Integrated Optical Delay Lines for Time-Division Multiplexers

The purpose of this study was to examine and compare the classification accuracy of early static prereading measures and early dynamic assessment reading measures administered to 600 kindergarten students. At the beginning of kindergarten, all of the participants were administered two commonly used static prereading measures. The participants were then administered either a dynamic assessment featuring an onset-rime decoding strategy or a dynamic assessment featuring a sound-by-sound strategy. At the end of first grade, those same participants’ reading ability was assessed using multiple reading measures. Results indicated that the dynamic assessments yielded significantly higher classification accuracy over the static measures, but that the classification accuracy of the two dynamic assessments did not differ significantly. Sensitivity for the static measures was less than 80%, and specificity ranged from 33% to 51%. The sensitivity and specificity for the dynamic assessments was greater than 80% for all children, with the exception of specificity for the Hispanic children, which was at or greater than 70%. Results also indicated that the combination of static and dynamic measures did not improve the classification accuracy over the dynamic assessments alone. Dynamic assessment appears to be a promising approach to classifying young children at risk for future reading difficulty.

We report on the design and preliminary testing of an interferometric interrogator capable of large-scale time-division multiplexing of FBG sensors. The scheme employs a passive algorithm for phase demodulation, allowing changes in FBG sensor reflected wavelengths to be calculated instantaneously upon arrival, and incorporates a technique for identification of initial absolute sensor wavelengths in order to overcome the measurement ambiguity associated with interferometric schemes. The proposed system will allow for high-speed interrogation of large-scale FBG sensor arrays with interferometric resolution and the capability for dynamic, static, and absolute FBG wavelength measurement.

Highly stable and small size local oscillators is a very important component of any remote sensing, imaging, and telecommunication systems. The key factor influencing the frequency stability is quality factor of the resonance structure. Related close-in to carrier phase noise for offset frequencies above active device corner frequency reduces at least at a rate of 20 dB/decade while offset below corner frequency increases at rate of 30 dB/decade. A new approach in realization of the electrical oscillators is to augment electrical quality factor by optical energy storage components (e.g., fiber optic delay lines and ring resonators) to enhance effective quality factor (Q) to 10^4-10^6, well beyond available electrical Q of 2000 in dielectric resonator oscillators (DRO). Moreover, stability of resonance frequency has been impacted by the environmental induced (e.g., piezo and pyro properties of material) sensitivities. In addition, micro-scale design approaches are reported using multi-mode (both semiconductor and solid state) lasers for low phase noise intermodal oscillations. Finally, forced oscillation techniques of injection locking, phase locking, and mode-locking are attractive to further stabilize electrical and optical oscillation methods. In this thesis, development of broadband stable frequency sources is reported covering both X- and K-band using forced opto-electronic oscillator technique. The broadband frequency tuning is achieved using coarse electrical tuning of YIG bandpass filter combined with fine-tuned optical transversal filter using dispersive delay component and wavelength control of a fiber laser, as optical source. Forced opto-electronic oscillation techniques of self-injection locking (SIL), self-phase locked loop (SPLL), and self-injection locked phase locked loop (SILPLL) are optimized for further frequency stabilization of a frequency synthesizer. In SILPLL application, long delay line is crucial for substantial phase noise reduction; therefore, kilometer long optical fiber delay lines have been used to construct the optical feedback since their loss is extremely low compared to electrical delay lines. Meantime, open loop gain is another key parameter to achieve low phase noise in these feedback systems, as the phase noise reduction is proportional to phase locking loop gain. The phase noise and pull-in time can be greatly reduced in SILPLL as opposed to SIL or SPLL alone. A forced oscillation of fixed frequency DRO at 10 GHz system provide -137 dBc/Hz phase noise at 10kHz offset with under 10 fs aperture jitters, while OEO based X-band and K-band synthesizers provide phase noise of -137 dBc/Hz (<10 fs jitters) and -127 dBc/Hz (<12 fs jitters) at offset 10 kHz respectively in a computer controlled 19" rack-mountable OEO systems. After realization of the desired modular frequency synthesizer, development a compact opto-electronic oscillator system is demonstrated in my PhD study. Monolithic design and testing of multi-section quantum well lasers are reported on 5x2 mm2 InP chip using a commercial foundry service (i.e., SmartPhotonics). The designed lasers consist of 4 major sections of semiconductor optical amplifier (SOA), optical phase modulator (PM) and distributed Bragg reflector (DBR) mirrors. The DBR section provides wavelength selectivity while phase section and gain medium provide output wavelength tuning. An electro-absorption modulator (EAM) is prepared for mode number control using its wavelength sensitive absorption coefficient. The experiments supported predicted performance of this multi-mode laser structure and impact of combined forced oscillation of intermodal oscillations with mode locking method to realize a frequency stabilized and tunable RF signal source. Meantime, forced technique SILPLL and optimum mode locking techniques are applied in order to achieve improved phase noise performance. The free-running inter-modal oscillation frequencies suffers from poor phase noise of -5 dBc/Hz at 1 kHz and -32 dBc/Hz at 10kHz offset around 11.54 GHz, while under forced oscillation a -58 dBc/Hz at 1 kHz offset and -98 dBc/Hz at 10 kHz offset are achieved. A frequency tuning range of 800 MHz is also measured. In mode locked laser operation, the RF beat-notes forced with SILPLL topology provides a better performance. Improved phase noise of -79 dBc/Hz at 1kHz, -110 dBc/Hz at 10 kHz is measured with under 50 fs aperture jitters, while a broadband frequency tuning from 11 GHz to 13 GHz range is measured. The tuning range is potentially to be further improved, if the shared DBR laser pair symmetry could be improved. In summary, this thesis provides the solution for building RF synthesizer using forced opto-electronic oscillator and laser beat-notes oscillation output. The experimental results are corroborated with detailed analytical and numerical modeling to optimize oscillator phase noise performance. The modular design solution shows great stability and low phase noise, while the compact monolithic design solutions are quite attractive for a smaller size. Potential for full integration of multi-mode multi-section MQW laser with optical delay lines are also presented as a logical development path towards a compact frequency synthesizer.

Modern optical communication systems require tunable optical delay lines for synchronization of data packages. Chirped fiber grating are typically used as a dispersive element for this application. Fiber-based schemes, however, suffer from bulkiness, slow response and/or low time resolution. Integrated photonics on silicon is one alternative approach. Several more advanced device architectures have been subsequently demonstrated on silicon, including ringresonator and photonic crystal (PhC) line-defect waveguide types. The coauthors of this paper have recently proposed a novel class of tunable optical delay lines based on apodized grating waveguides. It was shown that high bit-rate operation is achievable by cascading two complementary (inward and outward) apodized gratings. In this paper, we have experimentally demonstrated our proposed approach and studied performance of the fabricated delay lines for optical telecommunication applications. The bit-rate was extracted from broadening of transform-limited input pulses of the measured dispersion of the delay lines. Characterization of the compact delay lines shows that the single grating devices offer true-time delays as long as 164 ps, tuning range of ~ 81 ps, and a minimum bit rate of ~ 15 Gb/s. The cascaded scheme offer true-time delays of 82 ps and tuning range of 32 ps and can potentially operate at bit rates as high as 107 Gb/s.

An 8:1, 5 Gb/s, time division multiplexer has been implemented using optoelectronic or metal-semiconductor-metal switches for sampling. The device was fabricated on InP and the switches activated via optical fiber delay lines by pulses from a GaAlAs laser diode array. This device concept is applicable to chip and to board level computer multiplexing. Time division multiplexing (TDM), serializing parallel data for high speed transmission, is an important element in most concepts and implementations in computer networking as well as other areas of communications. An optoelectronic TDM (OE-TDM) approach[1] is advantageous in speed, power, and signal-control isolation. It was conceived initially to offer serial transmission off VLSI chips and recently has shown promise as a stand alone multiplexing technique. We report an improved multiplexer in InP giving an 8:1 multiplex ratio, a 26 dB signal-to-noise ratio, and a 5 Gb/s serial data rate while using a realistic parallel data level of 2 volts instead of the earlier 15 V[1].

TNO, in cooperation with Micromega-Dynamics, SRON, Dutch Space and CSL, has designed a compact breadboard cryogenic delay line (figure 1) for use in future space interferometry missions. The work is performed under ESA contract 17.747/03 in preparation for the DARWIN mission. The breadboard (BB) delay line is representative of a flight mechanism. The delay line has a single stage voice coil actuator for Optical Path Difference (OPD) control, driving a two mirror cat’s eye. Magnetic bearings provide frictionless and wear free operation with zero-hysteresis. The design of the BB delay line has been completed. The development test program, including operation at 100 K has been completed. The verification test programme is currently being carried out and will include functional testing at 40 K.

In this paper, we demonstrate the relation between the amount of slowing and the amount of insertion loss in an optical slow wave structure when the material used has finite absorption. The delay properties are calculated as a function of wavelength for a single Fabry-Perot resonator and a delay line consisting of multiple coupled resonators. In all of these delay lines, if the amount of delay increases, the insertion loss of the line likewise increases. For low material loss, the normalized increase in delay is equal to the normalized increase in insertion loss. We also compare a coupled resonator delay line to a simple waveguide made of the same material and with the same amount of delay. The simple waveguide always has less insertion loss than the coupled resonator line because of the unavoidable reflection from the coupled resonator line. Even in the case of an asymmetric mirror delay line with zero reflection at the input, the simple waveguide has less insertion loss.

This study was designed to determine normal values of pedobarography during standing and walking in adolescents in our country and to investigate correlations between demographic data and pedobarographic values. Fifty volunteers (25 girls, 25 boys; mean age 14 years; range 13 to 15 years) who were found to have healthy feet according to the AOFAS (American Orthopaedic Foot and Ankle Society) clinical rating system for the ankle and foot were enrolled into the study. Plantar pressures were measured during standing and walking tasks with the use of the Mini-Emed pedobarographic device. Static measurements showed significantly higher pedobarographic values for right medial forefoot and toes in girls, and for left midfoot in boys (p<0.05). Overall, no significant differences existed between static pressure values for the right and left feet. The mean right medial foot pressure was higher than that of the contralateral foot in girls. There were no significant differences between the right and left feet in boys. Dynamic measurements showed a significantly larger contact area of the right foot in boys, and a significantly higher maximum plantar pressure of the left medial forefoot in girls (p<0.05). The strength of the correlation of body weight and body mass index was high with maximum plantar pressures (r=0.87 and r=0.83), and moderate with contact area of the foot (r=0.63 and r=0.59) in static measurements. Body weight (r=0.64) and body mass index (r=0.54) were moderately correlated with contact area of the foot in dynamic measurements. Appreciation of normal plantar pressure values in adolescents is important in monitoring the development stages of foot, in the assessment of foot disorders, and in making proper footwear modifications in compliance with age.

The audiofrequency delay line reported at the 63rd Meeting of the Acoustical Society has been improved and used to synthesize transfer functions with specified characteristics in the time and frequency domains. Time delays from 8 to 20 msec are obtained using a 0.4-mil-diam platinum-alloy wire with transverse wave velocities from 168 to 67 m/sec. Magnet boards with 64 and 256 magnets have been used for signal synthesis. The magnets can be magnetized with specified amplitudes (within 5%) and polarities with a push-button magnetizer in about 15 min. A linear FM chirp was set up with five 20-msec delay lines in series giving 75 msec differential delay between 800 and 1600 cps and approximately uniform amplitude response. Viscous damping in the liquid termination is obtained using liquid propane for long time delays and liquid pentane for short time delays. The delay lines cover a 10 to 1 frequency range, from about 200–2000 cps for a 20-msec delay line and 1500–15 000 cps for an 8-msec delay line. Each delay line has a Vernier adjustment permitting the time delay to be varied ±5%. The group delay phase errors are small and in good agreement with classical theory.

Summary form only given. We have developed a polygonal scanner based optical delay line that allows for potentially higher axial scan speeds than traditional linear or resonant galvanometers while supporting higher bandwidths. This type of delay line is based on designs used for signal autocorrelation measurement and demonstrated for OCT. In this type of optical delay line, a grating dispersed spectrum is focused onto a planar mirror with a controllable tilt angle. Implementation will be demonstrated by the in vivo OCT imaging of Xenopus laevis (African frog) tadpole cardiac function. This optical delay line has broad applicability in the fields of medicine and biology where both high resolution and high speed OCT are required.

A continuously tunable integrated optical delay line architecture with large bandwidth and bandwidth-delay product is proposed and demonstrated. The non-resonant delay line is based on cascaded Mach-Zehnder interferometers with tunable couplers. The device is operated with a single control signal and outperforms the common ring-resonator-based delay lines in terms of bandwidth-delay product. A device with a delay tuning range of 124 ps is experimentally demonstrated over a transmission bandwidth of 4.5 GHz.

Using only a single bidirectional optical delay line lattice, we present a technique for performing ultrahigh-data-rate compression and decompression of optical time-division-multiplexed (TDM) packets for photonic packet switching networks. We also present the first experimental demonstration of simultaneous compression and decompression of 100-Gb/s optical TDM packets using our proposed structure.

We report a novel wideband microwave detection and analysis system realized by utilizing photonic-assisted wavelength and time division multiplexing, in conjunction with an optical delay line. Deploying a coherent electro-optical dual comb and a gated recirculating optical frequency shifter with ~ 1.28 μs round-rip delay, the proof-of-concept experimental system demonstrates the interrogation of both fast varying and continuous RF signals with ~ 1 μs temporal duration and up to 8 GHz instantaneous bandwidth at 1 MHz resolution using a 80 MHz RF detection unit. The proposed system can be easily upgraded to higher bandwidths, finer resolution and longer measurement durations with suitable hardware.

This paper describes a photonic time division multiplexing (TDM) highway switch, called FRONTIERNET, that uses optical frequency as routing information. This switch architecture can be applied to asynchronous transfer mode (ATM) switching systems. The N/spl times/N switch consists of N tunable frequency convertors and N frequency-division-multiplexed (FDM) output buffers connected through an N/spl times/N frequency router. The router can interconnect N input highways with N output highways in a completely noninterfering way. It is possible to address each output highway uniquely by the choice of frequency (frequency routing) and each output highway can receive any given frequency from only one input. This switch architecture therefore has three advantages: its novel output buffering scheme achieves the best possible performance, there is no need for a complicated contention resolution mechanism between input highways, and there is no splitting loss of the transmitted optical power. An experimental switch with a one-cell FDM buffer was constructed. The tunable frequency convertor based on fast tunable frequency lasers can transmit high-speed optical cells to which frequencies are assigned on a cell-by-cell basis. The frequency router is an integrated-optic arrayed-waveguide grating 16/spl times/16 filter produced by using planar-lightwave-circuit (PLC) technology. The one-cell FDM output buffer based on optical fiber delay lines can store FDM cells and select only one cell at each timeslot over the output highway. A 2.5-Gb/s experimental switch was successfully operated, And an experimental FDM loop buffer was also demonstrated. This stores two cells at a data rate of 2.5 Gb/s. The bit error rate (EER) of the cells after up to 10 circulations is <10/sup -9/. The performance of the buffer in terms of the probability of cell loss and the cell wafting time in the buffer is analyzed numerically. It is concluded that fewer optical buffers are needed to satisfy the desired probability of the cell loss compared with the conventional electronic buffers. The scale of the switch can be expanded in a modular fashion in two ways using a multistage frequency router and a multistage switching network. And the multihop FRONTIERNET architecture is proposed to reduce the required frequency channels rather than the single-hop FRONTIERNET. The switch scale is also very easy to expand by connecting the frequency-router-based switching submodules.

We introduce an ultra-thin attosecond optical delay line based on controlled wavefront division of a femtosecond infrared pulse after transmission through a pair of micrometer-thin glass plates with negligible dispersion effects. The time delay between the two pulses is controlled by rotating one of the glass plates from absolute zero to several optical cycles, with 2.5 as to tens of attosecond resolution with 2 as stability, as determined by interferometric self-calibration. The performance of the delay line is validated by observing attosecond-resolved oscillations in the yield of high harmonics induced by time delayed infrared pulses, in agreement with a numerical simulation for a simple model atom. This approach can be extended in the future for performing XUV-IR attosecond pump-probe experiments.