CWDM4 Transmission Technology for Data Center

Evolution of Optical Transmission Technology in Data Center
With the popularization and application of mobile Internet, data center has developed rapidly and become an important infrastructure in the information society. The data center consists of a large number of servers. High speed and large capacity data transmission and exchange are needed between servers. The traditional cable transmission cannot meet the speed requirements. Optical fiber transmission technology has entered the data center since 2010, and has become the mainstream transmission technology.

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The applications of Raman WDM

Distributed optical fiber sensing technology
Optical fiber sensing technology is a new type of sensing technology that developed rapidly with the development of optical fiber communication technology in the 1970s. It uses light waves as a carrier and optical fiber as a medium to sense and transmit external measured signals. Compared with conventional sensors, optical fiber sensors have many advantages such as high measurement sensitivity, anti-electromagnetic interference, anti-radiation, high pressure resistance, corrosion resistance, small size, light weight, and adaptation to harsh environments. The optical fiber component itself is both a detection element and a transmission element , which can connect many optical fiber sensing units on the optical fiber trunk to form a large-scale remote sensing system for distributed monitoring and measurement.

Overview of hybrid devices

Introduction
In recent years, the integrated optical passive devices are smaller in size and more mature in technology, occupying a considerable part of the market share. As one of the key devices of optical communication, erbium-doped fiber amplifier (EDFA) has become the technical focus of competition among many manufacturers due to its integration, miniaturization, multi-function and low cost. The integration of hybrid optical passive devices is not to use integrated technology to make devices, but to integrate separate devices together. The above competitive advantages of EDFA can be realized by integrating optical isolator, wavelength division multiplexing (WDM) devices, optical circulator and test access port (TAP) splitter into a hybrid device. At the same time, the manufacturing process of hybrid optical passive devices is also one of the key factors to realize the competitive advantage of the above-mentioned EDFA technology.

Passive Optical Devices for 5G Application(Part III)

In the Passive Optical Devices for 5G Application(Part II), we introduce Tunable Optical Filter (TOF) for Coherent Receiving, Optical Performance Monitoring (OPM) Module, Optical Channel Monitoring (OCM) Module. This article will show you other important passive optical devices for 5G application.

Dynamic Gain Equalization (DGE) Filter
For the complicated fiber links transmitting DWDM signals, OPM and OCM just provide solutions for monitoring of OSNR and channels. However, the DWDM signals need to be equalized before they leave each ROADM node or relay station. In the ROADM-based optical network, the power levels of the DWDM channels are always changing. Thus DGE is required to provide dynamic equalization of the DWDM channels, which is different from the fixed GFF (Gain Flattening Filter) for an EDFA.

Passive Optical Devices for 5G Application(Part II)

With the rise of 5G technologies and massive deployment of 5G base stations, wireless access of terminals with high speed and large capacity is realized. Meanwhile, the traffic in optical fiber network increases rapidly. It is predicted that the current optical fiber network will become the bottleneck of information exchange in the future 12-18 months. The upgrading of optical fiber network is urgent. The representative trend is that the technologies for long-haul network (LHN) will be sunk to metropolitan area network (MAN), including DWDM (Dense Wavelength Division Multiplexing), ROADM (Reconfigurable Optical Add-Drop Multiplexer) and coherent receiving techniques. This paper discusses some of the passive optical devices for the coming 5G applications.

Tunable Optical Filter (TOF) for Coherent Receiving
In DWDM optical network, tunable optical filter (TOF), as one of the most important dynamic optical devices, is used to realize such functions as channel selection, optical performance monitoring (OPM) and optical channel monitoring (OCM) in the wavelength domain. The requirements of optical network for TOF include low loss, wide tuning range and good filtering characteristics.

Passive Optical Devices for 5G Application(Part I)

With the rise of 5G technologies and massive deployment of 5G base stations, wireless access of terminals with high speed and large capacity is realized. Meanwhile, the traffic in optical fiber network increases rapidly. It is predicted that the current optical fiber network will become the bottleneck of information exchange in the future 12-18 months. The upgrading of optical fiber network is urgent. The representative trend is that the technologies for long-haul network (LHN) will be sunk to metropolitan area network (MAN), including DWDM (Dense Wavelength Division Multiplexing), ROADM (Reconfigurable Optical Add-Drop Multiplexer) and coherent receiving techniques. This paper discusses some of the passive optical devices for the coming 5G applications.

1. CDC ROADM Based on MCS
The demand for increasing bandwidth promotes the upgrading of all-optical network (AON). As key parts of AON, the market of ROADM and related passive optical devices is expected to grow rapidly. In the nodes of optical fiber network, any wavelengths can be downloaded/uploaded via ROADMs. With the rapid growth of Internet traffic, the traditional ROADM nodes can’t meet the requirements. The new generation of ROADMs are required to be colorless, directionless and contentionless (CDC ROADM).

WDM Technologies for 5G Carrying Network

5G Application Scenarios
The development of 5G networks starting in 2019 is generally believed to bring changes not limited to people’s daily life. It will support the evolution of Internet from mobile internet to intelligent internet, which will influence the industrial-ecology deeply.

The international standard organization 3GPP defined the three main application scenarios of 5G: eMBB (Enhance Mobile Broadband), uRLLC (Ultra-Reliable Low Latency Communications), mMTC (Massive Machine Type Communication). eMBB requires the bandwidth experienced by the customers to be more than 1Gbps supporting mobile broadband surfaces such as 3D and ultra-high definition video. uRLLC requires the transmitting delay to be <1ms supporting real time applications such as self-driving cars, industrial automation, and remote surgery. mMTC means application in massive internet of things (IOT) which requires high density terminal connection of more than one million per square kilometer.

What is Polarization Maintaining(PM) fiber connector?

Polarization maintaining(PM) optical fiber connectors are usually used for special applications, such as optical fiber sensing, interferometry, planar waveguides, coherent optical transmission, and long-distance bidirectional optical transmission systems. To understand polarization-maintaining connectors, we need to know what polarization-maintaining fibers are.

The PM fibers currently on the market basically have the following cross-sectional types:

What is CCWDM(Compact Coarse Wavelength Division Multiplexing)?

CCWDM is Compact CWDM (Compact Coarse Wavelength Division Multiplexing), which is a wavelength division multiplexing technology based on TFF (Thin Film Filter). It works in the same way as CWDM modules, except that CCWDM uses free space technology (As shown in Figure 1), compared with the common CWDM fiber cascading method (as shown in Figure 2). The package size of CCWDM is smaller than CWDM and with lower insertion loss and better consistency. CCWDM can be used to replace the CWDM products in telecommunications, corporate networks, PON networks, cable TV and other fields. The lower insertion loss makes the CCWDM module have lower signal attenuation when used, thereby reducing the power requirements of the signal transmitter.

Crystal-based Devices — High-power Optical Isolators

The research and application of fiber lasers flourish in recent years. Optical isolators are important devices to ensure the reliability of fiber lasers. Depending on the actual applications, different types of optical isolator are employed. For some applications under relatively low optical power, wedge-type in-line optical isolator is employed, just with more consideration on heat dissipation. While for some applications under high optical power, BD-type in-line optical isolator is employed instead of wedge-type. The reason is that the FR for telecom applications can’t be used anymore.