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Engineering Note
EN-FY1304
Revision 2 – March 20, 2013
Overview
The purpose of this document is to outline the capabilities of the Optical Backscatter Reflectometer (OBR)
4600 in characterizing a chirped fiber Bragg grating (FBG). Data taken with the OBR instrument on a
chirped FBG are presented and several competing technologies are mentioned.
OBR 4600
The OBR 4600 enables ultra-high resolution reflectometry with backscatter-level sensitivity. The
technology contained in the OBR is based on a patented interferometric measurement technique that
provides a spatial resolution of 10 microns over 30 meters of fiber device length or 20 microns over 70
meters of fiber device length. The OBR 4600 provides -130 dB sensitivity and 70 dB of dynamic range in
a commercially available product. Wavelength scan ranges of either the C and L bands or the O band
are available.
Luna’s unique swept wavelength interferometric measurement technique provides both amplitude and
phase information as a function of wavelength and distance. With the OBR 4600 and the OVA 5000 with
OFDR capability, a user can fully characterize the features of a chirped grating, including wavelength as a
function of distance, amplitude as a function of distance, and amplitude as a function of wavelength, all
with a single scan.
Example Data
Below are a few screen captures taken from Luna’s OBR software displaying data on a chirped FBG.
Note that this data was taken w ith 20 micron spatial resolution. The grating measured is well over 1 meter
in length.
In the first screen capture shown in Figure 1, the top graph shows reflected amplitude as a function of
distance. This allows the user to view the response and shape of the grating as a function of distance
along the fiber. Highlighting the grating with one of the two integrated cursors allows for the processing of
only the selected segment of data. The bottom graph in Fig. 1 plots the phase derivative as a function of
distance, or the wavelength of the grating as a function of distance along the fiber.
Chirped Fiber Bragg Grating Measurements
EN-FY1304
Figure 1: Phase Derivative (Wavelength) of Grating Versus Distance
In addition to the phase derivative information displayed in Figure 1, the user also has the capability of
viewing the return loss of the grating as a function of wavelength, as shown in the bottom graph of Figure
2. The user can switch between these views in seconds, using the simple, intuitive user interface of the
OBR 4600 product. The data may be saved to files and recalled for further analysis at a later time.
Figure 2: Return Loss of Grating as a Function of Wavelength