A 2×2 spatial optical switch based on PT-symmetry

We show a PT-symmetric coupler having an arm with a tunable gain and a no-loss arm when appropriately designed to possess reciprocal behavior, unlike its rivals having a fixed gain/loss arm, can perform as a tunable 2×2 spatial optical switch. The degree of the tunability equals the ratio of the coupler's length to the total coupling length.     

Fabrication of 1×2 asymmetric plastic optical fiber coupler for portable optical access-card system

We proposed a simple low-cost acrylic and metal-based Y-branch plastic optical fiber (POF) splitter which utilizes a low cost optical polymer glue NOA63 as the main waveguiding medium at the waveguide taper region. The device is composed of three sections: an input POF waveguide, a middle waveguide taper region and output POF waveguides. A desktop high speed CNC engraver is utilized to produce the mold inserts used for the optical devices. Short POF fibers are inserted into the engraved slots at the input and output ports. UV curable optical polymer glue NOA63 is injected into the waveguide taper region and cured. The assembling is completed when the top plate is positioned to enclose the device structure and connecting screws are secured. Both POF splitters have an average insertion loss of 7.8 dB, coupling ratio of 55: 45 and 57: 43 for the acrylic and metal-based splitters respectively. The devices have excess loss of 4.82 and 4.73 dB for the acrylic and metal-based splitters respectively.     

Free-space 1×2 wavelength-selective switches for wavelength-division multiplexing optical networks

A free-space 1 ×2 wavelength-selective switch （WSS） based on thin-film filter technology is proposed. The 1 × 2 WSS is fabricated with an electromagnetic actuator, a reflecton prism, a narrow-band thin-film filter, and three fiber collimators. The working principle and the configuration of WSS are illuminated. The experimental results indicate a fiber-to-fiber insertion loss ranging from 1.109 to 1.249 dB with 2-V voltage input, which satisfies the application of optical fiber communication.     

6×6 matrix formalism of optical elements for modeling and analyzing 3D optical systems

Although conventional 2×2 ray matrices, i.e. ABCD matrices, provide a convenient means of obtaining initial estimates of the performance of an optical system during the early stages of the design process, they are suitable only for optical systems with the axisymmetric property. Accordingly, this study utilizes the 6×6 matrix formalism, which was proposed by our group, for optical boundary surfaces to develop a new approach for modeling and analyzing 3D optical systems comprising multiple lenses and/or mirrors and clarifying many of the system’s basic properties, e.g. the effective focal length, primary aberration and cardinal points, and so forth. To reduce the complexity of the modeling process, general matrix formalisms of sub-systems in a 3D optical system are presented. The validity of the proposed approach is evaluated by modeling and analyzing a simple 3D optical system and comparing the results with those obtained from the skew ray-tracing computer program and commercial optical design software. The results confirm that the proposed methodology provides a convenient means of obtaining initial insights into a variety of 3D optical systems with non-coplanar axes.     

Polarization-independent bidirectional 4×4 optical switch in free space

Optical switches play an important role in all optical communication networks and multiprocessor computer systems. The 2×2 and 4×4 optical switches are the basic units of large-scale switch matrices. Using a conventional polarization control method, the optical switch system and structure is optimized, and a novel optical switch is proposed, which has the advantages of relatively low crosstalk and insertion loss, compact and simple construction, higher performance and cost effectiveness. First, a novel 2×2 optical switch is proposed using phase spatial light modulator (PSLM), polarizing beam splitter (PBS) and mirror. This configuration uses fewer optical components, is compact in structure, efficient in performance, and insensitive to polarization of the signal beam. Second, a new optical experimental module of 4×4 optical switch is presented by cascading a 2×2 optical switch. The routing method of polarization-independent bidirectional 4×4 optical switch is investigated. Finally, the operational characteristics of the polarization-independent bidirectional 2×2 and 4×2 optical switches are discussed in detail.     

Wavelength-selective 4 × 4 nonblocking silicon optical router for networks-on-chip

We design and fabricate a wavelength-selective nonblocking 4 × 4 silicon optical router based on microring resonator for use in future integrated photonic interconnection networks. We successfully demonstrate 12 possible I/O routing paths and present 13 nonblocking operating states, including four broadcasting states, with worst-case extinction ratio and cross talk of 21.05 and -21.56 dB, respectively. Thermal tuning is employed to compensate the resonance shift of microring resonators caused by fabrication errors and adjust the resonance to match the International Telecommunication Unit grid with the channel spacing of 100 GHz.     

4×4 multiple-input multiple-output coherent microwave photonic link with optical independent sideband and optical orthogonal modulation

A 4 × 4 multiple-input multiple-output coherent microwave photonic(MWP) link to transmit four wireless signals with an identical microwave center frequency over a single optical wavelength based on optical independent sideband(OISB) modulation and optical orthogonal modulation with an improved spectral efficiency is proposed and experimentally demonstrated. At the transmitter, the OISB modulation and optical orthogonal modulation are implemented to generate an OISB signal using a dual-parallel Mach–Zehnder modulator(DPMZM) driven by four microwave orthogonal frequency-division multiplexing(OFDM) signals with an identical microwave center frequency. At the receiver, the OISB signal is coherently detected at a coherent receiver where a free-running local oscillator(LO) laser source is employed. Digital signal processing is then used to recover the four OFDM signals, to eliminate the phase noise from the transmitter laser source and the LO laser source, and to cancel the unstable wavelength difference between the wavelengths of the transmitter laser source and the LO laser source. Error-free transmission of three 16 quadrature amplitude modulation(16-QAM) 1 Gbps OFDM signals and one 16-QAM 1.5 Gbps OFDM signal at a microwave center frequency of 2.91 GHz over a 10 km single-mode fiber is experimentally demonstrated.     

4 × 20 GHz silica-based AWG hybrid integrated receiver optical sub-assemblies

Both the 4 × 20 GHz coarse wavelength division multiplexing and LAN-WDM receiver optical sub-assemblies(ROSAs) were developed. The ROSA package was hybrid integrated with a planar lightwave circuit arrayed waveguide grating(AWG) with 2% refractive index difference and a four-channel top-illuminated positive-intrinsicnegative photodetector(PD) array. The output waveguides of the AWG were designed in a multimode structure to provide flat-top optical spectra, and their end facet was angle-polished to form a total internal reflection interface to realize vertical coupling with a PD array. The maximum responsivity of ROSA was about 0.4 A/W, and its 3 dB bandwidth of frequency response was up to 20 GHz for each transmission lane. The hybrid integrated ROSA would be a cost-effective and easy-assembling solution for 100 Gb E data center interconnections.     

Improvement of the fractional uncertainty of a neutral-atom calcium optical frequency standard to 2×10-14

We have investigated the two major effects that limit the accuracy of an optical frequency standard based on laser-cooled neutral calcium atoms, i.e. the residual Doppler shift and atomic collisions. A new correction method was applied to reduce the contribution of the residual Doppler effect to the total fractional uncertainty to 1×10^-14. Measurements of the shift of the clock transition frequency due to cold collisions allowed us to reduce their contribution to 4×10^-15. With these improvements we have reduced the total fractional frequency uncertainty of the standard by nearly an order of magnitude to 2×10^-14. Received: 9 August 2002 / Revised version: 16 November 2002 / Published online: 26 February 2003 RID="*" ID="*"Permanent address: Russian Academy of Sciences, P.N. Lebedev Physical Institute, Samara Branch, Novo-Sadovaya st. 221, Samara 443011, Russia RID="**" ID="**"Corresponding author. Fax: +49-531/592-4305, E-mail: uwe.sterr@ptb.de     

Two-dimensional 4 × 4 optical switching element by using HOE and SLM

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A novel 1 × 2 optical power splitter with PBG structures on SOI substrate

A novel 1 × 2 optical power splitter in size of 8.0 μm × 4.2 μm is presented in this paper, by using photonic bandgap (PBG) structures on silicon-on-insulator (SOI) substrate. The splitting ratio can be adjusted by changing the air hole position to get wide tuning range. The design is examined by the commercial finite-difference-time-domain (FDTD) software for various splitting ratios. Some approximated formulas are obtained through curve-fitting to facilitate design process.     

Fabrication of SiO_2 microdisk optical resonator

The silica microdisk optical resonator which exhibits whispering-gallery-type modes with quality factors of 9.67×10~4 is fabricated with photolithographic techniques.Reactive ion beam etching(RIBE)is used to get the silica disks with photoresist masks on SiO_2/Si made by standard ultraviolet(UV)photolithography, and spontaneous silicon etching by XeF_2 is used to fabricate the silicon micropillars.This fabrication process can control the microcavity geometry,leading to high experiment repeatability and controllable cavity modes.These characteristics are important for many applications in which the microcavity is necessary,such as the quantum gate.     

单块晶体2×2光开关

利用晶体的双折射和全内双反射现象以及晶体的电光效应 ,设计了一种单块晶体集成的 2× 2光开关 ,将一个电光调制器和两个光束分束器集成到一块铌酸锂晶体上 ,实现了光束合束、偏振态调制和光束分束三种功能。根据这种光开关的工作原理 ,给出两种开关结构 ,一种是易于级联的垂直入射结构 ,另一种是有较低操作电压的倾斜入射结构 ,并对倾斜入射结构的光开关进行了制作和测试。实验结果表明 :这种集成结构的 2× 2光开关操作电压低 ,串扰小 ,能量损耗小 ,抗干扰 ,稳定可靠 ,适用于各种光学互连网络。     

1×4 buried optical power splitter fabricated by Tl~+-Na~+ ion-exchange

A new 1×4 buried optical power splitter with curved Y-junction structure has been successfully designed by a beam propagation method (BPM) software and fabricated by two-step ion-exchange in glass. The optical qualities of the device are favorable in comparison with that obtained with dry etching fabrication techniques.     

与偏振无关双向2×2和4×4自由空间光开关

利用成熟的偏振控制技术,设计了一种由偏振光分束器、相位型空间光调制器和反射镜构成的2×2光开关,该光开关所用器件少,具有结构简单紧凑、控制灵活方便、功能实现与信号光的偏振态无关以及可以双向交换等特点;在此基础上通过2×2光开关的串连,设计了一种与偏振无关的双向4×4光开关的实验模块,根据其路由选择与控制方法,得到了4×4光开关实现信号光全排列无阻塞输出与交换对应的路由状态表,并对该实验模块的功能实现进行了详细的分析与讨论。     

2-μm singly resonant optical parameter oscillator

We experimentally realize a singly resonant optical parameter oscillator （OPO） which operates at the degenerate point of KTiOPOa （KTP） crystal. A thin film plate polarizer （TFP） is used as the output coupler to obtain linearly polarized 2.12 μm laser. A maximum output power of 2.2 W at 2.12 μm is obtained from a near-degenerate, type-II KTP OPO by utilizing a Q-switched diode-pumped Nd：YAG laser operating at 5 kHz.     

保偏光纤2×2定向耦合器

介绍一种已研制成的低损耗、宽带、结构紧凑的保偏光纤定向耦合器(PPFDC),它可用于今后的相干纤维光学传输系统或陀螺仪上。这种耦合器由两块直径为200μm蓝宝石球透镜、一块3dB分光器和四根锥形氧化铝陶瓷套管组成,套管上的基准扁平面用于使光纤在接点保持偏振。由于直管内光纤只有很短一段经过抛光,故光纤的固有热应力变化最小。光轴和机械轴成一定角度,因而光纤端面或透镜表面不会出现串扰光。耦合器的光学方向性大于50dB,在1.3μm波长区的反射损耗大于40dB。在1.2到1.4μm内的过量损耗小于1dB。消光比大于25dB。耦合器耦合区的长度包括两块球透镜和分光器在内约1mm,光纤端面分布反馈激光二极管的谱线宽度用耦合器由延迟自零检测系统测量。采用调相耦合器的新型保偏光纤陀螺仪的实验结果表明,灵敏度和稳定度均是适用的。这些实验结果证实耦合器的上述各种特性均是正确的。     

GaAs2×2Mach-Zehnder光波导开关调制器

报道了GaAs2×2非对称Mach-Zehnder光波导开关调制器的研制结果,分析了这种开关的工作原理和产生串音的因素.采用两个非对称X型耦合器代替传统的Y分支耦合器,得到了性能良好的X型3dB耦合器.λ=1.15μm时,器件的串音比小于-22.4dB,开关电压约1.2V.