| The lasers operating at 1.5 pm wavelength region perform the attractvie features of eye safety, strong smoke penetration and low loss transmission over optical fiber, so the 1.5 μm lasers are widely used in the area such as laser ranging, laser radar and remote sensing, atmospheric sounding, optical communications, quantum optics, quantum information processing and so on. Particularly, continuous variable quantum key distribution based on the quantum entanglement at 1.5 μmcan extend the transmission distance. Thus, the high power, low noise, continuous wave (CW) and single frequency 1.5 μm lasers are firstly developed to produce the quantum entanglement at the telecommunication wavelength. In recent years, the singly resonant optical parametric oscillators (SRO) gradually become an important device for the generation of high power CW single frequency laser at 1.5μm owing to the maturity of the manufacturing technique for quasi-phase matching nonlinear crystals and the improvement of output power of the CW single frequency lasers.In this thesis, the works of stable, high power, low noise, CW and single frequency 1.5 μm laser generated by a SRO are investigated in detail. The main contents are as follows:(1) 6.2 W of narrow linewidth, CW single frequency laser at 1.56 μm is obtained by optimizing the output coupling of the SRO. Firstly, two pump schemes of single-pass pumping (SPP) and double-pass pumping (DPP) are considered. The effects of the overlap between the pump and signal beam waists on the operation of the two pump schemes SROs are theoretically investigated under the collimated Gaussian approximation. Theoretical calculations show that the pump depletion of the DPP-SRO is higher than that of the SPP-SRO under the same condition. The theory gives a guideline for the design and optimization of the SRO. Secondly, the DPP-SRO is set up experimentally under different output couplers. The SRO comprises a periodically poled lithium niobate (PPLN) based two-mirror standing-wave cavity SRO and is pumped by an homemade, all solid state, low noise, CW single-frequency Nd:YVO4 laser at 1.064 μm. The mirror coatings are selected to realize DPP scheme and to resonate the signal at 1.5 μm in the SRO cavity and have the signal output partially. The output characteristics of the DPP-SRO under different output couplers are measured and agreed well with the theoretical prediction. When the pump power is 14.5 W, the better performance of the SRO is obtained by using 2.5% output coupler. The pump threshold is as low as 3.7 W, and 6.2 W of signal at 1.56 μm with the linewidth of 62.5 kHz is obtained. The measured signal frequency drift and peak-to-peak power fluctuation are less than ±40 MHz and ±0.9% in a given 1 hour, respectively. The signal wavelength can be tuned from 1.56 μm to 1.592 μm when the PPLN temperature is controlled from 120℃ to 180℃.(2) Stable operation of 1.56 μm laser is realized by carefully controlling the PPLN temperature and actively locking the SRO cavity. Firstly, we have theoretically analyzed the instability factors in SRO, and calculated the effects of the pump frequency stability and PPLN temperature stability on the stability of the SRO. Secondly, the DPP-SRO is set up under the output coupling of 1.8%, and the characteristics of it are investigated in detail. The SRO stability is improved by controlling the PPLN temperature stability to be better than 0.004 ℃, and the large frequency drift of the signal light is reduced by locking the SRO cavity to an external reference cavity. We have observed the effects of serious thermal lens in PPLN on the performance of the SRO under high power and found that thermal lens in PPLN is due to the absorption of PPLN on high intra-cavity signal power and idler power.5.3 W of CW single frequency laser at 1.5 μm with beam quality M2<1.23 is obtained at the pump power of 16 W. After improving the stability of PPLN temperature, the SRO can keep long-term mode-hop free operation, and the peak-to-peak power fluctuation is better than ±0.9% in 2 hours. The frequency drift is 3 MHz/min after actively locking the SRO cavity.(3) The noise characteristics of the 1.5 μm signal light from the SRO is investigated theoretically and experimentally. During the experiment, both the intensity noises of the pump and the signal reach the shot noise limit (SNL) at the analysis frequency of 6 MHz, however the extra phase noise in the signal light exists and oscillates depending on the analysis frequency, while the phase noise of the pump reaches the SNL at the analysis frequency of 6 MHz. The phase noise of the signal increases with increasing the output signal power and decreases with decreasing the PPLN temperature, and has no relation with the output coupling used in SRO. To explain this experimental phenomenon, a semi-classical theory model for the noise characteristics of a DPP-SRO is presented with considering the guided acoustics wave Brillouin Scattering (GAWBS) existing in PPLN crystal. The theoretical predictions are in good agreement with the experimental results.The innovations of the thesis are as follows:(1) The theory model of the DPP-SRO output characteristics under collimated Gaussian approximation is set up, and different output couplers are used in the DPP-SRO to optimize the output in experiment. High power, low threshold CW single frequency laser at 1.5 μm is obtained, and the experimental results agree well with the theoretical prediction. The pump threshold is as low as 3.7 W, and 6.2 W of signal at 1.56 μm with the linewidth of 62.5 kHz is obtained at the pump power of 14.5 W and the output coupler of 2.5%. The measured signal frequency drift and peak-to-peak power fluctuation are less than ±40 MHz and ±0.9% in a given 1 hour, respectively.(2) The stability of the DPP-SRO is investigated. A CW single frequency laser at 1.5μm with power of 5.3 W is obtained at the pump power of 16 W when the output coupling is 1.8%. After improving the temperature stability of PPLN to be less than 0.004℃, the SRO can keep long-term mode-hop free operation, and the peak-to-peak power fluctuation is better than ±0.9% in 2 hours. The frequency drift is 3 MHz/min after actively locking the SRO cavity.(3) The noise characteristic of the signal light from the SRO is investigated. We have observed that both the intensity noises of the pump and the signal reach SNL at the analysis frequency of 6 MHz, and the extra phase noise in the signal light is oscillated depending on the analysis frequency. The GAWBS is assumed to exist in PPLN and the noise spectrum is presented by using a semi-classical analysis of the noise characteristics of a DPP-SRO, the theoretical model can explain the experimental results properly.
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