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1. Fiber-Integrated Supercontinuum with a 20 GHz Resonant Electro-Optic Frequency Comb

   https://doi.org/10.1364/CLEO_SI.2021.STu2D.2  

   Sekhar, Pooja; Fredrick, Connor; Leifer, Stephanie; Diddams, Scott A. (January 2021, Conference on Lasers and Electro-Optics)

   J. Kang, S. Tomasulo (Ed.)

   We employ an efficient 1550 nm resonant waveguide-type electro-optic comb generator with PM nonlinear fiber optics to generate 50 fs pulses and 500 nm broad super- continuum at 20 GHz. 

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2. 20 GHz fiber-integrated femtosecond pulse and supercontinuum generation with a resonant electro-optic frequency comb

   https://doi.org/10.1063/5.0165681  

   Sekhar, Pooja; Fredrick, Connor; Carlson, David_R; Newman, Zachary_L; Diddams, Scott_A (November 2023, APL Photonics)

   Frequency combs with mode spacing of 10–20 GHz are critical for increasingly important applications such as astronomical spectrograph calibration, high-speed dual-comb spectroscopy, and low-noise microwave generation. While electro-optic modulators and microresonators can provide narrowband comb sources at this repetition rate, a significant remaining challenge is a means to produce pulses with sufficient peak power to initiate nonlinear supercontinuum generation spanning hundreds of terahertz (THz) as required for self-referencing. Here, we provide a simple, robust, and universal solution to this problem using off-the-shelf polarization-maintaining amplification and nonlinear fiber components. This fiber-integrated approach for nonlinear temporal compression and supercontinuum generation is demonstrated with a resonant electro-optic frequency comb at 1550 nm. We show how to readily achieve pulses shorter than 60 fs at a repetition rate of 20 GHz. The same technique can be applied to picosecond pulses at 10 GHz to demonstrate temporal compression by 9× and achieve 50 fs pulses with a peak power of 5.5 kW. These compressed pulses enable flat supercontinuum generation spanning more than 600 nm after propagation through multi-segment dispersion-tailored anomalous-dispersion highly nonlinear fibers or tantala waveguides. The same 10 GHz source can readily achieve an octave-spanning spectrum for self-referencing in dispersion-engineered silicon nitride waveguides. This simple all-fiber approach to nonlinear spectral broadening fills a critical gap for transforming any narrowband 10–20 GHz frequency comb into a broadband spectrum for a wide range of applications that benefit from the high pulse rate and require access to the individual comb modes. 

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3. Sub-picosecond timing jitter between optically synchronized femtosecond and picosecond laser systems

   https://doi.org/10.1088/1361-6501/acc41b  

   Jiang, Zhenfei; Strycker, Benjamin; Hand, Lucian; Adamonis, Jonas; Yi, Zhenhuan; Sokolov, Alexei; Scully, Marlan (March 2023, Measurement Science and Technology)

   Abstract Synchronized optical pulses are widely used. We report here characterization and measurement of synchronized femtosecond and picosecond pulses from a Ti:Sapphire laser (nominally 800 nm) and a Nd:YAG laser (1064 nm), respectively. Synchronization is achieved by utilizing soliton self-frequency shift in a photonic-crystal fiber that allows the 800 nm femtosecond oscillator to seed the third-harmonic generation (355 nm) of picosecond regenerative amplifier. The relative timing jitter between the amplified femtosecond and the third-harmonic generation of picosecond pulses is (710 ± 160) fs, which is only (1.17 ± 0.26)% of the picosecond pulse duration. This work paves way for applications in stimulated Raman scattering spectroscopy and amplification. 

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4. Ultrabroadband, few-cycle pulses directly from a Mamyshev fiber oscillator

   https://doi.org/10.1364/PRJ.8.000065  

   Ma, Chunyang; Khanolkar, Ankita; Zang, Yimin; Chong, Andy (December 2019, Photonics Research)

   While the performance of mode-locked fiber lasers has been improved significantly, the limited gain bandwidth restricts them from generating ultrashort pulses approaching a few cycles or even shorter. Here we present a novel method to achieve few-cycle pulses ( $\sim 5\text{cycles}$) with an ultrabroad spectrum ( $\sim 400\mathrm{nm}$at $-20\mathrm{dB}$) from a Mamyshev oscillator configuration by inserting a highly nonlinear photonic crystal fiber and a dispersion delay line into the cavity. A dramatic intracavity spectral broadening can be stabilized by the unique nonlinear processes of a self-similar evolution as a nonlinear attractor in the gain fiber and a “perfect” saturable absorber action of the Mamyshev oscillator. To the best of our knowledge, this is the shortest pulse width and broadest spectrum directly generated from a fiber laser. 

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5. Temporal and spectral unmixing of photoacoustic signals by deep learning

   https://doi.org/10.1364/OL.426678  

   Zhou, Yifeng; Zhong, Fenghe; Hu, Song (May 2021, Optics Letters)

   Improving the imaging speed of multi-parametric photoacoustic microscopy (PAM) is essential to leveraging its impact in biomedicine. However, to avoid temporal overlap, the A-line rate is limited by the acoustic speed in biological tissues to a few megahertz. Moreover, to achieve high-speed PAM of the oxygen saturation of hemoglobin, the stimulated Raman scattering effect in optical fibers has been widely used to generate 558 nm from a commercial 532 nm laser for dual-wavelength excitation. However, the fiber length for effective wavelength conversion is typically short, corresponding to a small time delay that leads to a significant overlap of the A-lines acquired at the two wavelengths. Increasing the fiber length extends the time interval but limits the pulse energy at 558 nm. In this Letter, we report a conditional generative adversarial network-based approach that enables temporal unmixing of photoacoustic A-line signals with an interval as short as $\sim <\#comment/>38\mathrm{n}\mathrm{s}$, breaking the physical limit on the A-line rate. Moreover, this deep learning approach allows the use of multi-spectral laser pulses for PAM excitation, addressing the insufficient energy of monochromatic laser pulses. This technique lays the foundation for ultrahigh-speed multi-parametric PAM. 

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