Study On Tunable Laser Design And Linewidth Compression Technique Based On Reconstruction-Equivalent-Chirp Technology

With the continuous development and advancement of network technology,optical communication systems require higher communication bandwidth and speed,and these new challenges bring new development opportunities to the optical communication field.Tunable lasers play an important role in optical communication,sensing and other fields.The optical communication system faces new challenges in optical signal processing and analysis,and it also puts forward new requirements for the linewidth of the laser.Tunable narrow linewidth lasers are also the core optoelectronic devices in high-speed coherent optical communication systems.In this paper,based on the Reconstruction-Equivalent-Chirp technology,a twosection HR-AR coated laser and its array are designed and fabricated,and we study on a new method to narrow the linewidth of tunable laser.The main contents and results of this paper are as follows:(1)A two-section HR-AR coated laser and its array based on ReconstructionEquivalent-Chirp technology are proposed.The laser of this structure adopts a twoelectrode design,and the effective refractive index difference can be introduced by injecting different current into the section lasers to compensate the uncertain phase caused by cleavage of the HR coated facet,so that the single longitudinal mode can be achieved.DFB lasers of this construction can achieve a single longitudinal mode ratio of 100% by varying the current injection ratio of the two lasers.After the verification design,a four-laser array with the wavelength in the C-band was designed based on the structure,and the designed wavelength interval of 1.6 nm could be achieved by varying the current injection ratio with a guaranteed constant temperature(25°C)and a total injection current of 100 mA.The temperature tuning characteristics of each laser in the array were essentially consistent at 0.108 nm/°C.With a total injection current of 100 mA and varying the current injection ratio and temperature,it is realized that each laser covers 4 channels for a total of 16 channels with a channel interval of 0.4 nm,good single-mode characteristics and a minimum side mode suppression ratio of 45.2 dB.(2)The linewidth compression of tunable laser was achieved by using the external cavity self-injection feedback technique and the experimental results are analyzed in detail.In the proposed self-injection feedback scheme,the linewidth of the laser narrows with the increase of the feedback intensity at a feedback optical path length of 7.2 m.When the feedback intensity is-20 dBm,the linewidth narrows from 3.4 MHz in free operation to 34.35 kHz.Changing the feedback cavity length with the guaranteed constant feedback intensity narrowed the laser linewidth as the cavity length increased.When the length of the feedback optical path is 50 m,the linewidth will be compressed to 4.3 kHz,but the side mode suppression ratio will deteriorate.With a feedback optical path of 7.2 m,adjust the output power of the sub-laser to 3 dBm and the feedback optical power to-20 dBm.This solution can narrow the linewidth of all sub-lasers of the tunable laser to below 100 kHz and the minimum 34.4 kHz.