Analysis method of additional coupling loss caused by assembly error of self-focusing lens collimation system of fingerprint sensor

When two single-mode fiber collimators are coupled, the mismatch of the collimators will cause additional loss between the single-mode fibers.

When the length of the self-focusing lens is 1/4 pitch, that is, A=-rc/2, according to According to the mode-field coupling theory, the light field distribution is many, and the coupling efficiency of the Gaussian beam and the Gaussian beam is a conjugate complex number of Ga2. The fiber-to-fiber coupling efficiency of the fiber collimator under the conditions of off-axis coupling, off-angle coupling and spacing coupling is obtained.

In recent years, the self-focusing lens collimation system of fingerprint sensor of Fingerprint Scanner, gradient index optics have been applied in material preparation, testing and theoretical research, especially in the application of long-distance optical communication, information sensing and imaging. Rapid development, among them, self-focusing lenses are widely used in optical fiber sensing systems because of their advantages such as small size, small optical imaging aberration, and easy coupling and connection with optical fibers.
Since the self-focusing lens has the functions of focusing and collimating, it can be used in various occasions that require focusing and collimating functions, such as couplers, collimators, optical isolators, optical attenuators, optical switches, wavelength division multiplexers The typical structure is "fiber 1-self-focusing lens 1-functional or non-functional optical element-self-focusing lens 2-fiber 2" Self-focusing lens 1 and self-focusing lens 2 are used for collimation and focusing respectively In this way, various optical devices, such as filters, polarizers, Faraday rotators, prisms, etc., can be added between the two self-focusing lenses to form various optical devices or light sensors.
The typical structure of self-focusing lens collimation and focusing is used in fiber optic sensors, which are mainly used in fiber optic sensors measuring gas concentration and measurement based on prism reflected light. In fiber optic sensors measuring gas concentration, the optical devices in the typical structure are actually It is a measuring gas chamber. In the optical fiber sensor based on prism reflected light measurement, the optical device in the typical structure is a prism, so this book focuses on analyzing the additional coupling loss of the self-focusing lens as a collimating lens, self-focusing lenses 1 and 2 Add the additional coupling loss after turning to the right angle prism and the additional coupling loss of the self-focusing lens 1 and the self-focusing lens 2 in the reflection direction of the prism mirror as a collimated coupling system.
As shown, the assembly error produces a certain additional coupling loss. Among the three losses, the loss caused by the angle tilt is the largest, the loss caused by the lateral offset is the second, and the loss caused by the longitudinal offset is the smallest.