Matching Diode Laser Radiation With Single-Mode Optical Fiber

When matching the radiation of a diode laser with an external cavity with an optical fiber, it was found that the transmission of a single-mode fiber used in most external electro-optical modulators is about 3.2%. The serial connection of multimode and single-mode fiber allows to increase the transmittance of the last one by 2.7 times (up to 8.4%). Moreover, when the injection current changes from 60 to 90 mA, the transmission of various types of optical fibers remains unchanged. The distribution of the intensity of the light beam recorded by the CCD camera at the laser output showed that the horizontal and vertical dimensions differ by about two times (0.8 and 1.6 mm). After passing the optical fiber, the cross-section shape of the light beam becomes close to the correct circle. With increasing distance from the output of the optical fiber, the dimensions of the light beam change linearly. At distances comparable to the cell size (about 20 cm), about 0.6 mm remains, which is significantly smaller than the beam size at the laser output. The obtained data can be further used for external modulation of radiation propagating in the fiber and registration of CPT resonances in a cell with rubidium-87.