Explanation: In optical fiber propagation context, the first, second, and third window refer to different wavelength intervals where the WDM (Wavelength Division Multiplexing) optical transmission occurs.
The first window is the lowest loss window and is typically in the range of 1300-1324nm. This is the most commonly used window for long-haul communications.
The second window is the 1550 nm window and is the most widely used window for long-haul and ultra-long-haul communications. This window has a lower attenuation than the first window, but it also has more dispersion, which can limit the maximum transmission distance.
The third window is the range of 1625-1675 nm, it is also called the L-band window. This window has lower attenuation than the first and second window but its usage is limited due to the high cost of equipment and lack of commercial devices.
These windows are used in WDM systems to increase the capacity of the fiber by transmitting multiple channels of data at different wavelengths on the same fiber.
A,C,D are not correct as they are not related to the meaning of first, second, and third window in the optical fiber propagation context.
