We successfully transmitted a 40 Gbit/s PAM4 signal over 300 m at 980 nm using a two-mode VCSEL and standard single-mode fiber, exhibiting bi-modal behavior and high modal bandwidth at this wavelength.

This paper investigates advanced stacked and interleaved DSCM architectures for 100G and $200 G$ coherent-PONs, achieving single wavelength bi-directional transmissions with low backreflection. Spectral efficiency is optimized via comparative analysis of subcarrier spacing and roll-off factors.

This study evaluates the impact of MPI on short fiber segments of single-mode fiber in an $O$ Band transmission system. The performance can be characterized using a figure-of-merit based on the MPI and differential group delay.

As data center interconnects surge towards a 1.6 Tbit/s data rate, achieving cost-effective and technically viable solutions present challenges. Intensity-modulation and direct-detection (IM/DD) transmission over O-Band using standard single-mode fiber has emerged as a promising low-cost option. However, understanding the limitations imposed by factors like chromatic dispersion (CD) and fiber non-linearity (FWM) is crucial, particularly in different scenarios, such as operating at 8 × 100 GBaud PAM4 in an LWDM-8 configuration. In this paper, we adopt a statistical approach to assess outage probability and consider practical fluctuations in link parameters. Numerical modeling suggests IM/DD can span distances up to 5 km with transmission power under 0 dBm using this architecture. In addition, we evaluate recently proposed architecture to achieve 800 Gbit/s and 1.6 Tbit/s using an LWDM4 configuration and assess the impact of FWM to understand the role of zero-dispersion wavelength (ZDW) of the fiber. Coherent transmission leverages more powerful signal processing capabilities which extends the transmission range. Yet, reducing coherent transmission complexity is desirable for cost-effective and power-efficient data center applications. By exploring dual wavelength transmission and DP-16 QAM transceivers, akin to IM/DD counterparts, the feasibility of streamlining this architecture is also studied. The analysis indicates that the complexity of the coherent approach can be reduced without significant penalties for distances up to 10 km.

The data center interconnect is moving toward 1.6 Tbit/s, which is posing challenges for reaching a solution that is cost effective and technically feasible. Intensity modulation and direct detection (IM/DD) transmission over O-Band using standard single-mode fiber is a potential low-cost solution. However, limitations imposed by chromatic dispersion and four-wave-mixing (FWM) needs to be understood, such as in the case when operating at 8 x 100 GBaud PAM4 in LWDM configuration. In this paper, a statistical approach has been adopted to evaluate the probability of outage by considering practical link parameter fluctuations such as wavelength variation and drift, polarization variation and the natural variation of the fibers zero dispersion wavelength. Numerical modeling shows that IM/DD can be used up to distances of 5 km if transmission power is maintained under 0 dBm. Coherent transmission can extend the distance beyond 5 km due to its signal processing capabilities. However, it is desirable to reduce its complexity for cost effective and power efficient data center applications. Using dual wavelength transmission and DP-16 QAM transceivers, which share similar components to the IM/DD counterpart, the feasibility of simplifying this architecture is studied. The analysis shows that the complexity of the coherent approach can be reduced without significant penalties for distances up to 10 km.

Transmission of 56-Gbps signals across a 500-meter 980 nm optimized multimode fiber with 14.2 GHz·km bandwidth using 980 nm multimode VCSEL is demonstrated. The results show promising performance within IEEE standards for short reach applications.

1.6T IM/DD transmission based on LWDM grid using 200G/lane over 2–5 km of single mode fibers is studied. The impact of FWM is assessed over the different fiber distances. FWM can have a significant impact even over 2 km distance, if the zero-dispersion wavelength overlaps with one of the LWDM transmission wavelengths or exactly in the middle of any two wavelengths used. However, when taking into account the LWDM wavelength variation- or drift statistically, the results show significant less impact of FWM degradation. Optical launch power limits are explored to achieve 1.6 T transmission over 5 km distance using KP4 FEC threshold criterion.

The impact of Four-Wave-Mixing is analyzed for CW-WDM data-center architecture interconnects that rely on low latency and low Bit-Error-Rates. This analysis shows that novel dispersion-shifted-fibers are advantageous and extend the reach up to 15 km.

1.6T IM/DD transmission based on LWDM grid using 200G/lane over 2–5 km of single mode fibers is studied. The impact of FWM is assessed over the different fiber distances. FWM can have a significant impact even over 2 km distance, if the zero-dispersion wavelength overlaps with one of the LWDM transmission wavelengths or exactly in the middle of any two wavelengths used. However, when taking into account the LWDM wavelength variation- or drift statistically, the results show significant less impact of FWM degradation. Optical launch power limits are explored to achieve 1.6 T transmission over 5 km distance using KP4 FEC threshold criterion.

The industry is moving toward higher data rate for dater center campus interconnect, i.e., 800G or higher. Intensity modulation direct detection technology based on 200G/lane has difficulty meeting the distance target of 10 km and hence, coherent transmission technology becomes an alternative to meet the need in this space. O-band coherent transmission is a potential approach for lower-cost and low power consumption for campus interconnect. We study the coherent transmission in O-band using LAN-WDM with one to four wavelengths at 800G/Lane for 10 km link distance. Detailed modelling is conducted to understand the limitations imposed by fiber nonlinearities, laser linewidth and equalization length on the power budget.

Single-mode VCSEL technology has advanced significantly in the past few years. The advantages of single-mode VCSELs lie primarily on the narrower linewidth, lower numerical aperture, and smaller spot size compared to multimode VCSELs. They are suitable for transmitting over both multimode fibers and few-mode fibers. For multimode fiber systems, the narrow linewidth can reduce the chromatic dispersion penalty and increase the system reach. A single-mode VCSEL also allows the coupling into graded-index single-mode fiber, which is few-mode around 850 nm with high bandwidth, for few-mode transmission. We review recent progress and present new experimental results and modeling analyses of single-mode VCSEL transmission over both types of fibers. The experiments and analyses shed new light on how single-mode VCSELs can be used with multimode fibers and graded-index single-mode fibers and relative merits between 850 nm single-mode VCSELs versus 980 nm and 1060 nm single-mode VCSELs to address the needs of various applications.

We discuss fiber designs of graded-index profile single-mode fiber for both 1310 nm single-mode transmission and 850 nm few-mode transmission and present fiber characterization and system transmission performance results using a single-mode VCSEL

We investigate experimentally the feasibility of single-mode VCSEL transmission at 910 nm over a graded-index single-mode fiber and achieve a BER < 10 −12 for a transmission distance of 1-km at 25 Gb/s.

Short distance optical communication in data centers has been dominated until now by multimode-fiber links based on multimode vertical cavity surface emitting lasers (VCSELs). Their large wall-plug and energy efficiency, as well as the relaxed requirements for fiber connectivity, reduces the overall cost of the system. A single-mode (SM) VCSEL has lower NA and smaller spot size making it suitable for coupling the light into the standard single-mode fiber. We show that a SM VCSEL can be implemented at 910 nm with high bandwidth (> 25 GHz) and high side mode suppression ratio (> 40 dB) at wavelengths beyond 850 nm to add more capacity for SM VCSEL transmission. The performance of the 910 nm SM VCSEL is evaluated at 25 Gbit/s using two single mode graded index fibers. These fibers are single mode at 1310 nm and 1550 nm, enabling their use for long-reach and high bandwidth applications, while still providing enough bandwidth for short wavelength, short-reach, and cost sensitive applications. Error free (BER < 10(-13)) data transmission of 25 Gbit/s across 1 km is achieved using a 910 nm optimized fiber and 150 m transmission using a fiber optimized for dual wavelength (850 nm and 910 nm) transmission.

Graded-index standard single-mode fiber offers few-mode operation around 850 nm with better modal bandwidth over step-index fiber. We investigated feasibility of VCSEL transmission through link model analysis and demonstrated 100 m VCSEL transmission at 25Gb/s.

We report on a public field trial demonstrating seamless handover in a multi Radio Access Technology mobile network supporting WiFi, LTE, and new 5G radio access in the 60 GHz band for full-duplex enhanced mobile broadband and 5G broadcast hotspots.

The transmission characteristics of the universal fiber concept are shown and its performance is compared to standard OM4 fiber using a directly modulated VCSEL at 50 Gb/s using PAM4 modulation format. Results show almost identical performance up to a distance of 152 m without any digital signal processing. Coupling loss of less than 0.5 dB is achieved between VCSEL and universal fiber using free space optics, which is higher by only 0.2 dB compared to coupling into an OM4 fiber.

A public field trial showcasing an operational RAT mobile network was implemented in one of the largest shopping malls in Warsaw, Poland. The network supports novel 60 GHz 5G mobile access as well as legacy LTE and WiFi services All mobile access services of the network are interconnected via optical fiber to the data centers of a mobile network operator and an Internet service provider. Fronthauling for the 60 GHz 5G hotspot RAU and for LTE is realized by analog RoF via a fiber optic DAS. The 60 GHz 5G RAUs for the eMBB use case and the WiFi AP are both backhauled via optical Gigabit Ethernet. The 60 GHz RAUs for the eMBB and hotspot use case feature 2D beam-switching and 1D beam-steering, respectively. Inter-RAT switching between the different mobile services with seamless user experience is achieved using a Mobile IP system with FILS.

A fast, accurate and simple field coupling model is presented which is capable of describing mode coupling effects due to bends and splices in multimode fibers with parabolic index profile as well as the coupling losses induced by this process. This model is validated numerically by comparing the results to the well-known coupled amplitude theory model yielding the same relative bandwidth increase behavior as long as the coupling losses are the same. It is shown, that the number of discrete segments used in this model can be reduced considerably as long as the coupling losses are kept constant. The effect of mode coupling on the differential group delay, mode dependent loss, bandwidth gain and impulse response width reduction are analyzed. It is shown that the relative bandwidth gain induced in MMF links induced by the coupling process is independent of fiber parameters or number of guided modes; it can be fully characterized by coupling induced losses. The model is compared to well-known results given by power coupling models and a good agreement is observed for high steady state loss values.

MIMO Receiver complexity in terms of required filter taps is compared for a few mode fiber guiding six modes in mode division multiplex operation using the principal modes and LP-modes as carriers. Principal mode transmission shows a factor of two improvement if the coupling losses induced by splices or bending is less than 2.5 dB.