Spatial solitons, beams that do not spread owing to diffraction when they propagate, have been demonstrated to exist by virtue of a variety of nonlinear self-trapping mechanisms. Despite the diversity of these mechanisms, many of the features of soliton interactions and collisions are universal. Spatial solitons exhibit a richness of phenomena not found with temporal solitons in fibers, including effects such as fusion, fission, annihilation, and stable orbiting in three dimensions. Here the current state of knowledge on spatial soliton interactions is reviewed.

https://science.sciencemag.org/content/sci/286/5444/1518.full.pdf

Optical Spatial Solitons and Their Interactions: Universality and Diversity.

Recent developments in rare-earth doped materials for optoelectronics

Cascading is the process by which the exchange of energy between optical beams interacting via second order nonlinearities (χ(2)) leads to various effects such as nonlinear phase shifts, the generation of new beams, all-optical transistor action, the formation of soliton-like (solitary) waves, etc. Here we review the fundamentals of the processes and discuss experimental verification of the effects and various related applications.

χ(2) cascading phenomena and their applications to all-optical signal processing, mode-locking, pulse compression and solitons

Lithium niobate on insulator (LNOI) technology is revolutionizing the lithium niobate industry, enabling higher performance, lower cost and entirely new devices and applications. The availability of LNOI wafers has sparked significant interest in the platform for integrated optical applications, as LNOI offers the attractive material properties of lithium niobate, while also offering the stronger optical confinement and a high optical element integration density that has driven the success of more mature silicon and silicon nitride (SiN) photonics platforms. Due to some similarities between LNOI and SiN, established techniques and standards can readily be adapted to the LNOI platform including a significant array of interface approaches, device designs and also heterogeneous integration techniques for laser sources and photodetectors. In this contribution, we review the latest developments in this platform, examine where further development is necessary to achieve more functionalities in LNOI integrated optical circuits and make a few suggestions of interesting applications that could be realized in this platform. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Status and Potential of Lithium Niobate on Insulator (LNOI) for Photonic Integrated Circuits

Optical solitons due to quadratic nonlinearities: from basic physics to futuristic applications

The erbium incorporation into LiNbO3 by diffusion doping is investigated in detail by means of Secondary Ion Mass Spectrometry, Secondary Neutral Mass Spectrometry, Rutherford Backscattering, Atomic Force Microscopy, X-ray Standing Wave technique and optical site-selective spectroscopy. The diffusion of erbium in LiNbO3 can be described by Fick’s laws of diffusion with a concentration-independent diffusion coefficient. The diffusion constants and activation energies for Z-cut (X-cut) LiNbO3 are 4.8×10-5 cm2/s (12.0×10-5 cm2/s) and 2.28 eV (2.44 eV), respectively. A limited solubility of erbium in LiNbO3 has to be taken into account increasing exponentially with rising temperature. During the first step of diffusion an Er
 x
 Nb
 y
 -oxide layer is formed at the surface of the sample acting as diffusion reservoir. Erbium is incorporated into LiNbO3 on vacant Li-sites slightly shifted from the original Li-position along the (-c)-direction. Site-selective spectroscopy found four distinguishable energetically different erbium centres at this lattice site resulting from locally different symmetries of the crystal field.

Erbium incorporation in LiNbO3 by diffusion-doping

Single-pass and double-pass Er-diffused Z- and X-cut Ti:LiNbO/sub 3/ waveguide amplifiers, optically pumped at /spl lambda//sub p//spl ap/1484 nm, have been investigated. With a 48 mm long Z-cut amplifier device, Er-diffusion doped at 1100/spl deg/C, 6.7 dB (coupled pump power P/sub p,c/=170 mW) and 14.7 dB (P/sub p,c/=90 mW) net small-signal gain have been achieved with a single-pass and a double-pass configuration, respectively, at the signal wavelength /spl lambda//sub s/=1531 nm. A Z-cut sample doped at 1135/spl deg/C showed a considerably improved behavior. 11.3 dB single-pass net small-signal gain has been obtained (P/sub p,c/=170 mW; sample length 5.7 cm). Theoretical calculations predict gain figures up to 20 dB in single-pass and 40 dB in double-pass Er:Ti:LiNbO/sub 3/ amplifiers with increased (realistic) lengths of 10 cm. >

Erbium-doped single- and double-pass Ti:LiNbO/sub 3/ waveguide amplifiers

The development of a Fabry-Perot-type Ti,Er:LiNbO/sub 3/ waveguide laser of optimized CW output power up to 63 mW (/spl lambda//sub s/=1561 nm) at a pump power level of 210 mW (/spl lambda//sub p/=1480 nm) and a slope efficiency of up to 37% is reported. The theoretical model for the waveguide laser is presented and applied to determine the optimum resonator configuration using waveguide parameters obtained from a detailed characterization of the laser sample. With pulsed pumping, waveguide laser pulses of up to 6.2 W peak power were observed. Apart from residual relaxation oscillations, the laser emission proved to be shot-noise limited.

Ti:Er:LiNbO/sub 3/ waveguide laser of optimized efficiency

We report on intensity-dependent switching in lithium niobate directional couplers. Large nonlinear phase shifts that are due to cascading detune the coupling between the coupler branches, which makes all-optical switching possible. Depending on the input intensity, the output could be switched between the cross and the bar coupler branches with a switching ratio of 1:5 and a throughput of 80%.

/pdf/all-optical-switching-in-lithium-niobate-directional-3vygml4j8c.pdf

All-optical switching in lithium niobate directional couplers with cascaded nonlinearity

The first integrated optical DBR waveguide laser with dry-etched Bragg grating (345 nm period) is demonstrated in Er-diffusion-doped doped zeta -cut LiNbO/sub 3/ with Ti-diffused waveguide. Three different resonator configurations have been investigated. The best device has a threshold of 40 mW coupled pump power ( lambda /sub p/=1484 nm) and emits up to 2 mW CW output power at lambda /sub s/=1531 nm with a typical bandwidth of 3.6 GHz.

I. Baumann

Papers

Erbium incorporation in LiNbO3 by diffusion-doping

Erbium-doped single- and double-pass Ti:LiNbO/sub 3/ waveguide amplifiers

Ti:Er:LiNbO/sub 3/ waveguide laser of optimized efficiency

All-optical switching in lithium niobate directional couplers with cascaded nonlinearity

DBR waveguide laser in erbium-diffusion-doped LiNbO3