Skip to content 
QSFP+ 40G PSM4 and SR4 MPO cable are consistent in terms of polarity selection, but differ fundamentally in their application scenarios and fiber type.
Recommended Polarity: Type B (Cross)
Whether for single mode PSM4 MPO cable or multi mode SR4 MPO cable, Type B is the industry-standard polarity for 40G, 100G, and 400G parallel transmission.
Why use Type B?
The operating principle of parallel fiber transceiver module is “transmit on the left, receive on the right” (e.g., fibers 1–4 transmit, and fibers 9–12 receive). A MPO Type B patch cord completely reverses the internal fiber sequence (connecting 1 to 12), thereby ensuring that the transmitting fibers at end A align perfectly with the receiving fibers at end B.
What happens if you accidentally use a Type A MPO jumper?
Type A is a straight-through cable (connecting 1 to 1); consequently, the transmit signals from end A will be directed into the transmitter at end B. As a result, the link will never establish a connection (i.e., the indicator light will not turn on).
Usage Scenario Comparison
QSFP 40G SR4 MPO Cable (Multimode OM3/OM4/OM5 fiber)
SR4 S MPO sables are primarily used in short-distance, high-density indoor environments within 100 meters (typical distance for OM4, 70meter for OM3 fiber). It is the the lowest cost of comprehensive solution (fiber transceiver modules + mpo mtp patch cords) and serves as the mainstay for cabling within enterprise-grade data centers。
Typical Scenarios:
- Intra-cabinet Interconnection: Direct connections between switches and servers.
- Cross-cabinet Interconnection (Within the Same Computer Room): Connections from End-of-Row (EoR) cabinets to the Main Distribution Frame (MDF) within a data center.
PSM4 40G Breakout Cable (single mode OS2)
PSM4 Single mode MPO cables are primarily used in medium-distance scenarios where a balance between cost and performance is required.
Typical Scenarios:
- Cross-Data Center /Cross-Floor: When the 100 meter reach of multimode SR4 transceivers is insufficient, PSM4 transceivers can extend the transmission distance up to 500 meters.
- Hyperscale Data Centers: These facilities span vast physical areas; consequently, PSM4 transceivers are frequently deployed to interconnect core switches located across different zones (PODs). A prime example is the campus network of a cloud service provider, which requires cost-effective, high-speed connectivity across a massive number of single-mode fiber cores.
- 1 to 4 Breakout Kits: When a single 400G DR4 port is split into four separate 100G links, PSM4 transceivers are used at the termination points of these individual links.
Note:
- The PSM4 SFP MPO transceivers must be used with APC (green) connectors; otherwise, return loss will severely degrade performance.
- Single mode fiber trunk cabling is inexpensive, and PSM4 transceiver modules are significantly cheaper than LR4 modules (10 km class).
Summary Table of Polarity and Mechanical Specifications
| Features | PSM4 40G Breakout Cable Applciations | QSFP 40G SR4 MPO Cable Applications |
| Common Polarity | Type B (Required) | Type B (Required) |
| Fiber Color | Yellow (OS2) (Single-mode) | Purple (OM4) / Aqua (OM3) (Multimode) |
| Connector Color/Shape | Green (APC Angled) | Black / Aqua (UPC Flat) |
| Primary Applications | Medium-to-Long Distance Interconnects (within 500m) | Within 100 meters; within the same data center / cabinet |
| Hardware Cost | Medium | Extremely Low |
Conclusion
If your goal is to maximize the utilization of a 12 fiber backbone, specifically in a scenario involving a Base-8 architecture (e.g., upgrading via a 2×12-to-3×8 conversion cable). You must ensure that the end-to-end link (comprising the backbone cable and conversion patch cords) ultimately establishes a Type B polarity.
Furthermore, PSM4 40G breakout cable must be paired with green (APC) connectors, while QSFP 40G SR4 MPO cable must be paired with non-green (UPC) connectors.
- For multimode SR4 environments, please select Type B + OM4 + Black/Aqua connectors.
- For single-mode PSM4 environments, please select Type B + OS2 + Green (APC) connectors.
Yingda will paste a label with product information in detail, including fiber type, fiber connector, cable type, polarity type and test datas. You can rest assured to buy them from Yingda.
FAQ
What does it mean if a switch port’s status is displayed as “Initializing” or “Down”?
When a switch port displays a status of “Initializing” or “Down”—even if the correct physical port has been selected—it typically indicates a failure in the physical link layer (Layer 1) handshake process.
What happens if the polarity setting is incorrect?
If the polarity setting is incorrect, the switch port will immediately enter a “Down” state and will be unable to establish a connection.
What price is the PSM4 40g breakout cable?
PSM4 single mode cable price wil be differ from length and quantity. Yingda are high-efficiency mpo cable factory, we ensure best price and fast delivery for you.
How long does it take to produce 500 QSFP 40G SR4 MPO cables?
Typically, the lead time is kept within 7 to 15 days. For large-volume orders, the timeline is determined based on the company’s production schedule.
How do you manage quality control?
All products are manufactured with international production and testing equipment, based on ISO international quality requirements. Our production staff have undergone comprehensive training and certification, and they strictly adhere to Standard Operating Procedures (SOPs). This ensures the consistent execution of every detail and process, thereby guaranteeing that products are completed on time, meeting both quality and quantity specifications.
