Optical data transmission device for carrying out optical time domain reflectometry measurement in an optical access network, comprising - a laser transmission unit, operable to generate an optical transmission signal, - at least one driving unit, which is operable to control said laser transmission unit, such that said optical transmission signal is modulated in dependence on a data signal, - an optical reception unit, adapted to convert at least a fraction of a received optical signal into an electrical measurement signal, using a photo diode and an electrical amplifier, wherein said optical reception unit is separate from said laser transmission unit in the sense, that said optical reception unit and said laser transmission unit have respective casings that are not directly connected to each other, - at least one control unit (MC, OC), operable to control said laser transmission unit, such that said optical transmission signal is modulated in dependence on a measurement signal, characterized in that said control unit (MC, OC) is furthermore operable - to measure multiple electrical measurement signals during a measurement interval and to determine an averaged received electrical measurement signal based on the measured signals, - and to control said electrical amplifier, such that said electrical amplifier is turned off during at least a fraction of a time interval prior to said measurement interval and such that said electrical amplifier is turned on during said measurement interval, and such that thermal heat generated by said electrical amplifier dissipates from said optical reception unit to said laser transmission unit for causing a temperature change at said laser transmission unit and a change of a center wavelength of said optical transmission signal generated by said laser transmission unit. - a laser transmission unit, operable to generate an optical transmission signal, - at least one driving unit, which is operable to control said laser transmission unit, such that said optical transmission signal is modulated in dependence on a data signal, - an optical reception unit, adapted to convert at least a fraction of a received optical signal into an electrical measurement signal, using a photo diode and an electrical amplifier, wherein said optical reception unit is separate from said laser transmission unit in the sense, that said optical reception unit and said laser transmission unit have respective casings that are not directly connected to each other, - at least one control unit (MC, OC), operable to control said laser transmission unit, such that said optical transmission signal is modulated in dependence on a measurement signal, - to measure multiple electrical measurement signals during a measurement interval and to determine an averaged received electrical measurement signal based on the measured signals, - and to control said electrical amplifier, such that said electrical amplifier is turned off during at least a fraction of a time interval prior to said measurement interval and such that said electrical amplifier is turned on during said measurement interval, and such that thermal heat generated by said electrical amplifier dissipates from said optical reception unit to said laser transmission unit for causing a temperature change at said laser transmission unit and a change of a center wavelength of said optical transmission signal generated by said laser transmission unit.