Nanosecond channel-switching exact optical frequency synthesizer using an optical injection phase-locked loop (OIPLL)

Experimental results are reported on an optical frequency synthesizer for use in dynamic dense wavelength-division-multiplexing networks, based on a tuneable laser in an optical injection phase-locked loop for rapid wavelength locking. The source combines high stability (50 dB), narrow linewidth (10 MHz), and fast wavelength switching (<10 ns)

Design and simulation of 1.28 Tbps dense wavelength division multiplex system suitable for long haul backbone

Wavelength division multiplex (WDM) system with on / off keying (OOK) modulation and direct detection (DD) is generally simple to implement, less expensive and energy efficient. The determination of the possible design capacity limit, in terms of the bit rate-distance product in WDM-OOK-DD systems is therefore crucial, considering transmitter / receiver simplicity, as well as energy and cost efficiency. A 32-channel wavelength division multiplex system is designed and simulated over 1000 km fiber length using Optsim commercial simulation software. The standard channel spacing of 0.4 nm was used in the C-band range from 1.5436-1.556 nm. Each channel used the simple non return to zero - on / off keying (NRZ-OOK) modulation format to modulate a continuous wave (CW) laser source at 40 Gbps using an external modulator, while the receiver uses a DD scheme. It is proposed that the design will be suitable for long haul mobile backbone in a national network, since up to 1.28 Tbps data rates can be transmitted over 1000 km. A bit rate-length product of 1.28 Pbps.km was obtained as the optimum capacity limit in 32 channel dispersion managed WDM-OOK-DD system.Comment: Accepted for publication in Journal of Optical Communications - De Gruyte

A monolithic MQW InP-InGaAsP-Based optical comb generator

We report the first demonstration of a monolithic optical-frequency comb generator. The device is based on multi-section quaternary/quaternary eight-quantum-well InP-InGaAsP material in a frequency-modulated (FM) laser design. The modulation is generated using quantum-confined Stark-effect phase-induced refractive index modulation to achieve fast modulation up to 24.4 GHz. The laser was fabricated using a single epitaxial growth step and quantum-well intermixing to realize low-loss phase adjustment and modulation sections. The output was quasicontinuous wave with intensity modulation at less than 20% for a total output power of 2 mW. The linewidth of each line was limited by the linewidth of the free running laser at an optimum of 25 MHz full-width at half-maximum. The comb generator produces a number of lines with a spacing exactly equal to the modulation frequency (or a multiple of it), differential phase noise between adjacent lines of -82 dBc/Hz at 1-kHz offset (modulation source-limited), and a potential comb spectrum width of up to 2 THz (15 nm), though the comb spectrum was not continuous across the full span

Phase and Amplitude Responses of Narrow-Band Optical Filter Measured by Microwave Network Analyzer

The phase and amplitude responses of a narrow-band optical filter are measured simultaneously using a microwave network analyzer. The measurement is based on an interferometric arrangement to split light into two paths and then combine them. In one of the two paths, a Mach-Zehnder modulator generates two tones without carrier and the narrow-band optical filter just passes through one of the tones. The temperature and environmental variations are removed by separated phase and amplitude averaging. The amplitude and phase responses of the optical filter are measured to the resolution and accuracy of the network analyzer

Broadband quantum-dot frequency-modulated comb laser

Frequency-modulated (FM) laser combs, which offer a periodic quasi-continuous-wave output and a flat-topped optical spectrum, are emerging as a promising solution for wavelength-division multiplexing applications, precision metrology, and ultrafast optical ranging. The generation of FM combs relies on spatial hole burning, group velocity dispersion (GVD), Kerr nonlinearity, and four-wave mixing (FWM). While FM combs have been widely observed in quantum cascade Fabry-Perot (FP) lasers, the requirement for a low-dispersion FP cavity can be a challenge in platforms where the waveguide dispersion is mainly determined by the material. Here we report a 60 GHz quantum-dot (QD) mode-locked laser in which both the amplitude-modulated (AM) and the FM comb can be generated independently. The high FWM efficiency of -5 dB allows the QD laser to generate an FM comb efficiently. We also demonstrate that the Kerr nonlinearity can be practically engineered to improve the FM comb bandwidth without the need for GVD engineering. The maximum 3-dB bandwidth that our QD platform can deliver is as large as 2.2 THz. This study gives novel insights into the improvement of FM combs and paves the way for small-footprint, electrically-pumped, and energy-efficient frequency combs for silicon photonic integrated circuits (PICs)

Design and Simulation of 1.28 Tbps Dense Wavelength Division Multiplex System Suitable for Long Haul Backbone

Wavelength division multiplex (WDM) system with on/off keying (OOK) modulation and direct detection (DD) is generally simple to implement, less expensive and energy efficient. The determination of the possible design capacity limit, in terms of the bit rate – distance product in WDM – OOK –DD systems is therefore crucial, considering transmitter/receiver simplicity, as well as energy and cost efficiency. A 32-channel WDM system is designed and simulated over 1000 km fiber length using Optsim commercial simulation software. The standard channel spacing of 0.4 nm was used in the C–band range from 1.5436 to 1.556 nm. Each channel used the simple non return to zero – on/off keying (NRZ – OOK) modulation format to modulate a continuous wave (CW) laser source at 40 Gbps using an external modulator, while the receiver uses a DD scheme. It is proposed that the design will be suitable for long haul mobile backbone in a national network, since up to 1.28 Tbps data rates can be transmitted over 1000 km. A bit rate length product of 1.28 Pbps.km was obtained as the optimum capacity limit in 32 channel dispersion managed WDM – OOK – DD system

Tecnologias coerentes para redes ópticas flexíveis

Next-generation networks enable a broad range of innovative services with the best delivery by utilizing very dense wired/wireless networks. However, the development of future networks will require several breakthroughs in optical networks such as high-performance optical transceivers to support a very-high capacity optical network as well as optimization of the network concept, ensuring a dramatic reduction of the cost per bit. At the same time, all of the optical network segments (metro, access, long-haul) need new technology options to support high capacity, spectral efficiency and data-rate flexibility. Coherent detection offers an opportunity by providing very high sensitivity and supporting high spectral efficiency. Coherent technology can still be combined with polarization multiplexing. Despite the increased cost and complexity, the migration to dual-polarization coherent transceivers must be considered, as it enables to double the spectral efficiency. These dual-polarization systems require an additional digital signal processing (DSP) subsystem for polarization demultiplexing. This work seeks to provide and characterize cost-effective novel coherent transceivers for the development of new generation practical, flexible and high capacity transceivers for optical metro-access and data center interconnects. In this regard, different polarization demultiplexing (PolDemux) algorithms, as well as adaptive Stokes will be considered. Furthermore, low complexity and modulation format-agnostic DSP techniques based on adaptive Stokes PolDemux for flexible and customizable optical coherent systems will be proposed. On this subject, the performance of the adaptive Stokes algorithm in an ultra-dense wavelength division multiplexing (U-DWDM) system will be experimentally evaluated, in offline and real-time operations over a hybrid optical-wireless link. In addition, the efficiency of this PolDemux algorithm in a flexible optical metro link based on Nyquist pulse shaping U-DWDM system and hybrid optical signals will be assessed. Moreover, it is of great importance to find a transmission technology that enables to apply the Stokes PolDemux for long-haul transmission systems and data center interconnects. In this work, it is also proposed a solution based on the use of digital multi-subcarrier multiplexing, which improve the performance of long-haul optical systems, without increasing substantially, their complexity and cost.As redes de telecomunicações futuras permitirão uma ampla gama de serviços inovadores e com melhor desempenho. No entanto, o desenvolvimento das futuras redes implicará vários avanços nas redes de fibra ótica, como transcetores óticos de alto desempenho capazes de suportar ligações de muito elevada capacidade, e a otimização da estrutura da rede, permitindo uma redução drástica do custo por bit transportado. Simultaneamente, todos os segmentos de rede ótica (metropolitanas, acesso e longo alcance) necessitam de novas opções tecnológicas para suportar uma maior capacidade, maior eficiência espetral e flexibilidade. Neste contexto, a deteção coerente surge como uma oportunidade, fornecendo alta sensibilidade e elevada eficiência espetral. A tecnologia de deteção coerente pode ainda ser associada à multiplexação na polarização. Apesar de um potencial aumento ao nível do custo e da complexidade, a migração para transcetores coerentes de dupla polarização deve ser ponderada, pois permite duplicar a eficiência espetral. Esses sistemas de dupla polarização requerem um subsistema de processamento digital de sinal (DSP) adicional para desmultiplexagem da polarização. Este trabalho procura fornecer e caracterizar novos transcetores coerentes de baixo custo para o desenvolvimento de uma nova geração de transcetores mais práticos, flexíveis e de elevada capacidade, para interconexões óticas ao nível das futuras redes de acesso e metro. Assim, serão analisados diferentes algoritmos para a desmultiplexagem da polarização, incluindo uma abordagem adaptativa baseada no espaço de Stokes. Além disso, são propostas técnicas de DSP independentes do formato de modulação e de baixa complexidade baseadas na desmultiplexagem de Stokes adaptativa para sistemas óticos coerentes flexíveis. Neste contexto, o desempenho do algoritmo adaptativo de desmultiplexagem na polarização baseado no espaço de Stokes é avaliado experimentalmente num sistema U-DWDM, tanto em análises off-line como em tempo real, considerando um percurso ótico hibrido que combina um sistema de transmissão suportado por fibra e outro em espaço livre. Foi ainda analisada a eficiência do algoritmo de desmultiplexagem na polarização numa rede ótica de acesso flexível U-DWDM com formatação de pulso do tipo Nyquist. Neste trabalho foi ainda analisada a aplicação da técnica de desmultiplexagem na polarização baseada no espaço de Stokes para sistemas de longo alcance. Assim, foi proposta uma solução de aplicação baseada no uso da multiplexagem digital de múltiplas sub-portadoras, tendo-se demonstrado uma melhoria na eficiência do desempenho dos sistemas óticos de longo alcance, sem aumentar significativamente a respetiva complexidade e custo.Programa Doutoral em Engenharia Eletrotécnic

Diamond Integrated Optomechanical Circuits

Diamond offers unique material advantages for the realization of micro- and nanomechanical resonators due to its high Young's modulus, compatibility with harsh environments and superior thermal properties. At the same time, the wide electronic bandgap of 5.45eV makes diamond a suitable material for integrated optics because of broadband transparency and the absence of free-carrier absorption commonly encountered in silicon photonics. Here we take advantage of both to engineer full-scale optomechanical circuits in diamond thin films. We show that polycrystalline diamond films fabricated by chemical vapour deposition provide a convenient waferscale substrate for the realization of high quality nanophotonic devices. Using free-standing nanomechanical resonators embedded in on-chip Mach-Zehnder interferometers, we demonstrate efficient optomechanical transduction via gradient optical forces. Fabricated diamond resonators reproducibly show high mechanical quality factors up to 11,200. Our low cost, wideband, carrier-free photonic circuits hold promise for all-optical sensing and optomechanical signal processing at ultra-high frequencies

A dual-wavelength fiber laser sensor with temperature and strain discrimination

This work presents a dual-wavelength C-band erbium-doped fiber laser assisted by an artificial backscatter reflector. This fiber-based reflector, inscribed by femtosecond laser direct writing, was fabricated into a single mode fiber with a length of 32 mm. The dual-wavelength laser obtained, centered at 1527.7 nm and 1530.81 nm, showed an optical signal-to-noise ratio over 46 dB when pumped at 150 mW. Another feature of this laser was that the power difference between the two channels was just 0.02 dB, regardless of the pump power, resulting in a dual emission laser with high equalization. On the other hand, an output power level and a central wavelength instability as low as 0.3 dB and 0.01 nm were measured, in this order for both channels. Moreover, the threshold pump power was 40 mW. Finally, the performance of this dual-wavelength fiber laser enhanced with a random reflector for sensing applications was studied, achieving the simultaneous measurement of strain and temperature with sensitivities around 1 pm/µε and 9.29 pm/°C, respectively.This work is part of the projects PID2019-107270RB, funded by MCIN/AEI/10.13039/ 501100011033 and FEDER 'A way to make Europe', and PDC2021-121172 funded by MCIN/AEI/10.13039/ 501100011033 and European Union 'Next generation EU'/PTR, the Ministerio de Educación, Cultura y Deporte of Spain (PhD grant FPU2018/02797)