The multiplexing of vortex beams carrying orthogonal orbital angular momentum (OAM) modes holds the potential to enhance the channel capacity (CC) of wireless optical communication systems. This paper proposes a method that utilizes optical phase conjugation (OPC) wavefront shaping by spatial light modulator (SLM), and regards the scattering medium diffuser (SMD) as an optical modulator to achieve the demultiplexing of multiplexed OAM beams through space channel. We also analyze the communication capability of the demultiplexing system in the atmospheric turbulence (AT) channel. In the proposed system, a simulation setup is employed where multiplexed OAM beams propagate through an AT channel simulated by a random phase screen. At the receiving end, the OPC method is used to obtain a phase mask that is loaded onto the SLM for wavefront shaping of the input multiplexed OAM light. The light field is then modulated through the SMD's multi-scattering effect, enabling the separation of multiplexed OAM beams to distinct detection positions for demultiplexing. This paper investigates the influence of the OAM mode and AT strength on the focusing of single-mode OAM beams. Additionally, it examines the impact of OAM multiplexing combinations, AT strength, and transmission distance on the detection probability, bit error rate (BER), and CC. The results demonstrate the effectiveness of the demultiplexing system in mitigating mode expansion caused by AT, offering valuable insights for the design of robust OAM multiplexing systems.
Orbital angular momentum (OAM) of vortex beams can extend the capacity and spectral efficiency of free-space optical (FSO) communication for its orthogonality provide an extra dimension. However, atmospheric turbulence (AT) will lead to wave-front distortion, crosstalk between OAM modes and eventually reduce the communication system performance. This paper uses a Phase Diversity (PD)-based adaptive optics (AO) schema to compensate the OAM beam. With the General Regression Neural Network (GRNN), the relationship between the intensity distribution and the wave-front distortion of propagation in AT channel is established, and the wave-front aberration is retrieved. This method is simple in structure without phase sensor and probe beam, and reduces computation compared with the common phase retrieval algorithms. Therefore, it can compensate OAM beam in a second and ensure the similar retrieve effect.
Effects of oceanic channels degrade the performance of underwater optical communication (UOC) systems based on orbital angular momentum (OAM) multiplexing. Considering both oceanic turbulence and water attenuation, a more comprehensive channel model is proposed. We derive the expressions of bit error rate (BER) and aggregate capacity of UOC-OAM systems. We also investigate the system performance with wavelengths of 400-700 nm . The numerical simulation results show that the blue-green wavelength is not always the best choice to provide large channel capacities for UOC-OAM systems. For large chlorophyll-a concentration channel, due to the strong attenuation the optimal wavelength is shifted toward red wavelength region. Meanwhile, with increasing of oceanic turbulence strength, the frequency bandwidth decreases and systems with larger wavelength show better performance. These results will be beneficial to the design and application of UOC-OAM systems.
In terms of spherical vector wave functions (SVWFs) utilizing integral localized approximation method, the incident field and scattering field expansion coefficients can be derived. Using Generalized Lorenz Mie Theory (GLMT), the radiation force (RF) exerted on a single spherical particle by a LG beam is calculated. The effects of OAM states, beam waist, particle size, dielectric constants of particle and surrounding medium of axial RF have been numerically analyzed in detail.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.