## 1 Introduction  
Radially and azimuthally polarized beams have been increasingly studied in recent years because of their unique characteristic of axial polarization symmetry, and they can break the diffraction limit with a strong longitudinal electromagnetic field in focus [1; 2; 3]. The applications of these beams include high-resolution microscopy, surface plasmon excitation, optical trapping, material processing, and high-density data storage [4; 5; 6]. Various generation theories and methods for these beams have been proposed. The generation methods can be categorized as intracavity and extracavity methods. For the intracavity method, a specially designed birefringent crystal, an adjustable aperture, conical and axicon prisms, or a non-periodic sub-wavelength grating is set inside the resonant cavity of a laser to generate the radially or azimuthally polarized beam [7; 8]. However, laser cavity structures are typically complicated. This complicated structuring could cause difficulty for alignment and thus additional power loss in laser manufacturing. Additionally, limited by the form of the laser cavity, the intracavity method is not suitable for fiber lasers, lithography ultraviolet (UV) lasers, or semiconductor lasers. By contrast, the extracavity method (which refers to two types of techniques), achieves radially and azimuthally polarized beams outside of the laser cavity. The first type of technique uses a cut half-waveplate, polarization converter, or liquid-crystal spatial light modulator to convert a linearly or circularly polarized beam into a radially or azimuthally polarized beam [9; 10]. The second type of technique uses various interferometric structures to obtain a radially or azimuthally polarized beam [11; 12]. The implementation of these methods could be restricted by the requirements of a highly coherent light source and environmental stability. This possibility makes the implementation of these methods potentially difficult. In addition, the generated beam is typically limited by low power. [PERSON] and [PERSON] proposed a simple manipulation method that uses birefringent crystals and half-wave plates to coherently generate a radially polarized beam [13]. In their method, the structure fulfills the demands of compactness, mechanical stability, and robustness for practical high power applications. However, because of the birefringence of the crystal polarization mode, dispersion occurs during the manipulation of different states of polarization. To eliminate the temporal walk-off problem, a second birefringent crystal is required to compensate the optical path difference between two orthogonal polarized modes. Therefore, the cost of the method could be high.  
In this paper, we propose a modified method for the generation of radially and azimuthally polarized beams. Based on a Mach-Zehnder-like interferometric arrangement, a pair of lateral displacement beamsplitters (LDBs) is used to replace the expensive birefringent crystals. Half-size and full-size half-wave plates (h-HWP and f-HWP) are applied to manipulate the states of polarization of the incident beam. The operation principles of this method, accompanied with a Jones matrix calculus, are described. With coherent superposition, radially and azimuthally polarized beams can be simultaneously achieved in the far-field region. To demonstrate the feasibility of the method, a prototype of the proposed polarization converter was successfully assembled and tested. Because of the application of LDBs, the design has a simple, symmetric, compact, and robust structure; furthermore, this design reduces the cost of the device substantially. In addition, the device can operate with a broadband pulsed laser and has considerable potential for high-power applications.