Search

The linear polarized (LP) mode multiplexer based on the inverse designed multi-plane light conversion (MPLC) has the advantages of low insertion loss and low mode crosstalk. However, the multiplexer also requires the fabrication and alignment accuracy in experiments, which have not been systematically analyzed. Here, we perform the error tolerance analysis of the MPLC and summarize the design rules for the LP mode multiplexer/demultiplexer. The error tolerances in the fabrication process and experimental demonstration are greatly released with proper parameters of the input/output optical beam waist, the pitch of optical beam array, and the propagation distances between the phase plane. To proof this design rule, we experimentally demonstrate the LP mode multiplexer generating LP01, LP11a, LP11b, LP21 modes and coupling to the few mode fiber, with the insertion loss lower than -5 dB. The LP modes are demultiplexed by MPLC, with the crosstalk of different mode groups lower than -10 dB. LP modes carrying 10 Gbit/s on-off keying signals transmit in a 5 km few mode fiber. The measured bit error rates (BER) curves of the LP01, LP11a, LP21 modes have the power penalties lower than 12 dB.

A parallel bit-interleaved filter-bank multicarrier/offset quadrature amplitude modulation (FBMC/OQAM) security strategy based on four-dimensional chaos is proposed in this paper. After the QAM constellation point distribution is disturbed, the modulated FBMC bits and symbols are interleaved and encrypted to realize the improvement of the FBMC/OQAM system physical layer security performance. The chaotic sequence generated by the four-dimensional hyperchaotic system is optimized and calculated to control the disturbance process, which enhances the performance of the system against illegal malicious attacks. The parallel encryption scheme proposed in this scheme increases the encryption efficiency by 1.43 times; can provide a keyspace of 1090 size, which effectively resists brute force attacks; and improves the physical layer security of the system. The proposed FBMC/OQAM parallel bit interleaved encryption scheme using a 5 km weakly coupled four-mode fiber achieves a 3×10 Gb/s multiple-input multiple-output-free transmission. The experimental results show that this scheme can effectively improve the security performance of the system, and combines the few-mode multiplexing technology with advanced modulation. It is a candidate for the future large-capacity and high-security optical transmission system.

Given by the Shannon theorem, the data rate in a single mode fiber is approaching the capacity limit of 100 Tbit/s, which even applies to all existing wavelength division multiplexing and advanced modulation formatting techniques. Optical vortex beams, including orbital angular momentum (OAM) beams with phase singularities and cylindrical vector beams (CVBs) with polarization singularities, are orthogonally structured light beams providing new degrees of freedom for multiplexing optical communication, for which the multiplexer is the key component. Although there are various OAM detection approaches such as the optical geometric transformation and vortex grating, CVB sorting with high efficiency and large dynamic range has not been demonstrated before. In this work, we propose and demonstrate an efficient approach for multiple coaxial CVB sorting based on the spin-dependent optical geometric transformation using the Pancharatnam–Berry optical element device fabricated with the photoaligned liquid crystal....

With growing data demands, the capacity of the single-mode fiber will reach its limit. Cylindrical vector beams (CVBs) as the eigenmodes of fiber have been demonstrated to increase the capacity in multiplexing optical communication. As a key component of CVB multiplexing, the sorter based on spin-dependent optical geometric transformation has the advantages of high efficiency and a large channel number. However, the demonstrated spatial resolution of the CVB sorter was not sufficient to separate the adjacent CVB orders. Therefore, there were still serious crosstalk issues for the CVB multiplexing channels. Here, we propose and demonstrate the high-resolution CVBs sorting by introducing fan-out structures in the spin-dependent optical geometric transformation. The crosstalk among the CVBs are suppressed compared with the original design. In addition, a cylindrical lens is used to modify the output beams to Gaussian shape. We experimentally demonstrate the sorting of 4 coaxial CVB channels to standard multimode fiber array. In the numerical modeling, we also design the CVB sorter for free space to integrated waveguide array demultiplexing.

The amount of information is increasing rapidly to reach the capacity limit of single mode fiber. Cylindrical vector beams (CVBs) as the eigenmodes of fiber have been demonstrated to increase the capacity in multiplexing optical communication. As a key component of CVB multiplexing, a sorter based on spin-dependent vortex Dammann grating has advantages of uniform power distribution and compact size. Here, we propose and demonstrate a spin-dependent vortex Dammann grating device that can realize the sorting of multiple CVBs. By a spin-dependent focusing lens, the spin components of the CVBs are selectively focused or derived; therefore, the coaxially incident CVBs are separated effectively. We also experimentally demonstrate the CVB demultiplexing communication enabled by the grating with low channel cross talk satisfying the communication requirement.

The cylindrical vector beams (CVBs) as the spatially orthogonal modes in fiber provide additional degree of freedom for optical fiber communication. The ring-core fibers with a high refractive index area matching with the beam shape of CVBs are suitable for stable transmission of CVBs. We simulate and experimentally characterize the CVBs transmission in ring-core fibers with different geometric structure parameters. We demonstrated the transmission of CVBs from 2nd to 7th orders with mode purities higher than 80% and demonstrate the multiplexing communication of coaxial high order CVBs in ring-core fiber. The model we build to calculate the largest CVB mode number and order supported in the ring-core fiber are consistent with the experimental results of our three ring-core fibers. From the simulation results, the higher order CVB modes show larger effective refractive index differences and less crosstalk compared with the lower orders modes. According to the calculation, it is possible to transmit up to 4 mode groups of high order CVB modes in the ring-core fiber with optimized geometric parameters, given by the effective refractive index threshold of 2 × 10−3.

A cascaded phase-only mask architecture (or an optical diffractive neural network) can be employed for different optical information processing tasks such as pattern recognition, orbital angular momentum (OAM) mode conversion, image salience detection and image encryption. However, for optical encryption and watermarking applications, such a system usually cannot process multiple pairs of input images and output images simultaneously. In our proposed scheme, multiple input images can be simultaneously fed to an optical diffractive neural network (DNN) system and each corresponding output image will be displayed in a non-overlap sub-region in the output imaging plane. Each input image undergoes a different optical transform in an independent channel within the same system. The multiple cascaded phase masks in the system can be effectively optimized by a wavefront matching algorithm. Similar to recent optical pattern recognition and mode conversion works, the orthogonality property is employed to design a multiplexed DNN.

Mode division multiplexing provides mutually orthogonal communication channels to break the capacity-per-fiber limit given by the Shannon theorem. Cylindrical vector beams (CVBs) as a set of orthogonal eigen modes in optical fiber have the potential application in high capacity optical communication. However, there is still no efficient multiplexing/demultiplexing scheme for coaxial multiple CVBs generation and detection. In this work, we propose and demonstrate the efficient sorting of coaxial multiple CVBs based on the anisotropic geometric optical transformation approach using the Pancharatnam-Berry optical element (PBOE) device. The device is fabricated by the photo-alignment liquid crystal (LC) in a thin film with a total pixel number of 768×768 and a pixel size of 11.7 μm. Since the PBOE has the circular polarizations selective property, the device can independently modulate the left-handed circular polarized and right-handed circular polarized light components of CVB. The anisotropic geometric optical transformation is capable of transforming the ring-shape intensity distribution of CVB to two straight lines. Through the phase correction and fourier transform, the CVB is finally converted to a spot with a lateral displacement proportional to the input CVB orders. In the proof of concept experiment, we demonstrated CVB sorting with a large dynamic sorting range of 20 different orders of CVBs with efficiency up to 61.7%. The coaxial multiple CVBs with a minimal order interval of 3 are separated in the experiment. We also implement the CVB sorting approach in optical fiber communication system as a demultiplexer after 2.8 km signals transmission.

Optical vortex beams, including the orbital angular momentum beam (OAM) with the phase singularity and cylindrical vector beams (CVBs) with the polarization singularity, are orthogonal structured light beams providing a new degree of freedom for multiplexing optical communications. There are already several mature approaches for the OAM detection such as the fork grating and geometric optical transformation. However, the technique for efficient CVBs sorting has not been demonstrated yet. In this work, we propose and demonstrate the efficient sorting of multiple CVBs based on the anisotropic geometric optical transformation approach using the Pancharatnam-Berry optical element (PBOE) device. The device is fabricated by the photo-alignment liquid crystal (LC) in a thin film with a total pixel number of 768×768 and a pixel size of 11.7μm. Since the PBOE has the circular polarizations selective property, the device can independently modulate the left-handed circular polarized and right-handed circular polarized light components of CVB. The anisotropic geometric optical transformation is capable of transforming the CVB from the donut shape to two straight lines shape. Through the phase correction and a Fourier transform by lens focusing, the CVBs is finally converted to a single light spot with a lateral displacement proportional to the input CVBs orders. In the proof of concept experiment, we demonstrated the CVBs sorting from -10 to 10 orders with an efficiency up to 61.7%. We also demonstrated multiple coaxial CVBs demultiplexing. The CVB sorting approach shows potential applications in optical multiplexing communication.

We propose and demonstrate high order cylindrical vector beams transmission in air-core photonics crystal fiber. According to the numerical simulation and experiment, the mode purities of CVBs are measured as high as 67%.