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The relative intensity noise (RIN) behavior of coherently combined DFB laser array by injection locking is experimentally investigated. A monolithically integrated four-element DFB laser array with a splitter and an output coupler is fabricated, and the frequency stabilities of the DFB lasers are improved to ensure a stable injection locking of DFB laser array by a master laser. It is demonstrated that the RIN of the coherently combined laser array is reduced by almost 20 dB at low frequencies compared with the free-running state. The results indicate that monolithic integration of DFB laser array under injection locking can help improve the RIN performance by eliminating variation in coupling delays and phase jitters.

Study of multipaction breakdown margins in the output connector of a travelling-wave tube (TWT) is essential for application in satellite-borne systems. A TWT uses a coaxial ceramic window, a coaxial output coupler and / or a waveguide output coupler that are prone to multipaction breakdown boosted by high RF power due to the ion accumulation in critical regions during the transition of the satellite through plasma pockets in space. A detailed procedure for estimating the multipaction susceptibility margins in a TWT using CST studio and analytical equations is presented in this paper, and output couplers of two typical TWTs are analysed and the results are presented.

In this article, we present a new broadband power amplifier (PA) architecture with a back-off efficiency enhancement that supports very wide modulation bandwidths. The unbalanced PA is composed of two cooperating sub-PAs using the Lange couplers as input power splitter and output power combiner. The PA operation is controlled by the transistors' width ratio and coupling coefficients of the Lange couplers. The output power back-off (OPBO) level is given by the transistors' width ratio and coupling coefficient of the output coupler, while the maximum efficiency is achieved at the back-off point. These features provide more design flexibility compared with the conventional Doherty PA, where the OPBO can be set only by the transistors' width ratio, and the maximum efficiency is achieved at the peak power. Using broadband harmonic matching networks, the main and auxiliary sub-PAs operate in the continuous mode to improve efficiency over a broad bandwidth. A fully integrated unbalanced PA, implemented in a 250-nm GaN-on-SiC process, achieves 32.2-34.3-dBm output power, 27%-37% efficiency at peak power, and 27%-40% at 5-6-dB back-off, across 4.5-6.5 GHz. The PA provides 3.7/4.5% (-28.6/-26.9 dB) rms error vector magnitude (EVMrms) and 30% average efficiency for a 256-QAM signal with 100-/200-MHz bandwidth, 7.2-dB PAPR, and 25.5-dBm average output power, without using any predistortion. Science Foundation Ireland Trinity College Dublin (TCD)

The 3.92 μm laser pumped by 888 and 962 nm sources in a high concentration holmium-doped InF3 fiber is predicted and verified by simulation for the first time. Most parameters involved in the numerical model are taken from published results about the fundamental properties of holmium in fluoroindate glasses. The remaining unknown parameters are estimated from published 888 nm single-wavelength pumping experimental data. Simulated results indicate that the dual-wavelength pumping system can give a more powerful output than the single-wavelength pumping system when the total launched power is at the same level. The laser output as a function of the power of each source, as well as several macro factors such as fiber length and output coupler reflectivity, are investigated to find the best condition for higher output. To evaluate the importance and influence of the known interionic energy transfer processes, we analyze the corresponding laser output and changes of population densities of laser upper and lower levels by isolating each process. This investigation gives a preliminary insight into the 3.92 μm laser performance and interionic dynamics of the dual-wavelength pumping system in holmium-doped InF3 fibers.

Disordered crystals have garnered increasing attention as new laser materials because of their broad emission bandwidths. This paper reports a novel Yb-doped strontium yttrium phosphate (Yb:YSr3(PO4)3) crystal with a disordered structure, as well as its crystal growth, structure, spectral properties, and laser performance. The crystal structure (cubic, 3m point group) was refined using the Rietveld method. The absorption cross-section and fluorescence lifetime were determined to be 1.31 × 10−20 cm2 at 976 nm and 1267 μs, respectively. The stimulated emission cross-section was 1.04 × 10−20 cm2 at 1013 nm, with an emission bandwidth of 55 nm. In addition, continuous-wave laser operation was realized using the Yb:YSr3(PO4)3 crystal with different output coupler transmissions, where the obtained maximum output power and slope efficiency were 1.3 W and 61%, respectively. A dual-wavelength regime with wavelengths centered at 1039 nm and 1047 nm (Δν = 2.2 THz) was achieved under certain conditions; thus, this crystal is expected to be employed for developing terahertz sources. In addition, the laser can operate at multiple wavelengths, ranging from 1023 to 1050 nm. The results indicate that the Yb:YSr3(PO4)3 crystal with a disordered structure may be a promising multi-wavelength laser crystal.

We present an EO Q-switched Tm:YAP laser constructed with a periodically poled Mg-doped congruent lithium niobate (PPMgCLN) Bragg modulator. A 2-mm-thick PPMgCLN modulator was adopted, and the internal stress generated in the electric poling process was released by annealing. The peak stress-induced refractive index variance for e-wave was deduced to be 2.29 × 10-5 at 1064 nm. When the absorbed pump power and repetition rate were 13.4 W and 1 kHz, respectively, the laser had a Q-switched pulse energy of 2 mJ, a pulse duration of 60 ns, and a peak power of 33.3 kW. By varying the reflection of the output coupler, output wavelengths of between approximately 1985 and approximately 1940 nm can be selected, making this laser a potential tool for pumping mid-IR sources and biomedical applications.

Yttrium aluminium perovskite YAlO3 (YAP) crystal, doped with rare-earth ions, has been extensively studied as a diode-pumped laser host material. The wide interest to rare-earth ions doped YAP crystals is explained by its good thermal and mechanical properties, high natural birefringence, widely used Czochralski growth method. The aim of this work was to study the Yb3+:YAlO3 crystal as an active medium for high power mode-locked laser.Yb3+-doped perovskite-like aluminate crystals have unique spectroscopic and thermooptical properties that allowed using these crystals as an active medium of high power continuous wave (CW) and modelocked (ML) bulk lasers with diode pumping.growth method. The aim of this work was to study the Yb3+:YAlO3 crystal as an active medium for high power mode-locked laser.In our work spectroscopic properties of Yb:YAP crystal and laser characteristics in CW and ML regimes are investigated. Maximum output power of 4 W with optical-to-optical efficiency of 16.3 % and 140 fs pulse duration have been obtained for Yb:YAP E //c-polarization with 10 % output coupler transmittance. Tunability range as wide as 67 nm confirms high promise of using Yb:YAP crystal for lasers working in wide spectral range.

We investigate the operating modes of diode lasers in the external cavity scheme of spectral beam combining, using the virtual laser-diode array method. We determine the spectral range of the diode array and the watt–ampere characteristics of a single-diode laser for various wavelengths. We experimentally show that by varying the output coupler transmission with the wavelength, one can optimize the generation power of laser diodes in the array and force it to work in different regions of the gain bandwidth of the active medium.

In this article, a potentially pseudoperiodic slow wave structure (SWS) for a broadband, high-power, helix traveling-wave tube (TWT) is studied. The structure considered here suppresses the back-wave oscillations caused by a large working current. These oscillations do not have conventional uniform pitch distributions in the radial dimension; rather, the two configurations studied in this article are a uniform pitch gradient and a conical helix. Through a reasonable design and a large number of calculations, the entire tube consists of four tapered, pitch-varying SWSs. In addition, to achieve an 8–18-GHz broadband, high-power output, a double-ridged waveguide window output coupler is designed, fabricated, and tested. The 3-D electromagnetic simulation software CST STUDIO SUITE is used to verify the performance of the tube. The simulation results show that the potentially pseudoperiodic SWS can adequately suppress the backward-wave oscillations, and the tube is capable of achieving an output power of over 6 kW, even with a very wide bandwidth of 8–18 GHz. Additionally, the electronic efficiency varies from 21.5% to 25.8%. The maximum output power is 7.45 kW, corresponding to an electronic efficiency of 25.8% at 14 GHz.

Exploiting a specially designed Fabry-Perot filter as output coupler, a continuous 1 052 nm and 1 061 nm dual-wavelength laser is realized. The threshold, slope efficiency and maximum power of the 1 052 nm and 1 061 nm dual-wavelength laser are 2.55 W, 17.5% and 571 mW, respectively. The competition and coexistent relationships between 1 052 nm, 1 061 nm and 1 064 nm are analyzed. Involved non-degenerate Stark energy level structures are used to classify dual-wavelength lasers. According to this method, dual-wavelength lasers can be classified as different upper and lower non-degenerate Stark energy levels, the same upper but different lower Stark energy levels, different upper but the same lower Stark energy levels. Representative Nd:YAG dual-wavelength lasers are classified according to this criterion. It is found that the realization of front two type lasers is easy and that of third type lasers is challenging. This method can be used as a level of difficulty reference for the realization of dual-wavelength lasers.

In an effort to realize a compact and integrated ultrafast fiber laser system, we propose a fiber component serving as a wavelength division multiplexer (WDM), output coupler (OC), and mode-locker by a magnetron-sputtering saturable absorber (SA) on a laboratory-tapered coupler. With the function-integrated coupler, an Er-doped mode-locked fiber laser with 112 MHz repetition rate, 286 fs pulse width, and 87 dB signal-to-noise ratio (SNR) is demonstrated. The noise feature of the mode-locked laser is also characterized. To the best of our knowledge, this is the first demonstration of a mode-locked fiber laser based on a WDM/OC/SA integrated device.

To date, terahertz quantum-cascade vertical-external-cavity surface-emitting lasers (QC-VECSELs) have tended to oscillate in only one or two lasing modes at a time. This is due to the fact that the interaction between all of the longitudinal external cavity modes and the QC gain material is mediated through a single metasurface resonance, whose spatial overlap changes little with frequency; this suppresses spatial-hole-burning induced multi-mode operation. In this Letter, a VECSEL external cavity is demonstrated using an output coupler based upon a high-resistivity silicon etalon, which presents a periodic reflectance spectrum that is nearly matched with the external cavity mode spectrum. As the cavity length is varied, a systematic transition between a single/double-mode lasing regime and a multi-mode lasing regime is realized due to the Vernier effect. Up to nine modes lasing simultaneously with a free-spectral-range of approximately 21 GHz is demonstrated. This result provides a path toward the multi-mode operation necessary for eventual frequency comb operation.

A 3X3 plastic optical fiber (POF) twisted coupler has been fabricated as a compact sensor of multiple variables. The POFs are twisted into a combined body and the clad was removed by chemical method. Three LEDs of red, green, and blue colors can be used to shape a broad spectrum. Each led was connected at a different input port of the coupler. Since the twisted coupler makes the coupling of light from the input ports, we have a wide spectrum at each one output port. We develop a different sensor at each one output coupler: mass concentration (At the output-1), and curvature (At the output-2). The multi-sensing proposed in this work can increase the number of sensors as increase the number of output ports, and the bandwidth increase as increase the colors of light sources. On the other hand, we can use a wide spectrum lamp in a single input port and in the same way make multiple sensors in the output ports. The variation is evident in all wavelengths of the spectrum for measurements of sugar concentrations and fiber curvature. However, we can directly associate the sugar concentration variations with the spectrum in a range from 570 to 600 nm; and across the full spectrum for curvature measurements.

We present an ultrathin metasurface working as both a highly reflective wavelength-selective mirror and a high transmittance output coupler for a semiconfocal Fabry-Perot cavity. The numerically optimized 2-μ m-thick metasurface achieves a peak reflectivity of R = 99.35% at ω0 = 94 GHz and peak transmittance of T ≈ 90% at the fourth harmonic (4ω0). Experimental results show that the metasurface FP cavity exhibits comparable quality factors to cavities enclosed by either a copper mirror or Bragg grating mirror. Our work highlights the potential for ultrathin metasurfaces to function as frequency selective mirrors in millimeter or terahertz wave cavities for various applications, such as nonlinear terahertz wave generation, material characterization, and imaging.

A theoretical design of a multi-layer for Nd:YAG mirrors resonator is described in this work. An output coupler was designed and fabricated by successive thin layers to achieve very high transmittance at optical wavelengths around 1064 nm for Nd:YAG mirrors resonator. The different film optical filters were used to control the transmittance and reflectance. The three samples of dielectric materials composed of HfO2/Y2O3, Sc2O3 + MgO, and Ta2O5 + TiO2 were used and compared with each other in transmittance, reflectance, full width at half maximum (FWHM), physical thickness, optical thickness, geometric thickness, and incident angles by the software [1].