Distributed Optical Fiber Acoustic Sensing Based on Chaotic Laser Interference

A high slope efficiency vertical-cavity surface-emitting laser (VCSEL) is described. The InGaAs/GaAsP strain compensated multiple quantum wells (MQWs) are designed by PICS3D. The wavelength redshift occurs due to the thermal effect, the lasing wavelength of MQWs is designed to be around 928 nm. The active region consists of five compressively strained 4.4 nm thick In0.16Ga0.84As quantum wells separated and surrounded by 6.2 nm thick GaAs0.88P0.12 tensile strained compensation layers to obtain the high quantum efficiency and ensure the stress release. Subsequently, the MQWs are grown by metal-organic chemical vapor deposition (MOCVD) and the photoluminescence (PL) spectrum is measured using an Nd:YAG laser (532 nm excitation), of which the peak wavelength is approximately 928 nm and the full width at half maximum is nearly 17.1 nm. The resonant cavity is surrounded by p- and n-DBRs. The n-DBRs are designed to be a 28-period AlAs/Al0.12Ga0.88As and 3.5-period Al0.90Ga0.10As/Al0.12Ga0.88As, and the p-DBR is designed to be a 23-period Al0.90Ga0.10As/Al0.12Ga0.88As. The thickness of each a material is <inline-formula><tex-math id="M2">\begin{document}$\lambda/4n$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M2.png"/></alternatives></inline-formula> (<inline-formula><tex-math id="M3">\begin{document}$\lambda$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M3.png"/></alternatives></inline-formula> = 940 nm, n represents refractive index), and 20 nm graded layer is inserted in the interface between two types of materials. The p-/n-DBRs’ experiment PL reflection spectra (using a white illuminant) are carried out, the central wavelength is around 938.7 nm, and the reflectivity values of p-/n-DBRs are nearly 99.0% and 99.7%, respectively. The VCSELs are grown by MOCVD technique, and treated by dry etching, wet oxidation, metal electrode technology and other processes. In the process of dry etching, the top mesa is treated by inductively coupled plasma with BCl3 and Cl2 chemistry. In order to expose the oxide layer the wet oxidized process is carried out, and the etching depth is nearly 3500 nm. An oxidation furnace is heated for 15 min prior to oxidation. Then the oxide aperture is shaped by the wet nitrogen oxidation furnace at 425 °C with an N2 flow of 200 sccm, and the oxide rate is approximately 0.40 <inline-formula><tex-math id="M4">\begin{document}${\text{μm}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M4.png"/></alternatives></inline-formula>/min for A0.98Ga0.02As. The diameter of oxide aperture is made into an 8 <inline-formula><tex-math id="M5">\begin{document}${\text{μm}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M5.png"/></alternatives></inline-formula> diameter. In the process of metal electrode technology, AuGeNi alloy is sputtered on the top surface to form p-type ohmic contact, and Ti/Pt/Au is evaporated on the back surface of substrate to form an n-type ohmic contact. Rapid thermal annealing at 350 °C in a nitrogen atmosphere is carried out subsequently to obtain a good-quality ohmic contact. Finally, we test the VCSELs’ L-I-V characteristics and spectra in different areas. In area 1, room-temperature lasing at around 940 nm is achieved with a threshold current of 0.95 mA, a slope efficiency of 0.96 W/A, and an output power of 4.75 mW. In area 2, threshold current is 1 mA, a slope efficiency is 0.81 W/A at 25 °C and threshold current is 1.9 mA, slope efficiency is 0.57 W/A at 25 °C. The output power values reach up to 3.850 mW and 2.323 mW at 25 °C and 80 °C, respectively.

Design and fabrication of 940 nm vertical-cavity surface-emitting lasers

Yu¹,

Shun²,

Zhang³

et al. 2019

Chaotic characteristics of output light from semiconductor laser with self-chaotic phase modulation and optical feedback

Pang¹,

Feng²,

Yu³

et al. 2022

Distributed feedback semiconductor lasers (DFB-SL) are the class B lasers, and would output chaotic laser under the external disturbances, such as external optical feedback and optical injection. Chaotic laser are widely applied in many fields, including optical fiber sensing, chaotic laser secure communication, and better entropy sources for generating high-speed random number, etc. However, time delay signature (TDS) will arise in the chaotic laser from the semiconductor lasers with external cavity optical feedback, and the TDS will restrict the applications of chaotic laser. On the other hand, the bandwidt (BW) of chaotic carrier signal plays the important role for the transmission rate of information signal. Therefore, the TDS and BW are two important parameters that will affect chaotic laser's applications, and they are usually used to express the chaos characteristics of chaotic laser. In this paper, we present a new scheme used to suppress the TDS and investigate the BW of chaotic laser from semiconductor laser. For this scheme, the output laser from a DFB-SL with external single optical feedback are injected by double ways into another DFB-SL with phase modulation optical feedback by self chaos light. Thus they form a semiconductor laser system with external double optical injection and phase modulation optical feedback by self chaos light (SL-EDOI-PMOFBSCL). We investigate numerically the influences of the system parameters on TDS, such as the injection coefficient and feedback coefficient, etc. Then the suppression effect on TDS are contrasted and analyzed with two other systems, that are semiconductor laser with external double optical injection and optical feedback (SL-EDOI-OF) and semiconductor laser with external single optical injection and phase modulation optical feedback by self chaos light (SL-ESOI-PMOFBSCL), respectively. The results indicate that the proposed scheme in this paper has the best suppression effect on TDS. Then the BW of the chaotic laser are investigated under the parameters conditions of effectively suppressing TDS.The simulation results show that the scheme proposed in this paper can enhance the BW of chaotic laser by properly selecting the parametric values, and the maximum BW value of the obtained chaotic laser is about 16 GHz.

Effect of amorphous carbon film on secondary electron emission of metal

Hu,

Liu,

Chu

et al. 2024

Amorphous carbon films have attracted much attention in the field of abnormal discharge of vacuum microwave devices and equipment due to their extremely low secondary electron yield (SEY). However, the dynamic process and microscopic mechanism of the effect of amorphous carbon films on secondary electron emission are still poorly understood. In this work, a numerical simulation model of the secondary electron emission of amorphous carbon film on copper surface was developed by the Monte Carlo method, which can accurately simulate the dynamic processes of electron scattering and emission of the films and the substrate. The results show that the maximum SEY decreases by about 20% when the film thickness increases from 0 to 1.5 nm. Further increasing the thickness, the SEY no longer decreases. However, when the film is thicker than 0.9 nm, the SEY curve exhibits a double-hump form, but with the thickness increasing to 3 nm, the second peak gradually weakens or even disappears. The electron scattering trajectories and energy distribution of secondary electrons indicate that this double-hump phenomenon is caused by electron scattering in two different materials. Compared with previous models, the proposed model takes into account the change of work function and the effect of interfacial barrier on electron scattering path. Our model explains the formation of the double-hump of SEY curve and provides theoretical predictions for the suppression of SEY by amorphous carbon film.