The color change of oil palm Fresh Fruit Bunches (FFB) is one of the important parameters for harvesting decisions. However, human visual identification is prone to errors due to uncontrolled ambient lighting and the far distance of fruit bunches on tall palm trees. These errors can lead to inaccurate harvesting and significant revenue loss. This study introduces a laser remote sensor for non-destructive FFB ripeness assessment. Based on the unique spectral reflection curves of the FFB at different ripeness, laser modules at three different wavelengths (visible- NIR region) have been employed for the measurement. The photodetector and laser sources are configured in a coaxial manner to enable long work distances up to 9 m. This portable laser remote sensor has undergone successful on-plant testing in oil palm estates, with measurements validated against oil content by conventional bunch analysis. It is a potential tool for precision harvesting and oil yield prediction.
An optical-based pressure sensor for a 150 × 150 mm surface was designed and fabricated. The sensor utilizes a fiber Bragg grating (FBG) attached to a 30 × 30 × 30 mm actuator as the pressure sensing mechanism. The middle section of the actuator, which is circular, can bend into an elliptical form and, in the process, pull the FBGP via both ends when force or pressure is applied, thus converting the pressure applied to its surface into a wavelength shift. In laboratory testing, a sensitivity of 0.152 nm / kPa was obtained. Subsequently, the pressure sensor was tested in the field by burying it 20 cm underground to measure soil pressure, while another FBG was spliced in series to the FBGP to compensate for temperature variations. Testing shows that the proposed design can realize a compact optical-based pressure sensor with enhanced soil monitoring applications such as dynamic soil pressure caused by soil movement.
A mode-locked thulium–holmium fiber laser operating in the 2.0-μm wavelength region was demonstrated using a MAX phase titanium aluminum nitride (Ti2AlN)-based saturable absorber (SA). The Ti2AlN was prepared in the solution form and then drop-casted onto a homemade arc-shaped fiber, which served as the SA device. The mode-locked pulses were generated when the pump power was at 119 mW, and the pulses were sustained up to a pump power of 249 mW. The mode-locked fiber laser using the Ti2AlN-based SA operated with a center wavelength of 1900.6 nm, having a repetition rate and a pulse width of 12.14 MHz and 1.61 ps, respectively. At the maximum pump power, the mode-locked pulses had maximum pulse energy of 0.35 nJ and peak power of 216 W. We propose the generation of short pulses using a MAX phase-based SA that could be useful for various applications in the eye-safe region.
An innovative vibration sensor based on a Fabry–Perot interferometer (FPI) using fiber Bragg grating (FBG) reflectors was demonstrated in this work. The sensor was designed to be compact and easy to fabricate, independent of temperature, to overcome limitations seen in previous designs, providing an effective correction for temperature effects in FBG-based FPI (FBG-FPI) sensors. A laser source with a peak wavelength of 1547.42 nm obtained from the FBG reflective peak was used to illuminate the FBG-FPI so that the light source was always within the FBG-FPI optimum wavelength operating range of 1547.15 to 1547.80 nm. The sensor was shown to capture a 3-kHz burst signal from a signal generator in 1-, 2-, and 3-Hz intervals. In addition, the work carried out has revealed that the sensor could be used to capture sinusoidal signals at frequencies up to 9 kHz, creating a performance comparable with many existing conventional piezoelectric sensors. Furthermore, the ability to operate regardless of any ambient temperature changes [from 26.5°C (room temperature) up to 80°C] opens the way to use such a sensor system over a wide range of engineering applications taking advantage of the next generation of FBG-based FPIs.
A Q-switched ytterbium-doped fiber laser incorporating a molybdenum ditelluride saturable absorber for operation at 1046 nm is demonstrated. The laser cavity has a low Q-switching threshold of ∼48 mW. At the maximum pump power, the laser is able to generate pulses with a duration, repetition rate, and output power of 4.88 μs, 39.6 kHz, and 0.76 mW, respectively, as well as a pulse energy of 18.9 nJ. The output of the laser can be tuned from 1064 to 1099 nm, giving a tuning range of 35 nm. The generated pulses have a signal-to-noise ratio of around 60 dB. No interference frequency components or spectral modulation is observed, indicating that the proposed system is highly stable and suitable for use as a fiber laser source in the 1.0-μm region.
Laser ablation (LA) has been acknowledged as a universal laser processing tool to develop new devices. Typically, LA involves removal of material with a high energy femtosecond (fs) laser, which has a relatively low-pulse repetition rate (kHz). This constricts the processing speed to avoid separation between successive pulses during the device patterning. Hence, it is reasonable to use a high-repetition-rate laser as an alternative approach to enable high-speed laser processing. We experimented on the surface ablation of poly allyl diglycol carbonate (PADC) using a high-repetition-rate (MHz) fs laser. The objective of this study is to investigate the laser-ablated pattern on PADC and the effect of the number of laser pulses on the ablation rate. For the purpose of this experiment, straight trenches were formed directly on the PADC surface with 800-nm fs-pulsed laser writing. It was found that the ablation mechanism in the high-repetition-rate regime was primarily controlled by the number of irradiated pulses. At a fixed pulse energy, the ablation rate dropped from 9.6 to 3.4 pm / pulse for 1 × 105 and 8 × 105 pulses, respectively. This outcome stemmed from the disruption of laser focusing via thermally induced surface morphology changes due to excessive energy accumulation.
A multiwavelength praseodymium fiber laser (MWPFL) operating at the 1300-nm region is proposed and demonstrated. The MWPFL incorporates a polarization maintaining fiber acting as a Lyot birefringence filter, and when combined with the nonlinear polarization rotation effect, generates the desired multiwavelength output. Careful adjustment of the polarization controller at different angles allows for the generation of up to five channels above a power level of −3.4 dBm and a spacing of 0.2 nm. The peak power fluctuation and wavelength shifts of these lasers are measured to be less than 2.1 dB and 0.04 nm, respectively, over an observation period of 60 min. The demonstrated MWPFL shows good stability combined with a simple structure for generating a multiwavelength output at the 1300-nm wavelength region.
A highly stable mode-lock fiber laser with a thin film coating of graphene oxide (GO) nanoparticles on a D-shaped fiber is proposed and demonstrated. The GO-coated D-shaped fiber, which serves as the cavity’s saturable absorber (SA), is fabricated by drop-casting GO nanoparticles on the smooth and consistently polished area of the D-shaped fiber made using a disk-polishing machine. Mode-locking is induced through the interaction of the evanescent field from the D-shaped fiber and GO nanoparticle layer. The cavity has a length of 12.5 m with a fundamental frequency of 16.5 MHz and operates in the anomalous dispersion regime. Stable soliton mode-locking is obtained above a pump power of 76.6 mW, with a central lasing wavelength of 1555.7 nm and well-defined Kelly’s sidebands. The generated pulses have a repetition rate of 16.5 MHz and pulse duration of 1.18 ps over a pump power range of 76.6 to 280.5 mW, with only minor fluctuations observed. A signal-to-noise ratio of 58.3 dB is computed, indicating a highly stable output. The proposed SA fabrication technique provides a simple, cost-effective, and consistent method of generating mode-locked pulses in fiber lasers.
We report, for the first time to our knowledge, the usage of platinum silver bimetallic alloy forms on the synthesized N-Gns (PtAg/N-G) as a saturable absorber (SA) for the mode-locking of a thulium-doped fluoride fiber laser. The experimental results have demonstrated that PtAg/N-G exhibits saturable absorption in the 1.5-μm wavelength range and supports ultrashort pulse generation. Mode-locking occurred when the pump power rose to 340 mW, and the output spectrum had a peak at 1506 nm with the 3-dB bandwidth of ∼0.76 nm. The mode-locked pulse train against a cavity roundtrip time of 146 ns that corresponds to a pulse repetition rate around 6.85 MHz. The autocorrelation trace 7.43 ps with a full width at half maximum pulse width of 4.8 ps, and experimental data were closely fit with a sech2 pulse shape and it indicates the generation of soliton pulse. The output power of this fiber laser is 3.24 mW; hence, the pulse energy is 0.31 nJ and peak power is about 56.9 mW as well. We demonstrate graphene-polymer nanocomposites could be an appropriate SA for high-power fiber laser mode-locking.
This paper reports a few-layer black phosphorus (BP) as a saturable absorber (SA) or phase-locker in generating modelocked pulses from a double-clad ytterbium-doped fiber laser (YDFL). We mechanically exfoliated the BP flakes from BP crystal through a scotch tape, and repeatedly press until the flakes thin and spread homogenously. Then, a piece of BP tape was inserted in the cavity between two fiber connectors end facet. Under 810 mW to 1320 mW pump power, stable mode-locked operation at 1085 nm with a repetition rate of 13.4 MHz is successfully achieved in normal dispersion regime. Before mode-locked operation disappears above maximum pump, the output power and pulse energy is about 80 mW and 6 nJ, respectively. This mode-locked laser produces peak power of 0.74 kW. Our work may validates BP SA as a phase-locker related to two-dimensional nanomaterials and pulsed generation in normal dispersion regime.
Mode-locked generation of erbium-doped fiber laser (EDFL) with MoSe2 thin film as saturable absorber is practically demonstrated. Bulk MoSe2 is exfoliated into few-layer MoSe2, which is achieved based on the liquid phase exfoliation technique. The few-layer MoSe2 is mixed with polyvinyl alcohol to become a thin film. Mode-locked occurs between pump powers of 65 and 218 mW. The mode-locked is operated at fundamental frequency of 8.8 MHz, and the spectrum is centered at 1560 nm. The SNR of mode-locked EDFL is more than 50 dB. At pump power of 218 mW, 91.3 pJ of pulse energy is achieved.
We describe a successful demonstration of highly stable and narrowly spaced dual-wavelength output via an ytterbium-doped fiber laser. A microfiber-based Mach–Zehnder interferometer and a tunable bandpass filter were both placed into the laser ring cavity for the purpose of ensuring a stable and narrowly spaced dual-wavelength output. Experimental results comprised three sets of dual-wavelength lasing output with wavelength spacing of 0.06, 0.09, and 0.22 nm, respectively, and side-mode suppression ratio of ∼50 dBm. A subsequent stability test provided evidence that maximum power and wavelength fluctuation were less than 0.8 dB and 0.01 nm, respectively, and thus, the obtained output was considered to be highly stable in dual-wavelength operation. The proposed system offers advantages of flexibility in dual-wavelength laser generation in addition to excellent reliability.
This paper describes numerical and analytical analyses relating to the use of nonlinear four-wave mixing in a semiconductor optical amplifier medium for anticipated wavelength conversion at ultrahigh data rates of 320 and 640 Gb/s. The proposed system guidelines and design show that a maximum wavelength shift of 30 nm can be achieved at 640 Gb/s, while still maintaining an acceptable bit error rate. In addition, the impact of the pump–probe ratio and semiconductor optical amplifier bias current are investigated and the results are reported.
This work describes efficient and polarization insensitive, all-incoherent four-wave mixing wavelength conversion achieved within a short length of highly nonlinear fiber medium, created by using both spectrally sliced pump and probe channels from a single-amplified spontaneous emission source coupled to two narrowband Fiber Bragg grating (FBG) filters. This simple and cost-effective scheme is capable of generating a down-converted probe channel across a 17.2-nm wavelength span, while still maintaining a high conversion efficiency of around −22 dB and an optical-signal-to-noise ratio of ∼21 dB. The effects of pump power, FBG detuning, and polarization are also reported.
An enhanced dental cavity diameter measurement mechanism using an intensity-modulated fiber optic displacement sensor (FODS) scanning and imaging system, fuzzy logic as well as a single-layer perceptron (SLP) neural network, is presented. The SLP network was employed for the classification of the reflected signals, which were obtained from the surfaces of teeth samples and captured using FODS. Two features were used for the classification of the reflected signals with one of them being the output of a fuzzy logic. The test results showed that the combined fuzzy logic and SLP network methodology contributed to a 100% classification accuracy of the network. The high-classification accuracy significantly demonstrates the suitability of the proposed features and classification using SLP networks for classifying the reflected signals from teeth surfaces, enabling the sensor to accurately measure small diameters of tooth cavity of up to 0.6 mm. The method remains simple enough to allow its easy integration in existing dental restoration support systems.
In this paper, a novel optical approach is proposed and demonstrated for the non-contact measurement for the thickness
of silica thick films. This approach is based on the principal of an optical based displacement sensor. The calibration
curve for the measurement of the thickness of an unknown sample is obtained using four sample with known thicknesses
of 6.90, 10.23, 19.69 and 25.47 μm respectively. As compared to a prism coupler, which is assumed to provide the most
precise measurement of thick film thicknesses, the proposed system has an error of approximately 8%. The proposed
method is able to provide a simple, low cost and time saving approach in measuring thick films thicknesses during
fabrication.
The purpose of this study is to investigate the potential of intensity modulated fiber optic displacement sensor scanning system for the imaging of dental cavity. Here, we discuss our preliminary results in the imaging of cavities on various teeth surfaces, as well as measurement of the diameter of the cavities which are represented by drilled holes on the teeth surfaces. Based on the analysis of displacement measurement, the sensitivities and linear range for the molar, canine, hybrid composite resin, and acrylic surfaces are obtained at 0.09667 mV/mm and 0.45 mm; 0.775 mV/mm and 0.4 mm; 0.5109 mV/mm and 0.5 mm; and 0.25 mV/mm and 0.5 mm, respectively, with a good linearity of more than 99%. The results also show a clear distinction between the cavity and surrounding tooth region. The stability, simplicity of design, and low cost of fabrication make it suitable for restorative dentistry.
Rigorous modal solutions of silicon nanowires are presented by using a H-field based finite element formulation. It is
shown that beam profiles of a circular nanowire are not circular. It is also shown that most of the optical power in a
silicon slot waveguide can be confined in the low-index slot region. It is shown here that dispersion properties can be
easily controlled by waveguide design of silicon nanowires, as waveguide dispersion dominates over the material
dispersion for such sub-wavelength optical structures. Bending losses of such silicon nanowires are also presented.
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