OPtical microdisk is based on circularly symmetric micro- resonator and featured of the 'whispering-galley' modes with high quality of factor Q. However, the non-preferred directional emission and lack of high output from the disk are its drawbacks for application. Recently, a remarkable advance in the novel deformed microdisk laser at middle-IR wavelength is highly attractive. In this report, as a preliminary try for microdisk at visible range, the InGaAlP quantum well circular cylindrical and deformed microdisks with radii about 2.5 to 10 micrometers emitting at wavelength of 0.62-0.67 micrometers were prepared by electron beam lithography and wet etching processing etc. The optical emission properties of these microdisks and studied by employing the scanning electron microscopy, atomic force microscopy, fluorescence image microspace and scanning near-field optical microscopy etc. The preferential emission in these deformed microdisks was visually observed. When the cross section of microdisk was gradually deformed from circle, the change of fluorescence image from uniform ring towards 2 or 4 favorable emission along the circumference of microdisks was confirmed. The deformation could be caused by either the shape or etching profile of the disk waveguide. In addition, the microdisks patterned with some microstructures were proposed.
Proc. SPIE. 3791, Near-Field Optics: Physics, Devices, and Information Processing
KEYWORDS: Near field, Near field optics, Gallium nitride, Luminescence, Indium gallium phosphide, Indium gallium nitride, Semiconductors, Near field scanning optical microscopy, Optical microscopy, Optical microcavities
Microcavity shows the growing importance of the intensity enhancement, inhibition and spectral narrowing of spontaneous emission. The advantages of microcavity lasers are the very low threshold and small size. We have fabricated three types of semiconductor microdisks: InGaP, GaN, and InGaN multi-quantum-well microdisk with sun-like E- beam resist microstructure. The diameters are ranging from 5 - 20 micros. The photoluminescence of those microdisks in far-field and near-field observation are compared. Far-field fluorescence imaging shows bright emission of fluorescence around the circumference of the microdisks that can be interpreted as whispering-gallery mode in the disks. However, due to the different disk structures, near-field fluorescence images give several other different views of the light distribution of the microdisks corresponding to different optical modes in the disks. A theoretical calculation of the light distribution of InGaP microdisk based on the theory of optical modes in microdisk lasers is presented in this paper. The near-field mapping of the InGaN microdisks with sun-like E-beam resist structure demonstrates the possibility of using gratings made on the circumference to achieve directional emission without lowering output power.
We have constructed a versatile low temperature scanning near-field optical microscope with the capability of near- field spectroscopy, operating at liquid nitrogen (LN) temperature. The compact low temperature scanning head was built on one piece of Marco with a unique linear nano-motor as the coarse approach. A tuning fork mechanism was adopted to detect and regulate the fiber tip-sample separation. The x-y scan can be performed either by the single tube scanner on triple tube scanner, depending on the application. A double shield dewar was used where the outer chamber was filled with LN. The core chamber was evacuated before cooling and then filled with cooled nitrogen gas, hence the working temperature can be controlled at around 80 K. A special designed coaxial double lens was used to introduce the illumination beam through a 200-micron fiber; the detected optical signal was transmitted via a fiber tip to a PMT or an APD. The performance test shows the stability of the new design. The resolution of shear force imaging and optical image of standard sample are shown.
Two types of resonator configuration, i.e. the axis-asymmetric resonator and improved off- axis resonator are used to reduce the beam parameter product in the large direction of the slab. Experiments performed with a slab (Nd,Ce):YAG laser have shown remarkable improvement of beam quality.