A single-mode patch cord is a short OS2 cable with 9/125 µm fibre and a connector at each end, used to connect long-reach optics, telecom frames, FTTH equipment and test sets. It comes with LC, SC, FC, ST or MPO connectors, UPC or APC polish, and G.652.D or bend-insensitive G.657 fibre. Radix Fibrotech makes them to order in Pune and tests each cord.
Single-mode patch cord configurations
A single mode patch cord carries one optical mode through a 9 µm core, so it suits links measured in hundreds of metres or in kilometres. The same product is sold as an OS2 patch cord, a 9/125 patch cord or, in US catalogues, a single mode fiber patch cable. Radix makes single-mode cords to order in Pune: each row below is chosen per order line, and each finished cord is tested before it is packed. For one connector pair in depth, see LC to LC patch cords and the other pairings under fibre optic patch cords.
| Option | Choices | Notes |
|---|---|---|
| Connectors | LC, SC, FC, ST or MPO, the same at both ends or mixed (LC to SC, LC to FC, SC to FC, MPO to LC) | LC for transceivers and dense panels, SC for access networks, FC for instruments |
| End face | UPC or APC, chosen for each end | Hybrid UPC to APC cords join ports that differ |
| Fibre count | Simplex or duplex; MPO in 8, 12, 16 or 24 fibres | Duplex cords are wired A-to-B unless the order says otherwise |
| Fibre | ITU-T G.652.D, or bend-insensitive G.657.A1 or G.657.A2 | G.657.A1 is specified to a 10 mm bend radius, G.657.A2 to 7.5 mm; both mate and splice with G.652.D |
| Jacket | LSZH, PVC, riser (OFNR), plenum (OFNP) or armoured | Riser and plenum are US National Electrical Code ratings |
| Diameter | 1.6, 2.0 or 3.0 mm simplex or duplex zip; round duplex; armoured | Thinner cords suit full frames |
| Length | Any length to order | State a tolerance for tight routes and long cross-connects |
Where single-mode patch cords are used
Long-reach, DR and FR optics
Single-mode Ethernet optics mostly run at 1310 nm, and the cord must match both the fibre and the connector on the module.
| Optic | Connector on the module | Published reach |
|---|---|---|
| 10GBASE-LR, 25GBASE-LR | LC duplex | 10 km |
| 100GBASE-DR | LC duplex | 500 m |
| 100GBASE-LR4 | LC duplex | 10 km |
| 400GBASE-FR4 | LC duplex | 2 km |
| 400GBASE-DR4 | MPO-12, usually APC | 500 m over 8 fibres |
These are IEEE 802.3 channel reaches, not cord figures. A 400GBASE-DR4 port is often split into four 100GBASE-DR links with an MPO to LC duplex breakout, and the MPO end must match the polish and pin gender of the module. Single-mode MPO cords are covered under MPO patch cords.
Telecom frames and FTTH
Exchange ODFs and street cabinets use single-mode cords to cross-connect equipment to outside plant fibre. Passive optical networks run SC/APC through most of the distribution network, and GPON carries downstream at 1490 nm and upstream at 1310 nm on one fibre, so access cords are mostly simplex. Cords from OLT line cards are often UPC at the equipment end and SC/APC at the frame.
Broadcast
Fibre-SDI converters, camera fibre systems and venue tie lines run on single-mode fibre for its reach between trucks, galleries and stages. LC is usual on SFP-based converters; older equipment may carry ST or FC, so check each port.
Test leads
Power meters, light sources and OTDRs connect through test reference cords, which need low-loss, carefully inspected connectors because every reading includes them. FC is common on instrument ports, and APC leads are needed to test APC links. IEC 61280-4-2 describes the reference methods for testing installed single-mode cabling.
APC patch cords and where they are required
An APC patch cord has its end face polished at 8 degrees, so light reflected at the joint leaves the core instead of travelling back towards the laser. The usual industry figures are return loss of 60 dB or better for APC against 50 dB or better for UPC. APC is required, or normally specified, in these cases:
- PON and FTTH. SC/APC is the access network norm, and an RF video overlay at 1550 nm is sensitive to reflections.
- Cable TV and analogue RF over fibre. Analogue signals degrade with reflected light.
- Parallel single-mode MPO. DR4 and DR8 modules generally use angled MPO end faces.
- Some test and sensing equipment. Lasers and OTDRs are often fitted with FC/APC or SC/APC ports.
Ethernet LR, DR and FR optics with LC ports are normally UPC. An APC connector must never be mated with a UPC one: the air gap raises loss and can damage both faces. Where two ports differ, order a hybrid cord, UPC at one end and APC at the other. The UPC vs APC guide explains the end-face geometry.
Colour conventions for single-mode cords
TIA-598 assigns yellow to single-mode premises cable, so indoor single-mode cords are yellow almost everywhere. Connector bodies show the polish: blue for single-mode UPC, green for APC. Boots follow the body or the jacket colour, depending on the maker.
Colour has limits. Armoured and outdoor cords often have black outer sheaths whatever the fibre, and some sites colour-code cords by network or service instead of fibre type. Ask for the fibre type in the jacket legend and on the label, so a cord can still be identified when the colour scheme has drifted.
OS2 is an ISO/IEC 11801 category for cabled fibre, defined by attenuation per kilometre, and over a few metres of cord it makes no measurable difference to loss. What matters in a cord is the fibre standard, G.652.D or G.657. If project documents call for an OS2 patch cord, say whether the legend must read OS2. The single-mode fibre optic cable guide explains OS1a and OS2.
Testing each cord at 1310 and 1550 nm
Radix tests each single-mode cord before dispatch. The usual checks are insertion loss on every connector at 1310 and 1550 nm, return loss on every connector, and end-face inspection under magnification against IEC 61300-3-35 criteria.
Testing at both wavelengths has a purpose. Bend and stress loss rise with wavelength, so a cord that passes at 1310 nm but reads high at 1550 nm usually has a tight bend, a stressed fibre in the boot or a jacket fault. APC cords are measured against APC reference cords, since a UPC reference would itself be a mismatch.
| Measure | Industry reference | Source |
|---|---|---|
| Insertion loss, mated connector pair | 0.75 dB maximum for channel planning | TIA-568 |
| Return loss, UPC | 50 dB or better | Common industry figure |
| Return loss, APC | 60 dB or better | Common industry figure |
| Connector performance | Graded random-mated loss and return loss | IEC 61753-1 |
Factory-made cords normally test well inside the 0.75 dB planning allowance. Put the maximum insertion loss you need per connector on the quote, with the report format: a printed sheet per cord, a serialised spreadsheet or both.
Ordering checklist
Give one line per configuration, each with:
- Connector and polish at end A and end B, for example LC/UPC to SC/APC.
- Simplex or duplex; for MPO, fibre count, pin gender and polarity.
- Fibre standard: G.652.D, G.657.A1 or G.657.A2.
- Jacket material, fire rating for the country of installation, and outer diameter.
- Length and tolerance, measured along the cable route.
- Duplex polarity, if not A-to-B.
- Maximum insertion loss and minimum return loss, if the project sets them.
- Label text, jacket legend and test report format.
- Quantity for that line.
Send the list through the request a quote page.
What sets the price of a single-mode patch cord
Single-mode patch cords are priced on request against the specification. The main factors:
- Connectors. MPO and FC cost more to terminate than LC or SC, and a duplex cord has four connectors where a simplex has two.
- Polish. APC and hybrid cords take longer to polish and inspect.
- Fibre. Bend-insensitive G.657.A2 costs more per metre than G.652.D.
- Jacket. Plenum and armoured constructions cost more than LSZH or PVC.
- Loss limits. A tighter insertion loss maximum leaves fewer acceptable parts.
- Length. Cable is a small share of a short cord and a large share of a long one.
- Paperwork and volume. Serialised reports and custom labels add handling, and many identical cords cost less each than a mix of small lines.
Questions buyers ask
Is an OS2 patch cord the same as a 9/125 patch cord?
In practice, yes. 9/125 describes the single-mode fibre geometry, a 9 µm core in 125 µm cladding, and OS2 is the ISO/IEC 11801 cabled category most single-mode cords are sold under. For a cord, also specify the fibre standard, G.652.D or bend-insensitive G.657, because that is what changes bend performance.
Can I use a single-mode patch cord with a multimode transceiver?
No. A multimode 850 nm optic launches light into a 50 µm core, and a 9 µm single-mode core captures only a small part of it, so the link fails or runs with very high loss. Match the cord to the fibre type stated on the transceiver datasheet.
When is an APC patch cord required?
When the port it plugs into is APC. That is usual in PON and FTTH frames, cable TV and RF video systems, parallel single-mode MPO optics and some test lasers. Green connector bodies mark APC. Most Ethernet LR and FR optics with LC ports are UPC, so check the port before ordering.
Should I choose G.652.D or G.657.A2 fibre for patch cords?
G.657.A2 is specified down to a 7.5 mm bend radius, far tighter than G.652.D, so it keeps loss low in crowded racks, cabinets and wall outlets. It mates and splices with G.652.D. Choose G.652.D where the project specifies it and the routing is generous.
Can a single-mode cord have a different connector at each end?
Yes. LC to SC, LC to FC, SC to FC and MPO to LC cords are made to order, and the polish can differ by end as well, for example LC/UPC to SC/APC. State the connector and polish for end A and end B separately on the order.