Broadband microwave frequency doubler based on left-handed nonlinear transmission lines

A bandwidth microwave second harmonic generator is successfully designed using composite right/left-handed nonlinear transmission lines(CRLH NLTLs) in a GaAs monolithic microwave integrated circuit(MMIC) technology. The structure parameters of CRLH NLTLs, e.g. host transmission line, rectangular spiral inductor, and nonlinear capacitor,have a great impact on the second harmonic performance enhancement in terms of second harmonic frequency, output power, and conversion efficiency. It has been experimentally demonstrated that the second harmonic frequency is determined by the anomalous dispersion of CRLH NLTLs and can be significantly improved by effectively adjusting these structure parameters. A good agreement between the measured and simulated second harmonic performances of Ka-band CRLH NLTLs frequency multipliers is successfully achieved, which further validates the design approach of frequency multipliers on CRLH NLTLs and indicates the potentials of CRLH NLTLs in terms of the generation of microwave and millimeter-wave signal source.     

A GaAs planar Schottky varactor diode for left-handed nonlinear transmission line applications

The left-handed nonlinear transmission line(LH-NLTL) based on monolithic microwave integrated circuit(MMIC) technology possesses significant advantages such as wide frequency band,high operating frequency,high conversion efficiency,and applications in millimeter and submillimeter wave frequency multiplier.The planar Schottky varactor diode(PSVD) is a major limitation to the performance of the LH-NLTL frequency multiplier as a nonlinear component.The design and the fabrication of the diode for such an application are presented.An accurate large-signal model of the diode is proposed.A 16 GHz-39.6 GHz LH-NLTL frequency doubler using our large-signal model is reported for the first time.The measured maximum output powers of the 2nd harmonic are up to 8 dBm at 26.4 GHz,and above 0 dBm from 16 GHz to 39.6 GHz when the input power is 20 dBm.The application of the LH-NLTL frequency doubler furthermore validates the accuracy of the large-signal model of the PSVD.     

Understanding Soliton Wave Propagation in Nonlinear Transmission Lines for Millimeter Wave Multiplication

In this paper, soliton propagation in nonlinear transmission lines (NLTLs) periodically loaded with symmetric voltage dependent capacitances is studied. From the lumped element equivalent circuit of the line we have analyzed the influence of nonlinear shunt reactances on soliton propagation characteristics. It is shown that by increasing the non linearity of the C–V characteristic, a faster separation of input signal into solitons is achieved. The fact that frequency multiplication in NLTLs is governed by soliton formation makes the results of this work relevant to understand the influence of nonlinear loading devices on multiplier performance. Since a heterostructure barrier varactor (HBV)-like voltage dependent capacitance has been considered for the nonlinear devices, this study can be of interest for the design of millimeter wave frequency multipliers loaded with HBVs.     

Effects of Line Parameters on Soliton-Like Propagation in Nonlinear Transmission Lines: Application to the Optimization of Frequency Triplers

In this paper, soliton propagation in nonlinear transmission lines (NLTLs) periodically loaded with heterostructure barrier varactors is studied. From the lumped element equivalent circuit of the line we have analyzed the influence of transmission line parameters (i.e, per-section inductance and capacitance) on soliton propagation characteristics. It is shown that by increasing these parameters, a faster separation of input signals into solitons is achieved. From the point of view of NLTL harmonic generation, this gives additional flexibility to optimize multiplier performance by appropriate circuit design. These conclusions are supported from the analysis of a frequency tripler, where device losses are included.     

Design of Cavities for a Short Pulse Powerful Large Orbit Gyrotron

Designs of cavities for fundamental and high harmonic operation in Large Orbit Gyrotron (LOG) are discussed. The fundamental operation allows one to use beam currents in the range from 200 A to 300 A achieve output power of the order of 9–10 MW at frequency 143.6 GHz. Mode competition calculations show that stable oscillations in the TE^1,4 mode using high beam currents are possible even with the pitch factor 1.3 which is significantly lower than the design value 1.55. For the second harmonic operation, the maximum current used for excitation of the TE^2,4 mode is 60 A and the optimum magnetic field is 7.6 T. A cavity design for fourth harmonic operation using the TE^4,4 mode is also presented.     

Millimeter wave monolithic high electron mobility (HEM) varactor diode-grid frequency tripler arrays

High Electron Mobility (HEM) varactor structures have been studied for millimeter-wave monolithic diode-grid frequency tripler array applications. The improved HEM varactor diode structures provide a highly nonlinear C-V characteristic (i.e., a steep slope of the C-V curve and a large capacitance ratio) which produces high harmonic generation efficiency and reduce the power requirement for efficiently pumping each device. The effects of the light illumination on the C-V characteristics of the Barrier-Intrinsic-N⁺ (BIN) varactor diode have also been studied and the results will be discussed in this paper. In the development of a monolithic diode-grid frequency multiplier array, the low-loss quasioptical configuration is used for the construction of the multiplier circuit. The study of the effects of the light illumination on the C-V characteristics of varactor diode is important in understanding the potential applications of the quasi-optical varactor diode-grid frequency multiplier array circuit.     

400 mW and 16.5% wavelength conversion efficiency at 488 nm using a diode laser and a PPLN crystal in single pass configuration

Continuous wave power of more than 400 mW at 488 nm has been generated by frequency doubling of 2.45 W at 976 nm obtained from a distributed Bragg reflector tapered diode laser. This results in a wavelength conversion efficiency of 16.5% and an electrical-to-optical efficiency of more than 4.5%. We used a 50 mm long periodically poled MgO:LiNbO₃ bulk crystal in single-pass configuration for the second harmonic generation. This is to the author’s knowledge the highest output power and the highest wavelength conversion efficiency at 488 nm generated by a monolithic semiconductor laser device in single pass configuration with a bulk crystal. A deviation from the quadratic dependency of the frequency doubling is explained by the decrease of the beam quality of the fundamental wave.     

New concedpts for high frequency and high power frequency multipliers and their impact on quasi-optical monolithic array design

Varactors have been extensively employed for harmonic generation, where high cut-off frequency is dependent upon small C _min , which is typically achieved using small device active area. However, small area limits the output power. Furthermore, the power and frequency dependences of the series resistance in the epitaxial region degrade the efficiency and cut-off frequency as well. As a result, currently utilized varactors are only officient for relatively low power generation and limited output frequency. Herein, we describe our new approach where by epitaxially stacking single quantum barrier structures, more than an order of magnitude improvement in cut-off frequency and power handling ability may be possible. Alternatively, by combining a Schottky barrier with stacked single quantum barriers, superior performance can also be achieved. These concepts can be readily employed for quasi-optical frequency multiplier arrays, and appear to result in simplified fabrication compared to other devices.The design of high performance quasi optical arrays requires optimization of the passive (metalization) grid as well as the embedded semiconductor devices. Recent work has resulted in an improved impedance model for the standard diode-loaded strip array, including a quantitative estimate of the shunt capacitance introduced across the diode by the discontinuity of the metal strip at the diode site (gap). The value of this capacitance exceeds the predictedC _min for these new devices. We discuss two grid design approaches that can suppress this capacitance.     

All-solid-state CW Nd:GdVO<Subscript>4</Subscript>-LBO red laser under direct 912 nm pumping

We report a red laser at 670.5 nm generation by intracavity frequency doubling of a continuous wave (CW) laser operation of a 1341 nm Nd:GdVO₄ laser under in-band diode pumping at 912 nm. An LBO crystal, cut for critical type I phase matching is used for second harmonic generation of the laser. At an incident pump power of 8.9 W, as high as 347 mW of CW output power at 670.5 nm is achieved. The fluctuation of the red output power was better than 3.7% in the given 30 min, and the beam quality factor M ² is 1.65.     

5.3 W deep-blue light generation by intra-cavity frequency doubling of Nd:GdVO4

We report the efficient compacted deep-blue laser at 456 nm generation by intra-cavity frequency doubling of a continuous-wave (cw) laser operation of a diode-pumped Nd:GdVO₄ laser on the ⁴ F _3/2→⁴ I _9/2 transition at 912 nm. The different long LiB₃O₅ (LBO) crystals, cut for critical type I phase matching at room temperature, are used for second harmonic generation (shg) of the laser. At an incident pump power of 30 W, up to 5.3 W of cw output power at 456 nm is achieved with 15-mm-long LBO (3.8 W with 10 mm-long LBO). The conversion efficiency is 17.7% from pump diode input to second harmonic wave output.PACS 42.70.Hj; 42.55.Xi; 42.65.Ky     

Diode grids for electronic beam steering and frequency multiplication

Loading a grid with diodes offers the possibility of two-dimensional control of millimeter waves that is analogous to holography and nonlinear optics. These grids are attractive because they are suitable for monolithic integration with gallium-arsenide Schottky diodes and for high-power operation. Here we present grid designs for electronic beam-steering and harmonic generation. The beam-steering grid is a programmable reflector, where the diode bias controls the phase shift of the reflection. The variation of the phase across the grating sets the direction of the reflected beam. The reflection loss in computer simulations is 3dB at 90GHz. The harmonic-generating grid acts as a nonlinear reactive surface, where the nonlinear capacitance of the diodes produces the harmonic frequencies. Quasioptical filters select the desired harmonic. Computer simulations predict that a 65GHz-to-130GHz doubler would have an output power of 0.56W/cm² and a conversion efficiency of 35%.     

Characterization of laser-diode end-pumped intracavity frequency doubled, passively Q-switched and mode-locked Nd:YVO4 laser

Simultaneous Q-switching and mode-locking in a laser-diode end-pumped intracavity frequency doubled Nd:YVO₄/KTP green laser using Cr⁴⁺:YAG saturable absorber is experimentally demonstrated. The influence of the initial transmission (T₀) of the Cr⁴⁺:YAG crystal on the Q-switched mode-locked green pulses as well as on the average green power is characterized by using Cr⁴⁺:YAG crystal with various T₀. The effect of T₀ on the pulse build-up time in intracavity second harmonic configuration is theoretically investigated. It was found that the depth of modulation for the mode-locked pulses is greatly improved at the second harmonic wavelength as compared to that for the fundamental wavelength. The average pulse duration of the individual mode-locked pulse for the second harmonic beam measured to be less than 500 ps with a repetition rate of 400 MHz.     

在BBO中获得230.8—223.2nm高功率和频输出

用Q-YAG泵浦的Rh·6G染料激光在一块45°切割的β-BaB₂O₄(BBO)晶体中倍频,产生294.8—282.5nm范围的连续调谐输出,其能量为8mJ(在285nm处)。用这个倍频光与泵浦染料后剩余基波(1064nm)在另一块45°切割的BBO中和频,已获得230.8—223.2nm范围的连续调谐输出,其能量为120μJ,相应的峰值功率为12kW。还简述了获得高功率和频输出的关键技术。     

Diode pumped Nd:Lu<Subscript>0.5</Subscript>Y<Subscript>0.5</Subscript>VO<Subscript>4</Subscript>-LBO red laser at 671 nm

We report a efficient compact red laser at 671 nm generation by intracavity frequency doubling of a continuous wave laser operation of a diode pumped Nd:Lu_0.5Y_0.5VO₄ laser on the ⁴ F _3/2-⁴ I _13/2 transition at 1342 nm. An LBO crystal, cut for critical type I phase matching at room temperature is used for second harmonic generation of the laser. At an absorbed pump power of 17.8 W, as high as 2.25 W of continuous wave output power at 671 nm is achieved with 10-mm-long LBO. The optical-to-optical conversion efficiency is up to 12.6%, and the fluctuation of the red output power was better than 3.6% in the given 30 min.     

HIGH CONVERSION EFFICIENCY TANDEM KTP FREQUENCY DOUBLER

The two-piece tandem KTP frequency doubler with mutually perpendi-oular KZ planes has been studied both theoretically and experimentally.Its conversionefficiency of second harmonic generation(SHG)exceeds 80% and the dynamic range ismuch greater than that of monolithic KTP doubler at the laser power used in theexperiments.The experimental result shows that this doubler has excellent performancesand the second harmonic beam is elliptically polarized.     

Continuous-wave Nd:GdVO<Subscript>4</Subscript>/LBO laser at 541.5 nm under diode pumping into the emitting level

We report a green laser at 541.5 nm generation by intracavity frequency doubling of a continuous wave (cw) laser operation of a 1083 nm Nd:GdVO₄ laser under 880 nm diode pumping into the emitting level ⁴ F _3/2. A LiB₃O₅ (LBO) crystal, cut for critical type I phase matching at room temperature is used for second harmonic generation of the laser. At an incident pump power of 17.8 W, as high as 2.52 W of cw output power at 541.5 nm is achieved. The optical-to-optical conversion efficiency is up to 14.2%, and the fluctuation of the green output power was better than 3.6% in the given 30 min.     

Efficient Nd:Y0.5Gd0.5VO4-KTiOPO4 green laser under diode pumping into the emitting level 4F3/2

We report a green laser at 532 nm generation by intracavity frequency doubling of a continuous wave (cw) laser operation of a 1064 nm Nd:Y_0.5Gd_0.5VO₄ laser under diode pumping into the emitting level ⁴ F _3/2. A KTiOPO₄ (KTP) crystal, cut for critical type-II phase matching at room temperature is used for second harmonic generation (SHG) of the laser. At an incident pump power of 17.8 W, as high as 4.21 W of cw output power at 532 nm is achieved. The optical-to-optical conversion efficiency is up to 23.6%, and the fluctuation of the green output power was better than 2.8% in the given 30 min.     

Continuous wave Nd:LuVO<Subscript>4</Subscript>-LBO blue laser under direct 888 nm diode laser pumping

We report the efficient blue laser at 458 nm generation by intracavity frequency doubling of a continuous wave (CW) laser operation of a diode pumped Nd:LuVO₄ laser on the ⁴ F _3/2 → ⁴ I _9/2 transition at 916 nm. An LiB₃O₅ (LBO) crystal, cut for critical type I phase matching at room temperature is used for second harmonic generation of the laser. At an incident pump power of 18.2 W, as high as 1.73 W of continuous wave (CW) output power at 458 nm is achieved. The optical-to-optical conversion efficiency is up to 9.5%, and the fluctuation of the red output power was better than 3.5% in the given 30 min.     

All solid-state CW Nd:GdVO<Subscript>4</Subscript>-GdCOB laser at 670 nm

We report the efficient compact red laser at 670 nm generation by intracavity frequency doubling of a continuous wave laser operation of a diode pumped Nd:GdVO₄ laser on the ⁴ F _3/2 → ⁴ I _13/2 transition at 1340 nm. An GdCa₄O(BO₃)₃ (GdCOB) crystal, cut for critical type I phase matching at room temperature is used for second harmonic generation of the laser. At an incident pump power of 18.2 W, as high as 1.32 W of continuous wave (CW) output power at 670 nm is achieved with 15-mm-long GdCOB. The optical-to-optical conversion efficiency is up to 7.3%, and the fluctuation of the red output power was better than 3.5% in the given 30 min.     

可调频高功率宽谱微波的产生和辐射

 设计了一种可调谐频率的高功率宽谱微波辐射装置,装置由可调谐长度的1/4波长低阻同轴谐振器、环形开关、电容耦合器和宽谱辐射天线组成,中心频率调谐为200～400 MHz。低阻传输线与环形开关构成1/4波长短路谐振器,它产生的宽谱微波振荡通过耦合器耦合到宽谱辐射天线上辐射,而耦合器由集中电容与分布电感组成,实现宽谱微波在频率调谐范围内以较为一致的耦合度提取微波能量。通过转动螺杆滑动安装在同轴谐振器内芯上的环形开关,达到改变谐振频率的目的。最后,将可调频宽谱辐射装置与输出电压为500 kV的Tesla变压器脉冲功率源联试,得到200～400 MHz宽谱微波辐射,辐射因子为95～130 kV,频谱百分比带宽为10%～30%。