We present a new functional near infrared spectroscopy (fNIRs) technique based on dual-comb optical interrogation applied to dispersive media (DC-fNIRS) that can retrieve the frequency response of a living tissue (such as the brain) by parallel sampling of its frequency response in amplitude and phase at specific frequencies. With this information, we can retrieve the impulse response (diffuse-time-of-flight measurements, DTOF) of the medium and extract the absolute optical properties of the tissue and the spatial localization of perturbations for functional analysis with millisecond temporal resolution and noiseless optical gain, increasing the penetration. We have tested these predictions studying a biomimetic phantom with the same optical characteristics as brain tissue confirming the capacities of the DC-fNIRs technique for diffuse media. The system is patent pending PCT/ES2022/070176.
We analyze the full counting statistics of photons emitted by a Nitrogen Vacancy center (NV) under non-resonant laser excitation and resonant micro-wave (MW) control. This allows to build a phenomenological model which relates the relevant physical parameters with the detected fluorescence. Furthermore, we can investigate the time correlations of the emitted photons and elaborate detection and polarization protocols to optimize the energy and time resources while maximizing the system sensitivity.
A theoretical analysis of optical frequency combs associated with the main and suppressed linear polarization modes of a gain-switched long-wavelength VCSEL is performed. We have studied the VCSEL polarization-resolved dynamics by using an extension of the spin-flip model to include nonlinear carrier recombination. Our results show that two orthogonally polarized combs are generated that combine to produce a wider overall optical comb. The dependence of combs on the VCSEL parameters and on the amplitude and frequency of the modulation is analyzed. Bistability between the two orthogonally polarized combs is found.
This work presents a theoretical design and experimental optimization study on the improvements to pulsed diode laser
Gain-Switched (GS) optical sources and an external compressor based on a Nonlinear Loop Mirror (NOLM). The
designed and optimized NOLM will be adapted to the characteristics of GS optical sources by using a microstructured
optical fiber and a semiconductor optical amplifier in a nonlinear Sagnac loop, avoiding the need to include in the
compression and reshaping scheme pre-processing stages of the input optical pulses. This scheme reduces the system
complexity and the assembly of an input stage being a commercial or Cost Of The Shelf (COTS) gain-switched diode
laser and a compressor and reshaping stage giving rise to a compact, reliable low cost new picosecond optical pulse
sources at high repetition rates, that can be used in many fields and applications.
In this work we report a NOLM configuration based on a Semiconductor Optical Amplifier (SOA) and a highly
nonlinear Microstructured Optical Fiber (MOF) that offers a stable compression ratio and reshaping capabilities for
pulses obtained from Gain Switching diode laser sources. The device is perfectly adapted to the particularities of such
sources, namely their low power, their asymmetric nature and the presence of wide pedestals, without the need of
intermediate stages to pre-process these optical pulses.
Experimental and numerical studies are presented where the influence and importance of the dynamic of the
Semiconductor Amplifier on the overall pulse compression performance of the NOLM is explored. Results show that the
saturation and gain compression are important to understand the system behavior. Along with these effects, the influence
of the alpha factor and its dependence on the carrier density under high input conditions is evaluated. Numerical and
experimental results show relevant agreement, what sheds light on the device behavior and helps understand the
influence of the several physical effects behind it.
The experimental work presented in this paper investigates the quality improvement of gain-switched (GS) sources. GS is a straightforward technique to achieve short pulses from diode lasers; however, such pulses exhibit long duration (10-100 ps), low power (in the milliwatt range), are asymmetric and are often generated along with pedestals or subpulses. Simultaneous compression and reshaping of these low quality pulses has been observed experimentally for several input power values. These effects have been achieved using a highly nonlinear optical-loop mirror, based on a microstructured optical fiber and a nonlinear semiconductor optical amplifier. It is designed to be compact and to directly process these complex pulses thus eliminating the requirement for prepulse conditioning. This offers overall benefits in terms of reduced system complexity. The quality of the pulses is characterized by their temporal width, pedestal height, duration, and spectral components. A maximum overall compression factor of 6 for a 10-mW average input power is observed. Additionally, the pulses obtained are observed to have improved quality for the input power range considered (500 µW to 30 mW, GS typical operational range) and the experimental scheme used preserves the compactness, efficiency, and simplicity of GS light sources.
This work presents a theoretical and experimental investigation on the improvement of complex low quality pulses
obtained from a pulsed diode laser Gain-Switched (GS) optical sources by using a Highly Nonlinear Optical Loop Mirror
(HNOLM) directly coupled to the diode laser source without any previous conditioning of the pulses. First, a design of
the HNOLM device is evaluated. The proposed HNOLM is compact, containing 20 m of optical fiber and does not
require any intermediate stage to process the pulses. The device is based on the use of a Microstructured Optical Fiber
and a Highly Nonlinear Semiconductor Optical Amplifier. An experimental study of the achieved improvement of the
quality of GS pulses is presented. The pulses have been characterized through the evaluation of their autocorrelation
traces and a study using a Temporal Information Via Intensity (TIVI) algorithm. Results show that HNOLM provides
direct compression and pulse shaping for picosecond complex pulses obtained from a DFB COTS laser operating within
the 1550 nm window. The experimental observations are contrasted with a theoretical modeling of the system, and an
excellent agreement is observed.
This experimental work presented in this paper investigates the quality improvement of pulsed diode laser Gain-
Switched (GS) optical pulses. GS is a straightforward technique, however, these pulses exhibit long duration (10ps -
100ps), low power (in the mW range), are asymmetric and often come accompanied by pedestals or subpulses.
Simultaneous compression and reshaping of these input low quality pulses has been observed experimentally for several
input power values. These effects have been achieved using a Highly Nonlinear Optical Loop Mirror (HNOLM)
designed to directly process these long duration complex pulses thus eliminating the requirement for pre-pulse
conditioning. The NOLM is based on a Microstructured Optical Fiber and a Highly Nonlinear Semiconductor Optical
Amplifier. This device is compact, and offers overall benefits in terms of reduced system complexity.
Nonlinear Optical Loop Mirrors have been considered as nonlinear compressors for high input
power optical pulses. The present work proposes a NOLM scheme that compresses and reshapes low
power picosecond optical pulses in the miliwatts range. This scheme is based on a Semiconductor Optical
Amplifier and the use of highly nonlinear Photonic Crystal fibers. The attention of this study is the
amplitude noise and timing jitter behavior of this scheme.
The compression and reshaping of optical pulses is a key issue for many of the applications in which ultrashort
optical pulses are present since dispersion, nonlinearity and losses degrade their quality. We present a novel numerical
procedure for designing pulse compressors based on Nonlinear Optical Loop Mirrors (NOLM). To exemplify the
performance of the model, we apply this tool to the design of a NOLM intended to compress and reshape low energy
pulses obtained by means of diode laser pulsed sources. This way, the quality of the pulses generated with this
techniques can be improved.
The present work presents the study of an ultrashort pulse high quality laser source. This source is based on Gain Switching diode lasers and pulse compression schemes. Gain switching is one of the most interesting methods used to obtain short pulses from diode laser. This technique is easy to implement, cheap and does not require any specific fabrication. It also offers repetition rate tunability. Pulse compression is also studied as a means of shortening and improving the shape and quality of the pulses obtained from Gain Switching sources. Several compression techniques are evaluated. Linear pulse compression phenomenon is studied, as well as compression devices based on nonlinear optical pulse propagation. A comparative study of these compressors is performed in order to develop a monolithic source based on InP semiconductor technology.
Short pulsed laser sources have recently been under investigation for applications in high speed optical communications systems. A key issue to achieve high quality reliable short pulses is the need to compress and improve the shape of the pulse train. Nonlinear Optical Loop Mirrors (NOLM) provides both compression and reshaping of the optical pulses. The present work turns the attention to the influence of noise in the compression behavior of NOLM. Characteristics such as compression factor, signal to noise ratio, dynamic RIN level, BER and timing jitter are considered. The results
obtained will be the basis for the design of a compact high quality ultrashort optical pulse source at 40 GB/s with monolithic semiconductor compressor. This device is under investigation within the MONOPLA European Project.
Short pulsed laser sources have recently been under investigation for applications in high speed optical communications systems. Studies concerning short pulse laser sources based on Gain Switching techniques and compression devices have been made. Nonlinear Optical Loop Mirrors (NOLM) provide both compression and reshaping of the optical pulses. As achieved pulse widths become shorter, timing jitter becomes crucial. The present work turns the attention to the influence of timing jitter in the performance of the NOLM pulse compression device. The results obtained will be the basis for the design of a compact high quality ultrashort optical pulse source at 40 GBs with monolithic semiconductor compressor. This device is under investigation within the MONOPLA project.
Generation of high quality ultrashort optical pulses for optical communications in the 1,55 μm window is an important field of study. A key issue is the need to compress pulse width. Several techniques provide this compression functionality. Nonlinear Optical Loop Mirrors provide both compression and reshaping of the optical pulses. This work presents a comparative numerical study of several NOLM schemes whose results will be the basis for the design of a compact high quality ultrashort optical pulse source at 40 GBs with a monolithic InP semiconductor compressor. This source is under investigation within the MONOPLA project. A model based on the Nonlinear Schrödinger Equation is used. Input pulses are considered to be generated by a Gain Switching diode laser source. Characteristics such as time-bandwidth product, peak-power, pulse shape and pedestals are being considered.
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