A device for an optical network, the device comprising: a transmitter configured to: generate an Optical Time Domain Reflectometer (OTDR)-modulated optical supervisory channel (OSC) signal by applying an OTDR modulation to an optical supervisory channel (OSC) signal using an OTDR signal; and transmit the OTDR-modulated OSC signal through an optical fiber ; and an OTDR module configured to: generate the OTDR signal; monitor a returned light signal from the optical fiber ; determine transmitter noise compensation information to recover a fiber loss function; and to use the fiber loss function to generate OTDR trace information, characterised in that the OTDR module is configured to determine transmitter noise compensation information by computing a modified code c'(t) to recover a fiber loss function f(t), as expressed by: c ′ t = c t + g ′ t ; f t = c ′ t ∗ r t , where c(t) is the OTDR-modulated OSC signal (1+OTDR(t)) ∗ OSC(t), OTDR(t) represents the OTDR signal, OSC(t) represents the OSC signal, r(t) is the returned light signal, and wherein g'(t) meets a condition: c t ∗ g t + g ′ t ∗ g t + g ′ t ∗ c t = 0 where g t = c t d t − c t , c(t)d(t) represents a monitored OTDR-modulated OSC signal, d (t) ≠ 1. a transmitter configured to: generate an Optical Time Domain Reflectometer (OTDR)-modulated optical supervisory channel (OSC) signal by applying an OTDR modulation to an optical supervisory channel (OSC) signal using an OTDR signal; and transmit the OTDR-modulated OSC signal through an optical fiber ; and generate an Optical Time Domain Reflectometer (OTDR)-modulated optical supervisory channel (OSC) signal by applying an OTDR modulation to an optical supervisory channel (OSC) signal using an OTDR signal; and transmit the OTDR-modulated OSC signal through an optical fiber ; and an OTDR module configured to: generate the OTDR signal; monitor a returned light signal from the optical fiber ; determine transmitter noise compensation information to recover a fiber loss function; and to use the fiber loss function to generate OTDR trace information, characterised in that the OTDR module is configured to determine transmitter noise compensation information by computing a modified code c'(t) to recover a fiber loss function f(t), as expressed by: c ′ t = c t + g ′ t ; f t = c ′ t ∗ r t , where c(t) is the OTDR-modulated OSC signal (1+OTDR(t)) ∗ OSC(t), OTDR(t) represents the OTDR signal, OSC(t) represents the OSC signal, r(t) is the returned light signal, and wherein g'(t) meets a condition: c t ∗ g t + g ′ t ∗ g t + g ′ t ∗ c t = 0 where g t = c t d t − c t , c(t)d(t) represents a monitored OTDR-modulated OSC signal, d (t) ≠ 1. generate the OTDR signal; monitor a returned light signal from the optical fiber ; determine transmitter noise compensation information to recover a fiber loss function; and to use the fiber loss function to generate OTDR trace information, characterised in that the OTDR module is configured to determine transmitter noise compensation information by computing a modified code c'(t) to recover a fiber loss function f(t), as expressed by: c ′ t = c t + g ′ t ; f t = c ′ t ∗ r t , where c(t) is the OTDR-modulated OSC signal (1+OTDR(t)) ∗ OSC(t), OTDR(t) represents the OTDR signal, OSC(t) represents the OSC signal, r(t) is the returned light signal, and wherein g'(t) meets a condition: c t ∗ g t + g ′ t ∗ g t + g ′ t ∗ c t = 0 where g t = c t d t − c t , c(t)d(t) represents a monitored OTDR-modulated OSC signal, d (t) ≠ 1. <EOS>