Design and comparative analysis of fiber-coupled laser diode system using ball, cylindrical, and toroidal lens

Three different fiber-coupled laser diode system of size 500 μm are designed and simulated using Zemax optical design software. The performance of each designed system is compared in terms of output power and coupling efficiency. At the wavelength of 808 nm, the output of a 10-watt single emitter laser diode is coupled into the multimode fiber. Since the laser diode beam is highly divergent, in order to reduce the divergence angle and collimate the beam, the ball, cylindrical, and toroidal lenses are used as a collimator. The focused beams are coupled into a 200 μm core diameter multimode fiber, which has a numerical aperture of 0.22. Beam parameter product is calculated as the product of half waist width and half far-field divergence angle to evaluate the beam quality. The ray simulation results revealed that the output power with the ball lens is 9 watts, corresponding to a total coupling efficiency of 90%. Similarly, the calculated output power is 9.2 watt from the cylindrical lens, resulting to a total coupling efficiency of 92%. The calculated output power with the toroidal lens is greater than 9.5 watts, corresponding to a total coupling efficiency of more than 95%. The comparative analysis of newly designed system shows that with a toroidal profile, fiber-coupled laser diode attained the highest coupling efficiency with minimum aberrations.