A set top box with a firewall is disclosed. In at least one implementation, a lighting fixture can incorporate a lighted core and lighted or unlighted elements surrounding the lighted core. In particular, as a typical structure of the optical amplifier, the rare-earth-element-doped optical fiber has a cutoff wavelength \u03bbc set longer than the pumping light wavelength \u03bbp but shorter than the signal light wavelength \u03bbs, and mainly allows a pumping light component in a fundamental mode to propagate therethrough. The gate of the first transistor and the gate of the third transistor are connected to the drain of the second transistor.