Low resistance is an important requirement for microcoils which act as a signal receiver to ensure low thermal noise during signal detection. High-aspect ratio (HAR) planar microcoils entrenched in blind silicon trenches have features that make them more attractive than their traditional counterparts employing electroplating through a patterned thick polymer or achieved through silicon vias. However, challenges met in fabrication of such coils have not been discussed in detail until now. This paper reports the realization of such HAR microcoils embedded in Si blind trenches, fabricated with a single lithography step by first etching blind trenches in the silicon substrate with an aspect ratio of almost 3∶1 and then filling them up using copper electroplating. The electroplating was followed by chemical wet etching as a faster way of removing excess copper than traditional chemical mechanical polishing. Electrical resistance was further reduced by annealing the microcoils. The process steps and challenges faced in the realization of such structures are reported here followed by their electrical characterization. The obtained electrical resistances are then compared with those of other similar microcoils embedded in blind vias.
A continuously tunable, coherence-free microwave photonic notch filter is proposed and demonstrated experimentally. This filter is based on two polarization beamsplitters with a high-birefringence linearly chirped fiber Bragg grating used as the tunable component. High stability is obtained. The polarization-maintaining structure is free from the random optical interference problem. By adjusting the operating wavelength, more than 5 GHz free-spectral-range tunability with 40-dB notch rejection is achieved.
A continuously tunable, coherence free microwave photonic filter is proposed and experimentally demonstrated. The
filter is based on a high-birefringence linearly chirped fibre Bragg grating (Hi-Bi LCFBG) as the tuning component. The
filter response tunability is realized through changing the differential group delay of the Hi-Bi LCFBG by applying
gradient tension or adjusting the operating wavelength. Free spectral range tuning by 1.11 GHz with about 40 dB notch
rejection is achieved.
A novel scheme to realize optical single-sideband modulation using only one electroabsorption modulator is presented. The scheme is based on the cancellation between the nonlinear phase due to dispersion and the linear phase due to optical delay in a Sagnac loop. Our theoretical analysis and experiment results show that optical single-sideband modulation can be realized in a very simple configuration. The scheme is independent of optical wavelength; it also avoids the problem of coherent interference, resulting in stable generation of optical single-sideband signals.
Several measurement methods for polarization dependent transmission in an optical fiber link are compared. The
relationship between these methods is discussed. Guidelines for choosing a particular method are provided based on
accuracy, speed, and system characteristics.
We use the expression relating the output state of polarization and PMD vector. Based on this expression we get the power fading including first-order PMD and chromatic dispersion, which is dependent on the angle of precession of output state of polarization around the PMD vector. From the expression for power fading, we get the average power penalty for chromatic dispersion and PMD. We propose a novel and fast PMD and chromatic dispersion monitoring technology. Measured results agree well with theoretical analysis.
We propose a novel, continuously tunable, photonic microwave notch filter configuration that uses, for the first time, single-sideband (SSB) modulated optical signals together with a linearly chirped fiber grating in a Sagnac loop. Measured results are presented to show a large notch rejection and an easily tunable free spectral range (FSR) by tuning the chirped fiber Bragg grating (FBG). The configuration enables doubling of time delay in the Sagnac loop. Use of SSB offers the potential to overcome chromatic dispersion.
We demonstrate a tunable microwave-photonic notch filter based on a variable polarization beamsplitter, a Hi-Bi coupler, and a variable time delay line. The configuration is free from the problems of optically coherent interference and chromatic dispersion. An expression for the filter transfer function is derived. Measured results match the calculated results and show a notch rejection greater than 35 dB. The notch frequency is continuously tunable by adjusting the time delay value. The scheme can operate over a wide range of optical carrier frequencies.
We propose a new tunable polarization-mode-dispersion compensator, which is substantially free from chromatic dispersion. The design uses a pair of high-birefringence linearly chirped fiber gratings. Each grating can adjust the differential group delay (DGD) nonlinearly by using a cantilever beam. The compensator can be tuned to operate over a range of wavelengths and can yield DGD values starting from 0 ps. Measured eye diagrams for a 10-Gbit/s system show that this compensator can greatly reduce the chromatic dispersion induced by a chirped grating.
During the last decade, there has been an explosive growth in the systems based on optical fibers. These systems require a correspondingly large number of optical components. Most of these components have been realized in integrated-optic form with a number of advantages compared to other forms. Therefore it is extremely important to impart education and training to students in the area of integrated optics. A course on 'Integrated Optics' has been offered during the last few years at the Electrical Engineering Department, Indian Institute of Technology, Delhi (IIT Delhi), India. An integrated optics laboratory in the same department has supported the course. This paper presents various aspects related to this course, viz., the topics covered, laboratory demonstrations, and some of the student projects that have been undertaken over the past few years.
For integrated-optic waveguides, propagation loss and mode- profile are important parameters. In this work, a camera has been utilized to measure the propagation loss for planar waveguides and mode profile for channel waveguides. Measurements have been carried out on ion-exchange waveguides, at 633 nm and 1310 nm. The measured mode profiles have been used to calculate coupling loss between an optical fiber and channel waveguides. It is proposed that mode profile measurements may also be used for determining propagation loss of channel waveguides.
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