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摘要: 基于电光晶体的偏振调制技术在激光三维成像领域起着越来越重要的作用。受限于铌酸锂(LN)材料的低视场和高半波电压,采用传统电光调制技术难以进一步提升三维成像性能。随着钙钛矿结构电光材料制备工艺的日趋成熟,基于新型材料的电光调制技术将成为突破激光三维成像探测精度的最佳手段,铌镁酸铅-钛酸铅(PMNT)、锆钛酸镧铅(PLZT)和钽铌酸钾(KTN)3种典型材料具有优良的电光性能和介电性质;能够突破视场和半波电压的限制,但应用到电光调制领域时存在PMNT调制带宽较低、PLZT透过性能较差、KTN实际应用带宽较低等难题。未来的研究将着眼于将该调制技术的实用性,一方面通过掺杂改性等手段提升电光调制性能,另一方面通过建立性能表征模型优化系统的信噪比。Abstract: Polarization modulation technology based on electro-optic crystals is playing an increasingly important role in the field of three-dimensional laser imaging. Due to the low field of view and high half-wave voltage of LiNiO3 (LN) materials, it is difficult for traditional electro-optic modulation technology to further improve 3D imaging performance. As the preparation technology of perovskite-structured electro-optical materials becomes more mature, electro-optic modulation technology based on new materials will become an excellent means to create a breakthrough in the detection accuracy of laser 3D imaging. PMNT, PLZT and KTaxNb1-xO3 (KTN) three typical materials have excellent electro-optical properties and dielectric properties that might surpass the field of view and half-wave voltage limitation. However, their applications in electro-optic modulation has lead to difficulties such as a low modulation bandwidth for PMNT, poor transmission performance for PLZT, and low practical application bandwidth for KTN. Future research will focus on the practicality of this modulation technology. The electro-optic modulation performance can be improved by doping and the signal-to-noise ratio of the system can be optimized by establishing performance characterization models.
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图 3 Bridgman方法生长的PMNT单晶[25]
Figure 3. PMNT single crystal grown with the Bridgman method
图 4 锆钛酸镧铅(PLZT)光电陶瓷材料[36]
Figure 4. PLZT optoelectronic ceramic material
图 5 钽铌酸钾(KTa1-xNbxO3, KTN)晶体材料[50]
Figure 5. KTN crystal material
表 1 室温下632.5 nm波长测得PMNT材料的二次电光系数和1 kHz电场下的介电常数
Table 1. The secondary electro-optic coefficient of the PMNT material measured at a wavelength of 632.5 nm at room temperature and the dielectric constant under an electric field of 1 kHz
表 2 室温下在632.5 nm波长测得PLZT材料的二次电光系数和1 kHz电场下的介电常数
Table 2. The secondary electro-optic coefficient of the PLZT material measured at a wavelength of 632.5 nm at room temperature and the dielectric constant under an electric field of 1 kHz
PLZT材料La/Ti/Zr QEO系数10-16 m2/V2 文献 PLZT材料La/Ti/Zr 介电常数 文献 8/65/35 PLZT(λ=532 nm) 25 [35] 9/65/35PLZT+0.15 mol% Li+Bi(T=348 K) 7819 [37] 8.8/65/35 PLZT(T=258 K) 2.8 [33] 9/65/35PLZT+0.25 mol% Bi2O3+CuO(T=373 K) 11290 [38] 9/65/35 PLZT(λ=532 nm) 3.7 [35] 9/65/35PLZT(T=373 K) 10539 [39] 9.4/65/35 PLZT(T=244 K) 1.48 [33] 7/65/35PLZT+0.08 wt% Cr2O3(T=427 K) 13985 [40] 10/65/35PLZT(λ=532 nm) 1.3 [35] 薄膜PLZT+2%La(f=100 Hz) 1502.59 [42] 11/40/60PLZT+0.1 mol%Dy(T=385 K) 5.59 [34] PLZT+1.50 mol%Al(T=385 K) 16000 [45] 表 3 KTN材料二次电光系数对比分析
Table 3. Comparative analysis of quadratic electro-optic coefficient of KTN materials
单位 KTN(Ta/Nb) QEO系数/(10−16 m2/V2) 测量条件 备注 NTT公司 —— 224 T=314 K λ=685 nm 山东科学院 0.75/0.25 65 λ=633 nm 调研已经达到10−14量级 0.63/0.37 86 室温λ=633 nm 美国宾夕法尼亚大学 0.7/0.3 20 T=299 K λ=532 nm Kovacs前 694 0.45 K/s降温 Kovacs后 哈尔滨工业大学 0.61/0.39 59.6 T=296 K λ=632.8 nm 表 4 PMNT、PLZT和KTN电光调制可行性分析(附LN作为比较)
Table 4. Feasibility analysis of electro-optic modulation by PMNT, PLZT and KTN (with LN for comparison)
材料名称 有效电光系数/(m2·V−2) 半波电压/V 调制电压/V 视场 产品成熟度 LN 6.8×10−12 1 900 ~600 <5° 非常成熟 PMNT ~4×10−15 ~60 ~20 较成熟(硅酸盐所) PLZT ~5×10−16 ~160 ~50 较成熟(硅酸盐所) KTN 0.2×10−15 ~260 ~80 ~30° 较成熟(宾夕法尼亚) 4~9×10−15 ~50 ~16 较成熟(山东科学院) 2.24×10−14 ~24 ~8 较成熟(NTT公司) 表 5 PMNT、PLZT和KTN电光调制适用性分析
Table 5. Applicability analysis of different electro-optic modulations
调制器
类型调制性能 衍生难题 解决方式及效果 低电压调制 大视场 LN × × PMNT √ √ 响应速度慢、
光散射严重难以应用于高速
电光调制PLZT √ √ 半波电压高 Dy掺杂使二次电光
性能明显提高透过率低 Dy掺杂和Al掺杂使
透过率明显提高,
但无法突破65%KTN √ √ 实际应用调制
带宽低通过优化系统结构,理论上可以达到ns级响应及数百兆赫兹调制带宽,但实际仍未实现 -
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