A method for realizing optical label switching by constructing XOR optical logic gate based on XGM effect of SOA

0 Introduction
Optical label switching (OLS) refers to the process of extracting and replacing optical labels to realize the routing and switching of user information. In recent years, many novel solutions for OLS technology have been proposed at home and abroad, such as subcarrier optical labels, time-division multiplexing optical labels, multi-wavelength optical labels, optical code labels, orthogonal modulation optical labels, etc. At present, optical label switching technology has become a research hotspot in the field of optical switching.
Optical labels are usually generated by optical modulation and processed by optical or electrical methods. Regarding label processing, according to the methods currently proposed, one is to use Fabry-Perot filter (FP Filter), nonlinear optical loop mirror (NOLM) optical filter, terahertz optical asymmetric demultiplexer (TOAD) and ultra-high-speed nonlinear interferometer (UNI) to erase the label first, and the insertion of new label information is usually achieved by using LiNbO3 external modulator. The other is to use SOA or optical logic gate devices to achieve label erasure and regeneration.
This paper applies the XOR optical logic gate constructed by the XGM effect of SOA to optical label switching. Through simulation, label switching is realized in a non-return-to-zero code DPSK/ASK orthogonal modulation optical label switching system with a payload information rate of 10Gbit/s and a label information rate of 2.5Gbit/s.

1 Working principle
1.1 Principle of XOR logic gate based on SOA XGM
The structure of XOR gate based on SOA XGM is shown in Figure 1. Signal A is used as the detection light and signal B is used as the pump light. The power of B is much greater than the power of A. When both A and B signals are "1", for SOA-1, because there is a strong pump light B incident on the right end, B will compete for most of the carriers in SOA-1, and signal A will be saturated and absorbed, so the right end of SOA-1 can be regarded as outputting "0"; only when there is no input on the right end, A can be amplified by SOA1 and output as "1". That is, SOA-1 realizes logic operation. Similarly, SOA-2 realizes logic operation. Then the two output signals are coupled to realize the XOR operation between signal A and signal B, that is.

1.2 Principle of optical label switching based on XOR
Assume that the optical label pulse sequence of the input signal is 01001, and the optical label to be exchanged is set to the 1st, 4th and 5th bits, and control the sequence of the detection light entering the XOR optical logic gate. After the XOR logic operation, the required label exchange can be achieved, and the final output result is 11010. At the same time, the old label information is also erased in this process.
0 Introduction
Optical label switching (OLS) refers to the routing and exchange of user information by extracting and replacing optical labels. In recent years, many novel solutions have been proposed for OLS technology at home and abroad, such as subcarrier optical labels, time division multiplexing optical labels, multi-wavelength optical labels, optical code labels, orthogonal modulation optical labels, etc. At present, optical label switching technology has become a research hotspot in the field of optical switching.
Optical labels are usually generated by optical modulation, and optical labels are processed by optical or electrical methods. Regarding tag processing, the methods proposed so far include: one is to use Fabry-Perot filter (FP filter), nonlinear optical loop mirror (NOLM) optical filter, terahertz optical asymmetric demultiplexer (TOAD) and ultra-high-speed nonlinear interferometer (UNI) to erase the tag first, and the insertion of new tag information is usually achieved by using LiNbO3 external modulator. The other is to use SOA or optical logic gate devices to achieve tag erasure and regeneration.
In this paper, the XOR optical logic gate constructed by the XGM effect of SOA is applied to optical tag switching. Through simulation, tag switching is realized in a non-return-to-zero code DPSK/ASK orthogonal modulation optical tag switching system with a payload information rate of 10Gbit/s and a tag information rate of 2.5Gbit/s.

1 Working Principle
1.1 Principle of XOR Logic Gate Implementation Based on SOA
XGM The structure of XOR gate implemented based on SOA XGM is shown in Figure 1. Signal A is used as detection light and signal B is used as pump light. The power of B is much greater than the power of A. When both A and B signals are "1", for SOA-1, because there is strong pump light B incident on the right end, B will compete for most of the carriers in SOA-1, and signal A will be saturated and absorbed. Therefore, the right end of SOA-1 can be regarded as outputting "0"; only when there is no input on the right end, A can be amplified by SOA1 and output as "1". That is, SOA-1 implements logic operation. Similarly, SOA-2 implements logic operation. Then the two output signals are coupled to realize the XOR operation between signal A and signal B, that is.

1.2 Principle of optical label switching based on XOR
Assume that the optical label pulse sequence of the input signal is 01001, the optical label to be exchanged is set to the 1st, 4th and 5th bits, and control the sequence of the detection light entering the XOR optical logic gate. After the XOR logic operation, the required label exchange can be achieved, and the final output result is 11010. At the same time, the old label information is also erased in this process.
2 System design and simulation experiment
The simulation structure of the DPSK/ASK orthogonal modulation optical label switching system is shown in Figure 3. It mainly consists of three parts: the generation of DPSK/ASK modulated signals, label exchange by XOR optical logic gates, and reception and demodulation of DPSK/ASK modulated signals. At the transmitting end, a continuous wave is generated by a distributed feedback laser, and its wavelength is set to 1550nm. The optical carrier is differentially phase modulated by a Mach-Zehnder modulator to generate load information with a rate of 10Gbit/s. Then, the carrier is intensity modulated by a Mach-Zehnder modulator to generate label information with a rate of 2.5Gbit/s. The pulse sequence of the label information is set to 01001. In the tag exchange part, XOR optical logic gate is used to realize tag exchange. The pulse sequence of control information entering XOR optical logic gate is set to 10011. After tag exchange, a new optical packet is formed and transmitted through 80km single-mode fiber (SMF) and 16km dispersion compensation fiber (DCF). At the receiving end of the system, the pre-placed erbium-doped fiber amplifier (EDFA) is used for signal amplification. Then, the orthogonal modulated signal first passes through a narrow-band optical filter and then is separated by a coupler. One signal is directly photoelectrically converted to extract the tag signal, and the other enters a 1-bit delay interferometer for optical domain demodulation. After coherent demodulation, the optical phase signal is converted into an optical intensity signal. The two signals are respectively photoelectrically converted, filtered by a low-pass filter, and difference calculation is performed to finally obtain the payload information.

Before the XOR optical logic gate is used for tag exchange, the time domain waveform of the original ASK tag information is shown in Figure 4(a), and the time domain waveform of the new tag information after the optical tag exchange is shown in Figure 4(b). As can be seen from the figure, when the DPSK/ASK signal passes through the XOR optical logic gate generated by the XGM effect of SOA, the DPSK payload information will not be changed. However, through the XOR logic operation, the old ASK tag information is erased and a new ASK tag information is generated. As can be seen from Figure 4(b), the output result is 11010, which is consistent with the theoretical value.

3 Conclusion
This paper uses the XGM effect of SOA to form an XOR optical logic gate, and applies it to the DPSK/ASK orthogonal modulation optical tag exchange system to complete the tag exchange. Optisystem7.0 is used for simulation analysis. The results show that the full optical domain tag exchange of 2.5Gbit/s ASK tag information is successfully achieved through the XOR optical logic gate.
This scheme of implementing optical labeling based on SOA to form XOR logic gates has the advantages of simple structure, easy implementation, high label exchange rate, etc. At the same time, this scheme also takes advantage of the high spectrum utilization of orthogonal modulation; simple separation of label information and payload information; DPSK payload information has strong anti-nonlinear ability, etc. However, this scheme is completed in a specific optical label exchange system, and ASK label information is easily affected by factors such as carrier recovery time and other nonlinear effects in SOA, which has certain reference value for the application and development of optical label exchange technology.