We demonstrate a full C-band wavelength-tunable mode-locked fiber laser with a repetition rate of 250 MHz, representing the highest repetition rate for C-band tunable mode-locked lasers thus far to the best of our knowledge. The polarization-maintaining fiber-based Fabry–Perot cavity enables a fundamental repetition rate of 250 MHz with a semiconductor saturable absorber mirror as a mode-locker. We observed a stable and single soliton mode-locking state with wide tunability of the center wavelength from 1505 to 1561 nm by adjusting the incident angle of a bandpass filter inside the cavity. The wavelength-tunable high-repetition-rate mode-locked laser covering the full C-band is expected to be a compelling source for many frequency-comb-based applications, including high-precision optical metrology, broadband absorption spectroscopy, and broadband optical frequency synthesizers.
The spectral domain interferometer (SDI) has been widely used in dimensional metrology. Depending on the nature of the SDI, both wider spectral bandwidth and narrower linewidth of the light source are paradoxically required to achieve better resolution and longer measurable distances. From this perspective, a broadband frequency comb with a repetition rate high enough to be spectrally resolved can be an ideal light source for SDIs. In this paper, we propose and implement a broadband electro-optic frequency comb to realize a comb-mode resolved SDI. The proposed electro-optic frequency comb was designed with an optically recirculating loop to provide a broadband spectrum, which has a repetition rate of 17.5 GHz and a spectral range of 35 nm. In a preliminary test, we demonstrated absolute distance measurements with sub-100 nm repeatability. Because of these advantages, we believe this electro-optic frequency comb can open up new possibilities for SDIs.
High-accuracy distance measurements with compact configurations and robust operations are necessary in areas ranging from precision engineering to scientific missions. Here, we report a precise and accurate amplitude-modulation-based all-fiber distance measurement method without periodic errors. To realize an all-fiber configuration towards on-chip devices in the future, certain selective components for easy fabrication on the chip scale were employed. Despite this constraint, sub-100 nm precision was demonstrated with the help of the all-photonic microwave mixing technique introduced in our previous work. In this paper, accuracy as another important factor for measuring distances was investigated to ensure better performance than in previous studies with an optical amplitude-modulation technique. By performing theoretical and experimental analyses of the periodic error while blocking electrical crosstalk signals and optimizing signal processing, accuracy of 2.6 μm (1 σ) was achieved in terms of measurement linearity according to a comparison with a laser displacement interferometer. With the best capabilities of precision and accuracy, the proposed all-fiber distance measurement method is expected to be utilized in diverse long-distance applications, such as large-machine axis tool work and formation flying by multiple satellites. Further, this study demonstrates the possibility of developing an on-chip-based distance-measuring device for the fourth industrial revolution.