The question in the title keeps many network owners awake at night. While extending 1 Gbps or 10 Gbps transmission over a longer fiber span is usually straightforward, delivering 100 Gbps over distance is far from trivial.
We have already raised this topic in previous articles from the “How to launch…” series (40G on a single fiber, 40G on a single fiber when the distance exceeds 40 km). Now it is time to provide an answer.
Large telecom operators handle this with ease, so the first idea is usually to copy their approach and use solutions from the major optical transport vendors. Everything looks promising until you receive a quote in your inbox… does it really have to cost that much?
Paradoxically, the answer is YES, it really has to cost that much. Wavelength-division multiplexing, optical amplifiers, coherent optics and OTN platforms are complex technologies, and they come with a price tag. But this raises a different and more practical question: as a network owner, do you actually need such a platform? You just want to carry a single 100 Gbps service – can this be done more cost-effectively?
To that question the answer is also YES – you can transport a single 100 Gbps link over a longer distance at low cost. How? This is where it may surprise you: the solution uses a standard QSFP28 LR4 optical transceiver. On the optical side this module transmits over four wavelengths: 1295 nm, 1300 nm, 1304 nm and 1309 nm.
Looking more closely at the parameters of this module, you will notice that it offers an optical link budget of around 6 dB. In the second optical window this allows you to reach only a distance of several to a dozen or so kilometers. Is that already a “long distance”?
For us, definitely not. Under “long distance” we typically mean spans of about 50 km, 80 km, 100 km or even more. So how do we get there? The key is to use an optical amplifier – more precisely a Semiconductor Optical Amplifier (SOA). Such an amplifier operates in the 1290–1330 nm band, which means it can amplify all four wavelengths generated simultaneously by the QSFP28 LR4 module mentioned above. This provides up to 20 dB of gain, which, even in the second optical window, translates into an additional 40–50 km of reach. Sounds interesting? And what if you need more than 50 km? You simply add another SOA amplifier and regenerate your optical signal once again.
LightOptics offers both the QSFP28 LR4 transceivers and the SOA amplifier in its portfolio.
SOA amplifier: LO-SOA-1U – a 1U “pizza box” equipped with two power supplies, AC and DC. The device can be managed via WEB and SNMP. During installation you can also configure it locally using the buttons and display on the front panel.
QSFP28 LR4 transceiver: LO-QSP28-100G-LR4 – a QSFP28 module that enables 100 Gbps transmission over a distance of several to a dozen or so kilometers.
So we now have an answer to the question raised in the earlier articles: what if 40G is not enough and you need 100G? One question remains: how do you carry 100 Gbps over a single fiber? Interested?
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