Polymeric variable optical attenuator based on long range surface plasmon polaritons

Proposed is a polymeric variable optical attenuator based on long range surface plasmon polaritons (LRSPPs) along a thin metal stripe embedded in polymers. The device is operated by controlling radiation loss of the LRSPP mode resulting from the temperature gradient of the polymer cladding caused by a heater. For guiding LRSPPs and efficient coupling of singlemode fibres, gold stripes 20 nm thick, 4 /spl mu/m wide and 1 cm long are utilised. To obtain a long physical lifetime, the heater is formed on the top of the polymer cladding with a 200 nm Au film which is about ten times thicker than the thin metal waveguide. The fabricated device is characterised at a wavelength of 1.55 /spl mu/m, exhibiting high attenuation of less than 30 dB with an operating power of 100 mW. A fibre-to-fibre total insertion loss of 6.1 dB is achieved when using singlemode fibres.     

The Design and Fabrication of Monomode Optical Fiber

The design of monomode fibers is discussed in the context of optimizing fiber loss and dispersion simultaneously, with reference to the materials choices and limitations to preform and fiber fabrication by the MCVD technique. Two classes of monomode structure-matched cladding and depressed cladding-are considered. Ultralow attenuation has been achieved reproducibly in both classes of fiber. The control of fiber geometry and dispersion is also discussed. Matched cladding fiber suitable for systems operating at both 1.3 and 1.55 µm has been studied and mean losses of 0.45 dB/km at 1.3 µm and 0.28 dB/km at 1.55 µm have been achieved for a total of 130 km. The behavior of depressed cladding fiber is compared with predictions from the theory of propagation in W fibers. Depressed cladding fiber with stable guidance has been demonstrated with attenuation of 0.37 dB/km at 1.3 µm and 0.21 dB/km at 1.55 µm.     

A design technique for a 60 GHz-bandwidth distributed basebandamplifier IC module

A DC-60 GHz, 9 dB distributed amplifier IC module is fabricated with 0.15 μm InAlAs-InGaAs low-noise HEMTs with 155 GHz f_T and 234 GHz f_max. The device is mounted in a metal package with 1.8 mm coaxial cable signal interfaces. The package is specially designed using three-dimensional electromagnetic field analyses, resulting in very flat frequency characteristics of the module within 1.5 dB gain ripples over the entire bandwidth. A multichip module loaded with two amplifier ICs in cascade is also fabricated, and operates at a 17.5 dB gain from 60 kHz to 48 GHz. The 1 dB gain compression output power is about 5 dBm for both modules. The noise figure of the single-chip module is approximately 4 dB over a 10-40 GHz frequency range     

双包层光纤激光器中包层光的滤除

双包层光纤激光器的输出性能及稳定性与包层光的滤除程度有关。光纤激光器输出光中的剩余抽运光不仅会影响到输出光的单色性,还会对输出设备造成损害,甚至破坏光学器件。通常在内包层外涂一种高折射的导光胶来滤除包层光,但此方法使包层光在较短的长度内被大量地滤除,导致热沉上功率密度较高,给散热带来较大的压力。实验中采用3种不同折射率的导光胶,分步滤除包层光,减小局部温度过高。采用Zemax和Matlab软件研究了此滤除方式的特点,搭建了验证实验系统。实验结果表明,输出激光中的包层光已被滤除,滤除效果可达到20 dB,且热量分布均匀,不会引起局部温度过高。     

Wide-band superconducting microstrip delay line

This paper describes the design, fabrication, and testing of a novel microstrip superconducting delay line. The structure of the delay line is a double-spiral meander line. The device is patterned from a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//(YBCO) thin film deposited on both sides of a 2-in-diameter LaAlO/sub 3/ substrate with a thickness of 0.25 mm. It exhibits low insertion loss up to 20 GHz. At 10 GHz, the measured attenuation is 0.031 dB/ns at 30 K, 0.049 dB/ns at 60 K, and 0.118 dB/ns at 77 K. The magnitudes of the ripples are below 2 dB across the entire band. The total delay at low frequency is approximately 29 ns.     

Optical spot-size converters for low-loss coupling between fibersand optoelectronic semiconductor devices

Structures of spot size converters that allow low loss and easy coupling between an optical semiconductor device and a fiber are proposed and designed theoretically. These spot-size converters have a tapered small core for expanding the mode field. They also have a double cladding region which consists of an n⁺-doped InP substrate as the outer cladding and a p-doped or nondoped InP layer as the inner cladding with a ridge structure. This double cladding utilizes the plasma effect of a carrier which makes the refractive index of highly doped n-InP lower than that of p-doped or nondoped InP. The double-cladding structure can tightly confine an expanded mode field in the inner cladding, and results in low radiation loss at the tapered waveguide, in addition, this structure reforms the mode field shape into a Gaussian-like shape and achieves a low loss coupling of less than 1 dB with a large misalignment tolerance for fiber coupling. These spot-size converters are easily fabricated and applicable to all types of optical semiconductor devices     

Transmission characteristics and reliability of pure-silica-core single-mode fibers

Transmission characteristics and reliability for pure-silica-core single-mode fiber with matched cladding are presented. On account of the "pure" silica core, without any additives, the fiber features the low attenuation and improved chemical stability under the existence of hydrogen and γ-ray radiation. High mechanical reliability and good splicing behavior of the fibers were also confirmed. More than 2000 km of pure-silica-core fiber have been fabricated, exhibiting median attenuation of 0.35 dB/km at 1.3 μm and 0.21 dB/ km at 1.55 μm. The achieved minimum attenuation was 0.154 dB/km at1.55-1.56 mum, which is the lowest attenuation ever reported.     

Variable optical attenuator based on a cutoff modulator withtapered waveguides in polymers

A variable optical attenuator was demonstrated by using a thermooptic cutoff modulator in polymers. It combined horizontally and vertically tapered waveguide structures to improve both the attenuation efficiency and the fiber coupling. The rib height of the waveguides in the input and output region was chosen to achieve minimum fiber coupling loss. For the waveguide in the active region with the electrodes, the rib height was reduced and the width was tapered in order to enhance the attenuation performance by weakening the mode confinement. The two waveguides with different rib heights were connected smoothly by employing a vertical taper, which was realized by utilizing two steps of reactive ion etching with a shadow mask. Then a fiber coupler built in a silicon block was attached directly to the output end of the device. A fraction of the main attenuator output was tapped and fed back to the electrical driver to achieve constant output regardless of variations in input light power and polarization. The measured insertion loss of the attenuator was 2.5 dB at 1550 nm. The dynamic range was more than 20 dB with an electrical power consumption of 160 mW. And the optical response time was faster than 1.5 ms. The effect of polarization on the attenuation was reduced to 0.1 dB by employing a continuous electronic feedback control. The wavelength uniformity was as small as 0.3 dB over the range from 1530 to 1560 nm. Finally, the attenuator was successfully used to regulate channel powers within 0.4 dB in a wavelength division multiplexed transmission system     

Suppression of cladding mode coupling loss in fiber Bragg gratings

We have demonstrated, for the first time, the suppression of cladding mode coupling loss to ~0.1 dB in 30-dB fiber Bragg gratings for both nonhydrogenated and hydrogenated fibers. These fibers have also been optimized to give 0.04-dB average splice loss to SMF-28 fiber. The suppression of cladding mode coupling is achieved by accurately characterizing and controlling the photosensitive profile. This low level of cladding mode coupling loss has opened up a new range of broadband applications, previously restricted by the limited free spectral range of fiber Bragg gratings     

Monolithic implementation of air-filled rectangular coaxial line

An air-filled rectangular coaxial line has been monolithically fabricated. Coaxial line is a suitable structure for reducing the coupling between two close transmission lines. Over the measurement range (from 4 to 38 GHz), the fabricated coaxial line has very low attenuation (<0.08 dB/mm) and low return loss (<-33 dB). The isolation between the two close lines separated by 40 μm is below -43 dB with 1 mm coupling length     

Quantum well vertical light modulator

A waveguide modulator is proposed whose operation is based on the dissipative coupling of light from a waveguide into an appropriate quantum-well structure. This approach uses the electric-field-induced change of the refractive index for light modulation. A particular geometrical configuration is numerically evaluated. The advantages of this configuration are that the combination of high switching speed ( approximately=1 ps), high on/off ratios (e.g. 1/16 dB or 2/25 dB), and low-driving voltage (4 V) could be combined in one device. The proposed modulator exhibits negligible phase shifts when the attenuation is smaller than about 10 dB.<>     

Achievement of uniform attenuation from 1.25 to 1.6 μm using anew three-layered Co2+ doped optical fiber

We report a new high attenuation fiber, whose cross section is a three-layered structure-the cobalt-doped core, the depressed inner cladding, and the outer cladding doped with cobalt in a ring. The proposed doping profile of cobalt ions both in the core and the cladding effectively attenuated the cladding modes to result in reduction of the modal interference. Enhancement of attenuation uniformity over a factor of three compared with prior techniques was achieved with the attenuation deviation less than 0.03 dB from 1250 to 1600 nm     

Fiber Inline Core–Cladding-Mode Mach–Zehnder Interferometer Fabricated by Two-Point CO$_{2}$ Laser Irradiations

We report a fiber inline Mach–Zehnder-type core–cladding-mode interferometer fabricated by two-point CO$_{2}$ laser irradiations on a single-mode fiber. The laser irradiations caused efficient light coupling from the core mode to the lower order cladding modes and vise versa. High-quality interference spectra with a fringe visibility of about 20 dB were observed for four different interferometer lengths (5, 10, 20, and 40 mm). The temperature sensitivity of the device with a length of 5 mm was measured to be 0.0817 nm/$^{circ}$C. The sensitivity for refractive index measurement of the device was comparable with a long-period fiber grating of LP$_{04}$ cladding mode.      

Cladding layer thickness-controlled directional coupler opticalswitch

The AlGaAs/GaAs cladding layer thickness-controlled directional coupler optical switch (CTC-SW) is discussed. To increase the efficiency of coupling between two waveguides, the CTC-SW was designed with a thin i-AlGaAs cladding layer h between the two waveguides. The coupling length L_c can be reduced, without reduction of the extinction ratio and increase of the switching voltage. For instance, L_c of CTC-SW (h=0.07) can be reduced 40% more than that of a conventional directional coupler switch (h=0). The extinction ratio is near 20 dB, both for the crossover (applied voltage V=0 V) and straight-through (V =19 V) states. A technique for adjusting L_c to the device length was developed     

An adaptive resonant filter

A solid-state adaptive (analog storage) device with stable electrical characteristics is described and demonstrated. The device is a resonant bandpass electronic filter with adaptable voltage gain; that is, the voltage gain-frequency transfer characteristic can be "set" to different values of attenuation by the application of an adapt signal and will retain that "setting" after the adapt signal has been removed. Ferroelectric materials are used as the dielectric in a filter structure composed of two capacitors bonded together so that resonant mechanical vibrations established in one (the input resonator) are coupled to the other (the output resonator). Converse and direct piezoelectric effects generate the mechanical vibrations and the output voltages, respectively. Ferroelectric effects in either capacitor provide the analog storage capabilities. The acoustical coupling mechanism employed in the device design results in electrically stable device characteristics. Previous ferroelectric adaptive devices used unstable field effect coupling mechanisms which led to unacceptable device performance. Experimental adaptive resonant filters fabricated with ceramic lead zirconate-lead titanate material compositions are discussed. These filters have electronic Q values near 100 at resonant frequencies in the range 10²to 10⁷Hz. The voltage gain-frequency characteristic has a maximum value at resonance of about 0 to +10 dB. Application of a voltage adapt pulse (100 to 300 volts) of low energy (mJ) to either side of the filter can adapt the entire gain characteristic by any value between 0 and about -60 dB within an arbitrary switching time (limited to a practical range of roughly 10⁺³to 10^-4seconds) as determined by the pulse amplitude. Voltage gain settings are electrically stable and can be reproduced by the same or an equivalent sequence of adapting pulses.     

Single-Mode Perfluorinated Polymer Optical Fibers With Refractive Index of 1.34 for Biomedical Applications

We demonstrate a technique for the fabrication of single-mode perfluorinated polymer optical fiber (PPOF). The PPOF preform is composed of poly-methyl-methacrylate (PMMA)-based outer cladding and a graded-index multimode PPOF as the core. A photosensitive graded-index single-mode PPOF with a core diameter of about 6.6 $ mu{hbox {m}}$ and cladding diameter of 400 $ mu{hbox {m}}$ was fabricated. The fiber has a cutoff wavelength of 854 nm and exhibits single-mode characteristics at wavelengths of 1310 and 1550 nm. The transmission loss is less than 0.2 dB/m in the wavelength range of 1410–1540 nm and less than 0.5 dB/m for wavelengths up to 1610 nm, significantly less than the typical transmission loss of $sim$100 dB/m for PMMA fiber. Another important feature of the PPOF is its low refractive index of 1.34, close to aqueous solution of biomaterials, permitting strong optical coupling for biomedical applications.      

一种低通带波纹的EBG带阻滤波器

分析了串联加载的电磁带隙结构(EBG)带阻滤波器的通带波纹,比较了电容、电感和并联谐振加载的影响,设计和制作了一种低通带波纹的EBG带阻滤波器。该结构共有4个周期,通过在微带线的接地面上蚀刻螺旋形结构来实现。滤波器的中心频率为2.44GHz,阻带中心衰减大于50dB,相邻通带内的波纹小于0.29dB。仿真结果与试验结果相吻合,说明了分析和设计的正确性。     

Lens-free optical fiber connector having a long working distance assisted by matched long-period fiber gratings

Optical fiber connectors that had a long working distance and wide alignment tolerance were implemented by utilizing long-period fiber gratings (LPGs) written in double-cladding fiber. The power coupling between two separated pieces of fiber was accomplished through the inner cladding modes of both fibers. Assisted by the LPGs, approximately 450 /spl mu/m was achieved for a 1-dB working distance, as well as about 3 mm of 3-dB working distance. When the separation between two fiber tips was 1.5 mm, the 3-dB lateral tolerance was measured to be about 30 /spl mu/m, which was five times better than was the case when not utilizing the LPGs. By using the inner cladding mode of a dispersion-compensating fiber, it was possible to implement a fiber connector that was insensitive to the perturbations at the cladding surface of the fiber. The total insertion loss of the device at the maximum coupling was 2.06 dB, from which the loss purely induced by inserting the fiber gratings was analyzed to be smaller than 0.9 dB. The experimental results show strong feasibility for implementing a simple and cost-effective fiber connector that does not require any bulk optic elements.     

Ultra-broadband optical filter based on chirped long-period fiber grating using leaky mode coupling

An ultra-broadband optical filter was proposed and demonstrated based on leaky mode coupling in a coated chirped long-period fiber grating (CLPFG). The CLPFG was coated with a material whose refractive index (RI) was higher than that of the fiber cladding, enabling the coupling of the core mode to leaky modes, to achieve a desired coupling efficiency. Complex coupled-mode theory was used to investigate the power evolution of the core mode that resulted from the coupling. From this, the conditions in which the core mode power attenuates the most rapidly were identified. In addition, phase matching turning point (PMTP) was used in the design, to overcome the conflict between the range of grating period change and the grating length in the CLPFG. Finally, an optimized CLPFG-based filter with a length of 3.5 cm was obtained, which has a symmetrical attenuation band with an operating bandwidth over 300 nm. Within the operating bandwidth, the flatness is less than 2.5 dB and the transmittance is lower than 0.1%.     

Optical waveguide polariser with synchronous absorption

It is shown that a high TM-mode attenuation may be obtained in a buffered metal-clad optical waveguide with large buffer thickness. This is due to synchronous coupling to a highly lossy interface mode. The geometry offers significant advantages as a polarising structure. A TM/TE attenuation ratio of greater than 100 and a TE attenuation of < 1 dB/cm were measured.