Industry: Manufacturing Region: Germany Transaction price: US$ 1 million Transaction method: equity investment
Project introduction:
Scientists at the University of Gö ttingen in Germany proposed to use stretched flexible hollow fibers as waveguides for high-energy pulse compressors. This method is almost unaffected by the length of optical fiber, so it has good straightness. It is especially suitable for optical fiber whose inner diameter is much larger than the wavelength. In this case, the main limiting factor of optical fiber length is the loss caused by unwanted fiber bending.
Industry dilemma
In order to generate ultra-short and short-period laser pulses, ultra-wideband radiation is necessary. Because no gain material has a wide enough gain bandwidth, nonlinear spectral broadening method must be adopted for the amplified pulse. This is particularly important in the ultraviolet spectrum, because the existing gain materials in this area cannot amplify pulses shorter than 100 fs. The spectral expansion of high-energy laser pulses is usually realized by self-phase modulation of inert gas filled in hollow waveguide. A key point of this technology is that the hollow fiber is a multimode waveguide, and the refractive index of the core material (inert gas) is smaller than that of the cladding material (molten Shi Ying), so total internal reflection will not occur at the interface. Therefore, the guided wave ability is not as good as that of traditional optical fiber, which leads to the increase of propagation loss, thus limiting the length of nonlinear interaction. In addition, due to the bending of optical fiber, the loss of basic mode increases faster than that of high-order mode. Due to technical and other reasons, in most practical cases, the length of optical fiber is limited to less than 1 meter.
Innovative solutions
By using stretched flexible hollow fibers as waveguides, the inventors introduced an alternative method of using rigid hollow fibers, which allowed the use of longer fibers than previously set without introducing considerable bending losses. It is necessary to compress pulses with higher energy. Considering the characteristics of available inert gases, it seems possible to compress pulses of several millijoules and several tens of millijoules in ultraviolet and infrared. In these cases, due to the ionization problem, the cross section of the optical fiber must be greatly increased, which leads to a rapid decrease in propagation loss, so that a relatively long optical fiber can be used.
In addition, in order to prevent the nonlinear effect in front of the waveguide, it is desirable to apply a pressure gradient along the capillary, which also requires a longer optical fiber by reducing the effective interaction length. These ideas resulted in the optical fiber unit shown in the figure below. This structure allows a pressure gradient to be applied between the two ends of the optical fiber, which is beneficial to the compression of high-energy pulses, because it allows us to evacuate the focus area in front of the optical fiber and optimize the beam emission by preventing the defocusing effect caused by ionization. In the manufacturing process, the capillary tube passes through the glass tube and is pulled by a force of 10-15N. Support the glass tube assembly in such a direction that it will not touch the stretched capillary tube over the whole length. Then the two ends of the waveguide are bonded to the tube with epoxy resin glue, and the length is about 10 mm. After curing, the fibers were cut in the bonded area with a diamond tool. Because the bracket only fixes the optical fiber at both ends, the bracket does not have to be straight; It is sufficient to maintain a constant shape during and after the bonding process.
The feasibility of this method is tested in a 3-meter-long device, and the results show that its transmission has reached the theoretical limit, and the beam exiting from the optical fiber is limited by diffraction. Further tests confirm that the newly designed optical fiber module can achieve considerable spectral broadening. The proposed method is also very suitable for realizing pressure gradient in hollow fibers. Due to its properties and expandability, the stretched flexible capillary waveguide opens up a new prospect for compressing multi-millijoule laser pulses, especially in the ultraviolet spectrum, and increasing the fiber length has obvious advantages.
Advantages and applications
● The length of optical fiber can be adjusted freely, and the transmission rate is high.
● Laser pulses with higher energy can be compressed.
Diffraction-limited output beam
● It opens up a new prospect for compressing multi-millifocal laser pulses, especially those in the ultraviolet spectrum.
Cooperation mode:
The process test of this technology is successful, and many improvements have been added, which can provide further development and cooperation based on patents.