Optimization of DWDM Demultiplexer Using Regression Analysis

We propose a novel twelve-channel Dense Wavelength Division Multiplexing (DWDM) demultiplexer, using the two-dimensional photonic crystal (2D PC) with square resonant cavity (SRC) of ITU-T G.694.1 standard. The DWDM demultiplexer consists of an input waveguide, SRC, and output waveguide. The SRC in the proposed demultiplexer consists of square resonator and microcavity. The microcavity center rod radius (Rm) is proportional to refractive index. The refractive index property of the rods filters the wavelengths of odd and even channels. The proposed microcavity can filter twelve ITU-T G.694.1 standard wavelengths with 0.2 nm/25 GHz channel spacing between the wavelengths. From the simulation, we optimize the rod radius and wavelength with linear regression analysis. From the regression analysis, we can achieve 95% of accuracy with an average quality factor of 7890, the uniform spectral line-width of 0.2 nm, the transmission efficiency of 90%, crosstalk of −42 dB, and footprint of about 784 μm2

Nonlinear photonics with applications in lightwave communications

This doctoral dissertation investigates the use of nonlinear photonics in targeted Lightwave communication applications. Different highly nonlinear optical materials have been considered for the investigation of Lightwave communications data carriers, with a focus on the optical carrier pulsewidth. A state-of-the-art novel method has been developed to measure pico-second optical carrier pulses using highly nonlinear optical fiber. This method is based on the nonlinear optical loop mirror (NOLM), with consideration focused on the third order nonlinearity. Silicon is considered to be one of the most attractive materials for photonics integrated circuit technology (PIC) due to its compatibility with complementary metal oxide semiconductor (CMOS). As such, the method has been applied to the SOI platform Mach-Zehnder interferometer (MZI), also by considering the third order nonlinearity. In the NOLM approach, the picosecond optical data carrier pulsewidth is measured by using an optical power meter. Simulations for both the self-phase and cross-phase modulation schemes are carried out, and as expected, the cross phase modulation gives an increment in the sensitivity twice that of the self-phase modulation. Due to very high repetition rates of the order 10 GHz, the effect of counter propagating non-linear interactions in the NOLM are also considered in the theoretical evaluation. In the experimental validation, the pulses from an active fiber mode-locked laser at a repetition rate of 10 GHz were incrementally temporally dispersed using an SMF-28 fiber. The optical data carrier pulses over a range of 2-10 ps were successfully measured with a resolution of 0.25 ps. By extrapolating the theoretical evaluation and by selecting different physical parameters for the setup, the method was found to exhibit an extended range of 0.25 to 40 ps.;The concept described above is then extended to the investigation of nonlinear SOI devices using an MZI, thus miniaturizing the setup. In this investigation, the silicon waveguide has been simulated for self-phase and cross-phase modulation by solving the nonlinear Schrodinger equations using the split step method. Silicon has strong two photon absorption at telecommunication wavelengths, i.e. 1550 nm, and therefore all nonlinear losses (i.e. TPA and free carriers generated through TPA) are included in the split step simulations. The results obtained show that the on-chip nonlinear MZI (based on the SOI platform) can also be used for the measurement of optical data carrier pulse-widths of up to 10 ps. In the last part of this doctoral dissertation, a novel design for a temperature insensitive MZI is presented. Temperature dependence is one of the main challenges in the design of the SOI platform due to the large thermo-optic coefficient of its core material. A change in temperature can cause the device properties to deviate significantly, and can also alter the nonlinear properties of the device. Therefore, a design of an all-passive athermal MZI device based on the SOI platform has been developed and investigated. The MZI's temperature compensation is achieved by optimizing the relative length of the wire and subwavelength grating arms, and by tailoring the thermal response of the subwavelength structure. The simulation results of the athermal MZI design indicated that an overall temperature sensitivity of 7.5 pm/K could be achieved over a 100 nm spectral range near the 1550 nm region.This doctoral dissertation investigates the use of nonlinear photonics in targeted Lightwave communication applications. Different highly nonlinear optical materials have been considered for the investigation of Lightwave communications data carriers, with a focus on the optical carrier pulsewidth. A state-of-the-art novel method has been developed to measure pico-second optical carrier pulses using highly nonlinear optical fiber. This method is based on the nonlinear optical loop mirror (NOLM), with consideration focused on the third order nonlinearity. Silicon is considered to be one of the most attractive materials for photonics integrated circuit technology (PIC) due to its compatibility with complementary metal oxide semiconductor (CMOS). As such, the method has been applied to the SOI platform Mach-Zehnder interferometer (MZI), also by considering the third order nonlinearity. In the NOLM approach, the picosecond optical data carrier pulsewidth is measured by using an optical power meter. Simulations for both the self-phase and cross-phase modulation schemes are carried out, and as expected, the cross phase modulation gives an increment in the sensitivity twice that of the self-phase modulation. Due to very high repetition rates of the order 10 GHz, the effect of counter propagating non-linear interactions in the NOLM are also considered in the theoretical evaluation. In the experimental validation, the pulses from an active fiber mode-locked laser at a repetition rate of 10 GHz were incrementally temporally dispersed using an SMF-28 fiber. The optical data carrier pulses over a range of 2-10 ps were successfully measured with a resolution of 0.25 ps. By extrapolating the theoretical evaluation and by selecting different physical parameters for the setup, the method was found to exhibit an extended range of 0.25 to 40 ps.;The concept described above is then extended to the investigation of nonlinear SOI devices using an MZI, thus miniaturizing the setup. In this investigation, the silicon waveguide has been simulated for self-phase and cross-phase modulation by solving the nonlinear Schrodinger equations using the split step method. Silicon has strong two photon absorption at telecommunication wavelengths, i.e. 1550 nm, and therefore all nonlinear losses (i.e. TPA and free carriers generated through TPA) are included in the split step simulations. The results obtained show that the on-chip nonlinear MZI (based on the SOI platform) can also be used for the measurement of optical data carrier pulse-widths of up to 10 ps. In the last part of this doctoral dissertation, a novel design for a temperature insensitive MZI is presented. Temperature dependence is one of the main challenges in the design of the SOI platform due to the large thermo-optic coefficient of its core material. A change in temperature can cause the device properties to deviate significantly, and can also alter the nonlinear properties of the device. Therefore, a design of an all-passive athermal MZI device based on the SOI platform has been developed and investigated. The MZI's temperature compensation is achieved by optimizing the relative length of the wire and subwavelength grating arms, and by tailoring the thermal response of the subwavelength structure. The simulation results of the athermal MZI design indicated that an overall temperature sensitivity of 7.5 pm/K could be achieved over a 100 nm spectral range near the 1550 nm region

Silicon photonics devices for integrated analog signal processing and sampling

Silicon photonics offers the possibility of a reduction in size weight and power for many optical systems, and could open up the ability to build optical systems with complexities that would otherwise be impossible to achieve. Silicon photonics is an emerging technology that has already been inserted into commercial communication products. This technology has also been applied to analog signal processing applications. MIT Lincoln Laboratory in collaboration with groups at MIT has developed a toolkit of silicon photonic devices with a focus on the needs of analog systems. This toolkit includes low-loss waveguides, a high-speed modulator, ring resonator based filter bank, and all-silicon photodiodes. The components are integrated together for a hybrid photonic and electronic analog-to-digital converter. The development and performance of these devices will be discussed. Additionally, the linear performance of these devices, which is important for analog systems, is also investigated

Power Control In Optical CDMA

Optical CDMA (OCDMA) is the multiplexing technique over the fiber optics medium to increase the number of users and this is a step towards all optical Passive Optical Networks (PON). Optical OFDM, WDM and Optical TDM have also been studied in this thesis which are also candidates to all optical passive optical networks. One of the main features of Optical CDMA over other multiplexing techniques is that it has smooth capacity. The capacity of OCDMA is constrained by the interference level. Hence, when some users are offline or requesting less data rates, then the capacity will be increased in the network. Same feature could be obtained in other multiplexing techniques, but they will need much more complicated online organizers. However, in OCDMA it is critical to adjust the transmission power to the right value; otherwise, near-far problem may greatly reduce the network capacity and performance. In this thesis Power control concepts are analyzed in optical CDMA star networks. It is applied so that the QoS of the network get enhanced and all users after the power control have their desired signal to interference (SIR) value. Moreover, larger number of users can be accommodated in the network. Centralized power control algorithm is considered for this thesis. In centralized algorithm noiseless case and noisy case have been studied. In this thesis several simulations have been performed which shows the QoS difference before and after power control. The simulation results are validated also by the theoretical computation.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Building blocks of a silicon photonic integrated wavelength division multiplexing transmitter for detector instrumentation = Bausteine für einen integrierten siliziumphotonischen Wellenlängenmultiplexsender zur Detektorinstrumentierung

In dieser Arbeit werden Datenübertragungssysteme für die Detektorinstrumentierung und die Herausforderungen dieser einzigartigen Anwendung untersucht. Begrenzt durch die hohe Strahlungsintensität, den verfügbaren Platz, niedrige Temperaturen usw., liegt die Auslesebandbreite von Detektoren nach dem derzeitigen Stand der Technik im Bereich von einigen zehn Gb/s pro Faser. Angesichts des ständig wachsenden Datenvolumens ist die Verbesserung der Übertragungsbandbreite ein dringend zu lösendes Problem. Daher wird in dieser Arbeit ein universell einsetzbares Konzept für einen integrierten, siliziumphotonischen Sender auf Basis der Wellenlängenmultiplex-Technologie vorgeschlagen. Die angestrebte Übertragungsbandbreite in der ersten Version beträgt 40 Gb/s. Zwei Schlüsselbausteine des integrierten Senders, der Mach-Zehnder-Modulator und der Wellenlängen-Demultiplexer, werden im Detail untersucht. Eine Reihe von Modulatoren mit unterschiedlichen Längen und Ätztiefen werden entworfen, hergestellt und charakterisiert. Für den Entwurf des Demultiplexers wird eine angepasste Entwurfsmethode entwickelt, die mit zwei dedizierten Brennpunkten arbeitet. Ein neuer Entwurfsparameter wird in diese Methode eingeführt, um sie flexibler und leichter anwendbar zu machen. Die Auswirkung der Modifizierung des eingeführten Parameters wird anhand einer Reihe vergleichbarer Bauelemente untersucht. Alle Charakterisierungen bestätigen die Machbarkeit des vorgeschlagenen Konzepts

Tunable Silicon integrated photonics based on functional materials

This thesis is concerned with the design, fabrication, testing and development of tunable silicon photonic integrated circuits based on functional materials. This tunability is achieved by integrating liquid crystals, 2D materials and chalcogenide phase-change materials with silicon and silicon nitride integrated circuits. Switching the functional materials between their various states results in dramatic changes in the optical properties, with consequent changes in the optical response of the individual devices. Furthermore, such changes are volatile or non-volatile depending on the materials.Engineering and Physical Sciences Research Council (EPSRC