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Diamond is a promising platform for sensing and quantum processing owing to the remarkable properties of the nitrogen-vacancy (NV) impurity. The electrons of the NV center, largely localized at the vacancy site, combine to form a spin triplet, which can be polarized with 532 nm laser light, even at room temperature. The NV’s states are isolated from environmental perturbations making their spin coherence comparable to trapped ions. An important breakthrough would be in connecting, using waveguides, multiple diamond NVs together optically. However, still lacking is an efficient photonic fabrication method for diamond akin to the photolithographic methods that have revolutionized silicon photonics. Here, we report the first demonstration of three dimensional buried optical waveguides in diamond, inscribed by focused femtosecond high repetition rate laser pulses. Within the waveguides, high quality NV properties are observed, making them promising for integrated magnetometer or quantum information systems on a diamond chip.

In this Letter, we report on the successful fabrication of low loss, high refractive index contrast waveguides via ion migration upon femtosecond laser writing in phosphate glass. Waveguides were produced in two different phosphate glass compositions with high and low La 2 O 3 content. In the La-rich glass, a large refractive index increase in the guiding region was observed due to the incoming migration of La accompanied by the out-diffusion of K. The much smaller refractive index change in the La-less glass is caused by rearrangements of the glass structure. These results confirm the feasibility of adapting the glass composition for enabling the laser writing of high refractive index contrast structures via spatially selective modification of the glass composition. The origin of the refractive index modification caused by femtosecond (fs) laser irradiation in phosphate glasses has been investigated by several research groups. In such reports, mostly commercial glass from Kigre, Inc. (QX and MM2) and Schott AG (IOG) are used [1][2][3][4][5]. Most of these glasses were developed for telecommunication research and industry as base materials for waveguide fabrication by Ag-Na ion exchange [6][7][8]. With the advent of fs-laser-inscription techniques, demand for new glasses grew even higher due to the ability of fast prototyping and fabrication of complex 3D custom components [5]. Still, little effort was made to optimize the glass composition for this new technique. Due to the versatility of fs-laser writing, many problems were surmounted by adjusting the processing conditions to produce excellent results in various glasses [1,5]. However, there is little doubt that glass composition is a key parameter for further optimizing fs-laser-written optical devices. Among various commercial phosphate glass compositions, we have identified and isolated a set of glass with and without La 2 O 3 to demonstrate the importance of optimizing the glass matrix composition for fs-laser writing. We show that the presence of La 2 O 3 enables us to achieve a large positive refractive index contrast (RIC) in the written structures. The responsible mechanism is identified as the migration of La to form a region of increased refractive index accompanied by out-diffusion of K. The compositional changes unambiguously correlate to positive and negative refractive index modifications. Indeed, the refractive index changes observed via La migration are far beyond what can be attributed to changes in the glass structure.In the present work, we have investigated in detail the role of La 2 O 3 in the photo-inscription mechanisms in phosphate glasses. The addition of La 2 O 3 to P 2 O 5 -Al 2 O 3 glasses is known to increase the refractive index of the glass [9,10] as well as to improve its thermal, mechanical, and optical properties. We have used two different QX special melt phosphate glass samples from Kigre, Inc., both doped with 2 wt. % Er and 4 wt. % Yb (QX was introduced as a laser glass capable of withstanding high thermal loading and shoc...

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This review focuses on the engineering of the structural, thermal, optical and spectroscopic properties of tellurium oxide (TeO 2 ) glasses for their applications in fibre optic and waveguide devices. Unlike silica optical fibres, tellurium oxide glass fibres and light waveguides support propagation of light beyond y2 mm, where silica fibres become opaque. Silica fibres also have limited solubility for rare earth oxides due to silica's structure, which is where tellurium oxide fibres and light waveguides can offer significant opportunities to engineer novel lasers and amplifiers for integrated optics. In this review, we compare the structural properties of TeO 2 based glasses, modified by incorporating alkali, alkaline earth, and other oxide compounds. Based on Raman, UV, visible and infrared spectroscopic data, the structural aspects of tellurite glasses are discussed. The effects of compositional modification on the thermal and viscous flow properties are also compared and related with the resistance against devitrification. The significance of glass to crystal phase transformation during cooling and heating is explained in the context of preform and fibre fabrication. The review also reports on the characterisation of OH 2 impurities in tellurite glasses. Recent developments in tellurite fibre lasers and femtosecond laser inscribed waveguide fabrication are discussed.

Diamond's nitrogen vacancy (NV) center is an optically active defect with long spin coherence times, showing great potential for both efficient nanoscale magnetometry and quantum information processing schemes. Recently, both the formation of buried 3D optical waveguides and high-quality single NVs in diamond were demonstrated using the versatile femtosecond laser-writing technique. However, until now, combining these technologies has been an outstanding challenge. In this Letter, we fabricate laser-written photonic waveguides in quantum grade diamond which are aligned to within micron resolution to single laser-written NVs, enabling an integrated platform providing deterministically positioned waveguide-coupled NVs. This fabrication technology opens the way toward on-chip optical routing of single photons between NVs and optically integrated spin-based sensing.

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The properties of structures written inside dielectrics with high repetition rate femtosecond lasers are known to depend strongly on the complex interplay of a large number of writing parameters. Recently, ion migration within the laser-excited volume has been identified as a powerful mechanism for changing the local element distribution and producing efficient optical waveguides. In this work it is shown that the transient plasma distribution induced during laser irradiation is a reliable monitor for predicting the final refractive index distribution of the waveguide caused by ion migration. By performing in-situ plasma emission microscopy during the writing process inside a La-phosphate glass it is found that the long axis of the plasma distribution determines the axis of ion migration, being responsible for the local refractive index increase. This observation is also valid when strong positive or negative spherical aberration is induced, greatly deforming the focal volume and inverting the index profile. Even subtle changes in the writing conditions, such as an inversion of the writing direction (quill writing effect), show up in the form of a modified plasma distribution, which manifests as a modified index distribution. Finally, it is shown that the superior control over the waveguide properties employing the slit shaping technique is caused by the more confined plasma distribution produced. The underlying reasons for this unexpected result are discussed in terms of non-linear propagation and heat accumulation.