A tunable cavity-locked diode laser source for terahertz photomixing

An all solid-state approach to the precise frequency synthesis and control of widely tunable terahertz radiation by differencing continuous-wave diode lasers at 850 nm is reported in this paper. The difference frequency is synthesized by three fiber-coupled external-cavity laser diodes. Two of the lasers are Pound-Drever-Hall locked to different orders of a Fabry-Perot (FP) cavity, and the third is offset-frequency locked to the second of the cavity-locked lasers using a tunable microwave oscillator. The first cavity-locked laser and the offset-locked laser produce the difference frequency, whose value is accurately determined by the sum of an integer multiple of the free spectral range of the FP cavity and the offset frequency. The dual-frequency 850-nm output of the three laser system is amplified to 500 mW through two-frequency injection seeding of a single semiconductor tapered optical amplifier. As proof of precision frequency synthesis and control of tunability, the difference frequency is converted into a terahertz wave by optical-heterodyne photomixing in low-temperature-grown GaAs and used for the spectroscopy of simple molecules. The 3-dB spectral power bandwidth of the terahertz radiation is routinely observed to be ≾1 MHz. A simple, but highly accurate, method of obtaining an absolute frequency calibration is proposed and an absolute calibration of 10^(-7) demonstrated using the known frequencies of carbon monoxide lines between 0.23-1.27 THz

Recent advances in solid-state organic lasers

Organic solid-state lasers are reviewed, with a special emphasis on works published during the last decade. Referring originally to dyes in solid-state polymeric matrices, organic lasers also include the rich family of organic semiconductors, paced by the rapid development of organic light emitting diodes. Organic lasers are broadly tunable coherent sources are potentially compact, convenient and manufactured at low-costs. In this review, we describe the basic photophysics of the materials used as gain media in organic lasers with a specific look at the distinctive feature of dyes and semiconductors. We also outline the laser architectures used in state-of-the-art organic lasers and the performances of these devices with regard to output power, lifetime, and beam quality. A survey of the recent trends in the field is given, highlighting the latest developments in terms of wavelength coverage, wavelength agility, efficiency and compactness, or towards integrated low-cost sources, with a special focus on the great challenges remaining for achieving direct electrical pumping. Finally, we discuss the very recent demonstration of new kinds of organic lasers based on polaritons or surface plasmons, which open new and very promising routes in the field of organic nanophotonics

III-V-on-silicon photonic devices for optical communication and sensing

In the paper, we review our work on heterogeneous III-V-on-silicon photonic components and circuits for applications in optical communication and sensing. We elaborate on the integration strategy and describe a broad range of devices realized on this platform covering a wavelength range from 850 nm to 3.85 μm

Performance of Widely Tunable Multi-Quantum-Well and Bulk Laser Diodes and the Main Limiting Factors

The output power and tuning performance of multi-quantum-well (MQW) and bulk InGaAsP/InP-distributed Bragg reflector (DBR) tunable laser diodes (TLDs) are investigated over a wide wavelength tuning range using physics-based PICS3D and VPI laser simulation tools within the travelling-wave formalism. The key result of our simulations is the discovery of a new effect in TLDs due to intervalence band absorption (IVBA) in passive phase and DBR sections, which limits the wavelength tuning range. The physical mechanism responsible for such a behavior is a collapse of the spectral-mode selectivity by the DBR due to large IVBA losses in the phase or/and DBR sections. We fundamentally demonstrate different roles played by the IVBA in the active and passive sections of a TLD. It is shown that the IVBA in passive sections and the carrier relaxation broadening (CRB) of the Lorentzian lineshape function in the lasers' active and passive sections play a crucial role in TLD tuning operation. The IVBA coefficient k IVBA and the intraband relaxation time τ in are the major limiting factors that define the output power variation and the achievable tuning range of the lasers. Both bulk and MQW lasers with small k IVBA demonstrate a wide wavelength tuning range above 30 nm, while for large k IVBA , the tuning range drops below 10 nm. We show that the output power variation with tuning due to the CRB parameter τ in is qualitatively different in bulk and MQW TLDs. The TLD tuning and power performance is also strongly affected by the shapes of the net gain and the cavity mirror loss spectra and their mutual positioning with respect to the lasing cavity mode during the tuning. The limiting parameters k IVBA and τin as well as gain and mirror loss spectra must be thoroughly evaluated in each TLD structure prior to the device design and optimization in order to achieve the best performance in terms of the wavelength tuning and the output power stability

New approaches to widely tunable semiconductor lasers

Widely tunable lasers can signi??cantly reduce the costs and increase the functionality of optical networks. So far, the performance of integrated semiconductor based tunable lasers lagged behind the performance of the ??xed wavelength sources they need to replace. The objective of this thesis is to investigate new widely tunable laser concepts and compare their performance with the alternatives. In this work two new concepts for widely tunable lasers are introduced: the Cascaded Sampled Grating (CSG) laser and the T-MMI (Tunable Multi-Mode Interference section) laser. The tuning element in the Cascaded Sampled Grating (CSG) consists of two sampled grating sections. The re ection spectra of these elements add to give a CSG-re ection spectrum with one dominant re ection resonance. The design of this element is detailed and simulations are presented. Experimental devices were processed and characterized. In these devices an output power of up to 10 mW was achieved with an SMSR of at least 30 dB over a tuning range of 57 nm. Simulations, based on the experimental results, predict a capability to generate > 30 mW output power and an SMSR > 37 dB over a 40 nm tuning range. The tuning element in the T-MMI consists of a sampled grating and a novel tuning element, the T-MMI section. The transmission curve of this element can be shifted over a wide wavelength range by current injection in the center of the MMI section. By shifting the transmission curve of the T-MMI section, subsequent sampled grating resonances are selected. The design of this laser is detailed and simulations on the ??nal design are presented. Experimental devices were demonstrated with up to 7 mW output power. The SMSR was more than 25 dB over a tuning range of 38 nm. Over this tuning range a 10 dB variation in output power was observed. Simulations based on these experimental results predict a capability to generate 30mWoutput power and an SMSR of 40 dB over a tuning range of 40 nm (for a maximum gain section current of 220 mA) for an optimized design. An aspect of tunable lasers that has not been given su??cient attention in the past is the role of absorption of optical power in the tuning sections. In this thesis it was demonstrated that for 30 mW operation the composition of the material in the tuning layer is critical. For a tuning layer with bandgap wavelength close to the laser wavelength, the re ection spectrum of the tuning elements saturates before 30 mW output power is achieved. In the comparison between the CSG and T-MMI with other concepts for widely tunable lasers, it follows that both CSG and T-MMI are similar or better than other concepts in the area of output power and SMSR. An important di??erentiation for the T-MMI is achieved in its simplicity of operation

A Sub-λ3\rm \lambda^{3}-Volume Cantilever-based Fabry-P\'erot Cavity

We report on the realization of an open plane-concave Fabry-P\'erot resonator with a mode volume below $\lambda^3$ at optical frequencies. We discuss some of the less common features of this new microcavity regime and show that the ultrasmall mode volume allows us to detect cavity resonance shifts induced by single nanoparticles even at quality factors as low as $100$. Being based on low-reflectivity micromirrors fabricated on a silicon cantilever, our experimental arrangement provides broadband operation, tunability of the cavity resonance, lateral scanning and promise for optomechanical studies

Characterization of wavelength tunable lasers for use in wavelength packet switched networks

The telecom industry's greatest challenge, and the optical systems and components vendors' biggest opportunity is enabling providers to expand their data services. The solution lies in making optical networks more responsive to customer needs, i.e., making them more rapidly adaptable. One possible technique to achieve this is to employ wavelength tunable optical transmitters. The importance of tunability grows greater every year, as the average number of channels deployed on DWDM platforms increases. By deploying tunable lasers it is much easier to facilitate forecasting, planning and last minute changes in the network. This technology provides with solution for inventory reduction. It also offers solution for fast switching at packet level. The conducted research activities of the project was divided in two work packages: 1. Full static characterization-the laser used in the experiment was a butterfly-packaged Sampled Grating DBR laser with four electrically tunable sections. LabView programme was developed for distant control of the equipment and the laser itself. The parameters required for creating a look-up table with the exact currents for the four sections of the laser, namely wavelength, side mode suppression ratio and output power, were transferred to tables. Based on those tables the currents were defined for each of the 96 different accessible channels. The channel allocation is based on the 50 GHz spacing grid. A detailed analysis of the tuning mechanisms is provided. 2. Dynamic characterization and BER performance in wavelength packet switched WDM systems-a commercially available module was used supplied with the software package for controlling the wavelength channels and setting the laser to switch between any accessible channel. The laser is DBR laser without SOA integration so the dynamic tunability can be investigated. As the switching in the nanosecond regime is executed in the electrical domain, analysis of the switching parameters concerning the electrical circuit as well as laser structure is provided. The actual switching time was defined. The degradation in system performance due to spurious wavelength signals emitted from the tunable module during the switching event and their interference with other active channels was demonstrated by examining the presence of an error floor in the BER rate against received power measurements

Analysis, Selection and Control of Optimal Driving Current Combinations in Wavelength Switching for DBR Lasers

[[abstract]]In this paper we exploit a basic type of three-stage Distributed Bragg Reflector (DBR) laser that by adjusting its input driving currents in the tri-electrode to generate signals with wavelengths that are in the International Telecommunication Union (ITU)-Band. Many driving current combinations can generate the same ITU wavelength; we will consider in this paper the situation when the input currents are restricted within certain range and to find for all those input current combinations that generate output signals with wavelengths locating in the ITU defined wavelength range. And we will through simulations to determine which set of current combinations will generate the shortest switching time. We will also propose a new current control method, when we know in advance the signal will be switched to certain band, to determine the best current switching combinations that resulting in faster and shorter switching time than that of the conventional system structure which has the drawback that it has only one fixed current combinations for each channel.[[notice]]補正完畢[[incitationindex]]EI[[booktype]]電子

AI-optimised tuneable sources for bandwidth-scalable, sub-nanosecond wavelength switching

Wavelength routed optical switching promises low power and latency networking for data centres, but requires a wideband wavelength tuneable source (WTS) capable of sub-nanosecond switching at every node. We propose a hybrid WTS that uses time-interleaved tuneable lasers, each gated by a semiconductor optical amplifier, where the performance of each device is optimised using artificial intelligence. Through simulation and experiment we demonstrate record wavelength switch times below 900 ps across 6.05 THz (122×50 GHz) of continuously tuneable optical bandwidth. A method for further bandwidth scaling is evaluated and compared to alternative designs