Jianguo Chen

Carrier deficit from the nominal threshold density and mode-suppression ratio of an above-threshold biased semiconductor laser.

An analytical expression for the carrier deficit DeltaN from the nominal threshold carrier density N(t) of an above-threshold biased semiconductor laser has been deduced. As a result, both the mode spectra and the mode-suppression ratio of a semiconductor laser can be studied analytically. The measured dependence of the mode-suppression ratio on the wavelength difference between the gain peak and its nearest cavity mode of the semiconductor laser confirms the theoretical predictions.

Computer Model of Time Response of Fabry-Perot Etalon Filters to Short Optical Pulses

The time response of a Fabry-Perot etalon filter to the short optical pulses has been studied. The transmitting pulse from the etalon filter has been analytically expressed in a series of sub-pulses. Under certain circumstances, the sub-pulses merge together resulting in a broadened output pulse, and the temporal difference between the peaks of the output and input pulses may not equal to the one-way traverse time of light inside the etalon. Studies have also been carried out for the chirped pulse and dispersion etalon, which have led to the expression of the transmitting sub-pulses.

Studying semiconductor lasers with ray trace method

Tracing the amplified spontaneous emission light inside the cavity of the semiconductor laser, the expression of the photon density of various diode modes inside the cavity has been derived based on the mean carrier density approximation. After summing up the photon densities, an analytical expression for the deficit ΔN of the carrier density from the conventional nominal threshold carrier density N, has been deduced. As a result, both the mode spectra and the mode suppression ratio (MSR) can be expressed analytically, irrespecting whether the peak wavelength of the gain is coincident with one of the resonant modes of the diode or not

Time delay of Fabry-Perot filters to short optical pulses

In this paper, the time delay, defined as the temporal difference between the peaks of the output and input pulses, of Fabry-Perot filters to short input optical pulses has been investigated theoretically in detail. The results reveal that due to the interference between the multireflected beams inside the etalon, the input pulse widths have intense influence on the time delay. Moreover, the time delay depends on the chirp of input pulse and the difference between the central frequency of the input pulse and the resonance frequency of the fllter.

Influence of the reflectivity distribution of fiber grating on the output characteristics of fiber grating external cavity diode lasers

The dot function approximation of reflectivity distribution of a fiber grating (i. e., supposed that the fiber grating supplies feedback only in bragg reflection wavelength and the reflectivity at other wavelengths is regarded as zero), which is usually used to analyze the output characteristics of a fiber grating external cavity diode laser (FGECDL), has been proved to be unreasonable from physical facts. As a result, a theoretical model including the reflectivity distribution of fiber grating applicable to FGECDLs is presented. Taking the mode suppression ratio (MSR) of FGECDLs as a example for comparison, the results show that MSR obtained by the model is obviously lower than that obtained by the dot function approximation.

Influence of a Fabry–Perot etalon on a chirped optical pulse

Abstract Taking into consideration the fact that the output from a Fabry–Perot etalon is formed on the basis of the interference of the multi-reflected beams of the input pulse that enters the etalon, an analytical expression of the output pulse intensity has been derived for an input chirped Gaussian pulse passing through an etalon. Using the expression, the temporal width and the peak power of the output pulse is investigated. Results show that for a given etalon, the chirp factor and the width of the input pulse have intense effects on the width and the peak of the output pulse.

Specify various derivatives of output powers with respect to bias current of semiconductor lasers

Starting from the multimode rate equations of the semiconductor lasers, taking into consideration the contribution of the spontaneous emission, an implicit analytical solution to the rate equations has been derived. Using the analytical solution, derivatives, up to the third order, of the laser output power with respect to the bias current have been deduced analytically. It is belived that these expressions are useful in specifying the linearity of the diode lasers when used in lightwave CATV transmission systems.

IDENTIFYING THE OUTPUT SPECTRA FROM END FACETS OF SEMICONDUCTOR LASERS

We report a simple way of determining the spontaneous-emission spectrum from the output spectrum directly detected at the end facet of a semiconductor laser and measuring the wavelength difference between the peaks of the gain and the spontaneous emission. This difference can be used to explain the blue shift of the peak wavelength of the output spectrum after the facets of the diode have been antireflection coated during the process of making a traveling-wave semiconductor amplifier.

Bidirectional chaos synchronization and communication based on mutually coupled semiconductor lasers with asymmetrical bias currents

In this paper, a bidirectional chaos secret communication system, based on mutually coupled semiconductor lasers (MCSLs) with asymmetrical bias currents, is proposed, and the synchronization characteristics and the communication performances of such a system are numerically investigated. The results show that the stable leader-laggard chaos synchronization can be achieved under relatively large asymmetrical bias current levels. Meantime, the influence of the intrinsic parameter variations of the laser on the synchronization quality is also considered, and the simulation reveals that this system still possesses good robustness to the parameter variations. Moreover, the influences of delay time and mutually coupling strength between the two lasers on chaos communication performance have also been discussed. Finally, unidirectional and bidirectional secret communication performances of such a system are examined under the chaos masking (CMS) encryption scheme, and the security of this system is also discussed.

Synchronization Characteristics of Feedback-Induced Chaos in Strongly Injection-Locked Semiconductor Lasers

The modulation bandwidth enhancement and the chaos synchronization characteristics of feedback-induced chaos in strongly injection-locked semiconductor lasers are studied numerically by establishing the theoretical model. With extra external optical injection, the modulation bandwidth of a unidirectional close-loop chaos synchronization system is greatly enhanced about three times. The robustness of injection-locked synchronization to parameter mismatches is discussed in terms of cross-correlation coefficient and synchronization error. Finally, the transmission of high bit rate signals with directly current modulation in this system is briefly investigated, and the results show that this system possesses a high transmission speed and a good robustness.