Electro-Optic Swept Source Based on AOTF for Wavenumber-Linear Interferometric Sensing and Imaging

Abstract

Abstract:We demonstrate a novel electro-optic swept source for wavenumber-linear interferometric sensing and imaging applications. The electro-optic swept source based on an acousto-optic tunable filter (AOTF) provides high environmental stability and arbitrary drive function sweeping because the electro-optic wavelength selection does not depend on a mechanical moving component to tune the output lasing wavelength. We show improved stability of the suggested electro-optic swept source, compared to a conventional swept source based on a fiber Fabry-Perot tunable filter (FFP-TF). Various types of wavelength sweeping are demonstrated by applying the programmed drive function to the applied radio frequency (RF) of the AOTF. We demonstrated improved image quality of optical coherence tomography (OCT) by using the wavenumber-linear drive function of a simple triangular signal, which has a high wavenumber-linearity with an R-square value of 0.99991.

Acousto-Optic–Based Wavelength-Comb-Swept Laser for Extended Displacement Measurements

“…Figure 5 shows the linear relationships between the applied RF signal and the output wavenumber [14] for both WSL and WCSL, which have a high wavenumber linearity of R 2 = 0.9999. When the WCSL based on the AOTF has a high wavenumber linearity, it does not need an additional process for the k -linear spacing of the interferometric signal to ensure equally spaced wavelength combs in the wavenumber domain during mass signal processing for imaging and sensing.…”

“…Owing to the dense wavelength spacing of the multiple longitudinal modes in a long laser cavity, the broad linewidth of the laser peak in the conventional WSL corresponds to a limited displacement measurement of less than 6 mm of the point spread function (PSF) by monitoring the decreased sensitivity roll-off [ 14 ]. When we insert an etalon filter with a periodic bandpass spectrum into the fiber cavity to partially suppress the multiple longitudinal modes in the cavity, the narrowing of the spectral linewidth can be easily implemented to extend the coherence length of the laser light.…”

“…Because the proposed WCSL, which is based on an AOTF, has no mechanical moving parts for the selection of the wavelength and is solely driven by an electro-optic signal, it has some advantages in comparison to other types of WCSLs using an FFP-TF, such as high environmental stability, wavenumber linearity, and adaptability to various types of driving functions [ 5 , 6 , 7 , 8 ]. Figure 5 shows the linear relationships between the applied RF signal and the output wavenumber [ 14 ] for both WSL and WCSL, which have a high wavenumber linearity of R 2 = 0.9999. When the WCSL based on the AOTF has a high wavenumber linearity, it does not need an additional process for the k -linear spacing of the interferometric signal to ensure equally spaced wavelength combs in the wavenumber domain during mass signal processing for imaging and sensing.…”

“…The output wavelength is inversely proportional to the frequency of the applied radio frequency (RF) signal in the AOTF. A comb-like spectral laser source with a narrow spectral linewidth is implemented for extended interferometric displacement measurements by combining an AOTF [ 14 ] and an etalon filter [ 15 , 16 , 17 , 18 ].…”

Multi-spectral laser speckle contrast images using a wavelength-swept laser

“…An acoustooptic tunable filter was used in the laser cavity, owing to its superior stability and wavelength-linear tunability compared to conventional mechanical filters, such as a tunable Fabry-Pérot etalon or a tunable micro electro mechanical system. 11 The spectral bandwidth of the wavelength-swept laser output spans 51 nm from 770 to 821 nm as shown in Fig. 1(b).…”