A Parabolic Waveform Generator Based on the Chirp Characteristics of a Directly Modulated Laser

Round 1

Reviewer 1 Report

The manuscript proposes a simple scheme for the parabolic pulse generation by the use of the carrier dynamic, when the DML is driven by a triangular signal. The theoretical analysis, numerical simulation, and experimental verification are presented. The current submission can be considered, after the following queries are properly addressed.

1.       In this work, DML is the key device to implement the parabolic pulse generation. The authors should provide the specific operation parameters during your experiment, including the threshold current, the bias current and other related parameters.

2.       I personal feel that, (1) omga in Eq. (4) should be changed to omga_c; (2) In line 61, the and should be K and –K, in relevant to the Eq. (3).

3.       From the calculation result, the degree of fitting values of the parabolic pulses with fundamental frequency or doubling frequency are almost the same. However, in the experimental results, the quality of the parabolic pulses with doubling frequency seems worse than that with fundamental frequency? The explanation and discussion are helpful.

Author Response

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Reviewer 2 Report

This manuscript demonstrates an interesting parabolic waveform generator utilizing the chirp characteristic of DML. Under a triangular drive signal, bright and dark parabolic pulses with fundamental frequency as well as frequency doubling dark parabolic pulse can be flexibly generated by simply adjusting the window of an optical filter. The simulation and experimental results are in good agreement. The author should consider the comments as follows:

1． Equation. (3) describes the spectral transfer function of the filer window corresponding to Fig. 2. As seen in Fig. 2, the slope and range of the rising and falling edges of the filter are key parameters, but they are not fully involved in Eq. (3). Therefore, such parameters should be added in Eq. (3).

2．From the principle, the parabolic pulse scan be generated due to the drive signal and chirp signal with linear edges. As we know, the sawtooth waveform also has linear edge, except for the triangular signal. Whether the sawtooth waveform also achieve the same results? Please explain it.

Author Response

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Reviewer 3 Report

Overall, the findings of this study can be quite intriguing as they provide a practical and straightforward approach to transforming the output waveform of semiconductor lasers. In general, the proposed modulation approach described by the authors in the introduction is well-known. Within the scope of this study, a practical implementation using readily available components such as a directly modulated laser (DML) and a gaussian optical filter is demonstrated. If the paper is published, there are several suggested additions that should be made to the text.

Firstly, it would be beneficial to include an extended description of the characteristics of the DML. This should cover details such as the type of laser (F-P, VCSEL, DFB), the model (if it is a commercially available laser), the cavity length, the drive current at the operating point, the amplitude of optical power modulation (Fig. 7b), the current modulation amplitude, and the frequency bandwidth of the DML modulation.

Additionally, could the authors please specify the frequency bandwidth of the photodetector in the circuit depicted in Fig. 5? This information is necessary as it measures the output waveform. It would also be helpful if the authors could provide the model of the photodetector.

Regarding Fig. 11c, the waveform appears to resemble a dark parabolic waveform. Could the authors comment on this difference?

Furthermore, in Fig. 7a, the modulated optical spectrum for the free output of the DML is shown. Could the authors indicate at which frequency this spectrum is measured? Additionally, it would be valuable to include spectra for the free output of the DML at frequencies of 2 and 3 GHz, corresponding to the findings presented in Fig. 11.

Author Response

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