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Technology

Stable, tunable frequency conversion

< 0.1 nm/h
Record passive stability
< 0.1 nm
Unique dynamic reproducibility
< −160 dBc/Hz
Ultra-low RIN
< 0.5 %rms
Power stability
< 10 µrad
Beam pointing

Technology Q&A

What makes our systems different?

We use a hybrid concept of fiber-feedback and parametric gain in a bulk nonlinear crystal. The intra-cavity fiber acts as a mode-cleaner and pins the pointing.
We use dispersive stretching of our feedback pulse. By adjusting the timing between pump and feedback pulse we can tune continuously and gap-free with < 0.05 nm accuracy.
The fiber is purely passive and does not emit amplified spontaneous emission (ASE) or other spurious signals. We measured a temporal pulse contrast below 130 dB (Opt. Express 30, 1 (2022)). The intensity noise figure only depends on the pump noise.
The intra-cavity fiber is single-mode, so it guides only the fundamental transverse mode. Higher-order spatial modes couple poorly into the fiber and stay below threshold, so the oscillator runs in a clean, near-diffraction-limited TEM00 beam. Because the output beam is defined by the fiber, its pointing is fixed and repeatable, independent of free-space alignment drift.
The system is fully automated and provides a websocket interface (ethernet or WiFi connection) that can be accessed with any common programming language. The included GUI is written in C++, but comes with templates in Python and LabVIEW. Simultaneous access from multiple clients is possible.
They are fiber-feedback OPOs (FFOPO): a compact OPO cavity with passive fiber feedback. The design is passively stable over long periods and preserves the low RIN of the pump in typical configurations.

Our frequency converters are fiber-feedback optical parametric oscillators (FFOPO): an OPO cavity that combines an intra-cavity single-mode fiber with a bulk nonlinear crystal that provides parametric gain.

The fiber serves two roles. It guides only the fundamental transverse mode, giving a clean, repeatable TEM00 beam with fixed pointing; and its dispersion stretches the recirculating pulse in time. Because the wavelength that is amplified is set by the pump’s arrival time rather than by a finely tuned cavity length, the FFOPO is far less sensitive to drift. Depending on wavelength, 20 to 100× more dispersion than a conventional OPO means 20 to 100× slower wavelength drift.

In day-to-day operation the oscillator therefore runs without active wavelength locking: no piezo loops, highly repeatable wavelength settings, and a compact footprint. Pump sources include femtosecond and picosecond solid-state and fiber lasers.

Staying on wavelength as the cavity drifts

The same cavity drift moves the pump in time. More intra-cavity dispersion means the amplified wavelength moves less.

(a) Conventional OPO

Low intra-cavity dispersion

Conventional OPO: large wavelength shift under cavity drift

Tap diagram to enlarge.

Little dispersion: a small cavity drift moves the output wavelength a lot, so an active piezo lock is used to hold it. Cavity length is continuously corrected by a feedback loop.

(b) Fiber-feedback OPO

20 to 100× more dispersion

Fiber-feedback OPO: small wavelength shift under the same cavity drift

Tap diagram to enlarge.

Large dispersion stretches the signal in time, so the same drift barely changes the amplified wavelength. Wavelength is set by pump and signal timing, not by a control loop.

Architecture

Why SI Technology?

Free-space OPOs and SI Technology balance cavity design, locking, and tuning differently. The comparison below states typical design points, not a ranking of all systems.

Typical free-space OPO

SI Technology

Stability
Often stabilized with active cavity locking
Passive fiber feedback, without an active lock loop
Pulse duration
Typically set by the pump and cavity
Selectable across 100 fs – 100 ps
Repetition rate
Typically set by the pump laser
Configurable from 100 kHz – 100 MHz
Average power
Depends on pump, crystal, and cavity design
Up to 3 W in standard configurations
Noise
Influenced by pump noise and cavity dynamics
Designed for low-noise, near shot-noise-limited operation
Tuning range
Set by nonlinear crystals and cavity optics
0.7 – 20 µm with modular output coverage

Contact

Contact us

Phone+49 711 3420325 0

Emailcontact@s-instruments.de

AddressSI Stuttgart Instruments GmbH
Ernsthaldenstr. 17, 70565 Stuttgart, Germany

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