Scientists at Aston university show the world's longest lasers.The non-destructive transmission of optical communication signals with wavelength of 1550nm was realized by using this 75km fiber laser cavity.

In the long distance fiber-optic link, the distributed amplification can make up for the attenuation of the signal in the transmission process.In order to achieve nearly lossless transmission in optical fiber, the scientists used various methods to make along the optical fiber transmission for gain, and realize the amplified spontaneous emission (ASE) noise control.The Aston team has provided a solution by using the transmission optical fiber as a Raman laser, achieving a near-lossless transmission and minimizing the ASE noise.

World's Longest Lasers

The 75km Raman laser implements the lossless transmission between emitter T and receiver R.The wavelength and wavelength of Raman wavelength and signal wavelength of main pump laser wavelength and fiber grating are 1365, 1455 and 1550nm respectively.

From two power equal to the wavelength of 1365 nm pump laser laser respectively from both ends into silicon-based single-mode fiber (SMF), the two-way pump structure need to be located at the ends of the fiber optic fiber Bragg grating reflector.In order to match the main stokes wave peak of the pump laser in optical fiber, the center wavelength of the grating is 1455nm.This pair of grating and the entire length of optical fiber to form a laser cavity, if the main pump power is greater than the threshold needed for the stimulated Raman scattering, which can overcome the reflector of center wavelength of optical fiber attenuation, the whole becomes a long period of fiber laser.In this way, a dynamic stable secondary pump with a wavelength of 1455nm will be produced in the cavity.

The signal light of 1550nm is matched with the Stokes pump of 1455nm and can be effectively amplified with a constant multiple, thus compensating for the attenuation of the beam along the optical fiber.The specific wavelength of the pump light and grating used in this example is not fixed in other applications, and the signals of different bands can be transmitted through appropriate changes.

In this experiment, the approximate nondestructive transmission of the optical fiber with a span of 75km can be obtained with almost no change of light signal at 25km or more.The team also provided a theoretical analysis that matched the results of the experiment.

"We first realized only need through the experiment of two laser pump nearly lossless optical fiber transmission", put forward the scheme in 2004 and led the team of Juan Diego Ania - castannn said, "they are a new type of laser, we know this is the longest of laser, with interesting properties, and, more importantly, their condition transmission characteristics will have a positive impact in other fields.Non-destructive optical fiber are potentially more light transmission capacity, its flat gain bandwidth can reach 36 nm, not only can be applied to optical communication, also can be used Yu Quanguang nonlinear data processing, and also opened may be developed based on the theory of integrable nonlinear system mathematics new photonic devices."

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