Wavelength Division Multiplexing Technology Research Articles

From Optical Fiber Communications to Bioimaging: Wavelength Division Multiplexing Technology for Simplified in vivo Large-depth NIR-IIb Fluorescence Confocal Microscopy.

Near-infrared II (NIR-II, 900-1880nm) fluorescence confocal microscopy offers high spatial resolution and extensive in vivo imaging capabilities. However, conventional confocal microscopy requires precise pinhole positioning, posing challenges due to the small size of the pinhole and invisible NIR-II fluorescence. To simplify this, a fiber optical wavelength division multiplexer (WDM) replaces dichroic mirrors and traditional pinholes for excitation and fluorescence beams, allowing NIR-IIb (1500-1700 nm) fluorescence and excitation light to be coupled into the same optical fiber. This streamlined system seamlessly integrates key components-excitation light, detector, and scanning microscopy-via optical fibers. Compared to traditional NIR-II confocal systems, the fiber optical WDM configuration offers simplicity and ease of adjustment. Notably, this simplified system successfully achieves optical sectioning imaging of mouse cerebral blood vessels up to 1000µm in depth. It can discern tiny blood vessels (diameter: 4.57µm) at 800µm depth with a signal-to-background ratio (SBR) of 5.34. Additionally, it clearly visualizes liver vessels, which are typically challenging to image, down to a depth of 300µm.

The KM3NeT Broadcast optical system network

The optical data transport system of the KM3NeT neutrino telescope at the bottom of the Mediterranean Sea will serve more than 6000 optical modules in the detector arrays with a point-to-point optical connection to the control stations onshore. The ARCA and ORCA detectors of KM3NeT are being installed at a depth of about 3500 m and 2500 m, respectively and their distance to the control stations is about 100 km and 40 km. The two detectors are optimised for the detection of cosmic neutrinos with energies above about 1 TeV (ARCA) and of atmospheric neutrinos with energies in the range 1 GeV– 1 TeV (ORCA). The expected maximum data rate is 200 Mbps per optical module. The implemented optical data transport system matches the layouts of the networks of electro-optical cables and junction boxes in the deep sea. For efficient use of the fibres in the system the technology of Dense Wavelength Division Multiplexing is applied. To comply with the scientific goals of KM3NeT, a time calibration of 1 ns between the many optical modules in the detector arrays is essential for the reconstruction of the neutrino events. For the first time in a deep sea neutrino telescope the White Rabbit protocol over Ethernet is used for the clock distribution. Downstream slow control and base module signals are broadcasted to all optical modules in the detector array. Synchronisation is achieved by communication between a White Rabbit master onshore and a White Rabbit slave unit inside the optical modules. In this contribution the KM3NeT broadcast optical data transport system is presented.

Routing and assignment of wavelengths for bicube in linear array WDM optical networks

Optical networks leverage the principles of optical communication to transmit data over long distances with high bandwidth and low signal loss. They have lots of applications supporting the backbone of modern communication systems. Wavelength division multiplexing (WDM) enables the simultaneous transmission of many signals with distinct wavelengths via one optical fiber, thereby increasing the overall capacity of the network. One of the significant aspects of designing and managing WDM optical networks involves routing and wavelength assignment (RWA), especially as the demand for high-capacity, low-latency communication continues to grow in recent times. Bicube networks possess many attractive properties, one of the salient features being low diameter as compared to a hypercube. Hence, research using bicube topology is very much prevalent in the last few years. In this paper, we use the technique of congestion to study the RWA problem for bicube in a linear array optical network that uses WDM technology. We also propose algorithms to efficiently compute the minimum number of wavelengths.

Real-time demonstration of 64 × 200 Gbps UDWDM-PON downstream transmission based on silicon photonic integrated transceiver

Coherent detection, high-order modulation, and dense wavelength division multiplexing (DWDM) technologies provide solutions for increasing bandwidth demand of future access networks. We experimentally demonstrate a real-time 64 × 200-Gb/s coherent ultra-dense wavelength-division (UDWDM) coherent passive optical networks (PONs) at 75-GHz channel spacing. The demonstrated downlink transmission is realized with the dual-polarization QPSK (DP-QPSK) modulation scheme. The cost is reduced by using silicon photonic integrated coherent transceiver modules and wider grid AWGs. The power budget is evaluated when all 200 channels are launched at C band. The power budget is 26 dB after 20-km G.652D standard single mode fiber (SSMF) transmission without amplifier at the receiver side under soft-decision FEC (SD-FEC) threshold of 1 × 10−2, and can achieve 32.5 dB with pre-amplified semiconductor optical amplifier (SOA) used at the receiver side.

A Sixteen‐user Time‐bin Entangled Quantum Communication Network With Fully Connected Topology

AbstractQuantum key distribution (QKD) promises unconditionally information‐theoretic secure communication guaranteed by the laws of physics and has become one of the most crucial candidates in future security aspects. Developing a large‐scale network with a scalable and integrated scheme is of great significance for expanding the advantages of QKD protocols among multiple users. Here, a sixteen‐user fully connected quantum network by using a novel time‐bin entangled source implemented in the integrated multi‐channel periodically poled lithium niobate waveguides is proposed. Based on this entangled source, the quantum processor prepares 120 entangled photon pairs to allocate 15 links to each user by utilizing dense wavelength division multiplexing technology. To enable the users’ communication with each other simultaneously, a phase‐compensated Mach‐Zehnder Interferometer based on a Fourier‐transform setup to control the relative phase of the interferometer for all the involved wavelength channels is developed. The experimental results show that the network can support sixteen users for long‐distance communication with each other simultaneously. The novel scheme of time‐bin entangled sources paves an efficient way for implementing large‐scale quantum resources in a compact integrated platform, and the time‐bin entangled network promises a new potential for constructing large‐scale and extensible quantum networks with an integrated photonic architecture.

Intensity noise reduction in quantum dot comb laser by lower external carrier fluctuations.

This work investigates the impact of carrier noise induced by an external current source on the linewidth enhancement factor (LEF) and relative intensity noise (RIN) of a 100 GHz quantum dot fourth-order colliding-pulse mode-locked laser (MLL), driven by a normal pump with Gaussian-distributed carrier sequences and a quiet pump with sub-Poissonian-distributed carrier sequences. The results indicate that under a normal pump, the LEFs are approximately zero for reverse saturable absorber (SA) bias voltages ranging from 0 to 2.5 V, and the laser achieves a RIN as low as -156 dB/Hz. When using a quiet pump, both the LEF and RIN are reduced across all SA bias conditions, particularly at low reverse SA bias voltages. Specifically, the LEF decreases by up to 0.58 at 0 V, and the average RIN spectrum is reduced by more than 3 dB at the same voltage. This work provides a straightforward approach for the development and optimization of multi-channel light sources for dense wavelength division multiplexing (DWDM) technologies with low optical noise.

Ultra-broadband similariton generation in a carbon disulfide core photonic crystal fiber for wavelength division multiplexing technology

Ultra-broadband similariton generation in a carbon disulfide core photonic crystal fiber for wavelength division multiplexing technology

Mode-pairing quantum key distribution based on wavelength division multiplexing in multi-user networks

Mode-pairing quantum key distribution (MP-QKD), a protocol that combines high performance and flexibility, not only eliminates the need for global phase locking but also beats the rate-transmittance bound. Such remarkable characteristics are poised to further advance the practical application of quantum communication networks. In this paper, MP-QKD is extended to the scenario of multi-user communication networks. MP-QKD enables concurrent operation across multiple channels by integrating wavelength division multiplexing (WDM) technology, facilitating secure communication among multiple users. The performance of MP-QKD in multi-channel concurrent operation is analyzed through simulating various experimental conditions. The asymmetric MP-QKD case is also considered and pulse intensity optimization improves performance for asymmetric network channels. These results delineate the performance of MP-QKD with WDM technology, highlighting its significant potential for application in quantum communication networks.

Theoretical design of a single-mode fiber-based bi-order Bessel beam for a STED system.

Stimulated emission depletion (STED) microscopy has attracted great research attention due to its applications to breaking diffraction limits for imaging and lithography. However, its implementation based on single-mode fibers often encounters challenges such as complex structural integration, costly fabrication processes, and the need for specific fiber designs. Herein, a low-cost bi-order Bessel beam based on one single-mode fiber integrated with a structurally simple wavelength-scale microstructure (WSM) on fiber end was proposed for STED system. Through simulation study for full-scale WSM optimization, we have successfully developed a bicolor laser beam (BLB) consisting of a zero-order Bessel beam at a wavelength of 405 nm and a donuts high-order Bessel beam at a wavelength of 532 nm. This fiber-based configuration allows us to achieve a diffraction-limited spot size with a working distance of 0.67λpump and a minimum FWHM of 0.395λpump. By combining wavelength division multiplexing technology with power modulation of the donuts beam, this work provides a promising way for achieving super-resolution imaging or lithography with only one single-mode fiber.

Silicon‐photonic four‐mode triple‐band multiplexing device for hybrid wavelength/mode division multiplexing networks

SummaryWhile wavelength division multiplexing (WDM) technology combines several wavelengths onto a single waveguide, the technology of mode division multiplexing (MDM) allows many orthogonal modes of the same wavelength to operate simultaneously without interchannel crosstalk. Thus, the hybrid WDM and MDM network in which the two above‐mentioned techniques cooperate could give a several‐fold increase in the overall network capacity. Constructing this network requires hybrid wavelength‐and‐mode multiplexers, especially ones with high integration and complementary metal‐oxide‐semiconductor (CMOS) compatibility. In this paper, we propose a design of a four‐mode triple‐band multiplexer that is capable of multiplexing up to 12 separate optical signal flows by utilizing four eigenmodes (TE0, TE1, TE2, and TE3) and three‐wavelength windows, which center at 1310, 1490, and 1550 nm. The device is on silicon‐on‐insulator (SOI) platform, consisting of four butterfly‐shaped multimode interference (MMI) couplers, four directional couplers, and a cascaded asymmetric Y‐junction coupler. Via numerical simulations, the proposed design is verified to be able to operate effectively on the three aforementioned bandwidth slots with an optical conversion efficiency of over 93% in all functions. Moreover, it exhibits insertion loss less than 1.5 dB and crosstalk smaller than −16 dB within 25 nm bandwidth at each wavelength window. These results can affirm the success of wavelength–mode combination, which leads to a massive improve in the channel capacity on the same optical multiplexing system for optical telecommunications and photonics on‐chip interconnections.

Turbidity-tolerant underwater wireless optical communications using dense blue–green wavelength division multiplexing

Underwater wireless optical communication (UWOC) has demonstrated high-speed and low-latency properties in clear and coastal ocean water because of the relatively low attenuation ‘window’ for blue–green wavelengths from 450 nm to 550 nm. However, there are different attenuation coefficients for transmission in ocean water at different wavelengths, and the light transmission more seriously deteriorates with fluctuations in the water turbidity. Therefore, traditional UWOC using a single wavelength or coarse blue–green wavelengths has difficulty tolerating variations in water turbidity. Dense wavelength division multiplexing (WDM) technology provides sufficient communication channels with a narrow wavelength spacing and minimal channel crosstalk. Here, we improve the UWOC in clear and coastal ocean water using dense blue–green WDM. A cost-effective WDM emitter is proposed with directly modulated blue–green laser diodes. Dense wavelength beam combination and collimation are demonstrated in a 20-metre underwater channel from 490 nm to 520 nm. Demultiplexing with a minimum channel spacing of 2 nm is realized by an optical grating. Remarkably, our WDM results demonstrate an aggregate data rate exceeding 10 Gbit/s under diverse water turbidity conditions, with negligible crosstalk observed for each channel. This is the densest WDM implementation with a record channel spacing of 2 nm and the highest channel count for underwater blue–green light communications, providing turbidity-tolerant signal transmission in clear and coastal ocean water.

Parallel wavelength-division-multiplexed signal transmission and dispersion compensation enabled by soliton microcombs and microrings

The proliferation of computation-intensive technologies has led to a significant rise in the number of datacenters, posing challenges for high-speed and power-efficient datacenter interconnects (DCIs). Although inter-DCIs based on intensity modulation and direct detection (IM-DD) along with wavelength-division multiplexing technologies exhibit power-efficient and large-capacity properties, the requirement of multiple laser sources leads to high costs and limited scalability, and the chromatic dispersion (CD) restricts the transmission length of optical signals. Here we propose a scalable on-chip parallel IM-DD data transmission system enabled by a single-soliton Kerr microcomb and a reconfigurable microring resonator-based CD compensator. We experimentally demonstrate an aggregate line rate of 1.68 Tbit/s over a 20-km-long SMF. The extrapolated energy consumption for CD compensation of 40-km-SMFs is ~0.3 pJ/bit, which is calculated as being around 6 times less than that of the commercial 400G-ZR coherent transceivers. Our approach holds significant promise for achieving data rates exceeding 10 terabits.

Energy-efficient regeneration routing in satellite optical networks under translucent optical payload architectures.

The translucent optical payload architecture is most economical and feasible for optical switching in the satellite optical network (SON) using laser inter-satellite links (LISLs), where the wavelength division multiplexing (WDM) technology enables lightpaths to transparently pass through relay satellites, minimizing on-board processing. For the long-distance lightpath in SONs, lightpath regeneration is necessary to ensure the acceptable quality of transmission (QoT), where optical-electrical-optical (OEO) conversion causes non-negligible energy consumption. The rechargeable battery is an important component for low-earth-orbit (LEO) satellites, and unrestrained use batteries at a deep depth of discharge (DOD) will accelerate battery aging and shorten satellite lifetime, causing extremely high expenditure costs. How to improve energy efficiency in lightpath regeneration is a key problem in SONs, which has no related studies. This paper proposes energy-efficient regeneration routing (EE-RR) in SONs under translucent optical payload architectures, which is to reduce the battery life consumption of lightpath regeneration. We define the maximum bypass hops (MBH) to ensure the bit error rate (BER) requirement of lightpaths in SONs, considering the noise accumulation of amplifier spontaneous emission (ASE) and Doppler shift (DS) crosstalk. Two greedy baselines are proposed for EE-RR, which are the regeneration routing scheme minimizing the number of regeneration nodes (RRS-MRN) and the regeneration routing scheme minimizing single satellite's battery life consumption (RRS-MBL), respectively. Based on two greedy baselines, the regeneration routing scheme using genetic algorithms (RRSGA) is developed to improve the optimization ability of EE-RR. To our knowledge, this is the first study to propose taking battery aging into account in lightpath regeneration in SONs. Through numerical simulation, we find that blindly reducing the number of regeneration nodes in lightpaths may not reduce overall battery life consumption, and RRSGA can effectively reduce battery life consumption of lightpath regeneration in SONs.

Data Center Four-Channel Multimode Interference Multiplexer Using Silicon Nitride Technology.

The operation of a four-channel multiplexer, utilizing multimode interference (MMI) wavelength division multiplexing (WDM) technology, can be designed through the cascading of MMI couplers or by employing angled MMI couplers. However, conventional designs often occupy a larger footprint, spanning a few millimeters, thereby escalating the energy power requirements for the photonic chip. In response to this challenge, we propose an innovative design for a four-channel silicon nitride (Si3N4) MMI coupler with a compact footprint. This design utilizes only a single MMI coupler unit, operating within the O-band spectrum. The resulting multiplexer device can efficiently transmit four channels with a wavelength spacing of 20 nm, covering the O-band spectrum from 1270 to 1330 nm, after a short light propagation of 22.8 µm. Notably, the multiplexer achieves a power efficiency of 70% from the total input energy derived from the four O-band signals. Power losses range from 1.24 to 1.67 dB, and the MMI coupler length and width exhibit a favorable tolerance range. Leveraging Si3N4 material and waveguide inputs and output tapers minimizes light reflection from the MMI coupler at the input channels. Consequently, this Si3N4-based MMI multiplexer proves suitable for deployment in O-band transceiver data centers employing WDM methodology. Its implementation offers the potential for higher data bitrates while maintaining an exemplary energy consumption profile for the chip footprint.

The application of optical fiber in network communication

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.

113Gbps rainbow visible light laser communication system based on 10λ laser WDM emitting module in fiber-free space-fiber link.

With the advent of the sixth-generation mobile communication standard (6 G), the visible light communication (VLC) technology based on wavelength division multiplexing (WDM) technology can effectively solve the problem of shortage of spectrum resources and insufficient channel capacity. This paper introduces one of our technical achievements, namely the construction of a near-real-time visible light laser communication (VLLC) system based on WDM, which includes a self-designed 10-λ fully-packaged visible light laser emission module, 1 m multimode fiber - 0.175 m free space - 1 m multimode fiber optical transmission link, and receiver array. In the transmitter system, we adopt adaptive discrete multitone (DMT) modulation technique combined with Quadrature Amplitude Modulation (QAM) modulation scheme to obtain maximum spectral efficiency (SE). In the receiving system, we utilize the sparse-structured reservoir computing post-equalization algorithm to achieve superior equalization performance on the basis of the traditional post-equalization algorithm. The experimental results indicate that this quasi-real-time communication system has achieved a signal transmission rate of 113.175Gbps. To the best of our knowledge, this work has set a record in the field of high-speed visible light laser communication. Therefore, the laser communication system constructed by this work, with its flexibility in deployment and high-speed performance, demonstrates the significant potential application of visible light laser communication in data center interconnection and high-speed indoor access networks.

Theoretical and experimental study on stable oscillation of dual-frequency signals in an optoelectronic oscillator.

Due to the gain competition effect, it is hard to simultaneously maintain oscillation at two frequencies in an optoelectronic oscillator (OEO) loop. In this paper, a study of the gain competition effect in a dual-frequency OEO is theoretically and experimentally demonstrated. The steady-state conditions in the dual-frequency OEO are theoretically analyzed by deriving dynamic equations. A nonlinear time-varying model, as well as its calculation methods, is carried out to design and study the dynamic process of the dual-frequency OEO. Thanks to this model, the waveform, spectrum, and amplitude evaluation of generated signals, as well as the gain variation in the OEO loop, are numerically simulated. Based on the theoretical analysis and numerical simulation results, three schemes that can suppress the gain competition effect are proposed, and the one based on wavelength division multiplexing (WDM) technology is experimentally realized. The experimental results show that the novel independently tunable dual-frequency OEO, to the best of our knowledge, can generate two-tone RF signals in a range from 1.8 to 18.6 and 1.5 to 18.3GHz, respectively.

Flow and heat transfer characteristics of high-pressure natural gas in the air gap of high-speed motor

High speed motors are widely used in industrial applications owing to their unique features, such as compact framework, high performance, and high reliability. Based on the finite volume method and numerical heat transfer theory, this study establishes a stator-air gap-rotor model, and the flow and heat transfer in the air gap between the stator and rotor in a high speed motor are investigated with high pressure natural gas as the cooling medium. Meanwhile, the ?radial tri-vortex partition, alternating axial distribution? feature of the turbulent Taylor-Couette vortex in the air gap of the motor is determined. Then, the optimal structural parameters which can realize the heat transfer enhancement of motor air gap are obtained. Finally, an optical fiber grating temperature measurement system based on the wavelength division multiplexing technology is utilized to attain the temperature distributions on the stator and rotor surfaces. The simulation results are compared with the experimental data to evaluate the simulation method?s precision.

High-speed data transmission based on mode-locked optical frequency comb

<sec>With the rapid development of emerging technologies such as multimedia services, live broadcasting, video conferencing, and high-definition television, traditional radio frequency communication is unable to meet people 's growing demand for communication capacity and transmission rate. In recent years, optical communication has received extensive attention from the industrial and scientific communities due to its advantages of large bandwidth, high speed, low power consumption, light weight, and strong anti-interference ability. As an emerging light source, the optical frequency comb (OFC) has a wide spectral range, multi-wavelength, high stability, and good phase coherence, providing a new idea for studying microwave signals with simple system structure, strong tunability and high frequency stability. At the same time, the multi-optical mode characteristics of OFC are compatible with the current communication system based on wavelength division multiplexing technology. Hundreds of laser arrays in a traditional communication system can be replaced by only one laser, which greatly reduces the power consumption of the system.</sec><sec>Combining the above advantages, in this paper, a large-scale parallel high-speed optical communication system based on mode-locked OFC is proposed. The linewidth of the OFC locked to the rubidium atomic clock can reach 1 Hz, which is sufficient to support the transmission of high-order modulation signals. The electro-optic modulators are used to adjust the amplitude and phase of each optical mode of the mode-locked OFC and self-coherently map to the RF domain. The high-speed high-order modulation signal with coded information is obtained by frequency screening through a narrow-band filter. The communication capability of the microwave photonic modulation signal in the 16 quadrature amplitude modulation (QAM) format is verified by simulation. The 16QAM communication with the rate of 2, 6, and 14 Gbit/s is realized by using the photonic microwave signal on the 100 m space optical link, and the bit error rate (BER) is less than 10<sup>–6</sup>. The proposed large-scale parallel optical communication system based on mode-locked OFC can achieve high-speed information transmission with a compact system structure, which is suitable for inter-satellite communication, emergency communication, military communication and other fields.</sec>

WDM C-band four channel demultiplexer using cascaded multimode interference on SiN strip waveguide structure

Back reflection challenges significantly constrain the efficiency of optical communication networks employing dense wavelength division multiplexing (DWDM) technology, particularly those based on Silicon (Si) Multimode Interference (MMI) waveguides. To mitigate this limitation, we present a novel 1×4 optical demultiplexer design using MMI within a Silicon-Nitride (SiN) strip waveguide configuration, operating within the C-band spectrum. Our design was optimized using AI-enhanced RSoft-CAD simulations that combined the Beam Propagation Method (BPM) and Finite-Difference Time-Domain (FDTD) techniques, integrated with convolutional neural network (CNN) machine learning algorithms. The simulation results demonstrate that the proposed device efficiently transmits four channels with 10 nm spacing in the C-band, showing low power loss ranging from 1.98-2.35 dB, a broad bandwidth of 7.68-8.08 nm, and excellent crosstalk suppression between 20.8-23.4 dB. Leveraging the low refractive index of SiN, we achieve ultra-low back reflection of 40.58 dB without requiring specialized angled MMI designs, which are often necessary in Si-based MMI technology. Consequently, this SiN-based MMI demultiplexer provides an effective solution for DWDM systems, enabling high data transmission rates with minimal back reflection in optical communication networks.