The RF behavior of a 35 GHz PBG cavity gyrotron operating in TE 3,4,1 mode is studied using the multimode analysis and the PIC simulation code. The design procedure and beam absent behaviour of the PBG cavity has already been reported . Here, the beam present behaviour of the PBG cavity is studied. The time dependent nonlinear multimode theory has been used to observe the RF behavior in the presence of all competing modes. The beam-wave interaction behaviour is also observed using commercially available PIC simulation code ‘CST Particle Studio’. The cavity operation is monitored to predict the desired frequency and mode of operation. Velocity spread is taken zero in the theory as well as simulation. Temporal signal growth and output power of designed mode as well as the possible competing modes is observed and the comparison of their amplitudes is discussed. Results obtained from the multimode analysis have been validated with those obtained through the PIC simulation.
thereby changes in the oscillation frequency as well as decrease in the RF power output. Hence, an efficient thermal management system needs to be designed and ensured for stable operation of the gyrotron device , , . Thermo-mechanical studies and its effect on RF behaviour of 1 MW power gyrotrons at 140 GHz, 170 GHz and 240 GHz has been investigated using computational fluid domain softwares, like, ANSYS, STAR CCM and COMSOL Multi-physics in -. J Koner and A K Sinha  have carried out thermal analysis of RF interaction cavity of a 200kW CW, 42GHz gyrotron using ANSYS code for different coolant flow rate with the axial fins provided on its outer surface. A Kumar et al.  extended this work for 170 GHz gyrotron with axial as well as radial cooling fins. Q Liu et al. ,  also carried out heat transfer analysis of the RF interaction cavity for the 140 GHz and 240 GHz gyrotrons using ANSYS code and shown the effect of cavity deformations on the multi-mode beam-wave interaction of the device. However, cooling fins and thermal system design and its optimization for the RFcavity of the device is not reported. In the present work, the thermal and structural analysis of a tapered cylindrical RF interaction cavity of the gyrotron is carried out. With the help of design relationships, radial cooling fins design on the outer jacket of the middle section of the RF interaction cavity is presented. An optimum thermal system is designed and simulated using “COMSOL Multiphysics” code. Implementation of commercial code “COMSOL Multiphysics” is simpler than those used in previously reported work though equally accurate for this purpose and not explored earlier . For the designed cooling system with different convective heat transfer coefficients, deformations in cavity profile are obtained through this simulation. Nonlinear time-dependent multimode theory is used further to obtain the RF output behavior of the gyrotrons , -. An optimum thermal system design thus obtained with maximum possible deformation in the inner dimension of the RFcavity ensures the gyrotron oscillator RF frequency and power output variations within the specified tolerance limit of the device.
The comparison of the results of Ansoft HFSS and mode matching for d = 20 mm is presented in Fig. 2 (for a 2.15–2.45 GHz wide band interval and a 100 MHz frequency change). HFSS is a commercial 3D full-wave Finite Element Method (FEM) solver for electromagnetic structures developed by Ansoft Corporation. The acronym originally stood for high frequency structural simulator. It to computes the electrical behavior of high-frequency and high-speed components. It is one of the common and powerful applications used for antenna design, and the design of complex RF electronic circuit elements including filters, transmission lines, and packaging. The software becomes the industry-standard simulation tool for 3D full-wave electromagnetic field simulation. HFSS provides E- and H-fields, currents, S- parameters and near and far radiated field results. Intrinsic to the
this problem, a mode-referencing technique was imple- mented into the frequency stabilization scheme similar in concept to a form of mode stabilization for a superstructure grating DBR 共SSG-DBR兲 laser. 13 Referencing 共adjustment of operation parameters 兲 of the ECDL 共 while maintaining frequency lock兲 ensures that the constant frequency emis- sion remains on a characteristic line in the power plane equidistant from adjacent mode boundaries, which corre- sponds to the optimum operating point. With the mode- referencing step, it was possible to achieve in situ monitor- ing of the position of the current/PZT voltage combination tuning path and compensate for any drift in the mode pro- file by locking the wavelength-tuning path to the center of the desired lasing mode. We demonstrate experimentally that it is possible to maintain frequency stabilization of an ECDL output to a H 2 O absorption line with the inclusion of the mode-referencing technique in the frequency-locking system, while applying a series of induced temperature steps, simulating thermal instability, to the device heat sink.
Lower arm cavity loss, coupled with an increase in the available power from the Nd:YAG laser, allows up to 800 kW of laser power to circulate in the arm cavities— 20 times higher than in initial LIGO — significantly reducing the high frequency quantum noise. The use of optically stable folded recycling cavities allows for better confinement of the spatial eigenmodes of the optical cavities . The signal recycling cavity , which was not present in initial LIGO, was introduced at the antisymmetric port to broaden the frequency response of the detector and improve its sensitivity at frequencies below 80 Hz and above 200 Hz. Because O1 was the first observing run, and work remains to be done on the detectors to bring them to their design sensitivity, not all of the interferometer parameters were at their design values during O1. Most notably, the laser power resonating in the arm cavities was 100 kW instead of the planned 800 kW. More power in the arm cavities improves the shot noise level as discussed in Sec. III B. Circulating optical power will be increased in future observational runs. Additionally, the signal recycling mirror transmissivity was 36%, in contrast to the design value of 20%. This higher transmissivity of the signal recycling mirror improves the quantum noise in the frequency range from 60 Hz to 600 Hz at the price of reducing the sensitivity at other frequencies. Finally, the best measured Advanced LIGO sensitivity in the frequency range 20 – 100 Hz, as discussed in Sec. III, is limited by a wide range of understood technical noise sources as well as currently unknown noise sources.
Due to the wavelength differences, <7 i 083 = 7.75cr389. Hence less light will be scattered by an equal number of atoms in the 389nm cell, and thus a smaller signal will be observed at equal laser powers. This consequently leads to higher laser powers being used. Secondly, there was a much larger intensity noise on the 389nm beam than the 1083 nm beam, which could be reduced but not be eliminated. This is both a consequence of the Ti:Sapphire intensity noise amplified by the non-linear conversion process, as well as instabilities in the external doubling cavity. The Ti:Sapphire laser also varied slightly in intensity when the frequency was scanned. For these reasons two photodiodes were used to subtract the common mode noise. Due to the greater noise levels, Zeeman shifting of the transitions was also harder to observe. Instead, the Ti:Sapphire laser frequency was dithered which resulted in the intensity stability of the laser being slightly compromised due to the greater frequency offset between the cavity and Ti:Sapphire output (around 800 kHz) to obtain the error signals. Details of the experimental procedure and the obtained signals are presented in the following section.
Hall mobilities of an n-type (GN l) and a p-type (GP 2) germanium single crystal were measured at a microwave frequency of 9 Gc/ sec from 80 °K to 300 °K. A bimodal rectangular cavity designed by Nishina was used in the present investigation. The microwave circuit was nearly the same as that described by Nishina except that the microwave signal was modulated by 1000 cycle per second square-wave signal. The microwave mobilities measured (with sample size correction factor of 0. 423 for n-type and 0. 687 for p-type germanium) were compared with the corresponding d. c. Hall mobilities. For n-type germanium, the discrepancy between the d. c. and microwave mobilities was believed to be predominatly due to the E: -1/2 dependence of the relaxation time (acoustical mode scattering). For p-type germanium, a large deviation occurred at low
By history, the RFID system is replacing the bar code technology which has been using past years . The type of bar codes system in RFID is effective which applied the Universal Product Code (UPC) for unique individual items compare to the Electronic Product Code (EPC) for unique to product. The RFID system gets the information from ID and dates which provide more information in real time and sensor temperature sensitive products entirely. The information is valuable in term of product shipment and the product in market based on current real time e-pedigree which can prevent missed used or food and drugs. The RF radiation can analyze in term of temperature and frequency combination. The thermal effect arise from noticeable change in temperature which comparable to conventional heating. The product heating factors may due to frequency of EM source, dielectric constant, content of water and the thickness of products [3,7]. The product and substance greater in conductivity absorb greater amount of radiation which turn generates more heat. Studies have shown that environmental levels of RF energy routinely encountered by the general public are far below levels necessary to produce significant heating and increased body temperature [29 -34].
Electronic assembly and testing include two basic types: the PCB board test and the product functional test. The PCB board test mainly measures the RF baseband signals to find out the PA to the antenna before the end of the baseband signal. The result of this test decides whether the transmitter power is good or not, but the naked version connects with the antenna module. As the overall RF performance must closely suit the user’s needs, with a mobile phone the RF performance testing of the final products is a must [6, 7]. Due to the rapid development of computer communications, many of the high- speed data buses are used to test and measure applications. However, each data bus has its advantages and disadvantages, which we must consider when making an appropriate choice for the type of application under examination. GPIB is an 8-bit (Bit) parallel digital communication interface with a data transmission speed of up to 1 Mbyte/s. This bus can not only support the controller but can also be very effectively used between the control apparatus and for communication between the computers, and is often chosen as the system for an equipment GPIB automation control connector. Most RF automated testing programs use the GPIB to control the measurement instrument. As those programs must install their company’s IO Library first to both access measurement test result images and create the database, the programs are large, and their portability is low. In addition, they are expensive .
The FlexWave Prism uses patented digital-over-fiber technology to distribute RF to desired locations. The Prism digitizes the entire designated RF band and/or multiplexes direct digital CPRI or OBSAI feeds over dark fiber or millimeter wave links and reconstructs the signal at full bandwidth, regardless of modulation technology or BTS vendor, at the remote location. TE’s digital RF transport allows RF signals to be replicated at full dynamic range, independent of the link length, for improved data throughput. As service providers migrate to 3G and 4G networks, high-data rate broadband services, networks utilizing a Prism backbone will be ready.
The lower limit of achievable repetition rate and associated power scalability in SESAM mode-locked VECSEL systems, to-date, has been limited due to a short upper state carrier lifetime in the semiconductor gain material, calculated to be typically a few nanoseconds [7,9]. It is found to be structure-dependent rather than being an intrinsic material property . The carrier lifetime should ideally be larger than the inter-pulse period of the FML pulse so that all energy from the excited carriers in the conduction band may contribute to pulse amplification. For a low PRF VECSEL, the interaction time between the incoming pulse and the excited carriers in the semiconductor gain chip is shorter than the cavity round-trip time. The excited carriers contribute to spontaneous recombination in the time between the pulses and decrease the differential efficiency . The semiconductor gain material, therefore, is intrinsically more suitable for higher repetition rate systems and destabilization of FML becomes more probable in low PRF VECSELs. Additionally, it has been proven that most gain recovery occurs within a few picoseconds . A recovery time faster than the cavity round-trip time of a few nanoseconds in the case of low PRF, favours splitting of the gain, resulting in multiple pulses circulating inside the laser cavity . Also, carrier-centric processes, including spontaneous recombination and Auger recombination, heavily affect mode-locking and have been shown to have lifetimes ranging from a few hundred picoseconds to a few nanoseconds . These processes are not constant over the cavity round-trip time of a long-cavity VECSEL. Combining this with the need to balance intracavity dispersion, it is a significant design challenge to maintain the entire gain in a single, fundamental pulse in a long cavity VECSEL system.
In this paper, three dual-mode band-pass filters are proposed. The dual-mode SIW cavity filter has a center fre- quency of 9.08 GHz with a bandwidth of 4.95%. The insertion loss is 0.43 dB and the return loss is better than 20 dB across the band of interest. In addition, a transmission zero at 9.38 GHz and Q-factor is 414. The EBG-SIW resonator has a center frequency of 9.12 GHz with a bandwidth of 4.38%. The insertion loss is 1.18 dB and the return loss is better than 15 dB across the band of interest. In addition, a transmission zero at 12 GHz and Q-factor is 179. The CSRR-SIW resonator has a center frequency of 8.66 GHz with a bandwidth of 2.54%. The insertion loss is 0.55 dB and the return loss is better than 20 dB across the band of interest. In addition, a transmission zero at 11.73 GHz and Q-factor is 640. The simulation processes of the structures are done by us- ing HFSS software. The design methods are discussed and presented.
The composite cavity configuration used in th is experim ent is sho'svn in Fig. 5.5.b. The same laser was used as in section 5.2.3. The m odulator was designed as a tra v e llin g wave Y -ju n ctio n m odulator. E ffe ctive ly, w ith in the laser ca vity i t acted as a M ach-Zehnder in te rfe ro m e te r structure. The waveguides were formed using a long, d ry diffusion on X- cut, Y -propagating lith iu m niobate. The Y -junction was form ed using a b ra n c h in g angle o f 0.5® in order to provide low-loss s p littin g and recom bination. The distance between the bran ch in g waveguides was 35|im, large enough to prevent any optical coupling. A 200nm Si 0 2 buffer layer was deposited on the top o f the waveguides in order to reduce the electrode loading loss. The electrodes were designed as a coplanar w aveguide s tru c tu re a llo w in g p u s h -p u ll o p eration o f the in te n s ity m odulator. A n in te ra ctio n length o f 1cm was chosen as a compromise between high-frequency capability and efficient m odulation. The w idths of the central electrode and the gap were 20|Lim and 15pm leading to the impedance o f 35Q. The electrodes were fabricated using chrome and gold evaporation and electroplated to the thickness of 1 . 1 pm. The measured DC resistance of the central electrode was IIQ . This m odulator was fixed to an a lu m in iu m holder and electrical connection was made w ith SMA connectors. The electrical re tu rn loss of the m odulator was o f the order of -lOdB in the frequency range from 3-18GHz. Two resonances o f the order o f -6 to -7dB have been detected below 3GHz and were probably caused by the m odulator package.
Laser diodes exploiting the coupled-cavity (CC) geome- try where two sub-cavities are separated by an air gap were first demonstrated in the 1980s as a means for achieving sin- gle mode operation, alternative to distributed Bragg reflec- tors (DBRs) or distributed feedback (DFB) lasers. 1–8 The attractiveness of this approach resides in its inherent fabrica- tion simplicity with, however, an important limitation given by the need to control the width of the air gap between the two sections with sub-wavelength precision in order to obtain single mode-operation with a high side mode suppres- sion ratio (SMR). In this work, we show that the CC tech- nique can be successfully implemented to obtain single mode emission for a quantum cascade laser (QCLs) operat- ing in the terahertz (THz) frequency range. Compared to the near-IR, the two orders of magnitude increase in wavelength considerably relaxes the difficulty in controlling the gap size and could help this technique to become a viable alternative to DFB resonators. 9–13 Indeed, we report single mode opera- tion in continuous wave (CW) with a SMR larger than 30 dB regardless of the pump current or operating temperature.
correspond to superpositions of the cavity modes which, when the cavity is confocal, are simulta- neously resonant, and it is destructive interference between them that generates the intensity minima of the trap. Our scheme is inspired by the ar- rangement suggested by Zem a anek and Foot  but, where they suggested equal axial intensities, the two beams here are of equal power. This modiﬁcation dramatically changes the trapping volumes from axial wells into a series of coaxial rings, spaced half a wavelength apart. This is, to the best of our knowledge, the ﬁrst method to be proposed for the realization of a dipole force trap with a blue-detuned toroidal geometry, and is achieved using simple concave mirrors and a single Gaussian beam.
processes that could be used to fabricate these micro- traps: a) Silicon-based microelectromechanical machin- ing (MEMS) techniques; b) Gallium-Arsenide (or other suitable material) based molecular-beam epitaxy (MBE) grown wafers and associated etching processes; or c) other relevant techniques such as anodic wafer bonding or flip-chip technologies. The length of the cantilevers is limited by allowable mechanical vibrations in the can- tilevers themselves, as well as limits to the mechani- cal stability of the cantilevers under electromechanical forces due to the applied RF and static voltages. The mechanical forces exerted on the cantilevers can be ap- proximated using structural cantilever analysis . Fol- lowing this analysis, the spring constant of the center rectangular cantilever can, for example, be expressed as
Abstract — Manufacturing of klystrons in the millimeter- wave frequency range is challenging due to the small size of the cavities and the ratio of the maximum gap voltage to the beam energy. The small dimensions also make difficult to produce devices with the output power required by a number of applications at millimeter wave, such as communications and spectroscopy. Operating with a higher order mode can be a potential solution, as a larger transverse size structure can be used. Unfortunately, high-order mode cavities have a lower impedance than in fundamental mode. In this paper is proposed a novel solution to overcome the reduced impedance by utilizing an upconverter, where all cavities except the output cavity are designed to work in high-order mode. To demonstrate the effectiveness of the approach, two klystron upconverters were designed. One has six cavities aiming to achieve a maximum output power of ∼90 W at 105 GHz. The second klystron upconverter was a simpler three-cavity structure designed for quick prototype. Millimeter-wave measurements of the three-cavity klystron upconverter are presented.
an optical confinement. It has also been shown, that the condensation of polaritons in a planar two-dimensional cavity is likely to occur in such natural potentials . An accurate characterization of the formation of polaritonic states in natural traps was performed in . Interestingly enough, these defect-induced traps are typically of a Gaussian shape, which is predicted to promote confined Q-factors strongly exceeding those of their mesa (vertical sidewall) counterparts for comparable mode volumes . This makes such natural crystal defect traps highly appealing for the demonstration of large polariton nonlinearities and even photon blockade effects . However, the scalability of this approach is strongly limited due to the randomness of these defects. In a later subsection, we will discuss in detail a technology enabling to implement similar structures in a microcavity in a fully controlled manner.
atom is loaded in the FORT, we use lasers to drive the cavity QED system in order to study the atom-ﬁeld interaction, as inferred from the output photon stream. The driving ﬁeld can address either the atom, by illuminating the system from the side with lattice or linearly polarized beams, or the cavity, usually by way of a linearly polarized probe beam coupled to one of the longitudinal cavity modes, and near- resonant with a Cesium transition (usually at 852 nm). Scattering the driving ﬁeld photons typically heats the atom, so in order to maintain a long trapping lifetime, we counteract this eﬀect with various cooling beams. Radial cooling is achieved by the lattice beams, whereas axial cooling is done in a Raman sideband conﬁguration involving a separate beam coupled oﬀ-resonantly to the same longitudinal cavitymode as the FORT. The light emerging from the cavity as a Gaussian beam is coupled into a ﬁber beam splitter, which leads to two single photon avalanche photo-detectors (APDs). The APD pulses signalling photon detection events are time-stamped and recorded by a computer data acquisition card. The experimental timing is set with the help of a computer-controlled programmable multi-channel TTL pulse generator. For more details on the lab setup, please see Ref. , Chapter 2, and references within.
Although there is still no ideal single photon source, a host of mate- rial systems has been researched for its ability to produce single photons on demand  and some of the more promising systems have been engi- neered to come close to the ideal single photon source. The question this might raise is therefore what such an ideal single photon source looks like. Aharonovich, Englund and Toth  describe the ideal single photon source as follows: “The ideal on-demand SPE (single photon emitter) emits exactly one photon at a time into a given spatiotemporal mode (high pu- rity), and all photons are identical so that if any two are sent through sep- arate arms of a beam-splitter, they produce full interference (a signature of indistinguishability).” But the demands on the source are even higher as for most applications the ideal single photon source also has to be sta- ble, bright, and fast. Here, stable means that the source does not blink or bleach, the brightness is the maximum rate at which single photons can be emitted (or collected), and fast means that the source has a short lived excited state.