For most fiber optic applications single mode and multi mode fiber optic cable made of glass is most suitable. Single mode and multi mode are the two transmission methods for fiber optics- having to do with how they get the signal to the other end of the glass. They are not interchangeable, so it’s important to know which you have. Single-mode fibers provide a single pathway for light to travel and are defined by their small core size of approximately 8.3 µm. Multimode fibers, on the other hand, have various paths, or modes, in which light can travel through optical fiber. These core sizes are larger, ranging from 50 µm to 62.5 µm.

Single Mode Fiber Optic Cable
Core Diameter: Approximately 8-10 micrometers.
Light Propagation: Uses a single light path (mode) to transmit data.
Wavelengths: Typically operates at 1310 nm and 1550 nm.
Distance: Ideal for long-distance communication (up to 100 km or more).
Bandwidth: Higher bandwidth and lower attenuation, providing high data transfer rates over long distances.
Applications: Long-haul telecommunications, cable television, and Internet backbones.

Multi Mode Fiber Optic Cable
Core Diameter: Approximately 50-62.5 micrometers.
Light Propagation: Uses multiple light paths (modes) to transmit data.
Wavelengths: Typically operates at 850 nm and 1300 nm.
Distance: Suitable for shorter distances (up to 2 km for slower speeds and up to 550 meters for high-speed networks).
Bandwidth: Lower bandwidth compared to single mode, with higher attenuation over long distances.
Applications: Local area networks (LANs), data centers, and intra-building networks.

Single mode fiber has very thin center core. You need a laser source that is very accurately shooting signal to it and all cable splices need to be very accurate. In typical telecommunications fiber, single mode operation is obtained with core diameters of 2–10 microns with a standard outer diameter of 125 microns. Once you get signal to single mode fiber, it will go through it with very little loss and other signal quality issues. Single-mode fibre are used almost universally in telecommunications over 1 km or so and are generally used at the 1300 nm and 1550 nm wavelengths. (Below 1100 nm, the Rayleigh-scattering dominates, while above 1600 nm the infrared absorption dominates). Single-mode fibers used in telecommunications typically operate at 1310 or 1550 nm and require laser sources (that some were expensive and many are still are expensive). OS1 and OS2 are standard single-mode optical fiber used with wavelengths 1310 nm and 1550 nm (size 9/125 μm) with a maximum attenuation of 1 dB/km (OS1) and 0.4 dB/km (OS2). Single-mode fibres are capable of wide bandwidths (e.g. >40 GHz) and are, therefore, ideally suited for long-haul and high capacity circuits.

Multimode fiber has core diameters considerably larger, typically 50, 62.5, 85, and 110 microns, again with a cladded diameter of 125 microns. Because of their larger core size, multi-mode fibers have higher numerical apertures which means they are better at collecting light than single-mode fibers. Multi mode fiber has thicker core, so sending light to it is easier (cheaper led technology will work and does not necessarily need laser transmitter). Multi-mode fiber has higher “light-gathering” capacity than single-mode optical fiber. In practical terms, the larger core size simplifies connections and also allows the use of lower-cost electronics such as light-emitting diodes (LEDs) and vertical-cavity surface-emitting lasers (VCSELs) which operate at the 850 nm and 1300 nm wavelength. Also cable splices do not need to be micrometer accurate to work OK. Multi mode is easier to work with and hardware for it is cheaper. As the name implies, multimode fibres are capable of propagating more than one mode at a time and they are ideally sited for high bandwidth (i.e. a few GHz) and medium haul applications. The disadvantages are much higher signal loss and more signal distortion – meaning supports less distance and less data bandwidth compared to single mode. Multimode fibers tend to have higher attenuation than single-mode fibers since the intrinsic loss of the multimode fiber is higher due to the natural loss of the fiber in the operating wavelengths of 850 nm and 1300 nm. The LED light sources sometimes used with multi-mode fiber produce a range of wavelengths and these each propagate at different speeds, which limits the available bandwidth over distance.

When transporting data over fiber optic cable, the transceivers have to match the cable type used. This means that the connector type in the transceiver and fiber optic type need to match. LC is the connector type tat is pretty common to find those when using SFP’s in network gear. Other connectors you may run into would be LC, SC, ST, and FC.

You need to select the transceivers that are designed to work with fiber type you have. Generally if you try to use multi mode transceivers with single mode cable, it will not work. Also trying to use single mode transceivers with multi mode cable does not give good results or work at all. Mixing different cable types on one fiber optic link is a recipe for a disaster.

Jacket color is sometimes used to distinguish multi-mode cables from single-mode, but it cannot always be relied upon to distinguish types of cable. The standard TIA-598C recommends, for civilian applications, the use of a yellow jacket for single-mode fiber, and orange for 50/125 µm (OM2) and 62.5/125 µm (OM1) multi-mode fiber.[3] Aqua is recommended for 50/125 µm “laser optimized” OM3 fiber.

Can you mix and match single mode and multi mode components / fiber? In some rare cases yes.

There are some special adapters that allow some mixing:
“The mode conditioning cables have allowed us to succesfully run Gb ehternet over our multimode cable using Single mode transcievers, but only at distances that would have worked using multimode transcievers. It did not work where we were exceeding the distance spec for multimode, must have been too much loss in the cable…”
“we just successfully ran from a SM Finisar FTLF1323P1BTR over a 400’ run of MM fiber to a media converter and it worked. I was trying to research this at this site so I posted our results.”
“I’m using 1000Base-LX/LH singlemode transceivers over 62.5 multimode fiber in several places, including a link over 1000’ long between two buildings. I do use mode-conditioning patch cables.”
Mode Conditioning Cable Selector: Launching a single-mode laser into the center of a multimode fiber can cause multiple signals to be generated that confuse the receiver at the other end of the fiber. A mode conditioning patch cord eliminates these multiple signals by allowing the single-mode launch to be offset away from the center of a multimode fiber. This offset point creates a launch that is similar to typical multimode LED launches. “The launch of the light coming out of the equipment begins on a Singlemode fiber. The Singlemode fiber is precision fusion spliced to the multimode fiber to a precise core alignment”

In a research laboratory environment I have run setup where a single mode transmitter sense signal to single or multi mode cable, and the signal was received with multi mode receiver. Also setup where single mode transmitter, single mode fiber, multimode fiber and multimode receiver has worked. Generally the direction that light goes from single mode to multi mode cable works somewhat OK, while the direction from multi mode to single mode causes a very high attenuation.

LiFi 802.11bb standard uses light for in-room data transmission up to 224GB/s
https://www.cnx-software.com/2023/07/14/lifi-802-11bb-wifi-standard-uses-light-for-in-room-data-transmission-up-to-224gb-s/
The 802.11bb WiFi-like standard, also called LiFi, was ratified in June 2023. It enables data transmission up to 224GB/s at a few meters range within a room using light instead of RF signals used in most other wireless standards

https://www.facebook.com/100063998805272/posts/pfbid0Dq8BBgTkxL91LjcFD6WR9YSU6SMwF96ZBKNfk7UMqD7CnSyV6GaCQMtZJRwEQhBhl/
The LiFi (802.11bb) standard has just been ratified. It uses light for private, high-speed data connectivity within a room and works like WiFi from the end-user perspective. #wireless #technology #innovation

POSTED ONJULY 14, 2023 BY JEAN-LUC AUFRANC (CNXSOFT) - NO COMMENTSON LIFI 802.11BB STANDARD USES LIGHT FOR IN-ROOM DATA TRANSMISSION UP TO 224GB/S

LiFi 802.11bb standard uses light for in-room data transmission up to 224GB/s

The 802.11bb WiFi-like standard, also called LiFi, was ratified in June 2023. It enables data transmission up to 224GB/s at a few meters range within a room using light instead of RF signals used in most other wireless standards.

The technology has been worked on for many years, and we first covered (a version of) LiFi in 2014 that was still part of the IEEE 802.15 standard with speeds up to 1 Gbps. But the Light Communications 802.11bb Task Group was only formed in 2018 chaired by pureLiFi and supported by Fraunhofer HHI, and led to be ratification of the IEEE 802.11bb standard last month.

https://www.cnx-software.com/2023/07/14/lifi-802-11bb-wifi-standard-uses-light-for-in-room-data-transmission-up-to-224gb-s/?fbclid=IwAR3-k5HAxyGO2J2FGYhNggXNWd0a8_BZ20UhgELxKHPUignVle9MA7-nrik

100x Faster Than Wi-Fi: Li-Fi, Light-Based Networking Standard Released
By Mark Tyson published 1 day ago
Proponents boast that 802.11bb is 100 times faster than Wi-Fi and more secure
https://www.tomshardware.com/news/li-fi-standard-released

LiFi specification released, enabling wide adoption of light-based wireless internet
Secure wireless speeds of up to 224GB/s through LED lights, cutting down on spectrum congestion
https://www.techspot.com/news/99377-lifi-specification-standards-released-enabling-wide-adoption-light.html

Laser Communications Relay Demonstration
TOPIC:
LASER COMMUNICATIONS
R&D AREA:
Communication Systems
R&D GROUP:
Advanced Lasercom Systems and OperationsOptical and Quantum Communications Technology
Optical communications technologies decades in the making at Lincoln Laboratory were transferred to NASA for its first two-way laser relay communications system.
https://www.ll.mit.edu/r-d/projects/laser-communications-relay-demonstration

Polymer ribbons have been used as waveguides to propagate electromagnetic signals before, but the direct compatibility with silicon chips, without any special manufacturing, is a big plus.

Source and more:
https://spectrum.ieee.org/tech-talk/computing/networks/plastic-polymer-cables-that-rival-fiber-optics

To mark the new name, the group has published 800G specification [PDF] that details its next step in Ethernet’s evolution.

Ethernet standards group leaves its name in the dust as it details new 800Gbps spec
Farewell, 25 Gigabit Ethernet Consortium. Arise, Ethernet Technology Consortium
https://www.theregister.co.uk/2020/04/07/ethernet_technology_consortium_rebrands_and_reveals_800gbps_spec/

25 Gigabit Ethernet Consortium Rebrands to Ethernet Technology Consortium; Announces 800 Gigabit Ethernet (GbE) Specification
https://ethernettechnologyconsortium.org/press-room/press-releases/25-gigabit-ethernet-consortium-rebrands-to-ethernet-technology-consortium-announces-800-gigabit-ethernet-gbe-specification-152/

800G specification
https://ethernettechnologyconsortium.org/wp-content/uploads/2020/03/800G-Specification_r1.0.pdf

This specification is based on reusing two 400G PCS/FEC blocks to handle 800G traffic (32x25Gb/s). On low level physical interface the architecture could support 8×106.15G or 16×53.125G serial interfaces. 800G will use either C2M or C2C interface to 800G module (emerging IEEE 802.3ck standard).

Here is block diagram from specification:

Researchers have now shown switching between LED and photodetector modes on new type component quickly enough for real-time use, the new diode offers potential for communications. Switching between LED and photodetector modes quickly enough for real-time use, the new diode offers potential for communications. The new LED at its peak emission (~804 nm) allows an optical signal exchange between two identical diodes. The operation speed for both functions can reach tens of megahertz.

“In order to demonstrate the potential of our diode with double function,” researcher Chunxiong Bao explains, “we have built a monolithic sensor that detects heart beats in real time, and an optical, bidirectional communication system.”

Researchers Create a Perovskite Diode That Can Transmit or Receive Optical Signals on Demand
https://www.hackster.io/news/researchers-create-a-perovskite-diode-that-can-transmit-or-receive-optical-signals-on-demand-8eb41a4c5e23

Bidirectional optical signal transmission between two identical devices using perovskite diodes
https://www.nature.com/articles/s41928-020-0382-3

Use of LEDs as a photodiode light sensor
https://wiki.analog.com/university/courses/electronics/electronics-lab-led-sensor

Fiber optic communications cables can be “hacked” for more than just to transport our data.

New research from Berkeley could turn existing undersea fiber optic cables into a network of seismographs.

New property of light discovered

https://phys.org/news/2019-06-property.html
A team of researchers affiliated with several institutions in Spain and the U.S. has announced that they have discovered a new property of light—self-torque.

Goodbye Aberration: Physicist Solves 2,000-Year-Old Optical Problem
https://petapixel.com/2019/07/05/goodbye-aberration-physicist-solves-2000-year-old-optical-problem/
“In this equation we describe how the shape of the second aspherical surface of the given lens should be given a first surface, which is provided by the user, as well as the object-image distance,” explains González. “The second surface is such that it corrects all the aberration generated by the first surface, and the spherical aberration is eliminated.”

Autofocal Glasses Prototype: Huge Improvement on Progressive Lenses
https://blog.hackster.io/autofocal-glasses-prototype-huge-improvement-on-progressive-lenses-b6eeaa0f36cb

A Neural-Net Based on Light Could Best Digital Computers
https://spectrum.ieee.org/tech-talk/computing/hardware/a-neural-net-based-on-light-could-best-digital-computers

Optimization is very important but is usually computationally very hard. Optimization encompasses far more than the traveling salesman problem. Scheduling is another difficult optimization challenge.

Given the fact that the era of steady, large improvements in computer-processor performance appears to be coming to a close, researchers have begun to explore machines specially designed for optimization.

One promising approach is to develop optical machines for optimization.

A system called a measurement-feedback optical parametric oscillator (OPO) Ising machine can solve optimization problems that are put in the form of an Ising model—a collection of electron spins and how they influence one another.
The main task is mapping: We need to convert our optimization problem into a form that can be solved by a machine designed to solve Ising optimization problems.

I have seen several optical signal processing tricks earlier – this is faciest I have heard of.

Researchers have written the paper describing their system, published in Science.

Need for a custom camera module. Check out this intetesting looking project.

uCameraCube is a parametric camera module build using OpenSCAD uCube library. It is build with Raspberry Pi and Raspberry Pi camera and comes in three versions, which vary in the type of optics used.

Thin Lens version
M12 Lens version
T-Mount version