External Optical Feedback Research Articles

High frequency modulation effects on the relative intensity noise properties of 405 nm InAlGaN laser diodes

AbstractThe high frequency modulation effects on the relative intensity noise (RIN) characteristics of 405 nm InAlGaN laser diodes have been investigated taking into account the strain and thermal effects on the laser diode itself as well as external optical feedback effects. The simulation results indicate that the critical external optical feedback for –125 dB/Hz RIN is around 0.1%, a typical order found in practical DVD operating environments.By optimizing the injection current levels and its frequency, one can reduce the RIN with 0.1∼1% external feedback effect by more than 15 dB/Hz. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dynamics of a Semiconductor Laser with Two External Cavities

We study numerically complex dynamics of a semiconductor with one and two external cavities. We show that dynamical regimes in the laser with one external cavity can be controlled by adding another external cavity and properly adjusting its length and feedback strength. We demonstrate the existence of difierent stable periodic, quasiperiodic, chaotic, and steady-state regimes which form Arnold's tongues in bi-dimensional parameter spaces of the length and feedback strength of the external cavities and the pump parameter. The dynamics of a semiconductor laser subjected to external optical feedback has been studied by many researchers, since this laser has many applications in optical communications, interferometric sensors, frequency stability, etc. (see, for example, Ref. 1 and references therein). For moderate and strong feedback strengths this laser can display a very rich dynamical behavior, from periodic and quasiperiodic oscillations to chaos and coherence collapse (2,3). When the laser injection current is close to the solitary laser threshold, the laser operates in a stable steady-state regime. As the pump current is increased, intermittent drops of the laser intensity appear, that gives rise to low- frequency ∞uctuations (LFF). At higher currents, the laser optical bandwidth broadens that is known as coherence collapse (4,5). The dynamical behavior of a semiconductor lasers with a single feedback was studied extensively and the basic mechanism for LFF is well understood (6,7). The possibility for controlling LFF in a semiconductor laser with an external cavity by using a second delayed optical feedback was initially deduced by Liu and Ohtsubo (8). Later their idea was developed by Rogister, etal., (9,10), who realized the suppression of antimodes, responsible for LFF crises by properly adjusting the second feedback strength. Recently Mendez, etal., (11) have demonstrated experimentally that the frequency of LFF can be locked by external periodic modulation applied to the feedback strength of the external cavity. They have found difierent periodic and quasiperiodic regimes which formed Arnold's tongues in the space of the amplitude and frequency of the external modulation. In this paper we demonstrate that the locking efiect can be achieved without any external forcing. We show how LFF in a semiconductor laser with external cavity can be adequately controlled by adjusting properly both the length and the feedback strength of the second external cavity. The feedback time and the feedback strength of the second external cavity act in a similar manner as the period and amplitude of external modulation. We demonstrate that the variation of the parameters of the second external cavity allows one to obtain difierent dynamical regimes of the laser operation without any modiflcations in the solitary laser with a single external cavity. A single-mode semiconductor laser with delayed feedback is usually modeled by the Lang- Kobayashi rate equations (12). Due to the inflnite dimension of the system, an analytical study is very di-cult. Therefore, to study the dynamics of a semiconductor laser with two external cavities shown in Figure 1, we make numerical calculations of the modifled equations similar to those ex- plored previously by Sivapakrasam, etal., (13) and Carr (14). For weak or moderate feedback the modifled equations can be written as follows d ¢ E0(t) = (1=2)G(N (t) i Nth)E0 (t) + •1E0 (t i ?1)cos(ˆ1 + `(t) i `(t i ?1))

External optical feedback effects in a frequency locking dual frequency laser

We present a systematic study of external optical feedback effects on the output characteristics of the two orthogonally polarized modes in a frequency locking dual frequency laser. Accompanied by the change of the external cavity length, the length of the resonance cavity is changed very slowly to set the oscillating modes sweeping across the laser gain curve. Comprehensive results are obtained and a strong mode competition is observed. Particularly, when the laser runs in the middle region of the gain curve, which mode can oscillate is determined by the movement direction of the external feedback mirror. Based on the phenomenon, a displacement sensor with directional discrimination is proposed and its capability is also discussed.

Effects of unwanted feedback on synchronized chaotic optical communications

The effects of unwanted external optical feedback on synchronized chaotic optical communication systems are studied numerically. We consider an open-loop configuration consisting of a transmitter laser with double external optical feedbacks and a receiver laser with optical injection from the transmitter laser. First, including the effects of unwanted optical feedback, the synchronization performances of both the complete synchronization and the generalized synchronization are examined. Then the encoding and decoding performances of the generalized synchronization and the effects of the introduced feedback are investigated, respectively. Finally, we study the control of the unwanted feedback on the dynamics of the transmitter laser and briefly discuss the system security when the transmitter laser is driven to operate in a steady state or periodic oscillation state by the additional feedback.

Self-mixing speckle interference in DFB lasers

Theoretical analysis and experimental results of self-mixing speckle interference in a distributed feedback (DFB) laser are presented in this paper. Self-mixing speckle interference occurs when external optical feedback comes from a moving rough surface. Dynamic output variations in the DFB laser as well as their probability density functions (PDFs) are analyzed on the basis of speckle theory and self-mixing interference in the DFB laser. Numeric simulations and experiments are in agreement with each other. The both results show that self-mixing speckle interference in DFB laser can be used to measure velocity of target.

Effects of spontaneous emission noise in semiconductor lasers on chaotic optical communication systems

A chaotic optical communication system based on external optical feedback is constructed. By introducing the Langevin noise sources, the master-slave rate equations including spontaneous emission noise characteristics are deduced. Utilizing the obtained mathematical model, two kinds of possible chaos synchronization in the system, i.e. complete chaos synchronization and generalized mode-locking chaos synchronization, are studied. The effects of the spontaneous emission noises of the two lasers on the two types of synchronization as well as the chaotic outputs of the transmitter and receiver are discucsed. Finally, for a sequence of pseudorandom digital bits at 2.5Gb/s bit rate, the encoding/decoding process basing on chaotic masking method is presented, and the effects of noise on decoding performance are examined.

Influence of external cavity feedback on the oscillating characteristics of a semiconductor laser

Through the introduction of effective reflectivity, the influence of external optical feedback on the oscillating characteristics of a semiconductor laser is discussed, such as the threshold gain, laser frequency and output power, according to the self-consistency condition and the photon and carrier density ratio equation. In the experiment, the threshold current of a laser diode decreased from 420mA to 370mA with external cavity feedback and the slope efficiency increased. The output power obtained by theoretical simulation agrees well with the experiment results.

Output Intensity Variations of the Laser Used in a PrismCoupling System and Its Application

The output intensity variations of the laser used in a prism couplingsystem are observed and found to be induced by the external opticalfeedback, which comes from the reflection on the prism. The intensityvariations are explained with laser theory. The trough in the intensityvariation corresponds to the position of the prism when the outputlight beam propagates perpendicularly to the prism. Based on the trougha new method for rotating the prism and reading out the step numbers isproposed, by which the angle 0° in the system need not to becalibrated. It is proven by experiment that the new method wouldimprove the accuracy of the refractive index up to ±0.00001 andthickness to ±1 nm.

Nonlinear dynamics of two mutually injected external-cavity semiconductor lasers

The nonlinear dynamics of two mutually injected semiconductor lasers subject to external optical feedback are studied numerically. Three types of dynamics are investigated, which are induced by external optical feedback, mutual coupling and a combination of both mechanisms, respectively. In an optical feedback system, a period-doubling route and a variety of nonlinear states are observed. In a mutually injected semiconductor laser system, both lasers show a period-doubling route to chaos; moreover, the frequency detuning plays an important role in determining the system behaviours, i.e. it can increase the system complexity or drive both lasers to exhibit periodic oscillations. When both effects are considered simultaneously, the system behaviours are determined by their relative strength. When one dominates in the competition, the hybrid system exhibits similar behaviours to those it introduced. It is also found that one of the two nonlinear mechanisms can be used to suppress the dynamics introduced by the other, or to produce a highly complex chaos. Finally, a high quality of synchronization between the two chaotic outputs is achieved, although the bias currents of the two lasers are different.

Control of nonlinear dynamics in external-cavity VCSELs with delayed negative optoelectronic feedback

Abstract The numerical investigation of introducing delayed negative optoelectronic feedback to suppress the external optical feedback-induced nonlinear dynamics in vertical-cavity surface-emitting lasers (VCSELs) has been presented. Simulation results show that when the external optical feedback is strong enough, not only the photon density but also the lasing frequency exhibit rich nonlinear dynamics. However, these dynamics can be eliminated completely by the optoelectronic feedback with proper feedback strength and delay time.

External optical feedback influance on the pulse analysis of the laser including direct plusing involvement

External optical feedback influance on the pulse analysis of the laser including direct plusing involvement

Broadband InGaAs tapered diode laser sources for optical coherence radar and coherence tomography

This letter reports on broadband laser sources based on InGaAs tapered diode laser amplifiers with external optical feedback. The generated 920nm radiation with a bandwidth of up to 20nm and a power of a few hundred milliwatts is emitted in an almost diffraction limited beam. Spectral filtering and subsequent amplification in a second tapered amplifier provides radiation with spectral widths in the range of 20to40nm and optical output powers of up to 2.5W.

Controlling chaotic dynamical behavior of a semiconductor laser with external optical feedback using sliding mode variable structure control scheme

In this paper, a semiconductor laser with external optical feedback is entered into chaotic motion by increasing the time of the external optical feedback at first. And then, the sliding mode variable structure control scheme is used to control the chaotic motion of this laser system. The advantage of this method is that the stable output laser can be obtained in a short time and the output power strength of the laser can be adjusted flexibly in accordance with the engineering requirement. Theory analysis and simulation results show that the results of the control have powerful stability and robust .Our research results have many helpful values to improve the speed of stable output, flexible adjustment of laser output power as well as efficiency of energy transformation for real laser system.

Polychromatic coupled cavity model of passive structures

The authors have developed a polychromatic coupled cavity model for passive optical structures to investigate the underlying 'cold-cavity' mode spectrum of active devices, such as semiconductor lasers. The model is validated using a simple Fabry-Perot test structure and then used to study how the mode spectrum of a semiconductor laser subject to external optical feedback is affected by variations in the optical properties of the configuration (in the 'cold-cavity' limit). Significant differences in behaviour are observed in the short and long cavity limits, indicating the potentially important role the mode spectrum has in determining the dynamics of such configurations.

An external-cavity laser diode at 635 nm for laser display applications

We describe a diode laser system at 635 nm, which has been developed for a colour laser display. The poor beam quality of conventional high power lasers has lead to the conception that these lasers are not suited for laser displays. In this paper, we introduce a new laser system that eliminates some of the previous problems. The system is based on a broad area laser diode with external optical feedback, which improves the spatial coherence of the beam emitted from the diode. We investigate the operation of the laser system in connection with acousto-optic intensity modulation. A diffraction efficiency from 0th to 1st order of 92% and 60% is achieved for modulation rise times of 80 and 10 ns, respectively. The advantages of the feedback scheme are the ability to use compact diode lasers for display purposes while simultaneously obtaining fast rise times and high output power. The results demonstrate that the new red source is suitable for laser display applications.

Suppressing nonlinear dynamics induced by external optical feedback in vertical-cavity surface-emitting lasers

A numerical study of using external optical injection to suppress the nonlinear dynamics introduced by external optical feedback in vertical-cavity surface-emitting lasers (VCSELs) has been undertaken. The model under consideration is a master–slave configuration where the master VCSEL provides the continuous wave to control the nonlinear behaviors arising in the slave VCSEL. Simulation results indicate that the feedback-induced nonlinear dynamics (e.g. chaotic, single-periodic, and multi-periodic oscillations), relative intensity noise (RIN) as well as the coherence collapse can be suppressed effectively as long as the injection is strong enough to overcome the nonlinear effects of the feedback.

Low-Frequency Fluctuations in Vertical-Cavity Surface-Emitting Lasers With Polarization Selective Feedback: Experiment and Theory

We present theory and measurements on a vertical-cavity surface-emitting laser (VCSEL) biased close to its solitary threshold and subject to polarization selective external optical feedback. The system shows low-frequency fluctuations (LFF) in the selected polarization mode (PM). Below solitary laser threshold, the orthogonal PM remains silent, while it only responds after a dropout event in the main mode above threshold. Our calculations show good agreement with the measurements and identify a type of synchronization between the low-frequency dynamics of the two PMs.

Transient Response of ARROW VCSELs Under External Optical Feedback

The effect of external optical feedback on the transient response of antiresonant reflecting optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) is studied. It can be shown that the proper design of ARROW can suppress the excitation of high-order transverse leaky mode as well as increase the critical feedback strength so that stable high-power single-mode operation of VCSELs can be obtained even under the influence of strong external optical feedback.

Field fluctuations and spectral line shape in semiconductor lasers subjected to optical feedback

This article reports on extensive investigations of the influence of external optical feedback (OFB) on the spectral line shape and the associated spectra of relative intensity noise (RIN) and frequency noise (FN) in semiconductor lasers. The study is based on a generalized simulation model that treats the OFB as a multiple-roundtrip time delay of the lasing field in the external cavity. We present criteria to apply the famous Lang–Kobayashi model to predict the operation characteristics of lasers under OFB. The accuracy of approximated models of calculating the spectral linewidth from the low-frequency components of the frequency noise is examined. We characterize the spectral line shape and the spectra of the RIN and FN in five distinct operating regions, namely, continuous-wave (cw), weak OFB-induced pulsation, period-doubling route-to-chaos, chaos or coherence collapse, and strong OFB-induced pulsation. InGaAsP lasers emitting in a wavelength of 1.5 μm are included in the calculations. The results show that the line shape is most enhanced with sharp central and satellite peaks when strong OFB induces either high-frequency pulsation or cw operation. The moderate range of OFB induces coherence collapse operation, which is characterized by most suppressed and most broadened central and satellite peaks. The cw operation induced under very strong OFB is characterized by RIN and FN levels lower than those of the case of cw operation induced under low OFB.

Feedback Sensitivity and Coherence Collapse Threshold of Semiconductor DFB Lasers With Complex Structures

A general method for evaluating the feedback sensitivity of semiconductor lasers is proposed based on Green's functions approach. The rate equations derived in this paper generalize works already published to any type of laser cavities such as those with axially varying parameters. The variation of the lasing frequency occurring under external optical feedback is then used to predict the coherence collapse threshold. The approach is validated for conventional DFB lasers by comparing the calculated feedback sensitivity with those obtained from analytical expressions. Both feedback sensitivity and coherence collapse thresholds are then calculated and analyzed for DFB lasers with a chirped grating. A remarkable agreement on the critical feedback level between simulations and measurements is obtained for all the lasers under study.