Abstract: An optical time domain reflectometer (OTDR) launches an optical pulse emitted from a pulse light source to one end side of an optical fiber, receives light returning to the one end side with an optical receiver, inputs an output signal of the optical receiver to an A/D converting unit so as to convert the signal to an N bit (N is the plural number) digital signal, implements a process for the N bit digital signal, and measures the transmission characteristics of the optical fiber. The A/D converting unit has the number of bits that is greater than the N bits by the number of A bits, wherein A is an integer greater than “0”. The A/D converting unit converts an input signal to an N+A bit digital signal, and compresses the N+A bit digital signal to N bit data.

Abstract: To avoid the occurrence of noise in an A/D converter at the time an excessive input is applied even if an inexpensive pipeline A/D converter is used, without deteriorating the S/N ratio or wasting the resources, such as the hardware, software, etc. that follow the A/D converter. An optical time domain reflectometer (OTDR) launches an optical pulse emitted from a pulse light source to one end side of an optical fiber, receives light returning to the one end side with an optical receiver, inputs an output signal of the optical receiver to an A/D converting unit so as to convert the signal to an N bit (N is the plural number) digital signal, implements a process for the N bit digital signal, and measures the transmission characteristics of the optical fiber. The A/D converting unit has the number of bits that is greater than the N bits by the number of A bits (A is an integer).

Abstract: An optical time-domain reflectometer (OTDR) having a light-emitting element, a branching section, a light-receiving section, and a processing section. The light-emitting element emits pulsating measuring light when driven. The branching section applies the measuring light emitted from the light-emitting element, to an optical fiber to be measured, and branches the light supplied from the optical fiber. The light-receiving section receives the light branched by the branching section and detects a level of the light received. The processing section detects a level of the light supplied from the optical fiber after the OTDR is connected to the optical fiber, while not driving the light-emitting element. The processing section drives the light-emitting element only when the level of the light received is equal to or lower than a preset value.