One of the most important directions in modern methods of micro-fabrication is stereographic two-photon polymerization lithography (TPP). This method enables creating three-dimensional polymer structures with a high accuracy, and is also very flexible for any production tasks.
Here we show how the TPP method can be useful for printing the basic elements of three-dimensional integrated optics. We fabricated polymer waveguides with attached prism adapters, as well as microresonators of various shapes and sizes. The waveguides suspended above a glass substrate with input/output prisms (Fig.1(a)) showed good efficiency in low-mode regime. The advantages of the proposed prism coupler are small size, wide spectral range and low losses (no more than 1.25dB). Another important feature of this work is the demonstration of printing of an active optical system using a polymer doped with various laser dyes. We also demonstrate  combined systems consisting of active microresonators and passive waveguides on a single substrate (Fig.(c)). The future development of such integrated optical system is very promising for creation of three-dimensional optical logic and sensor devices.

Figure 1. a) 3D model of a suspended waveguide with prism adapters, the blue line shows path of the optical beam, b) SEM image of the printed structure, c) optical image of the printed structure under illumination with white light and UV radiation, the blue ring is the luminescence of the dye in the cylinder.

A.Maydykovskiy, D.Apostolov, E.Mamonov, D.Kopylov, S.Dagesyan, T.Murzina
JETP Letters 117, issue 1 (2023)