Know More About 100GBASE-PSM4 QSFP28 Transceiver

There is an interesting phenomenon that multimode fibers are more expensive than single-mode fibers but the transceivers are the reverse. That is because the multimode core diameter is large and easy to align with VCSEL lasers and detectors while the single mode fiber cable is very hard to build and align transceiver components with and requires very expensive alignment equipment. Therefore, multi-mode transceivers are less expensive than single-mode transceivers. Now the 100G Ethernet network has been widely applied in data centers and there are various types of 100G fiber optic transceivers available on the market. Is there a type of 100G single-mode transceiver which can provide a low-cost solution for long-reach data center optical interconnects? The answer is Yes. The 100GBASE-PSM4 (parallel single-mode 4-lane) QSFP28 transceiver can do that.

Overview of 100GBASE-PSM4 QSFP28 Transceiver

The 100GBASE-PSM4 QSFP28 transceiver supports 100G link over eight single-mode fibers (four fibers for transmit and four fibers for receive) with data transmission distance up to 500 meters. It uses four parallel lanes for each signal direction and each lane carries 25G optical signal. In addition, the 100GBASE-PSM4 QSFP28 transceiver is structured with MTP/MPO interface, so it is usually used with single-mode fiber ribbon cable with MTP/MPO connector.

100GBASE-PSM4 QSFP28 transceiver
Working Principle of 100GBASE-PSM4 QSFP28 Transceiver

The figure below shows the working principle of the 100GBASE-PSM4 QSFP28 transceiver. The transmitter side accepts electrical input signals compatible with common mode logic (CML) levels, wile the receiver side converts parallel optical input signals via a photo detector array into parallel electrical output signals. The receiver module outputs electrical signals are also voltage compatible with CML levels. All data signals are differential and support a data rate up to 25Gbps per channel.

working principle of 100GBASE-PSM4 QSFP28 transceiver
Applications of 100GBASE-PSM4 QSFP28 Transceiver

The 100GBASE-PSM4 QSFP28 transceiver can be used for 100G to 100G connection. As the following figure shows, two 100GBASE-PSM4 QSFP28 transceivers are plugged into Host IC, then these two transceivers are connected by MTP/MPO patch cord and MTP/MPO patch panel.

100G to 100G connection with 100GBASE-PSM4 QSFP28 transceiver

From an optical transceiver module structure viewpoint, PSM uses a single uncooled CW laser which splits its output power into four integrated silicon modulators. Therefore, the 100GBASE-PSM4 QSFP28 transceiver can be used for 100G to 4x25G connection. As the following figure shows, the 100GBASE-PSM4 QSFP28 transceiver and four 25G-LR SFP28 transceivers are connected by MTP-LC breakout cable.

100G to 4×25G connection with 100GBASE-PSM4 QSFP28 transceiver

The 100GBASE-PSM4 QSFP28 transceiver meets the requirement for low-cost 100G connections at reaches of 500 meters in applications that fall in between the IEEE multi-wavelength 10 kilometers 100GBASE-LR4 single-mode fiber approach and its multimode-fiber based 100GBASE-SR10 short reach specifications. It can support a link length of 500 meters over single mode fiber cable, which is sufficient for data center interconnect applications.

Introduction to Fiber Optic Cable

Fiber optic cable uses one or more optical fibers to transmit large amounts of information at the speed of light, which plays an important role in optic communication network. As a new generation of transmission medium, fiber optic cable has a great improvement in the quality, safety, reliability, transmission speed and transmission capacity. Besides, the transmission distance of fiber optic cable has achieved dozens of km, which is the first option to be used in large-scale network.

Fiber optic cable consists of the core, the cladding, the coating, strengthening fibers and the cable jacket (shown in the following figure.).

Fiber Optic Cable

Core: The core is characterized by its diameter and it is a cylinder of glass or plastic that runs along the fiber’s length. And it is the light transmitting region of the fiber.

Cladding: It is the first layer around the core. The cladding causes light to be confined to the core of the fiber by total internal reflection at the boundary between the two.

Coating: It is the first non-optical layer around the cladding. The coating typically consists of one or more layers of a polymer that protect the silica structure against physical or environmental damage.

Strengthening Fibers: These are used to enhance the ability of cable to bear the load during the laying. Generally metallic or non-metallic fibers. The materials generally are metallic or non-metallic fibers.

Cable Jacket: This is the outer layer of any cable. The cable jacket is characterized by flame-retardant, damp-resistant, voltage-endurance and corrosion resistant and the main function of it is to protect the fiber optic cable.

Nowadays, different applications need different types of fiber optic cables which can be classified by different aspects.

Transmission Mode

Single-mode fiber cable: It allows only one mode of transmission. Because of this, the light can only be transmitted along the fiber core, completely avoiding optical dispersion and waste of energy. And single-mode fiber cable features low insertion loss and high return loss, good ability of adaptation to the environment, high data transfer rate and supporting simplex or duplex connector type. It is typically used in network connection which needs long distance transmission and high bandwidth.

Multimode fiber cable: It allows multiple modes of light transmission. Because of this, multimode fiber cable has higher “light-gathering” capacity. However, the quality of the signal is reduced over long distance for high dispersion and attenuation rate with this type of fiber. So multimode fiber cable is mostly used for communication over short distances, such as within a building or on a campus.

Transmission Way

Simplex Cable: It consists of a single strand of glass or plastic fiber. The data is transmitted almost in one direction, so it is applied in one-way data transfer.

Duplex Cable: It consists of two strands of glass or plastic fibers. Each fiber strand has independent coatings that are linked together by a thin layer of coating material. It is most used where separate transmit and receive signals are required, that is, one strand transmits in one direction while the other strand transmits in the opposite direction.

Core Count

Single-core Fiber: It is designed to carry light only directly down the one core and it is often used in household.

Multi-core Fiber: It consists of more than one core. It’s a revolutionary new approach to engineer a fiber for high capacity applications and it is often used in the trunk.

Fiber Road Laying

Pipe Fiber Optic Cable: It is used in the access network or user resident network. Pipeline laying is generally in urban areas and the environment is better, so there is no special requirement for cable sheath.

Direct-buried Fiber Optic Cable: It is especially designed to be buried under the ground without any kind of extra covering, sheathing, or piping to protect it. Most direct-buried cables are built to specific tolerances to heat, moisture, conductivity, and soil acidity.

Aerial Fiber Optic Cable: It is used on a pole. Aerial fiber optic cable laying can make use of the existing pole line, saving construction cost and shortening the construction period. And it can adapt to a variety of natural environment.

Submarine Cable: It is wrapped with insulating materials, laying at the bottom of the sea, to set up a telecommunication transmission between countries.

Environment & Situation

Indoor Cable: It is used for indoor environment and mostly adopts tight set of structure. Its characteristics are soft and flame-retardant which can satisfy the need of indoor wiring.

Outdoor Cable: It is used for outdoor environment. And it can bear the climate change, prevent the infiltration of water, resist the ultraviolet radiation and resist other forces.

Accompanied by the continuous advancement of network technology, fiber optic cable constantly participates in the construction of telecommunications networks, the construction of the national information highway, Fiber To The Home (FTTH) and other occasions for large-scale use. Although fiber optic cable is still more expensive than other types of cable, it can support today’s high-speed data communications because it eliminates the problems of twisted-pair cable. Therefore, fiber optic cable is still a good choice for people.