All-Fibered High-Quality Stable 20-GHz and 40-GHz Picosecond Pulse Generators

International audienceIn this work, we investigate the generation of stable 20- and 40-GHz pulse trains through the nonlinear compression of an initial beat-signal in a cavity-less optical-fiber-based device. Enhanced temporal stability is achieved by generating the sinusoidal beating thanks to a commercial LiNbO3 intensity modulator driven by a half repetition-rate external RF clock. We also show that the residual timing jitter induced by the RF phase modulation imposed to suppress Brillouin back-scattering can be reduced by managing the cumulated dispersion of the compression line, whereas complete polarization stabilization is obtained owing to a modified setup involving a Faraday rotator mirror. Finally, a high-quality 160-Gbit/s signal is generated from our low duty-cycle 40-GHz pulse source through optical time-division multiplexing

10 GHz pulse source for 640 Gbit/s OTDM based on phase modulator and self-phase modulation

We demonstrate a high-quality cavity-free 10 GHz 680 fs pulse source starting from a continuous wave (CW) laser. The pulse source is employed in a 640 Gbit/s on-off keying (OOK) OTDM data generation and demultiplexing experiment, where the error-free bit error rate (BER) performance confirms the high pulse quality. The pulse source is based on a linear pulse compression stage followed by two polarization-independent non-linear pulse compression stages. The linear pulse compression stage relies on a phase modulator, which is used to generate linear chirp and followed by a dispersive element to compensate the chirp. The non-linear pulse compression stages are based on self-phase modulation (SPM) in dispersion-flattened highly non-linear fibers (DF-HNLF). The pulse source is tunable over the C-band with negligible pedestal.</p

Dynamic Feedback Pulse Shaping For High Power Chirped Pulse Amplification System

The topic of this proposal is the development of high peak power laser sources with a focus on linearly chirped pulse laser sources. In the past decade chirped optical pulses have found a plethora of applications such as photonic analog-to-digital conversion, optical coherence tomography, laser ranging, etc. This dissertation analyzes the aforementioned applications of linearly chirped pulses and their technical requirements, as well as the performance of previously demonstrated parabolic pulse shaping approaches. The experimental research addresses the topic of parabolic pulse generation in two distinct ways. First, pulse shaping technique involving a time domain approach is presented, that results in stretched pulses with parabolic profiles with temporal duration of 15 ns. After pulse is shaped into a parabolic intensity profile, the pulse is compressed with DCF fiber spool by 100 times to 80 ps duration at FWHM. A different approach of pulse shaping in frequency domain is performed, in which a spectral processor based on Liquid Crystal on Silicon technology is used. The pulse is stretched to 1.5 ns before intensity mask is applied, resulting in a parabolic intensity profile. Due to frequency to time mapping, its temporal profile is also parabolic. After pulse shaping, the pulse is compressed with a bulk compressor, and subsequently analyzed with a Frequency Resolved Optical Gating (FROG). The spectral content of the compressed pulse is feedback to the spectral processor and used to adjust the spectral phase mask applied on the pulse. The resultant pulse iv after pulse shaping with feedback mechanism is a Fourier transform, sub-picosecond ultrashort pulse with 5 times increase in peak power. The appendices in this dissertation provide additional material used for the realization of the main research focus of the dissertation. Specification and characterization of major components of equipments and devices used in the experiment are present. The description of Matlab algorithms that was used to calculate required signals for pulse shaping are shown. A brief description of the Labview code used to control the spectral processor will also be illustrated

System-performance analysis of optimized gain-switched pulse source employed in 40-and 80-Gb/s OTDM systems

The development of ultrashort optical pulse sources, exhibiting excellent temporal and spectral profiles, will play a crucial role in the performance of future optical time division multiplexed (OTDM) systems. In this paper, we demonstrate the difference in performance in 40- and 80-Gb/s OTDM systems between optical pulse sources based on a gain-switched laser whose pulses are compressed by a nonlinearly and linearly chirped fiber Bragg grating. The results achieved show that nonlinear chirp in the wings of the pulse leads to temporal pedestals formed on either side of the pulse when using the linearly chirped grating, whereas with the nonlinearly chirped grating, pedestals are essentially eliminated. In an OTDM system, these pedestals cause coherent interaction between neighboring channels, resulting in intensity fluctuations that lead to a power penalty of 1.5 dB (40 Gb/s) and 3.5 dB (80 Gb/s) in comparison to the case where the nonlinearly chirped grating is used. Simulations carried out with the aid of Virtual Photonics Inc. verify the results achieved

Fabrication and High Speed Optoelectronic Characterization of Semiconductor Devices

This work is an investigation on the use of high speed optoelectronic techniques for the characterization of semiconductor devices. A low-frequency electrooptic probe station was demonstrated as well as the optoelectronic sampling scheme. The optoelectronic sampling technique relies on fast photoconductive switches for its operation. The autocorrelation signal detected in optoelectronic sampling was compared with signal detection by conventional techniques employing a sampling oscilloscope and a network analyser. The optoelectronic techniques described in this work depend critically on short-pulse lasers for the measurement of high speed devices. A fibre-grating pulse compressor was set-up to shorten the 120 ps pulses produced by a mode-locked Nd:YAG laser. Compression by a factor of 40 was demonstrated and nearly transform limited pulses of 3 ps duration were obtained. However, the output of the pulse compressor is very noisy and the output power is not high enough to enable electrooptic sampling experiments, in a jitter-free scheme. The same Nd:YAG laser was frequency doubled and used to synchronously pump a rhodamine 6G dye laser. Autocorrelation measurements obtained with the dye laser are again, very noisy and with poor reproducibility. The noise problems with the pulse compressor and with the dye laser were traced back to the Nd:YAG pump laser. It is concluded that this laser should be avoided as the source of short pulses for the electrooptic and optoelectronic measurement techniques. The use of a feedback loop is likely to reduce the noise in this laser, but drift in the intensity in a long time scale would still be present. A mode-locked Ti:Sapphire laser was also used for measurements in this project. Autocorrelation measurements taken with this laser are totally reproducible and contain little or no noise. The devices measured in this project were made by a combination of electron-beam lithography and photolithography. The use of these two lithography techniques together was made possible by the design of a mask set with alignment marks which can be used for registration in a mask aligner and in the electron beam lithography machine. Discrete devices were made and characterized by electrical techniques. Fabrication procedures were developed for resistors, Metal-Insulator-Metal (MIM) capacitors and for the Optoelecttonic Sampling Device (OSD). Discrete Mesfets were fabricated on MBE grown epilayers and their I-V characteristics were measured. A simplified optoelectronic sampling device was designed and made in a single lithographic step. It provides a quick way of producing devices in which autocorrelation measurements can be performed to determine the carrier lifetime in the substrate material. The optoelectronic sampling devices were made on four different substrate materials. The first one is a high purity, MBE grown GaAs epilayer, with very long lifetime (2ns). The control samples were made on "standard" semi-insulating GaAs, whose carrier lifetime is ~200 ps. Proton implantation in some of these devices made on SI GaAs substrate was used as a means of shortening the carrier lifetime, to produce fast turn-off times in the photoconductive switches. The lifetime after implantation of 4 x 10e14 protons/cm2 was estimated from an optoelectronic sampling measurement, to be around 40 ps. This is still a very long lifetime for the photoconductive switches. It is thought that self-annealing of the deep electron traps, caused by the lack of temperature control in the implanter, prevented the achievement of short lifetime in the switches. GaAs epilayers were grown by MBE at a temperature around 25

High pulse energy near-infrared ultrafast optical parametric oscillators

A source-demand in the near- and mid-IR wavelength spectrum exists for various applications such as waveguide inscription, multiphoton imaging, and nonlinear spectroscopy. All of the applications seek for higher repetitions rates for faster processing speed, better signal to noise ratios or to improve the results for applications like laser waveguide inscription. This is in contrast to the high pulse energies, required to drive the nonlinear processes involved with these applications. Available systems are either based on low-energy, high-repetition-rate optical parametric oscillators or high-energy, low-repetition-rate optical parametric amplifiers. In this thesis a sources was developed that can bridge the wide gap between these two extremes, providing sufficient energy to drive nonlinear processes, with repetition rates in the MHz domain. This was achieved by introducing three techniques previously employed for energy scaling in laser cavities. Firstly an exchange from the conventionally used Ti:sapphire pump to a commercial high power Yb:fibre laser system readily scaled the usable pump energy. This was combined with a technique known as cavity-length extension, which allows a lowering of the cavity roundtrip time offering the build-up of pulses with increased energy. In a final stage, cavity-dumping on basis of an acousto-optic modulator was introduced into the a redesigned cavity. The combination of these three techniques, novel to synchronously pumped optical parametric oscillators, enabled the extraction of record-high pulse energies and peak power

A new concept short pulse fiber laser source

Ultrashort-pulse fiber laser systems, which offer, due to their high peak pulse intensity in combination with high pulse frequencies (repetition rate), an innovative technology of nonlinear interaction with materials, help to fabricate components with unprecedented quality, precision and speed. Also due to the short pulse duration, laser energy can be introduced into the material in a shorter time than heat transfer occurs, which thus prevents thermal damage to the part. It is not surprising that industrial laser systems with a sub-nanosecond pulse length are widely used in the markets of precision processing, medical devices and in many other applications. The most critical component of such systems is the seed laser source. To date, the existing devices in the commercial market do not fully satisfy the industrial requirements. In this thesis I describe a new concept for the generation of ultrashort laser pulses using an all-passive, fiber-ring, mode-locked laser with at least two passive spectral filters incorporated. Also presented is a full theoretical model of the operation of the laser. I report on the development and the comprehensive characterization of a fully optimized laser configuration, finding excellent agreement of the theoretical model and the experimental results. Various practical configurations and their application were demonstrated. During the period of the project, a fully commercially developed laser scheme was implemented in a variety of IPG Photonics picosecond and femtosecond laser systems.Open Acces

Laser Systems for Applications

This book addresses topics related to various laser systems intended for the applications in science and various industries. Some of them are very recent achievements in laser physics (e.g. laser pulse cleaning), while others face their renaissance in industrial applications (e.g. CO2 lasers). This book has been divided into four different sections: (1) Laser and terahertz sources, (2) Laser beam manipulation, (3) Intense pulse propagation phenomena, and (4) Metrology. The book addresses such topics like: Q-switching, mode-locking, various laser systems, terahertz source driven by lasers, micro-lasers, fiber lasers, pulse and beam shaping techniques, pulse contrast metrology, and improvement techniques. This book is a great starting point for newcomers to laser physics