On‐Chip Polarization Rotators

Abstract

detection, [9,10] sensing, [11][12][13][14] and so on. Specifically, to process polarization-encoded information in PICs, controlling of the polarization states is necessary, which requires the combinations of polarization isolator, polarization rotator, polarizer retarder, and so on. [15][16][17][18] In free space, there are already many examples of implementing polarization manipulation. [19][20][21] Recently, metamaterials also allow polarization conversion with near-perfect conversion efficiency. [22,23] However, we focus on the on-chip polarization conversion using integrated waveguides. So far, the methods for manipulating the polarization states of photons in PICs can be roughly classified into three categories: I) The most common one is to make the waveguide cross-section asymmetric, so that the horizontal and vertical polarization modes are no longer orthogonal and interfere with each other. [24,25] This type of devices requires high accuracy in fabrication and is usually sensitive to wavelength. II) The second one is based on the mode evolution, where the polarization of the photon changes as the waveguide geometry is slowly engineered. Since the waveguide cross sections usually vary in the vertical direction, this type of devices is difficult to fabricate with the top-down process. [26,27] III) The third type relies on surface plasmon polaritons, which are excited selectively by perpendicular polarization of photons. [28,29] In 2015, Zhu's group has demonstrated a plasmonic polarization generator that can reconfigure an input polarization to all types of polarization states simultaneously. [8] Although these plasmonic devices can be made very small (several micrometers), their performance is severely encumbered by the absorption of the metal.For type-II polarization rotators, they have a lot of advantages. For example, their broad bandwidth benefits the operations involving pulsed lasers. And unlike the type-I ones, their requirement on fabrication accuracy is relaxed due to the nature of adiabatic mode evolution. [30,31] Although the top-down lithography techniques are restricted in their fabrication, people have developed many other techniques that can deal with 3D nanostructures, such as self-assembly and 3D printing. [32,33] Femtosecond direct laser writing (fs-DLW) is also one of them, which uses tightly focused ultrashort (fs scale) pulsed laser and changes the optical properties of materials via nonlinear multiphoton absorption. [34] Depending on the different materials and the applied laser power, the material properties may change because of polymerization, reduction, bond cleavage, phase change, and ablation. [35][36][37][38] Due to the small multiphoton absorption cross section and the short On-chip polarization manipulation is proposed via a waveguide that is adiabatically twisted along its longitudinal axis, which can be fundamental building blocks for polarization-encoded optical communication and information processing. With the help of femtosecond direct laser writing, the polarization ...

Laser 3D Printing of Inorganic Free-Form Micro-Optics

“…However, until now, it was quite limited for direct processing of transparent inorganics of ceramic and crystalline phases [8]. On the other hand, the current advances of the technique are driven vastly by the rapid progress for implementation in manufacturing of various micro-optical and nano-photonic monolith elements as well as fully assembled complex 3D components [9][10][11][12][13]. Thus, here we demonstrate the combination of ultrafast laser 3D nanolithography and thermal posttreatment for opening a route for production of free-form inorganic structures-specifically free-form micro-optics.…”

Micro‐Optics 3D Printed via Multi‐Photon Laser Lithography

“…[ 99 ] Alternatively, highly birefringent channel waveguides can rotate the polarization by adiabatically twisting them. By controlling the twisting angle of the waveguide, the polarization state changes to an arbitrary or intended state, [ 100 ] allowing the creation of polarization rotator [ 101 ] as presented in Figure 5c. A polarization rotator based on the same operation mode has been demonstrated on fiber‐to‐chip connections, in order to convert TM to TE polarization mode.…”

On‐Demand Polarization Controllable Liquid Crystal Laser

“…Previous reports that show polarization controllability using an LC device [26][27][28][29][30][31][32][33][34] do not typically control the orientation of the polarization state as well. Alternatively, the six-electrode-based device with SiO 2 -TiO 2 does enable control of orientation, but with an increase in the fabrication complexity.…”