We review the most recent progress in ultralow-noise mode-locked fiber lasers and fiber-based frequency-comb sources. With the rapid progress in theory, measurement, and control of noise in passively mode-locked fiber lasers, we have reached the point where the residual carrier–envelope-offset phase jitter (when stabilized) and pulse timing jitter performance of such laser sources can be fully optimized to the unprecedented levels of attoseconds regime. In this paper, first, major principles in building such low-noise passively mode-locked fiber lasers are reviewed. We then define noise in mode-locked fiber lasers and present the basic theoretical and numerical framework for analyzing the noise in mode-locked fiber lasers. More detailed discussions on theory, measurement methods, state-of-the-art performances, and stabilization methods of intensity noise, timing jitter, and comb-line frequency noise follow. Finally, we overview today’s most representative applications of such ultralow-noise mode-locked fiber lasers and frequency-comb sources. As an already powerful tool for various high-precision applications, ultralow-noise mode-locked fiber lasers will keep finding more exciting applications in optical science and photonic technology in the coming years.

Ultralow-noise mode-locked fiber lasers and frequency combs: principles, status, and applications

Femtosecond optical pulses have applications in optical communication, astronomical frequency combs, and laser spectroscopy. Here, a hybrid mode-locked erbium-doped fiber (EDF) laser with topological insulator (TI) is proposed, for the first time to our best knowledge. The pulsed laser deposition (PLD) method is employed to fabricate the fiber-taper TI saturable absorber (TISA). By virtue of the fiber-taper TISA, the hybrid EDF laser is passively mode-locked using the nonlinear polarization evolution (NPE), and emits 70 fs pulses at 1542 nm, whose 3 dB spectral width is 63 nm with a repetition rate and transfer efficiency of 95.4 MHz and 14.12%, respectively. Our experiments indicate that the proposed hybrid mode-locked EDF lasers have better performance to achieve shorter pulses with higher power and lower mode-locking threshold in the future.

http://in.iphy.ac.cn/upload/1603/201603181113371375.pdf

70-fs mode-locked erbium-doped fiber laser with topological insulator.

Citation: Droste, S., Ycas, G., Washburn, B. R., Coddington, I., & Newbury, N. R. (2016). Optical Frequency Comb Generation based on Erbium Fiber Lasers. Nanophotonics, 5(2), 196-213. doi:10.1515/nanoph-2016-0019

/pdf/optical-frequency-comb-generation-based-on-erbium-fiber-3egxiac9p8.pdf

Optical Frequency Comb Generation based on Erbium Fiber Lasers

Dual-comb spectroscopy has emerged as an attractive spectroscopic tool for high-speed, high-resolution, and high-sensitivity broadband spectroscopy. It exhibits certain advantages when compared to the conventional Fourier-transform spectroscopy. However, the high cost of the conventional system, which is based on two mode-locked lasers and a complex servo system with a common single-frequency laser, limits the applicability of the dual-comb spectroscopy system. In this study, we overcame this problem with a bidirectional dual-comb fiber laser that generates two high-coherence ultra-broadband frequency combs with slightly different repetition rates (frep). The two direct outputs from the single-laser cavity displayed broad spectra of > 50 nm; moreover, an excessively small difference in the repetition rate (< 1.5 Hz) was achieved with high relative stability, owing to passive common-mode noise cancellation. With this slight difference in the repetition rate, the applicable optical spectral bandwidth in dual-comb spectroscopy could attain ~479 THz (~3,888 nm). In addition, we successfully generated high-coherence ultra-broadband frequency combs via nonlinear spectral broadening and detected high signal-to-noise-ratio carrier–envelope offset frequency (fCEO) beat signals using the self-referencing technique. We also demonstrated the high relative stability between the two fCEO beat signals and tunability. To our knowledge, this is the first demonstration of fCEO detection and frequency measurement using a self-referencing technique for a dual-comb fiber laser. The developed high-coherence ultra-broadband dual-comb fiber laser with capability of fCEO detection is likely to be a highly effective tool in practical, high-sensitivity, ultra-broadband applications.

/pdf/high-coherence-ultra-broadband-bidirectional-dual-comb-fiber-4obs75bp1x.pdf

High-coherence ultra-broadband bidirectional dual-comb fiber laser

Dual-comb lasers simultaneously generating asynchronous ultrashort pulses could be an intriguing alternative to the current dual-laser comb source. When generated through a common light path, the low common-mode noises and good coherence between the pulse trains could be realized. Here we demonstrate the completely common-path, unidirectional dual-comb lasing using a carbon nanotube saturable absorber with additional pulse narrowing and broadening mechanisms. The interactions between multiple soliton formation mechanisms result in bifurcation into unusual two-pulse states with pulses of four-fold bandwidth difference and tens-of-Hz repetition rate difference. Coherence between the pulses is verified by the asynchronous cross-sampling and dual-comb spectroscopy measurements.

Unidirectional, dual-comb lasing under multiple pulse formation mechanisms in a passively mode-locked fiber ring laser

We report on an Er-doped fiber oscillator that produces 146 fs pulses with 156 mW average power at a repetition rate of 49.9 MHz. The pulse energy reaches 3.13 nJ, surpassing the conventional power limit in the dispersion-managed soliton regime. Such high pulse power is obtained by devising a hybrid mode-locking scheme that combines saturable absorption with nonlinear polarization evolution. The oscillator also offers excellent temporal purity in the generated pulses with high power, providing a robust fiber-based frequency comb well suited for industrial uses.

/pdf/hybrid-mode-locked-er-doped-fiber-femtosecond-oscillator-3m96514nv7.pdf

Hybrid mode-locked Er-doped fiber femtosecond oscillator with 156 mW output power

Damage-free cutting of chemically strengthened glass by creation of sub-surface cracks using femtosecond laser pulses

Selective thin-film removal is needed in many microfabrication processes such as 3-D patterning of optoelectronic devices and localized repairing of integrated circuits. Various wet or dry etching methods are available, but laser machining is a tool of green manufacturing as it can remove thin films by ablation without use of toxic chemicals. However, laser ablation causes thermal damage on neighboring patterns and underneath substrates, hindering its extensive use with high precision and integrity. Here, using ultrashort laser pulses of sub-picosecond duration, we demonstrate an ultrafast mechanism of laser ablation that leads to selective removal of a thin metal film with minimal damage on the substrate. The ultrafast laser ablation is accomplished with the insertion of a transition metal interlayer that offers high electron-phonon coupling to trigger vaporization in a picosecond timescale. This contained form of heat transfer permits lifting off the metal thin-film layer while blocking heat conduction to the substrate. Our ultrafast scheme of selective thin film removal is analytically validated using a two-temperature model of heat transfer between electrons and phonons in material. Further, experimental verification is made using 0.2 ps laser pulses by micropatterning metal films for various applications.

Selective laser ablation of metal thin films using ultrashort pulses

Selective thin-film removal is needed in many microfabrication processes such as 3-D patterning of optoelectronic devices and localized repairing of integrated circuits. Various wet or dry etching methods are available, but laser machining is a tool of green manufacturing as it can remove thin films by ablation without use of toxic chemicals. However, laser ablation causes thermal damage on neighboring patterns and underneath substrates, hindering its extensive use with high precision and integrity. Here, using ultrashort laser pulses of sub-picosecond duration, we demonstrate an ultrafast mechanism of laser ablation that leads to selective removal of a thin metal film with minimal damage on the substrate. The ultrafast laser ablation is accomplished with the insertion of a transition metal interlayer that offers high electron–phonon coupling to trigger vaporization in a picosecond timescale. This contained form of heat transfer permits lifting off the metal thin-film layer while blocking heat conduction to the substrate. Our ultrafast scheme of selective thin film removal is analytically validated using a two-temperature model of heat transfer between electrons and phonons in material. Further, experimental verification is made using 0.2 ps laser pulses by micropatterning metal films for various applications.

Selective Laser Ablation of Metal Thin Films Using Ultrashort Pulses

Recently, it has sometimes been impossible for fire-fighting personnel to access the site of a fire, even as the fire causes tremendous property damage and loss of human life, due to high temperatures or the presence of explosive materials. In such environments, fire-fighting robots can be useful for extinguishing a fire, and they should be controlled by remote operators. In order to help a remote operator who is located far away from the fire-fighting robot, wireless image communication systems have been investigated in this study. The developed system uses a High-Speed Downlink Packet Access (HSDPA) network to transmit images, showing the view from a fire-fighting robot. The fire-fighting robots and remote controllers are equipped with industrial computers, and image-transmitting and image-receiving programs function according to various protocols to allow communication between the robots and controllers

Sang-Uk Park

Papers

Hybrid mode-locked Er-doped fiber femtosecond oscillator with 156 mW output power

Damage-free cutting of chemically strengthened glass by creation of sub-surface cracks using femtosecond laser pulses

Selective laser ablation of metal thin films using ultrashort pulses

Selective Laser Ablation of Metal Thin Films Using Ultrashort Pulses

Wireless image communication system for fire-fighting robots