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.
Numerous studies have shown that the use of PAM-4 modulation format for DFB lasers with integrated passive regions (DFB IPE lasers) can greatly improve information transmission capabilities. In this paper, it is found by theoretical analysis that a passive waveguide can reduce the photon concentration and injection current in the cavity under the same output optical power. The DFB IPE laser has large saturated optical power and slope efficiency, which reduces the distortion of the electro-optical conversion of the PAM-4 signal. A DFB IPE laser was fabricated with a total cavity length and passive waveguide length of 130 um and 40 um, respectively. The saturation output power, slope efficiency, and modulation bandwidth of this laser are 23.5 mW (61 mA), 0.41 W/A, 22 GHz, respectively. The relative intensity noise is also below -145 dB/Hz. Besides, we have verified the high temperature working capability of this laser in a 40 Gbps PAM-4 signal back-to-back (BTB) transmission system. When the signal peak-to-peak voltage is 750 mV, a clear eye diagram with an eye height of 196 mV is obtained at 343 K.
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.
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