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Advances in vortex lasers with simplified robust designs that provide high purity vortex light with high power and efficiency, will help drive progress in material processing, communication and quantum technologies. We demonstrated in our earlier work [1] , [2] that a conventional laser, lasing on the fundamental Gaussian mode, can be converted to have a vortex output using a modified Sagnac ring, or vortex output coupler (VOC). This VOC provides handedness switchable LG 0±1 output, with variable output coupling. Here we report the highest average power vortex laser, to the best of our knowledge, operating in CW and Q-switched modes.

Here we compare the efficiency and beam parameters of different single-bounce Nd:YLF 4 resonators. A total of five cavities were made by changing both, the curved mirror and the output coupler of the resonator. The best configuration resulted in a cavity that generated a record optical-to-optical efficiency of 63.3% and 66.4% of slope efficiency, with a peak output power of 64.5 W for a pumping power of 101.8 W at 797 nm.

We report a new method for electronic control of lasing regimes in lasers with compact all-fiber cavities. The method relies on incorporation of a waveguide electro-optic switch which plays the dual role as a variable output coupler and an intracavity intensity modulator. We explored this method in a laser comprised of a semiconductor optical amplifier and an all-fiber cavity. Nanosecond pulse lasing at 1540 nm was achieved in mode-locked, harmonically mode-locked, and cavity-dumping regimes at different repetition rates on kHz and MHz scales. This method is suitable for different fiber lasers and will allow even picosecond pulse lasing with an appropriately fast switch.

A compact X-band power booster TWT was designed and developed for space applications that provides minimum of 350W of peak RF output power with 25% duty over a bandwidth of 800MHz with RF efficiency of 22% and minimum gain of 27 dB. This TWT uses an electron gun operating at a cathode voltage of 6 kV and current of 275 mA with beam filling factor of 0.5. The electron beam is focused using PPM structure with peak field of 2600G generated using Sm2Co17 magnets. The SWS comprises tungsten tape helix supported by three azimuthally, symmetrically placed T-shaped APBN support-rods inside a metallic envelope. The dimensions of SWS were derived using the in-house parametric codes and optimized using Eigen-mode solver of CST Studio to achieve the required dispersion characteristics. The beam-wave interaction analysis was carried out using the in-house 1D-codes and was optimized using 3D PIC simulations. The SWS employs positive velocity taper near the output coupler in order to enhance RF interaction efficiency and to reduce the second harmonic content. The length of the SWS is around 93 mm. A 3-stage depressed collector is used to enhance the overall efficiency of the TWT. A prototype TWT is developed and tested for performance and has achieved overall efficiency of 45% with TWT length of 250 mm and weight of 980 grams. This TWT is subjected for operational temperature cycling at +70°C and -20°C and also random vibration to verify the structural integrity and has met the requirements.

A low-voltage backward wave oscillator based on staggered double vane structure is designed in this paper and a novel straight-waveguide input/output coupler is also proposed. The high-frequency characteristics and transmission characteristics of the structure are calculated and the results of the circuit show that the reflection coefficient is below -10dB in the frequency range of 250-300GHz. The beam-wave interaction is also carried out and the output power is greater than 20mW within the frequency range of 290GHz to 300GHz, which the corresponding operating voltage is 3800V to 4500V. And a maximum output power of 2W is reached at 300GHz.

In this study, the output power and wavelength tuning performance of ring type erbium doped fiber laser (EDFL) were examined theoretically and experimentally. In order to investigate the effects of parameters such as erbium doped fiber (EDF) length, output coupler ratio, erbium ion density, pump power on the performance of ring-type EDFL, two-level model of EDFL was numerically analyzed and experimental characterization measurements were performed using an EDFL setup. Numerical results, which are in good agreement with the experimental measurements, showed that optimization of the parameters is extremely important for ring type EDFL performance. With the obtained optimum parameters, a moderate output power level (~+4.5 dBm) and a wide wavelength tuning range (~80 nm) covering C+L bands have been achieved.

This work presents the design of a high power, two-stage, wideband, balanced power amplifier (PA) implemented in a 90 nm SiGe BiCMOS technology. Asymmetric coupled-line couplers were employed at the input and output of the circuit for impedance transformation and quadrature signal splitting and combining. The design achieves 17.3 dB small-signal gain with 41.8 GHz 3-dB bandwidth from 28.1 GHz to 69.9 GHz. To obtain high output power, two novel Wilkinson baluns were included, together with the output coupler, to achieve an overall 4-way differential power combining. A 24.4 dBm saturated output power (P SAT ) is achieved with a 22.0 GHz 1-dB P SAT bandwidth covering from 45.0 GHz to 67.0 GHz. The circuit shows a peak power added efficiency (PAE) of 14.2% at 60 GHz and the peak PAE is above 11.50% across the 1-dB P SAT bandwidth. The two stages adopt common-emitter power cells with the first stage biased at 2.0 V and second stage at 1.8 V. The chip size is 1.22 mm2 including bondpads.

In this paper, the input and output couplers are designed and simulated for a frequency range of 14.9 to 15.4 GHz Ku-band over 1 kW power. The input coaxial coupler section comprises of an impedance transition with the coaxial ceramic window of 99.5% alumina to handle the maximal input power less than 1 watt. In the output coupler, coaxial to waveguide (WR-62) progression is used to handle the maximal power from the TWT. Initially, the couplers are designed theoretically. Further, the designs are optimized by commercially available 3-D electromagnetic simulation software, micro-wave studio (MWS), computer simulation technology (CST). The Eigen mode simulations for both the couplers give the voltage standing wave ratio (VSWR) value of less than 1.20.

This paper discusses the design and development of compact high-efficiency pulsed X-Band helix Travelling Wave Tube (TWT) delivering a minimum of 250W of peak output power over a bandwidth of 800 MHz with RF efficiency of 20% and minimum gain of 27 dB. Initial Electron-wave analysis was carried out using 1D-codes and was optimized using 3D PIC Solver in CST Studio. This TWT employs positive velocity taper near the output coupler in order to enhance RF interaction efficiency and reduce the second harmonic content at the output power from the device. The length of the SWS is around 95 mm with overall packaged TWT length of around 220 mm. Single stage depressed collector is used in the TWT and overall efficiency of 35% is achieved. Two prototype TWTs were developed and tested for performance.

In this paper, the planar three-beam is adopted to investigate the potential of high output power and broad bandwidth for W-band staggered double-vane slow wave structure (SDV-SWS) travelling wave tube (TWT). A simple input/output coupler is proposed for the three-beam SDV-SWS, which consists of non-taper structures for the TWT. The high frequency simulations are used to design SWS and broadband diamond output window. With the center frequency of 95 GHz, the high transmission frequency range of 80 GHz to 114 GHz can be achieved for the super bandwidth. The 3D PIC simulation for the W-band SDV-TWT combined with the broadband diamond output window are designed and optimized for its output characteristics with the sensitively and stability thoroughly. With the beam voltage of 22 kV and beam current of 3 × 0.15 A, the output power can be reached above 1000 W within the frequency range of 89GHz and 111 GHz. The highest output power is obtained at 108GHz of 1141 W, with the gain of 43.5 dB, the efficiency of 11.5%, and 3 dB bandwidth of 28 GHz. Thus, the physical model designed in this paper can be used as the engineering prototype to develop the high power and broadband SDV-TWT in W-band in future.

In this study, we construct a theoretical model to analyze the output characteristics of a pulsed Ho3+:BaY 2 f 8 (Ho3+:BYF) laser by taking both energy transfer up-conversion (ETU) and cross relaxation (CR) processes into account. The influences of the pump energy, pulse width, reflectance of an output coupler (OC), crystal length, and Ho3+ doping concentration on the physical performances are investigated in detail for an end-pumped structure. The calculation results reveal that the proper length of a Ho3+:BaY 2 f 8 crystal is from 5 to 10 mm for the Ho3+ doping concentration of 10–40 at.%. We also deduce that a high output can be obtained when the Ho3+ doping concentration is selected as 30 at.%. It has been demonstrated that the relaxation oscillation of a Ho:BYF laser can be observed for a pulsed pump source. We can see that the threshold peak power of a pump light source decreases with the increase of the pulse width. The conclusions might be useful for the realization of a pulsed mid-infrared Ho3+: BYF laser.

A new technique of radially polarized laser beams generation by suppressing the main mode of a gas laser in the case of a Brewster prism coupler placed in the laser cavity as a source of controlled intracavity losses and as a laser beam output coupler is proposed. The suppressing of the main intracavity mode leads to domination of the transverse electromagnetic (1,0) mode. Its electric field distribution has mirror symmetry for intensity and polarization. The obtained radially polarized beam is the result of the superposition of the outputted by the prism input face beam with one been rotated 90 degrees with mirrors.

A femtosecond pulsed laser has an extremely short pulse width and high peak power and is used for the field of microfabrication. On the other hand, laser cutting and drilling requires picosecond pulsed laser with high pulse energy. In general, a diffraction grating or a band pass filter is used to control pulse width. However, these compornents are not affordable and the optical system with them becomes complicated. Therefore, we have developed all fiber variable pulse width laser by applying a coherent resonator coupling technology that increases the output power by coupling the phases of longitudinal modes generated by sharing an output coupler in multiple laser resonators. In the coherent resonator coupling, resonator length diffarence decreases coupled longitudinal modes and narrows spectral width (Δν). Thus, pulse width (Δί) is widened according to equation (1).

The thermo-opto-mechanical strength of Yb:YAG gain media has enabled average power scaling of solid state lasers to the multi-kilowatt regime in thin-disk (TD) geometry. However, the relatively narrow emission bandwidth of Yb:YAG is an important limitation, restricting obtainable pulsewidths and tunability. Hence, research for alternative broadband TD laser (TDL) materials with suitable thermo-opto-mechanical parameters has been an active field. Part of this effort is focused on other Yb+3-doped gain media; however, with their ultra broad emission bandwidths, transition-metal-doped laser media are other potentially attractive alternatives. In that respect, the recent TDL work with Ti:Sapphire is quite interesting [1]. However, due to its low gain product (product of fluorescence lifetime and emission cross section) and its susceptibility for nonradiative transitions at elevated temperatures, Ti:Sapphire poses many challenges for power scaling even in TD geometry, resulting in limited continuous-wave (cw) laser performance (∼13% slope efficiency, 7.5 W output power using a 0.1% output coupler) [1]. Note that, due to the low gain of the system, the aforementioned performance is only possible with the usage of a high-quality factor cavity with minimal intracavity losses.

High-power ultrafast laser sources constitute a key technology to a wide variety of scientific and industrial applications that benefit from the combination of high average power and sub-ps pulse duration. While coherently combined amplifier systems now deliver kW-level average powers [1], ultrafast thin-disk lasers (TDLs) remain of considerable interest as compact, low-noise laser sources delivering multi-hundred-Watts with excellent beam quality. These oscillators are usually modelocked using either of two well-established techniques: SESAM or Kerr-lens modelocking (KLM) [2]. Recently, we demonstrated the first TDL modelocked using the frequency-doubling nonlinear mirror (NLM) [3, 4]. This technique relies on the combination of an intracavity χ(2) crystal used for second-harmonic generation (SHG) and a dichroic output coupler mirror (OC) that is highly reflective for the second harmonic (SH) and partially reflective for the fundamental wave (FW) (Fig. 1b). The NLM device (SHG crystal + dichroic OC) thus provides a saturable reflectivity (Fig. 1f) enabling modelocked operation. Our first NLM-modelocked TDL delivered 323 fs at a repetition rate of 17.8 MHz (Fig. 1a) [3].

Ultrashort-pulsed laser sources with repetition rates over 1 GHz are important for applications in telecommunications, frequency metrology and in fundamental physics. Here we present an approach to build-up compact ultrafast single-mode waveguide lasers with gigahertz repetition rate using graphene saturable absorber mirror (GSAM) as the output coupler [1, 2]. In particular, due to very efficient coupling of pump light into the femtosecond laser inscribed waveguide [3] and wavelength insensitive properties of graphene this approach demonstrates the possibility to achieve simultaneous generation of

In this paper, we propose and experimentally demonstrate a fiber laser operating at single azimuthally polarized mode (TE 01 mode) and stably outputting cylindrical vector beam. We use the self-designed ring-core fibers, which have an annular guided mode layer, to break the degeneracy of LP 11 mode and make TE 01 mode propagate stably in the fibers. A pair of fiber Bragg gratings which is inscribed on the passive ring-core fibers is used as the reflector and output coupler. A mode selective device is used to introduce different propagating losses for different modes, which is fabricated by corroding the fiber clad and depositing a layer of gold in the fiber surface. The slope efficiency of the fiber laser is 7.5% and its mode purity is about 92.4%. We believe that this single TE 01 mode fiber laser could be practically applied in a wide range of applications.

Thulium doped solid state lasers are well-known sources of radiation tunable around 2 pm. Obtainable wavelengths cover important spectral regions such as absorption lines of water, characteristic spectra of some gases or the atmospheric transmission bands. Tunable Tm3+ lasing was accomplished using various matrices, such as YAG, YAP or YLF [1]. Recently an interest re-emerged in the mixed garnets as host materials. Their multi-site structure induces broadening of spectra of the active ions, improving overlap with pumping diode emission and extending emission spectra and tunability [2]. In this submission, Tm3+ doped mixed gadolinium-gallium-aluminium-garnet Gd 3 (Ga 5-x Al x )O 12 (GGAG) is investigated. Focus is given to the Tm3+ concentration dependence of lasing and tunability parameters as a follow-up work to the first Tm:GGAG lasing report with one Tm3+ concentration sample [3]. The Tm:GGAG crystal was grown using Czochralski method in a slightly oxidative atmosphere. Five plane-parallel face-polished Tm:GGAG samples with concentrations varying from 1.4 at.% to 8.4 at.% (Tm/Gd) and thicknesses ranging from 2.7 mm to 3.6 mm were cut from the crystal. The samples were longitudinally pumped by fiber coupled (core diam. 400 pm, NA = 0.22) laser diode at wavelength 785 nm in QCW regime (pulse length 5 ms, repetition rate 10 Hz). The 145 mm resonator consisted of a flat pumping mirror (HR @ 1.85–2.11 pm, HT @ 0.78 pm) and concave output coupler (r = 150 mm, R = 97.5 % @1.8–2.10 pm). For the wavelength tuning, 1.5 mm thick birefringent SiO 2 plate was inserted in the cavity at the Brewster's angle.

This paper presents the design and simulation results of an output coupler for a gyro-amplifier operating at THz frequencies. The combination of a smoothly profiled horn and multilayer microwave window allow for the almost total conversion of the TE 11 mode to the Gaussian-like HE 11 mode while forming a vacuum tight seal with very low reflections. This assembly operates over the 360–384 GHz frequency range.

We report on a high-peak-power acousto-optically Q-switched Er:Y2O3 ceramic laser operating at room temperature. Stable pulses with a duration of 41-190 ns (FWHM) are generated at approximately 2.7 μm with the repetition rate varying from 0.3 to 10 kHz. The peak power at 0.3-kHz repetition rate is approximately 7.3 kW. An average output power of over 320 mW is generated at a repetition rate of 10 kHz using an output coupler with a transmission of 8%.

In this letter, we report a diode-end-pumped continuous wave (CW) and passively Q-switched Ho,Pr:LLF laser at 2.95 μm. A maximum CW output power of 98 mW was achieved. The highest output power of 58 mW was radiated with a pulse duration of 818.8 ns and a repetition rate of 71.05 kHz. Even shorter pulse duration of 731.5 ns was obtained at a minor output coupler transmission.

In this work, a combined power amplifier (PA) using branch-line couplers is designed over 3.4-3.8GHz covering 11% fractional bandwidth. The proposed power amplifier consists of a 5dB input coupler for input power splitting, a 10W amplifier, a 25W amplifier and a 6dB output coupler for power combination. The input matching networks and output matching networks of two harmonic-tuned mode sub-PAs are designed by using stepped-impedance matching network topology. The measured combined power amplifier shows 65%-70% drain efficiency at $46.1-46.5 dBm$ saturated output power, and the small signal gain is more than 10dB.

The paper represents the design and implementation of a RF pill box window, that will be used in BWO output coupler at a frequency of 100 GHz. The design and simulation has been carried out using CST microwave studio. In our proposed design we have attached a circular alumina disc, which is sandwiched between two circular waveguide. The alumina disc is lossy in nature and 99.5% pure with dielectric constant of 9.9. The disc has a thickness of $480\ \mu \mathrm{m}$ and radius of $1600\ \mu \mathrm{m}$ . The circular waveguide have thickness of $1144\ \mu \mathrm{m}$ and $924\ \mu \mathrm{m}$ in input side and output side respectively. Both the end of the circular wave guide is terminated by rectangular wave guide of standard dimensions. We have used WR 8 dimension for the rectangular waveguide. The obtained return loss is −34.91 dB and insertion loss is −0.0084 dB at 100 GHz. When the single side tapered coupler is coupled with the RF pill box window we have attain a return loss of −17.19 dB and insertion loss of −0.0835 dB at 100 GHz.

A vertically curved Si surface optical coupler for high-numerical-aperture optical fibers with 5-μm-mode-field-diameter was fabricated. The dome-like SiO 2 coupler-top could be successfully formed, and the fabricated coupler showed optical coupling with loss of 5.2 dB and the 0.5-dB bandwidth of 110 nm.

A novel graded index (GRIN) based substrate integrated waveguide (SIW) directional coupler is proposed for bandwidth enhancement. The suppression of higher order modes in the coupling region of the directional coupler is achieved by reduction in the permittivity in the coupling region by the utilization of GRIN substrate. An enhancement in the fractional bandwidth of 7% is achieved by proposed directional coupler based on GRIN SIW substrate as compared to the conventional SIW based coupler. The proposed coupler prototype bandwidth is 49% (8.5 GHz–14GHz).

In the past, we investigated degenerate cavity lasers (DCL) which allows manipulation of both near-field and far-field properties of the output beam. The DCL was comprised of a gain medium, two lenses in a 4f telescope configuration, an output coupler at one end and a back mirror at the other end. With the DCL we investigated topological defects in arrays of coupled lasers[1], simulation of classical spins arrays in a frustrated geometry[2], beam focusing after scattering media[3], and lasers with controllable coherence functions for speckles reduction[4]. In these investigations, the DCL usually included metallic masks of holes and filters that had to be specifically designed and fabricated for each application.

In this paper a new realization of a wideband waveguide hybrid coupler is proposed, which can be realized as a low-cost metallized injection-molded component. A key requirement for low costs is a split-block suited design approach. For that reason, the waveguide ports are stacked in the E-plane. The coupling mechanism is explained in a narrowband approach. By expanding the coupling region in the H-plane, the approach is optimized concerning bandwidth. At 160 GHz a measured bandwidth of 23% is achieved with an isolation better than 20 dB and a very low insertion loss.

The Load Modulated Balanced Amplifier (LMBA) uses a control signal (CSP), injected to the normally terminated port at the output coupler of a balanced amplifier (BA), to modulate the BA transistor's impedance. The hybrid circuit demonstrator described here uses metal-backed multilayer organic substrate and GaN discrete devices. Maximum output power levels above 39.5 dBm are achieved at around P3dB. DE above 60% is seen between 4.5 and 7.5 GHz for power back-off to 7 dB with a fixed CSP of 1 W, and the bias between 18 to 28 V.

A 120° optical hybrid based on 3× multimode interference coupler is reported. The device exhibits less than 10° phase deviation over 55 nm in the C- and L-band.

Application of active disks reduces thermally induced optical effects in powerful solid-state lasers significantly [1]. The next step to improve the quality of output laser emission together with increasing of the output power may be done while using multi beam pumping and degenerate laser cavity configuration [2]. The resonator should be designed to cover in series of all the pumped areas in the active disk with intracavity beam [2].

A low-cost and low-loss directional coupler implemented in the Silicon Image Guide (SIG) platform for high-end millimeter-wave and THz integrated systems is proposed. A novel idea of supporting beams is used for facilitating the high precision fabrication of such a monolithic structure. A 3-dB coupler is designed and simulated for working at the centre frequency of 150 GHz. The simulated average phase unbalance of the coupler within the range of 145–155 GHz is less than 1 degree. The proposed coupler is fabricated using a fast and mask-free laser micro-machining process. The measured insertion loss and 1-dB bandwidth of the coupler are

For rapid wavelength tuning in optical parametric oscillators (OPOs), a mandatary requirement for many applications including spectroscopy and trace gas sensing, the use of crystals with fan-out grating design at a fixed temperature has been a potential approach, as it is a fast process compared to temperature tuning. In the continuous-wave (cw) regime, this technique has been successfully deployed using MgO:PPLN [1]. However, for direct pumping in the green to generate wavelengths 1 =7.8–9.5 μm, Λ2=9.4–11.5 μm). The OPO is configured in ring cavity with two concave mirrors (r=-100 mm), a plane mirror, and a plane output coupler for the signal. The single-pass idler is separated from the pump using a dichroic mirror.

Here we present the study of the output characteristics of a semiconductor laser diode with a circular ridge waveguide resonator and two directional Y-junction coupler. Spatial soliton wave guiding due to optical nonlinearity was observed. Multi-stages lasing threshold which related to hybrid resonators of soliton waveguide was identified by Light-current (L-I) measurements and spectral analysis of the emission from each Y-junction coupler. Investigation of the detailed modes switching mechanism based on four waves mixing to explain the formation of spatial soliton cavity and its effect to the asymmetric output characteristic has presented.

A computational study on after cavity interaction (ACI) in a 140 GHz gryotron for fusion research has been performed using a 3-D conformal finite-difference time-domain (CFDTD) particle-in-cell (PIC) method. The ACI, i.e., beam wave interaction in the non-linear uptaper after the cavity has attracted a lot of attention and been widely investigated in recent years. In a dynamic ACI, a TE mode is excited by the electron beam at the same frequency as in the cavity, and the same mode is also interacting with the spent electron beam at a different frequency in the non-linear uptaper after the cavity while in a static ACI, a mode interacts with the beam both at the cavity and at the uptaper, but at the same frequency. A previous study on the dynamic ACI on a 140 GHz gyrotron has concluded that more advanced numerical simulations such as particle-in-cell (PIC) modeling should be employed to study or confirm the dynamic ACI in addition to using trajectory codes. In this work, we use a 3-D full wave time domain simulation based on the CFDTD PIC method to include the rippled-wall launcher of the quasi-optical output coupler into the simulations which breaks the axial symmetry of the original model employing a symmetric one. A preliminary simulation result has confirmed the dynamic ACI effect in this 140 GHz gyrotron in good agreement with the former study. A realistic launcher will be included in the model for studying the dynamic ACI and compared with the homogenous one.

This paper presents electromagnetic design of coaxial cavity for high power X-band coaxial magnetron. The initial dimensions of the cavity have been calculated by solving transcendental equation using graphical method. The eigenmode simulation has been carried out by using CST MW Studio. It is found that TE011 mode occurs at 9.3 GHz. Output coupler of cavity is designed to launch RF power into WR112. Proposed design is analyzed in terms of performance parameters i.e., unloaded, loaded, and external quality factors. Circuit efficiency and coupling coefficient are analyzed by varying critical geometrical parameters. Unloaded Q factor of 13108 is achieved for circuit efficiency of 93%.

A quasi-optical (q.o.) mode converter has been designed for the MW-level dual-frequency gyrotron which is under development for the upgrade of the electron cyclotron (EC) system of the TCV tokamak. The gyrotron design is essentially based on modifications of the W7-X gyrotron [1]. The launcher of the output coupler has been synthesized to adapt the geometry of the quasi-elliptical mirror with same size as in the W7-X gyrotron for both operating modes (TE17,5 @ 85GHz, TE26,7 @ 126GHz). The simulation results show that high conversion efficiencies and low stray radiations in the q.o. system can be achieved.

A 340 GHz staggered double-vane traveling wave tube (TWT) is designed in this paper. The high-frequency characteristics of the slow-wave structure are analyzed. And the results of transmission characteristics indicate that the S 11 is below −15 dB in the frequency range of 330-350 GHz, with ridge loaded waveguide input/output coupler and rectangular attenuator. The particle-in-cell simulation is also calculated and the results indicate that the tube can produce over 8 W output power in the frequency range from 320 to 345 GHz with an operating voltage of 21.3 kV, current of 0.04 A, and an input power of 10mW. The corresponding gain is more than 29dB. Finally, with one-step velocity-tapered method, the output power has been increased about 43% at 340 GHz with respect to the previous value.

A novel vertical grating coupler design and optimization is presented to enable coupling of mid-infrared light into silicon-on-insulator integrated optical gas sensor circuit. The target wavelength is around 3100 nm, where the acetylene gas and a group of hydrocarbons possess a strong absorption. The grating coupler dimensions are optimized according to the limits of a standard and low-cost fabrication technology for silicon on silica by Interuniversity Micro Electronics Center (IMEC). The design simulations were carried out using 2D and 3D finite difference time domain simulation in the mid-infrared. The optimized coupling efficiency is found to be approximately 10% and the 3-dB bandwidth of the coupler is approximately 160 nm depending on the grating fill factor. The reported bandwidth is compatible with the gas sensing application

A novel application of signal-interference technique to branch-line coupler design is proposed for miniaturization and wideband harmonic passband suppression. The coupler's second, third and fourth harmonic passband responses are attenuated due to a pole at each of these harmonics. Design equations and graphs are provided using lossless transmission line model. A prototype coupler, having a compact (λ g /6)2 area, that is 44.4% of the (λ g /4)2 conventional coupler area, is fabricated in microstrip form for validation purposes. The input matching, isolation, amplitude and phase balance bandwidths of the proposed coupler are comparable to those of the conventional coupler.

In this paper the practical design of the VHF quadrature hybrid coupler is presented. Knowing, before the production, what are the conditions that coupler has to satisfy, has enabled us to acquire, through computer simulation, the dimensions of the coupler that was later produced. Values of the S-parameters of the simulated coupler are being compared, to values of the S-parameters of the produced coupler to validate the design process. Coupler is designed as a broadside-coupled suspended strip-line coupler, for frequency range from 150 MHz to 200 MHz, with central frequency at 175 MHz. It consists of two overlapping brass strips of equal widths, placed on the top and bottom surface of a Teflon substrate, which is sandwiched between the top and bottom of an aluminum casing and separated from them by air layers of equal thickness. Purpose of the coupler is to combine two input signals, ports 1 and 4, in quadrature, who each have 16 KW of power, in to an output signal, port 2 or 3, of 32 KW.

The design of two fundamental mode rectangular to circular waveguide mode converters are presented. The waveguide transitions are optimized for operation as an input coupler on a 372 GHz gyro-TWA for Dynamic Nuclear Polarization (DNP) enhancement of NMR imaging. A T-junction input coupler and a multiple hole directional coupler were optimized for operation between 360–384 GHz. The T-junction coupler and the multiple hole coupler exhibited bandwidths of 10% and 35% respectively with a high coupling factor of > −1 dB.

The laser resonator with the infinitely adjustable of output light is represented. Adjustment is performed in a wide range. The diameter of the laser output beam is changed at the adjustment. This resonator suitable for lasers of a wide range of frequencies, including for terahertz lasers.

Two designs of fundamental mode rectangular to circular waveguide TE 10 to TE 11 mode converter are presented. The waveguide transitions are optimized for operation as an input coupler on a 372 GHz gyro-TWA for Dynamic Nuclear Polarization (DNP) enhancement of NMR imaging. A T-junction input coupler and a multiple hole directional coupler were optimized for operation between 360–384 GHz. The T-junction coupler and the multiple hole coupler exhibited bandwidths of 10% and 35% respectively with a high coupling factor of > −1 dB.

In order to design couplers based on side-polished photonic crystal fiber (SPPCF), we made the simulation and calculated the polished angle. A model of coupling region of SPPCF coupler was established. The optical propagation characteristics of SPPCF coupler was calculated with different angles by using the software Rsoft. The simulation shows that light field appeared alternately between two optical fibers of coupler and there was coupling effect. When the angle was 0°, it could provide the best design for the objective coupling ratio of 50%, because the relatively longer coupling period gives more convenience to fabricate a PCF based fiber coupler.

We report on first nonlinear mirror mode-locked praseodymium based solid-state laser. As an active medium, the Pr:YAlO 3 crystal was used. For mode-locking, a nonlinear BBO crystal together with a properly designed dichroic mirror were employed to form an output coupler with intensity dependent reflection. Using 1W InGaN pump laser diode, 22 mW of mean output power with pulse duration and repetition rate of ∼250ps and 105 MHz, respectively, was demonstrated at 747 nm wavelength.

An output power of CO-lasers has been studied for operation at room temperature of the cooling running water from +7 to +16°C. A cw output power of 41 W for stable resonator and 21 W for unstable resonator has been achieved. The new configuration of hybrid waveguide-unstable optical resonator with the external additional mirror for the lasers is proposed and realized. We carried out experiments about the possibility of the optimization of the coupling coefficient of optical resonator with the aid of the external mirror, that is plane-parallel plate with different reflection coefficients.