Development Background of Coherent Optical Communication

 As early as the 1980s, when optical communication was just emerging, developed countries such as the United States, the United Kingdom, and Japan had already carried out theoretical research and experiments on coherent optical communication and achieved good results.

For example, in 1989 and 1990, AT&T and Bell in the US successively carried out a 1.7Gbps FSK on-site coherence transmission experiment with 1.3μm and 1.55μm wavelengths without any relay between the Rolling Creek ground station and Sunbury hub in Pennsylvania in 1989 and 1990, and the transmission distance reaches 35 kilometers.

Later, in the 1990s, experts found that the increasingly mature EDFA (Erbium-Doped Fiber Amplifier) and WDM (Wavelength Division Multiplexing) technologies could solve the problems of relay transmission and capacity expansion of optical communication more simply and effectively. As a result, the technical research of coherent optical communication has been neglected.

Around 2008, with the outbreak of the mobile Internet, the data traffic of the communication network increased rapidly, and the pressure on the backbone network increased sharply. At this time, the potential of EDFA and WDM technology has become smaller. Optical communication manufacturers urgently need to find new technological breakthroughs, improve the transmission capacity of optical communication, meet user needs, and relieve pressure.

Manufacturers found that with the maturity of digital signal processing (DSP), optical device manufacturing, and other technologies, coherent optical communication based on these technologies is just a good choice to break the technical bottleneck of long-distance high-bandwidth optical fiber communication. As a result, it is logical that coherent optical communication has moved from behind the scenes to the front of the stage.

HTF can help you design coherent 400G/200G/100G DWDM/OTN solution, DWDM Single lamda 100G/200G/400G Dual fiber/Single fiber Ultra long distance transmission.

What is Coherent Optical Communication?

Many people may think that coherent optical communication is the use of coherent light for transmission communication, which is incorrect actually. Coherent optical communication and non-coherent optical communication basically use lasers without any essential difference in terms of light.

The reason why coherent optical communication is called “coherent optical communication” does not depend on the light used in the transmission process, but on the use of coherent modulation at the transmitting end and the use of coherent technology at the receiving end for detection.

The difference between the two is at both ends, not on the transmission path. The technology of the receiving end is the core of the entire coherent optical communication, and it is also the main reason why it is so powerful. Under the same conditions, compared with traditional non-coherent optical communication, the receiver of coherent optical communication can improve the sensitivity by 20db– 100 times more sensitive than the non-coherent communication! With the help of this 20db, the communication distance of coherent optical communication can reach the level of thousands of kilometers (non-coherent light is only about tens of kilometers).

HTF can help you design coherent 400G/200G/100G DWDM/OTN solution, DWDM Single lamda 100G/200G/400G Dual fiber/Single fiber Ultra long distance transmission.

What is Coherent Light?

 Before introducing coherent optical communication, let’s briefly introduce what coherent light is. We often talk about “coherence”, and everyone understands that it means “interrelated or involved”. Coherence of light means that two light waves meet the following three conditions at the same time in the process of transmission:

1. The frequency (wavelength) is the same;

2. The vibration direction is the same;

3. The phase difference is constant.

Such two beams of light can produce stable interference with each other during transmission. This interference can be either constructive interference (strengthening) or destructive interference (cancellation). As shown below:

It is obvious that constructive interference can make light waves (signals) stronger.

HTF can help you design coherent DWDM solution.

ROPA REMOTE OPTICAL PUMP AMPLIFIER

 Extended spans between two nodes with remote signal amplification

• used in long single-span lines to increase the distance between two communication nodes
• configurations with counter and forward pumping are possible

The Remote Optical Pumping Amplifier (ROPA) consists of two functional units such as a passive part (sealed sleeve with erbium fiber) and an active part (pumping unit near the 1480 nm wavelength). The passive part is located far from the service nodes in the optical cable system itself.

The pumping of such amplifiers is carried out remotely via a telecommunications or additional fiber. Configurations of ROPA amplifiers are possible with counter (pump radiation is delivered from the receiving part) and forward pumping (pump delivery from the transmitting part).

ROPA increases the distance between two communication nodes.

HTF can help you design DWDM solution, >150km or more distance.

What Is DWDM Technology ?

 DWDM stands for Dense Wavelength Division Multiplexing, which is an optical multiplexing technology used to increase bandwidth over existing fiber optic backbones. The “dense” here refers to the fact that DWDM technology supports more than 80 separate wavelengths, each about 0.8 of a nanometer (nm) wide on a single optical fiber.

Working Principle
DWDM technology increases the network capacity and makes efficient use of bandwidth. The data from various different sources is put together on optical fiber in which each signal travels at the same speed on its own light wavelength. At the receiver end, every channel is demultiplexed into original source, therefore different data formats with different data rates such as Internet data, Synchronous Optical Network data (SONET), and asynchronous transfer mode (ATM) data can be transmitted together at the same time through one optical fiber. The transmission capability of DWDM is 4 to 8 times of TDM (Time Domain Multiplexing) and here EDFAs (Erbium doped optical amplifier) are deployed to boost the strength of signal. The signal can be transmitted to more than 300 km before regeneration.

If want to choose suitable DWDM, welcome to contact HTF team. www.htfuture.com and www.htfwdm.com

200G QSFP-DD LR4

 Supports 200GBASE-LR4;

Lane bit rate 53.125 Gb/s with PAM4;
Up to 10km transmission on SMF;
LAN WDM laser and PIN receiver;
200GAUI-8 Electrical interface with 8 Lanes 26.5625Gb/s NRZ high-speed signal;
QSFP-DD MSA package with duplex LC connector;
Compliant with IEEE 802.3cn 200GBASE-LR4
Single +3.3V power supply;
Maximum power consumption 10W;
Operating case temperature: 0 to +70 °C;
Compliant to QSFP-DD CMIS & QSFP-DD MSA HW standard;
Complies with EU Directive 2015/863/EU;

200G QSFP-DD LR4 Application
200GBASE-LR4 Ethernet (PAM4)
5G Back-haul
Data center
Cloud application.

200G QSFP-DD ER4

 Supports 200GBASE-ER4

Lane bit rate 53.125 Gb/s with PAM4
Up to 40km transmission on SMF
LAN WDM laser and APD receiver
200GAUI-8 Electrical interface with 8 Lanes 26.5625Gb/s NRZ high-speed signal
QSFP-DD MSA package with duplex LC connector
Compliant with IEEE 802.3cn 200GBASE-ER4
Single +3.3V power supply
Maximum power consumption 10W
Operating case temperature: 0 to +70 °C
Compliant to QSFP-DD CMIS & QSFP-DD MSA HW standard
Complies with EU Directive 2015/863/EU

200G QSFP-DD ER4 Application
200GBASE-ER4 Ethernet (PAM4)
5G Back-haul
Data center
Cloud application.