International Core Journal of Engineering 2020-26 | Page 120

integrated into a rectangular wave by a non-return-to-zero code pulse trigger and then modulated onto the previous sine wave by OOK-modulation via the M-Z Modulator. Server A adds a delay, before the rectangular wave is modulated onto the carrier, to simulate an asynchronous scenario that the server may encounter. Two signals pass via a 50m fiber to the ToR for XOR encoding operation simulation design of optisystem for the platform. The above- mentioned Saganac-based all-optical logic gate is described in detail in [6]. The dynamic wavelength assignment algorithm for multi-server is described in [7]. The structure of the all-optical XOR gate at ToR is shown in Fig. 4. The XOR gate has two control ports, one for the clock signal and another for the ground. The principle of Saganac-based XOR gate requires signal of the control port and the input signal polarization orthogonal. Since the polarization angle of the light source of the input signal has been set to 90 degrees, the polarization angle of the clock control signal should be set to 0 degrees. The clock signal is also implemented by a non-return-to-zero code pulse trigger, and then the signal is modulated onto a light wave having a wavelength of 1550 nm and a power of 0.05 mW. The clock signal and the ground signal pass via the circulator to the X- type coupler. After coupling, the output signal and the input signal are respectively entered into the Saganac fiber ring via the polarization combiner. Since a power difference is required between the input signal and the control signal, the input signal is added to EDFA with a gain of 30 dB before entering the polarization synthesizer. The two signals are transmitted via a strong birefringent photonic crystal fiber and separated by a polarization beam splitter before reaching the coupler. Since the polarization of the polarization beam splitter is set to 0 degrees, the polarization angle of the output signal of the upper arm of the polarization beam splitter is 0 degrees. The clock signal is divided into CS and CSS signals by the coupler, which are respectively modulated by the input signals IP1 and IP2. After transmission via the fiber optic ring, a clock signal with a phase difference of " S " is output from the OP2 terminal, and a phase difference of "0" is output from the OP1 terminal. Therefore, the output of the OP2 terminal is an XOR result pulse sequence, that is, the result of the signal encoded. Fig. 5. (a)-(g) represent time traces of encoding and decoding processes at synchronous, asynchronous 0.25-bit and asynchronous 0.5-bit; (h) eye diagrams representing synchronous and asynchronous operations. IV. E XPERIMENTAL A ND S IMULATION R ESULTS The synchronous and asynchronous OPNC scheme was evaluated exerimentally by a 100 GHz subcarry. Fig.5 depicts time traces and eye diagrams of encoding and decoding processes at synchronous and asynchronous. Fig.5 (a) and Fig.5 (b) reveal the input time traces of the bit-level of Data A and Data B at synchronous and asynchronous. We insert as delay at Data A using sub-bit times-offsets of 12.5 ps (0.25 of the bit duration) and 25 ps (0.5 of the bit duration). The resultant traces are illustrated Fig.5 (c), where it is revealed that a logical “1”, when data A and B are different, and a logical “0”, when data A and B are the same. The figure can be seen the XOR encoded signal is damaged at asynchronous. They are no longer complete bits, and have many very narrow pulse waveforms smaller than 1 bit. Fig.5 (d) shows the decoded data A at the second Saganac-based XOR gate at synchronous and asynchronous, each generated by a bitwise XOR between the XOR encoded trace of Fig.5 (c). Fig.5 (e) reveals time trace after photoelectric conversion. The decoded time trace of Data A is equal to the initial pattern at synchronous. The trace of Data A can be successfully retrieved at asynchronous, too. However, the retrieved time trace of the sub-bit times-offsets of 0.25bit is worse than the sub-bit times-offsets of 0.5bit. Since the XOR encoded trace of sub-bit times-offsets of 0.25bit is narrower than 0.5bit. Narrow pulses are more susceptible to noise. In turn, Fig.5 (f) show the decoded data A at the second XOR gate at synchronous and asynchronous, each generated by a The encoded signal is broadcasted by a power splitter with a power division ratio of 1:2 and transmitted to the receiving end of A and B via a 50m optical fiber for decoding operation. For the sake of convenience, we simplified the system by sending the pulse signal of Data A directly to the server A via the optical fiber to replace the buffer data of the server A. The XOR decoding operation is performed with the encoding result of the ToR that has via the 50m fiber. Due to the power loss caused by the device and the fiber during the encoding operation, we need to use an EDFA to amplify the encoded signal to 2.08016 mW. The parameter setting of the XOR gate is the same as the previous encoding operation during decoding, and the encoded signal is XORed with the simultaneously transmitted A signal pulse to obtain the pulse waveform of the server B. The clock signal is divided into CS and CSS signals by the coupler, which are respectively modulated by the input signals IP1 and IP2. After transmission via the fiber optic ring, a clock signal with a phase difference of " S " is output from the OP2 terminal, and a phase difference of "0" is output from the OP1 terminal. The delay at the decoding is used to implement asynchronous decoding operations. The signal pulse waveform of the server B is obtained by passing the decoded signal via a photoelectric conversion and a low pass filter. Server B's bitstream is available after the threshold decision. This experiment is based on the 98