3 × 40 Gbit/s All-Optical Logic Operation Based on Low-Loss Triple-Mode Silicon Waveguide

Information capacity of single-mode fiber communication systems face fundamental limitations imposed by optical nonlinearities. Spatial division multiplexing (SDM) offers a new dimension for upgrading fiber communication systems. Many enabling integrated devices, such as mode multiplexers and multimode bending with low crosstalk, have been developed. On the other hand, all-optical signal processing (AOSP) can avoid optical to electrical to optical (O–E–O) conversion, which may potentially allow for a low cost and green operation for large-scale signal processing applications. In this paper, we show that the system performance of AOSP can be pushed further by benefiting from the existing technologies developed in spatial mode multiplexing (SDM). By identifying key technologies to balance the impacts from mode-dependent loss, crosstalk and nonlinearities, three-channel 40 Gbit/s optical logic operations are demonstrated using the first three spatial modes in a single multimode waveguide. The fabricated device has a broadband four-wave mixing operation bandwidth (>20 nm) as well as high conversion efficiency (>−20 dB) for all spatial modes, showing the potential for a large-scale signal processing capacity with the combination of wavelength division multiplexing (WDM) and SDM in the future.

Polarization Splitter-Rotator Based on Multimode Waveguide Grating

We demonstrate a polarization splitter rotator (PSR) based on multimode waveguide grating (MWG) on a silicon-on-insulator (SOI) platform. Bloch mode hybridization in mini-stopband is exploited to achieve high polarization conversion efficiency. The fabricated device yields a high extinction ratio of > 53 dB and > 31 dB, low crosstalk of < −26.4 dB and < −40 dB for the injected TE0 and TM0 mode, with average insertion loss of 1.2 dB and 1.5 dB in the wavelength regime 1552 nm–1562 nm. Such a device shows great design flexibility and an easy fabrication process, serving as a good candidate in integrated polarization diversity circuits, especially for applications requiring spectra manipulation. Additionally, the polarization conversion approach provides opportunities to develop novel polarization management devices.

Reflection of waves from a mobile elastic layer in a multimode waveguide

Waveguide structures are used to transmit energy and information signals in a wide range of wavelengths and, in terms of wave-guiding physical properties, usually have mutual (identical) properties in forward and backward directions. The asymmetry of the structure and external influences can often cause non-reciprocity of structures for waves, propagating in mutually opposite directions (this property, although limited, is already used in the so-called nonreciprocal devices of microwave, EHF and optical ranges such as ferrite valves, circulators, phase shifters). At the same time, the nonreciprocal properties of wave-guiding structures, independent of their physical nature, were not considered. It is found, that the motion of the medium filling the acoustic waveguide leads to nonreciprocity of its parameters in the forward and backward directions. The degree of nonreciprocity is proportional to the velocity of the medium. The velocity of the medium also affects the propagation velocity of acoustic waves and leads to a change in the critical frequencies or critical wavelengths of the waveguide modes. As the velocity of the medium increases, the number of modes for which the propagation condition is satisfied increases as well.

An Optimized Approach to Channel Modeling and Impact of Deteriorating Factors on Wireless Communication in Underground Mines

The environment of underground coal mines has challenging properties that makes this zone inadaptable for a stable communication system. Additionally, various deteriorating physical parameters strongly affect the performance of wireless networks, which leads to limited network coverage and poor quality of data communication. This study investigates the communication capability in underground coal mines by optimizing the wireless link to develop a stable network for an underground hazardous environment. A hybrid channel-modeling scheme is proposed to characterize the environment of underground mines for wireless communication by classifying the area of a mine into the main gallery and sub-galleries. The complex segments of mine are evaluated by categorizing the wireless links for the line-of-sight (LOS) zones and hybrid modeling is employed to examine the characteristics of electromagnetic signal propagation. For hybrid channel modeling, the multimode waveguide model and geometrical optic (GO) model are used for developing an optimal framework that improves the accessibility of the network in the critical time-varying environment of mines. Moreover, the influence of various deteriorating factors is analyzed using 2.4 GHz to 5 GHz frequency band to study its relationship with the vital constraints of an underground mine. The critical factors such as path loss, roughness loss, delay spread, and shadow fading are examined under detailed analysis with variation in link structure for the mine.