We propose a frequency-scanning interferometry using the Kalman filtering technique for dynamic absolute distance measurement. Frequency-scanning interferometry only uses a single tunable laser driven by a triangle waveform signal for forward and backward optical frequency scanning. The absolute distance and moving speed of a target can be estimated by the present input measurement of frequency-scanning interferometry and the previously calculated state based on the Kalman filter algorithm. This method not only compensates for movement errors in conventional frequency-scanning interferometry, but also achieves high-precision and low-complexity dynamic measurements. Experimental results of dynamic measurements under static state, vibration and one-dimensional movement are presented.
We present an effective method to extend the mode-hop-free (MHF) tuning range of an external-cavity diode laser (ECDL) by synchronous tuning of the longitudinal modes of the external cavity and the internal cavity, with the mode also matched in the initial state. Both the principle of synchronous tuning and the condition of mode matching in a Littman-configuration ECDL are introduced. The necessary tuning parameters could simply be estimated by the output power curve of the tuning with a single photodiode. By using this tuning method, we increased the MHF tuning range of an ECDL with a nonoptimized reflector pivot position from several gigahertzes to over 78 GHz around 774.5 nm. The tuning performance of the ECDL could meet the requirement of frequency scanned interferometry.
Mode hopping is a critical performance limitation of external cavity diode lasers (ECDLs). We developed a method to suppress the mode hops by shifting the internal cavity longitudinal mode spectrum to match the other mode spectra. A model of longitudinal mode structure based on Littman-Metcalf configuration has been deduced for analyzing the characteristics of external cavity mode hop and internal cavity mode hop. The best mode matching point appears at the peak of output power when tuning the ECDL. Both the short-term and long-term wavelength stability were investigated in different laser diode current values while the tuning element maintains a fixed position. The experimental results demonstrated the effectiveness of the proposed mode matching methods for improving the mode stability and reducing the sensitivity to environment change.
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