While 1.6T optical transceivers are taking center stage in AI data centers, with shipments of 800G/1.6T products hitting new highs month after month.

 

There exists another market segment where a seemingly outdated 155Mbps optical transceiver continues to deliver reliable long-distance communications for critical infrastructure including power private networks, rail transit, and security surveillance.

 

Operating at only 155Mbps, this transceiver supports single-hop transmission up to 160 kilometers—no repeaters or optical amplifiers required, with a single fiber link connecting two endpoints directly.

 

Today we break down this low-speed long-distance workhorse.

 

01 What Does 160km Transmission Mean?

A 160km fiber span is roughly equivalent to a round trip between Beijing and Tianjin, or twice the distance between Shenzhen and Guangzhou.

 

In optical communication, transmission distances are categorized as:

- Short-reach: ≤2km

- Medium-reach: 10–40km

- Long-reach: ≥60km

160km firmly falls into the ultra-long-reach category.

 

Conventional 155Mbps transceivers have very limited range:

- 850nm multimode versions only reach 550 meters

- 1310nm single-mode variants cover 10–60km

 

By contrast, the 1550nm 155Mbps transceiver leverages ultra-low fiber attenuation of 0.19dB/km, paired with DFB laser transmitters and APD photodetectors, enabling error-free transmission over 160km and beyond without signal regeneration.

 

The 1550nm wavelength is the core enabler for 160km links: longer wavelengths experience less signal loss in optical fiber, delivering extended transmission reach.

 

02 Why Can 155Mbps Reach 160km, But Higher-Speed Modules Cannot?

This is a common puzzle for communications engineers.

The core principle: lower bitrates impose looser signal integrity requirements and deliver stronger anti-dispersion performance.

 

High-speed transceivers (10G, 25G, etc.) are extremely sensitive to signal quality. Fiber chromatic dispersion broadens optical pulses, causing adjacent signal bits to overlap and become unrecognizable at the receiver. At 155Mbps, optical pulses are far wider, so dispersion creates minimal interference—allowing the system to tolerate vastly longer fiber spans.

 

In short: bitrate and transmission distance are inversely correlated. Higher speed comes at the cost of shorter reach, and extended distance requires reduced bandwidth.

 

This relationship explains the industry standard maximum spans:

- 1.25G transceivers with 1550nm wavelength max out at 120km

- 10G transceivers typically only support 80–100km

As data rate rises, hitting the 160km threshold becomes increasingly unfeasible.

 

03 Core Technologies of the 155Mbps 160km Transceiver

Two critical technical challenges must be solved to achieve 160km ultra-long-reach transmission:

1. Transmitter: Sufficient Optical Launch Power

Standard transceivers use FP lasers with limited output power. The 160km variant relies on DFB (Distributed Feedback) lasers, which deliver stable wavelengths, high launch power, and optimized performance for long fiber spans.

 

2. Receiver: Ultra-High Sensitivity Detection

After traveling 160km of fiber, optical signal power drops to an extremely faint level. Standard PIN photodiodes cannot detect such weak signals, so APD (Avalanche Photodiode) detectors are integrated. APDs amplify faint incoming optical signals by tens or even hundreds of times, enabling the receiver to recover data transmitted from remote endpoints.

 

The combination of DFB lasers, APD detectors, and the low-loss 1550nm wavelength forms the technical foundation for 160km repeater-free transmission.

 

04 Industry Applications for 155Mbps 160km Transceivers

With the industry fixated on 1.6T high-bandwidth modules, where does the 155Mbps 160km transceiver fit in the market?

 

Scenario 1: Power Private Communication Networks

Communication links between power substations and power plants often span dozens to over one hundred kilometers. 155Mbps bandwidth fully satisfies monitoring and dispatching data requirements, while the 160km capability creates direct fiber links without intermediate repeaters—reducing potential failure points and improving system reliability.

 

Scenario 2: Rail Transit

High-speed rail and metro lines feature widely spaced communication nodes operating in harsh environmental conditions. Industrial-grade 155Mbps transceivers support an extended operating temperature range of -40°C to 85°C, maintaining stable performance year-round in outdoor cabinets and tunnel deployments.

 

Scenario 3: Security Surveillance

Monitoring cameras along highways, national borderlines, and oil & gas pipelines are often situated dozens of kilometers away from central control rooms. 155Mbps bandwidth easily carries multiple high-definition video streams, and the 160km transceiver enables single-hop connectivity between cameras and control centers.

 

Scenario 4: Telecom Carrier Access & SDH/SONET Networks

The 155Mbps 160km SFP transceiver complies with telecom standards including SDH STM-1 and SONET OC-3, making it suitable for long-reach access networks and backbone transmission infrastructure operated by telecommunications carriers.

 

Unifying all use cases: these applications do not demand 1.6T bandwidth—their core requirements are ultra-long transmission distance, uninterrupted connectivity, and robust hardware. The 155Mbps 160km transceiver meets all three criteria with adequate bandwidth, extended fiber reach, and controlled total cost of ownership.

 

05 Key Selection Criteria – Avoid Misleading "160km" Labeling

1. Verify Fiber Type: 160km transmission exclusively requires single-mode fiber (9/125μm); multimode fiber cannot support such extended distances.

2. Confirm Operating Temperature Grade:

- Commercial grade (0°C ~ 70°C): For indoor data center deployments

- Industrial grade (-40°C ~ 85°C): For outdoor cabinet, tunnel, and field installations

3. Validate Optic Chip Configuration: Genuine 160km-capable 155Mbps transceivers must integrate DFB transmit lasers and APD receivers. If product specifications list FP lasers or PIN photodiodes, the module cannot reliably reach 160km.

4. Prioritize DDM Functionality: Digital Diagnostic Monitoring (DDM) provides real-time tracking of transmit/receive optical power, internal temperature, and supply voltage for long-reach links, enabling proactive fault alerts before signal degradation occurs.

 

Closing Remarks

As the optical transceiver industry races to develop ever-higher bandwidth products, the 155Mbps 160km module may appear out of step with market trends.

Yet it illustrates a fundamental engineering truth: not every deployment requires maximum bandwidth—but countless critical infrastructure projects demand maximum transmission distance.

 

Power grid communications, rail transit, border security, and pipeline monitoring systems do not require 1.6T throughput. They demand hardware that reliably transmits every bit of data across 100+ kilometer fiber spans, even in extreme temperatures ranging from -40°C to 85°C.

 

If you are sourcing optical transceivers for long-distance, low-bandwidth fiber communication projects, our industrial-grade 155Mbps 160km SFP modules are in stock for sample testing.

 

Next Article Preview: 1.25G 160km Transceivers – 8x Bandwidth Upgrade, Unchanged 160km Max Reach. Stay Tuned.

 

 

 Contact Information

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Website: www.flowlinktech.com

Email: zjt@flowlinktech.com

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