The ability to distinguish between different wavelengths depends on the resolving power or spectral resolution of the measurement system. In the case of fiber optic cables or other wavelength measurement devices, the resolving power is determined by factors such as the quality of the optical components and the detection method used.
The resolving power is commonly quantified using a parameter called the full width at half maximum (FWHM), which represents the width of a spectral peak at half of its maximum intensity. The smaller the FWHM, the better the resolving power of the system.
In fiber optic communication systems, wavelength division multiplexing (WDM) technology is used to transmit multiple signals simultaneously through a single fiber by assigning different wavelengths to each signal. The spacing between these wavelengths is typically in the range of a few nanometers.
For example, in dense wavelength division multiplexing (DWDM) systems, the spacing between adjacent channels can be as small as 0.8 nm or even less. This means that two neighboring wavelengths can be distinguished if their separation is larger than the resolution limit, which is typically around the FWHM value.
In practical terms, the ability to distinguish wavelengths that are very close together, such as 1000 nm and 1005 nm, depends on the specific measurement equipment and its resolving power. High-quality spectrometers or optical spectrum analyzers can have high resolving powers that enable the differentiation of wavelengths with small spacing. However, if the spacing between two wavelengths falls below the resolving power limit of the measurement system, they may not be accurately distinguished, and their signals may overlap or interfere with each other.
Therefore, the minimum wavelength spacing that can be reliably measured depends on the resolving power of the specific measurement device or system being used.