A 300 GHz quasioptical faraday rotation isolator

A quasioptical isolator has been developed at 285 GHz with insertion loss2 dB and isolation 18 dB over a 1% bandwidth. By improving matching techniques, the device should perform as well over bandwidths up to 5%. This design can be easily modified to make a circulator.     

Optical isolators using Bi-substituted rare-earth iron garnet films

Using Bi-substituted rare-earth iron garnet film, (GdBi)₃ (FeAlGa)₅O₁₂ or (YbTbBi)₃ Fe₅O₁₂, grown by liquid phase epitaxy technique, we have fabricated a compact, low cost and high performance optical isolator for near-infrared wavelength region, in comparison with conventional isolator using yttrium iron garnet (YIG) single crystal as Faraday rotator. Typical insertion loss and isolation of developed isolators are 0.6 dB and 35 dB respectively at =1.31 m and the size is 6×6 mm. The isolators, which could be used in the wavelength range of 1.31 to 1.55 m, are also fabricated with insertion loss of less than 1.1 dB and isolation of more than 35 dB.     

A mm-wave four-port quasi-optical circulator

A four-port quasi-optical circulator has been designed, built and tested for operation in the millimetre wave band. The specific circulator reported here was investigated over a 20 GHz bandwidth, centred on 94 GHz. Good performance characteristics were obtained over this bandwidth. Isolations of better than 30 dB and insertion losses of around 0.5 dB were achieved. The input vswr was found to be less than 1.35 over the whole bandwidth investigated and vswr's of less than 1.1 were achieved for narrower bandwidths. It is possible of course to configure the 4-port circulator as a 3-port circulator or indeed as 2-port isolator. Further optimization and consequent improvements in performance are almost certainly obtainable.     

棱镜分光式光学环行器及其应用

本文介绍梭镜分光式光学环行器设计理论与制备工艺以及在光纤通信和光纤传感系统中的应用。所研制的光学环行器光纤-光纤(单模)插入损耗小于2.8dB,隔离比大于25dB,回波损耗优于40dB.器件性能与偏振无关。     

Fiber devices using polarization- maintaining fibers

Fiber devices using polarization-maintaining fibers called PANDA fibers are presented. They are polarization-maintaining couplers and polarization-splitting couplers, optical isolators and optical circulators, and multi/demultiplexers designed for 1.3 μm wavelength. Crosstalk of-32 dB and excess loss of 0.03 dB for the polarization-maintaining coupler, and polarization-splitting ratio of 17 dB and excess loss of 0.5 dB for the polarization-splitting coupler have been fabricated by a fusion-elongation method. A fiber polarizer with the extinction ratio of more than 40 dB has been presented by using the difference of bending loss between the orthogonal modes in the PANDA fibers. Multi/demultiplexer with narrow band-pass of 1.4 nm utilizing combination of PANDA fiber polarization dispersion and the polarization-splitting coupler has been realized. An optical isolator consisting of fiber polarizers and a spherical YIG with a lens function and an optical circulator consisting of polarizing-splitting couplers and spherical YIGs have been achieved.     

1.3μm光学环行器正向损耗及反向隔离比的理论及实验研究

在理论及实验上分析了影响光环行器插入损耗及反向隔离比的因素,讨论了环行器中起、检偏镜参数对其性能的影响.结果表明,起、检偏镜的各组参数存在最佳选择,以保证环行器具有低插损、高隔离比及与偏振无关的特性.作者研制的环行器正向损耗小于1dB,反向隔离比在25.5dB与28dB之间.     

A self-frequency-locked multi-wavelength erbium-doped fibre ring laser

A self-frequency-locked laser in a 1.55 m band is demonstrated by adding a segment of samarium-doped fibre (SDF) into an erbium-doped fibre (EDF) ring laser cavity. The narrow band output signal, with a 3 dB down line width of less than 0.15 nm and a side-mode suppression ratio larger than 30 dB, is nearly polarization independent. A multiwavelength EDF ring laser source, using a 1×n synchronous optical switch and n segments of SDF with different lengths, is proposed.     

Fiber devices using polarization- maintaining fibers

Fiber devices using polarization-maintaining fibers called PANDA fibers are presented. They are polarization-maintaining couplers and polarization-splitting couplers, optical isolators and optical circulators, and multi/demultiplexers designed for 1.3 μm wavelength. Crosstalk of-32 dB and excess loss of 0.03 dB for the polarization-maintaining coupler, and polarization-splitting ratio of 17 dB and excess loss of 0.5 dB for the polarization-splitting coupler have been fabricated by a fusion-elongation method. A fiber polarizer with the extinction ratio of more than 40 dB has been presented by using the difference of bending loss between the orthogonal modes in the PANDA fibers. Multi/demultiplexer with narrow band-pass of 1.4 nm utilizing combination of PANDA fiber polarization dispersion and the polarization-splitting coupler has been realized. An optical isolator consisting of fiber polarizers and a spherical YIG with a lens function and an optical circulator consisting of polarizing-splitting couplers and spherical YIGs have been achieved.     

Millimeter wave microstrip circulator

A new and unique microstrip drop-in type Y-junction circulator has been designed and developed for operation in the millimeter wave frequency region. This device utilizes NiZn ferrite as the gyromagnetic material which is mounted on a duroid substrate.     

L-band all-optical gain-clamped EDFA by utilizing C-band backward ASE

By using an optical circulator and C/L-band wavelength division multiplexer to recycle the C-band backward ASE, an L-band gain-clamped erbium-doped fiber amplifier is presented. We have experimentally studied the static gain clamping property of this amplifier. As the ASE feedback attenuation is set to 0, the gain at 1585 nm can be clamped at 18.84 ± 0.26 dB within dynamic range of 25 dB and the critical power reaches about −15.09 dBm. The gain variation and saturated output power at 1585 nm for 0 dB attenuation are 1 dB lower and 2.17 dB higher than those for 30 dB attenuation, which indicates that the L-band EDFA gain can be effectively clamped via the ASE injection technique.     

3.5 μm optical communication experiment at 100 Mbits−1 using a PbCdS diode laser

A mid-infrared optical communication experiment using a lead-salt diode laser emitting at 3.5 m is reported. Bit-error rate measurements have been performed for pulse code modulated data at 100 Mbits^–1 using a fluoride glass fibre as a transmission channel. A bit-error rate better than 10^–10 was achieved at a signal-to-noise ratio of 20 dB.S. T. Eng has a joint appointment with the Jet Propulsion Laboratory, Pasadena, California 91109, USA.     

Study of noise characteristics of baw and SAW quartz resonators

The low-frequency noise of bulk- and surface-acoustic-wave (BAW and SAW) resonators at frequencies of from 100 to 600 MHz is studied. It is shown that both SAW and BAW resonators have parameter (resonant-frequency) fluctuations with 1/f power spectra with considerable intensity spreads: approximately 20 dB for SAW and more than 30 dB for BAW resonators. The phase-noise floor of 100-MHz oscillators with BAW resonators is –150 dB/Hz for a 1-kHz offset frequency. The phase-noise level of oscillators with SAW resonators at 400–600 MHz is higher by 5–10 dB (scaled to a 100-MHz carrier frequency).Presented at All-Union Coordinating Conference Low-Frequency Noise in Semiconductor Devices (Chernogolovka, Moscow Region, June, 1991).Ural Polytechnic Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 12, pp. 1143–1152, December, 1993.     

Investigation on an ultra-compact 1\times 2 polymer electro-optic switch using cross-coupling 2N+1 vertical-turning serial-coupled microrings

Generic model and thorough investigation are proposed for a novel $1\times 2$ 1 × 2 polymer electro-optic (EO) switch based on one-group $2N+1$ 2 N + 1 vertical-turning serial-coupled microrings. For realizing boxlike flat spectrum as well as low crosstalk and insertion loss, resonance order and coupling gaps are optimized. The MRR switches with $N \ge 1$ N ≥ 1 reveal favorable boxlike spectrum as when compared with the simple device with only one microring ( $N = 0$ N = 0 ). For obtaining $<-30\,\text{ dB }$ < - 30 dB crosstalk under through-state, the dependency of switching voltage on $N$ N is determined as $7.19 \times \text{ exp }(-N/0.72) + 1.72\,(\text{ V })$ 7.19 × exp ( - N / 0.72 ) + 1.72 ( V ) . Under the operation voltages of 0 V (drop state) and the predicted switching voltages (through state), the device performances are analyzed, and $1 \le N \le 10$ 1 ≤ N ≤ 10 is required for dropping the insertion loss (drop state) below 10 dB. The crosstalk of the ten devices ( $N = 1-10$ N = 1 - 10 ) are $< -19.5\,\text{ dB }$ < - 19.5 dB under drop state and $< -28.7\,\text{ dB }$ < - 28.7 dB under through state, and the insertion losses of the devices ( $N = 1-10$ N = 1 - 10 ) are $< 9.715\,\text{ dB }$ < 9.715 dB under drop state and $< 1.573\,\text{ dB }$ < 1.573 dB under through state. The device also has ultra-compact footprint size of only 0.33–1.06 mm, which is only 1/10–1/3 of those of our previously reported polymer EO switches based on directional coupler or Mach–Zehnder interferometer structures. Therefore, the proposed device is capable of highly integration onto optical networks-on-chip.     

1.55 μm AlGaInAs/InP polarization-insensitive optical amplifier with tensile strained wells grown by MOCVD

Polarization-insensitive AlGaInAs'InP semiconductor optical amplifier is realized at wavelength of 1.55 . The active layer consists of three tensile strained wells with strain of 0.40%. The amplifier is fabricated to ridge waveguide structure. The testing result shows the amplifiers have excellent polarization insensitivity (less than 0.8dB). The 1540 nm wavelength optical gain is 20 dB at the bias current of 200 mA.     

Novel Bandpass Filter Configuration Using Coupled Linear Tapered Line Resonators

A novel tapped bandpass filter composed of twocoupled linear taperedline resonators (LTLRs) is proposed. Multistepped resonators are applied to analyzing LTLRs, which are difficult to analyze directly. Through this analysis method, fundamental characteristics of LTLRs and their filter design parameters can be easily derived. This new filter has insertion loss less than 0.6dB at 1.9 GHz, the return loss less than 18dB in the range 1.81.93GHz and 12.3% 3dB bandwidth. Experimental results of fabricated filter are in good agreement with the design results.     

Analysis and design of a new type NRD-guide E-plane Y-junction circulator

A new type of E-plane Y-junction circulator has been developed based on the nonradiative dielectric waveguide (NRD-guide) in Ka- band. First, the circulation principle has been analysed by the theory of polarization wave. The field components in the nonreciprocal Y-junction zone and the conclusion of 60° phase difference between clockwise and counterclockwise rotating polarization modes has been obtained. And then, the resonant frequency of the non-dc biased triangle ferrite sample has also been calculated. This kind of structure is benefit to enlarge the bandwidth of the Y-junction circulator. As an example, we had designed and fabricated a circulator in Ka-band. Its operating frequency is 35. 1GHz, the 1.5dB insertion loss and 20dB isolation bandwidth is about 1. 0GHz.     

Controversial Variable Node Selection-Based Adaptive Belief Propagation Decoding Algorithm Using Bit Flipping Check for JSCC Systems

An end-to-end joint source–channel (JSC) encoding matrix and a JSC decoding scheme using the proposed bit flipping check (BFC) algorithm and controversial variable node selection-based adaptive belief propagation (CVNS-ABP) decoding algorithm are presented to improve the efficiency and reliability of the joint source–channel coding (JSCC) scheme based on double Reed–Solomon (RS) codes. The constructed coding matrix can realize source compression and channel coding of multiple sets of information data simultaneously, which significantly improves the coding efficiency. The proposed BFC algorithm uses channel soft information to select and flip the unreliable bits and then uses the redundancy of the source block to realize the error verification and error correction. The proposed CVNS-ABP algorithm reduces the influence of error bits on decoding by selecting error variable nodes (VNs) from controversial VNs and adding them to the sparsity of the parity-check matrix. In addition, the proposed JSC decoding scheme based on the BFC algorithm and CVNS-ABP algorithm can realize the connection of source and channel to improve the performance of JSC decoding. Simulation results show that the proposed BFC-based hard-decision decoding (BFC-HDD) algorithm (ζ = 1) and BFC-based low-complexity chase (BFC-LCC) algorithm (ζ = 1, η = 3) can achieve about 0.23 dB and 0.46 dB of signal-to-noise ratio (SNR) defined gain over the prior-art decoding algorithm at a frame error rate (FER) = 10−1. Compared with the ABP algorithm, the proposed CVNS-ABP algorithm and BFC-CVNS-ABP algorithm achieve performance gains of 0.18 dB and 0.23 dB, respectively, at FER = 10−3.     

A strained InAIAs/InGaAs superlattice avalanche photodiode with a waveguide structure for low bias-voltage operation

An InAIAs/InGaAs superlattice (SL) multiplication layer operating at an IC-power supply voltage was realized by introducing strain into the SL. Using this SL as an absorption and multiplication layer, edge-coupled InAIAs/InGaAs SL avalanche photodiodes with waveguide structures were demonstrated. An avalanche multiplication factor larger than 10 was achieved at a bias voltage of less than 7V. A wide 3 dB bandwidth of 8 GHz was obtained at a multiplication factor of 3 and a wavelength of 1.3 m.     

MRI dynamic range and its compatibility with signal transmission media

As the number of MRI phased array coil elements grows, interactions among cables connecting them to the system receiver become increasingly problematic. Fiber optic or wireless links would reduce electromagnetic interference, but their dynamic range (DR) is generally less than that of coaxial cables. Raw MRI signals, however, have a large DR because of the high signal amplitude near the center of k-space. Here, we study DR in MRI in order to determine the compatibility of MRI multicoil imaging with non-coaxial cable signal transmission. Since raw signal data are routinely discarded, we have developed an improved method for estimating the DR of MRI signals from conventional magnitude images. Our results indicate that the DR of typical surface coil signals at 3 T for human subjects is less than 88 dB, even for three-dimensional acquisition protocols. Cardiac and spine coil arrays had a maximum DR of less than 75 dB and head coil arrays less than 88 dB. The DR derived from magnitude images is in good agreement with that measured from raw data. The results suggest that current analog fiber optic links, with a spurious-free DR of 60–70 dB at 500 kHz bandwidth, are not by themselves adequate for transmitting MRI data from volume or array coils with DR 90 dB. However, combining analog links with signal compression might make non-coaxial cable signal transmission viable.     

Double-pass ytterbium-doped fiber amplifier with high gain coefficient and low noise figure

We have proposed and demonstrated a double-pass ytterbium-doped fiber amplifier using an optical circulator and a fiber Bragg grating as reflector. When the signal has passed through the ytterbium-doped fiber once, it reflects off a 0.2-nm passive fiber Bragg grating filter. This reduces amplified spontaneous emission (ASE) noise from the first pass. The input signal light is amplified both forward and backward through ytterbium-doped fiber. With this double-pass configuration, 1053.15-nm unsaturated signal gain of 28 dB, gain coefficient of 1.1 dB/mW, and noise figure of less than 4 dB are achieved at 977-nm pump power of 68 mW. It is also found that this double-pass configure provides enhancing gain coefficient and improving noise figure by comparison with single-pass configuration.