An ultra-wide passband (5-30µm) filter for FTIR studies of Photosystem II

This paper reports on the design and manufacture of an ultra-wide (5-30µm) infrared edge filter for use in FTIR studies of the low frequency vibrational modes of metallo-proteins. We present details of the spectral design and manufacture of such a filter which meets the demanding bandwidth and transparency requirements of the application, and spectra that present the new data possible with such a filter. A design model of the filter and the materials used in its construction has been developed capable of accurately predicting spectral performance at both 300K and at the reduced operating temperature at 200K. This design model is based on the optical and semiconductor properties of a multilayer filter containing PbTe (IV-VI) layer material in combination with the dielectric dispersion of ZnSe (II-VI) deposited on a CdTe (II-VI) substrate together with the use of BaF2 (II-VII) as an antireflection layer. Comparisons between the computed spectral performance of the model and spectral measurements from manufactured coatings over a wavelength range of 4-30µm and temperature range 300-200K are presented. Finally we present the results of the FTIR measurements of Photosystem II showing the improvement in signal to noise ratio of the measurement due to using the filter, together with a light induced FTIR difference spectrum of Photosystem II.

Novel window functions for digital filters

Window technique is one of the simplest methods to design Finite Impulse Response (FIR) filters. It uses special functions to truncate an infinite sequence to a finite one. In this paper, we propose window techniques based on integer sequences. The striking feature of the proposed work is that it overcomes all the problems posed by floating point numbers and inaccuracy, as the sequences are made of only integers. Some of these integer window sequences, yield sharp transition, while some of them result in zero ripple in passband and stopband.

Design of some 2-D filters through the transformation technique

The transformation technique is a tool FIR designing 2-D filters, useful for the design of specially shaped filters with passband/stopband regions not centred around the origin. The authors extend this technique to design two types or filters. A notch filter has a stopband centred about a small region in the 2-D frequency plane. The authors propose an extension to the transformation technique with the windowing concept to achieve the design of notch filters. A directional filter has a passband extending fully along: a straight line pacing through the origin. The transformation technique is: further extended to yield such directional filters. Design and application examples for both these fillers are also presented.

Novel Mach-Zehnder interferometer structure for tunable optical interleaver

A novel optical interleaver scheme based on nested optical glass pairs is proposed. The assembly of pairs behaves as a cascaded Mach-Zehnder interferometer. The interleaver, with simple structure, low cost, and compact size, can be easily implemented with inexpensive material and mature preparation technology. Small channel spacing (<= 50 GHz), high isolation (<-30 dB), a wide, flat passband and stop band (> 2/11 period), and center-frequency tunability can be obtained simultaneously. An optimum design of a 50-GHz tunable interleaver based on this structure is given as an example. Its environmental temperature sensitivity and fabrication tolerance are also analyzed. (c) 2006 Society of Photo-Optical Instrumentation Engineers.

窄带干涉滤光片抗击不同输出方式激光的损伤特性研究

利用Nd：YAG调Q单脉冲激光和自由脉冲激光对硬膜窄带干涉滤光片进行激光损伤阈值的测试，并且采用表面热透镜技术测量了滤光片的吸收率。实验发现：窄带干涉滤光片的吸收率和激光损伤阈值强烈依赖于辐照激光波长与窄带干涉滤光片通带的相对位置；在调Q单脉冲激光作用下，不同中心波长的滤光片损伤形貌存在明显的差别，而在自由脉冲激光作用下，各滤光片的损伤形貌则趋于相同．均表现为典型的热熔烧蚀破坏。根据实验结果，结合损伤形貌，通过驻波场理论对激光作用下滤光片内电场分布的分析与模拟．探讨了两种激光模式作用下滤光片的损伤特征和损

The viability of subcarrier modulation for enhancing the performance of installed-base MMF links

The technique of Subcarrier Modulation is assessed by statistical analysis as a viable solution to broadband data transmission over dispersion limited multimode fibre. It is shown that a suitable passband region for transmission of 2.5 Gb/s channels exists at 5 GHz in greater than 80% of worst-case fibres under standard SMF/MMF launch conditions. ©2002 Optical Society of America.

Flat-top arrayed waveguide grating using a tapered multimode interferometer

A 40-channel 0.8-nm-spaced flat-top silica-based arrayed waveguide grating (AWG) with a tapered multimode interferometer (MMI) at the end of its input waveguide has been experimentally demonstrated for the first time. By adding the MMI, the 1-dB and 3-dB bandwidths are increased to 0.45 and 0.62 nm, respectively. The insertion loss (IS) of the device ranges from 3.8 to 6.8 dB. The IS uniformity is better than 3.0 dB. The crosstalk is better than -25 dB. Compared to the AWG with a rectangular MMI, the AWG with a tapered MMI shows better IS, crosstalk, and ripple. (c) 2006 Society of Photo-Optical Instrumentation Engineers.

A Low Power Baseband Chain for CMMB Application

This paper presents experimental results of an analog baseband circuit for China Multimedia Mobile Broadcasting (CMMB) direct conversion receiver in 0.35um SiGe BiCMOS process. It is the first baseband of CMMB RFIC reported so far. A 8(th)-order chebyshev low pass filter (LPF) with calibration system is used in the analog baseband circuit, the filter provides 0.5 dB passband ripple and -35 dB attenuation at 6MHz with the cutoff frequency at 4MHz, the calibration of filter is reported to achieve the bandwidth accuracy of 3%. The baseband variable gain amplifier (VGA) achieves more than 40 dB gain tuning with temperature compensation. In addition, A DC offset cancellation circuit is also introduced to remove the offset from layout and self-mixing, and the remaining offset voltage and current consumption are only 6mV and 412uA respectively. Implemented in a 0.35um SiGe technology with 1.1 mm(2) die size, this tuner baseband achieves OIP3 of 25.5 dBm and dissipate 16.4 mA under 2.8-V supply.

A widely tunable continuous-time LPF for a direct conversion DBS Tuner

A continuous-time 7th-order Butterworth Gm-C low pass filter (LPF) with on-chip automatic tuning circuit has been implemented for a direct conversion DBS tuner in a 0.35um SiGe BiCMOS technology. The filter's -3dB cutoff frequency f(0) can be tuned from 4MHz to 40MHz. A novel translinear transconductor (Gm) cell is used to implement the widely tunable and high linear filter. The filter has -0.5dB passband gain, 28nV/Hz(1/2) input referred noise, -2dBVrms passband IIP3, 24dBVrms stopband IIP3. The I/Q LPFs with the tuning circuit draw 16mA (with f(0)=20MHz) from 3.3 V supply, and occupy an area of 0.45 mm(2).

A widely tunable continuous-time LPF for a direct conversion DBS tuner

A continuous-time 7th-order Butterworth Gm-C low pass filter (LPF) with on-chip automatic tuning circuit has been implemented for a direct conversion DBS tuner in 0.35μm SiGe BiCMOS technology. The filter's -3 dB cutoff frequency f0 can be tuned from 4 to 40 MHz. A novel on-chip automatic tuning scheme has been successfully realized to tune and lock the filter's cutoff frequency. Measurement results show that the filter has -0.5 dB passband gain, +/- 5% bandwidth accuracy, 30 nV/Hz~(1/2) input referred noise, -3 dBVrms passband IIP3, and 27 dBVrms stopband IIP3. The I/Q LPFs with the tuning circuit draw 13 mA (with f_0 = 20 MHz) from 5 V supply, and occupy 0.5 mm~2.

Evidence for the Flare Trigger Site and Three-Dimensional Reconnection in Multiwavelength Observations of a Solar Flare

Fletcher, L., Metcalf, T.R., Alexander, D., Brown, D.S. and Ryder, L.A., 2001, Evidence for the flare trigger site and 3D reconnection in multi-wavelength observations of a solar flare, Astrophysical Journal, 554, 451-463.

Liquid crystal tunable mm wave frequency selective surface

A frequency selective surface (FSS) which exploits the dielectric anisotropy of liquid crystals to generate an electronically tunable bandpass filter response at D Band (110-170 GHz) is presented. The device consists of two printed arrays of slot elements which are separated by a 130-mu m thick layer of liquid crystals. A 3% shift in the filter passband occurs when the substrate permittivity is increased by applying a control signal of 10 V. Measured results show that the insertion loss increases from -3.7 dB to -10.4 dB at resonance (134 GHz), thus demonstrating the potential to create a FSS which can be switched between a transmitting and a reflecting structure.