Coherent frequency-domain reflectometry for characterization of single-mode integrated-optical waveguides

High resolution optical frequency domain reflectometry for measurement of waveguide group refractive index

“…However, non-linear waveguide dispersion leads to a broadening of the reflection peaks which are observed in OFDR [5]. Therefore, the waveguide dispersion must be de-embedded to improve the temporal resolution.…”

Optical frequency domain reflectometry: A review

“…Due to these nonlinear tuning characteristics, sampling of the interference signal with a constant spacing in time gives rise to a non-uniform sampling in optical frequency which, in turn, degrades the spatial resolution of the OFDR measurement. It is well known that this problem can be avoided by sampling the interference signal at equidistant instantaneous optical frequency points rather than equally spaced time intervals [28]. There are three approaches to realize this:…”

High-Resolution FMCW Reflectometry Using a Single-Mode Vertical-Cavity Surface-Emitting Laser

“…2, the wavelength change of the VCSEL is about 4.5 nm at the above condition, and the resultant optical frequency change is about 830 GHz. The theoretical spatial resolution is then expected to be about 180 m for from (2). The total number of the sampled data is…”

“…In [1], the optical frequency of a Fabry-Pérot laser was swept by the injection current modulation and the propagation loss of a glass optical waveguide was estimated with the spatial resolution of 1 mm at 80 cm (which corresponds to 1.5 mm in air). In [2], the optical frequency of a DFB laser was tuned by the temperature tuning to achieve large optical frequency change, and the spatial resolution of 50 m in a few centimeter-long InP optical waveguide (which corresponds to about 150 m in air) was achieved. However the tuning speed was 20 s and then real-time measurements are impossible.…”

“…The emitted light from the VCSEL is divided into two beams; one beam is launched into the sensing interferometer, and the interference signal is sampled by a 12-bits analog-to-digital converter (AD converter) and then is stored in the computer for the Fourier analysis. The other beam is launched into the reference interferometer and the interference signal is used to generate the sampling clock signal of the AD converter [2]- [4], [9]. Such a sampling scheme is very useful to enhance the spatial resolution because the optical frequency cannot be linearly swept by linearly sweeping the injection current [5], [6], [10].…”