Simple and highly accurate technique for time delay measurement in optical fibers by free-running laser configuration

Abstract

A novel and simple technique for the measurement of time delay in the optical fiber by a free-running laser is proposed and demonstrated. The fiber to be measured was spliced to an erbium-doped fiber so as to form a ring-cavity laser. The mode beating frequency of the laser was measured to determine the round-trip time delay. This precise and efficient technique has an accuracy of 10(-8) for a fiber length of 100 km and of 10(-6) for a several-meters-long one.

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“…The length of the fiber can be obtained by the measurement of the mode beating frequency. Base on this method, an accuracy of 10 −8 for 100 km long fiber and an accuracy of 10 −6 for a several-meters-long one are achieved [13] .…”

“…The improvement of the performance of the optical time delay measurement technologies would greatly promote the development of the photonics-based radar, optical fiber hydrophones, and optoelectronic chips. [17] 10 km 340 μm [22] 100 km 2 m [19] OTDR based on chaotic light 25 km 6 cm [24] 300 m 50 μm [26] Frequency domain OFDR 35 m 22 μm [47] 151 km 11.2 cm [33] 40 km Sub-cm [34] Fiber laser 100 km 5 cm [12] 100 km 9 mm [13] Phase-locked loop 50 km 0.15 mm [14] Phase-derived ranging Direct phase-derived ranging 2 km Sub-100 μm [15,37] Indirect phase-derived ranging Tens of meters Sub-mm…”

“…Various optical time delay measurement technologies have been proposed and studied in the last decades, which can be generally divided into three categories: (1) the time domain measurement techniques, such as optical time domain reflectometry (OTDR), chaotic-light-based measurement, and optical femtosecond-pulse-based measurement [8][9][10] ; (2) the frequency domain measurement techniques, such as optical frequency domain reflectometry (OFDR) [11] , mode-locked laser repetition frequency measurement [12] , free-running laser mode-spacing measurement [13] , and phase-locked-loop-based measurement [14] ; (3) the phase-derived range measurement, including direct phase-derived range measurement [15] and indirect phase-derived range measurement.…”

Accurate and fast fiber transfer delay measurement based on phase discrimination and frequency measurement

“…Up to now, many techniques for FTD measurement in time domain or frequency domain have been developed and successfully employed [14][15][16][17][18][19][20][21]. However, most of them either have drawbacks of low accuracy and existing dead zones, or require complex and time-consuming process.…”

A simple and accurate measurement of fiber time delay in free-running linear-cavity laser configuration

“…However, mode-locking of such a long cavity, especially for the fiber under test (FUT) of some kilometers long, is very difficult and time-consuming. Therefore, we proposed a simple measurement by ring cavity free running laser last year [6]. Nevertheless, the ring cavity configuration is inconvenient when putting into practical measurement, because it is not practical to roll the other end back of the FUT to the measurement site.…”