A quantum cascade laser includes a semiconductor substrate, and an active layer being provided on the substrate, and having a cascade structure in which quantum well emission layers and injection layers are alternately laminated, and the laser has a base portion including the substrate, and a stripe-shaped ridge portion including the active layer. The magnetic element allows for reducing heat losses during the write operation and has reduced power consumption. The tank further includes a conduit for draining the liquid fuel originated from condensation of vapors present within the vent conduit. The cover system also has an inner cover for the flexible signal connection, the inner cover being for attachment to the opposite one of the stationary portion of the transit vehicle door system and a door panel. The multiplier multiplies data from the feedback circuit by the quantization step and outputs the resultant data to the adder.