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Nonlinear self-phase modulation is a universal phenomenon responsible, for example, for the formation of propagating dynamic solitons. It has been reported for waves of different physical nature. However its direct experimental observation for spin waves has been challenging. Here we show that exceptionally strong phase modulation can be achieved for spin waves in microscopic waveguides fabricated from nanometer-thick films of magnetic insulator, which support propagation of spin waves with large amplitudes corresponding to angles of magnetization precession exceeding 10°. At these amplitudes, the nonstationary nonlinear dynamic response of the spin system causes an extreme broadening of the spectrum of spin-wave pulses resulting in a strong spatial variation of the spin-wave wavelength and a temporal variation of the spin-wave phase across the pulse. Our findings demonstrate great complexity of nonlinear wave processes in microscopic magnetic structures and importance of their understanding for technical applications of spin waves in integrated devices.

Resist sidewall slopes frequently need to be adjusted in micro-and nanofabrication. In this paper, the authors present a straightforward approach to adjust sidewall slopes by using electron beam lithography and applying a background dose in addition to the feature dose. The underlying effect is attributed to an inhomogeneous energy deposition along the resist depth, for which a threedimensional point spread function is necessary to correctly describe the energy deposition in the resist even for large acceleration voltages and thin resist films. This enables adjacent features with different positive or different negative slopes within a single lithographic step. Corresponding experimental results obtained with the two positive tone resists poly(methyl methacrylate) and ZEP520A are shown, and their opposed sidewall behavior is explained. Moreover, a customized contrast curve is discussed that can, in theory, be used to achieve resist profiles with positive and negative slopes for the same resist. Therefore, a full range tuning on the same substrate becomes feasible. V

Because of appealing material properties and ease of fabrication, organic semiconductors have found a variety of applications in integrated photonics, including optical waveguiding in broadband communication systems, use as amplifiers and modulators in signal processing, and for realizing optical detectors and sensors. Polymeric carbon nitride thin films have emerged as a valuable alternative to currently employed inorganic materials in light manipulation and waveguiding owing to their structural flexibility, transparency over a wide wavelength range, and accessible synthesis from sustainable and cost-effective materials. Here, we demonstrate organic polymeric carbon nitride-based nanophotonic devices for telecommunication wavelengths. The high ordinary refractive index of the polymer of 2 or higher, covering both visible and near-infrared wavelength ranges, enables a small device footprint, strong mode confinement, and efficient fiber-to-chip coupling via grating couplers. Proof-of-concept experiments with photonic waveguides and microring resonators show broadband transmission in the visible wavelength range and quality factors exceeding 104 for a wavelength of 1550 nm. The outstanding material properties of polymeric carbon nitride will open new perspectives for polymeric photonic devices for a broad wavelength range.

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