A drill bit for attachment to an elongate drill rod, the drill bit including means for attachment to an end of the drill rod, and a leading end which defines a pair of diametrically opposed slots which open axially for receipt of a portion of a drill tip which projects axially from the slots. An integrated modulator chip generates optical RZ signal streams which are then interleaved in an integrated time-delay chip to produce an OTDM signal. Switching to the power-saving mode is inhibited when recording on the recording medium is not possible, thereby improving the operability of the video camera for the user. Alternatively, the filter loop may include a plurality of strut members coupled thereto. The above dielectric filter may include input and output sections, and a conductive film may be formed between the joint surfaces to provide a coupling portion of the input or output section.