A dielectric film stack of a solar cell is ablated using a laser. Another preferred embodiment light emitting device comprises a polar template; an n-type layer grown on the template; the n-type layer having a first polarization vector having a first projection relative to a growth direction; a p-type layer grown on the n-type layer having a second polarization vector that is larger than the first polarization vector. When one of the serial ports is selected as the main communication interface to communicate with one of external computers, the other one serial port thereof still can transmit signals from the micro-processor to another computer through its transmitting data pin. The cable identification system further includes a signal generator connectable between the electrical connector and the mating connector on a network device. Once validated, the refill amount candidate is the optimal refill amount, and the shared virtual postage meter is refilled accordingly.