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How to Connect Servers and Leaf-Spine Switches?

To meet ever-growing bandwidth requirements of service provider and data center networks, 100 Gigabit Ethernet was officially standardized in July 2010 under IEEE 802.3ba. In response, Gigalight’s engineers deliver industry-leading, standards-compliant, 100G pluggable optical transceivers.

This Multisource Agreement (MSA)-compliant, CFP modules help to provide connectivity options within service provider core networks, and from service provider networks to large data centers.

Modern data center traffic is becoming more and heavier, and east-west flow between servers if you haven’t adopted the new two-tier Ethernet switching architecture called leaf-spin. They get you the highest density interconnects between data center switches and to the outside world. Let’s see which ones belong where at the bottom we have the leaf switches and servers.

The 100G QSFP downlinks on the leaf switches break out into 425G QSFP connections one for each server copper cables are lowest cost solution for this distance typically less than 5m for the uplinks spine switches. We have some choices but as tied to the type of fiber cable infrastructure you choose or have already installed. If you have multimode fiber, you can use SR4 up to 100m, remember SR4 requires parallel fiber with MMF MPO connectors. For single mode fiber, you can use PSM4 or CWDM4. PSM4 goes up to 500m and CWDM4 goes up to 2km, don’t forget the PSM4 is a parallel fiber format and uses SMS and MPO connectors if you only need 30m of reach the don’t worry about installing fiber active optical cables will do the trick for the spine uplands to other data centers and data center layers use LR4 assuming you need up to 10km reach on doing fiber SMS CWDM4 works here too.
Short downlinks to 25G server ports can use copper breakout cables. Multimode fiber links between leaf and spine can be used SR4. Single mode fiber links between leaf and spine in either PSM4 or CWDM4.

AOC Uses in Modern Data Centers

AOC is composed of integrated optoelectronic devices for high-speed, high-reliability interconnected transmission device between data centers, high-performance computers, and large-capacity memory devices. It usually meets the industry standard electrical interface and transmits data by the superiority of fiber optic cable and electrical-to-optical conversion.

While AOC reaches can extend to the limits of the optical technology used (100-200m), installing a long 100m cable, complete with an expensive transceiver end, is difficult in crowded data center racks so the average reach typically used is between 3-30m. Only one “oops” per cable allowed. Damaging the cable means replacing it as it cannot be repaired in the field. AOCs are typically deployed in open access areas such as within racks or in open cable trays for this reason.

Gigalight 25G SFP28 Active Optical Cables (AOCs) are direct-attach fiber assemblies with SFP28 connectors, compliant with 25G Ethernet IEEE 802.3by 25GBASE-SR standard. They are suitable for short distances and offer a cost-effective solution to connect within racks and across adjacent racks. The length is up to 70 meters using OM3 MMF and 100 meters using OM4 MMF.

The Advantages of Gigalight 25G SFP28 AOC

Low power consumption <1W

The pre-FEC bit error ratio (BER) is guaranteed to meet E10-8 25.78125Gb/[email protected], 55℃,  Better than the IEEE pre-FEC BER of less than 5 E-5.

Mature COB technology

Low Cost

High capacity, timely delivery

CE, UL,  RoHS, GR-468 test report


The power and cost savings caught the eye of the Ethernet hyperscale and enterprise data center builders and has since become a popular way to link Top-of-Rack switches upwards to aggregation layer switches such as End-of-Row and leaf switches. Several hyperscale companies have publicly stated their preferred use of AOCs for linking Top-of-Rack switches. Additionally, single channel (SFP) AOCs have become very popular in high-speed, NVMe storage subsystems. Some hyperscale builders often run 10G or 25G AOCs from a Top-of-Rack switch to subsystems at reaches greater than DAC limits of 3-7m.

25G Low-Cost AOC

25G Ethernet, or 25Gigabit Ethernet (25GbE), is developed by IEEE 802.3 Task Force P802.3by. The IEEE 802.3by standard uses technology defined for 100Gigabit Ethernet implemented as four 25Gbps lanes (IEEE 802.3bj). Actually, 40G and 100G have already existed before the emergence of 25G. However, 25G Ethernet can provide a more convenient path to Ethernet speeds of 50G, 100G and beyond. With 25G, network operators are no longer to use 40G Ethernet (using four lanes of 10G) to migrate to 100G but using 4 lanes of 25G. The article introduces low-cost 25G AOC.

What Is A 25G AOC?

25G AOC can be overcome the bandwidth limitation of traditional high-speed cable, and the 25G AOC can provide an ideal alternative solution for high-speed cable and short-distance SFP28 optical transceiver, and the signal is more complete and higher performance. It is widely used in high-speed, high-density, and low-power data center networks.

The 25G AOC consists of optical transceiver devices at both ends and composed of different length of OM3 or OM4 multimode optical fibers. The transceiver devices at both ends can provide the function of photoelectric conversion and optical transmission. This function ensures data transmission stability and application flexibility.

The 25G SFP28 AOC is designed to operate over multimode fiber systems using a nominal wavelength of 850nm. The electrical interface uses a 20-contact edge type connector.

Features of Gigalight 25G SFP28 AOCs

● Hot-pluggable SFP28 form-factor connectors

● Transmission data rate up to 25.78Gbps

● 850nm VCSEL laser

● PIN photo-detector

● Internal CDR circuits on both receiver and transmitter channels

● Low power consumption < 1W per end

● Length up to 70m using OM3 MMF and 100m using OM4 MMF

● Operating case temperature range 0°C to +70°C

● 3.3V power supply voltage

● RoHS-6 compliant (lead-free)

Why Choosing Gigalight 25G SFP28 AOCs?

The Gigalight 25G SFP28 AOCs are direct-attach fiber assemblies with SFP28 connectors, compliant with 25G Ethernet IEEE 802.3by 25GBASE-SR standard. They are suitable for short distances and offer a cost-effective solution to connect within racks and across adjacent racks. The length is up to 70 meters using OM3 MMF and 100 meters using OM4 MMF.


Gigalight offers 25G SFP28 AOC to enable short reach options, as well as a range of optical transceivers in an SFP form factor for various fiber types and reach requirements.

A Widely Recognized Innovator That Meets Tomorrow’s Demands

It is crucial that the ability of continuous innovation is the source of sustainable development for a company. Gigalight is able to provide cost-effective products keeping up the times for customers. Gigalight designs products that meet the increasing demands for network bandwidth, data storage and so on. As an innovator in optical communication, Gigalight delivers specialist service, dependability and performance at competitive prices.

Gigalight has founded in 2006, is headquartered in Shenzhen, China. We have opened the Wuhan R&D Center in 2017. And we have representative offices in Russia, Taiwan. North America, Europe and India centers are in preparation. We cooperate with key channel distribution partners around the world.

We mainly focus on Internet operators such as Baidu, Alibaba, China Unicom, China Telecom and other traditional operators as well as data communications equipment manufacturers in China. Our overseas markets center on telecommunication, Internet operators and equipment suppliers in North America, Russia, Brazil, Israel, India, etc.

Our Innovation Road

In 2006–2009, Gigalight was committed to the R&D and production of optical components (from 100Mb to 10Gb/s) and built the global channel market of optical transceivers.

In 2010–2011, Gigalight launched 10G/40G/120G active optical cables for data center and high-performance computing applications.

In 2012–2013, Gigalight entered the passive optical components market and HD video communication market.

In 2014–2015, Gigalight completed the commercialization of its 10G/40G active optical cables in the data center.

In 2016–2017, Gigalight began to offer 25G/100G optical modules and active optical cables to customers worldwide.

In 2018, Gigalight was committed to large-scale production of 100G optical transceivers and accelerates the development of 200G/400G data center optics, coherent optics, 5G optical transceivers and 5G custom passive optical components.

In 2019, Gigalight is committed to developing 5G and the Next–Generation Data Center optical interconnection market.

At present, we obtained 5 items software copyright, invention patent more than 10 items and national patent total more than 100 items. The Gigalight R&D department has about 150 engineers which account for 25% of the company. And most of them are Master Degree or above.

Innovative Design Concept


Creative optical engine design

Creative automatic producing


Updated ID design

Updated Layout design


Complete FEMA design

Complete TR-468 qualified


Performance uniformity

Continue developing

Our Creations

Optics Micro Design

Reliability Design of Hardware

Uniformity Design

Visual Manufacturing and Cloud Design

Our Strengths

Gigalight will also continue developing its automatic production line, a creative production solution including Array Eutectic Soldering and a Passive coupling system, which it hopes will lead to a 200% increase in production capacity. These new processes should bring more products to the market in 2019.


Gigalight have achieved remarkable growth and wide recognition around the world based on the decade’s experiences.

At present, we have successfully developed 200G AOC and 400G AOC products based on PAM4 modulation technology. And we also developed mini TO platform with innovate design, which greatly reduced the cost for 40G/100G/200G SM products. The self-research project has made a great success in the automated production line. At the same time, a great breakthrough has been made in the coherent field, 100G CFP–DCO digital coherent optical transceiver with ultralow power consumption have been successfully developed. In 2019, Gigalight will commit to the next–generation data center, 5G and so on.

What Is 100G Digital Coherent Optical Receiver?

The backbone optical communication networks are an essential infrastructure supporting the networked society. They are used for the internet phone and video demand services and for business activities and public services and offices in order to provide more stress–free communication and better services.

Here introduce 100G technology a 100 gigabit per second digital coherent optical receiver which can be used to transmit 10 terabits per second of data over a single fiber.

What Is Digital Coherent Transmission Technology?

Let’s outline the history of the technical development that allows us to send a large capacity of information over an optical fiber before explaining this.

Time–Division Multiplexing

The first development was the use of time–division multiplexing. This made it possible for a single fiber to carry data at 10 gigabits per second.

Wavelength–Division Multiplexing

The next–generation was to adopt wavelength–division multiplexing by using 40 wavelengths each capable of 40 gigabits per second transmission it became possible to send 1.6 terabits per second of data over a single fiber.

Digital coherent Transmission

Now comes digital coherent transmission which is the most attention-grabbing technology today. This technology increases transmission capacity by using optical phase and polarization information the receiver extracts information by mixing the received light with a light from a local light source. Since a laser beam is normally polarized, it is possible to double the transmission capacity by using two orthogonal E polarized waves as different channels. In addition, instead of using binary values of on and off.

This technology makes use of four values of optical phase information thereby further doubling the transmission capacity. Consequently, the volume of information that can be carried is quadrupled.

We have implemented a system base on 28 to 32 gigabit per second transmission. We have doubled the transmission capacity by using phase information and further doubled it by using polarization information thereby achieving 100 gigabits per second transmission over a single wavelength by using about 100 wavelengths. It is possible to achieve 10 terabits per second transmission on a single optical fiber.

An optical receiver receives the phase and polarization information of digital coherent optical signals. It consists of three elements a passive optical circuit which is a silica base planar lightwave circuit or PLC a high–speed photodiode or PD array which is an optical semiconductor and a transimpedance amplifier which is a high–speed electronic device. This means that to implement a high-quality optical receiver. It is necessary to integrate silica-based PLC technology, optical semiconductor technology and high–speed electronic device technology.


Coherent optics provides the performance and flexibility to transport significantly more information on the same fiber. Coherent optical technology forms the foundation of the industry’s drive to achieve transport speeds of 100G and beyond, delivering terabits of information across a single optical fiber. And coherent optics enables greater network flexibility and programmability by supporting different baud rates and modulation formats. This results in greater flexibility in line rates, with scalability from 100G to 400G and beyond per single signal carrier, delivering increased data throughput at a lower cost per bit.

Gigalight 100G CFP-DCO Digital Coherent Optical Transceiver is a hot-pluggable CFP form-factor optical module designed for high-speed optical networking applications including 100-Gigabit Ethernet and OTU4. The CAUI and OTL4.10 electrical interface and MDIO management interface are built in the module.

The 100G CFP-DCO module converts 10-lane 10Gb/s electrical data streams to 128G DP-QPSK optical output signal in Egress and also converts DP-QPSK optical input signals to 10-lane 10Gb/s electrical data streams in ingress. This 10-lane 10Gb/s electrical signal is fully compliant with 802.3ba CAUI specification and OIF-CEI-03.1 specification and allows FR4 host PCB trace up to 25cm. Gigalight is committing to develop the 100G CFP-DCO module to provide innovative and cost-effective products for the customer.

What Is SFP?

SFP stands for Small Form-Factor Pluggable. It is a compact, hot-pluggable transceiver used for both telecom and datacom applications.

SFP module has two ports, one port has laser inside, which is the transmitter side. The other port has a photodetector inside, which is the receiver side. So basically, SFP is a transceiver module, since it has transmitter and receiver in a single unit.

Which Components Make Up the SFP Optical Module?

The SFP optical module is composed of laser, circuit board IC and external accessories. The external accessories include shell, unlocking part, buckle, base, gripper, rubber plug, PCBA, and the color of gripper can help you to identify the parameter type of the module. For the types of SFP module, there are many types for SFP module such as BIDI-SFP, Electrical interface SFP, CWDM SFP, DWDM SFP, SFP+ transceivers and so on. In addition, for the same type of XFP, X2, XENPAK optical transceivers, SFP optical transceivers can not only be directly connected with it, but also have the feature of lower cost than it.

How Are the SFP modules used on the PCB board?

The following picture shows a perspective view of the SFP module, so you can clearly see its mechanical outlines.


Gigalight 10G SFP+

SFP module’s mechanical interface and electrical interface are specified by a multi-source agreement, also called MSA.

MSA is an industrial group composed of many network component vendors, such as Finisar, Fujikura, Lucent, Molex, Tyco, etc.

Engineers from these major vendors came together and made a design that everybody agreed upon. So based on this MSA specification agreement, these companies can make products that can work together in a system without compatibility issues. It is almost like an industry standard.

SFP was designed based on the bigger GBIC interface, but SFP has a much smaller footprint in order to increase port density. That is why SFP is also called mini-GBIC.

SFP modules are classified based on the working wavelength and its distance reach. Let’s take a look at the list here.

For multimode fibers, the SFP module is called SX. SX modules use 850nm wavelength. The distance that the SX module supports depends on the network speed. For 1.25 Gbps, the reach is 550 meters. For 4.25 Gbps, SX modules support 150 meters.

For single mode fibers, there are a lot of choices. I am listing the most common types here.

LX modules use 1310nm wavelength laser and support up to 10km reach. ZX modules use 1550nm wavelength laser, and supports reach up to 80km. ZX modules also use 1550nm laser but support up to 120km reach.

There are also CWDM and DWDM SFP modules, which use multiple wavelengths in the module to support even more bandwidth and distance.

And don’t forget, the MSA also defined a SFP module based on the UTP twisted pair copper cables. But this SFP module currently only supports Gigabit Ethernet.

Traditional SFP modules support the speed up to 4.25 Gbps. But an enhanced version, which is called SFP+, supports up to 10Gbps, and is becoming more popular on 10Gigabit Ethernet and 8Gbit Fibre Channel.

SFP transceivers are used on all types of network applications, including telecommunication, data communication, Storage Area Network.

On the protocol side, there are SFP modules that support SONET/SDH, Gigabit Ethernet, Fibre Channel, Optical Supervisory Channel, and more.


Gigalight is committing to providing cost-effective products for customers. 10G optical modules such as 10G SFP+, 10G CWDM SFP+, 10G DWDM SFP+ can be provided by Gigalight. Gigalight has been investing in the development of colored (CWDM/DWDM) transceivers which have been widely sold around the world. You can find more relevant information from Gigalight’s official website.