Low-Cost Spatial Light Modulator for Applications in Free-Space Optical Communication

Spatial Light Modulators (SLMs) are core components deployed for Adaptive Optics (AO) to compensate for atmospheric distortions. AO is an enabling technology for Free-Space Optical Communication, whose performance is severely degraded by the atmosphere. This thesis proposes two low-cost AO strategies: (1) repurposing Liquid Crystal (LC) SLM from an old display projector and (2) sensorless correction enabled by the Stochastic Parallel Gradient Descent (SPGD) algorithm. A second-hand Mitsubishi XL8U projector is disassembled to extract its LC panel and characterized. The characterization is performed by Jones matrices and a Mach-Zehnder interferometer (MZI) to obtain the intensity and phase responses. Phase-mostly operation is achieved through the use of linear polarizers that result in a transmittance variation of 11.5x10^{-3} [a.u.] and a maximum phase range of maxphase=56.66 [deg.]. Atmospheric turbulence is modeled using Monte Carlo phase screens generated by Fourier filtering white Gaussian noise with the Kolmogorov spectrum in the spatial frequency domain. The simulated turbulence, validated against the theoretical coherence function at C_n^2=1x10^{-15} [m^{-2/3}] over a 5 [km] path at lambda=1550 [nm], is used to assess system performance. Then, the SPGD algorithm optimizes x-tilt, y-tilt, and defocus Zernike polynomials, improving the quality metric function by 13% under phase-limited conditions in simulation. Similarly, the SPGD algorithm is employed again for a propagation path 2.85 [m], where the system achieved a 406% increase in quality metric function. These results demonstrate that a low-cost, sensorless AO system using a repurposed LC SLM can achieve modest correction of atmospheric aberrations under phase-limited conditions. The SPGD algorithm yielded a 13% improvement in simulation and a 406% improvement in the experiment. Although modest, these improvements validate the cost-reducing strategies and highlight the potential for low-cost SLM in FSOC links where budget constraints are stringent.

Department dc:contributor.department

Electrical and Computer Engineering

Year dc:date.issued

2026

Author dc:creator

• Alrubaian, Abdulkareem

Advisor dc:contributor.supervisor

• Yam, Scott

• Adaptive Optics
• Atmospheric Turbulence
• Spatial light Modulators
• Angular Spectrum Propagation
• Free-Space Optical Communications
• Liquid Crystals
• Jones Matrix
• Kolmogorov Structure Function
• Stochastic Parallel Gradient Descent
• Zernike Polynomials
• Fourier Optics

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/1974/36113

OAI identifier oai:identifier

oai:queensu.scholaris.ca:1974/36113