Efficient Tuning Characteristics of Modulated Grating Y-Branch Lasers
Objective Because of their advantages of small size,light weight,and long lifespan,tunable semiconductor lasers have broad application prospects in the fields of coherent optical communication,fiber optical sensing,and gas sensing.In recent years,extensive research on laser-tuning methods has been conducted for various application scenarios.Modulated grating Y-branch(MG-Y)lasers have been widely studied owing to their wide tuning range,fast tuning speed,and high flexibility.To achieve the wavelength-tuning function of the MG-Y laser in practical applications,a wavelength-current look-up table(LUT)must be developed.A common method of constructing an LUT is to scan the reflector currents,which is inefficient.In this method,the LUT contains a large number of invalid wavelength data points.This is not conducive to regular calibration and makes it difficult to ensure wavelength accuracy.The wavelength-tuning characteristics of the MG-Y laser were investigated,and the tuning method was optimized to address the issues of low efficiency in constructing the wavelength-current LUT,the complexity of wavelength-tuning methods,and the large power drift during the wavelength tuning of the MG-Y laser.Methods First,the current characteristics of an MG-Y laser are analyzed.According to the principle of the additive Vernier effect of the MG-Y laser,adjusting the reflector currents can control the position of the comb reflection spectrum and realize a wavelength-coarse tuning function.Second,a universal wavelength testing framework is designed by utilizing the tuning characteristics of the left and right reflector currents and the principle of the orthogonal experiment.Third,a wavelength-tuning method based on a wavelength test framework is developed.All smooth wavelength-tuning paths can be obtained by scanning the reflector currents along the grid lines of the test framework.A wavelength-tuning range of 40 nm can be obtained by scanning the reflector currents along all smooth paths.A fine wavelength-tuning function is realized using the phase current of the MG-Y laser.Finally,a self-adaptive power calibration algorithm for wavelength tuning is developed.Using the principle of internal current loop feedback and based on the difference between the laser power feedback voltage and the threshold voltage,the laser output power calibration function is realized by self-adaptive adjustment of the current of the semiconductor optical amplifier.Results and Discussions Only 3147 reflector wavelength combinations are included in the LUT built on the wavelength test framework,which greatly improves the efficiency of the LUT construction and reduces the number of invalid data points.A tuning performance test system and an optical fiber extrinsic Fabry-Perot interferometric(EFPI)cavity length demodulation system are used to evaluate the wavelength-tuning performance of the MG-Y laser.To verify the accuracy and effectiveness of the optimized wavelength-tuning method,the wavelength accuracy is tested first.The laser is tuned from 1528 nm to 1568 nm in step of 5 pm at room temperature for 8001 wavelength points.Good spectral quality is observed using the spectrometer,with no side-mode suppression ratio(SMSR)of less than 40 dB or wavelength jumps.The wavelength accuracy is better than±2.9 pm with a standard deviation of 0.726 pm,and the laser also exhibits good linearity in output wavelength when tuned to 5 pm.In addition,the repeatability of the wavelength is tested.To improve the testing efficiency,the tuning step of the laser is set to 5 nm,and the laser is continuously tuned 30 times from 1530 nm to 1565 nm.The results show that the maximum drift at the same wavelength is only 1.9 pm,while the minimum drift is 0.4 pm.The output power of the laser is measured using an optical power meter,and the laser power is set to approximately 11.46 mW.Before calibration,the power drift can reach as high as 2.382 mW in one C-band scan,with a stability of 20.69％;after calibration,the maximum power drift is only 0.408 mW,with a stability of 3.57％.Finally,the accuracy and effectiveness of the optimized wavelength-tuning method and the superiority of the MG-Y laser-tuning performance are verified through an optical fiber EFPI cavity length demodulation experiment.The maximum fluctuation of the EFPI cavity length error is 7.58 nm,with a standard deviation of 1.60 nm after scanning the C-band 30 times continuously.The results verify the accuracy and effectiveness of the optimized wavelength-tuning method and the excellent tuning performance of the MG-Y laser in practical applications.Conclusions The wavelength-tuning characteristics of the MG-Y laser are investigated.Based on the tuning characteristics of the left and right reflector currents of the laser,a universal wavelength test framework is designed to locate all smooth tuning paths of the laser quickly and realize the fine-tuning function of the wavelength using the phase area currents.An adaptive power calibration algorithm is proposed to reduce the power drift of the laser during wavelength tuning.The results show that the LUT constructed based on the wavelength test framework contains only 3147 reflector current-wavelength combinations,the LUT construction method is simplified,and the number of invalid data in the table is considerably reduced.The wavelength-tuning range of the laser is 1528-1568 nm,the SMSR is greater than 40 dB,the offset between the actual wavelength and the set wavelength is less than ±2.9 pm,and the standard deviation is 0.726 pm.The wavelength repeatability is better than 1.9 pm after continuous wavelength tuning is performed 30 times.The maximum power drift during wavelength tuning is only 0.408 mW after power calibration,and the stability is 3.57％.The maximum fluctuation of the EFPI cavity length error is 7.58 nm,which can be applied to optical fiber EFPI spectral acquisition and cavity length demodulation experiments.The results show that the optimized wavelength-tuning method significantly improves the construction efficiency of the LUT of the MG-Y laser while simultaneously improving the power stability of the laser during wavelength tuning,which has good practical application value.
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