# All-Optical Non-Inverted Parity Generator and Checker Based on Semiconductor Optical Amplifiers
## 1 Introduction  
To solve the problem of data transmission in the future communication network, all-optical signal processing (AOSP) [1] technology with larger capacity, better flexibility, and good scalability has attracted more and more attention. Due to the invention of low-loss optical fiber [2] and Erbium-doped fiber amplifier (EDFA) [3], it has good progress in data transmission over long distances (thousands of kilometers). As the data transmission capacity, speed, and distance requirements of optical fiber networks increase, there has been an increasing interest in all-optical signal codes, and it has become a key technology for optical communications and optical networks in the future. However, long-distance transmission would cause data added, deleted, and flipped errors. If the error is not discovered and handled in time, it will lead to the wrong transmission of information and cause various negative effects. In order to detect coding errors, the most common solution is parity. In the parity checker circuit, the integrity of the data is verified by successive operations on the binary data. The parity bits are added before data transmission by theparity generator, and the parity checker is used at the receiving end to check whether there are errors and noise during the data transmission.  
The principle of the parity checker circuit is to check the total number of \"1\" codes in the data, so the summation properties of the XNOR gate and XOR can be used. If it does not match the initial setting (the number of \"1\" codes in the even parity checker is odd, the number of \"1\" codes in the odd parity checker is even), the parity check circuit will output an error signal. In recent studies, people have implemented the all-optical parity generator and checker circuit in various ways; for example, parity checker based on terahertz optical asymmetric demultiplexer interferometers [4], the parity generator and checker using semiconductor optical amplifiers (SOAs) based on Mach-Ze hinder interference [5; 6; 7; 8; 9; 10], parity generator and checker based on the microring cavity, parity generator and checker using an SOA-based optical tree architecture [11], parity generator and checker based on SOA assisted Sagnac switches [12]. Due to the integration of potential and good non-linear characteristics of semiconductor optical amplifiers, people have a strong research interest. There are extensive studies in all-optical signal processing and all-optical calculations, such as switches, clocked flip-flops [13], logic gates [14; 15; 16; 17; 18], subtracter and adder [19; 20; 21; 22], decoder/encoder [23; 24], and comparator [23; 24]. It can be seen from the research of various all-optical technologies that semiconductor optical amplifiers have broad application prospects in future optical communication systems.  
In this paper, we present an all-optical non-inverted 2-bits parity generator based on a single SOA and checker based on dual SOAs. It can check 2-bit data errors occur during the 2-bits (A and B) optical signal transmission. The device utilizes the cross-gain modulation (XGM) effect and the four-wave mixing (FWM) effect of the SOA. By adjusting the center wavelength of the tunable optical band-pass filter (TOBPF) to realize different logic gates, which provide parity and check bits for the all-optical parity generator and checker. It can check whether there are errors in the data during the signal light transmission process and completes the operation in the 10 Gb/s pseudo-random return-to-zero (RZ) codes. A saturable absorber (SA) is configured to reduce extinction ratio (ER) and optical signal-to-noise ratio (OSNR) deterioration because of \"0\" codes noise and amplified noise of small signal Clk probe light. In this article, the experimental principles of the parity generator and parity checker are discussed in Section 2. In Section 3, the experiment results of parity bit penetrator and checker are discussed. The conclusion is given in Section 4.