A novel method to extract the grating coupling coefficient of distributed feedback (DFB) lasers by comparing the theoretical and experimental values of the side mode spacing is demonstrated. Compared with the traditional method, the proposed method in this paper transforms the solution process of the lasing model with multiple unknown parameters into that with only the side mode spacing and coupling coefficient, which significantly reduces the computational workload. Furthermore, the bias current of the measured spectrum can be much higher than the threshold current, which makes the method less affected by noise. This paper theoretically analyzes the changing relationship between multiple parameters by calculating the lasing mode distribution, and the results show that the side mode spacing is only sensitive to the coupling coefficient. In addition, the grating coupling coefficients (57-61 cm −1 ) of the fabricated DFB laser diodes are experimentally extracted at 40-80 mA currents. The variation of the coupling coefficient with current is less than 2‰/mA, and the method exhibits pretty good stability. Meanwhile, the grating coupling coefficient extraction method for the complex grating types is also considered in this paper.
A multi-period-delayed feedback (MPDF) photonic circuit constructed by a Sagnac ring and two coupled rings was designed. By coupling a distributed feedback (DFB) laser diode (LD) with the MPDF, a narrow linewidth semiconductor laser was demonstrated. The linewidth of the DFB-LD with MPDF was narrowed to be around 2 kHz, which is reduced by three orders of magnitude, and the linewidth reduction capability could be maintained when the wavelength of the DFB-LD was tuned in a range wider than 3 nm. The laser frequency stability can also be improved using the proposed technique, and the frequency fluctuation was reduced for nearly 8 times in comparison with the DFB-LD.
We proposed a new type of distributed feedback laser with alternating active-and passive-cavities (APC DFB), which enjoys the same quantum well layer where the butt-joint re-growth process can be avoided. By utilizing the chirp characteristics of the APC DFB laser in a delayed self-heterodyne system, a chirped microwave signal with a sweep range up to 40 GHz and a sweep period of 25 μs is generated. The power fluctuation of the generated signal between 0-40 GHz within 30 minutes does not exceed 3 dB, and the scanning range fluctuates about 600 MHz. And experiment results show that the thermal efficiency of the current is always related to the working environment. In the static wavelength measurement, it is controlled by the injection current; when the chirped signal is generated, it is determined by the bias current. In particular, the waveform and the period as well as the sweep range of the generated chirped microwave signals can be accurately tuned by adjusting the modulating current, which has provided a deeper insight into the photonic generation of microwave signals.
Recently, external-cavity tunable lasers (ECTLs) have been widely used in WDM systems for their excellent characteristics, such as high side-mode suppression ratio (SMSR), low relative intensity noise (RIN) and narrow line width. In this paper, we propose an analytical model for external-cavity lasers using tunable etalons and elaborate on the selection of key parameters in the design scheme, which is rarely discussed in detail in previous researches. By numerically solving the model based on the rate equation and the transmission matrix, we analyzed the effects of different end-facet reflectivity on the SMSR, PI curves, electron and photon concentration distributions. In addition, By choosing appropriate physical parameters, we theoretically demonstrate an ECTL with a single wavelength tuning range of 1570.5-1603.6 nm (186.95-190.9 THz), and a power efficiency of 0.673 W/A, as well as an SMSR exceeds 50 dB.
We investigate on the wideband phase-modulation to amplitude-modulation (PM-AM) conversion based on the chromatic dispersion in fiber. To overcome the shortcomings of the single-tone or dual-tone modulation-based model in previous researches, we present a more intuitive time-frequency analysis method for the propagation of phase-modulated signals in dispersive fibers, and give the physical picture for the temporal waveform changes. By analyzing the amplitude variation near the transition zone, we establish a bit-by-bit correspondence between the pulse waveforms and the actual modulated data, and realized the non-return-to-zero (NRZ) differential phase-shift keying (DPSK) demodulation. Furthermore, the effect of fiber length and bit rate on PM-AM conversion is also investigated quantitatively and experimentally.
A physical model of an external-cavity tunable laser (ECTL) utilizing the vernier effect of a dual Fabry–Perot (FP) etalon is presented and simulated using the finite-difference traveling wave (FDTW) method. In this paper, we provide a detailed explanation of the physical principle and construction process of the model, as well as the simulation results for the laser. The model is precisely established by studying the time-dependent changes in the carrier concentration and optical field of different wavelengths inside the laser before reaching a steady state. By determining multiple parameters in the tuning region and gain region, the proposed model can calculate and predict various laser parameters, such as output power and side-mode suppression ratio (SMSR). Moreover, the FDTW method displays the change process of various parameters, such as carrier concentration and spectrum, in the convergence of various positions in the laser with femtosecond time resolution. This capability is promising for in-depth research on the inner mechanism of lasers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.