Shulou(Shulou.com)06/01 Report--

The standards related to the optical communication industry are mainly from IEEE, ITU and multi-source protocol MSA industry alliance and other institutions. 100G modules have multiple standards, and customers can choose the most cost-effective module types according to different application scenarios. Multi-mode fiber, VCSEL laser and 500m-40km transmission are mostly used in short-range applications within 300m. Single-mode fiber, DFB or EML laser are mostly used in transmission.

Compared with 2.5G, 10G or 40G wavelength division transmission systems, 100G optical transmission uses a digital coherent receiver to map all optical properties of optical signals to the electrical domain through phase diversity and polarization diversity. Mature digital signal processing techniques are used to realize polarization demultiplexing, channel damage equalization compensation, timing recovery, carrier phase estimation, symbol estimation and linear decoding in the electrical domain. While realizing 100G optical transmission, a series of major technological changes have taken place in 100G optical module, including polarization multiplexing phase modulation technology, digital coherent receiving technology, the third generation super error correction coding technology, etc., so as to meet the needs of users to keep pace with the times.

Optical module classification

The mainstream packages of 100g optical modules are CXP, CFP, CFP2, CFP4, CFP8 and QSFP28. With the development in recent years, the shipments of CFP series products have gradually decreased, and QSFP28 packages have won out with smaller size and lower power consumption, and most of the newly emerging 200G and 400G packages use QSFP-DD packages. At present, most optical module companies have 100G series products in QSFP28 package on the market.

CXP optical module

The transmission rate of the CXP optical module is as high as 1210Gbps and hot-swappable is supported. "C" represents 12 in hexadecimal, and the Roman number "X" represents the transmission rate of 10Gbps for each channel. "P" refers to a hot-swappable pluggable device. The CXP optical module is mainly aimed at the high-speed computer market and is a supplement to the CFP optical module in the Ethernet data center. Technically, CFP optical module and multimode optical fiber are used in short-distance data transmission. Because the multimode fiber market needs high-density panels, its size has not been really optimized in the multimode fiber market.

CXP optical module block length 45mm, wide 27mm, the size is larger than XFP optical module or CFP optical module, so it can provide higher density network interface. In addition, the CXP optical module is a copper connector system designated by the Wireless Broadband Trade Association, which can support 12 10G link transmissions for 100GbE, 3 10G links for 40GbE channels, or 12 12QDR links for 10G Ethernet fibre Channel or wireless broadband signals.

CFP/CFP2/CFP4 optical module

CFP Multi-Source Protocol (MSA) defines the requirements that hot-swappable optical modules can be applied to 40G and 100G network transmissions, including the next generation of high-speed Ethernet (40GbE and 100GbE). The CFP optical module supports transmission at multiple rates, protocols and link lengths over single-mode and multimode fibers, including all media-dependent (PMD) interfaces included in the IEEE 802.3ba standard. Hu San PMD:100GBASE-SR10 in 100G network can transmit 100m, 100GBASE-LR4 can transmit 10KM, and 100GBASE-ER4 can transmit 40KM.

CFP optical module is designed on the basis of small pluggable optical module (SFP) interface, which is larger in size and supports 100Gbps data transmission. The electrical interface used by the CFP optical module uses 1010Gbps channels for transmission in each direction (RX, TX), so it supports the interconversion between 1010Gbps and 4*25Gbps. The CFP optical module can support a single 100G signal, OTU4, one or 40G signal, OTU3 or STM-256/OC-768.

Although the CFP-MSA optical module can achieve 100G data applications, its large size can not meet the needs of high-density data centers, in this case, the CFP committee defined two other forms: CFP2 and CFP4 optical modules.

QSFP28 optical module

QSFP28 optical module has the same design concept as QSFP optical module. For QSFP28, each channel can send and receive data up to 28Gbps. Compared with CFP4 optical module, the size of QSFP28 optical module is smaller than that of CFP4 optical module. QSFP28 optical module has the advantage of density over CFP4 optical module, the power consumption is usually no more than 3.5W, while the power consumption of other optical modules is usually between 6W and 24W. In view of this, the power consumption is much lower than that of other 100G optical modules.

CFP2/CFP4/QSFP28 size comparison figure:

Optical module test

When testing, you need to pay attention to the wavelength and shape of the output waveform of the transmitter, as well as the jitter tolerance and bandwidth of the receiver. When testing the transmitter, you should pay attention to:

Transmitter part

The quality of the input signal used to test the transmitter must be good enough. In addition, the quality of electrical measurement must be confirmed by jitter measurement and eye map measurement. Eye map measurement is a common method to check the output waveform of the transmitter, because the eye map contains a wealth of information, which can reflect the overall performance of the transmitter.

2. The output optical signal of the transmitter must be measured by optical quality indexes such as eye graph test, optical modulation amplitude and extinction ratio.

Receiver part

Unlike the test transmitter, the quality of the optical signal must be poor enough when testing the receiver, so an optical pressure eye diagram representing the worst signal must be created, and the worst optical signal must be calibrated by jitter measurement and optical power test.

The electronic output signal of the receiver needs to be tested, and there are three main types of testing:

1. Eye map testing, which ensures that the "eyes" of the eye map are open. Eye map testing is usually implemented by the true depth of the bit error rate.

2. Jitter testing, testing different types of jitter

3, jitter tracking and tolerance, test the tracking of the internal clock recovery circuit can jitter.

Testing the optical module is a complex task, but it is also an indispensable step to ensure its good performance. As a widely used measurement method, eye map measurement can effectively test the transmitter of the optical module.

With the development of technology, 100G network applications are becoming more and more common, and 100G optical modules are becoming more cost-effective. The 100G QSFP28 optical module and 100G CFP/CFP2/CFP4 optical module supplied by the state road communication can meet the corresponding standards with wide selectivity, strong stability and high performance-to-price ratio, and provide comprehensive network system solutions to help users build a low-cost and cost-effective network system.

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