Thresholds and propagation constants for longitudinal modes in distributed feedback lasers with external reflectors are computed. The general case in which the reflectors are located asymmetrically with respect to the grating is treated, and it is shown that depending on reflector spacing and position, modes may have lower thresholds than conventional lasers with identical reflectors. Also computed is the ratio of transmitted power through the right−hand reflector to that transmitted through the left−hand reflector. In general, since the device is asymmetric that ratio differs from unity.
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