Ji Ho Jeong

Differential measurement scheme for Brillouin Optical Correlation Domain Analysis

We newly propose and experimentally demonstrate a differential measurement scheme for Brillouin optical correlation domain analysis, where the difference between Brillouin gain spectra constructed by a normal and a phase-modulated Brillouin pump waves are analyzed to measure local Brillouin frequencies in optical fibers. In experiments, a five-fold enhancement in the spatial resolution is obtained compared to an ordinary BOCDA system under the same modulation parameters, as a result of the improved dynamic range by the suppression of background noises.

Linearly configured BOCDA system using a differential measurement scheme.

We experimentally demonstrate a linearly configured Brillouin optical correlation domain analysis (BOCDA) system enhanced by a differential measurement scheme. On-off control of the pump phase modulation with an intentional loss at the end of a fiber under test is applied for the acquisition of a Brillouin gain spectrum. This application leads to a four-fold enhancement of the spatial resolution and doubling of the measurement range in comparison with the former system under the same modulation parameters.

Bidirectional measurement for Brillouin optical correlation domain analysis

We propose and experimentally demonstrate a bidirectional measurement for Brillouin optical correlation domain analysis as a novel and simple way of the performance enhancement. Brillouin gain and loss spectra of two adjacent correlation peaks are simultaneously and independently analyzed by applying midpoint attenuation in a fiber under test, which doubles both the speed and the range of the distributed measurement.

Variable-frequency lock-in detection for the suppression of beat noise in Brillouin optical correlation domain analysis

We propose and experimentally demonstrate a novel lock-in detection method to avoid a beat noise in Brillouin optical correlation domain analysis (BOCDA) which appears in the sweep of the sensing position and deteriorates the measurement accuracy by distorting the acquired Brillouin gain spectrum. In our analysis, the origin of the beat noise is shown to be the fluctuation of the Brillouin gain induced by the chopping of the intensity-modulated pump wave, and the optimal relation between the modulation and the lock-in frequencies is developed as an effective solution to circumvent the beat noise.

Measurement Range Enlargement in Brillouin Optical Correlation Domain Analysis Using Multiple Correlation Peaks

We propose and experimentally demonstrate a method for extension of measurement range in a Brillouin optical correlation domain analysis sensor system without resolution deterioration. In the experiment, a 300 m measurement range with about 8 cm spatial resolution was successfully obtained by cascading three different kinds of fibers as a sensing element.

In situ gas sensing using a remotely detectable probe with replaceable insert

We demonstrate a spectroscopic gas sensor using an optical fiber probe with a replaceable insert. The probe consists of a hollow-core photonic bandgap fiber (HC-PBGF) with a core diameter of 10.9 μm and a glass tube where a 2-μm hollow core fiber (HCF) with a gold coated end facet can be inserted. The HCF is designed to function as both a gate where gases can enter the HC-PBGF and a mirror reflecting the guided light back to the HC-PBGF. The opposite distal end of the probe is also designed to be able to regulate the gas pressure within the HC-PBGF for a high gas flow rate, while still transmitting the reflected light to the analysis instrument. The remote sensing probe, we believe, has much potential for detecting gases in hazardous environments.

Measurement range expansion in Brillouin optical correlation-domain analysis system

We propose and experimentally demonstrate a novel method for extension of measurement range in a Brillouin optical correlation domain analysis (BOCDA) sensor system by cascading fibers with different Brillouin frequency shifts.

Novel measurement method of Brillouin optical correlation domain analysis based on bidirectional detection scheme

We propose and experimentally demonstrate a bidirectional detection scheme in the Brillouin optical correlation domain analysis. The gain and the loss spectra for the probe waves are simultaneously analyzed, which enables the measurement range twice with a half measurement time.

High-performance in-line Brillouin optical correlation domain analysis

We demonstrate a high-performance single-ended correlation-domain Brillouin sensor based on a phase modulation of Brillouin pump and a differential measurement scheme. Large DC noise induced by direct reflection of Brillouin pump was successfully removed by the phase modulation-based differential measurement as well as additional 4-fold enhancement in the spatial resolution. By applying an intentional loss to the end of a sensing fiber one of two correlation peaks within the fiber is suppressed, leading to double enlargement of the measurement range compared to former in-line reflector based systems. In the experimental confirmation a distributed strain measurement with a range of 100 m and a spatial resolution of 5 cm is presented.

Simplified Brillouin optical correlation domain analysis sensor based on a chopped microwave applied single sideband electro-optic modulator

We propose and experimentally demonstrate a novel scheme of the Brillouin optical correlation domain analysis (BOCDA) using a single sideband electro-optic modulator (SSBM). In the work, the SSBM is used to get carrier suppressed upper sideband for the pump wave, and also lock-in detection is used by applying chopped microwave to SSBM for chopping the pump wave. This implementation enables us to eliminate an additional intensity modulator (IM) for lock-in detection in conventional BOCDA scheme. In the experiment, a 100-m measurement range with 8-cm spatial resolution is successfully achieved.