Do You Know What a BiDi SFP Is?

1. What is a BiDi SFP?

BiDi SFP means bidirectional small form-factor pluggable transceiver. The most distinct characteristic of the bidirectional SFP transceiver is that it is able to achieve bidirectional fiber optic communication by operating on a single fiber. Based on WDM (Wavelength-Division Multiplexing) technology, BiDi optics are able to split different wavelengths of light paths through an integrated wavelength-division multiplexing splitter of BiDi SFP transceivers.

1.1 What is the difference between an SFP and a BiDi SFP?

A common SFP module typically has two ports: a TX port for transmitting signals and an RX port for receiving signals. Unlike common SFP modules, BiDi SFP modules have only one port and use an integral WDM coupler to transmit and receive signals over a single optical fiber.

All SFP modules must be used in pairs. For common SFPs, we should connect two SFPs with the same wavelength. For example, if we use an 850nm SFP on one end, we must use an 850nm SFP on the other end.

Because BiDi SFPs use different wavelengths for transmitting and receiving signals, we should connect two BiDi SFPs with opposite wavelengths. For example, if we use a TX1310/RX1550nm BiDi SFP on one end, we should use a TX1550/RX1310nm BiDi SFP on the other end.

1.2 How Does a BiDi SFP Work?

A BIDI optical module works by filtering (removing unwanted central wavelengths) through filters within the module, simultaneously transmitting one wavelength optical signal and receiving another. To achieve bidirectional communication, the other end must be able to both receive and transmit one wavelength optical signal. For example, if one end transmits a 1310nm optical signal and receives a 1550nm optical signal, the other end must transmit the opposite wavelength: a 1550nm optical signal and a 1310nm optical signal. This is why BIDI modules are used in pairs.

1.3 What does BiDi stand for?

One refers to bidirectional text, meaning documents containing both right-to-left (RTL) and left-to-right (LTR) text.

The other refers to a bidirectional small form-factor pluggable optical module, a technology that enables bidirectional data transmission over a single optical fiber.

1.4 What is SFP+ BiDi?

The 10G BIDI SFP+ optical module uses an SFP+ package, offers a 10G transmission rate, and features an LC simplex connector. It has a transmission distance of up to 80 km when used with single-mode fiber. BiDi stands for single-fiber bidirectional transmission. It utilizes WDM (wavelength division multiplexing) technology to transmit and receive optical signals in two directions at different center wavelengths, enabling bidirectional transmission of optical signals over a single fiber.

1.5 How to Determine Whether an SFP is Single-Mode or Multi-Mode?

First, we can consider the wavelength of the fiber optic module. Generally, if the wavelength is 850nm, it is a multimode module. Single-mode fiber optic modules typically have wavelengths of 1310nm, 1330nm, 1490nm, or 1550nm. CWDM and DWDM color optical modules are both single-mode fiber optic modules.

Second, we can consider the transmission distance of the fiber optic module. Multimode fiber optic modules generally have a transmission distance of less than 2km and require multimode fiber optic patch cables. The transmission distance of a single-mode fiber optic module is generally over 2 km. Gigabit single-mode fiber optic modules can reach up to 160 km, and 10 Gigabit single-mode fiber optic modules can reach up to 100 km.

Next, we can look at the optical device type of the fiber optic module. Multimode fiber optic modules use VCSELs as the optical transmitter, while single-mode fiber optic modules use DFBs, EMLs, FPs, and other optical transmitters.

Finally, we can determine whether a fiber optic module is single-mode or multi-mode by the color of the pull tab. Multimode fiber optic modules with transmission rates below 40G (excluding 40G) generally have a black pull tab, while multimode fiber optic modules with transmission rates of 40G and above have a beige pull tab. Single-mode fiber optic modules with a wavelength of 1310nm have a blue pull tab. Other pull tab colors are available, but they are all single-mode fiber optic modules.

2. What is the difference between duplex and BiDi?

Duplex refers to the use of two independent optical fibers for full-duplex communication (simultaneous transmission and reception). BiDi is a technology that uses a single optical fiber to transmit and receive at different wavelengths to achieve full-duplex communication.

2.1 Is BiDi half-duplex?

Simple mode refers to data transmission in only one direction. In practical applications, these devices include printers, radio stations, and monitors. They only receive signals or commands, not send them.

Why is it called half-duplex? Half-duplex refers to data transmission that supports bidirectional transmission, but not simultaneous transmission. At any given moment, one end can only send or receive.

Duplex refers to data transmission in both directions simultaneously. It is a combination of simplex communication modes, requiring both the sending and receiving devices to have independent transmission and receiving capabilities. BiDi optical modules use this single-fiber full-duplex communication mode.

2.2 What is the Difference Between BiDi and Dual-Fiber?

BiDi optical modules have a compact structure and are primarily used in optical communications, including telecommunications and bidirectional data communications. Single-fiber bidirectional transmission, or BiDi, means that optical signals can be transmitted and received simultaneously in both directions on a single optical fiber, much like a road with two lanes separated by a median strip, allowing vehicles on each side to travel in their respective lanes without interfering with each other. Conventional optical fiber transmission is single-fiber, unidirectional, requiring two optical fibers to achieve bidirectional communication.

2.3 What is the Difference Between Duplex and BiDi?

BIDI optical modules have only one connector, available in either LC or SC types. They filter signals through filters within the module, simultaneously transmitting 1310nm optical signals and receiving 1550nm signals, or vice versa. Therefore, these modules must be used in pairs. Their greatest advantage is conserving fiber resources. However, single-fiber BIDI optical modules are more expensive than dual-fiber modules. However, since only one fiber is required for transmission, the actual cost of use is lower when the transmission link is long enough.

Furthermore, dual-fiber and single-fiber BIDI modules use different optical components. Dual-fiber modules use a TOSA and ROSA for optical transceivers, while single-fiber BIDI modules use a BOSA. A TOSA (Transmitter Optical Module) consists of a TO-CAN laser, adapter, die sleeve, isolator, and adjustment ring. A ROSA (Receiver Optical Module) consists of a detector and adapter. A BOSA combines the laser and detector, adding filters and a base to the TOSA and ROSA components.

3. YXFiber SFP BiDi 10G 40km

The YXF-PP-B23L-40D is a high-performance, cost-effective module that supports data rates up to 10.3125Gbps over single-mode fiber and a transmission distance of up to 40 km. This transceiver consists of two parts: the transmitter section includes a laser driver and a 1270nm DFB laser. The receiver section includes a PIN photodiode with an integrated transimpedance preamplifier (TIA) and limiting amplifier. The module is hot-swappable to a 20-pin connector. The high-speed electrical interface is based on low-voltage logic, with an internal differential impedance of 100 ohms and AC coupling.

The optical output can be disabled via the LVTTL logic-high input, TX_DIS. The transmit fault (Tx_Fault) output indicates that the module's transmitter has detected a fault condition related to laser operation or safety. The loss-of-signal (RX_LOS) output indicates the loss of the input optical signal at the receiver. The serial EEPROM in the transceiver allows access to transceiver monitoring and configuration data via the dual-wire SFP management interface. This interface uses a single address, A0h, and its memory map is divided into lower and upper memory areas. Basic digital diagnostic (DD) data is stored in the lower memory area, while specialized data is stored in a series of tables in the upper memory area.

The YXF-PP-B32L-40D is a high-performance, cost-effective module that supports data rates up to 10.3125 Gbps over single-mode fiber and a transmission distance of up to 40 km. The transceiver consists of two sections: the transmit section includes a laser driver and a 1330nm DFB laser. The receive section includes a PIN photodiode with an integrated transimpedance preamplifier (TIA) and limiting amplifier. The module is hot-swappable to a 20-pin connector. The high-speed electrical interface is based on low-voltage logic, with a nominal 100-ohm differential impedance and AC coupling within the module.

The optical output can be disabled via the LVTTL logic-high input TX_DIS. The transmit fault (Tx_Fault) output indicates a fault condition related to laser operation or safety at the module's transmitter. The loss-of-signal (RX_LOS) output indicates the loss of the input optical signal at the receiver. The serial EEPROM in the transceiver allows users to access transceiver monitoring and configuration data via the two-wire SFP management interface. This interface uses a single address, A0h, and its memory map is divided into lower and upper memory areas. Basic digital diagnostic (DD) data is stored in the lower memory area, while specialized data is stored in a series of tables in the upper memory area.