Orbital angular momentum (OAM) with mutually orthogonal advantage attribute to break through the high capacity and long-reach transmission limited in the classical passive optical network (PON). Employing Laguerre Gaussian (LG) mode as the orthogonal OAM excitation, a more dimensional multiplexing PON system is proposed to creatively hybridize OAM division multiplexing (OAM-DM) based on wavelength division multiplexing (WDM) and orthogonal frequency division multiplexing (OFDM). By utilizing the compatibility of OAM-DM and WDM, data of 40 Gbit/s OFDM signals is successfully transmitted in 80 km multimode fiber (MMF) with low crosstalk. Within this hybrid system, the effects of different wavelengths and different modes on the bit error rate (BER) are discussed at varying transmission distances. Moreover, the performance of several subsystems carrying quadrature phase-shift keying (QPSK), on-off keying (OOK), and OFDM modulation signals is also compared at a BER less than 3.8×10−3. It is observed that the proposed OAM-DM-WDM-OFDM-PON system has favorable performance, which is a reasonable solution for large-capacity PON architecture.
Microwave signals carry important intelligence information in electronic warfare. Hence, the measurement of microwave signals plays a very important role. Traditional electronic microwave measurement systems are not appropriate for the instantaneous frequency measurement (IFM) of high-speed signals. A simple and low-cost photonic approach to the IFM based on frequency-to-power mapping is proposed and demonstrated with a reasonable resolution. The measurement is performed on account of a double Mach–Zehnder modulator (MZM), single-mode fiber (SMF), photodetector (PD), and signal processing. The scheme using four wavelengths achieves resolutions of ±0.1 and ±0.09 GHz respectively for the 15.8–18.4 and 18.4−21.2 GHz frequency measurement ranges. Therefore, the scheme is a broad prospects method for high-resolution IFM. Moreover, it is of great importance for applications in electronic warfare and high-resolution sensor systems.
A technique of continuous shaping current waveform to suppress relaxation oscillations (ROs) of distributed feedback (DFB) laser for a high-performance optic system is demonstrated. To effectively suppress ROs, expressions for the shaping current waveform are theoretically derived based on the rate equations and different polynomials for the 3 rd , 5 th , and 8 th order Fourier basis functions are introduced. The convolutional neural network (CNN) is employed to predict the multi-parameter values that determine the results of the shaping input current, which exempt from the difficult and time-consuming process of parameter selection. Prior to training, preprocessing of the data obtained from DFB laser forward simulation using min-max normalization aims to improve the training efficiency of the CNN. The shaping current signals obtained from the CNN predicted parameters are put into the equivalent circuit model for the DFB laser to verify the effectiveness of the shaping current technique and CNN parameter optimization. Afterwards, the shaping current waveform is verified in a time division multiplex passive optical network (TDM-PON) utilizing the DFB laser model as a directly modulated source achieving remarkable performance with low cost. The results show that the high-order continuous shaping current modulated technique can successfully suppress the ROs and enhance the performance of the optic system.
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