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6 October 2003 Use of mathematical software for calculating the pointing angle of laser diode
Proceedings Volume 9663, Eighth International Topical Meeting on Education and Training in Optics and Photonics; 966327 (2003) https://doi.org/10.1117/12.2208505
Event: Eighth International Topical Meeting on Education and Training in Optics and Photonics, 2003, Tucson, Arizona, United States
Abstract
A practical method was developed by a production engineer and a technician to measure the pointing angle of laser diode using a circular aperture. The method provided qualitative measurement only. A theoretical analysis using a mathematical software such as Mathcad shows that the method can provide quantitative measurement as well.

A production engineer (BS degree) and a technician (no degree) developed a practical method for measuring the pointing angle of laser diode before the laser diode is coupled with a single mode fiber. First, the total power of the laser diode (assuming A mW) is measured before the laser diode is fixed in the fixture. After the laser diode is fixed in the fixture, a small circular aperture (smaller than the beam waist) is centered at the mechanical axis of the fixture. The power of light passing through the aperture (assuming B mW) is measured as shown in Fig. 1. The pointing angle can be represented by the value of B/A. The larger is the pointing angle, the smaller is B/A. After the aperture is removed, the light is focused into a single mode fiber at the mechanical axis using proper optics. The coupling efficiency is defined as C/A, where C is the measured output power (in mW) from the single mode fiber. The effect of the pointing angle of laser diode on the coupling efficiency is shown in the table of C/A versus B/A.

The power of light after passing through the aperture as a function of d (see Figs. 1 and 2) can be calculated, provided that the laser diode beam has been corrected to a circular Gaussian beam . The Gaussian intensity is I(x,y) = I0 exp{-[2(x+d)2+2y2]/α2}, where α is the beam waist, and I0 = 2A/παa2 (remember A is the total power). The power , where a is the aperture radius, and . Although B or P(d) cannot be derived analytically, it can be calculated and plotted using a mathematical software such as Mathcad. Therefore, we can calculate the pointing angle θ from the value B/A.

## Fig. 2.

Positions of laser beam and aperture on aperture plane. In conclusion, we have shown how to improve a practical qualitative method developed by an engineer and a technician in a real production facility to an academic quantitative method using a theoretical analysis and a mathematical software such as Mathcad. This will be a good teaching material in the class.

## Reference



S. Jutamulia, “Correction of laser diode beam using microlens optics,” Optical Memory and Neural Networks, 10, 113-116 (2001).Google Scholar 