Edge-emitting Semiconductor Diode Lasers Beam Shaping Base On Femtosecond Laser Direct Writing Technology

Semiconductor diode lasers have been applied in broad industrial fields fromfiber-optical communication to laser fabrication due to their advantages of smallsize, easy integration, high efficiency, long lifetime, and relatively low cost.Edge-emitting semiconductor diode lasers (EESDL) are particularly promising inlaser material processing and laser fabrication because of their high output powerand high reliability. While a major drawback that is hindering their currentapplication is the poor output-beam quality, i.e., the large and asymmetricoutput-beam divergence angles, generally30°–60°for fast axis and10°–15°forslow axis directions. It is different of beam waist positions in fast axis and slowaxis directions, i.e., intrinsic astigmatism exists in the output beam. It is verynecessary to propose an effective beam shaping method to solve the currentproblems on the EESDL.Femtosecond laser direct writing technology has been used in preparation ofshaping lens, which is becoming a popular technology in micro-machining fielddue to its advantages of high precision, breakthrough the diffraction limit, true3Dprocessing skill. Laser was focused by objective lens to the inside of materialwhich can occur two-photon absorption at the focus position causing the organiclight-induced polymerization of the monomers. The position of laser focus werecontrolled and the specific area of the material will happen artificial aggregation,then unexposed position will be removed using organic solvents and the designstructure were left. Arbitrary3D structures can be prepared using femtosecondlaser direct writing technology inducing two-photon polymerization.New shaping method was proposed innovatively using a single mic-shapinglens which was fully into account of the beam properties of EESDL. The overall of shaping lens was elliptical which has two hyperboloidal side profile, and lensheight was139μm and axial lengths were400μm and340μm, respectively. Focallengths of the shaping lens of long axial and short axial were320μm and200μm,respectively. The material is SU-8photoresist which has good mechanicalproperties, optical properties and almost no absorption when wavelength of lightgreater400nm.The current situation and development of semiconductor laser andfemtosecond laser direct writing technology were introduced firstly. Then theproperty of SSDEL beam was analyzed quantitatively and determined the optimalparameters of shaping lens. Then the shaping lens was prepared by femtosecondlaser direct writing technology, and the geometric and optical properties werecharacterized. Finally, the divergence angle and fiber coupling efficiency weretested after shaping, the divergence angles of fast-axis and slow-axis werereduced to6.9mrad and32.3mrad from60.20and9.30, respectively. The couplingefficiency with single-mode fiber were above85%, and the experimental resultswere analyzed theoretically. Practical solutions were proposed to improve thebeam quality of SSEDL, And promoting the application of SSEDL in theoccasion of high beam quality required.