摘要:
基于自旋反转模型,研究了可变偏振光注入1550 nm垂直腔面发射激光器(VPOI-1550 nm-VCSEL)的偏振开关(PS)及双稳(PB)特性。研究结果表明：对于一自由运行的1550 nm-VCSEL,在给定电流下,激光器中的平行偏振模式(Y偏振模式)激射,而正交偏振模式(X偏振模式)被抑制。引入可变偏振光注入后,在给定频率失谐?ν(定义为注入光与X偏振模式之间的频率差异)的条件下,当注入光偏振角θp(定义为注入光的偏振方向与自由运行1550 nm-VCSEL中主导偏振模式的夹角)足够大时,正向扫描(逐渐增加)注入光功率可观察到1550 nm-VCSEL发生I类PS,反向扫描(逐渐减小)注入光功率可使1550 nm-VCSEL产生II类PS,且两类PS 的开关点要求的注入功率不一致,即出现PB现象。对于一确定的频率失谐?ν,随着θp的增加, I类、II类PS开关点对应的注入功率以及PB区宽度都呈现减小的趋势,且|?ν|值越大,尽管I类PS的开关点所需注入功率更大,但PB区域更宽；在给定注入功率,对于特定?ν,通过正向及反向扫描θp也可观察到VPOI-1550 nm-VCSEL输出功率呈现的PS以及PB现象。当|?ν|较小时,发生I类和II 类PS所要求的θp近似相同,因此PB区宽度较窄,而当|?ν|较大时,发生两类PS所需的θp以及PB宽度随?ν的变化曲线均呈现较大波动。因此,在1550 nm-VCSEL 工作参数给定的条件下,通过调节可变偏振光注入的注入参量,可优化1550 nm-VCSEL呈现的PS及PB特性。
Abstract:
Due to the potential applications in optical storage, optical logic gates and all-optical signal shaping, the polarization switching (PS) and bistability (PB) of vertical-cavity surface-emitting lasers (VCSELs) under external disturbance have attracted much attention. In this work, based on the spin-flip model, the characteristics of PS and PB in a variable-polarization optical injection 1550 nm VCSEL (VPOI-1550 nm-VCSEL) are investigated numerically. In this scheme, the output from a master tunable laser passes through a rotating polarizer, an optical isolator (ISO), and a neutral density filter, then is injected into a 1550 nm-VCSEL. The polarization angle and power of the injection light are controlled by the RP and ISO, respectively. The results show that for a free-running 1550 nm-VCSEL, the parallel polarization-mode (Y polarization-mode) is lasing while the orthogonal polarization-mode (X polarization-mode) is suppressed in the 1550 nm-VCSEL. After introducing a variable-polarization optical injection, for a given frequency detuning ?ν (defined as the frequency difference between the injection light and the X polarization mode), type I PS occurs during continuously increasing the injection power and type II PS occurs in the inverse process if the polarization angle θp of the injection light (defined as the angle difference between the polarization direction of injection light and Y polarization mode of the 1550 nm-VCSEL) is large enough. Moreover, the injection power required for generating type I PS is different from that for generating type II PS, namely PB is observed. When?ν is fixed, with the increase ofθp, the injection power for the occurrences of the two types PS and the width of PB decrease. For a larger value of |?ν|, the injection power for the occurrence of type I PS is higher meanwhile the width of the PB is larger than that for a relatively small value of|?ν|. On the other hand, for a given injection power, type I PS, type II PS, and corresponding PB can also be observed in the 1550 nm-VCSEL through continuously increasing and reducingθp within the range from 0? to 90? under an appropriate?ν. For a relatively small |?ν|, the value of θp required for the occurrence of type I is similar to that for type II PS, which results in the very narrow width of the PB. Contrastively, for a relatively large|?ν|, the values ofθp required for the occurrences of the two types PS and the width of PB severely fluctuate with the variation of?ν. Therefore, for the fixed parameters of the 1550 nm-VCSEL, through adjusting the power and polarization angle of the injection light, the performances of the PS and PB can be optimized. It is expected that this work can provide an effective guidance for optimizing the VCSEL-based bistable devices.
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