Wavelength Stabilizer Of High-power980nm Semiconductor Laser

Optical fiber communication has many technological advantages such as low loss,high capacity, high transmission speed, electromagnetic interference insulation, lightweight and confidentiality. And it has developed into the most active and promisingcommunication industry since the1970s, with the rapid development of communicationtechnology and the growing demand for data information transmission. The high-powersingle-mode980nm semiconductor laser has the highest gain efficiency as a pumpsource of Erbium Doped Fiber Amplifier (EDFA), and therefore it becomes a coredevice of optical fiber amplifier in optical fiber communication systems. However, theuncooled980nm semiconductor laser has poor wavelength stability. To improve thewavelength stability can extend the relay distance of optical fiber communication,improve the performance of EDFA and reduce the cost of EDFA.First of all, we introduce the effective relation between the photon energy and thepopulation inversion of temporal carriers in the state of the thermal equilibrium ornon-equilibrium. Then, we introduce the basic theory of Fiber Bragg Grating (FBG).Based on the FBG coupled mode theory, we obtain the reflectivity of laser front facetand external-cavity dual-FBG reflection mirror, and integrate it into the rate equation ofexternal-cavity feedback semiconductor laser to study the temporal interdependencyamong the external-cavity structure, the drive current, the photon energy and thenumber of carriers.Based on the principles mentioned above, we propose and study three keytheoretical models to stabilize the output operating wavelength of uncooled980nmsemiconductor laser. They are the model of external-cavity dual-FBG weak feedback,the model of wavelength-temperature shift suppression and the model of dynamicstability under coherence collapse (CC) regime. For the external-cavity dual-FBGweak-feedback semiconductor laser, we mainly study the characteristics of thedual-FBG wavelength stability including the Full Wave Half Maximum (FWHM) oflaser spectrum, the Side Mode Suppression Ratio (SMSR), the central wavelengthdetuning, the power loss and low-frequency oscillation with the change of ambienttemperature, drive current and external-cavity parameters.We design the external-cavity dual-FBG structure to be a wavelength stabilizer foran uncooled980nm semiconductor laser to stabilize the operating wavelength. The analytical expression of transmittivity and reflectivity of external cavity, and the gainequations of the wavelength stabilizer have been obtained by the coupled mode theory.The distance of two FBGs, the distance between laser front face and the FBGs, the FBGrefractivity, the period of refractivity, the FBG length and the ambient temperature arediscussed to research how they can affect the laser gain curve, the spectral SMSR,FWHM and central wavelength detuning. Based on the research results, we furtheroptimize the structure of wavelength stabilizer to achieve a better wavelength stabilityof semiconductor in the case of the less output power loss.We research how to combine the active internal laser cavity and the passiveexternal dual-FBG cavity in the external-cavity feedback rate equation to furtheroptimize the external-cavity structure. Through the theoretical research, we manage toachieve the stable operating wavelength almost independent of the ambient temperaturefrom0℃to70℃. Based on the synergy between the external cavity and the internalcavity of laser chip, the discrete wavelength-temperature change can be inhibited by thewavelength stabilizer.The preconditions and controlling factors of coherence collapse are analyzed bythe rate equation and dual-FBG couple mode theory based on the physical process ofFBG external-cavity weak-feedback semiconductor lasers. A method of achieving andcontrolling CC multi-mode stable state is proposed for stabilizing the operatingwavelength of semiconductor laser. We establish the dynamic process with reference tothe dynamic performance of semiconductor laser and the structure parameters ofinternal and external cavities. Based on the research results, we analyze the mechanismof action on static external-cavity modes and output dynamic complex lasing modesfrom the interactional angle of light and carriers. Finally, we manage to achieve thestable operating wavelength of the laser under the CC multi-mode stable state.The experimental results confirm the validity of the three theoretical models. Theoriginal methodology of wavelength stabilization of external-cavity dual-FBGweak-feedback semiconductor laser has been completed through the establishment anddevelopment of these new mathematical models. Ultimately, I fulfill the all of theresearch tasks and obtain the ideal wavelength stabilizer for high-power uncooled980nm semiconductor laser.The dissertation has the following innovations:1) We optimize theexternal-cavity dual-FBG structure to improve the performance of high-power uncooled980nm semiconductor laser such as FWHM, SMSR and wavelengthstability with tiny power loss.2) We establish the dynamic process with reference tothe dynamic performance of semiconductor laser and the structure parameters ofinternal and external cavities. Specifically, we substitute the effective external-cavityreflectivity into the rate equation for unifying the active internal cavity and the passiveexternal cavity. Based on the method, we analyze the synergy between the externalcavity and the internal cavity of laser chip to suppress the operating wavelength shift ofsemiconductor laser with the increase of ambient temperature.3) We research andcontrol the CC multi-mode stable state of the external-cavity week-feedbacksemiconductor laser to achieve the wavelength stabilization.Without compromising the output power loss of laser, we manage to improve thespectral FWHM, SMSR and wavelength stability of high-power uncooled980nmsemiconductor laser to meet the low-cost, high-power, standardized, long-life,small-size, and high-reliability requirement in fiber amplifier systems.We choose the uncooled980nm pump laser with the Mini-DIL package tomeasure in the experiment. It has the stable thermoelectric performance, high reliabilityand wide dynamic operating range. The size is12.7mm×7.4mm×5.2mm. Theworking temperature is0℃~70℃. The operating wavelength is980nm and thewavelength shift is less than0.1nm. The FWHM is less than1nm. The SMSR is morethan45dB. The threshold current is24mA. The power consumption is less than1W.