Kelvin S. C. Yong

Theory of Reduction of Residual Amplitude Modulation in Mid-Infrared Wavelength Modulation Spectroscopy by Injection Locking of Quantum Cascade Lasers

A simplified rate equation model is used to investigate suppression of residual amplitude modulation in injection-locked quantum cascade lasers with the master laser modulated by its drive current. Quasi-static and dynamic expressions for intensity modulation suppression and frequency modulation reproduction by the slave laser are presented. The suppression peaks at a specific value of the injection ratio for a given detuning and linewidth enhancement factor. The frequency modulation reproduction is less than 100% and decreases rapidly at frequencies higher than 300 MHz. The intensity modulation suppression remains constant during this frequency range. The effects of injection ratio, detuning, coupling efficiency and linewidth enhancement factor are discussed.

Harmonic and Intermodulation Distortion in Direct Intensity Modulated Quantum Cascade Lasers

In this paper, nonlinear distortion in a quantum cascade laser arising from direct intensity modulation is studied. Harmonic and intermodulation distortion expressions for small sinusoidal modulation signals are derived using a perturbation method. The expressions are validated by making a comparison with a large signal simulation of a quantum cascade laser equivalent circuit. The effects of bias current, optical modulation depth, and modulation frequency on harmonic and intermodulation distortion are examined.

Turn-on analysis of quantum cascade lasers

An analytical analysis on turn-on delay and rise time for quantum cascade laser upon switching on is presented here. Numerical solution for the rate equations is presented and comparison between analytical and numerical solution shows good agreement. Effect of varying injected current value on turn-on delay and rise time is observed. Variation of bias current from zero up to threshold value is used.

Leverage Website Favicon to Detect Phishing Websites

Phishing attack is a cybercrime that can lead to severe financial losses for Internet users and entrepreneurs. Typically, phishers are fond of using fuzzy techniques during the creation of a website. They confuse the victim by imitating the appearance and content of a legitimate website. In addition, many websites are vulnerable to phishing attacks, including financial institutions, social networks, e-commerce, and airline websites. This paper is an extension of our previous work that leverages the favicon with Google image search to reveal the identity of a website. Our identity retrieval technique involves an effective mathematical model that can be used to assist in retrieving the right identity from the many entries of the search results. In this paper, we introduced an enhanced version of the favicon-based phishing attack detection with the introduction of the Domain Name Amplification feature and incorporation of addition features. Additional features are very useful when the website being examined does not have a favicon. We have collected a total of 5,000 phishing websites from PhishTank and 5,000 legitimate websites from Alexa to verify the effectiveness of the proposed method. From the experimental results, we achieved a 96.93% true positive rate with only a 4.13% false positive rate.

Approximate analytical expressions for pulse modulation response of quantum cascade lasers

Abstract Approximate analytical expressions for turn-on delay, rise time and fall time for pulse modulation of the drive current of quantum cascade lasers are presented. These time expressions are obtained using piece-wise analysis of rate equations. From the analytical expressions, the effects of laser parameters and off and on currents are discussed. A numerical analysis shows reasonable agreement with analytical results. It also confirms the predictions from analytical results. The pulse response is compared with that of near-infrared interband lasers.

Harmonic, Intermodulation and Cross-Modulation Distortion in Directly Modulated Quantum Cascade Lasers

Using a simplified rate equation model, expressions for harmonic, intermodulation and cross-modulation distortion for a directly modulated quantum cascade laser can be derived. This paper shows how such derivations can be done and discusses some implications for quantum cascade lasers. It is important to understand such distortion, especially for applcations in communication systems.

A Study of Residual Amplitude Modulation Suppression in Injection Locked Quantum Cascade Lasers Based on a Simplified Rate Equation Model

Using results that come out of a simplified rate equation model, the suppression of residual amplitude modulation in injection locked quantum cascade lasers with the master laser modulated by its drive current is investigated. Quasi-static and dynamic expressions for intensity modulation are used. The suppression peaks at a specific value of the injection ratio for a given detuning and linewidth enhancement factor. The intensity modulation suppression remains constant over a range of frequencies. The effects of injection ratio, detuning, coupling efficiency and linewidth enhancement factor are considered.

Comparison of harmonic and intermodulation distortions of directly modulated interband lasers and quantum cascade lasers

In this paper, a comparison of second harmonic and two-carrier intermodulation distortion of three near infrared interband lasers and three mid-infrared quantum cascade lasers is reported. These distortions arise from direct intensity modulation of semiconductor lasers. To make the comparison, the distortions in dBs are plotted against the frequency of the RF subcarrier. The lasers are considered to have the same DC optical power output and optical modulation depth.

A two-level model of rise time in quantum cascade laser materials applied to 5 micron, 9 micron and terahertz-range wavelengths

An equivalent circuit simulation of a two-level rate equation model for quantum cascade laser (QCL) materials is used to study the turn on delay and rise time for three QCLs with 5 micron, 9 micron and terahertz-range wavelengths. In order to do this it is necessary that the model can deal with large signal responses and not be restricted to small signal responses; the model used here is capable of this. The effect of varying some of the characteristic times in the model is also investigated. The comparison of the terahertz wave QCL with the others is particularly important given the increased interest in terahertz sources which have a large range of important applications, such as in medical imaging.