Thin film organic lasers with polymeric resonators

Abstract

Distributed feedback lasers (DFB) are some of the most studied thin film organic lasers, as they are cost-efficient, compact, and can be easily integrated with other devices. Besides, they are useful for a wide range of applications, such as spectroscopy, optical communications, and sensing. An organic DFB laser typically consists of an organic active thin film deposited over a relief grating engraved in an inorganic substrate (standard configuration), but it can present different architectures depending on the position of the resonator and the materials used for its fabrication. Here, a DFB laser architecture with a polymeric resonator deposited on top of the active film is studied. This architecture offers several advantages over the standard one. The device is easier to fabricate, as both films are organic and solution- processable, the active film presents a uniform thickness, and the grating period can be easily adjusted for each case as it is fabricated using holographic lithography. In this thesis, the optimization of DFB lasers based on polymeric diffractive resonators located on top of the active films has been achieved following two different goals: the resonator optimization through the control of the fabrication and the geometrical parameters; and the design and fabrication of optimized DFB lasers for new organic molecules to be used as active materials. The first step in the resonator optimization was to perform a systematic study of the effect of the fabrication process parameters on the final resonator characteristics in devices emitting in the visible, analyzing the influence of these parameters on the final DFB lasers emission properties. After that, the capability of the material used for the grating fabrication (dichromated gelatin, DCG) to form part of DFB lasers emitting at lower wavelengths (blue and deep-blue) was examined. Lastly, the DFB laser architecture with the resonator on top of the active film was compared to the standard configuration under variables not considered yet (such as the use of a dye which can be doped at high concentrations into the matrix, thus providing a way to change the refractive index of the active film) to prove its enhanced performance. Additionally, the whole fabrication process was upgraded with the study an implementation of a simple spectrophotometric method to measure the thickness and refractive index of polymeric thin films, which allows a better overall optimization of the devices. After the resonator optimization was fulfilled, DFB laser devices were fabricated and adapted to suit different active materials. Various families of novel compounds have been investigated with emissions from the UV to the NIR.