The need for one-fibre-technology may result from limited resources of fibre and high cost of fibre lease in situations when we want to carry out a project but don’t have our own fibre
It may also be the case that for years it was sufficient to realize transmission over one optical fibre, but today we have to face the challenge of realizing the transmission of as much as 40 GbE or even 100 GbE throughput using the same infrastructure. Thus, no matter whether we work on a new project or want to develop the existing one, it is not easy to provide such a throughput over one fibre.
Thus, to start a project, we must get prepared for sending and receiving data simultaneously over one fibre. Help comes with wavelength multiplexing technology (WDM). Here, we will focus on DWDM technology as this is the only one which enables us to provide the throughput of 40 GbE or 100 GbE. But is it possible to do it over one fibre?
To answer this question, we need to have a closer look at the optical transceivers available on the market. From previous articles you already know that CFP/CFP2 coherent transceivers and QSFP28 DWDM transceivers will enable you to achieve the throughput mentioned above. But can it be run over a single fibre?
Key elements in a standard coherent transceiver are PM-QPSK modulator and PM-QPSK integrated receiver which require a tunable laser, as it is illustrated in the schematic below.
If we make a connection according to the schematic, then both transmitting and receiving will be realised over the same wavelength, which makes this solution unsuitable for one-fibre transmission.
Of course, it is technically possible to create a transceiver consisting of two independent modules of a tunable laser and to enable the transmitter to work on a different wavelength than the receiver. In practice, however, such a solution would significantly influence the price of the transceiver, and in consequence such transceivers are not produced. And how is this solved in QSFP28 DWDM transceivers?
From the article: Data Centre Interconnect you already know that such transceivers are used in DWDM technology and that they are compliant with 100 GHz grid. The primary difference is that the receiver doesn’t have to be connected with the laser source, and thus the wavelengths of the receiver and transmitter don’t have to be identical. Different wavelengths are necessary to facilitate transmission over one fibre.
One-fibre technology makes it possible to realize connections of up to 100 GbE. What’s more, the application of DWDM technology enables sending several of such data streams. In order to do it, we need to use a properly prepared optical line system and QSFP28 DWDM transceivers.
100 GbE and a single fibre… it sounds like OPEX optimization!
