基于双片锯齿电极的宽带声光偏转器

Wideband Acousto-Optic Deflector Based on Double Sawtooth Electrodes

传统具有单片换能器结构的声光偏转器存在布拉格带宽与衍射效率的权衡关系。为了增加布拉格带宽而又不降低衍射效率,提出一种基于双片锯齿电极的换能器结构的声光偏转器。首先采用双片换能器结构实现超声跟踪,使超声波方向能随频率改变,提高布拉格带宽。在此基础上应用锯齿形电极增大超声波的发散程度,进一步提高布拉格带宽。仿真结果表明,电极的锯齿边缘使声波波动性增大,即增大了超声波的发散程度。实验结果表明,在相同实验条件下,具有双片锯齿电极换能器结构的声光偏转器的3 dB带宽比单片矩形电极换能器结构的声光偏转器高62.5%。

Objective Acousto-optic deflectors,which constitute a class of precision optical functional components,play a central role in modern optoelectronics technology owing to their excellent performance.Bandwidth,a key performance indicator,determines the frequency range of these devices.Conventional acousto-optic deflectors with single transducer structures face challenges related to bandwidth and diffraction efficiency.To increase the bandwidth,the transducer length must be reduced;however,this may lead to low diffraction efficiency.Therefore,the influence of transducer length on diffraction efficiency and bandwidth must be considered to maintain a balance between the two factors when designing an acoustooptic deflector.The proposed ultrasonic tracking technique addresses this challenge and provides simultaneous improvements in bandwidth and diffraction efficiency.Further optimization of the device's performance requires investigation of additional methods that can ensure high diffraction efficiency while enhancing bandwidth.Methods This paper proposes a design method that enhances the bandwidth of an acousto-optic deflector while maintaining high diffraction efficiency.Utilizing the principle of ultrasonic tracking,the proposed method employs two transducers in series to form an antiphase drive.This configuration generates an ultrasonic beam that can change its propagation direction according to frequency,enabling the device to achieve Bragg diffraction over an extended frequency range,thereby improving ultrasonic energy utilization and increasing Bragg bandwidth.By maintaining the same acoustooptical interaction area for single-and double-blade transducers,the overall transducer length remains constant,ensuring high diffraction efficiency.Additionally,the surface electrode of the two-piece transducer features a serrated design,which further enhances ultrasonic wave dispersion and Bragg bandwidth.To validate this method,the phase distribution of the acoustic field generated by the serrated and rectangular electrodes is simulated mathematically by the angular spectrum method.The simulation confirms that the sawtooth edge of the electrode increases ultrasonic waveform volatility.Bandwidth comparison experiments further verified the effectiveness of this approach,showing that the acousto-optic deflector with two-piece serrated electrode structure possesses a large bandwidth and high diffraction efficiency.Results and Discussions In designing the acousto-optical deflector with two-piece serrated electrode structure,two transducers featuring serrated surface electrodes are used.The geometric features of these serrated electrodes consist of the inner width,outer width,and period(Fig.2).Through the angular spectrum method,sound field simulations were established for the two-piece rectangular and serrated electrodes(Fig.4).A comparison of the phase distribution at the central plane of the acoustic field generated by the two-piece rectangular and serrated electrodes reveals that while the rectangular electrode produces a planar acoustic wave,the serrated electrode produces a more volatile acoustic wave with a large divergence angle(Fig.5).Since normal Bragg diffraction necessitates the ultrasonic wave direction to equally divide the incident and diffracted light,the increased angular dispersion of ultrasonic waves facilitates effective ultrasonic tracking over a large frequency range,resulting in a device with increased bandwidth.The acoustic fields of the two-piece sawtooth electrode structures with different parameters were individually simulated.Their comparison revealed that smaller serrated periods yield electrode shapes closer to rectangles and decreases acoustic wave volatility(Fig.6).To further validate these results,bandwidth comparison experiments were conducted for the acousto-optic deflectors with single rectangular,double rectangular,and double serrated table electrode transducer structures(Fig.9).The results show that the bandwidth of the acousto-optic deflector with two-piece serrated electrode structure(3 dB)surpasses that of the deflector with single-piece rectangular electrode structure(by 62.5%)under the same experimental conditions(Fig.10).Conclusions This paper proposes an acousto-optical deflector with two-piece serrated electrode transducer structure that effectively increases the bandwidth while maintaining high diffraction efficiency.Utilizing the two-blade transducer structure,the surface electrode is designed into a serrated shape.This design inherits the advantages of ultrasonic tracking multichip transducers while ensuring high diffraction efficiency of the device and enhancing the ultrasonic dispersion range,ultimately leading to an improved acousto-optic deflector bandwidth.The phase distribution of the two-piece rectangular and serrated electrodes is determined by the angular spectrum method.Further,the comparison of the simulation results reveal that the serrated edge of the electrode increases ultrasonic wave volatility.Bandwidth comparison experiments were conducted for acousto-optic deflectors with single rectangular,double rectangular,and double serrated table electrode transducer structures.The results show that the acousto-optic deflector with two-piece serrated electrode transducer structure can enhance the bandwidth while maintaining high diffraction efficiency.The implementation of this two-piece serrated electrode transducer structure in high-frequency acousto-optic devices will have a considerable effect on bandwidth enhancement.