25G BiDi 40KM vs 60KM Optical Transceiver: Laser,Wavelength,and Application Differences

1. What Is a 25G BiDi Optical Transceiver?

The C-LIGHT 25G BiDi (Bidirectional) optical transceiver utilizes Single Fiber Bidirectional (BiDi) transmission technology, enabling both transmit (TX) and receive (RX) signals to be carried over a single strand of single-mode fiber (SMF).

Its core technology is Wavelength Division Multiplexing (WDM), which uses two different wavelengths for simultaneous bidirectional communication. This design reduces fiber usage by up to 50%, making it an ideal solution for fiber-constrained network deployments.

C-LIGHT 25G BiDi SFP28 optical transceivers are widely deployed in:

• 5G Fronthaul Networks

• Telecom Access Networks

• Data Centers

• Enterprise Campus Networks

• Metropolitan Area Networks (MAN)

The most popular transmission distances on today's market include 10 km, 20 km, 40 km, and 60 km. Among them, the 40KM and 60KM models exhibit the most significant differences in optical design.

2. 25G BiDi 40KM vs. 60KM Specifications

Although the two modules share nearly identical specifications, the real performance differences lie in their laser design, wavelength selection, and receiver architecture.

3. Laser Technology Comparison – The Biggest Difference

The laser design is the most significant technical distinction between the two products.

4. Wavelength Design Differences

C-LIGHT 25G BiDi 40KM

Side A

• TX: 1270 nm

• RX: 1330 nm

Side B

• TX: 1330 nm

• RX: 1270 nm

Features

• Wider wavelength spacing

• Easier WDM isolation

• Mature optical components

• Lower manufacturing cost

C-LIGHT 25G BiDi 60KM

Side A

• TX: 1290 nm

• RX: 1310 nm

Side B

• TX: 1310 nm

• RX: 1290 nm

Features

• Narrower wavelength spacing requiring higher-performance optical filters

• Significantly improved chromatic dispersion performance for long-distance transmission

• More sophisticated optical component manufacturing

• Higher production cost

5. Receiver Comparison

The 60KM module employs a higher-sensitivity APD receiver, enabling improved optical power margin and enhanced long-distance transmission performance.

6. Why Does the C-LIGHT 25G BiDi 60KM Module Use Higher-Performance Components?

Several engineering considerations require the 60KM version to utilize higher-specification optical components.

(1) Higher Fiber Attenuation

Typical attenuation in G.652 single-mode fiber is approximately:

• 1270 nm: 3.5–4.5 dB per 10 km

• 1290/1310 nm: 2.5–3.5 dB per 10 km

Therefore:

• 40 km at 1270 nm: approximately 12–18 dB loss

• 60 km at 1270 nm: approximately 21–27 dB loss

A conventional 1270 nm DFB laser generally cannot provide sufficient optical budget for stable 60 km transmission.

By contrast, the 1290 nm/1310 nm wavelength pair experiences significantly lower attenuation, reducing total fiber loss to approximately 15–21 dB over 60 km, making it much better suited for long-distance links.

(2) Increased Chromatic Dispersion

At 25G NRZ, chromatic dispersion becomes a critical limiting factor.

Compared with the 1270 nm/1330 nm wavelength combination, the 1290 nm/1310 nm pair offers superior dispersion performance, allowing signals to maintain better integrity over longer distances.

(3) Larger Link Budget

Carrier-class optical networks typically reserve an additional 3–5 dB optical margin to compensate for:

• Fiber aging

• Temperature variation

• Fiber bending

• Connector contamination

• Future network expansion

As a result, most 60KM BiDi optical transceivers are designed with an optical link budget of approximately 21–24 dB, ensuring long-term transmission stability.

7. How to Choose Between 40KM and 60KM

Choose the 40KM Module If:

• Your actual fiber link is 35 km or shorter

• Cost efficiency is a priority

• You are deploying enterprise or campus networks

• Your application is standard data center interconnection

Choose the 60KM Module If:

• The fiber link exceeds 40 km

• The network is operated by a telecom carrier

• High link reliability is required

• Future expansion or additional splice points are expected

• Greater optical power margin is preferred

8. C-LIGHT 25G BiDi Optical Transceiver Solutions

C-LIGHT offers a complete portfolio of 25G Single Fiber BiDi optical transceivers, including:

Product Series

• 25G BiDi 10KM

• 25G BiDi 20KM

• 25G BiDi 40KM

• 25G BiDi 60KM

Product Advantages

• High-performance DFB lasers with multiple wavelength combinations

• High-sensitivity APD receiver design

• Precision WDM optical filtering

• Low bit error rate (BER)

• Industrial operating temperature support (-40°C to +85°C)

• 100% optical performance and compatibility testing

• Compatible with mainstream switches, routers, and telecom equipment

9. Conclusion

Although the C-LIGHT 25G BiDi 40KM and 60KM optical transceivers share the same form factor, interface, and overall appearance, they differ substantially in laser performance, wavelength design, receiver sensitivity, optical link budget, and long-distance transmission capability.

When selecting an optical transceiver, network designers should evaluate not only transmission distance but also factors such as fiber attenuation, splice count, future network expansion, and required system reliability. Maintaining adequate optical power margin is essential for ensuring long-term stable network operation.

10. Frequently Asked Questions (FAQ)