All-fiber polarization beam splitting and rotating based on vector-mode-assisted coupling.

Special issue “optical communications, sensing, and laser applications”

Brillouin scattering in microresonators has emerged as the driving process for developing high-coherence lasers for applications such as coherent optical communications, optical atomic clocks, microcomb solitons, and quantum communications. However, most of the demonstrations of microresonator Brillouin lasers have been limited to a 1550 nm wavelength regime, which benefits from the development of low-loss microresonator devices on different material platforms and the availability of tunable pump lasers. The development of wide bandwidth thulium-doped fiber amplifiers and low two-photon absorption in silicon around 2µm makes this wavelength region a potential candidate for applications in future optical communications, gravitation wave sensing, and atmospheric sensing. All these applications will benefit from the development of Brillouin lasers. However, there has not been much progress on microresonator-based 2µm Brillouin lasers. Here, we present a demonstration of a 2µm microresonator Brillouin laser. We use whispering gallery mode resonances in a ∼330µm silica microsphere to demonstrate a Brillouin lasing threshold of 35 mW. We achieve generation of second- and third-order Brillouin Stokes using pump powers of ∼60mW and 104 mW, respectively. By tuning the pump laser wavelength, we demonstrate high-resolution (∼10 pm) tuning of the Brillouin laser. From the beat signal of the first- and third-order Brillouin Stokes, we estimate a Brillouin laser linewidth of ∼135kHz, which is 15 times smaller than the pump linewidth. This work may find applications in optical communications, soliton combs, and atmospheric sensing in the 2µm wavelength region. Published by the American Physical Society 2024

Coupling analysis of non-circular-symmetric modes and design of orientation-insensitive few-mode fiber couplers

Thin films play an important role in modern science and technology. With the development of optical fibre communication technology and laser technology, thin films are used more and more widely in this field. The application of optical film in optical communication and laser technology is introduced systematically. The application of optical films in optical communications basically covers a variety of conventional optical films. Based on this research background, the paper mainly analyses the optical and physical properties of zinc oxide nano-films and discusses its application in optical communication.

This study explores the extended (3+1)-dimensional cubic and quartic conformable nonlinear Schrödinger equation, which is characterized by two distinct forms of nonlocal nonlinearities and has applications in optical fibre communications. Using the Kudryashov auxiliary equation approach and the simplest equation technique, a variety of innovative optical soliton solutions have been developed. The relevance and distinct features of these solutions are highlighted through visual representations such as contour diagrams, three-dimensional models, and two-dimensional plots. The effects of the fractional order and temporal parameter are investigated in detail, providing a deeper understanding of the conformable nonlinear Schrödinger equation's dynamics. Such models have significant applications in optical fibre communications, where solitons serve as stable carriers for high-speed data transmission over long distances with minimal distortion. The algorithms developed herein are applicable to other classes of nonlinear Schrödinger equations, making them valuable tools in nonlinear optics and applied mathematics.

In recent years, optical fiber communication has gained widespread use in daily life due to its robust communication and transmission capabilities, strong confidentiality, anti-interference properties, and the availability of convenient and accessible materials. This technology has made remarkable strides in network communication and integrated device design, among other areas. This article will commence by discussing the fundamental structure of optical fibers and illustrating the propagation of optical signals within them. It will then analyze the benefits, such as higher transmission rates, wider frequency bands, and the low loss characteristics of optical fibers. Subsequently, the article will enumerate two of the most commonly utilized Optical Fiber Communication (OFC) technologies: Wavelength Division Multiplexing (WDM) technology and optical amplifier technology. It will summarize their principles and strengths. Finally, the article will showcase the practical applications of optical fiber communication, particularly focusing on its role in 5G mobile communication, military operations, and radio and television communication.

Relaxed-tolerance subwavelength grating coupler

As the Internet of Things (IoT) develops, applying machine learning on optical communications has become a prospective field of research. Scholars have mostly concentrated on algorithmic techniques or specific applications but have been unable to address the distribution of machine-learning technologies and the development of its applications in optical communications from a macro perspective. Therefore, in this paper, machine-learning patents in optical communications are taken as the analytical basis for constructing a patent technology network. The study results revealed that key technologies were primarily in data input and output devices, data-processing methods, wireless communication networks, and the transmission of digital information in optical communications. Such technologies were also applied to perform measurement for diagnostic purposes and medical diagnoses. The technology network model proposed in this paper explores the technological development trends of machine learning in optical communications and serves as a reference for allocating research and development resources.

An optical vortex having an isolated point singularity is associated with the spatial structure of light waves. A polarization vortex (vector beam) with a polarization singularity has spatially variant polarizations. A phase vortex with phase singularity or screw dislocation has a spiral phase front. The optical vortex has recently gained increasing interest in optical trapping, optical tweezers, laser machining, microscopy, quantum information processing, and optical communications. In this paper, we review recent advances in optical communications using optical vortices. First, basic concepts of polarization/phase vortex modulation and multiplexing in communications and key techniques of polarization/phase vortex generation and (de)multiplexing are introduced. Second, free-space and fiber optical communications using optical vortex modulation and optical vortex multiplexing are presented. Finally, key challenges and perspectives of optical communications using optical vortices are discussed. It is expected that optical vortices exploiting the space physical dimension of light waves might find more interesting applications in optical communications and interconnects.

Multimode nonlinear dynamics in spatiotemporal mode-locked (STML) fiber lasers enable exploration of what we believe to be novel solitary waves. However, complex intermodal coupling in multimode fibers prevents precise control over the output parameters of multimode solitons (e.g., mode component and center wavelength), limiting their applications in fiber amplifiers and optical communications. Additionally, vector soliton dynamics have been overlooked due to polarization-dependent saturable absorbers (SAs) in prior STML systems, many unique nonlinear dynamics remain inadequately explained. This work presents a method to customize the output parameters of STML pulses by a spatial alignment structure (SAS). This polarization-independent SAS functions as an SA, spatial filter, and attenuator. Adjusting the SAS enables controllable multimode soliton characteristics and diverse STML dynamics, including soliton rain, tri-color solitons (TCS), and ultra-broad bandwidth spectrum (UBS) pulses (28 nm bandwidth, 94 fs duration) within the same cavity. Experimental results reveal the critical role of vector soliton dynamics in generating parametric sidebands and various STML pulses. This work demonstrates, to our knowledge, the first multimode vector conventional solitons and achieves the broadest bandwidth/shortest pulse duration in 1.5 μm STML lasers. Further research into multifunctional SAS and multimode vector soliton dynamics may uncover what are believed to be new spatiotemporal nonlinear effects, enabling compact, cost-effective STML fiber lasers with on-demand outputs.

Due to the advancement of technology, laser communication, fiber optic communication and optical quantum communication have been developed, not only in the field of life, but also in the field of aviation, military and information security. This paper, mainly compares the difference between optical quantum communication and other communication technologies in terms of security and effectiveness, presenting the current state of technology and applications and providing an outlook on future directions. Through the comparison, this paper argues that the application of technology in optical quantum communication can promote the rapid development of quantum communication technology and thus enhance the comprehensive strength of global communication technology.

Hollow fiber has become a research hotspot in the field of special fibers for its excellent characteristics, such as low loss, low delay, low dispersion, and low nonlinear coefficient. Due to the lack of fiber coupler matching hollow core fiber, the application development of hollow core fiber in the all-fiber integrated system is greatly hindered. Dual-core fiber is widely used in the development of fiber couplers because it can choose optical power, wavelength, and polarization state by the coupling between the two cores. For the urgent need for hollow core fiber coupler, the design and research of wideband fiber coupler based on dual-hollow core fiber are carried out in this paper. Based on the coupled mode theory, the theoretical correlation between the structural parameters and the coupling length in the dual-hollow core anti-resonant fiber was analyzed by using the COMSOL simulation software system. On this basis, a 50:50 wideband fiber coupler was designed by adjusting the structural parameters to reduce the coupling length and introducing the sleeve into the cladding pipe to reduce the loss. The bandwidth of the coupler is up to 150 nm and the transmission loss is on the order of 10−2 dB/m.

The vigorous development of network technology promotes the progress of communication transmission technology, and the progress of communication transmission technology also drives the development of network technology. Optical fiber communication technology is widely used in communication industry because of its strong anti-interference ability, fast transmission speed and large amount of information. With the explosive growth of network data traffic in recent years, the transmission capacity of optical fiber communication has been continuously improved, coherent optical communication technology has developed rapidly, the trend of intelligence, grouping and broadband has become more and more obvious, and new photoelectric devices have been continuously developed and used. Optical fiber communication technology is undergoing tremendous changes and will become more important. In this paper, the application of optical fiber communication transmission technology is discussed in detail, and an adaptive reverse design method of integrated optical fiber communication system is proposed in order to promote the rapid development of optical fiber communication transmission technology.

Standard optical fiber communication systems employ intensity-modulation/direct-detection schemes. This is noise-carrier communication and in a sense is more primitive than the radio engineering in Marconi’s age. However, it has the practical advantage of system simplicity and low cost. On the other hand, some applications of optical fiber communication exist in which a long repeater separation is the primary concern; an example is submarine optical cable communication between islands, in this case, the improvement of the bit-error rate (BER) by a coherent modulation/demodulation scheme such as PCM-PSK or PCM-FSK may be advantageous even at the sacrifice of simplicity and low cost.

This chapter is devoted to advanced modulation and multiplexing techniques suitable for both wireless and optical communication systems. The chapter starts with signal space theory concepts applied to wireless communication systems. After the geometric representations of signals, we describe various multidimensional modulators and demodulators suitable for wireless communication applications, in particular the Euclidean distance, correlation, and matched filter-based detectors, followed by the description of frequency-shift keying (FSK). Both continuous-time (CT) and discrete-time (DT) implementations for pulse amplitude modulation schemes, suitable for wireless communications, are described as well. After that the focus is moved to multilevel schemes suitable for both wireless and optical communication applications, including M-ary PSK, star-QAM, square-QAM, and cross-QAM. Regarding the optical communications, the transmitter for M-ary PSK, star-QAM, and square/cross-QAM is described in detail. The next topic in the chapter is related to multicarrier modulation, including description multicarrier systems with both nonoverlapping and overlapping subcarriers as well as introduction of various approaches to deal with fading effects at subcarrier level. The concept of OFDM is also introduced; however, details are provided in Chap. 7. The MIMO fundamentals are then provided, including the description of key differences with respect to diversity scheme, as well as the introduction of array, diversity, and multiplexing gains. The parallel MIMO channel decomposition is briefly described. The details on MIMO signal processing are postponed for Chap. 8. In section on polarization-division multiplexing (PDM) and four-dimensional (4-D) signaling, we describe key differences between PDM and 4-D signaling and describe how both types of schemes can be implemented in both wireless and optical communications. The focused is the moved to the spatial-division multiplexing (SDM) and multidimensional signaling. We describe how SDM can be applied in wireless communications first. Then we describe how various degrees of freedom including amplitude, phase, frequency, polarization states, and spatial modes can be used to convey the information in optical domain. In the same sections, the SDM concepts for fiber-optics communications are described as well. The section concludes with SDM and multidimensional signaling concepts applied to free-space optical (FSO) communications. The next topic is devoted to the signal constellation design, including iterative polar modulation (IPM), signal constellation design for circular symmetric optical channels, energy-efficient signal constellation design, and optimum signal constellation design (OSCD). The final section of the chapter is devoted to the nonuniform signaling, in which different signal constellation points are transmitted with different probabilities.