Short answer
Yes. When a Distributed Acoustic Sensing (DAS) interrogator is connected to an unused (dark) telecom fiber, the cable becomes thousands of virtual sensors that measure vibration every few metres. Traffic flow, excavation threats and urban vibration can then be monitored without laying new cable. DuyuSense designs pilot solutions of this kind for operators and municipalities, built on its patented DAS signal processing.
What is dark fiber and why can it work as a sensor?
Dark fiber is installed fiber that carries no data traffic. Operators and infrastructure owners usually lay cables with spare strands for future capacity, and many of those strands stay unused for years.
An unused strand is a ready-made sensing line for DAS. The interrogator sends laser pulses into the fiber and measures strain at every point along the cable from phase changes in the backscattered light. A single channel typically covers tens of kilometres, often cited around 40-50 km, with spatial resolution typically of a few metres.
- The cable already runs under roads, rail lines and pipeline corridors
- No power, maintenance or field electronics along the sensing line
- Continuous coverage over many kilometres from one interrogator
Does DAS interfere with data traffic on the same cable?
On a dedicated dark strand, DAS does not affect data traffic on neighbouring strands. Each strand is optically independent, which makes this the simplest and most common model.
Running DAS on a separate wavelength of a lit fiber is also possible, but it requires filtering and power planning. Optical amplifiers and isolators can block backscattered light, so long amplified links need an engineering review. For this reason, pilots usually start on a dark strand.
- Dedicated strand: lowest risk, easiest commissioning
- Wavelength sharing: saves strands, needs additional optical design
- In both models, route topology and splice points should be reviewed first
How does DAS monitor road traffic in a smart city?
DAS measures traffic flow by continuously recording the vibration signatures vehicles leave on fiber beneath the road. Each vehicle appears as a line in time and position; the slope gives speed and the density gives volume.
One system can deliver vehicle counts, average speed, queue formation and direction along kilometres of road. The stronger signal from heavy vehicles also supports classification. Counting accuracy depends on the cable's distance from the lanes, burial depth and ground conditions, so field calibration matters.
- Vehicle counting and speed profiles
- Detection of queues and the onset of congestion
- Monitoring of heavy vehicle volumes
- Continuous observation at junction and tunnel approaches
Can telecom operators detect digging near their cables before a cut?
Yes, excavation and heavy machinery can be detected by DAS before the cable is cut. Excavators, breakers and horizontal drilling rigs produce distinct, repetitive vibration signatures as they approach the cable.
This is the use case with the most direct return for an operator: the sensor network protects its own backbone. When the event is located to within metres, field crews can intervene before an outage. Given the cost of repairs, SLA penalties and customer churn after a cable cut, early warning creates tangible value.
- Located detection of digging, drilling and heavy machinery
- Alarms for unauthorised construction activity
- Event history to map high-risk route sections
Can road condition and urban vibration be monitored as well?
Yes, the same fiber also produces data on road surfaces, urban noise and seismic activity. Potholes, damaged joints or degraded pavement can appear as repeating irregularities in the signal of passing vehicles.
At city scale the fiber behaves like a dense seismic and vibration array; DAS seismology studies on telecom fiber in Istanbul have demonstrated this potential. Earthquake early warning is covered in detail as a separate topic; the point here is that the same infrastructure can supply seismic data alongside traffic and security data.
What does fiber sensing mean for privacy?
In normal configurations DAS measures vibration along the cable, not speech content. On a buried cable, with a gauge length of a few metres and sampling settings chosen for traffic monitoring, the data is vehicle, footstep or machinery vibration; it produces no images or audio recordings that identify people.
DAS does, however, measure in the acoustic frequency range and can partially pick up sound-induced vibration under certain conditions. Processing purpose, retention periods and access rights should therefore be defined from the outset, and events and statistics should be shared rather than raw data. In Turkey, the KVKK data protection framework should be part of this design.
- Camera-free monitoring that does not identify individuals
- Processed event and count output instead of raw data
- Clear purpose, retention period and access policy
What business models exist for operators and municipalities?
The most common model is fiber sensing as a service: the fiber owner provides the infrastructure, a technology provider supplies the interrogator and analytics, and the end user receives the data. The operator gains a new revenue stream from idle dark fiber.
In Turkey, telecom operators' networks, municipalities' own fiber and fiber running along rail lines are suitable infrastructure for this model. As an engineering company developing FBG and DAS systems, DuyuSense is open to working with these stakeholders on pilots, system integration and consultancy.
- Own use: the operator protects its own cable against excavation
- Data service: traffic and event data offered to a municipality by subscription
- Infrastructure lease: dark fiber leased to a third party for sensing
- Joint pilot: cost and benefit measured together on a limited corridor
| Feature | DAS on dark fiber | Camera | Inductive loop | Radar |
|---|---|---|---|---|
| Coverage | Tens of km of continuous line per interrogator | Point or zone limited by field of view | Single point, per lane | Point or short zone |
| Field installation | Uses existing fiber, no roadworks | Needs pole, power and communications | Cut into the pavement | Needs pole, power and communications |
| Weather and lighting | Unaffected | Degrades in fog, rain and darkness | Unaffected | Largely unaffected |
| Privacy | No images, measures vibration | Captures people and number plates | No images | No images |
| Vehicle classification | Coarse, depends on calibration | Detailed, via image processing | Limited, length based | Moderate |
| Additional uses | Excavation alerts, road condition, seismic data | Incident video, plate recognition | None | Speed enforcement |
Frequently asked questions
What is fiber sensing as a service?
It is a model in which a fiber owner's dark fiber is combined with a technology provider's DAS interrogator and analytics to deliver traffic, excavation or vibration data on a subscription or project basis. The customer receives event and statistical data without buying hardware, and the operator earns revenue from idle fiber.
Does DAS work on a cable that carries internet traffic?
Yes, when a separate dark strand in the same cable is used, and data traffic is not affected. Running on a separate wavelength of a lit strand is also possible, but filters, power levels and optical amplifiers require additional engineering. Pilots usually start on a dedicated strand.
How far can one DAS interrogator monitor on dark fiber?
A single channel typically covers tens of kilometres, often cited around 40-50 km. Actual reach depends on fiber attenuation, the number of splices and connectors, and the required spatial resolution. Longer routes are divided across several channels or interrogators.
How accurate is vehicle counting with DAS?
Accuracy depends on the cable's distance from the road, burial depth, ground type and traffic density. In light traffic individual vehicles separate clearly, while in very dense traffic flow and speed statistics are the more reliable output. Each route should be calibrated in the field against reference counts.
Can fiber sensing listen to conversations?
Not in normal configurations: DAS measures vibration along the cable, and data captured with traffic monitoring settings is vehicle or machinery vibration. Because the measurement spans acoustic frequencies, however, data purpose, retention and access rights should be clearly defined and designed to comply with data protection rules such as KVKK.
Will DAS replace cameras and inductive loops?
Not entirely; it is complementary. DAS provides continuous flow, speed and event data over long corridors, cameras offer visual verification and plate recognition, and inductive loops give precise counts at a single point. The most effective approach uses DAS as a wide-coverage layer alongside other sensors.
Which fiber infrastructure in Turkey is suitable for sensing?
Telecom operators' backbone and metro fiber, municipalities' own fiber networks and fiber running along rail lines are the strongest candidates. Suitability is confirmed by a site survey covering spare strand availability, route documentation and how well the cable is coupled to the ground.
What does DuyuSense offer for telecom fiber sensing?
DuyuSense develops patented DAS signal-processing and FBG interrogation technologies at ITU Teknopark, Istanbul. It is open to working with operators and municipalities on feasibility, pilot design, system integration and training. Contact: contact@duyusense.com, +90 212 285 6987.