Modular optical carrier
A repeatable mechanical and optical platform for installing quantum sources, detectors, filters, beam splitters, telescopes, fibre couplers and beacon channels.
KORUZA MOD-Q
A free-space optical platform for integrating and field-testing quantum key distribution.
What MOD-Q is, and what it is not
MOD-Q is a configurable free-space optical platform for integrating and field-testing third-party QKD transmitters, receivers and key-management systems, with optional high-speed classical data transport, alignment, tracking and environmental monitoring.
It is not a certified QKD product, and we do not claim it to be one. We supply the optical path and the physical layer. The quantum source, the detection, the protocol implementation, the security proof and the certification come from a QKD partner. A commercial product claim can only follow measured secret-key-rate and quantum-bit-error-rate results, security analysis, environmental testing and integration with a recognised key-management stack.
What quantum key distribution is
QKD uses the properties of single quantum states to establish a shared secret key between two parties, in such a way that an attempt to observe the channel disturbs it measurably. Under its security model, that lets the two ends detect eavesdropping rather than merely resist it.
Free-space optics is not a competing cryptographic method. It is the optical physical channel that carries the quantum states used to generate the keys. The user data itself normally stays on a classical high-speed link and is encrypted with symmetric cryptography such as AES, using keys the QKD system delivers. The QKD system additionally needs an authenticated classical channel for sifting, error correction and privacy amplification.
Free-space QKD matters where suitable fibre is unavailable, slow or expensive to install, and for temporary, mobile, airborne, maritime and satellite links. It is less mature than fibre QKD but strategically important for exactly those cases.
What a free-space QKD installation actually needs
A practical installation is considerably more than a laser pointing between two sites. It normally requires:
- A quantum transmitter and a quantum receiver
- Free-space transmit and receive optics
- Pointing, acquisition and tracking, or stable manual alignment
- Beacon and alignment cameras or sensors
- Narrow spectral, spatial and temporal filtering to suppress background light
- A polarisation-preserving or phase-stable optical path, depending on protocol
- An authenticated classical service channel for key distillation
- A key-management system and an interface to encryptors, VPNs or network equipment
- Environmental and link monitoring
- Stored-key buffers and a fallback mechanism for weather outages
What KORUZA contributes
Pointing and alignment
Coarse and fine adjustment, alignment cameras, a beacon channel and tracking modules — particularly valuable for field trials, vibration, moving platforms and longer links.
Parallel classical channel
The same installation can carry a 1 or 10 Gb/s classical FSO path for encrypted user traffic and the QKD service channel. Quantum and classical beams may use separate apertures or carefully isolated wavelengths, depending on the partner's security and noise requirements.
Hybrid fibre / free-space bridge
KORUZA can bridge a missing physical section between two fibre-connected sites — connecting two buildings across a road without installing new fibre. This is the clearest near-term urban use case.
Development and validation platform
Different QKD protocols, detectors, wavelengths, filters and pointing methods can be compared on the same mechanical platform. This is exactly what the MOD architecture is for.
Weather and availability evidence
Link monitoring records received power, visibility, temperature, alignment state and outages — field evidence that practical FSO-QKD deployment planning currently lacks.
Suggested MOD-Q modules
A MOD-Q configuration is assembled from the standard MOD platform plus quantum-specific modules, selected with the QKD partner:
- QKD transmitter interface module
- QKD receiver interface module
- Protocol-specific polarisation- or phase-preserving optics
- Quantum optical head, selected with the QKD partner
- Narrowband filter and stray-light suppression
- Beacon and coarse/fine pointing module
- Classical 1/10 Gb/s encrypted data and service channel
- Environmental and received-signal monitoring
- Key-management and API integration using recognised ETSI interfaces
- Redundant fibre, RF or stored-key fallback
A sensible first pilot
We would rather run a well-scoped experiment than sell a claim. The pilot we recommend:
- A fixed building-to-building link of up to 100 m
- A partner-provided, already characterised QKD transmitter and receiver
- Separate quantum and classical optical paths for the first experiment, reducing crosstalk and security uncertainty
- Day and night measurements in clear weather, followed by controlled degraded-link tests
- Measured: total optical loss, background count, sifted key rate, secret key rate, acquisition time, alignment drift, uptime and weather sensitivity
Constraints worth knowing before you start
Post-quantum cryptography is software-based, cheaper and easier to deploy at scale, and is the default migration path for most organisations. The UK NCSC currently recommends PQC as the preferred general approach. QKD is bought for high-value, specialised links — not as a universal replacement for ordinary key exchange. A hybrid QKD plus PQC position is the honest one.
A real system is not automatically secure because the protocol is theoretically secure. Detectors, sources, calibration, firmware, optical leakage and implementation side channels all have to be evaluated.
Free-space links need clear line of sight, low enough optical loss, stable pointing and careful suppression of sunlight and other background light.
Fog and cloud can stop key generation completely. Rain, turbulence, scintillation, vibration and thermal drift reduce the secret key rate or raise the quantum bit error rate.
Interoperability, certification and procurement requirements are still developing. ETSI and ITU are standardising QKD networks and interfaces; the EU NOSTRADAMUS programme is building testing and certification capability.
Standards and programmes
The relevant public references, if you want to read further:
Working on a QKD deployment?
We are looking for QKD vendors, research groups and integrators who need a flexible physical layer for a pilot. Tell us what you are building and what you need the optics to do.