For structure or material monitoring low impact serial fiber Bragg grating (FBG) networks have attracted increasing
research interest. Common sensor networks using wavelength division multiplexing (WDM) for FBG interrogation are
limited in their efficiency by the spectral width of their light source, the FBG tuning range and the spectral guard bands.
Overlapping spectra are strictly forbidden in this case. Applying time division multiplexing (TDM) or active resonator
schemes may overcome these restrictions. However, they introduce other substantial disadvantages like signal roundtrip
dependency or sophisticated control of active resonating structures. Code division multiplexing (CDM) as a means of
FBG interrogation by simple autocorrelation of appropriate codes has been shown to be superior in this respect.
However, it came at the cost of a second spectrometer introducing additional equalization efforts. We demonstrate a new
serial FBG sensor network utilizing CDM signal processing for efficient sensor interrogation without the need of a
second spectrometer and additional state of polarization (SOP) controlling components. It allows overlapping spectra
even when all sensing FBGs are positioned at the same centre wavelength and it shows a high degree of insensitivity to
SOP. Sequence inversed keyed (SIK) serial signal processing utilizing quasi-orthogonal balanced codes ensures simple
and quick sensor interrogation with high signal-to-interference/noise ratio.
Due to their variability Fiber Bragg Grating (FBG) sensors are introduced in a growing number of applications. Furthermore these sensors are predestined for serial networking, whereby the two properties spectral selectivity and reflectivity led directly to wavelength division multiplex (WDM) and time division multiplex (TDM), respectively. But, both technologies show big disadvantages with regard to the efficiency of resource utilisation. In contrast to WDMA, in our proposed system using sequence inversion keyed direct sequence code division multiplexing (SIK-DS-CDM), the FBG spectra can overlap. Also the light pulses, reflected with a unique delay by each sensor, can superimpose. Hence more information per time reaches the receiver compared to TDMA. A simulation with 20 FBGs in a spectral range of 2nm shows the abilities of this system, whereby theoretical works regarding optimal codes and network structure deal with its conditions.
Due to their variability Fibre Bragg Grating (FBG) sensors are introduced in a growing number of applications. Furthermore using their spectral selectivity and adjustable reflectivity these sensors are predestined for serial networking, whereby presently in most cases the addressing is realised by time division multiple access (TDMA) or wavelength division multiple access (WDMA). But these technologies have big disadvantages regarding the effective use of the prevailing resources time and wavelength, respectively.
In this paper a new scheme capable of addressing a large number of FBGs in a single serial network is proposed and compared to TDMA and WDMA. Using all optical sequence inversion keyed (SIK) direct sequence (DS) code division multiple access (CDMA) it overcomes the restrictions handling the resources time and wavelength without loosing accuracy. A simulation with 20 FBGs in a spectral range of 2nm shows the abilities of this system, which can be build up with nearly the same components as TDMA systems.