Urban rail transit communication systems demand fiber optic cables capable of supporting multi-service transmission at speeds exceeding 10 Gbps. The backbone network typically employs 24-48 core single-mode fibers to handle critical data streams including:
Train control signals (CBTC systems)
Real-time video surveillance feeds (4K resolution at 30fps)
Passenger information system updates
Emergency communication channels
For long-distance trunk lines exceeding 5km, the attenuation coefficient must remain below 0.22 dB/km at 1550nm wavelength. This ensures signal integrity across the entire rail network without requiring excessive signal regeneration. In high-density urban areas, the system should support wavelength division multiplexing (WDM) to enable simultaneous transmission of 32+ channels on a single fiber pair.
Fiber optic cables deployed in subway tunnels must withstand:
Vibration frequencies up to 50Hz from passing trains
Temperature ranges of -20°C to +60°C
Humidity levels exceeding 95% RH
Electromagnetic interference from 25kV traction systems
Cables should feature dual-layer armor consisting of:
Corrosion-resistant steel wire braid for mechanical protection
Aluminum polyethylene laminate for water blocking
Flame-retardant outer sheath meeting IEC 60332-3-24 standards
In curved sections with radii below 2m, the minimum bending radius of the installed cable must be maintained at 20 times the cable diameter to prevent microbending losses.
In passenger concourses and platform areas, cables must comply with:
Fire safety classification EN 50268-2 for low smoke zero halogen (LSZH) materials
Crush resistance of ≥1000N/10cm for cables installed under floor tiles
Rodent resistance meeting IEC 60794-1-21 requirements
For overhead installations, cables should be suspended using non-metallic hangers with a minimum clearance of 50mm from electrical conduits to prevent electromagnetic coupling. The vertical drop sections must include service loops with 1.5m excess length to accommodate future re-routing.
All fiber links must undergo:
Insertion loss measurement using OTDR with ≤0.05dB resolution
Chromatic dispersion testing per ITU-T G.650.1
Polarization mode dispersion (PMD) analysis with Q-factor ≥10dB
Return loss verification exceeding 26dB
For emergency communication channels, the end-to-end latency must remain below 2ms to ensure real-time voice transmission during crisis situations. The system should incorporate automatic fault localization with accuracy within ±1m for any break in the fiber link.
Cable assemblies must pass:
Tensile strength test of ≥2000N for armored cables
Repeated bending test (1000 cycles at ±90°) per IEC 60794-1-2-E4
Impact resistance test (10 joules) conforming to IEC 60794-1-2-E3
Long-term aging test at 85°C/85% RH for 1000 hours
The connector interfaces should demonstrate mating durability of ≥500 cycles with insertion loss variation <0.2dB. All field-installable connectors must achieve initial attenuation ≤0.3dB when terminated by certified technicians.
The fiber optic network must support:
Ethernet protocols from 100Mbps to 100Gbps
SDH/SONET standards up to STM-64/OC-192
OTN frameworks for G.709 encapsulation
Custom TDM protocols for legacy signaling systems
For video surveillance applications, the system should enable zero-latency switching between IP and analog camera feeds using media converters with <1μs processing delay. The passenger information displays require synchronized multicast transmission with jitter <100ns across all display terminals.
Where applicable, the network should support hybrid cables combining:
4-12 fiber strands for data transmission
2x2mm² copper conductors for DC power delivery
Dielectric strength of ≥15kV/mm for insulation
The power distribution system must incorporate:
Overcurrent protection at 150% rated capacity
Surge suppression meeting IEC 61643-21 requirements
Ground fault detection with 30mA sensitivity
Remote monitoring of voltage/current parameters
This technical framework ensures urban rail transit fiber optic networks meet the stringent reliability, safety, and performance requirements essential for modern metropolitan transportation systems.
