Effect Of Optical Feedback Research Articles

Impact of external optical feedback on the beat notes of dual-polarization fiber lasers

We present a theoretical analysis and an experimental study of the impacts of external optical feedback on dual-frequency fiber lasers. The external optical feedback can effectively suppress the phase noise of the beat notes of dual-frequency fiber lasers, provided some requirements are satisfied. The polarization of the optical feedback is important for the fiber laser’s stability, and it can also tune the beat note frequency. A side effect of external optical feedback, as demonstrated in the experiments, is lowering the sensitivity of the dual-frequency fiber laser-based sensors, although such degradation is not obvious.

Terahertz gas spectroscopy through self-mixing in a quantum-cascade laser

We demonstrate the feasibility of high-resolution terahertz gas spectroscopy based on the external optical feedback effect in a quantum-cascade laser. Tuning the frequency of the quantum-cascade laser across a molecular absorption line of CH3OH leads to a reduction of the optical feedback, which can be detected by monitoring the voltage across the quantum-cascade laser. This method provides a high spectral resolution of ν/Δν=106 and a sensitivity comparable to that obtained with a cryogenically cooled Ge:Ga photoconductive detector.

Stabilization and Frequency Control of a DFB Laser With a Tunable Optical Reflector Integrated in a Silicon Photonics PIC

We investigate the effect of tunable optical feedback on a commercial DFB laser edge coupled to a Silicon Photonics planar integrated circuit in which a tunable reflector has been implemented by means of a ring resonator based add-drop multiplexer. Controlled optical feedback allows for fine-tuning of the laser oscillation frequency. Under certain conditions it also allows suppression of bifurcation modes triggered by reflections occurring elsewhere on the chip. A semi-analytical model describing laser dynamics under combined optical feedback from the input facet of the edge coupler and from the tunable on-chip reflector fits the measurements. Compensation of detrimental effects from reflections induced elsewhere on a transceiver chip may allow moving isolators downstream in future communications systems, facilitating direct hybrid laser integration in Silicon Photonics chips, provided a suitable feedback signal for a control system can be identified. Moreover, the optical frequency tuning at lower feedback levels can be used to form a rapidly tunable optical oscillator as part of an optical phase locked loop, circumventing the problem of the thermal to free carrier effect crossover in the FM response of injection current controlled semiconductor laser diodes.

Improved dynamics of a tunnelling-injection quantum-dot laser under optical feedback

We report an investigation of the optical feedback effect on the dynamics of a tunnelling-injection quantum dot (TI QD) semiconductor laser. Assuming the external cavity to be short and using a small signal analysis, the modulation response of a TI QD laser is calculated under optical feedback conditions. The impact of the tunnelling probability, bias-current density, feedback ratio, external cavity length and linewidth enhancement factor on the modulation response of a TI laser is studied. With the optical feedback taken into account, the modulation responses of conventional and TI QD lasers are compared. The obtained results demonstrate that at an appropriate feedback ratio and external cavity length, the laser bandwidth and its relaxation frequency can be improved.

Model for a pulsed terahertz quantum cascade laser under optical feedback.

Optical feedback effects in lasers may be useful or problematic, depending on the type of application. When semiconductor lasers are operated using pulsed-mode excitation, their behavior under optical feedback depends on the electronic and thermal characteristics of the laser, as well as the nature of the external cavity. Predicting the behavior of a laser under both optical feedback and pulsed operation therefore requires a detailed model that includes laser-specific thermal and electronic characteristics. In this paper we introduce such a model for an exemplar bound-to-continuum terahertz frequency quantum cascade laser (QCL), illustrating its use in a selection of pulsed operation scenarios. Our results demonstrate significant interplay between electro-optical, thermal, and feedback phenomena, and that this interplay is key to understanding QCL behavior in pulsed applications. Further, our results suggest that for many types of QCL in interferometric applications, thermal modulation via low duty cycle pulsed operation would be an alternative to commonly used adiabatic modulation.

Controllable optical bistability in a hybrid optomechanical system

We investigate, theoretically, the effect of optical feedback from a cavity containing an ultracold two-level atomic ensemble, on the bistable behavior shown by a mean intracavity optical field in an optomechanical cavity resonator. It turns out that the optical bistability can be controlled by tuning the frequency and power of the driving laser and is largely affected by the presence of the atomic ensemble in the feedback cavity. In essence, our work emphasizes the possibility of realization of a controllable optical switch depending on the hybrid interaction, commanding lower threshold power than a single optomechanical cavity.

光反馈对光纤光栅外腔半导体激光器特性的影响

光反馈对光纤光栅外腔半导体激光器特性的影响

Low chirp and high-speed operation of transverse coupled cavity VCSEL

We present the modeling on the modulation bandwidth and frequency chirp of transverse-coupled-cavity vertical-cavity surface-emitting lasers (VCSELs), which enable us to tailor the transfer function of intensity and frequency modulations thanks to an optical feedback effect. The simulation shows the 3-dB-modulation bandwidth can be doubled and the chirp can be reduced by a factor of more than three. These improvements could be explained by an increase in differential net gain in coupled cavities. The result shows a possibility of high-speed and low-chirp operations of transverse coupled cavity VCSELs for higher data rates and longer link lengths of single-mode fiber transmissions.

Observation of laser feedback using a grating spectrometer

We describe an experimental setup for observing the effect of optical feedback in an extended cavity diode laser. A simple grating spectrometer is used to observe the naturally occurring wavelength spread and mode spacing for the diode. When the diode is provided with optical feedback from a grating in the Littman-Metcalf configuration, the tunability of the diode is easily observed. This setup presents an intuitive and cost-effective method for demonstrating optical feedback in an advanced undergraduate laboratory setting.

Numerical Analysis of the Effect of Temperature and External Optical Feedback Variation on the Output Characteristics of External Cavity Semiconductor Laser Based Fiber Bragg Gratings

The temperature and external optical feedback (OFB) effects on power characteristics of external cavity semiconductor laser model based fiber Bragg gratings (FBGs) are numerically analyzed. In this model, fiber Bragg grating (FBG) is used as a wavelength selective element to control the properties of the laser output by controlling the external OFB level. The study is performed by modifying output laser equations that are solved by considering the effects of ambient temperature (T) variations and external OFB. In this study, the temperature dependence (TD) of laser characteristics is calculated according to TD of laser parameters instead of using the well-known Pankove relationship. Results show that by increasing the external OFB level, the laser output power improves significantly. Also, results show that by changing the operating temperature 15℃ (from 15℃ to 30℃), there is no great impact on the output characteristics. The obtained results can provide an important idea for the practical fabrication for this type of lasers.

Optical feedback stabilization of photonic microwave generation using period-one nonlinear dynamics of semiconductor lasers.

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 Effects of Temperature, Injection Current and Optical Feedback on the Frequency Stabilization of External Cavity Diode Laser

A frequency-stabilized diode laser is widely used for applications in laser cooling and high-resolution spectroscopy. In this work, the 780-nm external cavity diode laser was constructed and subsequently frequency-controlled by three parameters, i.e., temperature, injection current and optical feedback. The laser frequency was measured with respect to the 5S1/2 → 5P3/2 (D2-lines) transition of Rubidium, while the laser mode was characterized by a Fabry-Perot interferometer. The laser temperature was passively controlled to a single value between 20 ̊C and 25 ̊C while the injection current was investigated in combination with course and fine adjustments of optical feedback. Only data relevant to a single-mode laser operation was collected. It was found that as the current increased, the laser frequency shifted linearly with slopes approximately 0.5-0.8 GHz/mA. Optical feedback from the external cavity was tuned by the voltage applied to the piezoelectric transducer, yielding a linear frequency response of approximately 0.2 GHz/V. The measured parameters were rearranged to represent the island of stability of the laser, suggesting suitable conditions that yielded single-mode operation, at a desirable laser frequency. The results were important for a design of an active feedback, in order to further reduce the frequency linewidth and intensity noise of the laser.

External optical feedback effects on stability of asymmetric DFB-FL and isolation method

The effects of external optical feedback mainly introduced by Rayleigh backscattering (RB) in long lead fiber, reflection of fiber end facet, and the fusion splices on the stability of asymmetric distributed feedback fiber laser (DFB-FL) have been investigated. Theoretical analysis based on the compound cavity model is presented, and the critical length Lp,c of lead fiber is obtained to evaluate the tolerance of DFB-FL to RB. Analysis and experimental results show that RB is the main factor causing the instability. The critical length for the shorter end of our asymmetric DFB-FL is measured to be about 170 m. To isolate the laser from the effect of RB, we propose a method using isolator and WDMs, which is experimentally proved to be an efficient way.

Internal and External Optical Feedback Effect in Fiber Linear Lasers

In this paper, models of internal and external optical feedback effect in fiber linear lasers have been presented. The effects of optical feedback could be equivalent to the variation of laser cavity loss, and the output expressions of two models are deduced. According to the simulation results, the optical feedback system in fiber linear lasers has the same phase sensitivity as the traditional self-mixing effect in semiconductor lasers. The experimental results show a good agreement with the simulated results. Comparing the output of internal structure with that of external structure, we can conclude that the internal optical feedback system can get higher output gain and stripe depth, which reveals that the internal feedback structure has better sensing characteristics

Inspecting and locating foreign body in biological sample by laser confocal feedback technology

A promising method is proposed to inspect and locate foreign bodies in biological samples. It combines advantages of confocal microscopy and optical feedback effect of microchip solid-state laser, and retrieves both spatial positioning and specific images by the sensitive detection of extremely weak signals retro-diffused by the interface in samples. By testing onion samples containing pins as foreign bodies, this approach has been demonstrated to examine the foreign body and locate its position within several millimeters depth below the sample surface.

Acceleration measurements upon micro- and nanodisplacements of an object using the autodyne signal of a semiconductor laser with allowance for the external optical feedback

The effect of the external optical feedback in a semiconductor laser autodyne on the acceleration measurements for the nonuniformly accelerated micro- and nanodisplacements of an object is analyzed. It is demonstrated that the correlation coefficients of the results of the acceleration measurements and the approximating linear dependence are 0.99 and 0.82 with allowance for and disregard of the feedback level, respectively.

Robust square-wave polarization switching in vertical-cavity surface-emitting lasers

We study theoretically and experimentally the combined effects of polarization-selective optical feedback and of crossed-polarization reinjection in a vertical-cavity surface-emitting laser. We show that the application of polarization-selective optical feedback, which induces an effective dichroism in the system, allows one to generate a robust and regular square-wave output signal in each polarization component. The period of the square-wave signal is determined by twice the reinjection delay. We analyze the regularity of the induced modulation as a function of laser bias current, dichroism, and of the levels and delays of reinjection and feedback, thus revealing the robustness of the square-wave emission in the parameter space. We also show that the feedback is more effective when acting on the long-wavelength polarization mode, which can be traced to the asymmetry of the bistable region of the vertical-cavity surface-emitting lasers for low dichroism.

Intensity noise in ultra-high frequency modulated semiconductor laser with strong feedback and its influence on noise figure of RoF links

We characterize the intensity noise associated with the ultra-high frequency direct modulation of semiconductor lasers under strong optical feedback over a millimeter-wave frequency passband between 54.5 and 56.5 GHz. Enhancement of the modulation response over this millimeter wave band due to optical feedback is clearly shown by time-delay rate equation analysis fully involving the strong optical feedback effect. The contribution of the relative intensity noise of the laser to the noise figure of an ultra-high speed radio over fiber link is evaluated. We show that subjecting the laser diode to strong feedback improves the noise figure of a 55.8-GHz radio over fiber link nearly by 20 dB in the regime of small-signal modulation and 10 dB under large-signal modulation.

Threshold gain dynamic of blue InGaN laser diode with optical feedback

The effect of external optical feedback (EOF) on the threshold gain of the single quantum well blue InGaN laser diode (LD) has numerically been investigated. Simulation results indicated that the amplitude and phase of EOF have potential effects on the threshold gain of InGaN LD. The effect of gain compression factor on the threshold gain of InGaN LD with and without EOF is also investigated. Lower threshold gain obtained with higher amplitude of EOF; while higher threshold gain obtained with lower gain compression factor.

Linewidth characteristics of un-cooled fiber grating Fabry–Perot laser controlled by the external optical feedback

The effect of external optical feedback (OFB) on the linewidth characteristics of un-cooled laser module is theoretically investigated. This laser that consists of a Fabry–Perot (FP) laser diode and fiber Bragg grating (FBG) realizes stable operation and relatively low-cost solution. The effects of external OFB and temperature on linewidth are calculated according to their effect on threshold carrier density (Nth). The temperature dependence (TD) of linewidth characteristics is calculated according to TD of laser parameters instead of well-known Parkovin relationship. Results show that, linewidth decreases as the external OFB reflectivity (Rext) increases. A narrow linewidth which is less than 3kHz is obtained for Rext≥0.5. In addition, the linewidth is not largely affected by temperature as compared to the DFB lasers. Also, we found that the linewidth temperature coefficient is 0.04kHz/°C, which is small enough in comparison to 18.5kHz/°C for the DFB laser.