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We all know that QSFP 100G DR1, FR1 and LR1 all belong to Single Lambda Transceivers, which uses a single 100G PAM4 laser chip internally. But why different lasers are used for them, we will analyze it from the perspective of the optical transceiver design, application scenarios, and the characteristics of the laser itself.
What is 100G DR1, FR1, LR1?
From the article ‘The difference between 100Gbase DR1, FR1, LR1‘, we can learn that, QSFP 100G DR1 / FR1 core standards are defined by the 100G Lambda MSA (Multi Source Protocol) organization. The original intention of their design is to cooperate with the 400G DR4/FR4 module for 1 to 4 Breakout, mainly serving the internal of ultra large scale data centers and providing them with a highly cost-effective interconnection solution.
While 100G QSFP28-LR1 module is not only complying with the MSA protocol, but also follows the IEEE 802.3cu standard. It is more commonly seen as a low-cost alternative to traditional 100G LR4 QSFP28 (4-channel 25G) for single link transmission in industrial parks or metropolitan area networks.
| Item | 100G DR1 (short distance) | 100G FR1 (medium distance) | 100G LR1 (long distance) |
| Max. distance | 500 m | 2 km | 10 km |
| Typical laser | Silicon Photonics / DML | DML / EML | EML (high-end) |
| reception sensitivity | Poor (-4.0 dBm to -5.9 dBm) | Medium (-4.5 dBm to -6.4 dBm) | Best (-6.1 dBm to -7.7 dBm) |
| link budget | Minimum (about 3.0 dB) | Moderate (about 4.0 dB) | Maximum (approximately 6.3 dB) |
| power consumption | Approximately 3.5W to 4.5W | Approximately 3.5W to 4.5W | Approximately 3.5W to 4.5W |
| working wavelength | 1311nm (single wavelength) | 1311nm (single wavelength) | CWDM 1311nm (single wavelength) |
| interface type | Duplex LC | Duplex LC | Duplex LC |
| 400G interconnection | Standard configuration for 400G DR4 breakout | Corresponding to 400G FR4 | Corresponding to 400G LR4 (6km/10km) |
| Main applications | Cabinet room/spine leaf architecture | Between buildings in the park | Metropolitan Area Network/Long Distance Backbone |
CWDM EML vs 1311nm EML
The core chips of CWDM EML and 1310nm EML may both be EML lasers, but due to significant differences in wavelength arrangement, working environment, and temperature control requirements, there are essential differences between them.
1311nm EML / 1310nm EML：LAN-WDM technology (refrigeration type)
In the IEEE standard LAN-WDM (Local Area Network Wavelength Division Multiplexing) used for 100G LR4 / ER4, the center wavelength of the first channel (L0) is 1310.92 nm. Some manufacturers write 1310nm in the datasheet as a general term for integers, while others write 1311nm as rounding. In the production and technical exchange of optical transceivers, 1311nm EML and 1310nm EML often refer to lasers in the same channel (Channel 1).
- Technical features: The wavelength spacing of LAN-WDM is very narrow (only 4.5 nm, with four channels of 1295.56,1300.05,1304.58,1310.92 nm). Due to the channel being too crowded, even a slight wavelength drift of 1 nm can cause severe crosstalk. Therefore, the 1311nm (1310nm) EML must be equipped with a TEC (thermoelectric cooler) for strict temperature control, which belongs to the cooling type laser.
CWDM EML: CWDM technology (uncooled/coarse wavelength division)
The wavelength spacing of CWDM is very wide, up to 20 nm, such as the common 4-channel: 1271, 1291, 1311, 1331 nm.
- Technical features: Due to the large spacing of 20nm, wavelength drift with temperature is allowed (laser temperature drift is generally 0.08nm/℃). Therefore, CWDM EML lasers do not require TEC cooling chips during design and belong to uncooled lasers. Its core task is to run naked in a wide temperature range (usually 0 ℃~70 ℃ or even industrial grade -40 ℃~85 ℃), achieving high dispersion tolerance through an external modulator (EAM). It is commonly used in high-performance versions of 100G CWDM4 (2km) or 200G/400G FR4 modules.
| Transmitter type | 1310nm / 1311nm EML | CWDM EML |
| Wavelength system | LAN-WDM (IEEE 800-GHz) | CWDM (ITU-T G.694.2) |
| Accurate center wavelength | 1310.92 nm (extremely precise) | Depending on the channel, such as 1311 nm integer (allowing left and right drift ± 6.5nm) |
| Wavelength channel spacing | 4.5 nm (extremely narrow, prone to crosstalk) | 20 nm (extremely wide, high fault tolerance) |
| Is TEC cooling included | Must bring (cooled) | No need to bring (uncooled) |
| Typical transmission distance | 10km-40km | 2km-10km |
| Cost and power consumption | High cost and high power consumption (due to TEC power consumption) | Relatively low cost and low power consumption |
| Typical application modules | 100G LR4 / ER4、200G LR4、400G LR8 | 100G CWDM4 、200G/400G FR4 |
After understanding the specific differences between the three modules and the differences between the two lasers, let’s take a look at the design intentions of the three modules:
Why both DR1 and FR1 use 1311nm (LAN-WDM)?
✅Perfect integration with 400G DR4/FR4 Breakout requirements:
In the data center, the four lasers inside the 400G DR4 module (4 independent 100G fibers, transmitting 500m) all use a wavelength of 1310.92nm (1311nm) according to the IEEE 8002.3 standard.
In order for a 400G port on the switch to be directly connected to four standard 100G ports through a 1 to 4 breakout cable, the wavelengths of these 4x 100G modules (i.e. 100G DR1) must be exactly the same as 400G DR4. Therefore, the selection of 1311nm EML for DR1 and FR1 is purely for ecological alignment, ensuring that 100G modules and 400G/800G parallel ports can communicate freely.
Why does LR1 choose CWDM EML?
At the 10km LR1 stage, its compatibility target has changed. Its mission is not to interface with multi fiber parallel DR4, but to interface with single fiber wavelength division multiplexing 400G FR4/LR4.
Why choose 1311nm CWDM EML for LR1?
Because 1311nm happens to be the third channel among the four channels of CWDM (backward compatible). When upgrading your network from 100G, or requiring single channel docking with 400G CWDM systems, or even low-cost wavelength division multiplexing (WDM), the CWDM chip of LR1 can be seamlessly integrated into existing CWDM MUX/DEMUX hardware without the need to customize special filters specifically for LR1.
What would happen if three were unified into one type of laser?
From the above analysis, we can see that the 1311nm EML of DR1/FR1 is cooled with TEC, and its wavelength is locked at 1310.92nm±1nm. Its spectral line is extremely narrow and its accuracy is extremely high. The CWDM 1311nm EML of LR1 is uncooled without TEC cooling. Its wavelength is allowed to drift freely with the external temperature (0 ℃ to 70 ℃) between 1304.5nm and 1317.5nm in the standard.
① If the DR1 chip is used for LR1: The expensive and power consuming TEC refrigeration chips must be added to LR1, resulting in a surge in power consumption and cost of the LR1 module, and losing market competitiveness.
② If the LR1 chip is used for DR1/FR1: Due to the lack of cooling in the CWDM chip of LR1, the wavelength will significantly drift away when the temperature changes (possibly up to 1306nm or 1315nm). Once it drifts away, the precision filter at the 400G DR4 receiver will directly treat it as “stray light” or filter it out, causing the Breakout link to be completely disconnected.
Conclusion
- The selection of 1311nm (LAN-WDM technology) for QSFP 100G DR1/FR1 is to ensure perfect one to four interoperability with the internal 400G/800G high-speed parallel interface of the data center.
- The selection of CWDM 1311nm laser and wavelength for LR1 is aimed at directly reusing the huge CWDM industry chain and wavelength division devices 400G FR4/LR over a long distance of 10km.
