From 402 Tbps to Over 1 Pbps: How Japan is Redefining Internet Speed

In the race for faster internet, Japan’s National Institute of Information and Communications Technology (NICT) is in a league of its own.
In June 2024, NICT researchers set a world record of 402 terabits per second (Tbps) using standard single-mode optical fiber—the same type already deployed in much of the world’s fiber-optic infrastructure. Then, less than a year later, in May 2025, they smashed their own record with a jaw-dropping 1.02 petabits per second (Pbps) over 1,808 kilometers of fiber using multi-core optical technology.

That’s 1,020 Tbps, or roughly 3.5 million times faster than an average U.S. broadband connection.

402 Tbps in 2024 — Single-Core Magic

The 2024 breakthrough was notable because it didn’t require exotic cables. The team used:

Standard single-mode fiber already in commercial use
Dense Wavelength Division Multiplexing (DWDM) to transmit over 1,500 wavelength channels
Advanced optical amplifiers to maintain signal quality
37.6 THz of spectrum across the O, E, S, C, L, and U bands

This meant the technology could theoretically be adapted to today’s infrastructure without ripping out existing fiber.

1.02 Pbps in 2025 — The Multi-Core Leap

While the 402 Tbps record showcased what’s possible with current fiber, the 2025 record explored what’s possible when we change the fiber itself.

The team used:

19-core optical fiber — multiple light-carrying cores inside a single cable
Multiple-input multiple-output (MIMO) digital signal processing to manage interference between cores
Recirculating loop tests to simulate long-distance performance over 1,808 km

Multi-core fiber essentially puts 19 parallel highways inside a single road, multiplying capacity without multiplying cable size.

Single-Core vs. Multi-Core: Key Differences

Feature	Single-Core Fiber	Multi-Core Fiber
Number of cores	1	2–19 (or more in research)
Deployment readiness	Already in global networks	Still experimental for large-scale use
Potential capacity	Limited by wavelength and modulation	Multiples of single-core capacity
Installation cost	Lower (uses existing infrastructure)	Higher (new fiber needed)
Complexity	Lower — standard amplification and multiplexing	Higher — requires crosstalk management, MIMO DSP

What Does This Mean for You?

In practical terms:

Single-core upgrades, such as the 402 Tbps demo, could enhance current backbone speeds without requiring cable replacements—ideal for near-term boosts in internet capacity.
Multi-core systems like the 1.02 Pbps record are next-generation infrastructure. They’re likely to appear first in undersea cables, hyperscale data center links, and future 6G backbone networks.

Don’t expect petabit speeds in your home anytime soon—the bottlenecks are in distribution networks, hardware costs, and consumer device limits. However, these experiments demonstrate that the physical medium of fiber is far from reaching its true capacity ceiling.

The Bottom Line

Japan’s fiber-optic achievements highlight two paths to a faster internet future:

Push today’s single-core networks to their absolute limits (as with the 402 Tbps test).
Adopt multi-core fiber for exponential capacity gains (as with the 1.02 Pbps breakthrough).

Either way, the numbers are staggering. And while we may still be waiting for petabit home internet, the backbone that powers tomorrow’s global connectivity is being forged in Japanese laboratories today.