Demonstration of LDPC-coded PS-64QAM OFDM employing novel bit-class distribution matching in a W-band RoF system

In this work,we proposed and experimentally demonstrated a novel probabilistic shaping(PS)64-ary quadrature amplitude modulation(QAM)orthogonal frequency division multiplexing(OFDM)with low-density parity-check(LDPC)-coded modulation in a W-band radio-over-fiber(RoF)system using envelope detection.The proposed PS scheme has the advantages of no complex multiplication and division operations and low hardware implementation complexity.In our experiments,the two-stage bit weight distribution matching-based PS-64QAM OFDM signals with a rate of 28.13 Gb/s transmission over 4 m wireless+45-km standard single-mode fiber transmission can be achieved.The system performance is investigated under one LDPC code rate(3/4)and two PS parameter values(k=3 and 9).The experimental results show that the receiver power sensitivity and the system fiber nonlinear effect tolerance can be significantly improved compared with uniformly distributed OFDM signals.

Neural network equalization based on delta-sigma modulation

We propose a neural network equalization delta-sigma modulation(DSM)technique.After performing DSM on the multiorder quadrature amplitude modulation(QAM)orthogonal frequency division multiplexing(OFDM)signal at the transmitting end,neural network equalizer technology is used in the digital signal processing at receiving end.Applying this technology to a 4.6 km W-band millimeter wave system,it is possible to achieve a 1 Gbaud 8192-QAM OFDM signal transmission.The data rate reached 23.4 Gbit/s with the bit error rate at 3.8×10^(-2),lower than soft-decision forward-error correction threshold(4×10^(-2)).

High-security multi-constellation shaping modulation with asymmetric encryption

This Letter proposes a high-security modulation scheme for optical transmission systems.By using multi-constellation shaping and asymmetric encryption,the information security can be enhanced and quantum computer cracking can be effectively resisted.Three-dimensional(3D)carrier-less amplitude phase modulation is utilized to superposition and transmit 3D signals.Experimental verification is conducted using a seven-core weakly coupled fiber platform.The results demonstrate that the proposed scheme can effectively protect the system from any illegal attacker.

3D waveguide device for few-mode multi-core fiber optical communications

Space-division multiplexing based on few-mode multi-core fiber(FM-MCF)technology is expected to break the Shannon limit of a single-mode fiber.However,an FM-MCF is compact,and it is difficult to couple the beam to each fiber core.3D waveguide devices have the advantages of low insertion loss and low cross talk in separating various spatial paths of multi-core fibers.Designing a 3D waveguide device for an FM-MCF requires considering not only higher-order modes transmission,but also waveguide bending.We propose and demonstrate a 3D waveguide device fabricated by femtosecond laser direct writing for various spatial path separations in an FM-MCF.The 3D waveguide device couples the LP01 and LP11a modes to the FM-MCF with an insertion loss below 3 dB and cross talk between waveguides below-36 dB.To test the performance of the 3D waveguide device,we demonstrate four-channel multiplexing communication with two LP modes and two cores in a 1-km few-mode sevencore fiber.The bit error rate curves show that the different degrees of bending of the waveguides result in a difference of approximately 1 dB in the power penalty.Femtosecond laser direct writing fabrication enables 3D waveguide devices to support high-order LP modes transmission and further improves FM-MCF communication.

High-speed Stokes vector receiver enabled by a spin-dependent optical grating

Stokes vector direct detection is a promising,cost-effective technology for short-distance communication applications.Here,we design and fabricate a spin-dependent liquid crystal grating to detect light polarization states.By separating the circular and linear components of incident light,the polarization states can be resolved with accuracy of up to 0.25°.We achieved Stokes vector direct detection of quadrature phase-shift keying(QPSK),8 PSK,and16-ary quadrature amplitude modulation signals with 32,16,and 16 GBd rates,respectively.We integrated the system,including the grating,photodetectors,and optical elements,on a miniaturized printed circuit board and demonstrated high-speed optical communications with 16 GBd rate QPSK signals.

Physical layer data encryption using two-level constellation masking in 3D-CAP-PON

A novel physical layer data encryption scheme using two-level constellation masking in three-dimensional(3D)carrier-less amplitude and phase modulation(CAP)passive optical network(PON)is proposed in this Letter.The chaotic sequence generated by Chua’s circuit model realizes two-level encryption of displacement masking and constellation rotation for3 D constellations.We successfully conduct an experiment demonstrating 8.7 Gb/s 3 D-CAP-8 data transmission over25 km standard single-mode fiber.With two-level constellation masking,a key space size of 2.1×1085 is achieved to bring about high security and good encryption performance,suggesting broad application prospects in future short-range secure communications.