Likarn Wang - Academia.edu (original) (raw)

Papers by Likarn Wang

IEEE Sensors Journal

The method of hierarchical clustering is for the first time employed to locate the intrusion-indu... more The method of hierarchical clustering is for the first time employed to locate the intrusion-induced disturbance on the sensing fibers of a dual Mach-Zehnder interferometer (DMZI). Such an intrusion-induced disturbance is located by finding the x coordinate of the centroid of the largest cluster on the Euclidean plane through hierarchical clustering with an appropriate linkage criterion employed for determining the distance between two observations. We compare average linkage and complete linkage criteria in the clustering analysis to see which one provides better locating accuracy. In the clustering analysis, the number of clusters is set to be 3-8 in finding the location of disturbance. To reduce the locating error, we also use differential signals here in the clustering analysis. Twelve intrusion events are simulated by knocking the sensing fibers to induce disturbances at a given location. The location of disturbance is determined through the clustering analysis for each intrusion event. The mean of the absolute values of locating errors [mean absolute error (MAE)] for the 12 intrusion events is then estimated. The experimental results in this study demonstrate a maximum MAE of 11.55 m in locating an intrusion with average linkage criterion employed for five-cluster analysis. Also, the MAE could be 3.55 m smaller by using the differential signals for clustering analysis, compared with the case when directly detected signals are used for clustering analysis. The results also confirm that the average linkage criterion provides only a small amount of improvement in MAE over complete linkage criterion. Index Terms-Average linkage criterion, complete linkage criterion, dual Mach-Zehnder interferometer (DMZI), fiberoptic intrusion detection, hierarchical clustering, positioning accuracy. I. INTRODUCTION T WO kinds of fiber intrusion detection techniques have been widely studied for detecting and locating the disturbance on the sensing fiber. One kind is to detect and locate the disturbance-induced phase variation in Rayleigh backscattered light employing the optical time-domain interferometer-based technique [1], [2], [3], [4], [5]. Meanwhile, optical interferometers have also been studied for the purpose of intrusion detection. A Sagnac loop

Journal of Renewable and Sustainable Energy, 2021

We present a new, simple and cost-effective etching method for forming inverted pyramid-like stru... more We present a new, simple and cost-effective etching method for forming inverted pyramid-like structures on the surfaces of single-crystalline diamond-wire sawn silicon wafers. The method follows a three-step process for etching silicon wafers without metal-assisted chemical etching involved. We used acidic etching to produce nano-to-micro-structured caves in the first two steps followed by anisotropic etching with an alkaline solution. This paper shows that the size of the opening of the inverted pyramid could vary from several hundred nanometers to about 4 μm, depending on the etch time periods in the second and the third steps. The cell performance was, however, only evaluated here for cases of smaller sizes of inverted pyramids. That is, solar cells were manufactured following an almost commercially standard procedure by using wafers with inverted pyramids of ~900 nm in size. The best cell with this type of structure has a conversion efficiency of 19.22%, which is higher relative to the cells with smaller inward recessed caves or upright pyramids on the surfaces. ________________________________________________________________________________ I. INTRODUCTION P-type silicon solar cells with PERC(passivated emitter and rear cell) structures have been well developed 1 and reached > 21 % in industry at the end of 2018. 2 And recently, a world record for full-cell size commercial p-mono PERC cells at > 24% has been reported. 3 Nowadays, studies of modulating surface morphology to enhance the performances of crystalline silicon solar cells have achieved some progresses, and such a topic has attracted much attention. Chen et al. used a simple pre-polishing step with TMAH priori to a routine alkaline texture process to form pyramid structures on the surfaces of diamond-wire sawn silicon wafers, demonstrating similar cell performances to those of traditional multi-wire-slurry-sawn solar cells. 4 Much attention has been paid to formation of inverted pyramids, because a silicon surface with inverted pyramids can have a 1 to 2 % lower light reflectivity compared with that with regular pyramids. 5 In earlier times, a photolithographic process was used to form inverted pyramids on the front surfaces of silicon solar cells and to obtain 24.7% cell efficiency. 6 A mass-production method for forming inverted pyramids is required yet by solar cell manufacturers. Many research works for forming inverted pyramids have been studied then. A method of metal catalyzed chemical etching (MCCE) followed by a post nano structure rebuilding treatment 7 was developed for forming inverted pyramids on the surface of multicrystalline silicon wafer, producing a low reflectivity of 3.29% over the band

International Journal of Photoenergy, 2020

We present a method of ozonation to form the rear-side passivation layers of crystalline silicon ... more We present a method of ozonation to form the rear-side passivation layers of crystalline silicon PERC cells. In the method, a thin aluminum film was deposited on the back surface of a silicon wafer and then was oxidized into an aluminum oxide layer by gaseous ozone. Lifetimes of the wafers with such passivation layers proved to be increased with respect to those untreated, and the resultant PERC cells showed a performance improvement compared with standard cells with full back surface fields.

International Journal of Photoenergy, 2013

A new method for fabricating crystalline silicon solar cells with selective emitters is presented... more A new method for fabricating crystalline silicon solar cells with selective emitters is presented. In this method, shallow trenches corresponding to metal contact area are first formed by screen printing and chemical etching, followed by heavy doping over the whole front surface of the silicon wafer. After a polymer mask is pasted by aligned screen-printing to cover the shallow trenches, the silicon wafer is etched such that the heavy doping remains at the shallow trench area, while other areas become lightly doped. With the presented method, two screening printing steps are required for obtaining a selective emitter structure on a solar wafer. Compared with existing etch-back methods, the presented one is believed to be able to easily conform with present industrial process. Experimental results show that optical responses at the short and long wavelengths were both improved by applying the proposed selective emitter technique to fabricate solar cells with an a-Si:H film deposited ...

Nanoscale Research Letters, 2014

We present a method to couple surface plasmon polariton (SPP) guiding mode into dielectric-loaded... more We present a method to couple surface plasmon polariton (SPP) guiding mode into dielectric-loaded SPP waveguide (DLSPPW) devices with spectral and mode selectivity. The method combined a transmission-mode near-field spectroscopy to excite the SPP mode and a leakage radiation optical microscope for direct visualization. By using a near-field fiber tip, incident photons with different wavelengths were converted into SPPs at the metal/dielectric interface. Real-time SPP radiation images were taken through leakage radiation images. The wavelength-dependent propagation lengths for silver- and gold-based DLSPPWs were measured and compared. It confirms that silver-based SPP has a propagation length longer than a gold-based one by 1.25, 1.38, and 1.52 times for red, green, and blue photons. The resonant coupling as a function of wavelength in dual DLSPPWs was measured. The coupling lengths measured from leakage radiation images were in good agreement with finite-difference time domain simul...

International Journal of Photoenergy, 2014

We demonstrate the performance improvement of p-type single-crystalline silicon (sc-Si) solar cel... more We demonstrate the performance improvement of p-type single-crystalline silicon (sc-Si) solar cells resulting from front surface passivation by a thin amorphous silicon (a-Si) film deposited prior to phosphorus diffusion. The conversion efficiency was improved for the sample with an a-Si film of ~5 nm thickness deposited on the front surface prior to high-temperature phosphorus diffusion, with respect to the samples with an a-Si film deposited on the front surface after phosphorus diffusion. The improvement in conversion efficiency is 0.4% absolute with respect to a-Si film passivated cells, that is, the cells with an a-Si film deposited on the front surface after phosphorus diffusion. The new technique provided a 0.5% improvement in conversion efficiency compared to the cells without a-Si passivation. Such performance improvements result from reduced surface recombination as well as lowered contact resistance, the latter of which induces a high fill factor of the solar cell.

Review of Scientific Instruments, 2011

A magneto-optic polarimetry based on auto-balanced photodetection is investigated. In this experi... more A magneto-optic polarimetry based on auto-balanced photodetection is investigated. In this experiment, a commercial auto-balanced photoreceiver is adopted to measure the Faraday rotation of air. With a proper setup to utilize its noise cancellation capability, the measurement can be flexible and sensitive. The angular sensitivity is 2.99×10 −8 rad Hz −1/2 , which is about 2.7 times the shot noise limit. The measured Verdet constant of air is +1.39×10 −9 rad G −1 cm −1 at 634.8 nm. Significantly we applied a small AC current to induce the magnetic field, so there was no heating in the coil. In addition, a double current modulation scheme was used to demonstrate that there was no zero drift and amplifier instability in the measurement. The possibility of improvement of the angular sensitivity and the potential applications are also discussed.

Optics Letters, 1989

A technique of Raman compensation for a two-channel soliton-based fiber communication system is i... more A technique of Raman compensation for a two-channel soliton-based fiber communication system is introduced. By fixing the wavelength spacing between two channels, one can calculate the pumping wavelength and intensity in such a way that balance between loss and gain is reached for each channel. In this computation the Raman conversion between two channels plays an important role in simultaneous compensation for both channels.

Optics Letters, 2005

We present a new design for beam splitting components employing a silicon-on-insulator rib wavegu... more We present a new design for beam splitting components employing a silicon-on-insulator rib waveguide structures. In the new design, a high-index thin-film layer is deposited in the rib section to reduce the wave field dispersive tails in the slab section and accordingly render the mode field a confined spot. This in turn improves the beam splitting performance of some conventional waveguide components such as y branches and multimode interference couplers (MMICs), in terms of the excess loss, fiber coupling loss, and compactness of these components. For a 1 x 2 y-branch beam splitter, the excess loss can be as small as 0.43 dB in the new design, which is much lower than that for a conventional rib waveguide structure (which is 1.28 dB). For a 1 x 2 MMIC in our example, the new rib waveguide structure presents an excess loss of 0.064 dB for the TE mode and 0.046 dB for the TM mode, with negligible nonuniformity in dimensions of 30 microm x 1040 microm, whereas its counterpart (i.e., the one with the same dimensions but without a thin-film layer) presents an excess loss of approximately 0.86 dB for both modes. A conventional MMIC must have dimensions larger than 70 microm x 5650 microm to maintain almost the same low excess loss.

Optics Letters, 1993

The effect of accumulated optical-amplifier-induced noise on the pulse propagation in a dispersiv... more The effect of accumulated optical-amplifier-induced noise on the pulse propagation in a dispersive single-mode optical fiber is theoretically investigated. As a result of this effect, the pulse is weakened at the central part and long dispersive tails are produced, resulting in significant loss of signal power during a 1-bit time period. This situation becomes more severe as the bandwidth of the noise spectrum increases.

Optics Letters, 1990

We introduce a new type of solitary wave in a lossless single-mode fiber in which a bright solito... more We introduce a new type of solitary wave in a lossless single-mode fiber in which a bright solitonlike pulse in the anomalous-dispersion range propagates together with a stationary dark pulse in the normal-dispersion range. Such a solitary wave can be generated by launching a bright pulse in the anomalous-dispersion range together with a long pulse of the same speed in the normal-dispersion range into a fiber. The results of numerical simulations show that the dark pulse is not a dark soliton. The generation and maintenance of such a solitary wave are attributed to the mutual chirping through cross-phase modulation between those two waves in the anomalous-and normal-dispersion ranges.

Optics Communications, 2007

This paper presents an idea of using residual pump power for implementation of low-noise and high... more This paper presents an idea of using residual pump power for implementation of low-noise and high-gain L-band erbium-doped fiber amplifiers (EDFAs). A single pump laser is employed to pump the first-stage EDFA, which serves as a low-noise preamplifier, in the proposed three-stage EDFA system. The residual pump power unabsorbed by the preamplifier is directed to pump the subsequent EDF. Experimental

Optics Communications, 2001

Two optical ®ber Bragg gratings (FBGs) of slightly separated Bragg wavelengths were tandem splice... more Two optical ®ber Bragg gratings (FBGs) of slightly separated Bragg wavelengths were tandem spliced for temperature-insensitive strain sensing. The two FBGs, one used for sensing and the other used for reference, were placed side by side in parallel to assure that they had the same thermal condition. Strain was calibrated simply through re¯ected power measurement of the system, which was determined by the union of the spectra of the two FBGs. Linear strain measurement up to 740 lS with strain accuracy of AE1.1 ls and thermal stability of <0.7% in detected power in the temperature range from 19 to 103°C was obtained.

Optics Communications, 2010

Power scalability of fiber lasers, today, is from few mW to several kW in CW operation and tens o... more Power scalability of fiber lasers, today, is from few mW to several kW in CW operation and tens of kW in pulsed operation. The wide range of power is possible due to various configurations of the fiber laser system. One such configuration is Master Oscillator Power Amplifier (MOPA), the topic of interest of our paper. We explain the design aspects of MOPA and discuss optimization methodology for MOPA based fiber lasers. We propose optimization, under co-directional pumping, of pump laser, seed laser and the fiber length. We have focused on the state of art technologies considering Ytterbium doped double clad single mode Nufern fiber.

Journal of the Optical Society of America B, 1991

Dark solitons evolving from a dark pulse, which is induced on a long pulse in the normal group-ve... more Dark solitons evolving from a dark pulse, which is induced on a long pulse in the normal group-velocity dispersion range by a bright pulse in the anomalous dispersion range through cross-phase modulation in a singlemode fiber, are numerically observed. In most situations dark-soliton evolution is observed after the copropagating bright pulse is filtered. The number of evolving dark solitons and their parameters, including the depth, shifting speed, and shifting direction, are controlled by the intensity and phase profiles of the induced dark pulse at the position where the bright pulse is filtered. The parameters of the induced dark pulse depend on those of the input bright pulse, the relative speed between the input bright pulse and the long pulse, and the position where the bright pulse is filtered. We obtain numerical results by using the beam-propagation method to solve the coupled nonlinear Schrodinger equations. A dark soliton that was almost a black soliton was generated.

Optical Fiber Technology, 2010

ABSTRACT We propose and demonstrate a bidirectional wavelength-division-multiplexed passive optic... more ABSTRACT We propose and demonstrate a bidirectional wavelength-division-multiplexed passive optical network system by using multi-wavelength light sources to lock FP lasers in order to achieve a colorless WDM-PON transmission. In the proposed system, we configured multi-wavelength light sources in C and L bands to, respectively, lock the FP lasers at a subscriber site and a central office. The multi-wavelength light source for upstream FP lasers can improve the pump power budget for locking FP lasers. Compared with the conventional spectral slicing technique, the proposed configuration would save more than a half of optical pump power in achieving a colorless WDM-PON system.

Optical Fiber Technology, 2008

ABSTRACT A new structure of multipoint temperature-independent strain sensing system with dual fi... more ABSTRACT A new structure of multipoint temperature-independent strain sensing system with dual fiber Bragg gratings as sensors is proposed. An optical switch is employed to bridge between the detection site and multiple far ends where fiber Bragg grating sensors are located. A voltage divider is used in the proposed optical power detection scheme to resolve the measurement instability caused by the power fluctuation of the light source in a long term and the nonflat spectrum of the light source. This new detection scheme is demonstrated to have a measurement linearity and resolution of ±0.25% and 0.4 μS, respectively.

Optical Engineering, 1997

A previous electric current sensing scheme employing two metal-coated single-mode optical fibers ... more A previous electric current sensing scheme employing two metal-coated single-mode optical fibers is modified for the purpose of much wider band measurement. As the same optical setup is used, the proposed sensing scheme incorporates the use of a differentiator that differentiates the measurand before it splits into two parts and flows on the two metallic coatings, respectively. Two kinds of optical fibers (which have different cladding sizes) are tested. With regular polarizationmaintaining fibers (which have a 125 m cladding diameter), a measurement bandwidth of ϳ500 Hz can be obtained. With thinner fibers (with 80 m claddings), the measurement bandwidth can reach ϳ1.1 kHz. The measurement scheme proposed compares much more favorably to the previously reported sensing scheme, in which the measurement bandwidth is only 0.06 Hz.

Optical and Quantum Electronics, 1996

A new cutback method based on the use of phase discrimination is proposed for Iowlinear-fibre-bir... more A new cutback method based on the use of phase discrimination is proposed for Iowlinear-fibre-birefringence measurement. In this destructive method, a detection scheme for determining the phase difference between two readily obtained signals is used to give the phase retardation of the test fibre directly. The detection scheme mainly consists of two wave plates, two sections of fibre and an electro-optic modulator. The features of this measurement scheme are twofold. First, the aforementioned phase difference between two detected signals, and, accordingly, linear fibre birefringence, can be determined in a simple manner, compared with the conventional cutback method. Second, the test fibre can be short in length despite the existence of fibre cladding modes. Experiments show that the proposed method can give a reliable measurement of linear fibre birefringence.

Journal of Modern Optics, 2005

In this paper, we propose a different method to study wave propagation in longitudinally invarian... more In this paper, we propose a different method to study wave propagation in longitudinally invariant waveguides with arbitrary index profile. In our method, both the electric field and the refractive index profile are expanded into two Fourier cosine series. With these series substituted into the wave equation, a differential matrix equation can then be obtained. We show here that such a matrix equation can be solved and an explicit expression for the wave field at any longitudinal position along an optical waveguide can be obtained. The solution proposed in this method can thus exclude the use of the beam propagation algorithm. This study demonstrates that our approach yields the same results as those obtained by using commercial softwares in which a beam propagation method with the Pade´approximation is used.