![]() In most applications of photonics, the propagating wavelengths are far from the material resonances to minimize the optical losses the fiber-optic communication window around 1550 nm in fused silica is a good example. In fact, many applications, such as waveguide lasers 9, electro-optic modulators 10, and frequency converters 11, require multi-scan-depressed cladding structures, which complicate or impede the fabrication or their guiding circuits. Another important limitation is the decrease in the refractive index that occurs in most crystals 5 and in a wide variety of glasses 6– 8. ![]() In particular, the miniaturization of many fs-laser-processed photonic devices is limited by the minimum bend radius of waveguides, which in turn depends on the magnitude of the induced refractive index contrast. However, a severe limitation of fs-laser inscription is related to the relatively low photoinduced refractive index contrast that is achievable 3, 4. ![]() One of the most relevant advantage is the micrometer-scale processing of complex three-dimensional structures, owing to the nonlinear nature of the laser absorption that precisely confines structural changes to the focal volume. Finally, the effect of the FLIBGS can compensate for the fs-laser-induced negative refractive index change, resulting in a zero refractive index change at specific wavelengths, paving the way for new invisibility applications.įemtosecond (fs) laser inscription in transparent materials has unique advantages 1, 2. ![]() We also demonstrate that the refractive index contrast can be switched from negative to positive, allowing direct waveguide inscription in crystals. First, we demonstrate waveguide bends down to a submillimeter radius, which is of great interest for higher-density integration of fs-laser-written quantum and photonic circuits. Supported by theoretical calculations, based on a modified Sellmeier equation, the Tauc law, and waveguide bend loss calculations, we experimentally show that several applications could take advantage of this phenomenon. We propose to address this issue by employing a femtosecond-laser-induced electronic band-gap shift (FLIBGS), which has an exponential impact on the refractive index change for propagating wavelengths approaching the material electronic resonance, as predicted by the Kramers–Kronig relations. However, the magnitude of the refractive index change is rather limited, preventing the technology from being a tool of choice for the manufacture of compact photonic integrated circuits. The holder must provide the straight pumping guides with the supports that will be integrated at the outlet of the section at the outlet coupler.Multiphoton absorption via ultrafast laser focusing is the only technology that allows a three-dimensional structural modification of transparent materials. The accelerator section will be temperature stabilized by means of cooling channels (copper tubes) that will be brazed to the cell surfaces or integrated in the copper mass. Painting on the guides, flanges, power divider is also prohibited. In case of leakage, any attempt to repair with glue, resin or varnish is strictly forbidden. The HF waveguides with CF pumping ports at the inlet and outlet of the accelerator section are supplied by the holder (factory). The pumping systems will be connected to the waveguides with CF pumping ports at the inlet and outlet of the accelerator section. The CF flanges for ultra high vacuum will also be made of the same material 1.4429 ESU stainless steel "316 LN". Rectangular HF flanges shall be LIL type and shall be made of "1.4429 ESU stainless steel". This HF copper structure will be brazed at high temperature with a solder that ensures good HF contact, tightness, and rigidity of the assembly. All components will be made of OFHC copper. It comprises elliptical iris cells including two coupling cells designed to achieve accelerator field symmetry and efficient power coupling. The accelerator section is a constant-gradient HF structure operating in the 2π/3 mode, S-band progressive wave. This contract is for the supply of a single package consisting of an S-band accelerator section with a flange-to-flange length of 4.8 m and equipped with two pumping waveguides at its output, a steel support beam and a W284 waveguide power splitter.
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