QSFP28 100G LR4 is an acronym with each part representing a specific characteristic. "QSFP" stands for Quad Small Form - Factor Pluggable, which indicates that it is a small - sized, pluggable module with four channels. "28" refers to the maximum data rate of up to 28Gbps per channel. "100G" represents the overall aggregated data rate of 100 Gigabits per second that the module can achieve. "LR" stands for Long Range, signifying its capability for long - distance transmission, and "4" denotes the four - channel architecture. In essence, it's a high - speed, long - range, four - channel optical transceiver module.

The QSFP28 100G LR4 is a four - channel optical transceiver module. Each of its four channels is capable of transmitting data at a rate of 25Gbps, which, when combined, enables the module to support a total data transfer rate of 100Gbps. This high - speed data transmission makes it an ideal choice for high - bandwidth applications.

It is primarily designed for use in 100G Ethernet networks, where it plays a crucial role in ensuring efficient and fast data transfer. One of its most notable features is its long - distance transmission capability. Over single - mode fiber, it can transmit data up to a distance of 10 kilometers. This long - range functionality makes it suitable for a wide range of applications, from connecting different servers within a large - scale data center to establishing connections between data centers located in different geographical areas.

The module operates within a specific wavelength range. The four channels use different wavelengths within the 1295 - 1309nm range, specifically 1295.56nm, 1300.05nm, 1304.58nm, and 1309.14nm. These wavelengths are carefully selected to optimize the performance of the module and ensure reliable data transmission over long distances. Additionally, it is designed to be hot - swappable, meaning it can be inserted or removed from a network device while the device is powered on. This feature provides great convenience for network installation, maintenance, and upgrades, reducing downtime and increasing network availability.

The Transmitter Optical Sub - Assembly (TOSA) is a crucial component within the QSFP28 100G LR4 module. Its primary function is to convert electrical signals into optical signals, a fundamental step in the data - transmission process.

Inside the TOSA, a laser diode is a key element. When an electrical current is applied, the laser diode emits light. The intensity of this light output is modulated according to the input electrical signal. For example, in a 100G QSFP28 LR4 module, four channels are used, and each channel within the TOSA has a laser diode. These laser diodes operate at different wavelengths within the 1295 - 1309nm range, specifically 1295.56nm, 1300.05nm, 1304.58nm, and 1309.14nm. By modulating the light output of these laser diodes, the electrical data signals are effectively encoded onto the optical signals.

The TOSA also includes a driver circuit. This circuit is responsible for driving the laser diode, ensuring that it operates at the correct power levels and modulation rates. It takes the incoming electrical data signals from the host device and amplifies and shapes them appropriately to drive the laser diode. Without a properly functioning driver circuit, the laser diode may not emit light accurately according to the data, leading to errors in the optical signal and ultimately, data - transmission failures. In the context of the 100G QSFP28 LR4, the TOSA plays a vital role in enabling high - speed data transfer. By converting 25Gbps electrical signals (in each of the four channels) into optical signals, it paves the way for the module to achieve an aggregated data rate of 100Gbps. These optical signals are then ready to be transmitted over single - mode fiber for long - distance communication.

The Receiver Optical Sub - Assembly (ROSA) is the counterpart of the TOSA in the QSFP28 100G LR4 module, and its function is equally critical. ROSA is responsible for converting the optical signals, which have been transmitted over the fiber, back into electrical signals that can be understood by the receiving device.

At the heart of the ROSA is a photodetector, typically a PIN (Positive - Intrinsic - Negative) photodiode or an APD (Avalanche Photodiode). When the optical signal, carrying the data, strikes the photodetector, it generates an electrical current. The intensity of this current is proportional to the intensity of the incident optical signal. In a 100G QSFP28 LR4 module, the ROSA has to detect the four different wavelengths of the optical signals that were transmitted from the TOSA.

After the photodetector generates the electrical current, a transimpedance amplifier (TIA) comes into play. The TIA converts the small electrical current generated by the photodetector into a more measurable voltage signal. This voltage signal is then further amplified and processed by other components within the ROSA, such as a limiting amplifier. The limiting amplifier ensures that the output electrical signal has a consistent amplitude, regardless of any fluctuations in the input optical signal strength within a certain range.

The ROSA is essential for the overall functionality of the QSFP28 100G LR4 module's receiving end. It enables the accurate retrieval of the data that was transmitted over the optical fiber. Any malfunction or low - performance of the ROSA can lead to high bit - error rates, where the received data does not match the transmitted data. This can disrupt communication in data - center networks, telecommunications systems, and other applications that rely on the 100G QSFP28 LR4 module for high - speed data reception.

The Multiplexer (MUX) and De - multiplexer (DEMUX) are integral components in the QSFP28 100G LR4 module, facilitating the efficient handling of multiple data channels.

The MUX is used on the transmission side. Its main function is to combine the four 25Gbps optical signals, each with a different wavelength, into a single 100Gbps optical signal. This is achieved through a process of wavelength - division multiplexing (WDM). By combining these signals, it becomes possible to transmit all the data over a single fiber, maximizing the utilization of the fiber's bandwidth. For example, in a data - center network where multiple servers need to send large amounts of data to a central switch, the MUX in the QSFP28 100G LR4 module on each server can combine the data from four different channels into one signal, reducing the number of fibers required for transmission.

On the receiving side, the DEMUX performs the reverse operation. It takes the single 100Gbps optical signal and separates it back into the four original 25Gbps optical signals, each with its distinct wavelength. This separation is crucial as it allows the ROSA to process each individual channel's data separately. The DEMUX uses optical filters or other wavelength - selective components to distinguish between the different wavelengths and direct each signal to the appropriate receiving channel. In a telecommunications network, when a 100Gbps optical signal is received at a base - station from a remote data - center, the DEMUX in the QSFP28 100G LR4 module installed at the base - station enables the extraction of the four individual channels of data, which can then be further processed and distributed within the base - station.

In addition to TOSA, ROSA, and MUX/DEMUX, the QSFP28 100G LR4 module contains several other important components.

One such component is the control circuit. The control circuit is like the "brain" of the module, regulating various functions to ensure stable operation. It monitors and controls parameters such as the power levels of the lasers in the TOSA, the gain of the amplifiers in the ROSA, and the overall temperature of the module. For example, it can adjust the drive current of the laser diodes in the TOSA to maintain a consistent optical output power, even if there are changes in the ambient temperature or the electrical supply voltage.

The module also has a digital diagnostic function, which is implemented through a combination of sensors and microcontrollers. This function allows the module to monitor its own performance, such as the transmit and receive optical power levels, the bias current of the lasers, and the temperature inside the module. The data collected by the digital diagnostic function can be accessed by the host device, providing valuable information for network management and troubleshooting. For instance, if the receive optical power drops below a certain threshold, the digital diagnostic function can send an alert to the network management system, allowing technicians to quickly identify and resolve the issue, whether it's a problem with the fiber connection, the module itself, or the transmitting device.