No abstract

Optical frequency combs (OFCs) have attracted attention as optical frequency rulers due to their tooth-like discrete spectra together with their inherent mode-locking nature and phase-locking control to a frequency standard. Based on this concept, their applications until now have been demonstrated in the fields of optical frequency metrology. However, if the utility of OFCs can be further expanded beyond their application by exploiting new aspects of OFCs, this will lead to new developments in optical metrology and instrumentation. Here, we report a fiber sensing application of OFCs based on a coherent link between the optical and radio frequencies, enabling high-precision refractive index measurement based on frequency measurement in radio-frequency (RF) region. Our technique encodes a refractive index change of a liquid sample into a repetition frequency of OFC by a combination of an intracavity multi-mode-interference fiber sensor and wavelength dispersion of a cavity fiber. Then, the change in refractive index is read out by measuring the repetition frequency in RF region based on a frequency standard. Use of an OFC as a photonic RF converter will lead to the development of new applications in high-precision fiber sensing with the help of functional fiber sensors and precise RF measurement.

No abstract

The correlation between the passivation film formation for InP/InGaAs heterojunction bipolar transistors and transistor current-voltage (I-V) characteristics is investigated. The I-V characteristics vary significantly depending on the kind of passivation films. The major change in I-V characteristics is the increase in base current (I b),which implies the generation of an additional recombination process around the surface of the emitter-base junction. A change in collector current (I c) is also observed, indicating that the electron injection mechanism changed near the passivated semiconductor surface. These surface currents are produced by the interaction of the semiconductor surface with the passivation films. It is shown that these surface currents are greatly suppressed using a buffered hydrofluoric acid solution before the passivation film formation.

No abstract