Adiabatic Mode Converter Research Articles

Analysis and Design of Compact Adiabatic Mode Converters Based on Adiabatic Mode Evolutions

This paper investigates the mode conversion in ridge waveguides. Based on the adiabatic mode evolution, several compact adiabatic mode converters with optimized waveguide shapes are proposed. Three types of adiabatic mode conversion from TM to TE modes are proposed. It is found that the designed adiabatic device is greatly shorter than the one based on the linear shape case, but is capable of achieving the same power mode conversion efficiency. Furthermore, an adiabatic TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> mode maintaining waveguide taper is proposed to guide the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> mode from narrow waveguide to wide waveguide. The efficiency of the designed adiabatic TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> mode maintaining waveguide taper considerably exceeds that obtained with the parabolic design. Then, combining the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> mode to TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> mode adiabatic mode converter and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> mode to TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> mode adiabatic mode converter, a TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> mode to TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> mode adiabatic mode converter (which is difficult to design and cannot be achieved even with a linear-shape connection) with a total length of 760 μm and 94% power mode conversion is proposed.

A heterogeneously integrated lithium niobate-on-silicon nitride photonic platform

The availability of thin-film lithium niobate on insulator (LNOI) and advances in processing have led to the emergence of fully integrated LiNbO3 electro-optic devices. Yet to date, LiNbO3 photonic integrated circuits have mostly been fabricated using non-standard etching techniques and partially etched waveguides, that lack the reproducibility achieved in silicon photonics. Widespread application of thin-film LiNbO3 requires a reliable solution with precise lithographic control. Here we demonstrate a heterogeneously integrated LiNbO3 photonic platform employing wafer-scale bonding of thin-film LiNbO3 to silicon nitride (Si3N4) photonic integrated circuits. The platform maintains the low propagation loss (<0.1 dB/cm) and efficient fiber-to-chip coupling (<2.5 dB per facet) of the Si3N4 waveguides and provides a link between passive Si3N4 circuits and electro-optic components with adiabatic mode converters experiencing insertion losses below 0.1 dB. Using this approach we demonstrate several key applications, thus providing a scalable, foundry-ready solution to complex LiNbO3 integrated photonic circuits.

Numerical method for designing ultrashort and efficient adiabatic mode converters

This paper proposes a fully numerical method for designing adiabatic mode converters (NM-AMCs). The proposed method can help compute efficient adiabatic guided-wave shapes for mode converters using a nonuniform section division technique. Such a scheme reduces the memory requirement and computational time for the design of adiabatic devices. Furthermore, the adiabatic mode converter comprises a ridge waveguide, which is difficult to design using analytical methods. This complex case of an adiabatic mode converter is used to demonstrate how the proposed method can readily generate a guided-wave shape that gives the same mode-connection power transfer with a far shorter length compared with a linear-shape converter. The efficiency of the device designed using this NM-AMC is significantly better than that of linear-shape converters; this designed adiabatic mode converter can enable a broad operating bandwidth. Moreover, the efficiency of the adiabatic mode converter that was designed using the NM-AMC method considerably exceeds that obtained using an analytical method proposed for a strip waveguide.

Adiabatic conversion between gigahertz quasi-Rayleigh and quasi-Love modes for phononic integrated circuits

Unsuspended phononic integrated circuits have been proposed for on-chip acoustic information processing. Limited by the operation mechanism of a conventional interdigital transducer, the excitation of the quasi-Love mode in GaN-on-sapphire is inefficient, and thus, a high-efficiency Rayleigh-to-Love mode converter is of great significance for future integrated phononic devices. Here, we propose a high-efficiency and robust phononic mode converter based on an adiabatic conversion mechanism. Utilizing the anisotropic elastic property of the substrate, the adiabatic mode converter is realized by a simple tapered phononic waveguide. A conversion efficiency exceeding 96% with a 3 dB bandwidth of 1.44 GHz can be realized for phononic waveguides working at GHz frequency band, and excellent tolerance to the fabrication errors is also numerically validated. The device that we proposed can be useful in both classical and quantum phononic information processing, and the adiabatic mechanism could be generalized to other phononic device designs.

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.

Orbital angular momentum mode generation system based on photonic lantern

We present an all-fiber-based method for generating orbital angular momentum (OAM) modes by using photonic lanterns in an adaptive-spatial mode control system. The device consists of a phase control part, a photonic lantern and a mode decomposition part. The use of photonic lanterns as adiabatic mode converters has been elaborated upon mathematically. To lock the desired OAM mode, the stochastic parallel gradient descent algorithm is used to control the phase modulators. The purities of the generated OAM modes with different topological charge are higher than 90% at 1550 nm, which has immediate utility for free-space propagation systems, and the superposition of different OAM modes at a specific ratio can be obtained to meet the requirements of mode multiplexing in optical fiber communication systems.

Highly efficient passive InP polarization rotator-splitter.

Monolithically integrated polarization beam splitters (PBSs) are needed to reduce the form-factor and assembly cost of optical coherent receivers. A highly efficient passive polarization rotator and splitter based on mode-evolution is demonstrated. The device is fabricated on InP substrate with a single etch-step and uses an adiabatic mode-converter and an asymmetric Y-coupler. Despite its simple fabrication process, the device shows a polarization extinction ratio (PER) better than 19 dB over 1520 nm to 1620 nm, thus covering both C- and L-band. The peak value of 24 dB is obtained for TE and TM polarizations. Its fabrication tolerance is large, so that even under a width variation of +/- 200 nm the PER remains above 17 dB over the entire C- and L-band.

Adiabatic mode converters for silicon photonics: Power and polarization broadband manipulators

Abstract

Photonic welding points for arbitrary on-chip optical interconnects

Abstract Photonic integrated circuits (PICs) are an ideal platform for chip-scale computation and communication. To date, the integration density remains an outstanding problem that limits the further development of PIC-based photonic networks. Achieving low-loss waveguide routing with arbitrary configuration is crucial for both classical and quantum photonic applications. To manipulate light flows on a chip, the conventional wisdom relies on waveguide bends of large bending radii and adiabatic mode converters to avoid insertion losses from radiation leakage and modal mismatch, respectively. However, those structures usually occupy large footprints and thus reduce the integration density. To overcome this difficulty, this work presents a fundamentally new approach to turn light flows arbitrarily within an ultracompact footprint. A type of “photonic welding points” joining two waveguides of an arbitrary intersecting angle has been proposed and experimentally demonstrated. These devices with a footprint of less than 4 μm2 can operate in the telecommunication band over a bandwidth of at least 140 nm with an insertion loss of less than 0.5 dB. Their fabrication is compatible with photonic foundry processes and does not introduce additional steps beyond those needed for the waveguides. Therefore, they are suitable for the mass production of PICs and will enhance the integration density to the next level.

Highly efficient mode converter for coupling light into wide slot photonic crystal waveguide.

We design, fabricate and experimentally demonstrate a highly efficient adiabatic mode converter for coupling light into a silicon slot waveguide with a slot width as large as 320 nm. This strip-to-slot mode converter is optimized to provide a measured insertion loss as low as 0.08 dB. Our mode converter provides 0.1 dB lower loss compared to a conventional V-shape mode converter. This mode converter is used to couple light into and out of a 320 nm slot photonic crystal waveguide, and it is experimentally shown to improve the coupling efficiency up to 3.5 dB compared to the V-shape mode converter, over the slow-light wavelength region.

Geometric requirements for photonic lanterns in space division multiplexing

We investigate the use of "photonic lanterns" as adiabatic mode converters for space-division multiplexing (SDM) systems to interface multiple single-mode fibers to a multi-mode fiber. In a SDM system, minimizing the coupling loss and mode-dependent loss best utilizes all spatial modes of the fiber which increases the capacity, the transmission distance, and minimizes the outage probability. We use modal analysis, the beam propagation method, and a transfer matrix technique to analyze the lanterns throughput along with its mode dependent loss and show that unitary coupling between single-mode fibers and a multi-mode fiber is only possible by optimizing the arrangements of the cores. Results include simulations for three, 12, 15, and 51 core lanterns to couple to six, 24, 30, and 102 spatial and polarization modes, respectively.