We generate, for the first time and to the best of our knowledge, a tunable ultraflat optical frequency comb (OFC) block from a 10-GHz bismuth-based actively modelocked fiber laser. A bismuth-based erbium-doped fiber (Bi-EDF) with a length of 1.5 m and a bismuth-based highly nonlinear fiber (Bi-HNLF) with a length of 4.1 m are used as a gain medium and a spectral broadening device, respectively. We also employ a wavelengthtunable and bandwidth-variable optical filter for an intracavity filter. The center wavelength of the OFC output can be widely tuned from 1535 to 1585 nm because the Bi-EDF has a broadband gain profile. A spectrally broadened ultra-flat OFC is successfully generated by the self-phase modulation in the Bi-HNLF. By tuning the filter bandwidth, the 10-dB spectral width and the pulsewidth of the generated OFC can be widely varied from 0.23 to 2.4 nm and from 3 to 20.1 ps, respectively. The fiber ring cavity is as short as 17.8 m. For the entire tuning ranges, the proposed bismuth-based tunable ultra-flat OFC generator also realizes stable bit-error-free mode-locking operation.
In this paper, we propose a distance estimation method using tilted lens optics. Our proposed method uses two input images: one is an all-in-focus image, and the other is a ground-infocus image. The method estimates a distance value for each pixel by comparing the amount of blur between the ground-in-focus image and multi-focus images that are synthesized by applying a Gaussian filter to the all-in-focus image. As our method needs only two input images and simple calculations, it is suitable for distance estimation applications that require a wide detection range and real-time processing, such as robotics and automotive tasks.
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