ID OSA Optical Spectrum Analyser for Quantum Key Distribution (QKD)

Why Quantum Key Distribution Needs Careful Spectral Planning

Quantum key distribution sends its signals at very low power, often over fibres that also carry ordinary data channels. That makes the spectrum around the quantum channel critical. Light from neighbouring classical channels, side modes of a source laser or a filter that passes more than it should can all add noise at the quantum receiver.

The quantum signal itself is far too weak for a spectrum analyser to see. What a QKD team can measure is everything around it: the source laser at its working power before attenuation, the pass and stop bands of its filters and the classical channels it shares the fibre with. Getting those right on the bench comes before any key is exchanged.

The Optical Spectrum Analyser in a QKD Lab

The ID OSA optical spectrum analyser from ID Photonics measures by coherent detection. It mixes the incoming light with an internal tunable laser reference and reconstructs the spectrum from the result, instead of scanning a diffraction grating.

In quantum key distribution development it is used on the classical side of the system: checking source lasers, confirming channel placement on DWDM grids and verifying that filters isolate the quantum channel from its neighbours.

Why Resolution and Frequency Accuracy Matter

Three figures decide how well the OSA can support QKD planning:

• Resolution: 2.5 pm sampling with a 1.7 GHz 3 dB bandwidth shows side modes and filter edges close to the channel.
• Frequency accuracy: ±1 GHz (±8 pm) confirms that the quantum and classical channels sit on their planned grid positions.
• Two power ranges: the standard port takes classical channels up to +23 dBm, and the high-sensitivity port reads down to −60 dBm for filtered and tapped signals.

Built for Quantum Communication Labs

The ID OSA is a half-width 19-inch, 1.8 kg instrument for benches and test racks.

Source laser checks

Centre wavelength, spectral width and side-mode suppression of the source laser are measured at working power, before the signal is attenuated to the quantum level, and again whenever the laser is retuned.

Filter verification

Filters, multiplexers and AWGs are swept with a broadband or tunable source, and the OSA shows their pass band and isolation from neighbouring channels.

Coexistence with classical channels

On DWDM grids at 50 GHz, 100 GHz or flexgrid spacing, the OSA checks the power and placement of the classical channels sharing the fibre.

Repeated checks

A full C-band or L-band sweep takes 0.5 s, and SCPI commands over USB or Ethernet let the same checks run after each change to the set-up. A 3.3 V TTL trigger in and out lets measurements be synchronised with other instruments on the bench.

Building a Complete QKD Test Bench

The source for a QKD experiment can be the Narrow Linewidth Tunable Laser Source, which the optical spectrum analyser checks before attenuation. Classical traffic on the same fibre is emulated with the Multi-Channel Tunable Laser Sources, combined by the Polarization Maintaining Multiplexer at 50 or 100 GHz spacing. Where the team modulates the source with its own modulators, the Automatic Bias Control System keeps them locked.

Who Uses It

• Quantum communication research groups at IITs and research institutes
• National and defence laboratories working on secure links
• Quantum technology start-ups building QKD systems
• Telecom operators and equipment makers testing QKD over existing fibre
• Optical component makers developing filters for quantum channels

Supply and Support in India

United Spectrum Instruments (USI), Chennai, supplies the ID OSA optical spectrum analyser in India as the distributor for ID Photonics, together with the narrow linewidth and multi-channel CoBrite lasers, Automatic Bias Control System and the PM multiplexer.

Sourcing the bench from one supplier gives quantum key distribution teams a single point of contact for band choice, port use, automation, installation and after-sales support, with pre-sales guidance on matching the analyser to the channel plan.

Request a Configuration

Download the brochure from this page, use the Enquire Now button, write to sales@unitedspectrum.in, or call +91 93631 83748 / +91 97899 04948. Please mention:

• The QKD scheme and the wavelengths of the quantum and classical channels
• Whether the quantum channel shares the fibre with data traffic
• What you will measure: source lasers, filters or classical channels
• The bands you need: C-band, L-band or both