The present application discloses a method and circuitry that improves the monitoring and/or reporting accuracy and of a TOSA transmitter output power. In the method, the output power of an optical transmitter is measured at 25° C. and at N individual temperatures to obtain N tracking error (TE) values corresponding to the N individual temperature values, then a lookup table covering an operating temperature range of the transmitter is created based on a one-to-one mapping relationship between the TE values and the N individual temperatures and a line fitting process. The transmitter output power is reported at an interface of the transmitter according to the TE value at the transmitter operating temperature in the lookup table. The present application also discloses optical modules and optical communication systems. The present method and transmitter effectively improve the monitoring and/or reporting accuracy of the transmitter output power.