A common phase-type spatial light modulator (SLM) can only modulate the phase part of a complex-amplitude hologram calculated from an object image. To calculate a phase-only hologram, iterative methods such as the Gerchberg–Saxton algorithm can be employed. However, one-step non-iterative phase-only hologram calculation is more favorable for real-time applications. This paper proposes a novel scheme to optimize a shared phase mask from a set of training images. Then a phase-only hologram can be simply calculated by phase truncation after any given object image similar to the training samples is multiplied with the shared mask and Fresnel diffracted. The speckle noise in the reconstructed images can be significantly suppressed if our optimized phase mask is used instead of a conventional random phase mask.
Traditional quartz optical fibers can not overcome their own shortcomings in non-linearity, Rayleigh scattering, dispersion and high delay[1,2], while anti-resonant hollow fibers can break through Shannon limit, and have the characteristics of low loss, low delay, high bandwidth and high damage threshold. With the development of new technologies such as Internet of Things and large data, people's increasing demand for information and traditional reuse. Ways including wavelength division multiplexing, frequency division multiplexing and space division multiplexing have gradually encountered bottlenecks . We need to explore new ways of multiplexing, improve the information capacity of communication networks, and meet the growing information needs of people. Through research, we find a new type of cylindrical vector beams, which is not only the spatial orthogonal mode, but also the basis of optical fibers. The signature mode can improve the communication capacity of the channel.
The data rate in a single-mode fiber is approaching the capacity limit given by the Shannon theory. Mode division multiplexing, such as few modes, orbital angular momentum, and cylindrical vector beam (CVB) multiplexing, has shown great potential to further increase data capacity in both free-space and fiber communication. We propose and demonstrate high-order CVB multiplexing communication in an air-core photonics crystal fiber (PCF). The simulation results show that the 19-cell air-core PCF supports transmission of CVB modes from ±1 to ±4 orders. In the experiment, ±1- to ±4-orders CVBs are transmitted in 8.25-m-long air-core PCF with the mode purities higher than 76.5%. We demonstrate four coaxial CVB channel communication by multiplexing the ±2- and ±3-orders CVB modes. Each CVB channel carries 10-Gbit/s on–off keying signals and the measured bit error rates satisfy the forward error correction threshold. CVB communications based on air-core PCF can be used in short-distance optical communication with high capacity and low optical latency.
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.
The Ring-Core fiber (RCF) which can support several cylindrical vector beam (CVB) modes is desirable for future ultrahigh capacity space-division multiplexing (SDM). However, the size differs between adjacent CVB modes which result in mismatch in coupling. In this study, we design a simple and stable scheme to generate PPVs with adjustable orders and beam sizes. By changing the holograms encoded on the SLM, different sides PPVs of the same order can be obtained. We demonstrate PPVs range from +1 order to +9 order. Furthermore, with the employment of 25× object glass we couple the PPVs into graded-index Ring-Core fiber (GI-RCF) supporting 3 CVB mode-groups (i.e. HE21, HE31 and HE41) at 1550 nm wavelength. We also demonstrate the mode-groups (HE31 and HE41) transmitting over a 3m GI-RCF, respectively.