Coherent Optical Frequency Domain Reflectometry Research Articles

A Novel Speckle Analysis Scheme for Coherence Measurement Using a Standard Phase Modulator

This letter describes a novel configuration and theory for the degree of coherence measurement based on the statistical speckle analysis in coherent optical frequency domain reflectometry. The difference from the previous letter is using a standard phase modulator instead of a single-sideband modulator, which not only simplifies the system configuration, but also yields modulation efficiency, resulting in the operation with lower light source power. A novel theory is presented to describe the operation of the proposed configuration, and experimental results show the validity of the new configuration and theory.

A linearly frequency modulated narrow linewidth single-frequency fiber laser

A novel linearly frequency modulated narrow linewidth single-frequency phosphate fiber laser has been demonstrated. The output power of the laser is more than 40 mW. A maximum frequency excursion of more than 700 MHz at the modulating bandwidth of 1 kHz has been achieved. Single longitudinal mode operation under modulation is confirmed and the linewidth of the laser is measured to be less than 2 kHz. This type of laser source shows real promise for applications in coherent optical frequency domain reflectometry.

Optical-fiber self-referred refractometer based on Fresnel reflection at the fiber tip

An optical fiber refractometer based on the Fresnel reflection in the fiber tip is reported. For light intensity referencing, the refractometer head uses two equal low-reflective Fiber Bragg Gratings located near the fiber tip. A thermally wavelength-tunable Distributed Feedback diode (DFB) laser was used for the sensor interrogation. Method of Coherent Optical Frequency Domain Reflectometry was implemented for interrogating the sensor head. It assists to distinguish signals that originated from the different reflectors. Signal processing in the Fourier domain and phase shift monitoring enables the refractive index (RI) of the medium surrounding the fiber tip to be measured for values between 1.0 and 2.0RI units. An accuracy of RI measurements of 5×10−5 was demonstrated experimentally using different liquids including fused silica index-matching liquid. A simple sensor construction and the use of low-cost components make it useful for application in the chem/bio sensing field.

High-reflectivity-resolution coherent optical frequency domain reflectometry using optical frequency comb source and tunable delay line

We propose a high-reflectivity-resolution coherent optical frequency domain reflectometry (OFDR) with a novel scheme of delay shift averaging (DSAV) by using an optical frequency comb source and a tunable delay line to suppress the fading noise. We show theoretically and experimentally that the novel DSAV scheme is equivalent, in realizing a high reflectivity resolution, to our previously reported frequency shift averaging (FSAV) of the same number of teeth of the optical frequency comb [1], but does not need the expensive narrow-pass-band tunable optical filter required in the previous scheme. Furthermore, by using this new method in combination with FSAV, better reflectivity-resolution is obtained compared to using only conventional FSAV with a single-wavelength laser source.

Planar waveguides with less than 01 dB/m propagation loss fabricated with wafer bonding

We demonstrate a wafer-bonded silica-on-silicon planar waveguide platform with record low total propagation loss of (0.045 ± 0.04) dB/m near the free space wavelength of 1580 nm. Using coherent optical frequency domain reflectometry, we characterize the group index, fiber-to-chip coupling loss, critical bend radius, and propagation loss of these waveguides.

Study of dynamic chirp in direct modulated DFB laser for C-OFDR application

A description of the chirp induced by direct modulated DFB laser is presented. Two approaches are considered: the first one is based on a resolution of laser rate equations; the second, on a simulation with a commercial software. We compare results of the two approaches, we demonstrate that the optical frequency can be controlled via the injected current. We also characterize the linear variation of the optical frequency in time (for triangular and sawtooth modulation), in order to choose the appropriate values of laser and modulation parameters for a perfect linearity of the chirp in time. This study will be very helpful to validate the use of direct linear modulated DFB laser as a tunable source in Coherent Optical Frequency Domain Reflectometry technique C-OFDR. We present a simulation result of Mach–Zehnder delay time measurement based on C-OFDR system using a direct modulated semiconductor laser source. The obtained results are very important because it depicts the beat frequencies relating to each delay time, with respect to the modulation format used. This is very encouraging for the implementation of an experimental C-OFDR.

Long-Range Coherent OFDR With Light Source Phase Noise Compensation

Recent progress on novel long-range coherent optical frequency domain reflectometry is reviewed along with its applications to diagnosing problems with optical fiber cables. The measurement range of a conventional C-OFDR is limited to the coherence length of the laser used as the light source, since the phase noise of the laser degrades the sharpness of the beat spectrum. We have developed phase-noise-compensated optical frequency domain reflectometry (PNC-OFDR) to overcome this limitation by introducing a novel phase-noise compensation technique, and we achieved a very high-resolution measurement over the fiber link length. We describe the principle of PNC-OFDR and recent related developments, and discuss its use in diagnosing issues with fiber networks.

Semiconductor laser amplitude and phase noises effects in coherent optical frequency domain reflectometry C-OFDR

We study the effects of the semiconductor laser noise on the generated beat signal, in Coherent Optical Domain Reflectometry device. By using a general laser noise analytical model, based on Volterra non-linear treatment of laser rate equations, we find a novel general expression of the beat photocurrent. We show that the coherence and the incoherence cases are observed for a different delay time intervals than the ones known in literature. We show that the coherence domain corresponds to a delay time lower than the half of the laser coherence time τ 0 < 1 / 2 τ c , and the incoherence domain corresponds for τ 0 > 2 τ c . An original shape of the beat signal autocorrelation function affected by the laser noises is obtained.

Long Range and cm-Level Spatial Resolution Measurement Using Coherent Optical Frequency Domain Reflectometry With SSB-SC Modulator and Narrow Linewidth Fiber Laser

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper describes coherent optical frequency domain reflectometry (C-OFDR) with cm-level spatial resolution over 5 km. We propose the use of a single sideband with a suppressed carrier (SSB-SC) modulator and a narrow linewidth fiber laser as a tunable light source for C-OFDR. The advantage of using SSB-SC modulation is clarified theoretically by comparison with a double sideband with suppressed carrier modulation. We achieved cm-level spatial resolution over a 5-km measurement range and high sensitivity with a noise level 30 dB lower than the Rayleigh backscattering level. </para>

Modeling, design, fabrication, and testing of a fiber Bragg grating strain sensor array

The modeling, design, simulation, fabrication, calibration, and testing of a three-element, 15.3 cm fiber Bragg grating strain sensor array with the coherent optical frequency domain reflectometry (C-OFDR) interrogation technique are demonstrated. The fiber Bragg grating array (FBGA) is initially simulated using in-house software that incorporates transfer matrices. Compared to the previous techniques used, the transfer matrix method allows a systemwide approach to modeling the FBGA-C-OFDR system. Once designed and simulated, the FBGA system design is then imprinted into the core of a boron-germanium codoped photosensitive fiber using the phase mask technique. A fiber optic Fabry-Perot interferometric (FPI) strain gauge calibrator is then used to determine the strain gauge factor of a single fiber Bragg grating (FBG), and the results are used on the FBGA. The FPI strain gauge calibrator offers nondestructive testing of the FBG. To test the system, the FBGA is then attached to a 75 cm cantilever beam and interrogated using an incremental tunable laser. Electric strain gauges (ESGs) are then used to independently verify the strain measurements with the FBGA at various displacements of the cantilever beam. The results show that the peak strain error is 18% with respect to ESG results. In addition, good agreement is shown between the simulation and the experimental results.

Characterization of 1050-nm Pumped $S$-Band TDFA With Different Dopant Concentrations by Coherent Optical Frequency-Domain Reflectometry

For thulium-doped fiber amplifier (TDFA) design, knowledge of the gain distribution within the active fiber is of great value. For the first time, the distributed gain along highly thulium-doped fibers was measured with high-resolution reflectometry. The technique of coherent optical frequency-domain reflectometry is a nondestructive and noninvasive method well matched to this task due to its dynamic range, spatial resolution, and measurement range. Using thulium-doped fibers with different Tm3+-dopant concentrations, we show precise measurements of Rayleigh backscattering levels for obtaining the optimum gain-length ratio for S-band TDFA pumped by 1050-nm laser diodes

Modeling the distributed gain of single--(1050 or 1410 nm) and dual-wavelength--(800 + 1050 nm or 800 + 1410 nm) pumped thulium-doped fiber amplifiers.

The distributed gain of single- and dual-wavelength-pumped thulium-doped fiber amplifiers is modeled. The excellent agreement between the model and coherent optical frequency domain reflectometry measurements enables us to estimate intrinsic loss, branching ratios of fluorescence originating from the 3H4 level, and cross sections of upconversion pumping at 1050 and 1410 nm for the Tm3+ ions in the fiber. With the branching ratios obtained it is possible to describe induced signal absorption when pumping at 800 nm.

Coherent optical frequency domain reflectometry for interrogation of bend-based fiber optic hydrocarbon sensors

The paper presents distributed fiber optic bending sensor for petroleum hydrocarbon leak detection based on coherent optical frequency domain reflectometry (C-OFDR) technique. In order to introduce bending losses a sensitive polymer, which reversibly swells under hydrocarbon influence is employed. In this work we used lumped reflectors, namely fiber Bragg gratings, placed between distributed sensitive elements. Design of proposed sensor utilizes the principle of distributed detection with section localization (DDSL) of perturbation. Analysis of signal-to-noise ratio (SNR) for multi-reflectors system was performed. We have demonstrated that the C-OFDR technique with bending sensor is capable to detect hydrocarbon presence within a few minutes for 20-cm perturbation-length with spatial resolution about 0.5 m for strong perturbation.

Comparison of distributed gain in two dual-wavelength pumping schemes for thulium-doped fibre amplifiers

Using the coherent optical frequency domain reflectometry technique, a non-invasive study has been made of the distributed gain in two pumping schemes for thulium-doped fibre amplifiers. The compared schemes employed 800+1050 nm or 800+1400 nm pump wavelengths, and it was concluded that the former is advantageous over the latter primarily due to the ground-state absorption and pumping mechanism.

Distributed-gain measurements in S-band TDFA by coherent optical frequency domain reflectometry

The implementation of the optical frequency domain reflectometry technique to characterise S-band Tm-doped fibre amplifiers (TDFA) is described. Using this non-destructive method, the gain-length product for a TDFA can be optimised against pump power. Insight into the distributed gain dynamics in the TDFA is also obtained.

Analysis of the polarization evolution in a ribbon cable using high-resolution coherent OFDR

Exploiting the inherent polarization dependence and good spatial resolution of optical frequency domain reflectometry (OFDR), the beatlength in a ribbon fiber can be straightforwardly measured. The results clearly show the different amount of polarization ordering for inner and outer ribbon fibers due to the stress-induced birefringence from the common outer coating.

Local birefringence measurements in single-mode fibers with coherent optical frequency-domain reflectometry

Measurements of intrinsic and induced birefringence of optical fibers are performed at 1550 nm using the optical frequency-domain reflectometry technique. The experiment confirms the theoretical analysis, which predicts the appearance of oscillations on the detected Rayleigh backscattering intensity, with periods equal to the polarization beat length L/sub b/ and to L/sub b//2. Polarization mode-coupling length values are obtained from local birefringence and polarization mode dispersion measurements.

High-resolution distributed-gain measurements in erbium-doped fibers

For the first time, the distributed gain along erbium-doped fibers was measured with high-resolution reflectometry. The coherent optical frequency-domain reflectometry detection technique intrinsically filters amplified spontaneous emission, allowing precise measurements of Rayleigh backscattering levels and nondestructive determination of the optimum length of the doped fiber for different pump and probe conditions.

Return loss measurements of WDM filters with tunable coherent optical frequency-domain reflectometry

Reflectivity measurements of wavelength-division multiplexed (WDM) filters were performed with polarization independent coherent optical frequency domain reflectometry (C-OFDR). The spectral resolution of 0.012 mn allowed to characterize side lobe spacing and reflectivity with 90-dB dynamic range. The off-channel reflectivity was also measured for estimating the interchannel crosstalk in WDM systems and the experimental results were fitted to a theoretical equation, extracting the physical parameters of the filter.

Coherent reflectometry of optical fiber amplifiers

The reflectivity of commercially available erbium-doped fiber amplifiers (EDFAs) was measured with coherent optical frequency domain reflectometry (C-OFDR). Reflections at the output isolator as well as the distributed gain along the erbium-doped fiber could be observed thanks to the high amplified spontaneous emission (ASE) rejection due to the coherent detection. Gain figures obtained with the OFDR technique are in good agreement with single-pass direct gain measurements.