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Register a new userFemtosecond laser inscription of Bragg grating waveguides in bulk diamond
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Femtosecond laser writing is applied to form Bragg grating waveguides in the diamond bulk. Type II waveguides are integrated with a single pulse point-by-point periodic laser modification positioned towards the edge of the waveguide core. These photonic devices, operating in the telecommunications band, allow for simultaneous optical waveguiding and narrowband reflection from a 4th order grating. This fabrication technology opens the way towards advanced 3D photonic networks in diamond for a range of applications.
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In-volume ultrafast laser direct writing of silicon is generally limited by strong nonlinear propagation effects preventing the initiation of modifications. By employing a triple-optimization procedure in the spectral, temporal and spatial domains, we demonstrate that modifications can be repeatably produced inside silicon. Our approach relies on irradiation at $approx 2$-$mu$m wavelength with temporally-distorted femtosecond pulses. These pulses are focused in a way that spherical aberrations of different origins counterbalance, as predicted by point spread function analyses and in good agreement with nonlinear propagation simulations. We also establish the laws governing modification growth on a pulse-to-pulse basis, which allows us to demonstrate transverse inscription inside silicon with various line morphologies depending on the irradiation conditions. We finally show that the production of single-pulse repeatable modifications is a necessary condition for reliable transverse inscription inside silicon.
Understanding the physical mechanisms of the refractive index modulation induced by femtosecond laser writing is crucial for tailoring the properties of the resulting optical waveguides. In this work we apply polarized Raman spectroscopy to study the origin of stress-induced waveguides in diamond, produced by femtosecond laser writing. The change in the refractive index induced by the femtosecond laser in the crystal is derived from the measured stress in the waveguides. The results help to explain the waveguide polarization sensitive guiding mechanism, as well as providing a technique for their optimization.
A first demonstration and complete characterization of mid-infrared waveguides in diamond are reported in detail. Waveguides were designed for 2.4 um and 8.6 um waveguiding, with their group velocity dispersion was analyzed using femtosecond pulses at 2.4 um wavelength propagated through the waveguide and the bulk substrate. The total dispersion was found to be dominated by the bulk material rather than the waveguide, and was on the range of 275 fs2/mm, demonstrating that femtosecond laser written modifications in diamond introduce negligible perturbations to the intrinsic material.
We demonstrate the first buried optical waveguides in diamond using focused femtosecond laser pulses. The properties of nitrogen vacancy centers are preserved in the waveguides, making them promising for diamond-based magnetometers or quantum information systems.
Optical microresonators are of paramount importance in photonic circuits requiring fine spectral filtering or resonant light recirculation. Key performance metrics improve with increasing resonance quality factor (Q) across all applications. The performance of silicon photonic circuits is often hampered by the low-quality factor of planar silicon microresonators, typically of Q~10^4-10^5. On the other hand, bulk whispering gallery mode resonators provide a wide range of materials with intriguing optical properties and exceptionally high resonant quality factors Q>10^7. However, the efficient coupling between bulk resonators and planar Si photonic waveguides is considered challenging, if not impossible, due to remarkably large mismatch in size and refractive index. Here, we show an efficient method to couple bulk resonators and Si waveguides based on subwavelength metamaterial engineering of silicon. Based on this approach, we experimentally demonstrate coupling between 220-nm-thick Si waveguides and bulk microresonators made of silica, lithium niobate and calcium fluoride with diameters in the 0.3-3.5 mm range, achieving high coupling efficiency of 75-99% and exceptional Q of 10^6-10^7. These results open a new route for the heterogeneous integration of bulk resonators and silicon photonic circuits, with great potential for applications in sensing, microwave-photonics, and quantum photonics, to name a few.
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