Implementing of photonic sampling and quantizing analog-to-digital converters (ADCs) enable us to extract a single binary word from optical signals without need for extra electronic assisting parts. This would enormously increase the sampling and quantizing time as well as decreasing the consumed power. To this end, based on the concept of successive approximation method, a 4-bit full-optical ADC that operates using the intensity-dependent Kerr-like nonlinearity in a two dimensional photonic crystal (2DPhC) platform is proposed. The Silicon (Si) nanocrystal is chosen because of the suitable nonlinear material characteristic. An optical limiter is used for the clamping and quantization of each successive levels that represent the ADC bits. In the proposal, an energy efficient optical ADC circuit is implemented by controlling the system parameters such as ring-to-waveguide coupling coefficients, the ring’s nonlinear refractive index, and the ring’s length. The performance of the ADC structure is verified by the simulation using finite difference time domain (FDTD) method.

Successive approximation-like 4-bit full-optical analog-to-digital converter based on Kerr-like nonlinear photonic crystal ring resonators

Optical-analog-to-digital conversion based on successive-like approximations in octagonal-shape photonic crystal ring resonators

Humidity remains in the atmosphere even on bright days. Water of all three states can be found naturally in the atmosphere: liquid (rain, fog, and clouds), solid (snowflakes, ice crystals), and gas (water vapour). Water in any state is an obstacle in the link of the electromagnetic wave. When the wave passes through the water particles, a part of its energy is absorbed and a part is scattered. Therefore the electromagnetic wave is attenuated. Prediction of the influence of these factors is very important in radio system design. Attenuation due to rain, fog, and clouds can lead to the perturbations of the wireless, mobile, satellite and other communications. Another problem is the refractive index of the atmosphere, which affects the curvature of the electromagnetic wave path and gives some insight into the fading phenomenon. The anomalous electromagnetic wave propagation can cause disturbances to radar work, because variation of the refractive index of the atmosphere can induce loss of radar coverage. Accurate prediction of losses due to these factors can ensure a reliability of the radio system, decrease an equipment cost, furthermore, the radio systems can become less injurious to health of people. When there are no possibilities to gather data for calculations of the specific attenuation due to rain, clouds and fog, and atmospheric refractive index, the values recommended by the International Communication Union’s Radiocommunication sector (ITU-R) can be used. But the recommended values are not always exact. In design of the radio links, the most desirable operating frequencies are below 10 GHz, because in such cases atmospheric absorption and rainfall loss may generally be neglected (Freeman, 2007). However, in most countries, the frequency-band below 10 GHz is highly congested. In addition, high frequencies provide larger bandwidth, narrower beam width, good resolution and smaller component size (Bhattacharyya et al., 2000). Therefore, the operating frequencies of 10 GHz and above are often used in design of radio systems. The higher the operating frequency, the greater attenuation due to hydrometeors (rain, cloud, fog, snow, and etc.) is observed (Tamosiūnaitė et al., 2010a). In (Ishimaru, 1978), it was mentioned that the electromagnetic wave attenuation due to snow is less than attenuation due to rain, and that the attenuation due to dry snow may be neglected

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Atmospheric Attenuation due to Humidity

A new S-type of IR integrated waveguide amplifiers, based on erbium-ytterbium co-doped phosphate glass integrated with medium thin film filter, is proposed. The intrinsical gain spectrum of the proposed amplifier is obtained by solving rate and power propagation equations, a thin film filter flattening this intrinsical gain spectrum is designed by genetic algorithm, and fabricated. An average gain >10dB is obtained between 1530nm and 1560nm, and the average gain about 18dB between 1531nm and 1550nm with gain difference of <3dB is achieved.

Thin Film Filter for Broadband IR Integrated Waveguide Amplifiers

A novel optical microwave and millimeter generation by using single mode fiber FP cavity (SMFFPC) with pulse laser injection is proposed and experimentally demonstrated. The frequency of output signal is determined by the birefringence degree of the SMFFPC, a general relationship between output signal frequency of SMFFPC and birefringence degree of single mode fiber is derived. The proof of concept device consists of a light source, a polarizer controller, a modulator, a RF generator, a single mode fiber Fabry-Perot cavity, a strain inspector, an erbium doped fiber amplifier, a filter, a polarizer, and a digital communication analyzer. The results demonstrate the new concept of optical microwave and millimeter generation and the technical feasibility.

Optical Microwave and Millimeter Generation by Using Birefringent Fiber FP Cavity with Pulse Laser Injection

A novel wideband and high-gain waveguide-amplifier structure, which consists of a folded geometry erbium-ytterbium co-doped phosphate glass waveguide integrated with a cascaded multilayer medium thin-film filter (CMMTFF), is proposed. This CMMTFF consists of some different filter-unit cells with different central wavelengths and bandwidths, and each of them can suppress a certain gain peak at a specific wavelength. The gain characteristics of this new optical amplifiers is obtained. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 64–66, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20208

High-Gain Broadband Optical-Waveguide Amplifiers

The effect of fog and clouds in millimeter communication is discussed, and the attenuation caused by fog and clouds is reviewed. Signal-to-noise ratio (SNR) of image is derived using relating models of fog and clouds attenuation. According to the relation of image quality and its signal-to-noise ratio, the system behavior is forecasted theoretically. It is shown that the signal-to-noise ratio of receiver at certain transmitter power is inverse with radio wave frequency, from about 70dB at 10GHz to 48dB for fog and 49dB for clouds. The image quality of received signal at certain transmitter power is inverse with radio wave frequency, from about 7 grade at 10GHz to 5.27 grade for fog and 5.37 grade for clouds. The above calculated results are consistent with experimental results.

Effect of Fog and Clouds on the Image Quality in Millimeter Communications

We propose a novel scheme that can realize high-precision and high-speed electro-optical analog-to-digital converter (ADC). The scheme is based on the Taylor's structure. In contrast to the conventional Taylor's structure, where modulators are in parallel, we use cascaded modulators which can solve the low precision problem of the conventional Taylor's structure. We have analyzed the performance of the proposed ADC structure in theory, the theoretical analysis shows that the precision of our scheme could be 10-bits. The speed in operating of our scheme is related with the speed of modulator. In our scheme, the modulator is LiNbO3 Mach Zehnder interferometric modulator with a low half-wave voltage, which 40 GHz can be achieved.

Electro-optical analog-to-digital converter based on LiNbO3 Mach-Zehnder modulators

IR integrated photonic amplifiers at 1.55μm operation will have good foreground in optical phased‐array radars for splitters and signal processing. The saturation gain characteristics of IR integrated photonic waveguide amplifiers (taken Er3+‐Yb3+ co-doped phosphate glass waveguide amplifiers as an example) are studied theoretically. For the home‐made laser glass materials the calculated saturation intensities are 2.22kw /cm2 for signal and 10.15kw/cm2 for pump. The effects of absorption saturation of signal and pump lights on the gain of amplifiers are discussed.

Jizhi Dai

Papers

High-Gain Broadband Optical-Waveguide Amplifiers

Thin Film Filter for Broadband IR Integrated Waveguide Amplifiers

Effect of Fog and Clouds on the Image Quality in Millimeter Communications

Electro-optical analog-to-digital converter based on LiNbO3 Mach-Zehnder modulators

Modeling and Simulation of Saturation Gain of IR Integrated Photonic Amplifiers