A method is described for providing a predetermined optical path in an optical module, the predetermined optical path being defined by predetermined optical characteristics for the optical module. a modifiable optical element is provided at a predetermined position in the optical module, thus generating an initial optical path of the optical module. The modifiable optical element comprising at least one optical interface in the initial optical path. An optical signal is detected from a radiation beam on the initial optical path of the optical module. The optical interface of the modifiable optical element is then physically modified to generate at least one modified optical interface of the modifiable optical element. The physical modification takes into account the detected optical signal so as to obtain substantially the predetermined optical characteristics for the optical module.