Hitachi Cable has developed a low-cost, long-life (10 years) CW-FTR that uses a continuous emitting laser light source and added it to its product lineup.

Hitachi Cable's FTR(R) emits optical pulses in an optical fiber at regular intervals and receives the returning scatter signals (the backward Raman scatter*1). The strength of the Raman scatter signal is highly dependent on temperature, and the place a scatter occurs can be determined by measuring how long it takes from when a laser pulse is emitted in an optical fiber until the scatter signal arrives back at the point of origin. By determining temperature dependency and the time required for the signal to make a round-trip, a sensor can measure the temperature distribution along the optical fiber.
Conventional FTRs used a high-output pulse oscillating laser. Due to the fact that the laser's peak strength was strong, they had the disadvantage of having a life span of approximately three years, which is short compared to the lasers generally used for telecommunications applications.
Aiming to remedy this shortcoming, as a means of suppressing the strength of the optical pulse, we have developed a method to separate a single pulse into several pulses and transmit them in succession. In the case of conventional FTRs, if the cycle of the emitted optical pulse is shorter than the time of the pulse's round trip through the length of the optical fiber, the next pulse will be emitted before the backward Raman scatter signal makes it back from the far end of the fiber. This makes it impossible to take an independent measurement of a backward Raman scatter signal that runs the length of the optical fiber.
However, now we have digitally modulated a single optical pulse to split it into multiple pulses that are transmitted in succession and have developed technology that restores the overlapping backward Raman scatter signals back to their respective pulses. As a result, even if the time between pulse emissions is shortened to less than the time it takes the pulse to make a full round trip, it has become possible to measure the backward Raman scatter signals independently (See Diagram 1).
Therefore, it has become possible to use the CW semiconductor lasers used in general telecommunications applications as light sources instead of high-output pulse oscillating lasers, enabling an extended life span (10 years), easier maintenance, and a reduction in operating costs.
SM optical fiber has a small core diameter, making it difficult to inject an optical pulse of a sufficient strength. For this reason, GI optical fiber, with its large core diameter, has been used as the optical fiber in conventional FTRs. Unlike conventional FTRs, even an optical pulse with a weak peak-strength can be measured in a CW-FTR, enabling the use of SM optical fiber. The use of SM optical fiber for telecommunications and other applications eliminates the need for the installation of new optical fiber for a temperature survey, thereby offering the advantage of low-cost system construction.
Moreover, with long-distance FTR, for measuring distances over 2km, the optical fiber offering the lowest level of transmission loss is the 1.5 micro meter frequency band optical pulse. Previously, semiconductor lasers lacked sufficient optical pulse strength, necessitating the use of solid lasers and resulting in a high price for the FTR. Since the CW-FTR can measure weak optical pulse strengths and is therefore efficient, it is possible for low-cost semiconductor lasers of the 1.5 micro meter frequency band to be used, enabling a substantial price reduction compared with conventional FTRs.

Hitachi Cable commenced sales of its FTR in 1988. This product is used to measure the temperature distribution in power cables, check for temperature abnormalities in electrical facilities, and monitor temperatures in all kinds of manufacturing plants. By expanding our lineup of fiber-optic temperature sensors, we aim to raise the balance of net sales from 0.5 billion yen to 1 billion yen (fiscal 2006 target).

Product Features

(1)	Light source has long life (10 years)
(2)	Easy to maintain
(3)	Low operating cost
(4)	Possible to use SM optical fiber in sensors (Also possible to use already installed SM optical fiber)
(5)	Offers drastic price reductions for measuring distances exceeding 2km

CW-FTR Features and Price

Model	FTR 1000
Optical fiber for use in sensors	SM GI-50/125
Light-source longevity	10 years
Measuring range	5km
Temperature precision	plus minus 2 degrees
Measurement intervals	5 minutes
Standard price*2	7 million yen

*1	When an optical pulse is emitted into an optical fiber, a portion of the refracted light returns to the point of origin. The Raman scatter signal is the portion of light that is reflected backward.
*2	The standard price does not include the price of optical fiber.

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(Diagram 1)
FTR is a registered trademark of Hitachi Cable, Ltd.