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Optical module - A comprehensive exploration

At present, the world’s AI large-scale models have been released one after another and combined with industry applications to promote the smart upgrade of thousands of industries, and continue to drive the demand for optical chips, optical devices, and optical module in the upstream of the data center industry chain. The optical module is one of the core devices of the optical communication system, and its development has a vital impact on its related industrial chain, from the upstream industry chip substrate, PCB to the downstream telecom market and data communication market, and the field of lidar driverless cars .

This article will explore optical modules comprehensively, including optical modules definition, packaging and optical modules PCB and how to choose optical modules?

Table of Contents

What is an optical module?

What is an optical module
What is an optical module

The optical module is one of the core components of the optical communication system. The optical module is composed of optoelectronic devices, functional circuits, and optical interfaces. It mainly performs photoelectric and electro-optical conversion, that is, the transmitting end of the optical module converts electrical signals into optical signals, and the receiving end converts optical signals into electrical signals.

As an important link in data transmission, optical module technology is indispensable for optical communication and plays the role of the cornerstone of communication. With the gradual increase of the conversion rate, the optical module has become a key element in various application fields, and its development is also of great significance to the entire artificial intelligence industry.

How to classify optical modules and its types

Nowadays, with the accelerated development of optical communication, the speed of the optical module is getting faster and faster, and the volume is getting smaller and smaller. There are various classification standards for optical modules, and there are often new classification standards.

Optical module classification

Traditional classification method: generally classified from the perspectives of packaging method, transmission rate, data transmission path, operating temperature, mode, wavelength, usability, and purpose.

New classification method: As technology is updated and iterated, optical module can be classified according to modulation methods, whether they support wavelength division multiplexing (WDM) applications, optical interface working modes, etc., and there are multiple subdivisions under each category.

Optical module types

Optical module types
Optical module types

According to the new classification method, optical modules can have different types, as following:
1. Modulation format – NRZ / PAM4 / CWDM / DWDM / PSM
NRZ signal: High and low signal levels are used to represent the 1 and 0 information of the digital logic signal to be transmitted;
PAM4 signal: 4 different signal levels are used for signal transmission;

The PMA modulation chip in the PAM4 optical module is technically difficult. The PAM4 optical module can reduce the cost of lasers and detectors.

2. Whether to support WDM
Gray optical module: does not support wavelength division multiplexing, one optical fiber can only transmit one signal;
Colored optical module(CWDM): support wavelength division multiplexing (divided into CWDM and DWDM, that is, sparse type and dense type, with different wavelength intervals). It can realize the transmission of multiple signals in one optical fiber, and each signal is transmitted by light of a specific wavelength .

The colored optical module technology is difficult and the cost is high. The colored optical module can greatly reduce the use of optical fibers.

3. Optical interface working mode
Dual-fiber bidirectional (Duplex): two optical fibers and two optical ports, responsible for signal transmission and reception respectively;
Single-fiber bi-directional (BiDi): one fiber and one optical port to realize simultaneous transmission and reception of optical signals in two directions by one fiber.

Single-fiber bidirectional technology is difficult and still in the prototype stage Single-fiber bidirectional can greatly reduce the use of optical fibers and optical ports

How does optical module work?

The optical module industry has a history of development for many years. At present, the continuous upgrading of optical communication, AI, algorithm and other technologies has driven the increasing types and functions of optical modules.

Optical module function

Optical module is composed of optoelectronic devices, functional circuits and optical interfaces. It undertakes the task of photoelectric signal conversion in the network connection. The optical module is also called an optical transceiver module. Although the optical module is small in size and seemingly simple in structure, it has high technical requirements.

Optical module structure

Optical module structure
Optical module structure

Optical modules are mainly packaged by optoelectronic devices TOSA/ROSA, functional circuits and optoelectronic interface components. The optical transceiver component TOSA/ROSA is the core part of the optical module, mainly including the optical receiving module and the optical transmitting module.

  • Transmitting module: The optical transmitting component TOSA is responsible for processing the received electrical signal by driving the semiconductor laser (LD) or light-emitting diode (LED) to emit a modulated optical signal at a corresponding rate. It has an automatic optical power control circuit inside , so that the output optical signal power remains stable.
  • Receiving module: The optical receiving component ROSA is responsible for converting the optical signal into the module and converting it into an electrical signal by a photodetector diode, and outputting an electrical signal with a corresponding code rate after passing through a preamplifier.

Optical modules packaging technology

With the development and integration of optoelectronic devices, the performance and transmission bandwidth of optoelectronic devices have gradually increased. In order to cope with different usage scenarios, the optical module has achieved higher rate transmission and smaller size, so its packaging method has been continuously developed and upgraded.

How to package optical modules?

The optical module packaging method is continuously developing and evolving. In its development process, there are several types, as follows:

  • CFP (C form-factor pluggable): The CFP package is proposed to support the early 100G optical module . The 100G CFP optical module uses 10 10Gbits channels to achieve 100G network transmission and is widely used in data centers. CFP packaging has the advantages of hot plugging, relatively small size, good thermal performance, and high power.

With the development of data communication network, many different types of CFP optical modules have been derived. At present, the common ones are CFP2 optical modules, CFP4 optical modules and CFP8 optical modules.

  • SFP (Small Form Pluggable): It is a small pluggable optical module, an interface device that can convert gigabit electrical signals into optical signals. Its volume is twice as small as GBIC, and it can be configured twice as much on a panel of the same size. The above port quantity mostly adopts LC type optical fiber interface. At present, different types such as SFP+, SFP28, and QSFP28 have been developed.
  • OSFP (Octal Small Form Factor Pluggable) : OSFP is a package that supports 8 sets of high-speed electrical transceiver channels and can provide a connection interface to 400Gbps (8x50G PAM-4).
optical modules

What is the development trend of optical module packaging?

With the change of packaging structure, the power consumption of optical modules is getting lower and lower, and the product volume is getting smaller and smaller. In this process, optical modules are moving towards high speed, long distance, low power consumption, low cost, miniaturization and thermal The direction of plugging and unplugging is developing.

1. Diversified optical module packaging methods: for different rates and scenarios, you can choose SFP+, SFP28, QSFP28, CFP, QSFP-DD, OSFP and other packaging forms;

2. The packaging volume of optical modules continues to decline: taking CFP as an example, the volume of CFP4 optical modules is a quarter of that of early CFPs, and the currently popular 100G QSFP28 packaging volume is smaller than that of CFP4;

3. The transmission rate of optical modules continues to increase: the transmission rate of optical modules has developed from the early Gigabit GBIC to 10G SFP, and then to today’s 800G OSFP.

What are the main applications of optical module?

What are the main applications of optical module
What are the main applications of optical module

At present, optical modules are mainly used in telecom and datacom .

In the telecommunication market, new requirements are constantly put forward for speed and transmission distance, and the continuous development of the telecommunication market will drive the increase in the application demand of telecommunication optical chips.

In the data communication market, with the rapid development of cloud computing, big data, ultra-high-definition video, artificial intelligence, and 5G industry applications, in the data center architecture, the connection between servers, the connection between switches, and the connection between servers and switches all need optical modules, optical fiber jumpers and other transmission carriers to achieve data intercommunication.

How to choose the most suitable optical module

When selecting an optical module, many aspects should be considered, such as transmission distance, transmission mode, transmission medium, and heat resistance. In order to help you choose the right optical module, here are some tips for choosing optical module:

Tip 1: Identify old and new optical modules. Use an optical power meter to test whether its optical power is consistent with the parameters on the data sheet.

Tip 2: Select the appropriate optical module interface type according to the needs. There are many types of optical fiber connector interfaces, FC, SC, ST, LC, MU, MTRJ, the most common is the LC interface, followed by the SC interface, this requires According to the actual situation.

Tip 3: Check the compatibility between the optical module and the device. When choosing, it should be noted that in the product description, which compatible devices the product can be used in will be marked.

Tip 4: Consider the temperature adaptability of the optical module. The working environment of the optical module is in the equipment room or switch, and the change of the ambient temperature will affect the optical power and optical sensitivity of the optical module.

Tip 5: Consider whether the parameters of the optical module meet the requirements of the equipmen. The parameters of the optical module that need to be considered include the central wavelength, transmission distance, and transmission rate.

How about PCB for optical module

optical module PCB and manufactuer
optical module PCB and manufactuer

PCB(printed circuit board), which realizes the electrical connection between the components in the circuit according to the PCB layout design on the PCB substrate, is the carrier for the electrical interconnection of electronic components. When components such as optical transceiver components and electrical chips form an optical module, a PCB is required to connect each component, so a PCB is essential in an optical module.

In order to meet the needs of market development, the upgrading process of the PCB industry is gradually accelerating, and the direction of high density, high reliability, and miniaturization is constantly developing. The production capacity and production technology of major products such as high-end multilayer boards, flexible PCB, and HDI PCB, many companies can also provide stable high-quality optical module PCB.

IBE is an ODM/OEM service provider, integrating industrial design, R&D, manufacturing and sales, and also a professional PCB manufacturer, which can provide high-quality PCB for electronic industry, multlayer PCB, high-speed PCB, high-reuency PCB, HDI PCB, rigid-flex PCB, and etc.

Conclusion

The continuous maturity of optoelectronics and cloud computing technologies will promote the emergence of more terminal application requirements and put forward higher requirements for communication technologies. Benefiting from the increase in demand for information application traffic and the upgrade of optical communication technology, optical modules, as the most important device in the optical communication industry chain, will continue to maintain growth.

At the same time, it will also drive the development of its upstream industries PCB, packaging substrates, and optical chips. The upgrading of downstream industries of optical modules such as Internet and cloud computing, telecommunications, data communication and optical communication equipment.

FAQ
Optical modules are mainly packaged by optoelectronic devices TOSA/ROSA, functional circuits and optoelectronic interface components. The optical transceiver component TOSA/ROSA is the core part of the optical module, that is, the optical receiving module and the optical transmitting module.

The main reasons for the failure of the optical module are the performance degradation of the optical module caused by ESD damage, and the failure of the optical link caused by the pollution and damage of the optical port.

The main causes of optical port pollution and damage are:
1. The optical port of the optical module is exposed to the environment, and the optical port is polluted by dust.
2. The end face of the optical fiber connector used has been polluted, and the optical port of the optical module has been polluted again.
3. End surface scratches
4. Poor quality fiber optic connectors are used.

When selecting an optical module, many aspects should be considered, such as transmission distance, transmission mode, transmission medium and heat resistance, etc.

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