Integrated polarization rotator/converter by stimulated Raman adiabatic passage

Advanced Light: Liquid Crystals-Based Ultra-Broadband Polarization Rotator for Functional Smart Devices

A novel ultra-broadband polarization rotator with advanced angular adjustability is proposed for functional devices such as displays and smart windows. The new solution offers dynamic control of light polarization across a broad range of wavelengths, encompassing the complete visible spectrum, ultraviolet and near-infrared. Moreover, it boasts a smaller footprint, faster response times, and lower dispersion compared to conventional rotators. The findings are remarkable in that they show that as the viewing angle increases, the hybrid alignment takes on a twist-like configuration, with the polarization rotation angle determined by the spatial variation in the twist angle. This intriguing behavior leads to an improved range of angular adjustability, as the effective polarization rotation depth is extended. The improved angular adjustability of reconfigurable smart devices surpasses the limitations of traditional polarization rotators, unlocking new innovative possibilities. For example, the rotator plays a crucial role in display technologies, allowing for effective control of viewing angles and minimizing reflection from disturbing external light. Similarly, in smart windows, it optimizes energy conservation by regulating direct sunlight transmission while ensuring clear visibility in normal conditions. It is believed that the proposed advanced ultra-broadband polarization rotator is a significant step forward in the development of reconfigurable smart devices.

Design of Waveguide Polarization Convertor Based on Asymmetric 1D Photonic Crystals

Photonic crystals possess metastructures with a unique dispersion relation. An integrated optical circuit plays a crucial role in quantum computing, for which miniaturized optical components can be designed according to the characteristics of photonic crystals. Because the stable light transmission mode for a square waveguide is transverse electric or transverse magnetic polarization, we designed a half-waveplate element with a photonic crystal that can rotate the polarization direction of the light incident on a waveguide by 90°. Using the dispersion relation of photonic crystals, the polarization rotation length and the optical axis’s angle of deviation from the electric field in the eigenmode can be effectively calculated. Polarization rotators designed on the basis of photonic crystal structures can effectively reduce the insertion loss of components and exhibit favorable polarization rotation performance.

On-chip beam rotators, adiabatic mode converters, and waveplates through low-loss waveguides with variable cross-sections

Photonics integrated circuitry would benefit considerably from the ability to arbitrarily control waveguide cross-sections with high precision and low loss, in order to provide more degrees of freedom in manipulating propagating light. Here, we report a new method for femtosecond laser writing of optical-fiber-compatible glass waveguides, namely spherical phase-induced multicore waveguide (SPIM-WG), which addresses this challenging task with three-dimensional on-chip light control. Fabricating in the heating regime with high scanning speed, precise deformation of cross-sections is still achievable along the waveguide, with shapes and sizes finely controllable of high resolution in both horizontal and vertical transversal directions. We observed that these waveguides have high refractive index contrast of 0.017, low propagation loss of 0.14 dB/cm, and very low coupling loss of 0.19 dB coupled from a single-mode fiber. SPIM-WG devices were easily fabricated that were able to perform on-chip beam rotation through varying angles, or manipulate the polarization state of propagating light for target wavelengths. We also demonstrated SPIM-WG mode converters that provide arbitrary adiabatic mode conversion with high efficiency between symmetric and asymmetric nonuniform modes; examples include circular, elliptical modes, and asymmetric modes from ppKTP (periodically poled potassium titanyl phosphate) waveguides which are generally applied in frequency conversion and quantum light sources. Created inside optical glass, these waveguides and devices have the capability to operate across ultra-broad bands from visible to infrared wavelengths. The compatibility with optical fiber also paves the way toward packaged photonic integrated circuitry, which usually needs input and output fiber connections.

70 dB long-pass filter on a nanophotonic chip

Integrated quantum photonic chips are promising for scalable, photonic based quantum information processing. Although on-chip quantum photon sources and single photon detectors have been demostrated separately, the full integration of these components on single chip is hindered by the background photons from the strong classical pump light. Here we design and fabricate an on-chip long-pass filter which can provide 70 dB attenuation for visible light near 775 nm with less than 3 dB insertion loss for light in the telecom C-band near 1550 nm. The adiabatic design makes this device broadband and robust against fabrication errors as well as working conditions. Combined with the previously demonstrated non-classical on-chip source based on spontaneous parametric down conversion on the same material system, this platform could enable 100 dB suppression of pump light and holds promise in realizing fully integrated quantum photonic chips where the sources, filters and detectors are monolithically integrated.

Spatial adiabatic passage: a review of recent progress

Adiabatic techniques are known to allow for engineering quantum states with high fidelity. This requirement is currently of large interest, as applications in quantum information require the preparation and manipulation of quantum states with minimal errors. Here we review recent progress on developing techniques for the preparation of spatial states through adiabatic passage, particularly focusing on three state systems. These techniques can be applied to matter waves in external potentials, such as cold atoms or electrons, and to classical waves in waveguides, such as light or sound.

Optimization of integrated polarization filters

This study reports on the design of small footprint, integrated polarization filters based on engineered photonic lattices. Using a rods-in-air lattice as a basis for a TE filter and a holes-in-slab lattice for the analogous TM filter, we are able to maximize the degree of polarization of the output beams up to 98% with a transmission efficiency greater than 75%. The proposed designs allow not only for logical polarization filtering, but can also be tailored to output an arbitrary transverse beam profile. The lattice configurations are found using a recently proposed parallel tabu search algorithm for combinatorial optimization problems in integrated photonics.

CMOS-compatible highly efficient polarization splitter and rotator based on a double-etched directional coupler

We present a highly efficient polarization splitter and rotator (PSR), fabricated using 248 nm deep ultraviolet lithography on a silicon-on-insulator substrate. The PSR is based on a double-etched directional coupler with a length of 27 µm. The fabricated PSR yields a TM-to-TE conversion loss better than 0.5 dB and TE insertion loss better than 0.3 dB, with an ultra-low crosstalk (-20 dB) in the wavelength regime 1540-1570 nm.

Acousto-optic resonant coupling of three spatial modes in an optical fiber

A fiber-optic analogue to an externally driven three-level quantum state is demonstrated by acousto-optic coupling of the spatial modes in a few-mode fiber. Under the condition analogous to electromagnetically induced transparency, a narrow-bandwidth transmission within an absorption band for the fundamental mode is demonstrated. The presented structure is an efficient converter between the fundamental mode and the higher-order modes that cannot be easily addressed by previous techniques, therefore can play a significant role in the next-generation space-division multiplexing communications as an arbitrarily mode-selectable router.

Efficient coupling between dielectric waveguide modes and exterior plasmon whispering gallery modes

Inefficient coupling between dielectric guided mode and plasmon mode has been overlooked in the past. The coupling mechanism is essentially different from the conventional coupling between dielectric modes. Based on qualitative theoretical analysis, we proposed two methods to strengthen the coupling between dielectric waveguide modes and exterior plasmon whispering gallery modes. One is using a U-shaped bent waveguide to break the adiabatic mode conversion process, and the other is to utilize higher-order dielectric mode to reach phase matching with plasmon mode. Both the transmission spectrum of waveguide and the energy spectrum of cavity demonstrate that the coupling efficiency can be greatly improved. These simple configurations are potential for wide applications, for example, tunable integrated optical devices and sensors.