In this research, a wide range linearly-tunable optical filter has been proposed and demonstrated for wideband CWDM applications. To implement wide tuning range linearly, the Lorentz force using permanent magnet has been introduced for the first time into the actuators. Since the research was focused on developing the tunable filter structure to satisfy the required mechanical requirement for CWDM applications, currently available PECVD silicon nitride/silicon dioxide were used for DBRs in this work. The tunable filter has been successfully fabricated and demonstrated using two-chip approach. Since the DBR and Au have mild tensile stress about 80MPa, the whole structure stays flat without serious deformation.
The optical characteristics of the fabricated tunable filter have been measured using a tunable filter and a receiver. Four objective lenses have been used to focus the laser to the center of the filter. The tuning range of the fabricated tunable filter has been measured as 200nm, which is the widest ever reported, at the power consumption of 24.3㎼. The mechanical actuation range is over 3㎛ that is more than enough for CWDM applications. The optical bandwidth is measured as wide as 20nm because PECVD silicon nitride and silicon dioxide have been uses in a DBR. However, as the design of a DBR and an actuator is independent, the bandwidth can be reduced easily using other materials such as PECVD deposited amorphous silicon and silicon carbide.
The mechanical characteristics of the fabricated filter have been measured using LDV. A simple mechanical model has been established and verified. From the measured transient and harmonic response of the filter, mechanical parameters such as spring constant, effective mass, and natural frequency of the fabricated filter have been extracted as 0.91N/m, 2㎍, and 3.37kHz, respectively. The tuning speed at the worst case tuning is measured as 3msec which is also enough for CWDM applications.
The possible errors of the fa...