Wave propagation and group velocity

Have you ever felt that the very title, Progress in Optics, conjured an image in your mind? Don’t you see a row of handsomely printed books, bearing the editorial stamp of one of the most brilliant members of the optics community, and chronicling the field of optics since the invention of the laser? If so, you are certain to move the bookend to make room for Volume 16, the latest of this series. It contains seven chapters on widely diverging topics, written by well-known authorities in their fields. These are: 1) Laser Selective Photophysics and Photochemistry by V. S. Letokhov, 2) Recent Advances in Phase Profiles (sic) Generation by J. J. Clair and C. I. Abitbol, 3 ) Computer-Generated Holograms: Techniques and Applications by W.-H. Lee, 4) Speckle Interferometry by A. E. Ennos, 5 ) Deformation  Invariant, Space-Variant Optical  Pattern Recognition by D. Casasent and D. Psaltis, 6) Light Emission from High-Current Surface-Spark Discharges by R. E. Beverly, and 7) Semiclassical Radiation  Theory within a  QuantumMechanical Framework by I. R. Senitzkt. The  breadth of topic  matter  spanned  by  these  chapters makes it impossible, for this reviewer at least, to pass judgement on the comprehensiveness, relevance, and completeness of every chapter. With an editorial board as prominent as that of Progress in Optics, however, it seems hardly likely that such comments should be necessary. It should certainly be possible to take the authority of each author as credible. The only remaining judgment to be  made on these chapters is their readability. In short, what are they like to read? The first sentence of the first chapter greets the eye with an obvious typographical error: “The creation of coherent laser light source, that have tunable radiation, opened the . . . .” Two pages later we find: “When two types of atoms or molecules of different isotopic composition ( A and B ) have even one spectral line that does not overlap with others, it is pos-

Progress in optics

The concept of parity-time symmetric systems is rooted in non-Hermitian quantum mechanics where complex potentials obeying this symmetry could exhibit real spectra. The concept has applications in many fields of physics, e.g., in optics, metamaterials, acoustics, Bose-Einstein condensation, electronic circuitry, etc. The inclusion of nonlinearity has led to a number of new phenomena for which no counterparts exist in traditional dissipative systems. Several examples of nonlinear parity-time symmetric systems in different physical disciplines are presented and their implications discussed.

Nonlinear waves in PT -symmetric systems

Owing to their atomic layer thickness, strong light–material interaction, high nonlinearity, broadband optical response, fast relaxation, controllable optoelectronic properties, and high compatibility with other photonic structures, 2D materials, including graphene, transition metal dichalcogenides and black phosphorus, have been attracting increasing attention for photonic applications. By tuning the carrier density via electrical or optical means that modifies their physical properties (e.g., Fermi level or nonlinear absorption), optical response of the 2D materials can be instantly changed, making them versatile nanostructures for optical modulation. Here, up-to-date 2D material-based optical modulation in three categories is reviewed: free-space, fiber-based, and on-chip configurations. By analysing cons and pros of different modulation approaches from material and mechanism aspects, the challenges faced by using these materials for device applications are presented. In addition, thermal effects (e.g., laser induced damage) in 2D materials, which are critical to practical applications, are also discussed. Finally, the outlook for future opportunities of these 2D materials for optical modulation is given.

2D Materials for Optical Modulation: Challenges and Opportunities.

Optical fibre nanowires and microwires offer a variety of enabling properties, including large evanescent fields, flexibility, configurability, high confinement, robustness and compactness. These distinctive features have been exploited in a wealth of applications ranging from telecommunication devices to sensors, from optical manipulation to high Q resonators. In this paper I will review the fundamentals and applications of nanowires and microwires manufactured from optical fibres.

https://iopscience.iop.org/article/10.1088/2040-8978/12/4/043001/pdf

Optical fibre nanowires and microwires: a review

We report on the trapping of noise-like pulse in a figure-eight fiber laser mode locked by nonlinear amplifier loop mirror (NALM). After achievement of noise-like vector pulse, it was found that the wavelength shift of the two resolved polarization components responsible for the pulse trapping was very sensitive to the cavity birefringence. By properly rotating the polarization controllers (PCs), the wavelength shift could be up to 4.8 nm, which is much larger than that of conventional soliton trapping. The observed results would shed some light on the fundamental physics of noise-like pulse as well as its vector features in fiber lasers.

Noise-like pulse trapping in a figure-eight fiber laser

Pulsating behavior is a universal phenomenon in versatile fields. In nonlinear dissipative systems, the solitons also pulsate under proper conditions and show many interesting dynamics. However, the pulsation dynamics are generally concerned with single-soliton cases. Herein, by utilizing real-time spectroscopy technique, namely, dispersive Fourier-transform (DFT), we reveal the distinct dynamical diversity of pulsating solitons in a fiber laser. In particular, the weak to strong explosive behaviors of pulsating solitons, as well as the rogue wave generation during explosions are observed. Moreover, the concept of soliton pulsation is extended to the multi-soliton case. It is found that the simultaneous pulsations of energy, separation and relative phase difference could be observed for solitons inside the molecule, while the pulsations of each individual in a multi-soliton bunch could be regular or irregular. These findings will shed new insights into the complex nonlinear behavior of solitons in ultrafast fiber lasers as well as dissipative optical systems.

Dynamical diversity of pulsating solitons in a fiber laser.

Passive harmonic mode-locking (HML) in a fiber laser with a microfiber-based graphene saturable absorber (SA) is presented. The microfiber-based graphene SA is employed to enhance the nonlinear effect of the laser cavity, which is beneficial to achieving high-order HML operation. Depending on the pump power level, up to 101st HML (555 MHz) was obtained. The results demonstrate that the microfiber-based graphene SA could be used as highly nonlinear photonic devices in fiber lasers for effectively realizing high-order passive HML operation.

https://iopscience.iop.org/article/10.1088/1612-2011/10/10/105107/pdf

Passive harmonic mode-locking in a fiber laser by using a microfiber-based graphene saturable absorber

Switchable and tunable dual-wavelength ultrashort pulse generation in a passively mode-locked erbium-doped fiber ring laser

The dual wavelength solitons with 412 nm spectral separation are achieved simultaneously via nonlinear polarization rotation technique One is the picosecond soliton, the other is femtosecond soliton The direct interaction of two solitons does not happen firstly for the temporal separation between them is beyond 5 times of their duration When the continuous wave (CW), as the roles to cause the direct soliton interaction through shifting the central wavelength of the solitons, are excited to appear, the interaction of dual wavelength solitons happens There are some dips present on the femtosecond soliton spectra, indicating the interaction between dual wavelength solitons The power of CW affects the intensities of dips in the spectra and the pulse numbers and relative position of pulse bunches The more the power of CW, the more the intensities of the dips at the femtosecond soliton spectra are

https://iopscience.iop.org/article/10.1002/lapl.200910074/pdf

Wei-Cheng Chen

Papers

Noise-like pulse trapping in a figure-eight fiber laser

Dynamical diversity of pulsating solitons in a fiber laser.

Passive harmonic mode-locking in a fiber laser by using a microfiber-based graphene saturable absorber

Switchable and tunable dual-wavelength ultrashort pulse generation in a passively mode-locked erbium-doped fiber ring laser

The interaction of dual wavelength solitons in fiber laser