periodic poling was continuously modulated to satisfy the QPM
condition at four different wavelengths. The frequency spacing of control signal-b is twice as large as the control signal-a.
The operating temperatures were 102.5 and 100.5 C for the first and the second QPM-LN wavelength converters,
respectively.
All-optical wavelength converters (AOWCs) that utilize nonlinearities in semiconductor optical amplifiers (SOAs) have
attracted considerable research interest. AOWCs based on cross gain modulation (XGM) have a large dynamic range of
the input optical signal power but a low extinction ratio (ER) and a high chirp, whereas AOWCs based on cross phase
modulation (XPM) provide a low chirp and a high ER but suffer from a relative small input power dynamic range. We
point out that there seems to be some complementarity between XGM and XPM. Based on this, we propose a novel
scheme for cascaded wavelength conversion based on cross gain modulation and cross phase modulation in SOAs thus is
expected to have a high ER and a large input power dynamic range simultaneously. The wavelength conversion
operation includes two stages, that is, XGM in the first stage followed by the stage of XPM. In the XGM stage, we use a
band pass filter to increase the frequency response of the SOA. In the XPM, we use the bidirectional input scheme for
MZI to improve the response of XPM and cancel XGM-induced intensity unbalance to get a relative perfect interference.
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