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. We demonstrate
a CVB multiplexing communication system in both free space and few-mode
optical fiber. The CVB sorter is compatible with wavelength division
multiplexing and shows the potential to further increase the communication
capacity by 1–2 orders of magnitude.
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.
Multiplexing and demultiplexing of optical orbital angular momentum (OAM) are critical operations in mode-division multiplexing communications. Traditional Dammann gratings, spiral phase planes, and optical geometric transformations are regarded as convenient methods for OAM mode (de)multiplexing. However, crosstalk between the different modes and the difficulty of mode multiplexing greatly limit their application to mode-division multiplexing communications. Here, using a set of inversely-designed phase planes, we demonstrate an OAM (de)multiplexer based on multiphase plane light conversion that can enable perfect OAM multiplexing communication. The sorted patterns are Gaussian-like and can be coupled easily into single-mode fiber arrays. Inputs from the fiber array are turned into coaxial OAM modes after the phase planes. OAM mode crosstalk generated by the multiplexer is less than
−
20
dB
, with insertion loss of less than 2.6 dB. OAM modes are sorted by the demultiplexer with mode crosstalk below
−
10
dB
, and the sorting results are coupled to the fiber array. OAM modes carrying 10 Gbit/s on–off keying signals were transmitted in a 5 km few-mode fiber. The measured bit-error-rate curves have power penalties of less than 10 dB. The proposed configuration is highly efficient and convenient and will be beneficial for potential applications in quantum information, information processing, and optical communications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.