High quality direct photo-patterned microdisk lasers with organic/inorganic hybrid materials

Optical microcavities are widely studied because they have many applications in fundamental physics, nonlinear optics, optical communication, and bio-sensing. At present, microcavity materials can be classified as two families: inorganic and organic materials. Organic microcavities usually have much lower cavity quality Q value, mostly due to the difficulties in obtaining very smooth cavity boundaries even with proper thermal reflow after complex patterning: process. Luminescent conducting polymers and dye-doped polymer 2-D microdisk lasers with different shapes were created by microlithography and O₂ reactive ion etching steps. So far the achieved Q values from organic microdisk lasers are between several hundred and 10000, Recently, the sol-gel technology based on the wet processes at low temperature has proven to be one promising approach to produce low-cost organic-inorganic integrated optical devices. Photosensitive organic-inorganic hybrid materials can be applied for direct photo-fabrication of optical waveguide devices. Their optical properties, such as refractive index can be precisely controlled by selecting the functionality of organic constituents and metal oxide composition. In this work, sol-gel organic-inorganic hybrid microdisk-on-chip technique based on the direct UV patterning and wet etching was used to fabricate microdisk lasers on silicon substrate. One-step patterning produces high quality microlaser arrays for experimental study. Moreover it was found that a thin polymer cladding on the microdisk can obviously improve the cavity boundary smoothness and thus, increase the Q value of the cavity to as high as 12000. The organic/inorganic hybrid matrix also enables many other gain materials:such as quantum dots and organic semiconductors to be incorporated. The organic-inorganic hybrid materials for microcavities were synthesized by hydrolysis and polycondensation of methacryloxypropyl trimethoxysilane (MAPTMS), methacrylic acid (MAA), and zirconium (IV) propoxide (ZPO). Two kinds of microcavities were prepared, one is a bare cavity, the other is cavity coated with a thin PMMA cladding. The microdisks Were optically pumped by using the frequency-doubled output of a. Nd:YAG mode-locked. laser. Fig. 1a and 1b shows the emission spectra from 4.0 μm-diameter circular disks with and without a cladding, layer. A bare disk (see Fig, 1 a) is more likely to have higher order modes, its Q value (= 8000) is also lower than that of the cladded disk (Q =12000). We believe that it is due to the improved disk smoothness with a cladding: layer. The improvement was confirmed from SEM measurement and also reflected: from the scattered light intensity, Fig. 1a and, 1b were pumped with the same light intensity, cladded disk obviously trapped light much: more efficiently. Fig. 1c and 1d are spectra from a cladded square-shaped microdisk with rounded corners. Strong F-P modes (Fig. 1c) emit normal to four cavity side walls, while, WG (Fig. 1a) modes emit from the four round corners. The measured Q is 9800. Only one set: of WGM. mode was observed, no higher modes appeared in the spectrum. This again demonstrates that a cladded disk has the privilege of eliminating high order modes. The fabrication process described in this paper can be easily extended to other systems such as semiconductor quantum dots doped cavities for visible and near-infrared micro-lasers.