In this paper, an encoding strategy is used to design specialized fiber Bragg grating (FBG) sensors. The encoding of each sensor requires two binary codewords to define the amplitude and phase patterns of each sensor. The combined pattern (amplitude and phase) makes each sensor unique and therefore two or more sensors can be identified under spectral overlapping. In this way, we add another dimension to the multiplexing of FBG sensors, obtaining an increase factor ‘n’ to enhance the number of sensors that the system can handle. A proof-of-concept scenario with three sensors was performed, including the manufacturing of the encoded sensors. Furthermore, an interrogation setup to detect the sensors central wavelength was proposed and its working principle was theoretically developed. Results show that total identification of the central wavelength is performed under spectral overlapping between the manufactured sensors, achieving a three-time improvement of the system capacity. Finally, the error due to overlapping between the sensors was assessed obtaining approximately 3 pm, which makes the approach suitable for use in real measurement systems.

In this paper, we present the simulation and experimental results of the first closed-loop system based on a directly modulated VCSEL in a gain-switching condition to generate optical frequency combs (OFC). In order to simulate the self-starting VCSEL-based optical frequency comb generator (SVOFC), we applied an intrinsic parameter extraction process to a C-band VCSEL using laser rate equations, static and dynamic measurements, and equivalent circuit models. The widest (62 GHz) and flattest (0.8) simulated OFC is obtained when the repetition frequency f₀ is 2.5 GHz. Implementation of the C-band SVOFC also shows that under constant electrical conditions, flatness higher than 0.85 and spectral widths of 50 GHz are obtained when f₀ = 2.5 GHz. The lowest phase noise at 10 kHz from the extracted electrical carrier is -127 dBc/Hz and is obtained when the optical fiber length is 5 km and f₀ = 1.25 GHz.

In this letter, a spectral encoding of fiber Bragg grating (FBG) sensors is proposed in order to solve their wavelength under overlapping conditions. Our technique uses optical orthogonal codes (OOCs) to define the spectral shape of the FBG sensors. In this way, we design encoded FBG sensors composed of more than one reflection band; the spectral location of the reflection bands is determined by the OOC, providing each encoded FBG sensor with a unique spectral signature. The demodulation technique for the proposed sensors makes use of their orthogonal nature: it obtains the wavelength position for each sensor by obtaining the autocorrelation product between the reflection spectrum and each sensor's spectral code. These FBG sensors have been manufactured and experimentally validated. The results demonstrate the overlap-proof nature of the encoded sensors. Furthermore, the very simple demodulation technique provides highly accurate wavelength detection and can be implemented in real-time detection systems.

The optical injection locking (OIL) technique is proposed to reduce the phase noise of a carrier generated for a vertical-cavity surface-emitting laser (VCSEL)-based optoelectronic oscillator. The OIL technique permits the enhancement of the VCSEL direct modulation bandwidth as well as the stabilization of the optical noise of the laser. A 2-km delay line, 10-GHz optical injection-locked VCSEL-based optoelectronic oscillator (OILVBO) was implemented. The internal noise sources of the optoelectronic oscillator components were characterized and analyzed to understand the noise conversion of the system into phase noise in the oscillator carrier. The implemented OILVBO phase noise was $−105.7dBc/Hz$ at 10 kHz from the carrier; this value agrees well with the performed simulated analysis. From the computed and measured phase noise curves, it is possible to infer the noise processes that take place inside the OILVBO. As a second measurement of the oscillation quality, a time-domain analysis was done through the Allan’s standard deviation measurement, reported for first time for an optoelectronic oscillator using the OIL technique.

This paper presents a temperature study of cellular spheroids of the line MCF-07 under a hyperthermia (HT) treatment. A 3D printed culture plate embedded with optical fiber Bragg grating (FBG) sensors was designed to perform real-time temperature measurements of the spheroids. The proposed culture plate preserves the fiber sensors' integrity and functionality while remaining immune to the high electromagnetic interference scenario. A custom microwave applicator was designed to eliminate direct contact between the heating element and the samples, while considering the culture plate material's permittivity to ensure efficient heating. The heating setup maintains the samples' temperature within the HT range, which is crucial for predicting treatment outcomes. The sensors embedded in the designed culture plate achieved an accuracy within 0.31 ${}^\mathrm{C}$ . Initial observations of the temperature effects on spheroids are discussed, highlighting the potential of this approach to understand how temperature variations within the HT range affect cell cultures.