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 an optical fiber device for temperature sensing and thermal expansion measurement are reported. The modulated intensity has been measured by using a pair of 450 μm core fiber, one acting as the source and the other one as receiving fiber. In this design, the light intensity modulation is based on the relative motion of the optical fibers and a reflective coated lens. By using displacement calibration data for this sensor, the linear thermal expansion of the aluminum rod is determined. This sensor shows an average sensitivity of about 11.3 mV/°C for temperature detection and 7 μm/°C for thermal expansion detection. Device resolution for a linear expansion measurement... 

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... 

Design and operation of an optical fiber sensor based on the light leakage from one fiber to another one causing intensity modulation are reported. Performance of this sensor is tested as a liquid level sensor for different liquids and the experimental results are reported. The dry and wet signals for this probe are measured for a series of measurements and important factors concerning sensor operation are described. The precision of measured values, reproducibility of the results (1.3%), and the stability of sensing operation as a function of time at different launching powers are also reported (0.8%). The reported results are promising and verify the successful operation of such a device... 

Integrated treatment planning for cancer patients has high importance in intensity modulated radiation therapy (IMRT). Direct aperture optimization (DAO) is one of the prominent approaches used in recent years to attain this goal. Considering a set of beam directions, DAO is an integrated approach to optimize the intensity and leaf position of apertures in each direction. In this paper, first, a mixed integer-nonlinear mathematical formulation for the DAO problem in IMRT treatment planning is presented. Regarding the complexity of the problem, two well-known metaheuristic algorithms, particle swarm optimization (PSO) and differential evolution (DE), are utilized to solve the model. The... 

Design and operation of a double-fiber sensor for displacement measurements are reported in this study. In this arrangement, one fiber transmits the laser light to the target and the second one receives the light reflected off the target and transmits to a photodetector. Utilizing inexpensive plastic optical fibers offers advantages such as higher reflexability and more robustness at a reasonable cost, which are required for some applications. The novelties of the reported design are compactness of the fiber probe, flexibility, long dynamic range (22 mm), and it is possible to use the source and the detector at the same side. The displacement of the target causes the intensity modulation and... 

An efficient low-complexity VLSI architecture for timing synchronization of a real-time intensity modulation direct detection optical OFDM (IMDD-OOFDM) system is proposed, which results in a significant area reduction. This architecture calculates the correlation among cyclic prefix (CP) regions to estimate the beginning of the OFDM symbol. The proposed architecture utilizes only one functional unit for this purpose, while the throughput is devised for high data-rate optical OFDM systems. Synthesis results of this architecture proves an area saving of 31% compared to the previous work. Moreover, the performance of the correlation method is significantly improved due to a modification applied... 

Operation of two different optical fiber sensor designs for distance measurements with a good sensitivity, resolution, and wide dynamic range is reported. Design is based on the intensity modulation due to reflectance measurement from a target surface. Two reported designs are fabricated with a triple-fiber assembly, in which one uses a double-transmitter, while another one uses a double-receiver fiber design. Reflection signals from different targets are tested with these sensors and results for the mirror and A4 paper surfaces are described. The response curve for both experiments starts from a near zero level, shows a maximum at a certain distance and gradually drops to the background... 

We introduce the capture effect concept in microwave photonic links (MWPLs) for the first time to our knowledge. The capture effect or the small-signal suppression is the change in the amplitude ratio of the two signals between input and output of the intensity-modulation direct-detection (IMDD) MWPLs. An analytical explanation of the performance of external IMDD MWPLs due to the effects of nonlinearity combined with sum of several input sinusoidal signals is given.We have investigated the suppression of a weaker signal in these links. General analytic expression for the small-signal suppression is derived using a nonlinear analytical approach. We show that the small-signal suppression is... 

In this article design and operation of a plastic optical fiber (POF) sensor based on the unconventional light leakage from one fiber to another one causing intensity modulation are presented. The dominant loss mechanism was found to be the evanescent loss and based on this phenomenon the optical fiber sensor was designed. The penetration depth of evanescent wave as a function of different refractive index of cladding was calculated. Operation of this sensor was tested as a liquid level sensor for different liquids and the experimental results are compared. The dry (air interface layer) and wet output (liquid interface layer) signals for this probe were measured for a series of measurements... 

Design and operation of an optical fiber sensor based on the intensity modulation is reported in this article. Two distinct mechanisms are considered for the optical power loss and the sensor operation is explained in terms of these effects. The dominant loss mechanism is found to be the evanescent loss and based on this phenomenon the optical fiber sensor is designed. Performance of this sensor is tested as a liquid level sensor for water and the experimental results are reported. The dry and wet signals for this probe are measured for a series of measurements and important factors concerning the design and operation of sensor are described. The precision of measured values, reproducibility... 

In this paper we use tunability of FBG to introduce a novel device for optically reading, writing or modifying the low-speed label(s). We utilize tunable FBG arrays as concurrent label modulating (multiplexing) elements. This second-level intensity modulation is used to send signaling messages between nodes of WDM networks. The fiber optic small-signal modulator is formulated, and its behavior is compared with the published reports  

A high sensitive optical MEMS accelerometer is proposed, which works by changing the effective refractive index of a microring relied on intensity modulation of light wave. The proposed optical sensing system consists of a microring, waveguide, and a proof mass. Acceleration causes lateral displacement of the proof mass. The proof mass is in the optical coupling length of the microring, and the displacement of the proof mass changes effective refractive index of the microring. Changes of the effective refractive index of the microring result in wavelength shift. The mechanical and optical parts of the proposed accelerometer are designed, and the obtained functional characteristics are... 

Design and operation of three different optical designs based on the light intensity modulation for investigation of the humidity effects on the air index of refraction are described. The measurement variable is the transmitted power, which depends on the refractive index of the medium in the path of a fiber-to-fiber optical design. Three different probes (probe #1, #2, and #3) are tested in which probe #1 and probe #2 can also check the presence of water or any other transparent liquid in the gap between the two axial fibers. Performances of the new systems are tested as a refractive index monitoring mean and experimental results are given. The variations of the modulated powers as... 

A low-drift optoelectronic oscillator (OEO) is developed and experimentally shown. In the proposed OEO, a fiber Sagnac interferometer, including an optical phase modulator (PM) and a nonreciprocal bias unit, functions as an intrinsically drift-free intensity modulator. The phase noise of the proposed OEO is modeled in phase space, which is verified by experiments. Phase noise and frequency stability of the photonically generated microwave signals are measured. The single-sideband phase noise of the generated microwave signal is -106.6 dBc/Hz at 10-kHz offset from the 10.833-GHz carrier, with 120-fs rms timing jitter integrated from 1 kHz to 10 MHz. Frequency drift measurements show ±0.85-ppm...