Terahertz wave generation from a dc-biased multimode laser

We present results achieved in the generation of terahertz wave by a semiconductor laser. It is a Fabry–Pérot based device with shallow grooves implemented on its p-side to engineer the longitudinal mode spectrum. The laser is dc-biased and temperature controlled at 298 K. The main two modes are separated by 3 nm at 1550 nm with a side-mode-suppression ratio of 25 dB. Using a frequency resolved optical gating, evidence of mode beating at 373 GHz is observed. With a bolometer interfaced to a Fourier transform interferometer, the second harmonic signal is measured at 690 GHz

Passively mode-locked semiconductor lasers and their applications

In this paper we present some characterizations of passively mode-locked semiconductor lasers. These lasers are multimode and they exhibit a modulation of their output power even though they are DC-biased. The modulation frequency corresponds to their free-spectral range. We demonstrate their potential: for generation of ultra-fast modulation for THz wave generation at room temperature without any direct modulations applied, in the radio frequency range they synchronise their modulation to the bit-rate of an incoming signal used for clock extraction. Therefore these devices can be used for all-optical clock recovery

RF or THz signals generated from DC biased multimode lasers

Although self pulsating (SP) lasers are DC biased, they feature a modulation of the output power. For the results presented in this paper, the SP frequency corresponds to the frequency spacing between longitudinal modes or its second harmonic. The performances of both a 40 GHz self pulsating distributed Bragg reflector laser and of a 660 GHz slotted laser are presented. For the first laser, the radio frequency (RF) signal was analysed on electrical spectrum analyser and its linewidth was smaller that the sum of the main optical modes, proving a passive modelocking of the mode phases. For the slotted laser, a bolometer interfaced to a FT IR spectrometer is used for the terahertz (THz) detection. A signal 10 times larger than the noise level was measured with this set up. Both lasers have demonstrated to be an easy solution to produce RF or THz signal generator

Radio frequency and terahertz signals generated by passively mode-locked semiconductor lasers

There are several different approaches to generating periodic signals using semiconductor lasers, for example: Q-switching, gain switching or mode-locking schemes. In general the active or passive mode-locking techniques require the use of a modulator or a saturable absorber in order to achieve the phase synchronisation. The laser diodes studied in this thesis, are demonstrated to operate in the mode-locked regime, while not requiring any direct or external modulation, nor the saturable absorbtion element in order to achieve the phase synchronisation. It has been demonstrated previously, that in a multimode semiconductor laser, the third order nonlinearities of a gain medium resulting in the four-wave-mixing effects, are responsible for the phase synchronisation and lead to phase locking. The repetition rate of the generated signal is fixed by the free-spectral range of the longitudinal spectrum. Therefore, with a passively mode-locked laser (PMLL) it is possible to cover a wide range of frequencies from the Radio-Frequency (RF) to the TeraHertz (THz) domain. Radio frequency signals generated by semiconductor lasers have many applications in optical communications, such as radio-over-fibre, or all-optical clock extraction. Terahertz signals are the focus of many research bodies nowadays, due to their interaction with matter. They have potential applications in areas like: industry, pharmacy, security (military), telecommunication and medicine. With continuous improvement of materials processing and technology, new ways of generation and detection of such types of signals have appeared. The key advantage of the optical RF or THz generation is that this type of device is direct current biased and operates at room temperature. In this thesis, a comprehensive study of various PMLLs, from distributed Bragg reflector bulk laser to quantum dashed Fabry-Perot lasers is given, demonstrating the origin of the phase synchronisation in these structures and some applications for these lasers such as all-optical clock recovery or THz signal generation

Wave-mixing analysis for THz-signals generation in dc-biased semiconductor optical devices at room temperature

Wave-mixing at 370-GHz in a SOA and FP semiconductor laser is investigated by using a FROG-system. A comparison of the optical time-fluctuations measured at their output stresses the importance of a resonant cavity in THz-signals generation from semiconductor optical devices

Investigation on the origin of terahertz waves generated by dc-biased multimode semiconductor lasers at room temperature

A technique to measure a terahertz wave generated by spectrum tailored Fabry–Pérot lasers (FP) is assessed. A dc-biased and 25 °C temperature controlled FP is probed by a continuous wave signal, tuned at 20 nm away from its lasing modes. With a 0.02 nm resolution optical spectrum analyzer (OSA), the terahertz generated signal frequency is measured from the interval between the probe and its side-band modulations. The terahertz waves emitted by these FPs are measured at 370±5 GHz and at 1.157±0.005 THz, respectively, within a precision set by our OSA. The origin of the terahertz wave is due to passive mode-locked through intracavity four-wave-mixing processes

Widely tunable laser source for gas sensing applications

In gas detection systems based on a single absorption line, wide-range, precision-tunable, continuous-wave laser sources are desired in order to allow for accurate targeting and measuring absorption profiles of particular gas species. A widely tunable ring laser using an intra-cavity wavelength tuning mechanism based on asymmetric Mach-Zehnder interferometers has been realized in the form of a monolithic indium phosphide photonic integrated circuit following a generic photonic integration approach. Furthermore, such integration technology enables the possibility of a co-integration of multiple lasers on a single photonic chip and allowing a gas detection system to monitor a few gas species simultaneously

Semiconductor optical amplifier-based heterodyning detection for resolving optical terahertz beat-tone signals from passively mode-locked semiconductor lasers

An all-optical heterodyne approach based on a room-temperature controlled semiconductor optical amplifier (SOA) for measuring the frequency and linewidth of the terahertz beat-tone signal from a passively mode-locked laser is proposed. Under the injection of two external cavity lasers, the SOA acts as a local oscillator at their detuning frequency and also as an optical frequency mixer whose inputs are the self-modulated spectrum of the device under test and the two laser beams. Frequency and linewidth of the intermediate frequency signal and therefore, the beat-tone signal are resolved by using a photodiode and an electrical spectrum analyze

Self-generation of optical frequency comb in single section Quantum Dot Fabry-Perot lasers: a theoretical study

Optical Frequency Comb (OFC) generated by semiconductor lasers are currently widely used in the extremely timely field of high capacity optical interconnects and high precision spectroscopy. Very recently, several experimental evidences of spontaneous OFC generation have been reported in single section Quantum Dot (QD) lasers. Here we provide a physical understanding of these self-organization phenomena by simulating the multi-mode dynamics of a single section Fabry-Perot (FP) QD laser using a Time-Domain Traveling-Wave (TDTW) model that properly accounts for coherent radiation-matter interaction in the semiconductor active medium and includes the carrier grating generated by the optical standing wave pattern in the laser cavity. We show that the latter is the fundamental physical effect at the origin of the multi-mode spectrum appearing just above threshold. A self-mode-locking regime associated with the emission of OFC is achieved for higher bias currents and ascribed to nonlinear phase sensitive effects as Four Wave Mixing (FWM). Our results are in very good agreement with the experimental ones

The usefulness of periostin determination in gynecology and obstetrics

Periostin (POSTN) is a multifunctional glycoprotein that belongs to the group of extracellular matrix (ECM) proteins. Dueto the molecular structure, cellular interactions, tissue locations as well functions of POSTN, we realize that its pivotalrole is organization and regulation of ECM microenvironment. In available databases there is a lack of data summarizingcurrent knowledge about POSTN expression in the field of gynecology and obstetrics. We conducted a search in PubMedof the National Library of Medicine and Google Scholar. Databases were extensively searched for all original and reviewarticles/book chapters published in English until December 2019 and related to periostin expression. All relevant articleswere reviewed and presented as appropriate.In the field of POSTN expression there is only one paper evaluating its involvement in cervical cancer cell metabolism andonly two studies analyzing its myometrial commitment: maintenance during pregnancy and induction of parturition inphysiology as well control of fibroids biology in pathology. Much more attention has been devoted to the expression ofdescribed protein in the endometriosis, and above all in ovarian cancer. Finally, a few studies carried out among pregnantwomen were presented.In this review study we presented current knowledge about periostin expression in the field of gynecology and obstetrics.Many achieved results are interesting and further studies are needed to verify some hypotheses. Structure, signalingpathways as well many functions of periostin are well-described. However, as it was clearly shown there is a lot of unknownissues which are waiting to be explored