Abstract: A U-shaped fiber optical cable assembly (11, 21) is arranged in a heated well (1) such that a nose section (13, 23) comprising the bent U-shaped cable section (11C, 21C) is located near the toe (1 A) of the well where the ambient well temperature is lower than the temperature of an intermediate section of the well which is heated by steam injection, electrical heating and/or influx of heated hydrocarbon fluids from a heated section of the surrounding formation to a temperature above 200 degrees Celsius, thereby inhibiting the risk of hydrogen darkening of the bent U-shaped cable section. It is preferred to make the nose section of a glass solder, to arrange the U-shaped fiber optical cable assembly in an aluminium guide tube (22) sealed at its lower end with end cap (31), and to use a heat resistant fiber optical cable to further inhibit the risk of hydrogen darkening of the assembly.

Abstract: A fiber optical sensing cable is inserted into an underwater well by: connecting a housing (12A) comprising a coiled or spooled U-shaped fiber optical sensing cable (21) to the wellhead (2) of the well (1) such that an opening (14) in the wall of the housing (12A) is connected to a guide tube (15) extending into the underwater well (1); —inserting the U-shaped nose section (21A) of the fiber optical sensing cable (21) via the opening (14) into the guide tube (15), thereby uncoiling at least part of a pair of substantially parallel sections of the fiber optical sensing cable of which the lower ends are interconnected by the U-shaped nose section; and connecting the upper ends (21B) of the substantially parallel sections of the fiber optical sensing cable to an optical signal transmission and/or receiving unit via e.g. a pair of wet mateable connectors that are connected to a pair of underwater fiber optical transmission cables (14).

Abstract: A method is disclosed for amplifying a light pulse (S) in an optical fiber (1), wherein a Raman pump signal (RPS) having a lower wavelength than the light pulse (S) is transmitted at a selected interval of time after the light pulse (S) into an end (IA) of an optical fiber(1), with dispersion such that the Raman pump signal (RPS) travels faster through the fiber(1) than the light pulse(S) and reaches and enhances the light pulse (S) after the light pulse has travelled along a selected distance (d1) through the fiber, wherein the Raman pump signal (RPS) is ramped in a substantially linear manner such that the amplification increases with the distance along which the light pulse has travelled along the length of the fiber from A1=S1+RPSmin at a distance d1 to A2=S+RPSmax at a distance d2>d1 from said end (IA) of the fiber 1 and such that the Raman gain increase is substantially similar to the fiber losses of the amplified signal.