When the OAU is used as a detection board, if the OAU is not connected to the DCM, the ALC adjustment range is the variable range of the nominal gain of the OAU; if the DCM is connected, the upper threshold of the ALC adjustment range is decreased. The decreased value is approximately equal to the DCM insertion loss.
In the case of the optical power budget, consider the DCM impact when reserving the adjustment margin for the ALC. After the OAU is connected to the DCM, the ALC adjustment range is [Lower threshold of the nominal gain, upper threshold of the nominal gain - DCM insertion loss].
After the OAU is connected to the DCM, if the gain adjustment is excessively large, the wavelength inclination ratio is affected. Hence, the variable range must be decreased.