100G Single lambda QSFP28 vs. 100G Traditional 4 channels QSFP28.

Articles | 26.04.2021

In today’s world, the 100G optics is heavily deployed and mainly based on QSFP28 (Quad Small Form factor pluggable 25G) which, as the name indicates, uses 4 parallel 25G lanes of different wavelengths combined into one fibre or four separated 25G lanes for ribbon fibre applications, to achieve a 100G link. In such traditional case, the optical modulation format is based on NRZ (Non-return to Zero) which is the most prevalent modulation format.

The new standardized (MSA) 100G Single Lambda optics converts 4 electrical channels of 25G to a single 100G optical channel based on PAM4 (4 level Pulse Amplitude Modulation). This conversation is done by an internal DSP (Digital Signal processor).

We can quickly realize that one of the main advantages of Single lambda parts is reduced cost of optical components since only one transmitter and receiver is necessary instead of four of each for the traditional QSFP28.

Let’s take as an example the traditional QSFP28 LR4 compared to Single Lambda LR1.

	QSFP28 LR4	QSFP28 LR1
Form Factor	QSFP28	QSFP28
Max reach	10km	10km
Connector	LC	LC
Electrical interface	4x25Gbps	4x25Gbps
Electrical Modulation format	NRZ	NRZ
Optical interface	4x25Gbps	1×106.25Gbps
Optical Modulation format	NRZ with integrated MUX/DEMUX	PAM4 with Integrated DSP
TX	4x LAN-WDM LD	1x CWDM LD
RX	4x PIN	1x PIN
Power consumption	3.5W	3.5W
Standard	IEEE 802.3-2012	100G Lambda MSA
Skylane P/N	Q28QD010C0xD	Q2C31010C00F
Pros	– No FEC Required	– Less points of failure – New technology – Better lifetime- Cost down solution
Cons	– Old technology, no way to have more cost down – Technology jungle	– Small latency induced by the Integrated FEC (Forward Error Correction)

Where does the single lambda attraction come from?

Taking into account that a single lambda part can be use in the exact same scenario as a traditional part (point to point), one of the major improvements using them is the datacenter breakout application for 400G links allowing a smooth migration from 100G to 400G connections.