Er‐doped silica‐based planar ring resonator

Abstract

AbstractA new configuration of a ring resonator is proposed by using an Er‐doped silica‐based waveguide. Its laser oscillation and variable finesse were realized. to determine the Er concentration suitable for the Er‐doped waveguide ring resonator, the Er concentration dependence of the threshold pump power for laser oscillation in an Er‐doped waveguide ring resonator is analyzed numerically. It was found that an optimum Er concentration is in the range of 0.3 fc 0.5 wt.%. Further, from the actual measurement, it is confirmed that the gain of the silica‐based waveguide with Er doping concentration in this range is larger than the loss of the ring resonator. Then, an optimum coupling condition of the directional coupler is studied. It is found that a maximum value of 91 percent is obtained as the coupling ratio at a wavelength of 1.533 μm for a coupling length of 1.0 mm. Based on these investigations, an Er‐doped waveguide ring resonator with a circumferential length of 9.2 cm is fabricated. As a result, an Er‐doped waveguide ring laser is realized that has an oscillation center wavelength of 1.533 μm, a threshold value of 93 mW for the pump power and a slope efficiency of 0.3 percent. the oscillation modes of the realized ring laser are longitudinal multimodes with its free spectral range (FSR) of 2.2 GHz. the narrow line characteristics of an average line width of 200 kHz are found. From the results of the transmission spectral measurement, it is confirmed that the Er‐doped waveguide ring resonator works as a stopband‐type optical frequency filter. In addition, it is found that the finesse can be varied by controlling the pump power. Maximum finesse is 36.