## 1 Introduction  
The photonic generation of a microwave waveform signal has become a quite attractive research area in recent years. The generation of square and triangular pulses has aroused widespread concern, as they are widely used in modern electronic systems such as wireless communication systems [1; 2], all-optical signal processing systems [3; 4], radars [5], and sensors [6]. Until now, various photonic square and triangular signal generation schemes have been proposed [7; 8; 9; 10; 11; 12]. Among them, the external modulation of a continuous wave (CW) is an efficient and promising solution to generate microwave waveforms with a full duty cycle. The basic principle is to generate the desired harmonics corresponding to the Fourier series expansion components of the desired pulse train in the frequency domain. For example, in paper [13], a Mach-Zehnder modulator (MZM) and a span of dispersion fiber were used to generate triangular pulses. In this scheme, the dispersive fiber was used to form a microwave photonic filter with a periodic response, so as to suppress the undesired even-order harmonics. In paper [14], a scheme for the generation of triangular pulse using a MZM was proposed. Additionally, an optical interleaver (IL) combined with a tunable optical delay line (ODL) was used to introduce a time delay between the first and third optical sidebands. However, the repetition rate was limited by the optical signal processing components in such schemes, such as dispersion compensation fibers (DCFs), ODLs, or ILs. The triangular signal generation could also be achieved by employing stimulated Brillouin scattering (SBS) effects in optical fiber [15; 16]. In paper [17], triangular and square waveforms were obtained with the assistance of a Sagnac loop and two single-drive MZMs. A more simplified scheme was realized by adjusting the DC bias voltage and modulation coefficient of a dual-parallel Mach-Zehnder modulator (DPMZM) appropriately [18; 19]. Furthermore, no optical filtering device was required in such schemes. However, two sub-modulators of DPMZM must have been driven by two different RF signals. Additionally, the accurate DC bias control was limiting the practicality of the system. In paper [20], a MZM and a hybrid coupler were employed to generate triangular and square waveforms. In this scheme, the MZM, a push-pull intensity modulator, which meant the input RF signals loaded on the two arms had a \(\pi\) phase difference, was operated at the quadrature bias point to effectively suppress the even-order harmonics at a high input power. In paper [21], [PERSON] proposed a novel scheme to generate a triangular-shaped waveform based on two cascaded DDMZMs, no electric filter or phase shifter was used in the system, while a Fiber Bragg Grating (FBG) was necessary after the DDMZMs. In this paper, we propose and experimentally demonstrate a simple photonic method for the simultaneous generation of square and triangular waveforms without any filtering or dispersive elements with a low RF signal power requirement. This scheme only requires a sinusoidal RF source, a DDMZM, a RF power splitter in conjunction with a phase shifter, a photodetector (PD), and a 90\({}^{\circ}\) hybrid coupler. By simply adjusting the input power of the RF signal applied to the power splitter appropriately, the first- and third-order harmonic signals of the photocurrent compose a spectrum of a desired pulse train. A hybrid coupler is utilized after the photodetector made the phase of the first- and third-order harmonics conform to the required relation. The signal generation is realized by using the characteristics of DDMZM to control the phase and amplitude of the optical sidebands. This scheme can greatly simplify the configuration of the system. The principle of the scheme is theoretically analyzed and experimentally verified. The generation of square and triangular waveforms is demonstrated. Furthermore, the pulse trains with repetition rates of 5, 8, and 10 GHz are successfully achieved, which guarantees the feasibility of the scheme.