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A novel method for the generation of an optical frequency comb (OFC) is presented. The proposed approach uses a laser diode with optical feedback and operating at a specific nonlinear dynamic state named periodic window. In this case, the laser spectrum exhibits a feature with a series of discrete, equally spaced frequency components, and the repetition rate can be flexibly adjusted by varying the system parameters (e.g., external cavity length), which can provide many potential applications. As an application example, a dual-OFC system for distance measurement is presented. The results demonstrate the system's ability to achieve target distance detection, underscoring its potential for real-world applications in this field. [ABSTRACT FROM AUTHOR]

With external optical feedback (EOF), a laser diode (LD) can operate at different dynamic states. In this work, an LD with EOF is set at period-one (P1) oscillation state to generate microwave photonic (MWP) signal for sensing. Firstly, the P1 state boundary of the LD is determined and then the influence of the LD controllable parameters on the boundary is studied by solving the well-known Lang–Kobayashi equations. A set of parameters selection rule for designing an LD based MWP sensing system is obtained. In addition, a measurement algorithm for recovering the displacement from an MWP sensing signal is developed. By making full use of the sensing information carried in both amplitude and frequency of the MWP signal, displacement sensing with high resolution and large range can be achieved. Both simulations and experiments are conducted to verify the proposed method and show it is capable of realizing wide measurable range, high measurement sensitivity, and high resolution sensing. [ABSTRACT FROM AUTHOR]

Laser dynamics have great potential for various applications, ranging from cryptography to microwave photonics and instrumentation. This letter presents a design for achieving high sensitive sensing and measurement using the dynamics of a laser diode (LD) with a dual external cavity. In the design, one cavity is used to control the dynamics, making the LD operate at the period-one (P1) oscillation state, and the other one is associated with the quantities to be measured. The Lang-Kobayashi equations are modified and solved to develop a bifurcation diagram for the design, from which we determine the P1 state and investigate the sensing performance within this state. It is shown that, when operating in P1, the laser intensity exhibits an oscillation with its amplitude modulated by a traditional optical feedback interferometric (OFI) signal (generated with a single cavity and LD operating at the steady state). It is also observed that the modulation depth is remarkably larger than the magnitude of a traditional OFI signal. This leads to a significant increase in the sensitivity of sensing and measurement and hence provides an attractive solution for the detection of very small or weak physical quantities. An experimental system is designed, and the experimental results verify the high sensitive sensing performance of the proposed design. [ABSTRACT FROM AUTHOR]

The paper presents a practical approach for measuring the linewidth enhancement factor α of semiconductor lasers and the optical feedback level factor C in a semiconductor laser with an external cavity. The proposed approach is based on the analysis of the signals observed in an optical feedback self-mixing interferometric system. The parameters a and C are estimated using a gradient-based optimization algorithm that achieves best data-to-theoretical model match. The effectiveness and accuracy of the method has been confirmed and tested by computer simulations and experiments, which show that the proposed approach is able to estimate α and C with an accuracy of 6.7% and 4.63%, respectively. [ABSTRACT FROM AUTHOR]

In this study, a novel distance sensing method is presented by using a semiconductor laser (SL) with optical feedback (OF) and operating the SL at a switching status happened between two nonlinear dynamic states (stable state and period-one state). In this case, without the need for any electronic or optical modulation devices, the laser intensity can be modulated in a square wave form due to the switching via utilizing the inherent SL dynamics. The periodicity in the switching enables us to develop a new approach for long-distance sensing compared to other SL with OF-based distance measurement systems and lift the relevant restrictions that existed in the systems. Moreover, the impact of system controllable parameters on the duty cycle of the square wave signals generated was investigated on how to maintain the proposed system robustly operating at the switching status. Both simulation and experiment verified the proposed sensing approach. [ABSTRACT FROM AUTHOR]

A novel Dual-frequency Doppler LiDAR (DFDL) is presented where the dual-frequency light source is generated by using external optical feedback (EOF) effect in a laser diode (LD). By operating a LD at period-one (P1) state and choosing suitable LD related parameters, a dual-frequency light source can be achieved. Such a dual-frequency source has advantages of the minimum part-count scheme, low cost in implementation, and ease in optical alignment. Theory and system design are presented for the proposed DFDL for velocity measurement with high measurement resolution. The proposed design has a potential contribution to the Light Detection And Ranging (LiDAR) in practical engineering applications. [ABSTRACT FROM AUTHOR]

This paper presents a new method for measuring the linewidth enhancement factor (alpha factor) by the relaxation oscillation (RO) frequency of a laser with external optical feedback (EOF). A measurement formula for alpha is derived which shows the alpha can be determined by only using the RO frequencies and no need to know any other parameters related to the internal or external parameters associated to the laser. Unlike the existing EOF based alpha measurement methods which require an external target has a symmetric reciprocate movement. The proposed method only needs to move the target to be in a few different positions along the light beam. Furthermore, this method also suits for the case with alpha less than 1. Both simulation and experiment are performed to verify the proposed method. [ABSTRACT FROM AUTHOR]

• A mathematical sensing model of a DOFI system working in P1 state was established. • Factors that determine the sensitivity enhancement were analyzed,and the operation region of a DOFI system in P1 state was investigated, based on which, design criteria of designing a DOFI-P1 sensing system were summarized. • Preliminary experiments have been performed to verify the high measurement sensitivity of a DOFI-P1 system as compared with the OFI system. • The results of this work provide helpful guidance for the construction of high-sensitivity DOFI sensing and measurement systems. Laser optical feedback interferometry (OFI) is a unique one-channel interferometric measurement technology with the advantages of compact structure, low implementation cost and easy alignment. However, it has a critical challenge that the visibility of interference fringe is often low and further induces low measurement sensitivity, especially in occasions when the optical feedback strength is feeble, e.g., biomedical and fluid detection. Recently, it has been demonstrated that period-one (P1) dynamics can enhance the measurement sensitivity by introducing extra optical feedback to form a dual optical feedback interferometry (DOFI) system. However, the details of the enhancement mechanism and how to design such a system are still required to unveil. In this paper, comprehensive discussions of designing a DOFI system with high measurement sensitivity enhanced by P1 dynamics are presented. First, based on the modified Lang-Kobayashi equations, a mathematical sensing model of a DOFI system working in P1 state was established. Then, simulations were carried out to verify the validity of the proposed model. After that, factors that determine the sensitivity enhancement were analyzed, based on which, theoretical analysis of achieving optimal sensitivity enhancement was performed. Next, we discussed the operation region of a DOFI system in P1 state and investigated the influence of the system parameters on the operation region. At last, experiments were conducted to verify the theoretical analyses. The results of this work provide helpful guidance for the construction of high-sensitivity DOFI sensing and measurement systems. [ABSTRACT FROM AUTHOR]

• In this work, we proposed to use a Microwave Photonic (MWP) sensing signal to achieve high displacement sensing resolution. The MWP sensing signal is generated by a laser diode (LD) with dual-cavity. In this configuration, the LD serves as both an MWP source and a sensor. The MWP sensing signals are directly generated by laser dynamics without need any external modulator. The information about the measurand is carried by both optical and microwave components of the MWP sensing signals. Hence, rich information about the measurand can be retrieved from the generated MWP sensing signals to greatly improve sensing performance. This work has the following contributions and significances. • We push an optical feedback interferometry (OFI) to operate at a laser state called 'period one' by using a dual-cavity configuration. In such configuration, one cavity is linked with measurand target, the other is used to control the LD dynamic states. Under the optimal system operation condition, a modulated laser intensity in microwave range (we call it as MWP sensing signal) can be generated and it is sensitive to a target movement external the LD and thus is used for displacement sensing. • It is found that the high frequency component contained in an MWP sensing signal can be used to subdivide OFI fringe signals. This is a novel method for subdivision of interference fringe and it is able to achieve super high sensing resolution (in a nano scale in theory) compared to the existing methods. Laser diodes (LDs) experiencing external optical feedback (OF) are known to demonstrate complex nonlinear dynamics and found various applications. Typical sensing configuration using an LD with OF is called optical feedback interferometry (OFI) that can produce an interferometric-like fringe signal (called OFI fringe) with a fringe resolution as half laser wavelength for displacement measurement. This work uses a dual-cavity OFI and operates the LD at Period-One (P1) state. By optimal configuration for such system, a microwave photonic (MWP) signal can be generated in oscillation form at a very high frequency with its amplitude modulated by an OFI fringe signal. The high frequency component contained in the MWP signal is used for subdivision of an OFI fringe to greatly improve sensing resolution. Both simulation and experiment are conducted to confirm the proposed approach for OFI fringe subdivision. [ABSTRACT FROM AUTHOR]