Widely tunable erbium-doped fiber ring laser covering both C-bandand L-band

We demonstrate a widely tunable erbium-doped fiber (EDF) ring laser covering both the conventional wavelength band (C-band) and the long wavelength band (L-band). It features a wide tunable range, high output power, low-coherent, and depolarized output. A tunable range over 80 nm (1520-1600 nm) has been achieved by optimizing the length of the EDF and by using an intracavity fiber Fabry-Perot (FFP) filter     

Stadium and quasi-stadium laser diodes

We present theoretical and experimental studies on two-dimensional microcavity laser diodes with stadium and quasi-stadium shapes. We report a demonstration of lasing for the first time in a fully chaotic microcavity-a stadium-shaped cavity which is rigorously known to be fully chaotic. We also present systematic studies on quasi-stadium laser diodes for three types of resonator conditions: stable, marginally stable, and unstable. Morphological dependence of lasing characteristics of quasi-stadium laser diodes is elucidated. We also show examples of the application of quasi-stadium laser diodes to beam switching operation and optical signal distribution by using patterned electrodes and the phase locking phenomenon between two resonator modes.     

Reconfigurable planar filters

Electronically reconfigurable or tunable microwave filters are attracting more attention for research and development because of their increasing importance in improving the capability of current and future wireless systems. For instance, emerging ultrawideband (UWB) technology requires the use of a wide radio spectrum. However, the frequency spectrum as a resource is valuable and limited, so the spectrum is always being used for several purposes, which means it is full of unwanted signals when an operation such as a UWB wireless system is concerned. In this case, existing undesired narrowband radio signals, which vary from place to place and from time to time, may interfere with the UWB system's range. A solution for this is to introduce an electronically switchable or tunable narrow rejection band (notch) within the passband of a UWB bandpass filter. Such an electronically reconfigurable filter is also desired for wideband radar or electronic warfare systems. This paper discusses the development of electronically reconfigurable filter types.     

Microring-Resonator-Based Widely Tunable Lasers

We describe widely tunable lasers incorporating microring resonators. By using a double-ring-resonator-coupled filter, a wide wavelength tuning range is achieved with a low tuning current. A double-ring-resonator-coupled tunable laser has series-connected microring resonators in the laser cavity. A tuning range of 50 nm is achieved with injection current of less than 5.2 mA. This low injection current reduces the frequency drift caused by thermal transients to less than 5 GHz. We also describe an integrated filtered feedback tunable laser consisting of a Fabry–Perot (FP) laser and integrated filtered feedback sections. In this device, the filter section is removed from the laser cavity. The device exhibits a 24-nm tuning range with a side-mode suppression ratio of 50 dB. The frequency drift is less than 1 GHz because the longitudinal mode of the laser is mainly determined by the FP laser section. We have also developed a filter-free widely tunable wavelength converter by monolithically integrating a tunable laser and a wavelength converter based on a semiconductor optical amplifier. Wavelength conversion for a 10-Gb/s nonreturn-to-zero signal is also demonstrated, tunable over a 40-nm range.      

Wavelength-swept fiber laser with frequency shifted feedback andresonantly swept intra-cavity acoustooptic tunable filter

This paper concerns a wavelength-swept fiber laser (WSFL) incorporating frequency shifted feedback and an intracavity passband filter, in which the wavelength of the modeless output is linearly, continuously and repeatedly tuned (in time) over a given range by modulation of the filter peak wavelength and filter strength. We show both numerically and experimentally that amplifier noise plays a key role in determining the operation of frequency-shifted fiber laser systems and that a “noisy” amplifier can be used to suppress the natural tendency of such lasers to pulse, allowing for continuous wave, modeless operation. Furthermore, we show that significant narrowing of a WSFL instantaneous swept linewidth can be obtained if the filter peak transmission wavelength is resonantly swept so as to follow the wavelength shift per pass due to the acoustooptic frequency shift. Using these ideas we go on to demonstrate and characterize a high-power diode-driven Er³⁺/Yb³⁺ WSFL incorporating a bulk-optic acoustooptic tunable filter (AOTF). Linewidths as narrow as 9 GHz, sweep ranges up to 38 nm and output powers as high as 100 mW are obtained. Furthermore, we demonstrate the generation of user definable average spectral output by synchronous modulation of the filter strength and multiwavelength pulsed output at higher sweep rates. Excellent agreement between the experimental results and those of the numerical modeling is obtained. Our simulations show that reduced linewidth (<0.02 nm) and improved scan linearity should be readily achievable with realistic system improvements. We believe such sources to be of considerable physical and practical interest, with applications ranging from sensor array monitoring and device characterization through to low-coherence interferometry     

Modeling of ring resonators with tunable couplers

Controlling the characteristic response of the ring resonator through adjustable coupling can be useful in variety of applications, such as add-drop filters, modulators, lasers, switches, sensors and others. Coupled mode theory (CMT) is effectively utilized for modeling of a generic micro-resonant cavity with two independently adjustable add/drop couplers and integrated phase-shifter(s). It is shown that for a lossy cavity the non-identical input/output coupling values are required to satisfy a resonance condition. The critical coupling and coupling/loss optimization is discussed for the regular and /spl delta//spl beta/-reversal tunable couplers. Resonance coupling diagram is derived for passive and perturbed resonator structure for these types of tunable couplers.     

Novel approach to RF photonic signal processing using an ultrafast laser comb modulated by traveling-wave tunable filters

The analogy between optical frequencies and RFs leads to a novel technique for RF photonic signal processing using a femtosecond laser comb modulated by a traveling-wave tunable filter, such as an acoustooptic tunable filter (AOTF) or a novel electrooptic tunable filter (EOTF). In this new scheme, the recent history of an applied RF waveform to-be-processed slides into the tunable filter and a femtosecond pulse train diffracts off the moving acoustooptically or electrooptically induced dielectric grating, producing a shaped optical pulse train with each shaped pulse as a compressed replica of the RF waveform contained within the device aperture that is sped up by the ratio between the center optical and RF frequency. For a CW RF tone input, only a narrowband group of the frequency comb lines in the incoming laser comb is spectrally filtered and modulated due to the phase-matching condition in the filter and is simultaneously Doppler shifted by that RF due to the traveling-wave grating obeying the conservation of energy. This allows us to use the traveling-wave tunable filter as a spectrally mapped Doppler-shifted modulator that encodes different RF components onto the corresponding optical frequency comb lines. RF signal processing can then be performed by using optical techniques to manipulate the spectrally modulated laser comb. To reconstruct the processed RF signal, the Doppler-shifted and optically processed pulse train is heterodyne detected by beating with a reference femtosecond pulse train from the same laser source. A high repetition rate femtosecond laser comb is modulated by an AOTF to experimentally demonstrate this novel RF photonic signal processing technique. We demonstrate an RF tunable bandpass/notch filter, an RF down-converter, and an RF jammer er as novel applications of ultrafast lasers.     

A frequency-locked adaptive filter

A frequency-locked RC active ladder filter is described, which is frequency-locked to a sinusoidal control tone. The tunable ladder filter is used as a frequency discriminator by using two of the filter branch voltages to generate a control voltage. The control voltage is then used to tune or frequency-scale the ladder filter transfer function to lock the filter to the frequency of the control tone. A simple linear frequency-signal control system is developed to describe the frequency-locked performance of the adaptive filter. The frequency-locked filter can be designed so that the sinusoidal control tone is rejected at the filter output, making it possible to adapt the filter transfer function during transmission of a message. A practical frequency-locked filter is given in which a frequency-locked third order elliptic lowpass filter is designed. The performance of the practical filter is analysed using a simple linear control system model.     

Electronically Tunable Filters

In this article, a brief introduction to the development of tunable filters was given. A classical design technique based on a combline filter approach was shown, where minimum degradation in passband performance could be obtained across a broad-tuning range. The fundamental disadvantages associated with the conventional resonator tuning approaches were also discussed, recognizing the importance of developing new techniques for realizing tunable microwave filters. It was shown that there is a possibility in realizing an electronically reconfigurable microwave filter based on parallel- coupled switched-delay lines, which possesses the important property of maintaining constant absolute bandwidth over almost an octave of tuning bandwidth. Furthermore, the filter has the ability to incorporate active switching elements in the filter circuit, without sacrificing its loss and linearity performance. With the exceptional linearity performance and power handling capability, the filter is readily adapted to poor environments. Although the use of p-i-n diodes as switching elements would result in large dc consumption, the approach could also be readily adapted for use with any switches, such as pHEMT or RF MEMS switches, to achieve extremely low power consumption. The integration of switchable couplings to enable both bandwidth and center frequency to be reconfigurable would be an enhancement.     

Silicon-on-Insulator-Based Retroreflective Optical Marker Chips for Simultaneous Identification and Localization

We demonstrate an omnidirectional, retroreflective optical marker in silicon on insulator that enables simultaneous identification and localization of objects. The most important chip requirement - its retroreflectivity - is realized by a large number of equally designed reflective ring resonator circuits, which operate at different angles of the incident light. The markers are characterized by an infrared camera that captures the response during flood exposure by a tunable infrared laser.     

基于微带三模谐振器的超宽带带通滤波器设计

提出一种基于微带三模谐振器的超宽带带通滤波器设计.该滤波器由一个中心加载阶跃阻抗开路枝节的三模谐振器,及两组用于抑制谐波的新型哑铃型缺陷地结构组成.使用交指型馈电方式及在馈电处的地板开槽实现超宽带需要的的强耦合,利用缺陷地结构抑制高次谐波实现良好的阻带特性.仿真结果表明,所设计的滤波器通带3 dB相对带宽达到80％(4.06～9.48 GHz),通带内插入损耗小于0.58 dB,回波损耗大24 dB,通带外10 dB阻带覆盖到30 GHz,通带两侧附近均有一个传输零点,获得了陡峭的通带边缘,较好地实现了美国联邦通信委员会(FCC)授权的超宽带通信系统的频谱使用要求.该滤波器结构简单,谐振器自身尺寸小于中心频率下0.5λg×0.5λg.最小带线和最小缝隙宽度均不小于0.1 mm,易于低成本加工,具有较高的实用价值.     

A broadly tunable erbium-doped fiber ring laser: experimentationand modeling

Broad-band tunability of erbium-doped silica fiber ring lasers in the 1.48-1.62 μm wavelength band is demonstrated through modeling and experiment. Tunability over the erbium-doped fiber amplifier (EDFA) C- and L-bands is achieved with a simple laser design using a single gain medium working in deep saturation. A comprehensive numerical model based on an iterative solution of propagation rate equations and spectrally resolved Giles parameters was used to analyze the impact of various laser variables. The dependence of laser output power on total cavity loss, erbium-doped fiber length, pump power, and lasing wavelength has been investigated. The calculated laser characteristics have been found in good quantitative agreement with the experimentally obtained data. Experimental results concerning wavelength tunability, output power, and lasing wavelength repeatability/stability and spectral purity are also presented     

Arbitrary amplitude and linear phase approximations for non-prototype ladder and lattice wave digital filters

Two different approaches are introduced for the design of non-prototype ladder and lattice wave digital filters (WDFs) exhibiting arbitrary amplitude in the baseband (passband, transition band and stopband) and linear phase in the passband. The first approach is based on the phase correction of a minimum phase lattice (or ladder) WDF designed to satisfy the amplitude specifications in the three bands. In the second approach the amplitude and phase requirements are approximated simultaneously. It is devoted to the design of a lattice WDF that is constructed from the parallel arrangement of two allpass subfilters. The design procedure relies on preconstructing one of the subfilters to have exact linear phase at all frequencies and constructing the other to interpolate an arbitrary phase at a set of frequencies distributed all over the baseband. The hidden relationship between the amplitude and phase functions of the filter is utilized to approximate both of them. The approximation problem is solved by applying an interpolation technique combined with the Remez exchange algorithm. Prototype filters with amplitude specifications in the passband and stopband and phase specifications in the passband are also considered as special cases. Design examples are presented to show the efficiency of the two methods.     

基于并联负载发夹型谐振器的四阶带通滤波器

针对现代无线通信系统中平坦带通滤波器的需求,提出了一种并联负载的发夹型谐振器,并利用提出的谐振器构建了四阶平坦带通滤波器。首先,通过在发夹型谐振器磁场最强的位置（中心位置）设置电阻,设计了一种新的并联型谐振器,从而可以通过改变电阻值来灵活地调整固有品质因数;其次,采用具有高、低固有品质因数的耦合拓扑来构建四阶平坦带通滤波器。最后,在印刷电路板上制备了一个具有传输零点和平坦带通的四阶带通滤波器。实验结果表明,该四阶带通滤波器的实测结果与仿真结果吻合较好,与其他多阶带通滤波器相比,该四阶带通滤波器具有可灵活控制的固有品质因数和小于0.2dB通带平坦度。     

High-Q tunable dielectric resonator filters

Tunable dielectric resonator filters can potentially address wireless and satellite applications that require very high Q values (4,000 and up) with a limited tuning range (less than 15%). Such high Q requirements cannot be met by any other known non-superconductor tunable filter technology at the present time. The intent of this paper is to provide newcomers and end users with the current status and prospective of using dielectric resonators for tunable filters. It is an enabling technology for high-Q tunable filter applications. A key challenge, however, is to increase the tuning range without degrading the Q value. While several techniques have been reported to demonstrate the feasibility of tuning dielectric resonators, the tunable dielectric resonator filter technology is still in its infancy. Very limited research effort has been dedicated to explore the potential for improving the tuning range. Most of the work reported thus far has focused on the use of TE_01delta modes and standard shape resonators demonstrating a narrow tuning range. We believe that the tuning range can be increased while maintaining reasonably high Q values by exploring the use of other modes and by the use of non-standard-shape dielectric resonators.     

采用阶梯 T 型谐振器的双陷波 UWB 滤波器

为有效抑制印度国家卫星通信C频段和X卫星频段对超宽带通信系统的干扰,提出了一种新型双陷波超宽带滤波器。该滤波器采用阶梯T型多模谐振器(multimode resonator, MMR)与缺陷地结构(defected ground structure, DGS)的交趾耦合,实现超宽带特性。采用非对称耦合线及在MMR两侧耦合分裂环谐振器的方法,分别在6.67～7.06 GHz, 7.47～7.57 GHz两个频段内产生陷波。实测结果与仿真结果吻合较好,该滤波器的通带范围为3.03～11.50 GHz, 3 dB带宽达到123%,插入损耗仅有0.87 dB,两处陷波中心频率分别在6.87 GHz和7.52 GHz,陷波深度均大于20 dB,且整体尺寸紧凑,仅有16 mm×8 mm大小。     

Fabrication technologies for vertically coupled microring resonator with multilevel crossing busline and ultracompact-ring radius

To eliminate the scattering loss at the crossing points of cross-grid busline waveguides, the multilevel crossing structure of the busline waveguides was introduced into a vertically coupled microring resonator (VCMRR) filter. To achieve this structure, two fabrication technologies were newly developed; one is a method to planarize perfectly the top surface of each buried waveguide, and the other is a method to fabricate microring waveguides with very smooth sidewalls. Using the latter method, an ultracompact VCMRR with a ring radius of 5 /spl mu/m was realized and a free spectral range of 37 nm was successfully demonstrated. Next, using the former method, single-ring and quadruple series-coupled ring resonators with multilevel crossing busline waveguides were fabricated. A clear filter response was obtained for the single-microring resonator, and a boxlike filter response was obtained for the quadruple series-coupled microring resonator with multilevel crossing busline waveguides.     

Widely tunable DS-DBR laser with monolithically integrated SOA: design and performance

We report recent device characterization results for a fully packaged widely tunable digital supermode (DS) distributed Bragg reflector (DBR) laser which has been monolithically integrated with a semiconductor optical amplifier. This new device gives all of the wide tunability and high side-mode suppression ratio performance previously reported for the DS-DBR laser with the added feature of output powers in excess of 14 dBm in fiber. In addition to output power and basic tuning behavior, we report on linewidth and relative intensity noise measurements for this device in order to investigate the noise characteristics of this laser.     

新型吸收式微带线带通滤波器的仿真设计

基于传统的梳妆线谐振式滤波器设计原理及微带线定向耦合器理论,提出了一种新型的吸收式带通滤波器,其特点是滤波器的电压驻波比不仅在通带内很好,通带外很大频率范围内驻波也小于3.5,这也是该滤波器与常用的反射式滤波器的区别。首先,该滤波器采用微带线结构实现,与传统LC结构滤波器相比,可应用于更高的频段;其次,该滤波器具有较宽的带宽;再者,该滤波器设计灵活简单、成本低、易于集成。通过MWO软件仿真优化,实现了通带中心频率为3500MHz、3d B带宽为479MHz、通带内插入损耗小于3d B、通带内电压驻波比小于2、带外驻波比在很大频率范围内小于3.5的新型微带吸收式带通滤波器的设计。     

新型双频窄带带通滤波器的设计

提出了1种新型双频窄带带通滤波器,由1段1/4波长的均匀阻抗线以及1/2波长的U型阶跃阻抗谐振器组成,输入输出采用抽头式.所设计滤波器中心频率为2.4/5.6 GHz,为无线通信系统中的常用频率.该滤波器的带外有3个传输零点的引入,增强了通带隔离度以及阻带的抑制特性,带内回波损耗低于-0.3 dB.双频窄带带通滤波器的...