OPTICAL-FIBER - SFP Documentation

SFP Form Factors

SFP modules are divided into different form factors based on their data rate and distance capabilities. Some of the common SFP types include:

• **Standard SFP**: Supports speeds of up to 1 Gbps over fiber.
• **SFP+**: An enhanced version of SFP supporting speeds up to 10 Gbps.
• **QSFP (Quad SFP)**: Supports up to 40 Gbps using four SFP+ modules in parallel.
• **SFP28**: Supports speeds of 25 Gbps.
• **QSFP28**: Supports speeds of 100 Gbps.

The form factor of the SFP is typically indicated on the module label, including the supported speed, fiber type, and wavelength.

Optical Fiber Types

The optical fiber used in SFP modules can generally be divided into two categories:

• **Single-mode fiber (SMF)**: Supports longer-distance transmission and typically uses 1310 nm or 1550 nm wavelength lasers. SMF modules are used for long-haul links.
• **Multi-mode fiber (MMF)**: Used for short-distance transmission and uses 850 nm or 1310 nm wavelength lasers. MMF is common in local area networks (LANs) or data centers.

Wavelength and Reach Specifications

Each optical SFP module is characterized by its transmission wavelength and its maximum reach. Typical specifications include:

• **Wavelength**: The optical wavelength used for transmission (e.g., 850 nm, 1310 nm, 1550 nm).
• **Reach**: The maximum distance over which the signal can be transmitted without excessive degradation, often measured in meters or kilometers.

Some common examples include:

• **SFP LX (Long Range)**: Typically supports single-mode fiber with a wavelength of 1310 nm and a reach of up to 10 km.
• **SFP SX (Short Range)**: Typically supports multi-mode fiber with a wavelength of 850 nm and a reach of up to 550 meters.

Transmitter and Receiver Specifications

SFP modules use laser diodes (LD) or light-emitting diodes (LED) for transmission. Depending on the optical module's specifications, different types of lasers are used:

• **VCSEL (Vertical-cavity surface-emitting laser)**: Used for short-range MMF connections (850 nm).
• **DFB (Distributed Feedback) Laser**: Used for long-range SMF connections (1310 nm, 1550 nm).

The receiver generally uses a photodiode (PIN or APD) to convert the optical signal into an electrical signal.

Electrical Interface

The SFP module has a standard electrical interface that allows it to be hot-plugged into network devices. The electrical interface consists of several pins that support the following functions:

• **Transmit Data (TD+) / (TD-)**: The electrical data output pins from the module.
• **Receive Data (RD+) / (RD-)**: The electrical data input pins to the module.
• **Module Monitoring (MDI)**: This set of pins is used for reading module status such as temperature, voltage, and optical power.

SFP Module Compatibility

While many vendors produce SFP modules, compatibility can vary. Transceivers from different manufacturers may work with a variety of devices, but it is important to ensure that the network hardware (switch, router, etc.) and the optical module are compatible. Some devices may require specific vendor SFPs to avoid issues with performance or compatibility.

Recapitulative Array

SFP Module Overview

Module Type	Speed (Gbps)	Fiber Type	Wavelength	Maximum Reach
SFP	1	Multi-mode / Single-mode	850 nm / 1310 nm / 1550 nm	550 m (MMF) / 10 km (SMF)
SFP+	10	Multi-mode / Single-mode	850 nm / 1310 nm	300 m (MMF) / 10 km (SMF)
SFP28	25	Multi-mode / Single-mode	850 nm / 1310 nm	100 m (MMF) / 10 km (SMF)
QSFP28	100	Multi-mode / Single-mode	850 nm / 1310 nm	100 m (MMF) / 10 km (SMF)

Useful Links

• [SFP Transceiver Standards - IEEE 802.3](https://ieeexplore.ieee.org/document/5574074)
• [SFP and SFP+ Transceiver Specifications](https://www.fs.com/c/sfp-and-sfp-plus-transceivers)
• [Optical SFP Module Compatibility Guide](https://www.cablingplus.com/sfp-compatibility-guide/)
• [Understanding SFP and SFP+ Modules](https://www.cablinginstall.com/cable/article/16472561/understanding-sfp-and-sfp-modules)