We demonstrate a visible light communications (VLC) transmission system based on a micro light emitting diode (LED) transmitter and orthogonal frequency division multiplexing (OFDM) modulation with a Volterra nonlinear predistorter having linear computational complexity, as well as a single-tap frequency domain nonlinear postdistorter. By using the proposed schemes we increased the data rate in the link almost by 25%, i.e. from 4.9 to over 6 Gbps.

In this Letter, a novel, to the best of our knowledge, Fabry–Perot cavity, based on Bragg grating technology for temperature and strain monitoring, is presented. Such a structure consists of two linearly chirped fiber Bragg gratings of a significant length written in a thermally tapered optical fiber. The technological process for manufacturing such a grating allows for utilization of almost every tapered fiber, by means of its profile and also phase masks with various chirp ratios. For this type of structure, a method for strain discrimination based on monitoring of the cavity length is proposed, enabling potential multiplexation of the sensor of two structures, which have the similar reflection spectra, by means of their spectral position. The utilized sensing mechanism allowed for achieving strain sensitivity by means of the cavity length change as high as 5 µm/µɛ. Also, as it has been experimentally shown a structure can also be employed for measurements of temperature, with the sensitivity equal to 8.96 pm/°C.

This article shows a novel approach for Bragg gratings interrogation, based on vertical-cavity surface-emitting laser with high-contrast grating cavity. It is shown that with such a light source, one may achieve simultaneous wavelength sweeping together with output light intensity modulation enabled by a single element. In turn, it allows for designing a two-dimensional (time and wavelength) Bragg grating interrogation scheme. The article consists of analytical deliberations that determine the limiting factors of such an interrogation unit, i.e. interrogation speed and size of the sensing network for given Bragg grating reflectivity, expressed in the form of signal-to-noise ratio. Moreover, an experimental and numerical proof of concept of the sensing unit consisting of fiber Bragg grating sensors with an interrogation speed of 1 kHz and the use of code division multiplexing is also presented.

In this Letter, we propose the application of a Volterra predistorter to compensate for the second-order nonlinear distortion generated in light-emitting diode (LED) communication systems. We demonstrate that a predistorter dedicated specifically to the LED has linear (not quadratic) numerical processing complexity. Experimental investigation performed using pulse amplitude modulation (PAM-4) indicates that it achieves similar performance as the classical Volterra equalizer located at the receiver. The highest measured gain in electrical signal to noise and interference power ratio of predistortion over linear equalization was at 300 Mbaud and was approximately 3.5 dB. At the same baud rate, the unpredistorted signal had a received optical power penalty of up to 2.5 dBm compared with the predistorted signal.

Bit and power loading (BPL) algorithms played a pivotal role in the success of orthogonal frequency division multiplexing (OFDM) in digital transmission, including light-emitting diode (LED) based wireless optical communications. Nevertheless, the conventional BPL algorithms do not distinguish the nonlinear distortion generated in LED transmitters from an additive noise, which leaves room for improvement. This letter presents a novel power loading and two BPL algorithms that maximize the transmission capacity while minimizing the nonlinear distortion generated in LED. The effectiveness of the proposed algorithms is evaluated through simulations and transmission experiments, revealing a throughput increase of up to 10% in comparison to what can be achieved employing classical algorithms.

In this article, a cost-effective and fast interrogating system for wide temperature measurement with Fiber Bragg Gratings is presented. The system consists of a Vertical Cavity Surface Emitting Laser (VCSEL) with a High Contrast Grating (HCG)-based cavity that allows for the fast tuning of the output wavelength. The work focuses on methods of bypassing the limitations of the used VCSEL laser, especially its relatively narrow tuning range. Moreover, an error analysis is provided by means of the VCSEL temperature instability and its influence on the system performance. A simple proof of concept of the measurement system is shown, where two femtosecond Bragg gratings were used to measure temperature in the range of 25 to 800 °C. In addition, an exemplary simulation of a system with sapphire Bragg gratings is provided, where we propose multiplexation in the wavelength and reflectance domains. The presented concept can be further used to measure a wide range of temperatures with scanning frequencies up to hundreds of kHz.