Mode-locked erbium-doped fiber ring laser using intracavity polarization-maintaining loop mirror

Erbium-doped fiber lasers at repetition rate of 40 and 80 GHz are demonstrated in an injection-locked and rational harmonic mode-locked ring cavity. The cavity has a polarization-maintaining loop mirror. The injection-locking pulse is generated at repetition rates of 20 and 40 GHz from another rational harmonic mode-locked fiber laser. When these pulses are injected into the second fiber laser, pulses at twice the repetition rates viz. 40 and 80 GHz are produced.     

Backscatter and attenuation by falling snow and rain at 96, 140,and 225 GHz

The results of measurements are presented for backscatter cross section per unit volume and attenuation for falling snow and rain at 96, 140, and 225 GHz. The attenuation due to rain is almost independent of the measurement frequency, but for snow the attenuation is considerably greater at 225 GHz than at 96 GHz. The rain attenuation generally varies with the rain accumulation rate in accordance with an aR^b relationship for a Laws and Parsons drop-size distribution where R is the rain rate and a and b are constants. The attenuation at all three frequencies is about 3 dB/km for a rain rate of 4 mm/h. The attenuation due to snow varies with airborne snow-mass concentration, with the average rates of increase being 0.9, 2.5, and 8.7 (dB/km)(g/m³) at 96, 140, and 225 GHz, respectively. Generally the attenuation for snow is lower than that for rain. The backscatter cross section per unit volume for rain at 96 GHz is about -35 dB m²/m³ for a rain rate of 4 mm/h. The backscatter from snow at 96 GHz is much lower than that from rain under equivalent accumulation rates or airborne mass concentrations. Snow backscatter at 140 GHz is comparable but higher than that at 96 GHz     

Synchronous mode-locking in passively mode-locked semiconductor laser diodes using optical short pulses repeated at subharmonics of the cavity round-trip frequency

Synchronous mode-locking was achieved in passively mode-locked semiconductor lasers using optical pulses with repetition rates at subharmonics of the cavity round-trip frequency. Stable and continuous mode-locked pulses at 8.5 GHz were generated when the repetition rate of the control optical pulses was 4.25 GHz (2nd subharmonic). The timing jitter of the mode-locked pulses was reduced to 1 ps. The relationship between repetition rates of the control pulses and the realization of stable and continuous mode-locking was examined.     

Rain attenuation at 15 and 35 GHz

In order to satisfy future earth-to-space communications needs, new regions of the electromagnetic spectrum must be exploited. A program to determine the feasibility of using millimeter waves for this application has been conducted at Air Force Cambridge Research Laboratories (AFCRL) for approximately 6 years and it has been shown that at frequencies of 15 GHz (lambda = 2.0cm) and 35 GHz (lambda = 8.6mm) atmospheric attenuation is relatively low except for conditions of heavy clouds and precipitation. A portable radiometric system designed to measure attenuation at 15 and 35 GHz under conditions of precipitation was constructed and located in Hilo, Hawaii, a region where it rains frequently thus making it possible to conduct many attenuation measurements for varying rainfall rates. Attenuation was determined from both extinction and emission measurements as a function of zenith angle and rain rate. On the basis of the results that were obtained, it is concluded that for orographic rain up to rates of 50 mm/h in Hawaii: 1) attenuations up to approximately 10 dB can be calculated quite accurately from an emission measurement; 2) zenith attenuations are well correlated with rain rate and can be estimated from the regression lines which have been obtained; 3) attenuations at angles off zenith are not as well correlated with rain rate and thus the values obtained from the regression lines are only approximate; 4) attenuations at 15 and 35 GHz are well correlated.     

Étude de l’affaiblissement de propagation à 13 GHz dû aux précipitations tropicales

Measurements of rainfall rates and attenuation due to rain at 13 GHz have been carried out in Ivory Coast during copt 81 experiment in May and June 81. Rainfall attenuation distributions for horizontal and vertical polarizations and rain rate distributions along the path are presented. Values of differential attenuation and specific attenuation are derived from experimental data as a function of rain rate. Some rain attenuation prediction models are tested against our experimental data at 13 GHz on a 19,2 km path length.     

Design and experiments on a high-resolution multi-gigahertzsampling rate superconducting A/D converter

Work towards a high-resolution multi-gigahertz sampling rate A/D converter is presented. A brief review of the overall architecture which consists of a coarse section and an interpolator section is given. Experiments on two designs for the coarse sections are discussed. One is a 6-bit A/D converter built with two-leaf phase tree periodic comparators. Asynchronous beat frequency tests at 2.01 GHz sampling rates indicate this circuit is capable of 6 bits of resolution at 2 GHz input bandwidth. The resolution falls off to about 5 bits at 4 GHz and 4 bits at 6 GHz. The other approach involves two related novel single threshold comparators with large dynamic range. For one of the comparators, dynamic range in excess of 60 db is demonstrated by transfer characteristic and input current noise measurements, while the other showed 54 db of dynamic range. A chain of 15 comparators based on one of the designs has been designed and tested. Asynchronous beat frequency tests at 2.01 GHz sampling rates show a monotonic response for input frequencies up to 8 GHz. Threshold offsets due to flux trapping limited the resolution in this set of experiments to about 5 bits. Experiments on a periodic interpolator circuit based on the two-leaf phase tree comparator are also presented. The results suggest that it should be possible to obtain 10-bits of resolution with this approach     

Comparison of mobile radio transmission at UHF and X band

Experimental measurements of mobile radio transmission have been made in a suburban area at 0.836 GHz and 11.2 GHz. The results are presented in terms of average transmission loss, level crossing rates, power spectra, average duration of fades, and probability distributions. Fading rates were predictably higher at 11.2 GHz but the average excess path loss over the free space calculation was comparable to the values obtained at UHF, lending encouragement to possible exploitation of the higher microwave bands for mobile radio.     

Microwave thermography: principles, methods and clinical applications.

We review the physical principles, method of operation, measurement limitations, and potential medical applications of microwave thermography. We present detailed results of a study of breast cancer detection at 1.3 and 3.3 GHz, including the dependence of detection rates on microwave frequency, time, tumor depth, and tumor size. At 1.3 GHz, microwave thermography detects breast cancer as well as infrared thermography (true-positive rate = 0.76 when true-negative rate = 0.63). When the two methods are combined, the true-positive rate increases by about 0.1 over that of either method alone.     

主动有理谐波锁模光纤激光器

利用有理谐波锁模,实现了锁模光纤激光器输出光脉冲重复频率的倍增,得到了重复频率10GHz~50GHz输出脉冲.     

Comparisons of system architectures for microwave-photonics transmissions at 60 GHz

We report here on different system architectures for a wireless link operating in the 60 GHz range, which has a high potential for use in short range and highly secure high data rate applications. The millimetre wave around 60 GHz is generated by photonic heterodyning or microwave-photonics using radio-over-fibre concept of transmission. Low error transmission using two techniques at data rates up to 4.2 Gb/s is experimentally demonstrated.     

High-speed QPSK modulator and demodulator with subharmonic pumping

The authors describe a subharmonically pumped QPSK modulator and demodulator using pairs of beam-leaded Schottky diodes and appropriate high-pass and low-pass filters on dielectric substrates. A modulator and a demodulator were operated in cascade at a carrier frequency of 13 GHz with a common pump at 6.5 GHz. This circuit showed clean eye diagrams of the recovered data trains up to 1.5 Gb/s with corresponding error rates of less than 10^-11. The circuits can be readily scaled to higher frequencies with a proportional increase of the information rate     

Ku-band subsampling track-and-hold amplifier with 8 ENOB resolution

A wideband subsampling track-and-hold amplifier has been designed for input frequencies up to Ku-band and clock rates up to 2.5 GS/s. Circuits were fabricated in 1 /spl mu/m InP SHBT technology. Spur-free dynamic range measured with two-tone input frequencies of 12.6 and 12.602 GHz and a 2.5 GS/s clock rate ranges from 53-69 dB at an input level of -1 dBFS for each tone. Signal-to-noise ratio (SNR) test results show that the master/slave (M/S) track-and-hold design provides 59 dB of SNR in a 1 GHz bandwidth at input frequencies up to at least 2.6 GHz. A single track-and-hold dissipates 1.5 W while the M/S configuration dissipates 2.5 W.     

Impact of Uncertainty in the Drop Size Distribution on Oceanic Rainfall Retrievals From Passive Microwave Observations

The variability of the drop size distribution (DSD) is one of the factors that must be considered in understanding the uncertainties in the retrieval of oceanic precipitation from passive microwave observations. Here, we have used observations from the Precipitation Radar on the Tropical Rainfall Measuring Mission spacecraft to infer the relationship between the DSD and the rain rate and the variability in this relationship. The impact on passive microwave rain rate retrievals varies with frequency and rain rate. The total uncertainty for a given pixel can be slightly larger than 10% at the low end (ca. 10 GHz) of frequencies commonly used for this purpose and smaller at higher frequencies (up to 37 GHz). Since the error is not totally random, averaging many pixels, as in a monthly rainfall total, should roughly halve this uncertainty. The uncertainty may be lower at rain rates less than about 30 mm/h, but the lack of sensitivity of the surface reference technique to low rain rates makes it impossible to tell from the present data set.     

First attempts at modelling earth-to-space radio propagation using SIRIO measurements in the 11 and 18 GHz bands

A bi-dimensional statistical model for earth-to-space radio links, characterized by effective rain rates and rain path lengths is proposed. These parameters refer to an equivalent homogeneous slab of rain having depth and rain rate such as to produce similar values of measured attenuations. Input data for the present study were attenuation data at 11.6 GHz (absolute and differential over a 520 MHz band) and 17 GHz, collected by the Sirio satellite: these data were found to be jointly log-normally distributed as were the effective rain rate and path length. A straightforward application of the model is the extrapolation of attenuation statistics to higher frequencies: the effectiveness of the method, when applied to 11.6 GHz data is tested against the data at 17 GHz; both the statistics and the time profiles are excellently reproduced. This suggests the use of a differential radiometer working at a relatively low frequency in order to acquire reliable higher frequency statistics and effective model parameters.     

A 1.35 GS/s, 10 b, 175 mW Time-Interleaved AD Converter in 0.13 µm CMOS

A time-interleaved ADC is presented with 16 channels, each consisting of a track-and-hold (T&H) and two successive approximation (SA) ADCs in a pipeline configuration to combine a high sample rate with good power efficiency. The single-sided overrange architecture achieves a 25% higher power efficiency of the SA-ADC compared with the conventional overrange architecture, and look-ahead logic is used to minimize logic delay in the SA-ADC. For the T&H, three techniques are presented enabling a high bandwidth and linearity and good timing alignment. Single channel performance of the ADC is 6.9 ENOB at an input frequency of 4 GHz. Multichannel performance is 7.7 ENOB at 1.35 GS/s with an ERBW of 1 GHz. The FoM of the complete ADC including T&H is 0.6 pJ per conversion step. An improved version is presented as well and achieves an SNDR of 8.6 ENOB for low sample rates, and, with increased supply voltage, it reaches a sample rate of 1.8 GS/s with 7.9 ENOB at low input frequencies and an ERBW of 1 GHz. At fin = 3.6 GHz, the SNDR is still 6.5 ENOB, and total timing error including jitter is 0.4 ps rms.     

2 cm long monolithic multisection laser for active modelocking at 2.2 GHz

A 2 cm long three-contact multisection laser has been fabricated for modelocking at very low repetition rates. Active modelocking yields 8.0-12.3 ps pulses at 2.2, 4.3 and 6.5 GHz corresponding to the fundamental, first, and second harmonics of the cavity resonance frequency. This device demonstrates the feasibility of fabricating monolithic pulse sources operating at rates as low as the OC-48 Sonet transmission rate (2.488 Gbit/s).<>     

60 GHz Single-Chip Front-End MMICs and Systems for Multi-Gb/s Wireless Communication

Single-chip 60 GHz transmitter (TX) and receiver (RX) MMICs have been designed and characterized in a 0.15mum (f_T~ 120 GHz/f _MAX> 200 GHz) GaAs mHEMT MMIC process. This paper describes the second generation of single-chip TX and RX MMICs together with work on packaging (e.g., flip-chip) and system measurements. Compared to the first generation of the designs in a commercial pHEMT technology, the MMICs presented in this paper show the same high level of integration but occupy smaller chip area and have higher gain and output power at only half the DC power consumption. The system operates with a LO signal in the range of 7-8 GHz. This LO signal is multiplied in an integrated multiply-by-eight (X8) LO multiplier chain, resulting in an IF center frequency of 2.5 GHz. Packaging and interconnects are discussed and as an alternative to wire bonding, flip-chip assembly tests are presented and discussed. System measurements are also described where bit error rate (BER) and eye diagrams are measured when the presented TX and RX MMICs transmits and receives a modulated signal. A data rate of 1.5 Gb/s with simple ASK modulation was achieved, restricted by the measurement setup rather than the TX and RX MMICs. These tests indicate that the presented MMICs are especially well suited for transmission and reception of wireless signals at data rates of several Gb/s     

Bistatic rain-scatter experiment at 34.8 GHz

A bistatic rain-scatter experiment was conducted at 34.8 GHz. The effect of severe rain-induced attenuation on received power from rain scattering was examined with the aid of a 5.33 GHz rain radar installed at the receiving site. It was found that an isolated small rainfall region with high rainfall rate caused a strong received power from rain scattering at 34.8 GHz, though the occurrence of such an event was not frequent. Angular dependence of rain scattering at 34.8 GHz was also examined.     

Gigabit QPSK modulator

We describe a QPSK (quaternary phase shift keyed) modulator operating at gigabit data transmission rates at a carrier frequency of 13 GHz. The modulator circuit can also be operated as a QPSK demodulator. A modulator-de-modulator pair operating in tandem showed clean eye diagrams of the recovered data trains on each port up to l.5 Gbit/s with corresponding error rates of less than 10?11. The circuit can be readily scaled to higher frequencies with a proportional increase in the information rate.     

Pulse repetition frequency multiplication with spectral selection in Fabry-Perot filters

We present methods for obtaining high-repetition-rate full duty-cycle RZ optical pulse trains from lower rate laser sources. These methods exploit the memory properties of the Fabry-Perot filter for rate multiplication, while amplitude equalization in the output pulse train is achieved with a semiconductor optical amplifier or with a second transit through the Fabry-Perot filter. We apply these concepts to experimentally demonstrate rate quadruplication from 10 to 40 GHz and discuss the possibility of taking advantage of the proposed methods to achieve repetition rates up to 160 GHz.