Abstract:We propose a novel refractive index sensor based on Michelson interferometer by using double-core microfiber. Through the reflection of the end and taper of double-core fiber (DCF), the Michelson interference spectrum is formed. Owing to the structure characteristic of double-core microfiber, this interferometer can achieve the measurement of refractive index (RI) and temperature. The experimental results show that the refractive index sensitivity of the interferometer is 2 377.80 nm/RIU at the diameter of the taper waist of 8.76 µm. In the temperature ranges from 30 °C to 60 °C, the temperature sensitivity is 0.070 48 nm/°C. This sensor has the advantage of high refractive index sensitivity.

Abstract:A conduction cooled high peak power, narrow linewidth, and sub-nanosecond multi-beam laser as an excellent candidate for non-scanning lidar is demonstrated. This laser is based on master oscillator power amplifier (MOPA) scheme which consists of a pulse pumped Nd:YAG/Cr4+:YAG microchip laser as the master oscillator and a high efficient grazing incidence Nd:YVO4 slab amplifier, and the output beam is expanded to 100 mm diameter by a 50× low aberration Galileo beam expander and then divided into a 50×2 staggered arrangement multi-beam array by a diffractive laser splitter. The laser operates at 1 064.28 nm with a spectral linewidth about 20 pm, which generates 1 mJ, 0.78 ns pulses at 7 kHz rate. The fluctuation of output power is less than ±2% when it works continuously for 1 h. The energy uniformity of the 100 sub-beams is up to 90%, the divergence of each sub-beam is about 20 μrad, and the total transmission efficiency of the diffractive laser splitter is more than 85%.

Abstract:The visible light communication (VLC) system employs large viewing divergence angle light-emitting diode (LED) to realize illumination and communication simultaneously, so the geometric loss of optical power may reach tens of decibels, moreover, considering the gain reduction of the LED at high frequency, signal power at the receiver will be too weak. To overcome these drawbacks, in this paper, a low output impedance power driver amplifier is presented to provide enough power to drive a medium power commercial LED used at the end of the optical transmitter. A 125 Mbit/s real-time communication with illumination and communication angle of 130° has been achieved at a distance of 3 m, the bit error rate (BER) is 3.13×10-11 at a divergence angle of LED of 0° and 1.21×10-6 at a communication angle of 130°. Experimental results indicated that this VLC system can be used for illumination and communication simultaneously.

Abstract:In this paper, we have successfully demonstrated a Q-switched pulse generation utilizing lutetium oxide (Lu2O3) thin film based saturable absorber (SA) in all-fiber erbium-doped fiber laser (EDFL) cavity with a bidirectional pumping. The Lu2O3 powder is mixed with isopropyl alcohol (IPA) solution before we add polyvinyl alcohol (PVA) as our host polymer to make the Lu2O3 into a thin film. By inserting the Lu2O3-PVA thin film into a bidirectional pumped EDFL cavity, a stable Q-switched pulse is realized with repetition rate in a range of rose from 43.67 kHz to 57.74 kHz whereas the pulse width decreased from 14.48 µs to 11.20 µs. This result indicates that the Lu2O3 can be implemented as an SA device in an EDFL as it owns a linear absorption of around 3 dB at 1 567 nm.

Abstract:In this paper, a hybrid technique using fast Hadamard transformation cascading a selective mapping (FHT-SLM) is proposed to reduce peak-to-average power ratio (PAPR) and complexity in coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. The Hadamard transform is used to reduce the autocorrelation of signals so as to reduce the PAPR of signals. The fast Hadamard transform (FHT) algorithm is obtained by recursive decomposition of sparse matrix of a simple Hadamard matrix, which improves the computational efficiency and greatly reduces the computational complexity. Then, a selective mapping (SLM) scheme is used to select the smallest frame of PAPR in the time domain to further reduce PAPR of OFDM system. The simulation results show that at the complementary cumulative distribution function (CCDF) of , the PAPR of the proposed scheme FHT-SLM (V=8) is optimized to 7.63 dB. Meanwhile, when the bit error rate (BER) is 10-3, the optical signals to noise ratio (OSNR) of FHT-SLM (V=8) algorithm is 21.2 dB. The total computational cost of the FHT-SLM (V=8) is 28 672. Consequently, the simulation results prove that the proposed algorithm provides a choice for a balance among PAPR, BER and complexity.

Abstract: A variable weight address code based on spectrum amplitude coding (SAC) is proposed for optical code division multiple access (OCDMA) networks to support different quality of service (QoS) requirements of different services. The zero cross-correlation magic square variable weight optical orthogonal code (ZMS-VWOOC) proposed in this paper has great flexibility in terms of code weight and number of users. Zero cross-correlation can eliminate the influence of multiple access interference (MAI) and reduce the system complexity. Numerical results show that ZMS-VWOOC can provide better quality of service than similar codes. Numerical results for a ZMS-VWOOC OCDMA network designed for triple-play services operating at 0.622 Gbit/s, 2 Gbit/s, 2.5 Gbit/s and 3 Gbit/s are considered.

Abstract:Building low-latency and high-capacity optical networks is vital for new high-speed cellular technologies. Coherent wavelength division multiplexing passive optical networks (WDM-PONs) are expected to play a key role in these applications. In this article, an overview of PON technologies for the 5th generation (5G) transport systems has been given. Moreover, a modified scheme based on coherent WDM-PON has been investigated using a dual polarization quadrature phase shift keying (DP-QPSK) transceiver. The aim of the scheme is to build a 1 600 Gbit/s network that will be used in the construction of the transport architecture of 5G and beyond cellular networks either in mobile front haul (MFH) or mobile back haul (MBH). The results indicate that the proposed scheme offers a promising solution for future 5G transport systems.

Abstract:In order to solve this problem, a new biological detection method is proposed, which makes use of the characteristics of optical transmission at the edge of the spectral band gap and sensitive to refractive index variation. When the probe light with wavelength at the edge of the Bragg band gap of porous silicon is incident on the surface of porous silicon, the change of refractive index caused by deoxyribonucleic acid (DNA) reaction in porous silicon will affect the detection light intensity transmitted from the porous silicon sensor. By analyzing the change of the average gray value of the transmitted light image, the concentration of the DNA can be obtained.

Abstract:The aim of this study is to investigate the relationship between the laser-induced optical breakdown energy threshold and the spectral signal changes with the spot radius. First of all, using the avalanche breakdown threshold theory calculates the threshold avalanche ionization rate ηc. Combining with the theory of light intensity distribution and the relationship between pulse energy and peak power, numerical calculations have obtained the law of change of spot radius and threshold laser energy. Secondly, the variation of the spectral signal-to-noise ratio (SNR) with the laser energy is measured according the experimental measurement, and the threshold laser energy required for optical breakdown at different spot radius is obtained. The theoretical threshold model of the relationship between the threshold laser energy and the quadratic function of the spot radius obtained by numerical calculation is verified, and it is revised, the results show that the relative error between the revised theoretical threshold model and the experimental threshold model is less than 5.3%. At last, the influence of the spot radius on the spectral signal and electron density is also analyzed, it is found that both the spectral intensity and the electron density have a maximum at the spot radius of 11 μm. The results show that it is necessary to find the best spot radius during the laser induced breakdown spectroscopy (LIBS) experiment. This provides a reliable theoretical basis and experimental reference for further study of the influence of spot radius on LIBS technology measurement.

Abstract:Uncertain environments, especially uneven lighting and shadows, can degrade an image, which causes a great negative impact on object detection. Moreover, unbalanced training samples can cause overfitting problem. Since available data that is collected at night is much rarer than that collected in the daytime, the nighttime detection effect will be relatively poor. In this paper, we propose a novel data augmentation method named Mask Augmentation, which reduces the brightness and contrast of objects, and also weakens the edge of objects to simulate the degraded scene. In addition, we propose a new architecture, by adding a classification loss branch and a feature extraction module named Multi-Feature Attention Module, which combines the attention mechanism and feature fusion on the basis of Darknet-53. This architecture makes the features extracted in daytime and nighttime images distinguishable. We also increase the loss weight of nighttime images during the training process. We achieved 78.68% mAP on nighttime detection and 73.14% mAP on daytime detection. Compared with other models, our method greatly improves the accuracy of nighttime detection, and also performs satisfactorily on daytime detection. We deployed our model on an intelligent garbage collection robot for real-time detection, which implements automatic picking at night and assists cleaning staff during the day.

Abstract:The superposition of basic non-diffracting beams triggered new research hotspots lately, laying opportunities for long-distance wireless optical communication. The Lommel-Gaussian (LMG) beam formed by the superposition of Bessel-Gaussian light not only possesses non-diffraction feature, but also has tunable symmetry. With the help of Poynting vector analysis, we observed a smaller radial energy flow component during the propagation of the high order symmetrical LMG beam, which allows it to maintain the original beam profile over long distance. Thanks to the energy oscillation of the mainlobe and sidelobes, the mainlobe blocked by the symmetrical LMG beam can be restored. Also, the random phase screen with angular spectrum method is used to describe the beam behaviors in turbulence. The results show that the symmetry LMG is preferred in free space optical communication, and the asymmetric LMG performs poorly due to asymmetric energy transfer.