Technology Expansion of Optical Transceivers and Optical Modules
Nov 26, 2025| Although the name "transceiver" literally means "transmitter + receiver," in engineering practice, it is far more than simply encapsulating two circuits in a single casing. It is a meticulously designed radio frequency or photonic system capable of generating, detecting, filtering, and converting signals under stringent performance constraints
.
Wavelength division multiplexing and backbone network
□Backbone optical communication system capacity
□Why can't NRZ be used for high-speed DWDM systems?
□100G optical modules: CFP, CFP2, CFP-DCO, CFP2-ACO
□Local oscillator light source in coherent optical modules
Difference between OTN and PTN transmission networks
When discussing transport networks, what are the differences between OTN and PTN? OTN mainly refers to the pipeline, while PTN mainly refers to the services. The development path and logical relationship of transport networks are shown in the diagram on the next page.
When fiber optic transmission began in the 1970s, the self-defined standard for businesses was simply to be able to transmit information and make it usable. As a result, two major systems of transmission formats emerged: one standard in Europe and one standard in the United States.
The three major regions-Japan, the United States, and Europe-were early players in fiber optic communication, each with its own transmission protocols.
This makes cross-continental information exchange very difficult.
In 1985, Bell Labs was researching a more standardized approach for the previous generation of communication formats, called SONET.
In 1988, the ITU-T (International Telecommunication Union) globally standardized SONET-based technology, defining SDH as the international fiber optic transmission standard that supports global interoperability, thus addressing global interoperability.
Meanwhile, wavelength division multiplexing (WDM) technology also began to develop, addressing the challenge of channel capacity.
Differences between SDH and WDM:
When Qin Shi Huang unified China, one of his monumental achievements influenced later generations: the standardization of weights and measures. One aspect of this standardization was "standardizing the axle width of carts." During the Warring States period, the chariots of different states varied in design, and the roads they built also differed in width. Standardizing the axle width meant that both the chariots and the roads needed to be standardized.
SDH focuses on transmission services; in other words, they researched the "standardization of chariots"-the size of the chariots and the interfaces of various components...
WDM studies "track synchronization," specifically multiple tracks running in parallel.
Previous fiber optic communication was mainly used for telephone calls, and this channel had a fixed bandwidth.
In the 1990s, internet services began to flourish, leading to increasingly larger volumes of data transmission with inconsistent bandwidth.
Based on SDH, MSTP was developed, which encapsulates both fixed-bandwidth and variable-bandwidth services within SDH, enabling interoperability between multiple services.
Further segmentation at the service level leads to PTN with increasingly smaller packet granularity, thus improving transmission efficiency. Small data volumes don't require large transmission trucks.
The evolution from SDH to MSTP and then to PTN represents the development path of services, acting as the vehicles. SDH uses fixed-length carriages to load fixed boxes, transitioning to MSTP technology that loads boxes of varying sizes into fixed carriages, and finally to PTN technology with multiple carriages and the ability to schedule the locomotives and carriages.
The evolution from WDM to OTN represents the development path of the pipeline, acting as the road. WDM is like a four- or six-lane flat road,
OTN is like an overpass, increasing the flexibility of road scheduling.
PDH【plesiochronous digital hierarchy】SDH【synchronous digital hierarchy】MSTP【multi-service transport platform】TDM【time division multiplexing】
ATM【asynchronous transfer mode】PTN【packet transport network】OTN【optical transport network】
5G and 5G optical modules
□Color optical modules: WDM, WDM and SDM
□Should a base station fronthaul use 6, 12, or 24 modules?
□Macrocell and Microcell Base Stations
□Differences between Wireless Base Stations and Repeaters
□DSFP Optical Module Packaging for 5G Fronthaul
□10G TOSA for 25G Transmission
5G's colored light and colorless light
What does it mean to have both colored and colorless optical modules?
A: Use colorless light modules to support colored light schemes.
However, the above explanation may still be confusing, so let's move beyond light modules and talk about color first.
The eye's perception of color is actually just the manifestation of different electromagnetic wave wavelengths in the eye.
For objects, a red object absorbs all colors except red, and the red color is perceived by the eye in the form of reflection; the same applies to objects of other colors.
Transparency means that an object transmits all wavelengths of light. For the eye, this means that it can perceive the wavelengths of the surrounding objects.
White is the color of an object reflecting all wavelengths; the eye perceives this mixture of wavelengths as white.
Black means that the object has absorbed all wavelengths, so the eye cannot perceive anything.
We usually think of transparent objects as colorless.In fact, in colorimetry, white is classified as "colorless".
The eye defines white as containing "all" wavelengths.
A 5G fronthaul colorless optical module refers to an optical module that can output any desired wavelength, also known as a wavelength-tunable optical module. This module supports the deployment of 5G colored light solutions through wavelength tuning.
Next, let's discuss why we prefer colorless optical modules.
Whether it's 6-wavelength or 12-wavelength light, if the optical module uses a fixed, single-wavelength laser solution, then the base station would need to stock all wavelengths of optical modules, because you don't know which wavelength module will fail.
Therefore, using tunable wavelength modules as backup optical modules facilitates rapid maintenance.
Alternatively, if colorless optical modules are very inexpensive, widespread adoption of colorless modules at the user end would be most convenient for ordinary base station builders during initial deployment. For them, this module would be a single model, plug-and-play, eliminating the need to select and configure multiple solutions and wavelengths of fiber optic input.
High-speed optical modules for data centers
□Infiniband optical modules SDR/DDR/QDR/FDR/EDR/HDR/NDR
□Can the reliability standards for data center optical modules/devices be relaxed?
□400G optical module MSA multi-source protocol
□8×50G Multimode 400G BiDi Specifications
□CWDM4-OCP Optical Module Specifications
In optical modules, KR, CR, SR, DR, FR, LR, ER and ZR
Let's talk about what FRKRCRRDRRER in 4GFR4 means.
802.3 belongs to the IEEE architecture, and the naming rules for -R are as follows:
For example:
100 Gbase-LR4, module rate 100Gb/s, LR stands for longreach (10km), n is four channels, this is a 4×25G optical module capable of transmitting 100G optical data over 10km.
100Gbase-LR, module rate 100Gb/s, LR 10km, n is omitted, it's a single channel,
1×100 G, capable of transmitting 100G optical data over 2km.
| PMD Type | Transmission Distance | Remarks / Notes |
|---|---|---|
| KR | Several tens of centimeters to more than ten centimeters | K: backplane, signal transmission between boards |
| CR | Several meters | C: copper, copper cable direct connection |
| SR | Several tens of meters | S: short, short distance, generally uses multimode fiber |
| DR | 500 m | D: datacenter, used for internal transmission in 500 m left-right data centers |
| PMDType | Transmission Distance | Remarks / Notes |
|---|---|---|
| FR | 2 km | F: far, used for transmission distances commonly seen in data center internal backbone, typically 2 km; is one of the 100G CWDM4 standards defined by MSA and later adopted by IEEE |
| LR | 10 km | L: long, long distance |
| ER | 40 km | E: extended, extended distance, relative to LR extended |
| ZR | 80 km | Non-IEEE standard |
Our optical modules are plugged into the front end of the line card, and the entire line card is then plugged into the backplane. The interconnection of signals between backplanes is called KR, which is several tens of centimeters long and is sometimes called KR bus, such as in data center switches.
PON Optical Module
OLT C++
The Origins of D1 and D2 in ComboPON
Google Fiber's Next-Generation Optical Access Architecture
The "Colorless" Nature of a Colorless ONU
What is an Optical Modem?
What are 8B10B and 64B66B?
Next-Generation PON Convergence
ONU ONT Difference
On the user side of JieRen.com, there are two terms: ONU and ONT. What's the difference between these two terms?
We usually look at the various methods of JieRen.com's FTTx platform as shown in the image below:
iber to the home,fiber to the office,fiber to the building
The three essential components of FTTx are: OLT, ODN, and ONU/ONT.
OLT stands for Optical Line Terminal.
ODN stands for Optical Distribution Network.
ONU stands for Optical Network Unit.
And there's also ONT, which stands for Optical Network Terminal.
The way ONU/ONT is labeled so often can be confusing for non-professionals like us.ONU: Refers to the optical network equipment that connects to the branch fiber of the ODN.ONT: Refers to the optical network equipment that connects to the end user (our home).With fiber to the home, we have an optical modem at home. This optical modem connects to the branch fiber of the ODN and also to the end user. It can be called ONU or ONT.For example, in FTTB (Fiber to the Building), the ONU box is placed at the entrance of our building, just like the main electricity meter for each building.At this point, the small device connecting the ODN fiber optic cable isn't in our end-user's home. We users are the customers, so we can't just equate the fancy term ONT with ONU.The ONU box of FTTB has a single fiber optic cable coming in and splitting into multiple network cables. We've all seen network cables before, right? Those pretty RJ45 connectors and colorful wires.
In FTTB, the MDU (multiple dwelling unit) is one type of ONU.An MDU can have multiple network cables routed out.
In simple terms:
ONU connects to the ODN.
ONT connects to the user.
In cases of overlap, where the ODN's fiber optic cable goes directly to the user, then ONU = ONT.
In cases of non-overlapping connections, an ONU is simply an ONU, and can only be an ONU.
Electrical interface
□Distinguish between optical module electrical interfaces XAUI, XLAUI, CAUI, and CDAUI.
□Gearbox in the optical module
□C2C and C2M in the AUI electrical interface
□DC coupling and AC coupling
□Optical module high-speed electrical interface CEI classification
SERDES
What are SERDES?
SERDES, or Serial Deserializer, is a mainstream Time Division Multiplexing (TDM) and Point-to-Point (P2P) serial communication technology.
SER: SERializer, DES: DESerializer.
Serial, as opposed to parallel, is like elementary school students lining up side-by-side to visit the zoo. That would require several ticket inspectors and several ticket windows.
Parallel data and multiple interfaces are used, but the speed requirements for ticket inspectors are not high, so it will not cause queue congestion.
Of course, our ticket inspectors can be very fast, and one person can cover many lines. That would require a serializer, which would save space, save two inspectors, and wouldn't affect the speed of entry into the park.
A deserializer is simply the reverse of a serializer. Children go out and go home.
TDM, Time Division Multiplexing, divides time into multiplexes.
What is P2P? Point-to-point. The signals transmitted are the same as the signals received.
Although we're not using three data lines for transmission, from the dotted lines, it's still point-to-point transmission and reception.
High-speed signal processing
□PAM4 CDR
□High-frequency signal processing methods for 25G TOcan
□Impact of TOcan pin eccentricity on bandwidth for 5G base station fronthaul
□Crosstalk solution for single-wavelength 100G differential lines
□Why are 400G high-frequency coupling capacitors all in the pF range?
A high-speed digital signal processor (DSP) is a programmable microprocessor specifically designed for real-time digital signal processing. It features high-speed computation, real-time performance, and low power consumption, and is widely used in communications, radar, audio, video, and industrial control.
Its core design employs a Harvard architecture (separate instruction and data buses), a RISC instruction set, hardware multipliers, and a DMA controller, supporting parallel processing and high-efficiency data throughput. It can quickly execute signal processing algorithms such as multiplication and accumulation. DSPs are classified into two types based on data type: fixed-point and floating-point. Fixed-point examples include TI's TMS320C62/C64 series, while floating-point examples include ADI's SHARC/TigerSHARC series, suitable for scenarios with different precision requirements.
