Laser-Based LiFi Network

Phase 1 asks a simple question: what does an indoor LiFi link gain when the usual LED transmitter is replaced with a laser? The design uses a 1552 nm continuous-wave laser at 17 dBm, trading the LED's broad glow for a narrow, directional beam with far higher optical power.

The complete link is built in OptiSystem at 10 Mbps. A pseudorandom bit stream is shaped into NRZ pulses and imposed on the optical carrier by a Mach-Zehnder modulator. The beam crosses a line-of-sight free-space channel, is cleaned by a Gaussian optical filter, and is converted back to current by a PIN photodiode. A transimpedance amplifier and a third-order Chebyshev low-pass filter then recover the signal.

At the 6 m design distance the link achieves a Q-factor near 15.8 and a minimum BER of about 1.6×10⁻⁵⁶, roughly a 9% improvement in Q-factor over a published LED-based design, and it remains reliable (Q > 6) well beyond 12 m.

Five recovery filters were compared (Gaussian, Bessel, Butterworth, Cosine, Chebyshev); the Chebyshev gave the best balance of noise rejection and signal quality. The work is written up as a research paper, publication pending.

Phase 2 introduces beam steering into the link. A digital micromirror device (DMD) is modeled electromechanically in COMSOL Multiphysics: an applied voltage produces an electrostatic torque, the micromirror tilts, and ray optics traces the redirected beam. This mirror response is embedded in the OptiSystem link as a MATLAB-based DMD element, allowing the complete system, from laser to receiver, to be simulated with physically accurate steering behavior.