Integrated Multi-wavelength Laser Source for Sensing

The instability of optical phase chaos synchronization between semiconductor lasers under master-slave open-loop configuration is investigated. The phase difference between the master and slave lasers is obtained and analyzed in experiment by heterodyne detection and Hilbert transform, and in simulation by solving the rate equations. The results show that the phase difference only maintains in a short duration time and then jumps to another value. A statistical analysis shows that both duration time and jumping values are random, proving that the phase chaos synchronization is unstable. A theoretical analysis shows that the instability of phase synchronization is caused by the jumping of the external cavity mode in the master laser.

We study the nonlinear dynamics of a vertical-cavity surface-emitting laser (VCSEL) subject to a repetitive optical pulse injection numerically using the SFM model. In our study, a linearly polarized slave laser is optically injected by a train of optical pulses from a master laser, where the polarization of the master laser is orthogonal to the polarization of the solitary slave laser (x-polarized). By varying the strength and the repetition frequency of the injected pulses, different dynamical states, including regular pulsations, period-doubled pulsations, chaotic pulsations, periodic oscillations, quasi-periodic oscillations, and chaotic oscillations, are found. Instead of having only one polarization mode at the slave laser output, both the y- and x-polarized modes are observed for the pulsation and oscillation states. While the pulsation states with y-polarization follow a period-doubling route to chaotic pulsations, the oscillation states with the x-polarization undergo a quasi-periodic route to chaos oscillations. Then, with adequate strength of the injection, the x-polarized mode will be suppressed (i.e. polarization switching) and eventually the slave laser will lock to the master laser with higher injection strength. Also, the switching points, the boundary of the injection-locked, and the regions of the chaotic states are found to be strongly influenced by the repetition frequency of the injection pulses and the detuning frequency between the two lasers.

A frequency tunable optoelectronic oscillator based on a directly modulated distributed-feedback (DFB) semiconductor laser under optical injection is proposed and experimentally demonstrated. Through optical injection, the relaxation oscillation frequency of the DFB laser is enhanced and its high modulation efficiency can enable the loop oscillation with a RF threshold gain of less than 20 dB. The DFB laser is a commercial semiconductor laser with a package of 10 GHz, and its packaging limitation can be overcome by optical injection. In our scheme, neither a high-speed external modulator nor an electrical bandpass filter is required, making the system simple and low-cost. Microwave signals with a frequency tuning range from 5.98 to 15.22 GHz are generated by adjusting the injection ratio and frequency detuning between the master and slave lasers. The phase noise of the generated 9.75 GHz microwave signal is measured to be -104.8 dBc/Hz @ 10 kHz frequency offset.

Photonic generation of wideband chaotic signals with time delay signature elimination is investigated experimentally and numerically based on a semiconductor laser (slave laser) with chaotic optical injection from a master laser. The master laser is subject to moderate optical feedback where the feedback strength and external-cavity length are fixed, while the slave laser stands alone. The experimental results show that wideband chaotic signals with successful time delay concealment can be generated in the slave laser by simply adjusting the coupling strength and frequency detuning between the two lasers. Furthermore, the numerical results are in accordance with the experimental observations. Finally, we propose a simple method for simultaneously generating multiple streams of high-quality chaotic signals using multichaotic lasers, where the time delay is effectively concealed in the autocorrelation function and delayed mutual information calculated from the chaotic time series.

A method of coherently summing the outputs of two diode-pumped ring lasers has been tested. The output of one such Nd:YAG laser (the master laser) at 1064 nm was mode-matched into a similar laser (the slave laser). The frequency of the slave laser was tuned toward that of the master laser by adjusting the crystal temperature (and thus the optical path length). The difference frequency was detected until the locking range was reached, when the free-running oscillation of the slave laser was completely injection-locked by the injected signal. With the master laser power of 15 mW and the slave laser power of 5 mW, the locking frequency occurred at ~23 MHz. The combined output power during locking ranged from ~20 to 21 mW with the maximum representing a 5% increase over the summation of the unlocked free-running lasers. Locking was held for periods >15 min. These results indicate the possibility of chaining together this type of laser to obtain coherent single-mode outputs with higher powers than currently possible.

Ultra-wideband signal generator based on cross gain modulation effect in a distributed feedback laser

The study of nonlinear dynamical systems is a subject of much interest, one application being in secure communication systems realized through the synchronization of chaotic dynamical systems. In this paper optical coupling is used to effect synchronization between two diode lasers in a master-slave configuration, and we study the effect of frequency detuning between the master and slave lasers on the character of the observed synchronization. Experimental conditions are found under which the synchronization plot (formed by plotting the output power of the slave laser against that of the master at each instant in time) makes a transition from a positive gradient to a negative gradient. The appearance of such a negative gradient is a new phenomenon, to our knowledge, which we term ``inverse synchronization.'' A rate-equation model is proposed which accounts for light injection into the slave laser, and which agrees with the experimental results. Using this model, we etablish that inverse synchronization is caused by nonresonant coupling between the master and slave lasers.

Recent work has shown the Quantum Dot (QD) material system to be well-suited to support dual-mode lasing. In particular, optical injection from a master laser (ML) into the residual Fabry-Perot (FP) modes of a 1310 nm Quantum Dot Distributed Feedback (QD-DFB) laser has been recently demonstrated to offer a highly reliable platform for stable dual-mode lasing operation. External controls on the ML, such as operating temperature and bias current, can be used to precisely adjust the spacing between the two lasing modes. This tunability of modeseparation is very promising for a range of applications requiring the generation of microwave, millimeter wave and terahertz signals. Considering the versatility and utility of such a scheme, it is imperative to acquire a deeper understanding of the factors that influence the dual-mode lasing process, in order to optimize performance. Toward this end, this paper seeks to further our understanding of the optically-injected dual-mode lasing mechanism. For fixed values of optical power injected into each FP residual mode and wavelength detuning, the dual-mode lasing characteristics are analyzed with regard to important system parameters such as the position and the intensity of the injected residual mode (relative to the Bragg and the other residual FP modes of the device) for two similarly-fabricated QD-DFBs. Results indicate that for dual mode lasing spaced less than 5 nm apart, the relative intensity of the injected FP mode and intracavity noise levels are critical factors in determining dual mode lasing behavior. Insight into the dual-mode lasing characteristics could provide an important design guideline for the master and QD-DFB slave laser cavities.

A novel method to reduce optical beat noise (OBN) which is critical in subcarrier multiplexed-based optical access link is suggested. The chirped optical signal was generated by using dual current modulation through master and slave lasers. The sidelobes of the slave laser decreased up to -90 dBm close to the noise floor. The OBN was reduced by 20 dB because of the spectral broadening of the slave laser resulted from the increased chirp.

A novel scheme to generate ultra-wideband (UWB) signals based on cross-gain modulation (XGM) effect in a DFB laser is proposed. In this scheme, a gain-switched laser (GSL) is used as master laser (ML), the optical pulses are optically injected into a DFB laser, which is used as slave laser (SL). By proper system configuration, UWB monocycle, doublet or triplet UWB signals can be generated after detection by a balanced photodiode. Besides, other modulation formats can also be realized, such as on-off keying (OOK) and pulse amplitude modulation (PAM) by properly modulating the ML optical pulses. Finally, fiber transmission of the modulated UWB signals is experimentally investigated.

Extreme events (EEs) are rare and unexpected events that emerge in many natural systems and are the object of intensive studies. Here, we experimentally investigate the evolution of deterministic optical EEs in a slave laser (SL) subject to chaotic optical injection from a master laser (ML) with optical feedback. Although the ML operates in the long-cavity regime, we observe occasional pulses that are high enough to be considered EEs, and the appearance probability of EEs can be significantly enhanced in the SL for certain injection parameters outside the injection-locking regions of the master-slave configuration. Additionally, the evolution of EEs can be readily identified from the two-dimensional maps. The numerical results show good qualitative agreement with the experiment. These results reveal the importance of injection parameters for the appearance of EEs in chaotic lasers and can be easily extended to other coupled systems.

We propose a novel, high-performance, and practical laser source system for optical clocks. The laser linewidth of a fiber-based frequency comb is reduced by phase locking a comb mode to an ultrastable master laser at 1064 nm with a broad servo bandwidth. A slave laser at 578 nm is successively phase locked to a comb mode at 578 nm with a broad servo bandwidth without any pre-stabilization. Laser frequency characteristics such as spectral linewidth and frequency stability are transferred to the 578-nm slave laser from the 1064-nm master laser. Using the slave laser, we have succeeded in observing the clock transition of (171)Yb atoms confined in an optical lattice with a 20-Hz spectral linewidth.

Synchronized mode-locking of monolithic mode-locked diode lasers has been demonstrated by injecting the light output from a master monolithic mode-locked diode laser. The master diode laser is a 10 GHZ hybridly mode-locked two section InGaASP quantum well laser. The slave lasers are a 10 GHz two section laser which is similar to the master laser, and a 20 GHz three section colliding pulse mode-locking laser. Both the slave lasers were greatly stabilized at 10 GHz frequency by a synchronous mode-locking mechanism under the injection of master laser pulses.

A primary frequency standard based on cold Cs atoms is under development at the Time and Frequency Division of the Centre Nacional de Metrologia, CENAM. A Cs magneto-optical trap has been developed using the standard sigma+sigma$4-horizontal 2-vertical laser beams of 1.9 cm in diameter, with 5 mW each. We use 852 nm, 5 mW, DBR laser as a master laser which is stabilized by saturation spectroscopy. Linewidth of the master laser is 1 MHz. A 50 mW, 852 nm, semiconductor laser is used as slave laser in order to amplify the light of the master laser. The slave laser is stabilized by injection light technique. 12 MHz red shift of the light is performed by double pass through two AOM's. In this paper we present some preliminary results of our MOT characterization as function of MOT's parameters such as intensity of laser beams and gradient of the magnetic field.

We perform numerical simulations of the dynamics of two VCSELs optically coupled in a master-slave configuration. We show that the interplay of nonlinearity and spontaneous emission noise can yield logic behavior, and the emergent outcome of such system is a reliable logic gate. Specifically in our case represents an all-optical logic gate, with the logic input encoded in the strength of the light injected in the slave laser by the master laser, and the fast and robust response decoded from the polarization state of the light emitted by the slave laser.