Tag: PON

Can I use single mode equipment over multimode cable and vice versa?

This is a question we get many times from our customers. Especially common is a situation, in older installations, back to the times when multimode cable was cheaper than single mode, and inside buildings, and some last mile installations were planned so, that multimode cables were laid.

Answer is not that easy, to answer simply yes or no. Let’s delve in a details.

Definitions:

  • SONET – Synchronous Optical Network
  • SMF – SingleMode Fiber
  • MMF – MultiMode Fiber
  • LED – Light Emitting Diode
  • DMD – Differential Mode Delay
  • Mode –
  1. light rays entering the fiber at the particular angle;
  2. paths of different length and transmission delays that travel through the cable.

SMF is using laser as a source for the light and therefore light beam is very concentrated. It allows higher bandwidth compared to MMF, while having greater transmission distance.

MMF is typically using LEDs for transmission of the optical signal. It is clear from the name, that it uses multiple modes of light at the same time. Entry angles differ for each mode of the light resulting in different speeds and distances that signal can travel.

single-mode-vs-multimode

Single mode vs Multimode

  1. It is possible to interconnect two devices using SMF interface at one end and MMF receiver at another one. But here, many depends also on devices. Like for example ,more sophisticated routers, like Huawei, Alcatel or Cisco while supporting that at physical layer, will not support it at TA. Problem is in DMD that may occur when two different modes are directly coupled. Degradation of the bandwidth also decreases the distance supported for transmission. Also, SMF transmitter should be calibrated in a way so the SMF signal would not overdrive MMF receiver.

Solution: Using the intermediate switch with SMF and MMF interfaces that is able to convert the signals is a good alternative.

  1. If you use simple devices, such as video over fiber, or media converters, then it depends, what wavelength are used for your equipment. The trick here is that as we know, single-mode fibers used in telecommunications operate at 1310 or 1550 nm and require bit (now only a little bit) more expensive laser sources, and in older equipment MMF wavelength used were 850 nm.

And if you have this kind of transceivers, then it won’t work over your single mode cable. If you have a newer generation media converters, which use 1300 nm lasers, it will most likely work.

Most common wavelengths

Table 1. Most common wavelengths (non WDM, CWDM or DWDM) used in optical transmission systems.

DK Photonics – www.dkphotonics.com  specializes in designing and manufacturing of high quality optical passive components mainly for telecommunication, fiber sensor and fiber laser applications,such as PLC Splitter, WDM, FWDM, CWDM, DWDM, OADM,Optical Circulator, Isolator, PM Circulator, PM Isolator, Fused Coupler, Fused WDM, Collimator, Optical Switch and Polarization Maintaining Components, Pump Combiner, High power isolator, Patch Cord and all kinds of connectors.

What is Passive Optical Network?

Passive Optical Network (PON) is a form of fiber-optic access network that uses point-to-multipoint fiber to the premises in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises. A PON system consists of an OLT at the service provider’s central office and a number of ONU units near end users, with an ODN between the OLT and ONU. PON reduces the amount of fiber and central office equipment required compared with point-to-point architectures.

PON Optical Network
Passive Optical Network (PON)

The most obvious advantage of the PON network is the elimination of the outdoor active devices. All the signals processing functions are completed in the switches and the user premises equipment. The upfront investment of this access methods are small, and the most funds investment is postponed until the user really access. Its transmission distance is shorter than the active optical access system. The coverage is also smaller, but it is low cost, no need to set the engine room, and easy to maintain. So this structure can be economically serve for the home users.

PON Development Background

Seen from the entire network structures, due to the larger numbers of laying optical fibers, and widely applications of DWDM technology, the backbone network has been a breakthrough in the development. The same time, due to advances in Ethernet technology, its dominant LAN bandwidth has increased from 10M, 100M to 1G or 10G.. At present, what we are concerned about is the part between the network backbone and local area networks, home users; this is often said that the “last mile”, which a bottleneck is. Must break this bottleneck, may user in the new world of the online world. It is as if in a national highway system, trunk and regional roads have been built in the broad high-grade highway, but leads to the families and businesses of the door was still narrow winding path, the efficiency of the road network cannot play.