Femtosecond Laser Written Depressed-Cladding Waveguide 2 × 2, 1 × 2 and 3 × 3 Directional Couplers in Tm3+:YAG Crystal

An Integrated Pump-Controlled Variable Coupler Fabricated by Ultrafast Laser Writing

The design and fabrication of a integrated symmetric directional coupler dependent o the pumping power and operating at a 1534 nm wavelength is reported. The twin-core waveguide was inscribed into Er³⁺/Yb³⁺ co-doped phosphate glass by a femtosecond laser direct writing technique. By optical pumping, the coupling ratio can be modulated due to the changes induced in the refractive index of the material. The experimental results demonstrated that the coupling ratio can be tuned continuously from 100/0 to 50/50 by increasing the pump's power from 0 to 350 mW. The developed twin-core coupler has promising applications for on-chip all-optical signal processing and communication systems.

Judd-Ofelt Analysis of High Erbium Content Yttrium-Aluminum and Yttrium-Scandium-Aluminum Garnet Ceramics

The Er1.5Y1.5Al5O12 (Er:YAG) and (Er1.43Y1.43Sc0.14)(Sc0.24Al1.76)Al3O12 (Er:YSAG) ceramics have been characterized using the Judd-Ofelt (JO) theory. The line strengths and oscillator strengths of several transitions from the ground state 4I15/2 to excited state manifolds have been evaluated from transmittance spectra measured at room temperature (300 K). The JO parameters have been calculated, and the values of the radiative decays rate and the radiative lifetimes for the 4I13/2 excited state, and the luminescence cross-section of 4I15/2 → 4I13/2 in Er-doped ceramic samples have been established. We have traced the influence of Sc3+ inclusion on spectroscopic properties and crystal quality and estimate prospects of application in laser systems.

On-Demand Integrated Quantum Memory for Polarization Qubits

Photonic polarization qubits are widely used in quantum computation and quantum communication due to the robustness in transmission and the easy qubit manipulation. An integrated quantum memory for polarization qubits is a useful building block for large-scale integrated quantum networks. However, on-demand storing polarization qubits in an integrated quantum memory is a long-standing challenge due to the anisotropic absorption of solids and the polarization-dependent features of microstructures. Here we demonstrate a reliable on-demand quantum memory for polarization qubits, using a depressed-cladding waveguide fabricated in a ^{151}Eu^{3+}:Y_{2}SiO_{5} crystal. The site-2 ^{151}Eu^{3+} ions in Y_{2}SiO_{5} crystal provides a near-uniform absorption for arbitrary polarization states and a new pump sequence is developed to prepare a wideband and enhanced absorption profile. A fidelity of 99.4±0.6% is obtained for the qubit storage process with an input of 0.32 photons per pulse, together with a storage bandwidth of 10 MHz. This reliable integrated quantum memory for polarization qubits reveals the potential for use in the construction of integrated quantum networks.

Plastic deformation as nature of femtosecond laser writing in YAG crystal

Longitudinal inhomogeneity of tracks inscribed in a YAG crystal and the statistics of nonlinear transmittance of the writing beam is studied under conditions of direct femtosecond laser writing in non-thermal mode. Nonlinear transmittance fluctuations inherent in the laser writing were discovered, and their correlation with track inhomogeneity is established. A model of femtosecond laser writing in crystals is built that includes three modes of plastic deformation in the laser impact zone. The modification threshold of the femtosecond direct laser writing is identified with reaching yield stress.