Sharif Digital Repository

Design and operation of an opto-mechanical sensor for mass measurements is reported. This device uses a pair of optical fibers and a reflecting coated lens. The light intensity modulation is based on the relative motion of the lens due to a given mass with respect to the optical fibers. The modulated intensity because of the weighing mass has been measured by using a digital voltmeter. A full-range sensitivity of about 11.5 mV/g for a dynamic range of 80 g is obtained. A mass resolution of better than 0.25 g has been measured with this device. The measured output response is checked against the expected theoretical one and a general agreement observed. A comparison with similar experimental... 

Design and operation of three different optical sensors based on the intensity modulation are reported in this article. These sensors are measuring absence or presence of any liquid and the measurement variable is refractive index and optical absorption. Reported devices can also check the presence of air bubbles in the liquid flow line. Performance of these sensors is tested as a liquid flow monitoring device while using different light sources. Sensor #1 uses a simple cell with the long transmitter and receiver optical fibers. Sensor #2 utilizes a small cell assembly that includes the short transmitter and receiver fibers. Sensor #3 employs a quartz flow cell with the direct light... 

In Part I, a new internally coded time hoping optical code division multiple access (TH/OCDMA) scheme for fiber optic communication systems has been proposed and its multiple access performance has been evaluated using optical orthogonal code (OOC). Due to low cardinality of OOCs with a correlation value of 1, the capability of the proposed scheme could not be utilized effectively for an increasing number of simultaneous users. In this part, we consider applying the internally coded technique introduced in part one to the frame time hopping/OCDMA scheme. We evaluate the multiple access performance of the system for the three detectors introduced in Part I. Our results demonstrate the... 

A novel two-level signaling technique in OOC-based fiber-optic CDMA systems is proposed. The users of the system are categorized into two classes. Users of class 1 and 2 transmit the optical pulses at power level P and 2P respectively. At the receiver side using optical ADC multi-access interference is considerably suppressed. © 2009 OSA/ACP  

A novel two-level signaling technique in OOC-based fiber-optic CDMA systems is proposed. The users of the system are categorized into two classes. Users of class 1 and 2 transmit the optical pulses at power level P and 2P respectively. At the receiver side using optical ADC multi-access interference is considerably suppressed. © 2009 OSA  

This paper presents a top-down approach to the design of all-silicon CMOS-based fully integrated optical receivers. From the system-level requirements, we determine the optimum block-level specifications, based on which the individual building blocks are designed. Measurement results of the manufactured design show operation at data rates exceeding 2.5-Gbps/channel for the detector, the amplification and the clock and data recovery circuits. This proof of concept is the first step towards design optimized, completely integrated, multi-channel optical receivers for high-bandwidth short-distance chip-to-chip interconnects. © 2006 IEEE  

A fiber Bragg grating (FBG)-based delay line (or phase shifter) has been developed for microwave over fiber and phased array antenna (PAA) applications. The scheme uses band edge time delay of tunable fiber gratings to provide a continuously controllable microwave time delay or phase shift. Following the formulation and analysis of the device behavior, simulations of amplitude and phase responses are conducted. The results confirm the validity of theoretical predictions  

We propose and experimentally demonstrate a method based on Brillouin optical time-domain analysis to measure the longitudinal signal power distribution along phase-sensitive fiber-optical parametric amplifiers (PS-FOPAs). Experimental results show that the amplification of a PS-FOPA could go through different longitudinal profiles and yet finish with the same overall gain. This behavior is in sheer contrast with theoretical expectations, according to which longitudinal gain distribution should follow certain profiles determined by the initial relative phase difference but can never end up in the same overall gain. The gap between theory and experiment only becomes evident when the pump... 

The performance of devices based on highly nonlinear fibers (HNLF) can be drastically impeded by even tiny fluctuations of the zero dispersion wavelength (ZDW) along the fiber. Being able to measure ZDW fluctuations along an HNLF is therefore essential for the design of efficient nonlinear optics based devices such as fiber optical parametric amplifiers (FOPA), regenerators and limiters. Different schemes using complex distributed sensing of localized nonlinear interactions have been used in order to derive the ZDW fluctuations along the fiber [1-2]. In [3], the distributed gain of a pulsed pump FOPA along an HNLF was measured using a Brillouin Optical-Time Domain Analysis (BOTDA) based... 

Operation of an optical system for surface profiling is reported here. Reflection signals for the plane and cylindrical surfaces with different materials are reported. To investigate the precision and sensitivity of the reported system the reflection results of the curved and flat structured surface are compared with that of a structure-free surface. Reported system provides a simple and accurate means for the object shape study through the optical reflection measurements  

In this study, a novel scheme for fiber optic strain sensor has been introduced. This scheme is indeed a Mach-Zehnder interferometer followed by a displacement sensor. The strain is applied to an optical fiber which is the main branch of the Mach-Zehnder interferometer and causes an alteration in the interferometer's output intensity. The output beam is then spread on a mirror located in front of the fiber head. The head of the fiber and the mirror form a displacement sensor configuration. The portion of the reflected beam, gathered by the fiber, is a function of the distance between the fiber head and the mirror. So, applying strain causes a new change in the gathered intensity due to the... 

The Virtually-Imaged-Phased-Array (VIPA) is a modified version of etalon used as a hyperfine spectral disperser. We have developed an analytical Gaussian beam tracing formulation which can model the VIPA output pattern and the effects of polarization changes  

We consider an internally coded time-hopping coherent ultrashort light pulse code division multiple access scheme (TH-CULP CDMA) and analyze its performance in the fiber-optic communication systems. This system combines the TH and CULP CDMA techniques and exploits the advantages of both. In our method, each bit time interval is divided into Ns frames, and the spectral phase-coded pulse is transmitted in one of these frames. Two exclusive PN sequences are assigned to each user. One is added to a superorthogonal convolutional encoder output to select the transmission frame, and the other is used to encode the phase of the ultrashort pulse in the spectral domain. We evaluate the bit error rate... 

The transient response of all optical gain clamped multi channel erbium doped fiber amplifiers (EDFA's) and optical fiber inverter is studied by a semi-classical model. Using the semi-classical theory, the electric field interacting with mater is considered classical and the medium is quantized according to the equations of motion for density matrix. The rate equations and "self consistency" equations, which yield amplitude and phase of the electric fields of oscillator and amplifying channels are derived by considering Maxwell's equations and equation of motion of density matrix. The governing equations form a system of coupled partial differential equations. The relaxation oscillation... 

In this letter, we introduce a whole new approach in defining and representing optical orthogonal codes (OOCs), namely, outer-product matrix representation. Instead of applying commonly used approaches based on inner product to construct OOC codes, we use the newly defined approach to obtain a more efficient algorithm in constructing and generating OOC codes. The outer-product matrix approach can obtain a family of OOC codes with a cardinality closer to the Johnson upper bound, when compared with the previously defined accelerated greedy algorithm using the inner-product approach. We believe the new look introduced in this letter on OOCs could help to devise new approaches in designing and... 

In this paper, we propose using a soft-input decoder for the decoding of internally convolutional coded Poisson noise-dominated fiber-optic code-division multiple-access (CDMA) communication systems using optical orthogonal codes. We first compute the coded symbol log-likelihoods at the output of the Poisson noise-dominated channel, which is then used by a soft-input maximum-likelihood decoder, for a fiber-optic CDMA system assuming both on-off keying and binary pulse position modulation schemes. Furthermore, we develop a discrete soft-output channel model for a Poisson noise-dominated channel, with which we evaluate the upper bound on the bit error probability of the internally coded... 

In this paper, we consider the structure and performance of a multistage decoding scheme for an internally bandwidth efficient convolutionally coded Poisson fiber-optic code division multiple access (CDMA) communication system. The decoder is implemented electronically in several stages in which in each stage, the interfering users' coded bit decisions obtained in the previous stage is applied for computing the likelihood of the coded symbols of the desired user. The first stage is a soft-input Viterbi decoder for the internally coded scheme, in which the soft-input coded symbol likelihood values are computed by considering the multiuser interference as a noise signal. The likelihood of...