100G Single-Mode Modules for Short Distance Transmission

As bandwidth demand continues to grow, network service providers are looking at 100G Ethernet network to accommodate the constant traffic surge. This new technology translates into greater speeds and a possible network infrastructure upgrade to compensate for various challenges that do not apply to slower networks, such as 10G, or 40G. 100G Ethernet provides high-speed connectivity while protecting current network infrastructures that requires broad expertise and wide-range testing to qualify the state of the fiber, perform fiber characterization and assess the integrity of data transmission over long-haul and ultra-long-haul networks. In response to 100 Gigabit Ethernet, many famous telecommunication companies, like Cisco, have delivered industry-leading, standards-compliant, 100G pluggable transceiver modules, such as single-mode QSFP-100G-LR4 for the transmission distance up to 10 km and multimode QSFP-100G-SR4 for the transmission up to 100 m. How about single-mode 100G modules for the transmission distance less than 2 km? Today, we’re going to introduce two 100G interfaces over single-mode fiber for short distance transmission: 100GBase CWDM4 and 100GBase PSM4.

The Development History of 100GBase CWDM4 and 100GBase PSM4

The IEEE standardized a cost-effective 100m solution known as “SR4”. Beyond 100m, there is only the “LR4” standard, which is targeted to achieve 10km. Customers, particularly hyperscale data centers are looking for solutions up to 2 km. To response, in 2014, a new industry group CWDM4(coarse wavelength division multiplexed 4x25G multi-source agreement) MSA which is consisted of Avago Technologies, Finisar Corp, JDSU, Oclaro, and Sumitomo Electric, announced the formation of an industry consortisum dedicated to defining specifications and promoting adoption of interoperable 2km 100 interfaces over duplex single-mode fiber, which smooths the process of getting to 100Gb Ethernet.

Like the development history of 100GBase-CWDM4, in order to fill the requirement of low-cost 100G connections at reaches of 500 m in applications that fall in between the IEEE standardized multi-wavelength 10-km 100GBase-LR4 single-mode approach and its multimode-fiber based 100GBase-SR10 short reach specification, six technology vendors aim to promote the creation and adoption of parallel single-mode 4-lane (PSM4) approach to 100G in the data center.

Main Features of 100GBase-CWDM4 and 100GBase-PSM4

100GBase-CWDM4: 100GBase CWDM4 module comply with the requirement of CWDM4 MSA. It is a 100G optical module using CWDM (coarse wavelength division multiplexing) technology with 4 lanes of 25Gbps optically multiplexed onto demultiplexed from a standard duplex G.652 single-mode LC or SC fiber for the link length from 2 meters to at least 2 kilometers. Transceiver modules compliant to CWDM4 MSA specification use a color code to indicate the application. The color code can be on a module bail latch, pull lab, or other visible feature of the module when installed in a system The image below shows the working principle of 100GBase-CWDM4.

100GBase-PSM4: 100GBase-PSM4 is a parallel module which provides increased port density, offering four independent transmit and receive channels, and each channel operates at 25Gbps, resulting in an aggregate data rate of 100Gbps for optical communication applications. It can support the link length up to 500 m over single-mode MPO or MTP fiber. The working principle of 100GBase-PSM4 is shown below.

Which One Is More Cost Effective?

From an optical transceiver module structure viewpoint, PSM4 can be more cost effective, this comes in two reasons: One is that it uses a single uncooled CW laser which splits its output power into four integrated silicon modulators, the other is that its array-fiber coupling to an MTP connectors is relatively simple.

However, from an infrastructure viewpoint, PSM4 would be more expensive when the link distance is long, mainly due to the fact that PSM4 uses 8 optical single-mode fibers, while CWDM4 uses only 2 optical single-mode fibers.

When take these two factors into considerations, a total cost comparison can be qualitatively shown in the figure below. As can be seen in the figure, PSM4 starts with a lower cost due to its lower transceiver cost, but as the link distance increases, its total cost climbs up very fast due to the fact that it uses 8 optical fibers. Besides, if deploying PSM4 modules, the entire optical fiber infrastructure within a data center, including patch panels, has to be changed to accommodate MTP connectors and regular single-mode fiber cables. In addition, cleaning MTP connector is not a straightforward task.

Conclusion

With the requirement for longer distances and higher data transmission speed increases, 100GBase-CWDM4 and 100GBase PSM4 which provide lower-cost, lower power option for what can be referred to as medium-reach distances that is future-proof for the next generations of data transmission speeds. FS.COM offers compatible 100GBase-CWDM4 and 100GBase-PSM4 for many brands at affordable price. You can choose the right one according to your need.

Choosing the Proper Polarity Method for MTP System

Whether in local area network (LAN) campus or data center backbones, we are in the process of migrating to higher-density cabling in order to meet system bandwidth needs and provide the highest broadband network connectivity density. Many network designers are turning to MTP trunk cable for today’s duplex fiber transmission and to provide an easy migration path for future data rates that will use parallel optics such as 40/100G Ethernet. To ensure reliable MTP system performance as well as support ease of installation, maintenance and reconfiguration, choosing the proper polarity method is very important. In this post, we are going to introduce three MTP polarity method for your reference.

What Is Polarity?

Polarity is the term used in the TIA-568 standards to explain how fiber (wire) to make sure each transmitter is connected to a receiver on the other end of a multi-fiber cable. To be specific, as we all know, optical fiber links typically require two fibers to make a complete circuit. Optical transceivers have a transmit side and receive side, and typically deploy a duplex fiber connector as the interface. In any installation, it is important to ensure that the optical transmitter at one end is connected to the optical receiver at the other. This matching of the transmit signal (Tx) to the receive equipment (Rx) at both ends of the fiber optic link is referred to as polarity.

Structure of MTP Multi-fiber Connector

To better understand each polarity method, it is important to make it clear for the MTP connector structure.

Each MTP connector has a key on one side of the connector body. When the key sits on top, this is referred to as the key up position, on the contrary, when the key sits on bottom, we call it key down position. Each of the fiber holes in the connector is numbered in sequence from left to right, and we call these fiber holes as positions, or P1, P2, etc. Besides, there is a white dot as shown below on the connector body to designate the position 1 side of the connector when it is plugged in. Generally, MTP multi-fiber connector is pin and socket connector—requiring a male side and a female side (male side has pins, while female side has no pins) as shown below. Cassette and hydra cable assemblies are typically manufactured with a male connector, while trunk cable assemblies typically support a female connector.

Three Polarity Methods for MTP System

Defined by TIA/EIA-568-B.1-7, there are three polarity methods for MTP system—method A, method B and method C. These methods define installation and polarity management practices, and provide guidance in the deployment of these types of MTP fiber links. Once a method is chosen, these practices must be put into place to insure proper signaling throughout the installation.

Method A: In method, it requires two type A cassettes with key-up to key-down adapters, a straight-through key-up to key-down MTP trunk cables as well as two patch cables. This method, shown below maintains registration of Fiber 1 throughout the optical circuit. Fiber 1 in the near end cassette mates to Fiber 1 in the trunk cable assembly, which mates to Fiber 1 in the remote cassette. The fiber circuit is completed by utilizing one “A-to-A” patch cord at the beginning and “A-to-B” patch cord to insure proper transceiver orientation.

Pros: It provides the simplest deployment, works for single-mode and multimode channels, and easily supports network extensions.

Cons: Requires pre-configured “A-to-A” patch cables, or field configuration of same.

Method B: In type B polarity method, method B cassette requires key-up to key-up adapters to link reversed cable or MTP trunk cable type B. The fiber circuit is completed by utilizing straight “A-to-B” patch cords at the beginning and end of the link, and all of the array connectors are mated key-up to key-up. This type of array mating results in an inversion, meaning that Fiber one is mated with Fiber twelve, Fiber two is mated with Fiber eleven, etc. To ensure proper transceiver operation with this configuration, one of the cassette needs to be physically inverted internally, so Fiber twelve is mated with Fiber one at the end of the link.

Pros: It requires single source for components and “A-to-B” patch cords only. Besides, it is a standard which provides migration path to parallel optics.

Cons: This key-up to key-up method requires a more in-depth planning stage in order to properly manage the polarity of the links, and to identify where the actual inversions need to occur. Moreover, it only support multimode fiber.

Type C: The method C shown below, with the key-up to key-down adapter in the cassette, looks like the type A method. However, the difference between this method and method A is that the flip does not happen in the end patch cords, but in the array cable itself. In this case, the fiber at position 1 on one end of the cable is shifted to position 2 at the other end of the cable. The fiber at position 2 at one end if shifted to position 1 at the opposite end, etc.

Pros: This method requires one cassette type, easy to produce and purchase, and it can support both single-mode and multimode fiber.

Cons: An additional drawback to this method is that it does not support parallel optics and is less reliable than method A.

Conclusion

We have discussed three polarity methods for MTP system, and indicate the pros and cons of each one. For choosing the proper method for MTP system, you should weight both advantages and disadvantages.