Effect of optical feedback on fast modulated semiconductor lasers

We present an experimental study on the effect of optical feedback in both ground and excited emission of a GaAs quantum dot passively mode locked laser. The experimental setup consisted of a long external cavity with variable cavity length and feedback level ranging from –50 to –20dB. The obtained experimental results show dependence of the emission properties on the cavity length regarding both the ground and excited state. In addition a strong tolerance of the laser operation to feedback at the excited state operation regime is observed.

We report theoretical and experimental results on optical-feedback effects in single-mode semiconductor lasers with feedback levels varying from very low (<< 1% feedback power) to relatively high (1-5%) feedback.

Due to many special applications,the 980 nm pumping source semiconductor lasers should have the characteristics of spectrum stability,low power consumption. Based on the optimization design of a 980 nm single mode semiconductor laser cavity length,cavity reflectivity and fiber Bragg grating reflectivity,the low threshold,high power 980 nm fiber Bragg grating external cavity semiconductor lasers with wavelength stability are developed. The pigtail output power of the low power consumption single mode semiconductor lasers with wavelength stability can reach 51 m W under 100 m A,3 d B bandwidth of 0. 16 nm. The side mode suppression ratio( SMRS) is greater than40 d B. The pigtail output power of the device can reach 120 m W under 250 m A.

With a proper perturbation, even a single-mode semiconductor laser can exhibit highly complex dynamical characteristics ranging from stable, narrow-linewidth oscillation to broadband chaos. In recent years, three approaches to invoke complex nonlinear dynamical states in a single-mode semiconductor laser have been thoroughly studied: optical injection, optical feedback, and optoelectronic feedback. In each case, the nonlinear dynamics of the semiconductor laser depends on five intrinsic laser parameters and three operational parameters. The dynamical state of a given laser can be precisely controlled by properly adjusting the three operational parameters. This ability to control the dynamical behavior of a laser, combined with the understanding of its characteristics, opens up the opportunity for a wide range of novel applications. This paper illustrates the utilization of the rich nonlinear dynamics of single-mode semiconductor lasers by focusing on the period-one oscillation for its applications in tunable photonic microwave generation, AM-to-FM conversion, and dual-frequency precision Doppler lidar.

We investigate experimentally how changes in the external cavity length and dc current affect the mean interspike-interval (ISI) in a modulated semiconductor laser with optical feedback operating in the low-frequency fluctuations regime. The variation of the mean ISI with the modulation frequency is shown to be more pronounced when time delay and dc current allow for low spike rate. We use the method of ordinal symbolic analysis to examine how time correlations (among three, four and five consecutive laser spikes) change with the spike rate. This method is able to capture subtle changes, otherwise hidden in the dynamics. We find that higher spike rates wash out the effects of the modulation in the time correlations. Simulations using the Lang and Kobayashi model are in good qualitative agreement with the experimental observations.

Fast intracavity tunable semiconductor lasers find their use in information acquisition systems (e.g. OCT) and may be of use in agile multiwavelength communications systems. We present numerical analysis of the dynamic behaviour of a semiconductor laser frequency swept by means of an ultrafast intracavity filter. The interrelated roles of the tuning speed, the filter bandwidth, the cavity length, and the self-phase modulation in laser dynamics are analysed.

On-chip integration of semiconductor lasers have shown a growing interest in recent years, especially for the development of photonic integrated circuits (PICs) which are of paramount importance for high-speed communication within and between data centers, and fast on-board data exchanges. For all these applications, a key challenge remains the stability of the laser sources integrated on a PIC in presence of external optical feedback with the view to avoid integrated bulky and costly optical isolation. In this study, the effects of external optical feedback are investigated in hybrid InAs/InP quantum dot comb lasers on silicon. The design of the cavity includes a semiconductor optical amplifier section, a saturable absorber and an on-chip external cavity incorporating a vertical coupler. We measured the resulting feedback properties with respect to the operation conditions (bias current and voltage) and to the length of the saturable absorber. We show that under most operating conditions, the laser remains stable against optical feedback, only few regimes of operation occur, which either improve or degrade the frequency comb and/or the radio-frequency beatnote power of the laser.

This work reports, for the first time as far as we know, the application of the PROUD technique to optical pulses generated by a semiconductor laser. The differentiator is implemented by means of a novel approach based on a polarization maintaining fiber (PMF) and two polarizers oriented at 45° with respect to the fiber axes.

We demonstrate a fast Quasi-Continuous frequency scanning semiconductor laser source for optical fiber sensor interrogation systems. The tunable laser covers a wavelength range of 32nm in C-band with tuning resolution of 8pm. The scanning time over the complete wavelength range in C band is less than 1ms while the switching time from one wavelength point to another point can be less than 100ns. A fast current driver controlled using FPGAs have been employed to drive a DSDBR laser for the realization of the fast tunable laser module. Experimental results have verified its possible application in optical sensor interrogation systems.

The quantum mechanical theory of semiconductor lasers based on Langevin equations1,2 is modified to include the effects of weak optical feedback with dispersive loss.3

Prisms are involved in many instruments of measurements of refractive indices. The optical feedback effect in a semiconductor laser introduced by the reflection of a prism was applied to the determination of zero incident angle. Without any additional optical components or calibration setups the angular resolution reached 0.00074°. This approach was used in refractometers and prism coupling system. Prisms, water, wintergreen oil and a quartz plate were measured by total internal reflection technique and the optical feedback effect. In the measurement of prism, we proposed that the base angle of a detected prism should be appropriately prepared so as that the refractive index of an isosceles prism made of any material can be precisely measured. The results for a SrTiO₃ prism with a base angle 30.0169 degree was 2.3780 at 659 nm. The measurements of water and wintergreen oil were performed by a reference prism made of SrTiO₃. We found that the result for a quartz plate wouldn't be influenced by the index matching liquid between the plate and a reference prism, which was intentionally introduced, only if the index of the liquid was larger than that of the quartz. The refractive index of a polymer film was measured accurately and the maximum of deviation from mean was ±0.0001.

We present a numerical study of the effects of optical feedback on the static and dynamic characteristics of vertical-cavity surface-emitting lasers (VCSELs) under both single-mode and two-mode operations. Our model includes transverse effects such as carrier diffusion and spatial hole burning (SHB) and is therefore capable of including gain-saturation-induced coupling among transverse modes. For short external cavities (/spl sim/30 /spl mu/m), optical feedback can completely suppress higher-order transverse modes. For relatively long external cavities (/spl sim/1 cm), VCSELs follow a period-doubling route to chaos. Numerical results show that multimode VCSELs exhibit self-pulsations at higher feedback levels compared with the single-mode case.

光反馈对光纤光栅外腔半导体激光器特性的影响

Effects of optical feedback on period-one nonlinear dynamics of an optically injected semiconductor laser are numerically investigated. The optical feedback can suppress the period-one dynamics and excite other more complex dynamics if the feedback level is high except for extremely short feedback delay times. Within the range of the period-one dynamics, however, the optical feedback can stabilize the period-one dynamics in such a manner that significant reduction of microwave linewidth and phase noise is achieved, up to more than two orders of magnitude. A high feedback level and/or a long feedback delay time are generally preferred for such microwave stabilization. However, considerably enhanced microwave linewidth and phase noise happen periodically at certain feedback delay times, which is strongly related to the behavior of locking between the period-one microwave oscillation and the feedback loop modes. The extent of these enhancements reduces if the feedback level is high. While the microwave frequency only slightly changes with the feedback level, it red-shifts with the feedback delay time before an abrupt blue-shift occurs periodically. With the presence of the laser intrinsic noise, frequency jitters occur around the feedback delay times leading to the abrupt blue-shifts, ranging from the order of 0.1 GHz to the order of 1 GHz.

The effect of optical feedback on the intensity-noise spectrum and the longitudinal-mode line shape of a 1.55-μm InGaAsP laser is investigated for reflections arising from the far end of a 7.5-km-long fiber. The intensity noise near the relaxation-oscillation frequency is significantly enhanced by the reflection feedback. Owing to the intercavity coupling, the enhancement is, however, frequency dependent and the noise spectrum exhibits high-contrast modulations with a period corresponding to the fiber-cavity longitudinal-mode separation. A simple rate equation model is used to explain the observed behavior.