## 1 Introduction  
To satisfy the increasing bandwidth demands of 5G/6G wireless networks and RIDAR systems, gigahertz-level high frequency microwave carriers with flexible tuning abilities are required since the generation of high-frequency tunable microwave carriers by traditional electronic methods is limited by the complexity of the system and the large loss of coaxial cables in high RF frequency regions [1; 2; 3]. Benefiting from terahertz-level bandwidth and low loss of the fiber, photo-generated microwave carrier technologies can produce high-frequency carriers with tunable properties using simple system settings, which has attracted lots of interests in recent work [4]. Additionally, due to the larger transmission loss of the higher frequency microwave carrier within the air environment, higher output RF power is a focus for satisfying the applications of radar and wireless communications, which requires a higher optical-to-electrical power conversion efficiency for photonics microwave generation systems [5]. Compared with O-band wavelengths, most microwave generation experiments are carried out on C-band wavelengths owing to the advantages of lower fiber loss and more mature devices at the C-band [6]. In this band, photonics microwave generation methodsinvolve the optical heterodyne method [7], optical injection locking [8], optical phase-lock loop [9], dual-wavelength laser source [10], external modulation method [11], and optoelectronic oscillator (OEO) [12]. Among the abovementioned methods, due to the simple system setup and lower cost, optical microwave carrier generation using the external modulation method has gained more attention in generating tunable, low phase noise, and high-quality microwave carriers despite physical bottlenecks existing in the standard single-mode fibers (SSMFs), involving random polarization state property, damage, and nonlinear effects from the high input power [13; 14]. Moreover, the erbium-doped fiber amplifier (EDFA) working around 1.55 \(\upmu\)m wavelengths struggles to provide a \(>\)30 dB optical gain for generating high-power microwave carriers [15]. Those challenges limit improvements in photo-generated microwave systems. Therefore, it is necessary to explore new and essential settlements that depend on novel optical fiber technologies. Around 2 \(\upmu\)m wavelengths, benefitting from the special micro-structure of optical fiber, hollow-core photonics band gap fibers (HC-PBGFs) not only have near-vacuum delays [16] and lower nonlinearities [17] but also have higher light power damage thresholds [18], stable polarization states [19], and lower losses of 0.1 dB/km [20]. Additionally, high-power photo-generated microwave carriers can be obtained due to the gain of \(>\)35 dB offered by the thulium-doped fiber amplifier (TDFA) working at 2 \(\upmu\)m wavelengths [21]. Specifically, assuming the same external quantum efficiency, a naturally higher photoresponsivity at 2 \(\upmu\)m wavelengths than that of the 1.55 \(\upmu\)m wavelengths was experimentally observed from the same indium-rich InGaAs photodiode with cut-off wavelengths of 2 \(\upmu\)m [22]. Therefore, using photonics microwave generation technology at 2 \(\upmu\)m wavelengths can take advantage of the higher opto-electric energy conversion efficiency for higher output RF power applications based on the same method and at the same RF frequency. In this paper, 7-12 GHz, stable, frequency-doubling, and tunable microwave carriers were experimentally obtained at 2 \(\upmu\)m using the double sideband carrier suppression (DSB-CS) modulation method for a comparison with the results at 1.55 \(\upmu\)m/1.31 \(\upmu\)m wavelengths tested using the same method at the same frequency. In the experiment, the light side band power (\(\sim\)7.7 dBm) output from the Mach-Zehnder Modulators (MZMs) was realized at those three different regions.