A photonic integated circuit gives long haul optic fibre cable the ability to carry much bigger loads than was possible before its development by Infinera in the USA.
A photonic integrated circuit (PIC) is conceptually very similar to an electronic IC. While the latter integrates many transistors, capacitors and resistors, a PIC integrates multiple optical components such as lasers, modulators, detectors, attenuators, multiplexers/de-multiplexers and optical amplifiers.
Large-scale PICs, like their electronic counterparts, extend the scope of integration so that upwards of dozens or more distinct optical components are integrated into a single device.
Photonic integrated circuits can be further characterised into passive and active PICs. Passive PICs, typically built using silica materials, integrate functions such as filters, wavelength multiplexers, couplers, and photonic switches.
They don’t generate or amplify light, but are “light in, light out”. Active PICs, by contrast, integrate optoelectronic functions such as lasers, modulators, PIN detectors, and amplifiers.
They may include passive devices as well. Active PICs, which can be used to convert between electronic signals and optical signals, are built using compound semiconductor materials such as indium phosphide (InP) so that they may generate, amplify, or detect light.
In optic fibre systems the PIC enables a seamless transmission of high capacity data between the optical and electrical domains. Based on the new PIC, Infinera developed a dense wavelength division multiplexing system capable of transmission of data for up to 2400 km without regeneration, but with amplification in between.
The amplification occurs in the optical domain, and the distance between amplification sites is dependent on the characteristics of the optic fibre cable, and can be as high as 250 km.
PIC–based DWDM technology was deployed for the first time in South Africa by Technology Integrated Solutions (TIS) to extend the Seacom submarine cable to a point of presence (POP) in Johannesburg. The project involved the installation of 300 Gbps DWDM transmission capacity between the submarine cable landing station at Mthunzini in KwaZulu-Natal and Teraco Park in Johannesburg. The Seacom link to Gauteng cable uses the current generation of Infinera equipment that carries 10 Gbps per wavelength.
Technology Integrated Solutions (TIS) as the local partner of Infinera is responsible for the operation and maintenance of the DWDM network. The company has committed to a service level agreement with Seacom of under four hours should a breakdown occur. “To achieve this we have deployed a team of engineers at five strategic points along the route between Mthunzini and Johannesburg,” said Andrew Matseke, MD of TIS.
“Cable characterisation was an important aspect of the planning process to ensure that the amplification was installed at the correct intervals. While the optimum distance can be as high as 250 km, it ultimately depends on the quality and type of fibre used. We tested the optic fibre cable between Johannesburg and Mthunzini and the final network design was based on the characterisation of the cable. We also have a lab at our premises in Midrand, where we have an Infinera network installed for demo and test purposes. The network is configured in a ring using a drum with 50 km of fibre cable.”
During the official launch of the Seacom network in August 2011, Infinera and TIS initiated a 500 Gbps trial with the next generation of Infinera equipment that uses 5 x 100 Gbps channels of coherent optical transmission. The trial was executed in a loop over more than 1700 km between Johannesburg and Mthunzini.
The Seacom project was executed by two teams, consisting of three and four members respectively from the TIS technical team; in addition Infinera provided two installation engineers and a project manager. One team started with the installation of the nodes from Midrand working towards the KwaZulu Natal coast.
The second team worked from Mthunzini in KwaZulu Natal moving inland. A total of 15 nodes consisting of twelve repeater sites and three add-drop nodes were installed over a period of seven working days.