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Stable, tunable frequency conversion

< 0.1 nm/h
Record passive stability
< 0.1 nm
Unique dynamic reproducibility
< −168 dBc/Hz
Ultra-low RIN
< 0.5 %rms
Power stability
< 30 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. The Alpha reproduces the relative intensity noise of its pump laser and can easily reach < −168 dBc/Hz. In the time domain, we measured a temporal pre-pulse contrast below −130 dB (M. Floess et al., Opt. Express 30(1), 1 (2022)).
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 Wi-Fi connection) that can be accessed with any common programming language. Every system is shipped with a fully featured GUI. Simultaneous access from multiple clients is possible and remote automation with any third-party language such as Python, LabVIEW and Matlab is supported.
The FFOPO design combines a compact and adaptive optical setup with passively long-term stable operation. Conventional technology requires a bulky cavity with individual redesign for different pump parameters and active wavelength-locking feedback loops.

Concept

How the fiber-feedback OPO works

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, it is 20 to 100x less sensitive to temperature than a conventional OPO, which yields correspondingly 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.

Sketch of the fiber-feedback OPO principle: a pump pulse is shaped by dispersive feedback through a fiber loop, then parametric gain in a nonlinear crystal produces the tunable output pulse
Dispersive feedback in the fiber stretches the recirculating pulse and reduces the effect of timing change against the pump (blue), while accurately setting the wavelength that gets amplified; a bulk nonlinear crystal then provides the parametric gain that produces the tunable output pulse.

Architecture

Why SI technology?

Fiber lasers

Quantum cascade lasers

Conventional OPOs

SI technology

Noise
Poor;
High RIN due to ASE and gain dynamics
Moderate/poor;
Very high RIN (pulsed)
Moderate RIN (cw)
Good;
RIN set by pump laser;
Lock electronics add noise
Excellent;
RIN fully set by pump laser
Repeatability
No tuning possible
Good
Moderate;
Cavity re-locking or recalibration
Good;
Passive dispersive tuning
Stability
Good;
Passively stable
Good;
Electronically regulated.
Moderate;
Electromechanical with optical instrumentation and PID-feedback
Good;
Passively stable
Spectral and temporal contrast
Poor;
Amplifier ASE; Higher order dispersion
Moderate;
ASE background
Good;
Nonlinear gain process
Good;
Nonlinear gain process
Robustness
Sensitive to damage from power outage
Sensitive to damage from backreflections
Sensitive to misalignment and thermal drift
Insensitive to misalignment; 20 to 100x reduced thermal drift
Beam quality
Excellent
Moderate;
Changes upon tuning
Good;
Alignment-dependent
Very good;
Cleaned by fiber

Contact

Contact us

Phone+49 (0)711 3420325 0

Emailcontact@s-instruments.de

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

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