19 research outputs found
New photonic architectures and devices for generation and detection of sub-THz and THz waves
The development of high-quality and reliable devices in the THz frequency region to fill the existing technological gap has become a major concern. This is chiefly motivated by the need of a widespread exploitation of the extensive variety of identified applications in this frequency region by a wide range of users, including the non-scientific community. The photonic approaches used for these purposes offer important and exclusive advantages over other existing alternatives, which have as a main representative the all-electronic technology, especially in terms of frequency range coverage, possibility of photonic distribution using optical fibers, weight and Electromagnetic Interference (EMI) immunity. Nevertheless, the optical techniques have traditionally provided with worse performance in terms of phase noise, tunability and dynamic range (in generation), and conversion ratio (in detection) when compared to state-of-theart all-electronic THz technology. The work accomplished in this thesis focuses on the design, development and validation of new photonic architectures and devices for both generation and detection of sub-THz and THz waves which overcome the drawbacks of optical techniques at this frequency region while maintaining all their advantages. In this thesis, several photonic sub-THz and THz generation systems have been developed using Difference Frequency Generation (DFG) architectures in which the DFG source is provided by an Optical Frequency Comb Generator (OFCG) and optical mode selection. Different devices and techniques are investigated for each part of the system before arriving to the final high performance synthesizer. Passively Mode-Locked Laser Diodes (PMMLDs) are firstly evaluated as integrated OFCG. An improved design of the OFCG is achieved with a scheme based on a Discrete Mode (DM) laser under Gain- Switching (GS) regime and optical span expansion by the use of a single Electro- Optical (EO) phase modulator. As optical mode selection, both high selective optical filtering and Optical Injection Locking (OIL) are used and evaluated. A commercial 50 GHz photodiode (PD) and an n-i-pn-i-p superlattice THz photomixer are employed as photodetector for Optical to THz conversion. The final reported system consists on an OFCG based on GS, OIL as mode selection strategy and an n-i-pn-i-p superlattice photomixer. This synthesizer offers a wide frequency range (60-140 GHz), readily scalable to a range between 10 GHz and values well above 1 THz. Quasi-continuous tunability is offered in the whole frequency range, with a frequency resolution of 0.1 Hz at 100 GHz that can be straightforwardly improved to 0.01 Hz at 100 GHz and 0.1 Hz at 1 THz. The measured FWHM at 120 GHz is <10 Hz, only limited by the measurement instrumentation. The system offers excellent frequency and power stability with frequency and power deviations over 1 hour of 5 Hz and 1.5 dB, respectively. These values are also limited by both the accuracy and uncertainty of the measurement setup. The performance achieved by this photonic sub-THz and THz synthesizer for most figures of merit matches or even surpasses those of commercial stateof- the-art all-electronic systems, and overcomes some of their characteristics in more than one million times when compared to commercial state-of-the-art photonic solutions. The detection part of this thesis explores the use of photonic architectures based on EO heterodyne receivers and the key devices that encompass these architectures: photonic Local Oscillators (LOs) and EO mixers. First results are developed at microwave frequencies (<15 GHz) using an Ultra-Nonlinear Semiconductor Amplifier (XN-SOA) as EO mixer and a GS based photonic LO. It is demonstrated how this LO device based on GS provides with a significant improvement in the performance of the overall EO receiver when compared to a traditional linearly modulated LO. Furthermore, this detection architecture is validated in an actual application (photonic imaging array), featuring scalability, flexibility and reasonable conversion ratios. After this, an EO heterodyne receiver is demonstrated up to frequencies of 110 GHz. The photonic LO employed is the abovementioned photonic sub- THz synthesizer developed in this thesis, while the EO mixer is an np-i-pn quasi ballistic THz detector. The first fabricated sample of this novel device is used, which is optimized for homodyne/heterodyne detection. The resulting sub-THz EO heterodyne receiver has conversion ratios around -75 dB. It works under zero-bias conditions, which together with the photonic distribution of the LO offers a high potential for remote detection of sub-THz and THz waves. In summary, new photonic architectures and devices are able to provide with state-of-the-art performance for generation of sub-THz and THz waves. In the case of EO heterodyne detection at sub-THz and THz frequency regions, photonic techniques are improving their performance and are closer to offer an alternative to all-electronic detectors. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------El desarrollo de dispositivos fiables y de alta calidad en el rango frecuencial
de Terahercios (THz) con el fin de cubrir el actual vac铆o tecnol贸gico se ha convertido
en una importante inquietud cient铆fica. Esto est谩 principalmente motivado por la
necesidad de explotar el gran n煤mero de aplicaciones identificadas en esta regi贸n
frecuencial por un gran n煤mero de usuarios, incluyendo a usuarios no cient铆ficos.
El enfoque fot贸nico empleado para estos prop贸sitos ofrece importantes y
exclusivas ventajas sobre otras alternativas existentes, que tienen como principal
representante a la tecnolog铆a electr贸nica, especialmente en t茅rminos de rango
de frecuencia de funcionamiento, posibilidad de distribuci贸n fot贸nica con fibras
贸pticas, peso, e inmunidad electromagn茅tica. No obstante, las t茅cnicas fot贸nicas
tradicionalmente han ofrecido peores prestaciones en t茅rminos de ruido de fase,
sinton铆a y rango din谩mico (en generaci贸n) y ratio de conversi贸n (en detecci贸n)
con respecto a la tecnolog铆a electr贸nica de THz en el estado del arte. El trabajo
realizado en esta tesis se centra en el dise帽o, desarrollo y validaci贸n de nuevas
arquitecturas y componentes fot贸nicos tanto para generaci贸n como detecci贸n de
ondas de sub-THz y THz que permitan solucionar las desventajas de las t茅cnicas
贸pticas manteniendo todas sus ventajas.
En esta tesis, varios sistemas de generaci贸n de sub-THz y THz han sido
desarrollados utilizando arquitecturas Difference Frequency Generation (DFG)
en las que la fuente DFG es prove铆da por un Optical Frequency Comb Generator
(OFCG) y selecci贸n de modos 贸pticos. Diferentes dispositivos y t茅cnicas
son investigados para cada parte del sistema hasta conseguir un sintetizador
de altas prestaciones. Passively Mode-Locked Laser Diodes (PMMLDs) son inicialmente evaluados como OFCG integrados. Un dise帽o mejorado del OFCG
es conseguido mediante el uso de un esquema basado en un l谩ser Discrete Mode
(DM) bajo r茅gimen Gain Switching (GS) y expansi贸n del ancho de banda 贸ptico
mediante el uso de un modulador de fase Electro-脫ptico (EO). Como estrategia
de selecci贸n de modos 贸pticos, tanto filtrado 贸ptico altamente selectivo como
Optical Injection Locking (OIL) son usados y evaluados. Un fotodiodo comercial
de ancho de banda 50 GHz y un fotomezclador de THz de superred n-i-pn-i-p
son empleados.
El sistema de generaci贸n final que se presenta en esta tesis consiste en
un OFCG basado en GS, OIL como t茅cnica de selecci贸n de modos 贸pticos y
un fotomezclador de THz de superred n-i-pn-i-p. Este sintetizador ofrece un
rango de funcionamiento de 60 a 140 GHz, directamente escalable a un rango
entre 10 GHz y valores m谩s all谩 de un THz. Sinton铆a cuasi-continua es ofrecida
en todo el rango de frecuencia de operaci贸n, con una resoluci贸n en frecuencia
de 0.1 Hz a 100 GHz que puede ser directamente escalable a 0.01 Hz a 100 GHz y 0.1 Hz a 1 THz. El ancho de l铆nea a 3-dB de la se帽al a 120 GHz es menor de
10 Hz, solo limitada por la instrumentaci贸n de medida. El sistema ofrece una
excelente estabilidad en potencia y frecuencia, con desviaciones sobre una hora
de operaci贸n de 1.5 dB y 5 Hz, respectivamente. Estos valores tambi茅n est谩n
limitados por la precisi贸n e incertidumbre de la instrumentaci贸n de medida.
Las prestaciones conseguidas por este sintetizador fot贸nico de sub-THz
y THz para la mayor铆a de figuras de m茅rito, igualan o superan aquellas de las
mejores soluciones comerciales electr贸nicas en el estado del arte, y supera algunas
de estas caracter铆sticas en m谩s de un mill贸n de veces en el caso de soluciones
fot贸nicas comerciales en el estado del arte.
La parte de detecci贸n de esta tesis explora el uso de arquitecturas fot贸nicas
basadas en receptores EO heterodinos y los componentes clave que forman estas
arquitecturas: Oscilador Local (OL) fot贸nico y mezcladores EO. Los primeros
resultados son desarrollados en el entorno de microondas (<15 GHz) usando un
amplificador de semiconductor 贸ptico ultra no lineal (XN-SOA) como mezclador
EO y un OL fot贸nico basado en GS. Se demuestra como este OL basado en GS
ofrece una mejora significativa de las prestaciones del receptor con respecto al
uso de OL fot贸nicos tradicionales basados en modulaci贸n lineal. Adem谩s, esta
arquitectura de detecci贸n es validada en una aplicaci贸n real (imaging array
fot贸nico), ofreciendo escalabilidad, flexibilidad y ratios de conversi贸n razonables.
Tras esto, un receptor EO heterodino es demostrado hasta frecuencias de 110 GHz. El OL fot贸nico empleado es el sintetizador de altas prestaciones
presentado en esta tesis, mientras que el mezclador EO es un nuevo detector de
THz: el np-i-pn cuasi-bal铆stico. La primera muestra fabricada de estos nuevos
dispositivos, especialmente dise帽ados y optimizados para detecci贸n homodina
y heterodina, es empleada. El receptor EO heterodino resultante ofrece ratios
de conversi贸n de -75 dB. Este dispositivo es capaz de trabajar sin alimentaci贸n,
lo que unido a la distribuci贸n fot贸nica del OL, ofrece un gran potencial para
detecci贸n remota de ondas de sub-THz y THz.
En resumen, las nuevas arquitecturas y dispositivos fot贸nicos presentados
en esta tesis son capaces de ofrecer prestaciones en el estado del arte para
generaci贸n de ondas de sub-THz y THz. En el caso de detectores EO heterodinos
en frecuencias de sub-THz y THz, las t茅cnicas fot贸nicas est谩n mejorando sus
prestaciones significativamente y est谩n cada vez m谩s cerca de ofrecer una
alternativa a detectores electr贸nicos en el estado del arte
Desarrollo de t茅cnicas para la optimizaci贸n de la resoluci贸n espacial y temporal en interferometr铆a l谩ser heterodina aplicada a medida de densidades electr贸nicas en plasmas de fusi贸n
Ingenier铆a de Telecomunicaci贸
Characterization of Ultra-Nonlinear SOA in a heterodyne detector configuration with remote photonic local oscillator distribution
A heterodyne receiver scheme based on electro-optical (EO) downconversion is introduced. The local oscillator (LO) and the retrieved intermediate frequency (IF) signals are remotely distributed over fiber to/from a single ultra-nonlinear semiconductor optical amplifier (SOA) device that acts as a highly nonlinear mixer device, enhancing the downconversion performance of the system. The photonic LO is generated modulating a DFB under gain switching (GS), eliminating the need of external elements and the polarization dependency. We evaluate the performance of the downconversion up to frequencies much higher than the bandwidth of the devices (15 GHz). Results show broadband heterodyne detection performance of the system. The presented scheme offers advantages in terms of compactness and cost efficiency and can be easily scaled to remotely reach multiple receivers in scalable detection arrays.The work by A.R. Criado has been supported by the Spanish Ministry of Science and Technology under the FPI Program, Grant# BES2010-030290.Publicad
Enhancing the performance of electro-optical heterodyne receivers using gain switched photonic local oscillators
The performance of a Gain Switched (GS) optical source used as a Photonic Local Oscillator (PLO) in an Electro-Optical (EO) heterodyne receiver is experimentally evaluated and compared to the use of a traditional linearly modulated PLO. The EO heterodyne receiver used is based on an Ultra Nonlinear Semiconductor Optical Amplifier (XN-SOA) that provides a compact, cost effective and energy efficient receiver with a remote distribution of both PLO and Intermediate Frequency (IF) signals and a direct 50-ohms input for the Radiofrequency (RF) component. The comparison between both GS and linearly modulated PLO is made in terms of the conversion efficiency (conversion ratio); linearity (1-dB compression point) and noise (integrated RMS timing jitter). The analysis results in a significant improvement of the evaluated figures of merit when using a Gain Switched PLO.This work was supported in part by the Spanish Ministry of Science and Technology through the project TEC2009-14525-C02-02. The work of A. R. Criado has been supported by the Spanish Ministry of Science and Technology under the FPI Program, Grant # BES2010-030290
Two color multichannel heterodyne interferometer set up for high spatial resolution electron density profile measurements in TJ-II
Proceedings of: 18th Topical Conference on High-Temperature Plasma Diagnostics, Wildwood, New Jersey (USA), 16-20 May 2010.Expanded-beam multichannel heterodyne interferometer has been installed on the TJ-II stellarator. Careful design of the optical system has allowed complete control on the evolution of both Gaussian beams along the interferometer, as well as the evaluation and optimization of the spatial resolution to be expected in the measurements. Five CO2 (measurement) channels and three Nd:YAG (vibration compensation) channels have been used to illuminate the plasma with a probe beam of 100 mm size. An optimum interpolation method has been applied to recover both interferometric phasefronts prior to mechanical vibration subtraction. The first results of the installed diagnostic are presented in this paper.This work was supported by Spanish Ministry of Education and Science Grant No. ENE2006-13559FTN . The authors would also like to acknowledge the help of Ernesto Garcia Ares and Jose Ramon Lopez Fernandez for setting up the signal conditioning systems
Photonic synthesis of continuous-wave millimeter-wave signals using a passively mode-locked laser diode and selective optical filtering
We report a photonic synthesis scheme for CW mm-wave signal generation using a single Passively Mode-Locked Laser Diode (PMLLD), optical filtering and photomixing in a fast photodiode. The phase noise of the photonically synthesized signals is evaluated and inherits the characteristics of the PMLLD electrical power spectrum.Publicad
Calibration of a high spatial resolution laser two-color heterodyne interferometer for density profile measurements in the TJ-II stellarator
Proceedings of: 17th Topical Conference on High-Temperature Plasma Diagnostics, Albuquerque, New Mexico, 11-15 May 2008A high spatial resolution two-color (CO2, lambda=10.6 mum, He-Ne, lambda=633 nm) interferometer for density profile measurements in the TJ-II stellarator is under development and installation, based in the currently operational single channel two-color heterodyne interferometer. To achieve the objectives of 32 channels, with 4-5 mm lateral separation between plasma chords, careful design and calibration of the interferometric waveforms for both the measurement and vibration compensation wavelengths are undertaken. The first step has been to set up in our laboratories an expanded-beam heterodyne/homodyne interferometer to evaluate the quality of both interferometric wavefronts, a reported source of poor vibration compensation and thus low resolution in the density profile measurements. This novel interferometric setup has allowed us to calibrate the spatial resolution in the profile measurements resulting in ~2 mm lateral resolution in the reconstruction of the interferometric wavefront
VCSEL-Based Optical Frequency Combs: Toward Efficient Single-Device Comb Generation
Optical frequency combs generators (OFCGs) have demonstrated to be extremely useful tools in a wide variety of applications. The current research trends look toward compact devices that are able to offer high phase correlation between optical lines, and in this sense, mode-locked laser diodes (MLLDs), with repetition frequencies in the few gigahertz (GHz) range, and especially microresonators, with repetition frequencies of hundreds of GHz, are the most promising devices fulfilling these requirements. Nevertheless, focusing in the few GHz frequency rate, MLLDs cannot provide continuous tunability and require special devices that are still far from offering reliability and repeatability for commercial use. In this letter, we demonstrate for the first time the generation of a flat OFCG based on a single commercial vertical cavity surface emitting laser under gain-switching regime with 20 optical lines (spaced by 4.2 GHz) in a 3-dB bandwidth, offering wide tunability range and very high phase correlation between optical modes. This OFCG does not need any external modulator and it is the most energy-efficient OFCG reported to date.Publicad
Continuous wave sub-THz photonic generation with VCSEL-based optical frequency comb
A simple and energy-efficient photonic system to generate continuously tunable, low phase noise, sub-THz waves based on COTS components is presented. The optical scheme is based on the use of a commercial vertical cavity surface emitting laser under gain switching modulation that provides a very flat optical frequency comb generator (OFCG) with 23 modes in a 20 dB bandwidth. The laser only needs 15 dBm continuous wave radiofrequency input power and 9 mA of bias current to provide this OFCG. Two optical injection locking stages filter and amplify the two desired modes that are detected in a photodiode to produce the desired sub-THz signal at the frequency difference of these two selected modes. As an example, demonstrated is the generation of a very stable 88.2 GHz tone with lower linewidth than 10 Hz using a reference of 4.2 GHz to generate the OFCG.The work by 脕.R. Criado has been supported by the Spanish Ministry of Science and Technology under the FPI Program, grant no. BES2010-030290Publicad