Due to the property of the photonic crystal, like bandgap, many researches on them are discussed. Photons with wavelength within the bandgap cannot propagate through the crystal. Then placing some defects in the crystal, because the periodic arrangement is destroyed, it is possible to build a waveguide to guide light along certain path. One kind is coupled cavity waveguide. The photons can propagate in a coupled-cavity waveguide by coupling without radiation losses. So it is widely used to implement a variety of optical devices. In this thesis, we use coupled cavity waveguide to construct devices. And the characteristics of Mach-Zehnder interferometer and power splitter are discussed. Then we propose two logic gate structures with an input port and two control ports. The state of control port determines the electric field at the output port. Besides, the four-port channel drop filter is proposed. It will make the three wavelengths ¢w1310, 1490 and 1550 nm¢w propagate in different waveguides. So it could be used as a wavelength demultiplexer for FTTH. Finally, the property of the PC-based rat-race circuit is investigated. By adjusting the phase of the control signal, we could decide the input signal to exit from output 1 or output 2. In this way, we could use it to function as a switch.

The reflection wavelength of Fiber Bragg Grating is sensitive to the strain and the temperature¡¦s variation. We use Fiber Bragg Grating to be the sensor head and measure the vibration frequency in constant temperature environment. The vibration of object can make the sinusoidal strain to Fiber Bragg Grating, and it will make a little phase difference to the light of the fiber. Using the interferometer and demodulation system, we can measure the phase difference and vibration frequency. Our sensor configuration is made up of imbalance Mach-Zehnder interferometer and Fiber Bragg Grating. The two light of different path need different time to pass through the vibration source, so they make phase difference. We use the demodulation circuit to measure the phase difference causing by vibration and get the vibration frequency. Our experiment structure is a novel configuration of Fiber Bragg Grating vibration sensor. Its intensity of signal is larger than the intensity of original sensor configuration, about 4dB.The novel sensor configuration is easier spread than traditional accelerometer and it is designed of all fiber. The accuracy for measuring low frequency vibration is 99.971%. The Dynamic range of the system is more than 45dB. It is larger than the dynamic range of original sensor configuration, about 9dB. The smallest signal that can be measured is about 0.0075rad.

Abstract The electrical microphone has came to maturity, which has some restrictions on high electromagnetic and wet environments¡CFiber-Optic sensor can improve the problems, because it has better characters in electromagnetic interference and wet environment than the traditional microphone. The structure of Sagnac interferometer is circulator, so the design of head to a sensor has to wind fiber around. Because the minimum radius of winded fiber has a threshold, we can not miniaturize the sensor-head. A typical Mach-Zehnder interferometer has to use high-coherence light source and the length of two arms in equality without any interference, so it is difficult in fabrication. If we make a microphone by FBG and Mach-Zehnder interferometer, and the advantage is that we can use low-coherence light source, and shorten the length of two arms in interferometer. By using the structure, the minimum measured pressure of sound is 0.6 Pa, and the dynamic range is 30dB.

This thesis report works on optically characterizing waveguide based biosensors consisting of thin, narrow Au stripes embedded in CYTOP. The devices were examined using an ever evolving and improving interrogation setup, variations of which are described in detail in this document. A number of changes were made to the setup configuration in order to reduce noise levels and increase efficiency and accuracy of acquired measurements. Waveguides of varying configurations (straight waveguides and Mach-Zehnder Interferometers with etched and cladded channels) are described and optically characterized. The characterization results of these devices are presented in this thesis. Bulk index measurements are carried out in order to determine a suitable bio-sensing solution with a refractive index matched to that of CYTOP. Step index measurements clearly distinguishing the introduction of sensing solutions of refractive indices varying from one another, are made available. Preliminary bio-sensing experiments involving detection of change in refractive index of sensing fluid as well as adlayer thickness with the introduction of analytes binding to the waveguide surface that has been functionalized with antibodies, using both straight and cladded waveguides with single mode outputs are studied.

Optical fiber sensors have been intensively studied and successfully employed in various human social activities and daily living, such as industrial production, civil engineering, medicine, transportation, national defense and so on. According to different structures, optical sensors could be divided into various categories. This thesis focuses on studying different kinds of in-line fiber Mach-Zehnder interferometers, which have played an important role among the optical interferometric fiber sensors. The structure composition, fabrication process, physical principle and practical applications of two novel in-line fiber Mach-Zehnder interferometers are proposed and discussed in detail in this work. The tapered bend-insensitive fiber Mach-Zehnder interferometer (BIF-MZI) is firstly fabricated and used as a fiber vibrometer. The unique double-cladding structure of bend-insensitive fiber not only provides higher mechanical strength to the sensor, but also guarantees a more uniform transmission spectrum， since only a few inner-cladding modes are left interfering with the core mode. A high sensitivity and fast response intensity demodulation scheme is employed by monitoring the power fluctuation of the BIF-MZI at the operation wavelength. Both damped and continuous vibrations are detected using the proposed sensor. It is demonstrated that this sensor responses to an extremely wide range of frequencies from 1 Hz up to 500 kHz with high signal-to-noise ratios (SNRs). The discrimination of temperature and axial strain is realized based on the dispersion effects of high-order-mode fiber (HOMF) by forming a single mode fiber-high-order-mode fiber-single mode fiber (SMF-HOMF-SMF) structure based in-line Mach-Zehnder interferometer. Unlike some kinds of in-line MZIs such as tapered and core–offset structures whose cladding modes are excited with different types under changing temperature and strain circumstances, the HOMF is capable of supporting three stable core modes, which guarantees a reliable and repeatable measurements within a large temperature or strain range. A new method based on the fast Fourier transform (FFT) is employed to analyze the mode couplings and their chromatic dispersion and intermodal dispersion properties in HOMF. The strong dispersion effects lead to a multi-peak feature in the spatial frequency spectrum. It is found that peaks that denote the waveform periods at positions that are beyond the critical wavelength possess highly sensitive and distinct phase responses to external disturbances, which provides the possibility to realize the discrimination measurements with high sensitivities and smaller errors by selecting appropriate peaks. The phase demodulation scheme is applied to quantify the temperature and strain changes in terms of phase shifts. Appropriate peak selections according to the practical needs would provide an easy access for applications where more than two parameters are required to be discriminated.

A key factor in the vertical integration of optical waveguide devices is the uniformity of the surface across which the coupling takes place. This thesis focuses on the fabrication of annealed proton-exchanged (APE) waveguides vertically integrated with chalcogenide waveguides. While titanium diffused waveguides form a surface bump that is approximately twice the size of the originally deposited film, an annealed proton-exchange process produces waveguides with surfaces having 90% less deformation. The theory behind wave guiding devices is explored in this work along with the modeling and simulation of APE waveguides. The results obtained from the simulations are used to aid in the fabrication of these devices. A detailed review of the fabrication process of APE waveguides and chalcogenide waveguides is provided with results obtained from measurements. The first known coupling results for vertically integrated chalcogenide waveguides on top of annealed proton-exchanged waveguides are recorded. This work is concluded with future directions for this research including lowering losses by obtaining better simulation parameters and vertically integrating ring resonators along with ways in which to do this.

Techn. University, Diss., 2004--Berlin.

This thesis report works on optically characterizing waveguide based biosensors consisting of thin, narrow Au stripes embedded in CYTOP. The devices were examined using an ever evolving and improving interrogation setup, variations of which are described in detail in this document. A number of changes were made to the setup configuration in order to reduce noise levels and increase efficiency and accuracy of acquired measurements. Waveguides of varying configurations (straight waveguides and Mach-Zehnder Interferometers with etched and cladded channels) are described and optically characterized. The characterization results of these devices are presented in this thesis. Bulk index measurements are carried out in order to determine a suitable bio-sensing solution with a refractive index matched to that of CYTOP. Step index measurements clearly distinguishing the introduction of sensing solutions of refractive indices varying from one another, are made available. Preliminary bio-sensing experiments involving detection of change in refractive index of sensing fluid as well as adlayer thickness with the introduction of analytes binding to the waveguide surface that has been functionalized with antibodies, using both straight and cladded waveguides with single mode outputs are studied.

Optical fiber sensors have been intensively studied and successfully employed in various human social activities and daily living, such as industrial production, civil engineering, medicine, transportation, national defense and so on. According to different structures, optical sensors could be divided into various categories. This thesis focuses on studying different kinds of in-line fiber Mach-Zehnder interferometers, which have played an important role among the optical interferometric fiber sensors. The structure composition, fabrication process, physical principle and practical applications of two novel in-line fiber Mach-Zehnder interferometers are proposed and discussed in detail in this work. The tapered bend-insensitive fiber Mach-Zehnder interferometer (BIF-MZI) is firstly fabricated and used as a fiber vibrometer. The unique double-cladding structure of bend-insensitive fiber not only provides higher mechanical strength to the sensor, but also guarantees a more uniform transmission spectrum， since only a few inner-cladding modes are left interfering with the core mode. A high sensitivity and fast response intensity demodulation scheme is employed by monitoring the power fluctuation of the BIF-MZI at the operation wavelength. Both damped and continuous vibrations are detected using the proposed sensor. It is demonstrated that this sensor responses to an extremely wide range of frequencies from 1 Hz up to 500 kHz with high signal-to-noise ratios (SNRs). The discrimination of temperature and axial strain is realized based on the dispersion effects of high-order-mode fiber (HOMF) by forming a single mode fiber-high-order-mode fiber-single mode fiber (SMF-HOMF-SMF) structure based in-line Mach-Zehnder interferometer. Unlike some kinds of in-line MZIs such as tapered and core–offset structures whose cladding modes are excited with different types under changing temperature and strain circumstances, the HOMF is capable of supporting three stable core modes, which guarantees a reliable and repeatable measurements within a large temperature or strain range. A new method based on the fast Fourier transform (FFT) is employed to analyze the mode couplings and their chromatic dispersion and intermodal dispersion properties in HOMF. The strong dispersion effects lead to a multi-peak feature in the spatial frequency spectrum. It is found that peaks that denote the waveform periods at positions that are beyond the critical wavelength possess highly sensitive and distinct phase responses to external disturbances, which provides the possibility to realize the discrimination measurements with high sensitivities and smaller errors by selecting appropriate peaks. The phase demodulation scheme is applied to quantify the temperature and strain changes in terms of phase shifts. Appropriate peak selections according to the practical needs would provide an easy access for applications where more than two parameters are required to be discriminated.

The development of reliable, affordable, and efficient sensors is a key step forward in providing tools for efficient monitoring of critical environmental parameters. Fiber-optic sensors are already widely used in various industrial sensing fields. They have proven themselves reliable in harsh environments and can measure different physical quantities, such as temperature, pressure, strain, refractive index (RI), and humidity. Fiber-optic Mach-Zehnder Interferometer (MZI) is a well-studied optical fiber interferometer that has proven capacity for sensing ambient refractive index. In this dissertation, we present Fiber Bragg grating (FBG) embedded in a microfiber Mach-Zehnder Interferometer designed for sensing temperature and refractive index. The MZI is constructed by splicing a short length of 40-μm-diameter microfiber between standard single mode fibers. A one-millimeter-long FBG is then written in the microfiber using a direct, point-by-point, ultrafast laser inscription method. The microfiber MZI shows only moderate sensitivity to ambient refractive index and temperature changes. In contrast, the microfiber FBG is insensitive to ambient refractive index change, while it exhibits typical sensitivity to temperature variation. These distinct characteristics of the FBG and MZI sensors enable the simultaneous measurement of refractive index and temperature as well as temperature compensation in ambient refractive index measurement. Further, we report the use of a fiber-optic Mach-Zehnder Interferometer to measure core refractive index changes written by femtosecond laser irradiation. The core-offset interferometer was constructed by splicing a lightly misaligned stub of standard single-mode fiber between the device’s lead-in and lead-out optical fibers. When the core refractive index of an in-fiber interferometer is altered, that process changes the phase of the core light. Since the phase of light propagating in the cladding (reference arm) remains unchanged, the transmission fringe pattern of the interferometer undergoes a spectral shift. In the present research, that spectral shift was used to quantify the effective core refractive index change in a standard single-mode fiber. In addition, we designed and developed a custom flame-based tapering machine that is used to fabricate miniaturized Mach–Zehnder interferometers (MZIs) using sharply tapered photonic crystal fiber (PCF). This technique produces sensors capable of highly sensitive ambient refractive index (RI) measurements. The sensor is fabricated by fusion splicing a small stub of PCF between standard single-mode fibers with fully collapsed air holes of the PCF in a splicing region. Tiny flame geometry enables the sharp tapering of the PCF, resulting in a short fiber length and high RI sensitivity. It appears that sharp tapering has a great impact on RI sensitivity enhancement, when compared with methods that decrease taper waist diameter. The tapering technique is further used to construct the Mach-Zehnder Interferometer-based fiber-optic refractive index (RI) sensor by uniformly tapering standard single mode fibers (SMF) for RI measurement. The fabricated MZI device does not require any splicing of fibers and shows excellent RI sensitivity. / Graduate