Trends in the Telecom Market for Optical Transceivers

Telecom networks are mainly divided into access networks, metropolitan area networks and backbone networks with different rates and transmission distances. Access Network is a transmission network unrelated to services and applications, which mainly completes cross-connection, multiplexing and transmission functions and connects enterprises, individual users and data centers to the network, including fixed network access and wireless access; Metropolitan Area Network (MAN) is the information communication infrastructure in a city area, mainly using optical fiber as the transmission medium. It is the intermediate link between the access Network and the backbone Network; Backbone Network is a high-speed network used to connect multiple regions and areas.

In terms of transmission distance, the transmission distance of access network is generally less than 100km, the transmission distance of metropolitan area network is generally 100-800km, and the transmission distance of backbone network is generally 800-2000km.

The number of optical transceivers at the access layer depends on the number of terminal devices, and the metropolitan area and backbone networks depend on the data traffic. At the access layer due to the high number of devices, the main focus is to meet the connectivity requirements. Therefore the number of optical transceivers is linked to the number of terminal devices, and there is greater redundancy in terms of data traffic, and the optical transceivers used have a lower rate but the largest number. In metropolitan area and backbone networks the network structure is leaner, so the number of optical transceivers is related to the data traffic. The higher the rate of optical transceivers used, the less the number is than the access layer.

The development trend of optical transceivers in telecom includes: 5G base stations bringing fronthaul/middlehaul/backhaul optical transceivers, especially 5G base stations spectrum widening to 160MHz or above. The introduction of wavelength division in fronthaul will let the demand for optical transceivers expand; Home Broadband Network upgrade from GPON to 10G PON; Metropolitan Area Network 100G sink and Backbone Network upgrade to super 100G.

Access Networks

Both fixed-line and mobile networks require a large number of low-speed optical transceivers.

1. Fixed Network Access

PON is generally used for fixed network access, and the consumption of optical transceivers is large. PON (Passive Optical Network) is an optical network built with passive equipment. PON network mainly consists of Optical Line Terminal (OLT), Optical Distribution Network (ODN) and Optical Network Unit/Terminal (ONU/ONT).

The connection between Olt, ODN and ONU/ONT devices is in great demand, so the number of terminal devices and the use of optical transceivers are also large. Using an OLT or ONU device consumes hundreds of optical transceivers, typically at a low speed of 1.5 GB/s. Due to the characteristics of the network, PON optical transceivers are often used in a one-to-many mode, and the transceivers are not used in pairs.

As PON is generally used in small areas, the transmission distance is short, generally within 20km, and the transmission rate is low, generally 1.5Gb/s. In addition, the uplink wavelength is 1310nm and the downlink wavelength is 1490nm. At present, operators mainly use transmission protocols for EPON and GPON, and their packaging forms include SFF, SFP/SFP+.

2. Wireless side access network

In the wireless side access network, the optical transceiver is mainly used to connect RRU and BBU. In 4G period, the access rate is mostly 10Gb/s. Most of the packages are SFP, SFP+ and QSFP28, and the transmission distance is 10km/40km.

Metropolitan Area Network(MAN)

Metropolitan Area Network:40G/100G optical transceivers are used according to the size of data volume.

Metropolitan Area Network plays the role of link up and down, is more sensitive to cost, can use Ethernet direct connection or CWDM to reduce costs. The type of MAN service is complex, which needs to carry traditional voice service, internet service and all kinds of new services in the future.

The convergence layer of MAN mostly adopts 40GE/100GE 10km, 40km and 80km optical transceivers, and the amount is linked to data traffic.

Backbone Network

Backbone network: low quantity and high rate, using high-speed colored optical transceivers.

The backbone network mainly adopts OTN technology that supports high-speed high-capacity long-haul transmission, and mostly uses CWDM/DWDM optical transceivers (i.e. colored optical transceivers) with a rate of mostly 100G, but the overall quantity is small.
OTN can provide huge transmission capacity, fully transparent end-to-end wavelength/subwavelength connectivity, and carrier-grade protection with enhanced subwavelength aggregation and sparing capability.

The granularity of OTN configuration, multiplexing, and crossover is significantly greater than that of previous-generation network technologies, thereby greatly enhancing the transmission efficiency and adaptability of high-bandwidth data services.

In addition, OTN can maximize the use of existing equipment resources and can provide more flexible service protection functions based on the electrical and optical layers.

Changes in the 5G Network

In the 5G period, the wireless network increases the fronthaul link, and the specifications of optical transceivers as well as the number of simultaneous upgrading. According to the technical proposal given by IMT-2020 (5G) promotion group, the optical transceiver requirements are as follows.

• 10G/25G/100Gb/s gray light or Nx25G/50Gb/s WDM colored light on the wireless access side.
• 100G/200Gb/s gray light or Nx100Gb/s WDM colored light at the convergence layer of the MAN.
• 200G/400Gb/s gray light or Nx100G/200G/400Gb/s WDM colored light is used in the core layer of the metropolitan area network and the backbone network.
  

The specifications of optical transceivers have been improved over previous 4G networks (10Gb/s on the access side, 40Gb/s on the aggregation layer, and 100Gb/s on the core and backbone networks).

1. Fronthaul in 5G

5G fronthaul: the largest number of connections, with a rate of mostly 25Gb/s.

5G fronthaul transmission technology solutions include: fiber direct connection, passive WDM, active WDM/OTN, sliced packet network (SPN), etc.

Fiber direct scenario generally uses 25Gb/s gray optical transceivers, supporting two types of dual-fiber bidirectional and single-fiber bidirectional, mainly including 300m and 10km two kinds of transmission distance.

Passive WDM scenario mainly includes point-to-point passive WDM and WDM-PON, etc., using a pair or a fiber to realize the connection between multiple AAU to DU, typically requiring 10Gb/s or 25Gb/s colored optical transceivers.

For active WDM/OTN scenarios, 10Gb/s or 25Gb/s short-range gray optical transceivers are typically required between AAU/DU to WDM/OTN/SPN devices. Between WDM/OTN/SPN devices, dual-fiber bidirectional or single-fiber bidirectional color optical transceivers with rates of N×10/25/50/100Gb/s are required.

The largest proportion of demand for fronthaul transmission optical transceivers, large market space for 25G products. In terms of the number of connections, the largest number of fronthaul transmission optical transceivers, the highest demand in the 5G bearer network. At the same time the application scenario is usually outdoor, industrial-grade optical transceivers are required with a rate of 25Gb/s, while the normal operating temperature range required is large, from -40 degrees to +85 degrees.

2. Middlehaul and backhaul in 5G

The optical transceivers used for backhaul in 5G access networks are mostly 50G/100Gb/s gray light or WDM colored light.

Since the optical transceiver is often used in the room with good heat dissipation conditions in the middlehaul and backhaul scenarios, commercial-grade optical transceivers can be used.

The current transmission distance below 80km, mainly apply 25Gb/s NRZ or 50/100/200/400/Gb/s PAM4 optical transceiver, the long distance transmission above 80km will mainly use coherent optical transceiver (single carrier 100/400Gb/s).

5G bearer network is generally divided into metropolitan area access layer, metropolitan area convergence layer, metropolitan area core layer/provincial trunk, to achieve the 5G service fronthaul, middlehaul transmission function, which mainly relies on optical transceivers between the layers of equipment to achieve interconnection, its typical application scenarios and demand analysis as shown in the table.


5G backhaul covers the metropolitan area access layer, convergence layer and core layer, the required optical transceivers and the existing transport network and data center optical transceiver technology is not very different.

Access layer will mainly use 25Gb/s, 50Gb/s, 100Gb/s and other rates of gray light or colored optical transceivers, convergence layer and above will be more use of 100Gb/s, 200Gb/s, 400Gb/s and other rates of DWDM colored optical transceivers.

3. Summary

Fronthaul: 4G uses CRPI interface with 20MHz spectrum bandwidth, 2T2R. The bandwidth of the fronthaul interface is about 2.48G, if replaced by 8*8MIMO, the bandwidth requirement is 9.8G.

Therefore, the 4G forward transmission mainly uses 10G optical transceivers. 5G uses 100MHz spectrum bandwidth (common shared, then need 200MHz), 64T64R. 320G CPRI bandwidth requirement, the introduction of eCPRI interface will be compressed to 25G forward transmission bandwidth. Therefore, the 5G forward transmission will be mainly 25G.

Middlehaul: a DU needs 10G, if the bandwidth demand of the ring-forming access layer exceeds 25G, 50G or 100G optical transceivers are required (considering later evolution).

Backhaul: According to model calculations, the convergence and core layer bandwidth demand exceed 100G, so 200G or 400G optical transceivers are required.