Proposal of Polarization Optical Correlation-Domain Reflectometry (POCDR)

Abstract

We propose a new scheme for polarization-sensitive distributed fiber-optic sensing, called polarization optical correlation-domain reflectometry (POCDR), and experimentally demonstrate its fundamental operations. In this scheme, the states of polarization (SOPs) of reference lights are controlled so that they are uniformly distributed on the Poincaré sphere using a calibration method, which cancels the effect of unknown birefringence in the fibers used in the system. Then the SOP of spontaneous Brillouin scattering in a sensing fiber is estimated using a least-squares method, by measuring the interference powers for the multiple reference lights with different SOPs. As a pilot demonstration, the SOP transitions along a fiber including a three-paddle polarization controller are measured under different conditions. We also measure the SOP transition of a fiber wound on a bobbin and calculate its polarization beat length, which agrees well with the theoretical value. By exploiting its unique nature called random accessibility, high-speed measurement of the roundtrip birefringence between two arbitrary points in a sensing fiber will be potentially achieved.

Fiber-tip temperature sensing probe based on standard Brillouin optical correlation-domain reflectometry with sinusoidal modulation

“…To date, no technique (except for the one we have developed) has been reported that enables low-cost temperature measurement near the tip of a commercially available optical fiber without necessitating any specialized processing. Alternatively, distributed sensing techniques capable of providing longitudinal temperature variations along the fiber have been explored, [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] but these too come with a high cost.…”

“…Brillouin-based single-end-access distributed sensors can be categorized into three types: Brillouin optical time-domain reflectometry (BOTDR), [12][13][14] Brillouin optical frequency-domain reflectometry (BOFDR), 15) and BOCDR. [16][17][18][19][20][21][22][23][24][25][26] Each technique has its own merits and demerits, and here we focus on BOCDR.…”

Noise mechanism clarification in external-modulation Brillouin optical correlation-domain reflectometry with double-sideband modulator

“…2) Various distributed sensing techniques have been developed and can be categorized into two types: analyzers, which require light injection at both ends of the FUT to induce stimulated Brillouin scattering, [4][5][6][7][8][9][10] and reflectometers, which rely on spontaneous Brillouin scattering by injecting light at only one end of the FUT. [11][12][13][14][15][16][17][18][19][20][21][22][23][24] These techniques are further differentiated by their spatial resolution capabilities, categorized into time, [4][5][6][7][11][12][13] frequency, 8,14) and correlation domains. 9,10,[15][16][17][18][19][20][21][22][23][24] This study specifically examines Brillouin optical correlation-domain reflectometry (BOCDR), [15][16][17][18...…”

“…[11][12][13][14][15][16][17][18][19][20][21][22][23][24] These techniques are further differentiated by their spatial resolution capabilities, categorized into time, [4][5][6][7][11][12][13] frequency, 8,14) and correlation domains. 9,10,[15][16][17][18][19][20][21][22][23][24] This study specifically examines Brillouin optical correlation-domain reflectometry (BOCDR), [15][16][17][18][19][20][21][22][23][24] which utilizes correlation control of continuous lightwaves within a selfheterodyne setup. BOCDR is distinguished by its ability to operate with single-end light injection, offering relatively high spatial resolution, high sampling rates, random accessibility, and cost efficiency.…”

“…Direct modulation involves altering the laser driving current and is valued for its simplicity and cost effectiveness, 15) though it results in unavoidable power modulation; besides, not all lasers can endure large modulation amplitude. In contrast, external modulation, [19][20][21][22] typically employing a double-sideband modulator (DSBM), circumvents these issues. However, DSBM-based external-modulation BOCDR introduces distinctive noise spectra that can obscure strain and temperature measurements.…”