Current-modulated Semiconductor Laser Research Articles

Interferometric Technique for the Spectral Characterization of High Frequency Current-Modulated Mid-Infrared Semiconductor Lasers

We describe two methods, based on Michelson interferometery, that enable the determination of the absolute wavelength of current-modulated semiconductor lasers. By non-linear regression of the instantaneous frequency of the interference signal, the rate of change of the wavelength of the radiation can be inferred. Alternatively, the absolute wavelength can be directly calculated from the maxima and minima of the interference signal. In both cases a reference absorption line enables the determination of the absolute wavelength. Both methods offer respective advantages. The methods allow a highly resolved wavelength measurement under lower kilohertz range current-modulation with relatively little effort. As a result, we present the rates of wavelength change and absolute wavelengths exemplarily for a specific interband cascade laser. It is furthermore shown that the spectral dynamic range of the laser decreases with increasing modulation frequency.

A new line-shape asymmetry model for wavelength modulation spectroscopy in gaseous flows

Abstract This communication reports technical notes on the development and application of an automated line-shape fitting procedure for wavelength modulation spectroscopy (WMS). Near-infrared transitions of carbon dioxide (CO2) around 1573 nm were measured in vertical cold (nonreacting) flow of CO2 at atmospheric pressure using WMS with demodulation at second harmonic frequency. Semi-empirical model based on the set of so-called Gabor functions was developed and parameters of Lorentzian line-shape profile and its asymmetry resulting from simultaneous frequency and amplitude response of the current-modulated semiconductor laser were determined. Nonlinear least-square fitting procedure employing differential evolution algorithm was successfully utilized for performing this task. Line-shape fitting procedure enabling efficient signal de-noising and background subtraction of wavelength modulation spectra was implemented into an open-source code.

Tunable Ultra-Broadband Microwave Frequency Combs Generation Based on a Current Modulated Semiconductor Laser Under Optical Injection

We have demonstrated and characterized the generation of ultra-broadband microwave frequency combs (MFCs) based on a current modulated distributed feedback semiconductor laser (DFB-SL) subject to optical injection, and the comb spacing of MFCs can be tuned easily through adjusting the modulation frequency $\text{f}_{m}$ . For the DFB-SL under only current modulation with modulation frequency $\text{f}_{m }= 1.2$ GHz and modulation power $\text{P}_{m }= 22$ dBm, the generated MFC has a bandwidth of about 15.6 GHz within ±5.0 dB amplitude variation. Further, introducing continuous-wave optical injection into the current modulated DFB-SL with injection power $\text{P}_{i }= 1170~\mu \text{W}$ and no frequency detuning between the injection light frequency and the oscillation frequency of the free-running DFB-SL, the bandwidth of MFC can be increased to 57.6 GHz. Through measuring the single sideband (SSB) phase noises of some representative comb lines, the performances of the MFCs generated before and after introducing optical injection are compared, and the SSB phase noises at 10 kHz offset frequency can be increased by 10 dB for the harmonics with frequencies of more than $40\text {f}_{m}$ after adopting optical injection. Moreover, the influences of operation parameters on the bandwidths of MFCs are analyzed, and the optimized parameter range for generating ultra-broadband MFCs has been determined.

Signal synchronous transmission of current-modulated semiconductor laser under bounded noise

The synchronous transmission problem of chaotic signal between current-modulated semiconductor lasers is investigated using variable coupling method. The theoretical analysis about characteristics of current-modulated semiconductor lasers is derived. According to Lyapunov theory, the condition which can realize synchronous transmission between semiconductor lasers is derived through determining maximum Lyapunov exponent of the coupling system. Further study the synchronization performance between semiconductor lasers under the influence of bounded noise, the results show that it has a strong anti-interference ability.

N+CPT clock resonance

In a typical compact atomic time standard a current modulated semiconductor laser is used to create the optical fields that interrogate the atomic hyperfine transition. A pair of optical sidebands created by modulating the diode laser become the coherent population trapping (CPT) fields. At the same time, other pairs of optical sidebands may contribute to other multiphoton resonances, such as three-photon N-resonance [Phys. Rev. A65, 043817 (2002)]. We analyze the resulting joint CPT and N-resonance (hereafter N+CPT) analytically and numerically. Analytically we solve a four-level quantum optics model for this joint resonance and perturbatively include the leading ac Stark effects from the five largest optical fields in the laser's modulation comb. Numerically we use a truncated Floquet solving routine that first symbolically develops the optical Bloch equations to a prescribed order of perturbation theory before evaluating. This numerical approach has, as input, the complete physical details of the first two excited-state manifolds of Rb87. We test these theoretical approaches with experiments by characterizing the optimal clock operating regimes.

Power emitted by an array of ultra high frequency current modulated semiconductor lasers with global coupling

We report the output power emitted by an array of ultra high frequency current modulated semiconductor lasers (CMSCL) whose elements are mutually coupled in a ring configuration and globally coupled through an external mirror. By varying the coupling strengths, we determine the domain where the in-phase state occurs. The dependence of the output power on the coupling strengths is analyzed. The power increases with the number of lasers and shows an abrupt increase or decrease as the coupling strengths increase. This particular behaviour is related to synchronization.

Wavelength modulation photoacoustic spectroscopy: Theoretical description and experimental results

A theoretical description of photoacoustic spectroscopy generated by wavelength modulation of a semiconductor laser source is reported for a Lorentzian absorption line. This model describes the first- and second-harmonic photoacoustic signals produced by a current-modulated semiconductor laser. Combined intensity- and wavelength-modulation is considered with arbitrary phase shift. Experimental results obtained when probing a CO 2 absorption line with a 2-μm distributed feedback laser are presented and validate the relevance of the reported model.

Cluster synchronization in coupled chaotic semiconductor lasers and application to switching in chaos-secured communication networks

In this paper, we study the phenomenon of cluster synchronization occurring in a shift-invariant set of coupled Ultra-high frequency current-modulated semiconductor lasers in their chaotic regime. We analytically investigate the nature of these cluster patterns through Floquet theory, and we derive the conditions under which the switching procedure between the various cluster states can be led. Numerical simulations are performed to support the analytic approach.

Stability analysis for the synchronization of semiconductor lasers with ultra-high frequency current modulation

We study the nonlinear dynamics of ultra-high frequency current-modulated semiconductor lasers. A retroactive coupling scheme is applied to achieve their synchronization both in the regular and chaotic regimes. The stability analysis is performed to determine the suitable coupling parameters leading to high-quality synchronization. The consequences of parameter mismatch are also highlighted. Numerical simulations confirm the analytic approach.

Wavelength modulation spectroscopy: combined frequency and intensity laser modulation.

A theoretical model of wavelength modulation spectroscopy that uses a laser diode on a Lorentzian absorption line is presented. This theory describes the general case of a current-modulated semiconductor laser, for which a combined intensity and frequency modulation with an arbitrary phase shift occurs. On the basis of this model, the effect of several modulation parameters on the detected signals is evaluated. Experimental signals measured on an absorption line of CO2 by use of a 2-microm distributed-feedback laser are also presented and validate this analysis. These experimental results agree with the calculated signals, confirming the relevance of the model.

Discussion

In this paper, we study the phenomenon of cluster synchronization occurring in a shift-invariant set of coupled Ultra-high frequency current-modulated semiconductor lasers in their chaotic regime. We analytically investigate the nature of these cluster patterns through Floquet theory, and we derive the conditions under which the switching procedure between the various cluster states can be led. Numerical simulations are performed to support the analytic approach.

Chirp reduction of directly modulated semiconductor lasers at 10 Gb/s by strong CW light injection

The influence of strong light injection on the reduction of the dynamical linewidth broadening of directly current-modulated semiconductor lasers at high bit rates is theoretically investigated and experimentally verified for 10 Gb/s NRZ pseudorandom modulation with a large current swing of 40 mA pp. Significant chirp reduction and single-mode operation are observed for bulk DFB, quantum well DFB lasers at 10 Gb/s and a weakly coupled bulk DFB laser at 8 Gb/s, so that an improvement of the transmission performance using standard monomode fibers in the 1.55 /spl mu/m low-loss wavelength region can be achieved for all these laser types, where dispersion otherwise causes severe penalties for long-haul transmission. The properties of injection-locked bulk DFB and quantum well DFB lasers with respect to high bit rate modulation have been systematically studied by the use of the rate equation formalism. A dynamically stable locking range of more than 30 GHz under modulation has been found for both laser types with injection ratios higher than 0.5.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High frequency heterodyne spectroscopy with current-modulated diode lasers

The use of current-modulated semiconductor lasers for optical heterodyne spectroscopy has been investigated at modulation frequencies up to 2.6 GHz. The current modulation produces a simultaneous frequency and amplitude modulation of the laser output. A characteristic heterodyne spectrum occurs when the modulated laser probes a narrow absorption line. In order to analyze the measured spectra, a complete line shape theory has been derived for heterodyne spectroscopy with frequency- and amplitude-modulated laser light. The results show how the obtained signals depend on the modulation frequency and the phase difference between the frequency and the amplitude modulation. The measurement technique permits investigation of the FM-AM phase difference of current-modulated semiconductor lasers.

Interferometric measurement of time-varying longitudinal cavity modes in GaAs diode lasers

Measurement of mode chirping in a current-modulated semiconductor laser was performed using a Michelson interferometer. For a current step excitation, the rate of this chirping decays as a function of time, and two characteristic time constants were identified. Their interpretation is discussed, and the thermal impedance of the device is calculated. In addition, the significance of such a measurement for the analysis of chirp-induced modal noise in optical fibers is discussed, and experimental results are presented.