基于偏振全息光栅的全光逻辑序列发生器

偏振全息近年来引起了人们的广泛关注,许多关于偏振光栅的研究已经成为热点。近日,上海交通大学王长顺教授课题组提出了基于两种不同偏振全息光栅的全光逻辑序列发生器,它有一个输入端口和四个输出端口,输出端口的逻辑信号完全取决于输入端口光信号的偏振。相关研究结果发表于Chinese Optics Letters 2019年第17卷第8期 () 。

该全光逻辑序列发生器可以产生四种逻辑序列输出信号:1000、0100、0010、0001,对应于四种不同偏振态的输入光信号:P线偏振、S线偏振、左旋圆偏振和右旋圆偏振。该逻辑序列发生器不需要额外的电控,因此可以做得很薄,使之能较容易地集成到各种光学系统中,例如光通信系统中的光路切换领域。全光逻辑序列发生器结构如图1所示。

图1 全光逻辑序列发生器原理图。DW1和DW2是两种不同的偏振全息光栅, QWP是四分之一波片,B1和B2分别代表DW1的-1级和+1级衍射光。

当入射光为P线偏振时,衍射光信号可以在2、3、4方向检测到。当入射光为S线偏振光时,衍射光信号可以在1、3、4方向检测到。对于左旋圆偏振入射光,衍射光信号可以在1、2、4方向检测到。入射光是右旋圆偏振光,则衍射光信号可以在1、2和3的方向上检测到。如果每个输出端口有信号表示逻辑态0,没有信号表示逻辑态1,则可以得到一个逻辑序列表。P线偏振光输出逻辑序列信号1000,S线偏振光输出逻辑序列信号0100,左旋圆偏振光输出逻辑序列信号0010,右旋圆偏振光输出逻辑序列信号0001。

图2 (a)不同偏振态的入射光信号及相应的输出光信号图;(b)逻辑序列表。I1列表示入射光的四种不同偏振态,O1、O2、O3和O4列分别表示四个方向的衍射光,对应于图1中的黄色、绿色、蓝色和红色圆柱体。输出端口有信号表示逻辑态0,无信号表示逻辑态1。

得益于较薄的厚度,这种逻辑序列发生器可以很容易地集成到需要光信号控制的各种光系统中,因此,它在光通信系统中的光路切换等领域内具有潜在的应用前景。希望将来能将这种结构集成到一些复杂的光通信系统中,以测试其实际效果,相信它能在未来的应用中发挥良好的作用。

Design of an all-optical logic sequence generator based on polarization holographic gratings

Polarization holography has attracted much attention in recent research。 Many studies on polarization gratings have been carried out。 The research group led by Prof。 Changshun Wang from Shanghai Jiao Tong University designs an all-optical logic sequence generator, which has one input port and four output ports, based on two different polarization holographic gratings。 The logic signals of output ports depend entirely on the polarization of the input light signal。 This work has been published in Chinese Optics Letters, Volume 17, Issue 8, 2019 ()。

The all-optical logic sequence generator can produce four kinds of logic sequence output signals: 1000, 0100, 0010, and 0001, corresponding to the input light signal of four different polarization states: the p-linear, s-linear, left-handed circular, and right-handed circular. There is no need for additional electronic control in this logic sequence generator, so it is very thin and can be easily integrated into various optical systems requiring optical signal control, such as optical path switching in optical communication system. The all-optical logic sequence generator is shown in Fig. 1.

Fig. 1. Schematic of all-optical logic sequence generator. DW1 and DW2 are two different kinds of polarization holographic gratings. QWP is the quarter-wave plate. B1 and B2 represent the -1 and +1 order diffraction light of DW1, respectively.

When the incident light is p-linearly polarized, the diffraction light signals can be detected in the directions of 2, 3 and 4. When the incident light is s-linearly polarized, the diffraction light signals can be detected in the directions of 1, 3 and 4. As for the left-handed circularly polarized incident light, the diffraction light signals can be detected in the directions of 1, 2 and 4. If the incident light is right-handed circularly polarized, the diffraction light signals can be detected in the directions of 1, 2 and 3. If the signal of port denote logic state 0, no signal denote logic state 1, the logic sequence table can be obtained. The output of p-linearly polarized incident light is logic sequence signal 1000, the output of s-linearly polarized incident light is logic sequence signal 0100, the output of left-handed circularly polarized incident light is logic sequence signal 0010, and the output of right-handed circularly polarized incident light is logic sequence signal 0001.

Fig. 2. (a) The diagram of the incident light signal of different polarization states and corresponding output light signals. (b) The logic sequence table. Column I1 represents four different polarizations of the incident light; columns O1, O2, O3 and O4 represent the diffraction light in four directions respectively, corresponding to the yellow, green, blue and red cylinders in Fig. 1. Signal of port denotes logic state 0, no signal denotes logic state 1.

In this work, an all-optical logic sequence generator based on two different polarization holographic gratings is designed. The polarization states of the input signal light are controlled to produce four different logic sequence signals and the working principle of the logic sequence generator is analyzed. This logic sequence generator has many potential applications, such as optical path switching in optical communication system. The structure is very thin so it can be easily integrated into various optical systems requiring optical signal control. The research group hopes to integrate the structure into some complex optical communication systems to test its actual effect in the future, and they believe it can make a good function in the further applications.