Multimode Optical Transmission Research Articles

Compact mode converters in thin-film lithium niobate integrated platforms.

Mode converters, crucial elements within photonic integrated circuits (PICs) designed for multimode optical transmission and switching systems, present a challenge due to their bulky structures in thin-film lithium niobate (TFLN) integrated platforms, which are incompatible with the compact and efficient nature desired for dense PICs. In this work, we propose TE1-TE0, TE2-TE0, and TE3-TE0 mode converters in shallowly etched TFLN, within small footprints. The experimental results show that the insertion loss is 0.4 dB, 0.6 dB, and 0.5 dB for the compact TE1-TE0, TE2-TE0, and TE3-TE0 mode converters, respectively, and these devices can be operated within a wide 1 dB bandwidth (BW) over 100 nm. This work facilitates the development of low-loss, broadband, and compact monolithically integrated photonic devices for future multimode communication networks in TFLN integrated platforms.

Multi-dimensional data transmission using inverse-designed silicon photonics and microcombs

The use of optical interconnects has burgeoned as a promising technology that can address the limits of data transfer for future high-performance silicon chips. Recent pushes to enhance optical communication have focused on developing wavelength-division multiplexing technology, and new dimensions of data transfer will be paramount to fulfill the ever-growing need for speed. Here we demonstrate an integrated multi-dimensional communication scheme that combines wavelength- and mode- multiplexing on a silicon photonic circuit. Using foundry-compatible photonic inverse design and spectrally flattened microcombs, we demonstrate a 1.12-Tb/s natively error-free data transmission throughout a silicon nanophotonic waveguide. Furthermore, we implement inverse-designed surface-normal couplers to enable multimode optical transmission between separate silicon chips throughout a multimode-matched fibre. All the inverse-designed devices comply with the process design rules for standard silicon photonic foundries. Our approach is inherently scalable to a multiplicative enhancement over the state of the art silicon photonic transmitters.

A compact silicon-based TM0-to-TM2 mode-order converter using shallowly-etched slots

Mode-order converter is a pivotal component in the on-chip multimode optical transmissions with different mode orders. In this work, we propose a compact and highly-efficient TM0-to-TM2 mode-order converter using shallowly-etched rectangular slots on the silicon-on-insulator platform. The proposed device consists of four same shallowly-etched slots in symmetrical arrangements (two by two) along the light propagation direction and a smaller one between them, which can change the refractive index distribution of the silicon waveguide and add accumulated phase difference through light propagation. With detailed optimizations, we realize the efficient mode conversion from input TM0 mode to output TM2 mode, which is different from some reported TE-polarized mode-order converters, and the insertion loss and conversion efficiency of the present device are 0.21 dB and 94.3%, respectively, in a total device length of only 8.97 μm. Meanwhile, the modal crosstalk is lower than −15 dB and the bandwidth can be extended to ∼100 nm. We believe this device could be applied in the on-chip multimode optical transmission systems with different mode orders to further improve the link capacity.

Ultra-compact dual-polarization silicon mode-order converter.

The mode-order converter is a building block in a multimode optical transmission and switching system. It can be used for switching signals carried on different mode channels. However, such devices constructed by conventional structures can commonly accomplish one mode-order conversion process. It is because the phase-matching condition, which is utilized by a majority of designs, can usually be fulfilled between only one mode pair for specific device geometry. In this Letter, we propose a dual-polarization mode-order converter referring to the concept of a silicon planar metasurface. It can realize mode-order conversions on transverse electrical and transverse magnetic polarizations in parallel. In order to verify our concept, we design and experimentally demonstrate a prototype that can realize conversions from TE0 to TE1 and from TM0 to TM1 simultaneously. The footprint is 4 μm×1.6 μm. The measured insertion losses for both polarizations are smaller than 2.3dB, and the crosstalk is lower than -11.5 dB within the wavelength range of 1525-1565nm. We envision that the device can be a building block in polarization and mode multiplexed optical switching systems and endow the systems with simpler structure and a more compact footprint.

Planar microoptical multiplexer and demultiplexer for multimode optical transmission lines

A matching pair of 10-channel planar grating multiplexer/demultiplexer has been numerically analysed and fabricated. Basic construction elements are a planar slab waveguide with a cylindrical mirror facet, a standard plane blazed reflection grating and an array of input/output fibres. The arrangement has proved to work sufficiently well without special measures to reduce aberration such as inclining the input/output facet. The ray tracing method satisfactorily describes the characteristics of the devices. Measured insertion losses range from 2.2 to 7.8 dB, full 1-dB passband widths are 14 nm for the demultiplexer and 25 nm for the multiplexer.

Optical Transmission System

The present invention has been achieved to provide a novel optical transmission system realizing high-speed optical transmission over greater distance by suppressing waveform degradation caused by mode dispersion and mode transition in a multimode optical transmission line. The optical transmission system of the present invention includes: an optical transmitter for transmitting incoherent light; an excitation mechanism for exciting a predetermined mode in the incoherent light transmitted from the optical transmitter; a multimode optical transmission line for transmitting the incoherent light transmitted from the excitation mechanism; a transmission mechanism for transmitting a predetermined mode in the incoherent light transmitted from the excitation mechanism; and an optical receiver for receiving the incoherent light transmitted from the transmission mechanism or the incoherent light transmitted from the transmission mechanism.

Slab waveguide demultiplexer for multimode optical transmission in the 10–14-μm wavelength region

Slab waveguide demultiplexer for multimode optical transmission in the 10–14-μm wavelength region