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The core difference between CWDM DFB laser and ordinary DFB (distributed feedback) laser lies in the precise control of wavelength, the distribution of wavelength channels, and the process design of internal anti crosstalk.
Although they both belong to DFB lasers in terms of physical structure (with built-in Bragg gratings and extremely narrow spectral line widths), CWDM DFBs have undergone deep customization improvements to adapt to wavelength division multiplexing (WDM) technology.
Hereafter is a comparison of their depth in four dimensions:
Wavelength Distribution and Accuracy (core difference)
Ordinary DFB laser:
- The wavelength is relatively single and fixed: usually only serving standard communication windows, such as 1310nm or 1550nm.
- The center wavelength has a large tolerance: its actual emission wavelength allows for a wide drift range (for example, 1310±20nm or 1310± 10nm are both qualified). Because it is a “single person mono” transmission in fiber optics, with no other wavelengths of light nearby.
CWDM DFB laser:
- Strictly distributed in 18 designated channels: must strictly comply with the ITU-T G.694.2 international standard, with wavelengths ranging from 1271nm to 1611nm, and each channel strictly separated by 20nm (such as 1271, 1291, 1311) .. 1611nm）。
- The center wavelength tolerance is extremely small: its center wavelength control is extremely strict, usually requiring within ±2nm or even ±1nm. If the wavelength deviates too much, it will cause the other end’s multiplexer/demultiplexer (MUX/DEMUX) to be unable to recognize it, or it may rush into the adjacent channel and cause interference.
Temperature Characteristics and Wavelength Drift Control
Semiconductor lasers have a physical characteristic: for every 1 ℃ increase in temperature, the emission wavelength shifts towards longer wavelengths by about 0.08n~0.1nm.
- DFB laser: Due to the lack of strong anti crosstalk requirements, a temperature drift of a few nanometers does not affect single channel communication, so it has a high tolerance for slight wavelength shifts caused by operating temperature.
- CWDM DFB laser: In order to operate in an industrial wide temperature environment of -40 ℃~+85 ℃ and ensure that the wavelength drift does not exceed the filter bandwidth limit of ± 2.5nm, the doping process, grating design, and heat dissipation structure of its internal chip have been specially improved (usually using an “uncooled” design, but with extreme optimization for temperature drift suppression at the chip level).
Production, Manufacturing, and Selection Costs (Yield Rate)
- DFB: The production yield is very high. After wafer cutting, as long as the wavelength falls within a large range around 1310nm, it can be directly packaged into ordinary LX or LH modules.
- CWDM DFB: The grating manufacturing process is extremely difficult. Because we need to accurately produce a complete set (18) of wafers with specific wavelengths. During the screening process, only chips with wavelengths perfectly aligned with a specific channel (e.g. 1471nm ± 2nm) can be labeled with that channel. Therefore, the chip screening cost and technical threshold of CWDM DFB are much higher than those of ordinary DFB.
System Application
- DFB: used for point-to-point transmission (only one gigabit or ten gigabit signal runs on a single optical fiber), the most typical representative of which is the SRX-SFP-1GE-LH (1550nm 80km) long-distance optical module we discussed earlier.
- CWDM DFB: specifically designed for CWDM systems. It allows network engineers to simultaneously insert 8 or 16 completely different wavelengths (different services) of light sources through a wavelength division multiplexer on a pair (or even one) of optical fibers. This can directly increase the transmission capacity of optical fibers by 8 to 16 times without laying new optical cables.
Comparison Table – DFB vs CWDM DFB
CWDM DFB laser and ordinary DFB laser are essentially distributed feedback (DFB) lasers, which use built-in Bragg gratings to achieve single longitudinal mode output. The ordinary DFBs are mostly used for single wavelength transmission (such as 1310nm, 1550nm), while CWDM DFBs are designed specifically for CWDM systems, with wavelengths fixed on specific grids of ITU standards (1271nm-1611nm), specifically designed for multiplexed transmission.
| Item | DFB | CWDM DFB |
| Working wavelength | Commonly use standard 1310nm or 1550nm wavelength | Fixed in specific channels of CWDM (such as 1271, 1291… to 1611nm) |
| Center wavelength error | Loose (± 10nm~± 20nm) | Extremely strict (± 1nm~± 2nm) |
| wavelength stability | Extremely high requirements, strictly limited to the center wavelength to prevent dispersion limitation | Moderate stability requirements (allowing drift with temperature, as the channel spacing is 20nm) |
| Channel spacing | No channel concept (single channel transmission) | Strict 20nm channel spacing |
| temperature control | According to the transmission distance, it is divided into refrigerated type (with TEC) and uncooled type | Usually uncooled, utilizing electronic tuning, with lower cost |
| End to end receiving accessories | Ordinary standard optical receiver | Must be paired with CWDM MUX/DEMUX (wavelength division multiplexer) |
| main value | Pursuing ultra long distances for single transmission (such as 80km) | Pursuing multiple parallel streams and doubling bandwidth on a single optical fiber |
| Application scenarios | Single channel transmission, commonly used for ordinary single fiber bidirectional (BiDi) or unidirectional long-distance transmission | Coarse wavelength division multiplexing (CWDM) system, where multiple wavelengths are multiplexed on a single fiber to increase capacity |
Which optical fiber module use regular DFB lasers?
Ordinary DFB lasers are mainly used for medium to long distance (10km-40km), single channel point-to-point communication. This type of optical fiber module does not require the use of a wavelength division multiplexer (MUX/DEMUX), as only one wavelength runs in one fiber.
| Data rate | Compatible Modules | Yingda Part No. |
| 1G SFP Transceiver | 1000BASE-LX (10km): Some high-performance or industrial grade 1310nm 10km SFP modules will use DFB (low-end or commercial grade typically use cheaper FP lasers) | SFP-1.25G-LX |
| 1000BASE-EX (40km): 3100nm or 1550nm 40 km long distance module, basically fully using ordinary DFB | SFP-1.25G-EX | |
| 1G BiDi (single fiber bidirectional 10km-40km): a module that achieves bidirectional transmission within a single optical fiber (such as TX1310/RX1550nm), and its transmitter widely uses ordinary DFB. | SFP-1.25G-BX10-3155 | |
| 10G SFP+ Transceiver – The most mainstream application | 10GBASE-LR (10km): The most classic 10 Gigabit single mode SFP module, with a center wavelength of 1310nm, and a standard DFB laser across the industry. | SFP-10G-LR |
| 10GBASE-ER (40km): A 10G long-distance module with a center wavelength of 1550nm, equipped with a standard DFB laser. | SFP-10G-ER | |
| 25G/100G Core Network and Data Center Series | 25GBASE-LR (10km): A commonly used 25G 10km module for 5G front-end and enterprise network core layers, using 1310nm ordinary DFB. | SFP28-25G-LR4 |
| 100G LR4 (10km): Long distance interconnection module within the data center. Although it has 4 wavelengths internally (LAN-WDM), due to the high-precision LAN wavelength division standard used for its wavelengths (with a spacing of only 4.5nm, usually requiring a cooled electroabsorbent modulation laser EML), in some low-cost, non cooled simplified versions (such as 100G Lite-LR4), a regular DFB array with 4 specific wavelengths will be used. | QSFP28-100G-LR4; QSFP28-100G-LR4L |
What common optical fiber modules use CWDM DFB laser?
The CWDM DFB laser is designed specifically for coarse wavelength division multiplexing (CWDM) systems. As long as the optical fiber module model or parameters contain the “CWDM” character and the distance is between 10km and 80km, the CWDM DFB laser must be used internally.
At high speeds above 10 gigabit, engineers directly integrated a “micro wavelength division multiplexer” inside the optical fiber module to save fiber and interfaces inside the module.
| Data rate | Compatible Modules | Yingda Part No. |
| 10G CWDM SFP+series (the most classic) | 10G CWDM 10km/40km/80km optical module: The housing label of this type of module will not be fixed at 1310nm or 1550nm, but will accurately label the ITU standard wavelength (e.g. CWDM-SFP10G-1470 represents 1470nm). They must be purchased as a complete set (usually 8 or 16 modules with different wavelengths), inserted into the switch, and jointly connected to a CWDM multiplexer. | SFP-1.25G-CWDM-xx-10km; SFP-1.25G-CWDM-xx-20km; SFP-1.25G-CWDM-xx-40km; SFP-1.25G-CWDM-xx-80km; |
| 25G CWDM series (5G fronthaul mainstay) | 25G CWDM 10km/20km modules: widely used in 5G base station construction (fronthaul network). Due to the tight fiber optic resources from the base station to the data center, operators use 25G CWDM DFB modules to simultaneously transmit multiple 5G signals on a single fiber optic cable (the first six waves with commonly used wavelengths ranging from 1271nm to 1371nm). | SFP28-25G-CWDM-xx-10km; SFP28-25G-CWDM-xx-15km |
| Internal Wavelength Division Module for 100G/400G Data Centers | 100G CWDM4 (2km): Currently, it is one of the most mainstream 100G modules within large data centers. It encapsulates four CWDM DFB lasers with different wavelengths (1271, 1291, 1311, 1331nm) internally, and directly achieves a total speed of 100G on a pair of single-mode fibers. | QSFP28-100G-CWDM4 |
| 400G FR4/LR4 (2km/10km): The new generation data center 400G module also uses four CWDM DFB laser arrays based on PAM4 modulation technology internally. | QSFP-400G-FR4;QSFP-400G-LR4 |
How to identify the module use CWDM DFB or DFB laser?
In practical work, you can quickly determine through appearance labels and parameter descriptions:
1. Look at the wavelength description:
- The label states 1310nm, 1550nm, and a distance of ≥10km — it is regular DFB (or longer distance EML) laser.
- The label states special non-traditional wavelengths such as 1470nm, 1271nm, 1510nm– it is CWDM DFB laser.
2. Look at multi-channel integration:
- The module names are CWDM4 and FR4 (with the suffix “4” and indicating single mode 2km/10km) — the module integrates 4 CWDM DFB lasers internally.
