Modal Bandwidth Research Articles

Wavelength Dependence of Modal Bandwidth of Multimode Fibers for High Data Rate Transmission and Its Implications

Vertical-cavity surface-emitting laser (VCSEL)-based transmission over multimode fiber (MMF) has achieved data rates of 100G per lane and is progressing towards 200G per lane. Recently, high-data-rate MMFs derived from OM3 and OM4 have been proposed. These fibers exhibit higher effective modal bandwidths at 910 nm, leading to a different wavelength dependence compared to conventional OM3 and OM4 MMFs. Understanding the wavelength dependence of these fibers is crucial to address their utilization in a broader range of applications. Through Monte Carlo simulations, we have obtained the low-end boundary of the effective modal bandwidths (EMBs) for these fibers, revealing capability improvements over the existing OM3 and OM4. The high-data-rate OM4 performs the same as or better than OM5 from 840 nm to 920 nm, while also showing a high bandwidth for the 850–870 nm wavelength window, favoring VCSELs with center wavelengths shifted toward 860 nm. We also obtained the link bandwidth, which includes both modal bandwidth and chromatic dispersion contributions, and the transmission reaches for various types of transceivers. We find that for both high-data-rate OM3 and high-data-rate OM4, the link bandwidth stays above the value at 850 nm until around 910 nm, delivering a similar transmission performance from 850 to 910 nm without declining towards longer wavelengths, unlike the standard OM3 and OM4. This characteristic favors a wider range of wavelength choices for VCSELs and enables optimal deployments for various applications.

Liner multimode fibers with high distributed optical amplification system based high efficient quadrature modulation system for reliable high capacity local area network

Abstract This paper clarified the liner multimode fibers with high optical amplification system based high efficient quadrature modulation system for high capacity local area optical networks. The clarified the lighted QPSK transmitter system based linear multimode fiber profile is clarified under modal bandwidth effects. The optimum power variations are studied with spectral base band wavelength variations for various modal bandwidths based linear multimode fiber. Optimum power is clarified with time variations for various modal bandwidths based linear multimode fiber. Total power for 1500 and 1700 MHz km modal bandwidth is demonstrated based linear multimode fiber. The Max-Min signal base band amplitude based QAM pulse generator is clarified after photo-detector by using electrical constellation visualizer. The optimum Q Factor form with Min BER is demonstrated after photo-detector for 1300, 1500, and 1700 MHz km modal bandwidth based linear multimode fiber. The base band lighted SNR is clarified and simulated with the modal bandwidth variations based linear multimode fiber. Optimum Q form factor through photo-detector is demonstrated with the modal bandwidth variations based linear multimode fiber. The electrical SNR through photo-detector is studied and simulated with the modal bandwidth variations based linear multimode fiber.

Standard Single-Mode Fiber with High Modal Bandwidth as Two-Mode Fiber around 1060 nm for High Data Rate Transmission

A step-index standard single-mode fiber as a two-mode fiber at 1060 nm can have a high modal bandwidth. In the current work, we conducted a detailed study and found that the LP11 mode of such a fiber is bending-sensitive and that the light excited to LP11 mode can be stripped out due to bending. The transmission experiments were conducted using offset launch with both LP01 and LP11 modes excited and center launch with only LP01 mode excited to show transmission performance in different conditions. We demonstrated the feasibility of 25 Gb/s NRZ transmission over 1 km of the fiber when both LP01 and LP11 modes were excited. We further explored the feasibility of a trench-assisted bending-insensitive step-index standard single-mode fiber with good bending properties for both LP01 and LP11 modes for two-mode transmission at 1060 nm. We found a fiber that has high modal bandwidth at 1060 nm and can sustain bending down to at least a 20 mm diameter. The high-bandwidth two-mode fiber can be potentially useful for future 1060 nm-based VCSEL transmission.

BER versus Data Rate Performance of SCM Transmission over Multimode Fibers at Low-Frequency Passbands with Linear Block Codes

The use of Multimode fibers (MMFs) in the low-frequency region has been studied. It is found that many available low-frequency passbands can be used as channels. However, these passbands are frequency-selective channels, which can negatively affect to the transmitted signal. To lessen this effect, Linear Block Code (LBC) along with a careful selection of passbands is applied. In this work, the performance in terms of BER and data rate for an MMF communication system using a 1-km length MMF at low-frequency passbands with different schemes of LBC is studied. This study uses subcarrier multiplexing (SCM) with a 3-dB modal bandwidth and other low-frequency passbands as channels. The results show that by using (31, 26) LBC and Type-I bit allocation, a data rate of 494 Mbps can be obtained with a BER lower than 10-9. Moreover, a BER lower than 10-14 can be achieved with a data rate of 399 Mbps, which is two-fold higher than the data rate obtained using only the 3-dB modal bandwidth. Additionally, the BER versus data rate for different cases in terms of applying LBC to the system are found and can be practically used as a guideline in selecting a BER and data rate that are suitable for the minimum requirement of a given communication system.

Differential mode delay and modal bandwidth measurements of multimode fibers using frequency-domain method

• A frequency-domain method is developed to measure the DMD of multimode fibers. • Vector network analyzer is used to measure the complex transfer functions. • The time-domain output pulses can be calculated from CTF with proper procedures. • Frequency-domain method yields DMD results equivalent to the time domain method. • The frequency domain method can conduct DMD measurements at very low optical power. We report a frequency-domain method for measuring the differential mode delay (DMD) and bandwidth of multimode fibers (MMFs). Using a frequency domain instrument, vector network analyzer (VNA), the method measures the complex transfer functions (CTFs) of multimode fibers for a given set of launch conditions. As a result of the fiber length, which is long relative to sampling points used in VNA, the frequency sampling is under-sampled and the measured CTF is aliased. Aliased CTF behaves very differently from fully sampled CTF with dependence on the sampling frequency step. With proper procedures, the CTF can be transformed to local time frame centered around DMD into a modified CTF. The time-domain output pulses can be further recovered through an inverse Fourier transform. By recovering output pulses using complex transfer functions of a multimode fiber at controlled launch offsets, one can subsequently follow the same procedures of existing time domain methods to determine the effective modal bandwidth of the multimode fiber under test (FUT). As a result of the method, DMD and modal bandwidth measurements can be undertaken using frequency domain instruments rather than time domain instruments in a mathematically equivalent manner for multimode fibers. The measurement method utilizes CW light sources that are readily available in a wide range of wavelengths, thus providing greater flexibility for measuring the modal bandwidth of MMFs at different wavelengths, including WDM applications other than 850 nm. The very high sensitivity of the VNA allows the measurement at much lower optical power compared to the time domain instrument. Several measurements at 850 nm have been conducted using the frequency domain method and validated by comparison with the results from the time domain method. The method is suitable for measuring MMFs from a short length of a few hundred meters to a very long length close to 20 km. We have also measured an MMF at 910 nm using the method to demonstrate its flexibility in adopting different wavelengths.

Modeling an MMF Connector via Point Radiance Matrix and its Application in Automotive SI-MMF Connection

Recently, multimode fibers and their application, such as in-vehicle systems where many in-line connectors are inserted in short-range transmissions, have garnered considerable research interest. As such applications require extremely high reliability, simulation technology that considers multimode fiber harnessing under unfavorable conditions, such as various fiber lengths and connector misalignments, has been required. Many calculation methods for modal bandwidth and connector loss have been proposed to date; however, the 3D modal power coupling equation at the connection point has not been derived due to the calculation difficulty by linking the near- and far-field patterns. Herein, we propose a ‘point radiance matrix model’ to compute the complex mode-power conversion at the step-index (SI) fiber connectors. Accordingly, we derived new equations for calculating the power distribution at the receiving fiber according to the fiber connector misalignment parameters, which can be used for link level evaluation from light source to detector. Moreover, the rules governing the power transferred from the emitting fiber to the receiving fiber were investigated under generic alignment conditions, including random combinations of longitudinal, lateral, and tilt misalignments. Applications of the proposed matrix method could contribute toward the computation of mode-power conversion at graded-index (GI) fiber connectors in case the point radiance on the emitting fiber end face is found.

Fabrication of Y-Branched GI Core Polymer Waveguide and its Application to CWDM MUX Device for Multimode Fiber

This paper describes the characteristics of graded-index (GI) core Y-branched polymer optical waveguides as optical couplers for multimode fibers (MMFs) in coarse wavelength division multiplexing links with a restricted mode launch function. In this paper, we compare two GI-core Y-branched waveguides fabricated using different methods: the Mosquito method and the imprint method. Error free transmission is confirmed when transmitting a 25.6125-Gbps NRZ optical signal (PRBS31) at 850-nm wavelength through a 100-m long OM3 fiber using the waveguide as an optical coupler. We also discuss the function of a restricted mode launch exciter for a 1-km long MMF. From the effective modal bandwidth analysis, realizing higher bandwidth-distance product in long MMFs should be possible by reducing the core size of the waveguide coupler.

Modal gain characteristics of a two-section InGaAs/GaAs double quantum well passively mode-locked laser with asymmetric waveguide

Monolithic two-section InGaAs/GaAs double quantum well (DQW) passively mode-locked lasers (MLLs) with asymmetric waveguide, consisting of the layers of p-doped AlGaAs waveguide and no-doped InGaAsP waveguide, emitting at ~ 1.06 μm, with a fundamental repetition rate at ~ 19.56 GHz have been demonstrated. Modal gain characteristics, such as a gain bandwidth and a gain peak wavelength of the MLL, as a function of the saturable absorber (SA) bias voltage (Va) as well as the injection current of gain section (Ig), were investigated by the Hakki-Paoli method. With the increase of Va, the lasing wavelength and net modal gain peak of the MLL both exhibited red-shifts to longer wavelength significantly, while the modal gain bandwidth was narrowed. Both the net modal gain bandwidth and gain peak of the MLL followed a polynomial distribution versus the reverse bias at the absorber section. In addition, for the first time, it was found that Va had an obvious effect on the modal gain characteristics of the MLL.

Fundamental mode transmission around 1310-nm over OM1 and OM2 multimode fibers enabled by a universal fiber modal adapter

Recently there has been an interest in upgrading legacy multimode fibers such as 50 μm OM2 fiber to higher data rates through single mode transmission. A fiber modal adapter hosting a modal conditioning single-mode fiber (MCSMF) has been demonstrated as one robust solution to convert OM2 links into single mode transmission links for higher data rate transmission. Legacy multimode fibers also include OM1 fiber which has higher index contrast between the core and cladding and a larger core of 62.5 μm diameter. In this paper, we conduct a study to understand the MCSMF mode field diameter and connector offset tolerance requirements for OM1 fiber, which affect the transmission performance of single mode transmission. We find that despite very different refractive index profiles between OM1 and OM2 fibers, the fiber modal adapter concept is still applicable to OM1 and only one modal conditioning single-mode fiber design is needed to accommodate the needs for both fiber types. The detailed tolerances to the mode field diameter mismatch and the connector offset are numerically studied. The transfer functions for 1000-m of OM1 and OM2 with the adapters are measured, which show very high modal bandwidths at tens of GHz in contrast to very low modal bandwidths without the adapters. Transmission at 25 Gb/s using a 25G LR transceiver, 100 Gb/s using a 100G CWDM transceiver, and 400 Gb/s using a 400G LR transceiver are demonstrated with error free performance and open eye diagrams over 1000-m of OM1 and OM2. We find that the approach of using MCSMF can support fundamental mode transmission up to 100 Gb/s over this distance without obvious limitations.

Theoretical Investigation of the Influence of Wavelength on the Bandwidth in Multimode W-Type Plastic Optical Fibers with Graded-Index Core Distribution.

The bandwidth of multimode W-type plastic optical fibers (POFs) with graded-index (GI) core distribution is investigated by solving the time-dependent power flow equation. The multimode W-type GI POF is designed from a multimode single-clad (SC) GI POF fiber upon modification of the cladding layer of the latter. Results show how the bandwidth in W-type GI POFs can be enhanced by increasing the wavelength for different widths of the intermediate layer and refractive indices of the outer cladding. These fibers are characterized according to their apparent efficiency to reduce modal dispersion and increase bandwidth.

An approach to adhesive bond characterisation using guided acoustic waves in multi-layered plates

Abstract An approach for the non-destructive characterisation of adhesive bonds using guided ultrasonic waves is presented. Pulsed laser radiation is used to thermoacoustically excite broadband ultrasonic waves in a multi-layered sample, consisting of a metal plate adhesively joined to a polymeric layer using synthetic resin. The resulting signals are received by a purpose-built piezoelectric transducer. Varying the distance between excitation and detection yields spatio-temporal measurement data, from which the dispersive properties of the propagating waves can be inferred using a two-dimensional Fourier transform, assuming the plates to act as coupled waveguides. Coupled multi-layered waveguides show an effect referred to as mode repulsion, where the distance between certain modes in the frequency-wavenumber domain is assumed to be a measure of coupling strength. Measurements at different stages of curing of the adhesive layer are performed and evaluated. A comparison of the results shows changes in the dispersive properties, namely an increased modal bandwidth for the fully cured sample as well as an increased modal distance.

A Physical Insight Into Reconfigurable Frequency Selective Surface Using Characteristic Mode Analysis

In this letter, we provide a physical insight into the operating mechanism of a reconfigurable bistate active frequency selective surface (AFSS) based on characteristic mode analysis. At first, we study the modal behavior of the unit structure under different load resistances and found that the modal significance bandwidths of the fundamental mode and the high-order modes increase with the load resistance. When the load resistance is very high, the fundamental resonant frequency will move to high frequencies and the high-order modes may not change. Such features can be used in the design of the reconfigurable transmission/reflection frequency selective surface. It is found that the isolation between transparent and reflective states is mainly determined by the radiated field from fundamental mode. At the same time, we provide two improvement approaches to design this kind of frequency selective surfaces. And a reconfigurable AFSS operating at 2.1 GHz is designed, fabricated, and measured. The letter makes sense for the design of reconfigurable bistate AFSSs.

Large core multimode fiber with high bandwidth and high connector tolerance for broadband short distance communications

We propose a large core multimode fiber with 100-µm core diameter for short distance communication that is compatible with existing transceivers designed for 50-µm diameter core multimode fibers. The fiber exhibits a bandwidth that is over four times higher than the 50-µm OM4 fiber, low bending loss, and large connector offset tolerance. We have studied the bandwidth capability through both detailed modeling and experiments. A prototype fiber was fabricated, and it achieves 24 GHz km peak modal bandwidth in the 850 nm window, and the wavelength window with bandwidth above 5 GHz km is more than 100 nm. The bending losses of the fiber measured at 850 and 1300 nm with an encircled flux launch condition exceed the requirements for bending insensitive multimode fibers. The fiber has much higher connector offset tolerance compared to conventional 50-µm diameter core fibers as has been exhibited by modeling and experimental study. The additional loss caused by up to 10-µm connector offset is only 0.3 dB. Transmission experiments using 25 G SR and 100 G shortwave wavelength division multiplexing transceivers over such a fiber show error-free performance over 500 and 300 m, respectively. The proposed large core multimode fiber can address versatile needs in short distance communication including the bandwidth for high data rate transmission and a wide wavelength window for wavelength multiplexed transmission. The large connector tolerance and low bending loss can also enable low cost, compact connectivity solutions with passive alignment and ease of handling.

A Feasibility Study of Representing the Electric Field in Perforated Rectangular Enclosure Based on Modal Expansion Method

In this letter, the modal expansion method (MEM) based on orthogonal property of resonant modes is utilized to represent the electric field in a perforated rectangular enclosure. By applying inner product between electric field obtained by finite integration technique (FIT) and transverse electric (TE) or transverse magnetic (TM) mode field respectively, the mode coefficient for each contributing mode can be accurately obtained over the modal bandwidth. Then the electric field in a perforated rectangular enclosure can be represented by the superposition of contributing mode fields multiplying their corresponding mode coefficients. And the figures of mode coefficients' magnitude and phase give an intuitive understanding of the internal electric field. The statistical properties of internal electric fields obtained by FIT and MEM are in agreement with each other. MEM provides a better understanding of the electromagnetic environment in perforated enclosures.

Modal Bandwidth and Single-Mode VCSEL Transmission Capability Over Multimode Fibers

Single-mode VCSELs have been demonstrated with great transmission capability over multimode fibers in the literature through restricted launch, which is beyond what is allowed by the effective modal bandwidth (EMB) defined for multimode transmission with the encircled flux launch condition. However, the impact of fiber index profile errors and their interactions with launch conditions have not been thoroughly studied. We conduct a detailed experimental study to gain insight on the impacts of the fiber index profiles and launch conditions on the system performance of single-mode VCSELs transmitting over multimode fibers. Experimentally, our results show that a launch spot roughly matching the fiber LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode field leads to very high bandwidth and robust performance, largely independent of the imperfection of the index profiles and therefore can perform well in very high data rates. For a restricted launch without mode matching, the performance highly depends on the quality of the fiber, in line with EMB. We found that the center offset tolerance is around <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2~\mu \text{m}$ </tex-math></inline-formula> for a mode matched launch. We also conducted single-mode VCSEL transmission experiments over 600-m and 1000-m multimode fibers, which agree well with the modal bandwidth results.

Spectral-dependent electronic-photonic modeling of high-speed VCSEL-MMF links for optimized launch conditions.

We present spectral-dependent electronic-photonic modeling of vertical-cavity surface-emitting laser (VCSEL)-multimode fiber (MMF) links for next-generation high-speed interconnects. The beam coupling processes, between the VCSEL and the MMF and between the MMF and the photodetector (PD), are discussed, with spectral-dependent three-dimensional launch conditions analyzed. The model accounts for fiber effects on the transmission performance, specifically modal attenuation, dispersion, mode mixing, and mode partition noise. An advanced split-step small-segment (4-S) method simulates the signal evolution over the MMF with high accuracy and high efficiency. Experimental validation at 25 Gbps confirms the high accuracy of the VCSEL-MMF link model. The model reveals that larger radial offsets can further excite lower-order mode groups reducing the power distributed to higher-order groups when a tilted beam couples to the input fiber facet. With an optimized misalignment launch, the modal bandwidth is greatly improved by 3.8-fold compared to the conventional center launch. The model helps determine the optimum launch condition to improve link performance metrics such as transmission reach.

The Modal Effect of VCSELs on Transmitting Data Rate Over Distance in OM4 Fiber

The effective modal bandwidth (EMB) limit for the multi-mode (MM) VCSEL on transmitting data rate over distance in OM4 fiber is commonly referenced to be within 4700 MHz*km. However, this limit may not be valid for the VCSELs with reduced-mode (RM) or single-mode (SM) emission spectrum for data transmission. In this work, we investigate the EMB limit of OM4 fiber through characterizing three types of 850 nm oxide-VCSELs, namely, MM, RM and SM. Each type of VCSEL is tested to the highest error-free NRZ data rate over transmitting distance up to 1 km. The MM VCSEL demonstrates 50 Gb/s (100 m) and 26 Gb/s (300 m) that are within EMB limit. In contrast, the RM and SM VCSELs demonstrate speed distance product beyond the OM4 EMB limit. The SM VCSEL delivers record speed-distance of 44 Gb/s (500 m), and 36 Gb/s (1 km) at 25 °C without the use of equalization. These results suggest the SM VCSEL-based MMF link can transmit much higher data rate over extended distance up to 2 km in data centers.

Linearly polarised modes enabled PAM‐4 data transmission over few‐mode fibre for data centre interconnect

This Letter proposes a high data rate optical transmission system for data centre interconnects, where the authors employ vertical cavity surface emitting lasers (VCSEL) and graded index few-mode fibre (GI-FMF) having modal bandwidth of around 24.3 GHz.km to enhance the link capacity and range. Additionally, they consider PAM-4 modulated data transmission at the rate of 2 100 Gbps using a pair of VCSELs and employing mode group division multiplexing of two linearly polarised (LP) modes and of the GI-FMF. Digital signal processing techniques are applied at the receiver to process the received PAM-4 signals for equalisation in order to mitigate the channel impairments. Furthermore, standard OM3 and OM4 fibres are considered as a benchmark to compare the transmission performance of the designed GI-FMF. They observe that the designed GI-FMF supports longer transmission distance for both and modes upto 900 and 450 m at 50 and 100 Gbps data rates, respectively, while achieving lower receiver sensitivities for forward error correction limit of . The proposed optical transmission system can be a potential applicant in future data centre networks supporting transmission rates in 800 Gbps to 1.6 Tbps range.

High-Speed Performance Evaluation of Graded-Index Multicore Fiber Compatible With Multimode and Quasi-single Mode Operation

A comprehensive study on the optical characteristics and high-speed transmission performance of a hexagonally arrayed seven-core fiber supporting both multimode transmission at 850 nm and quasi-single mode transmission at 1310 and 1550 nm are presented. We investigated its optical and transmission characteristics such as inter-crosstalk, modal bandwidth, chromatic dispersion, and misalignment tolerance. The results show that the multicore fiber (MCF) has a high bandwidth at 850 nm while remaining a comparable performance with standard single-mode fiber (SSMF) at 1310 and 1550 nm. The worst inter-core crosstalk is less than -43 dB over a 10 km-long MCF connected with a pairwise fanin/fan-out devices. The minimum effective modal bandwidth of 8.44 GHz·km is achieved with the MCF for multimode operation, while the chromatic dispersion of the MCF at 1550 nm only increases by 7% compared with that of SSMF. In experiment, we successfully performed the 7 × 25 Gb/s multimode transmission over a 300 meter-long MCF at 850 nm and quasi-single mode transmission over a 12.4 and 10 km-long fiber at 1310 and 1550 nm, respectively, with an OOK modulation format. There was no obvious degradation observed when all cores operated simultaneously. Moreover, we carried out 7 × 50 Gb/s PAM4 transmission over a 300 meter-long and 10 km-long MCF at 850 and 1310 nm, respectively, as well as 7 × 40 Gb/s PAM4 transmission over a 10 km-long MCF at 1550 nm. A BER which is well below the forward error correction (FEC) threshold (5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> ) was reached for different MCF links.

Investigation of 2-port UWB MIMO diversity antenna design using characteristics mode analysis

In this research work, a 2-port UWB MIMO diversity antenna is designed to operate from 2.7 to 10.5 GHz with −10 dB impedance bandwidth of 118.18%. The proposed design has a total size of 0.57λ2.7×0.28λ2.7 (λ2.7 is lowest operating wave-length) consists of bi-planar printed fractal radiators whose feeds are contorted in geometry and are diametrically-fed. Characteristics mode analysis (CMA) is introduced to investigate antenna design, feeding technique and modal current distributions. The analysis includes study of modal dynamics, resonance mechanism, bandwidth potentials and modal radiation quality factor. The port-isolation is ⩾−15 dB when ground plane is truncated by rectangular slots via ellipsoid slot. With an end-connected ground thin neutralization lines, mutual coupling is further reduced by 7.5 dB (>−22.5 dB, measured). The diversity performance metrics are evaluated from ECC, CCL, DG, multiplexing efficiency, MEG and TARC. ECC is low <0.17 (from far-field magnitudes) and mean effective gain for both ports are |MEG| < 3 dB with MEG1MEG2 ≊ 1, which is serviceable for UWB multi-standard mobile/wireless/sensor ad-hoc diversity systems. An equivalent circuit model is also designed and the prototype of antenna is fabricated and measured to validate its performance.