在ICND1 Vol.1 P.1-167 提到了一個我沒有注意到的SFP規格(1000BASE-BX10-D/U)，原來現在可以利用一蕊的Fiber同時提供傳送及接收的方向，很久以前，在這種規格尚未出現之前，我們通常會使用一種fiber transceiver來達成這種目標，主要的原因就是為了可以減少fiber蕊數的使用，現在看來是把這種技術直接整合進了SFP中。
1000BASE-BX10-D and 1000BASE-BX10-U SFP for Single-Fiber Bidirectional Applications
The 1000BASE-BX-D and 1000BASE-BX-U SFPs, compatible with the IEEE 802.3ah 1000BASE-BX10-D and 1000BASE-BX10-U standards, operate on a single strand of standard SMF.
A 1000BASE-BX10-D device is always connected to a 1000BASE-BX10-U device with a single strand of standard SMF with an operating transmission range up to 10 km.
The communication over a single strand of fiber is achieved by separating the transmission wavelength of the two devices as depicted in Figure 3: 1000BASE-BX10-D transmits a 1490-nm channel and receives a 1310-nm signal, whereas 1000BASE-BX10-U transmits at a 1310-nm wavelength and receives a 1490-nm signal. Note in Figure 3 the presence of a wavelength-division multiplexing (WDM) splitter integrated into the SFP to split the 1310-nm and 1490-nm light paths.
Figure 4. Bidirectional Transmission of a Single Strand of SMF
The GLC-BX-D and GLC-BX-U SFPs also support digital optical monitoring (DOM) functions according to the industry-standard SFF-8472 multisource agreement (MSA). This feature gives the end user the ability to monitor real-time parameters of the SFP, such as optical output power, optical input power, temperature, laser bias current, and transceiver supply voltage.
2-channel 1000BASE-BX10-D for Single-Fiber Bidirectional Applications
The 2-channel 1000BASE-BX-D SFP module, also known as Compact SFP, integrates two IEEE 802.3ah 1000BASE-BX10-D interfaces in one SFP module. The GLC-2BX-D is always connected to two 1000BASE-BX10-U interfaces over two single strands of standard SMF with an operating transmission range up to 10km.
GLC-2BX-D is designed to connect to any standard-based Customer Premises Equipment (CPE) in FTTx links.