Magnetic tape onto which information may be recorded on either side exhibits the risk of having information recorded on one side affect the opposite side when the two sides are adjacent, such as when the tape is wound in a tape pack. The IPWDM of the invention provides optical polarization beam splittingcombining, wavelength division multiplexing, and reverse optical path isolation. The liner absorbs vibration in the air gun to improve firing performance. A method for identifying and applying session services to a wireless link includes identifying a packet flow over the wireless link corresponding to a received message by employing a flow identifier and filter. In addition, since the CCD output level obtained when the storage time is set to be the same as that set at the time of scanning can be predicted, the illumination intensity of the lamp can be obtained by calculating an output level at which no saturation occurs in that situation.