KEYWORDS: Optical fibers, Light emitting diodes, Optical microscopy, Photonic crystals, Near field scanning optical microscopy, Near field, Sapphire, Analytical research, Near field optics, Blue light emitting diodes
In our study, the distribution of the near-field close to the chip surface of Photonic Crystal (PhC)-patterned GaN-based
blue LED is measured with Near-field Scanning Optical Microscopy (NSOM). The blue LED has the layer structure
consisted of Sapphire substrate - n-GaN - Multi Quantum Well (MQW) - p-GaN - ITO, where the PhC pattern is
incorporated onto the top p-GaN layer. When the current is applied to the MQW, the light is emitted out of LED and the
near-field on the surface of LED chip is picked up by the fiber probe of NSOM system. The system was made by
ourselves, and the distance between the probe and the surface is controlled by shear force feedback control method using
tuning fork, where lock-in amplifier was used for noise reduction and for dithering the probe.
In this paper, the measurement system based on optical low-coherence interferometry was constructed to characterize propagation characteristics of Optical-Printed Circuit Board (O-PCB). With this system, the propagation loss of optical waveguides embedded in O-PCB was measured, and the back-reflection from several interfaces within O-PCB was done also. The polymer optical waveguide was prepared with UV embossing technique and its core had the width of 50um, the height of 50um, and the length of 2cm, respectively. The propagation loss of the waveguide was measured to be less than 2dB/cm and the back-reflectance at each interconnection point was about 5.83%. In the near future, the sensitivity will be improved with applying the balanced detection and signal modulation techniques in order to measure propagation characteristics of more complex O-PCB.