{"id":6141,"date":"2025-08-12T10:57:28","date_gmt":"2025-08-12T02:57:28","guid":{"rendered":"https:\/\/ascentoptics.com\/blog\/?p=6141"},"modified":"2025-08-12T18:04:27","modified_gmt":"2025-08-12T10:04:27","slug":"understanding-the-100g-qsfp28-cwdm4-optical-transceiver","status":"publish","type":"post","link":"https:\/\/ascentoptics.com\/blog\/understanding-the-100g-qsfp28-cwdm4-optical-transceiver\/","title":{"rendered":"Understanding the 100G QSFP28 CWDM4 Optical Transceiver"},"content":{"rendered":"

The 100G QSFP28 CWDM4 optical module is a high-performance, cost-effective solution for short-to-medium distance interconnects in modern data centers, enterprise campus networks, 5G midhaul, and cloud backbone networks. Leveraging coarse wavelength division multiplexing (CWDM) technology, it achieves 100Gbps transmission over single-mode fiber with low latency, reduced power consumption, and simplified fiber infrastructure, making it an ideal choice for next-generation high-bandwidth applications.<\/p>\n

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What is 100G QSFP28 CWDM4\uff1f<\/strong><\/h2>\n

100G QSFP28 CWDM4<\/a> is a 100Gbps optical transceiver based on Coarse Wavelength Division Multiplexing (CWDM) technology. It adopts the QSFP28 form factor and transmits data over single-mode fiber via four 25Gbps optical channels, with a typical reach of 2 km and a duplex LC interface. Compliant with CWDM4 MSA and IEEE 802.3ba 100G CWDM4 standards, it is widely used in data center interconnect (DCI) and high-performance computing (HPC) networks.<\/p>\n

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Core Working Principle<\/strong><\/h2>\n

The 100G QSFP28 CWDM4 optical transceiver uses Coarse Wavelength Division Multiplexing (CWDM) technology to convert four 25G NRZ electrical signals into four optical signals of different wavelengths, multiplex them onto a single optical fiber, and achieve a total bandwidth of 100Gbps.<\/p>\n

The core of CWDM4 is to multiplex four wavelengths over a single fiber, thereby reducing the number of fibers required while maintaining high-speed transmission. The process can be divided into the Transmit (Tx) and Receive (Rx) sections. The working procedures of the Tx and Rx in the 100G QSFP28 CWDM4 module are as follows:<\/p>\n

On the transmit (Tx) side, the host device (switch\/router) inputs four 25G NRZ electrical signals compliant with the CAUI-4 standard via the QSFP28\u2019s 38-pin electrical interface, with each signal corresponding to an independent channel (Channel 1\u20134). These electrical signals respectively drive four uncooled directly modulated DFB lasers (DML), generating optical signals at four distinct wavelengths: 1271 nm, 1291 nm, 1311 nm, and 1331 nm. The CWDM multiplexer (MUX) then combines these four optical signals into a single output, which is transmitted through the Tx port of the duplex LC interface onto a single-mode fiber.<\/p>\n

On the receive (Rx) side, the multiplexed optical signal from the fiber enters the module via the Rx port of the duplex LC interface and is separated by the CWDM demultiplexer (DEMUX) into the four original wavelength signals. Each optical signal is converted into a 25G electrical signal by a PIN photodiode (with a receiver sensitivity of \u2264 \u201312 dBm, requiring FEC to achieve 2 km transmission) and is finally output to the host device through the QSFP28 electrical interface.<\/p>\n

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100G CWDM4 Working Principle<\/figcaption><\/figure>\n

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Why Choose 100G QSFP28 CWDM4?<\/strong><\/h2>\n

In short-to-medium reach applications within 2 km, 100G QSFP28 CWDM4 often offers greater advantages over 100G QSFP28 LR4<\/a>, primarily in terms of cost, power consumption, and performance alignment. CWDM4 adopts an uncooled DFB laser design combined with coarse wavelength division multiplexing (CWDM) technology, resulting in lower component costs and reduced manufacturing complexity compared to the EML lasers and high-precision multiplexers required by LR4. This translates into a typical module cost savings of 30\u201340%.<\/p>\n

In terms of power consumption, CWDM4 operates at around 3.5 W, compared to approximately 4.5 W for LR4, which significantly reduces overall data center energy usage and cooling requirements in large-scale deployments. Moreover, CWDM4 is specified for a 2 km reach (with FEC), which is sufficient for most Spine\u2013Leaf architecture interconnects and inter-floor links in data centers, avoiding the cost and energy overhead of LR4\u2019s extended 10 km reach where such capability is not needed. As a result, CWDM4 represents an optimal balance of performance, cost, and energy efficiency for data center and campus network environments where link distances are predictable and within 2 km.<\/p>\n

Product specifications<\/strong><\/p>\n

\n \n \n \n \n <\/colgroup>\n \n\n \n\n \n \n \n \n \n \n \n \n \n \n \n
\ufeffParameter<\/th>Specification<\/th><\/tr>\n<\/thead>\n
Form Factor<\/td>QSFP28 (Quad Small Form-factor Pluggable 28)<\/td> <\/tr>\n
Data Rate<\/td>4 \u00d7 25Gbps NRZ, total 100Gbps<\/td> <\/tr>\n
Wavelengths<\/td>1271nm, 1291nm, 1311nm, 1331nm (\u00b16.5nm)<\/td> <\/tr>\n
Optical Fiber Type<\/td>Single-mode fiber (SMF)<\/td> <\/tr>\n
Transmission Distance<\/td>Up to 2 km (with FEC)<\/td> <\/tr>\n
Transmitter Type<\/td>Uncooled DFB laser (DML)<\/td> <\/tr>\n
Receiver Type<\/td>PIN photodiode<\/td> <\/tr>\n
Power Consumption<\/td>\u2264 3.5W<\/td> <\/tr>\n
Compliance<\/td>CWDM4 MSA, IEEE 802.3bm, RoHS<\/td> <\/tr>\n
Connector Type<\/td>Duplex LC<\/td> <\/tr>\n
Digital Diagnostics<\/td>Supported, via I\u00b2C (DDM\/DOM)<\/td> <\/tr>\n <\/tbody>\n <\/table>\n