Optical Delay Lines – Phase Control

The VariDelay series of adjustable optical delay lines from Luna Innovations (the former General Photonics line) enable precise adjustment of the optical path of a signal — and therefore its delay and phase — in fiber-optic setups. The family includes motorized versions with remote control (MDL-002) and manual versions (VDL-001, VDL-002), with single-mode or polarization-maintaining fiber pigtails.

Applications

Optical path matching in interferometers and OLCR/OFDR measurement setups
Pulse synchronization in pump-probe experiments
Phase and delay control in microwave photonics (true time delay, beamforming)
Characterization of components and receivers in telecom laboratories
Research benches requiring repeatable, calibrated delay adjustment

Key parameters

Parameter	Value
Parameter	Value
Delay range	MDL-002: up to 330/560 ps (single-pass), 1120 ps (double-pass); VDL-001: up to 600 ps (single-pass), 1200 ps (double-pass)
Resolution (MDL-002)	0.3 µm of optical path per encoder step (approx. 1 fs)
Position accuracy / repeatability (MDL-002)	±3 µm
Insertion loss	typically 1.0 dB (1310/1550 nm, single-pass); 1.5 dB (840/1060 nm or double-pass)
Wavelengths	840, 1060, 1310, 1550 nm (λc ±50 nm); SM or PM fiber
Control (MDL-002)	keypad with LCD display, RS-232; scan speed up to 256 ps/s; module/OEM versions

How it works

The signal from the input fiber is collimated and routed through a free-space path segment of adjustable length, then coupled back into the output fiber. Changing the length of this segment translates directly into group delay (approx. 3.33 ps per 1 mm of optical path) with negligible dispersion, because the adjustable part of the path travels through air. In the motorized version the position is controlled by an encoder, giving single-femtosecond steps and full repeatability of settings — sufficient for phase tuning of optical and microwave signals.

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