Compact, High-Performance All-Polarization-Maintaining Er: Fiber Frequency Comb With Single Fiber Actuator

The large volume and weak environmental adaptability of fiber optical frequency combs (OFCs) have become the main obstacles for their applications in various fields. To address these issues, in this study, we present a compact, low-cost
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interferometer and fiber actuator with a large tuning range and a high control bandwidth for a 200-MHz OFC that is based on a 1.5-μm all-polarization-maintaining fiber mode-locked laser. By employing customized fiber-coupled gradient index lenses, our
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interferometer is encapsulated in a miniature tube with a diameter of only 4 mm and a length of 40 mm, which substantially reduces the optical section size of the frequency comb as compared to conventional devices. The carrier envelope offset beat with a signal-to-noise ratio of 40 dB is detected in a resolution bandwidth of 360 kHz. In addition, a laboratory-made piezoelectric transducer-driven mechanical actuator for repetition rate regulation exhibited a large tuning range of 106 kHz (corresponding to an effective temperature drift of 53 °C) and a high control bandwidth of approximately 1 kHz. This resulted in a robust repetition rate locking with an Allan deviation of 330 μHz at a gate time of 1 s and a residual integrated timing jitter of 418 fs [3 Hz to 1 MHz] when referenced to a hydrogen maser. Along with reducing the size and improving the environmental adaptability of the OFC, our design can also decrease the power consumption of the system significantly. Our findings provide a new direction to the development of OFCs for various applications.