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We propose a new type of optical resonator that consists of embedded ring resonators (ERRs). The resonators exhibit unique amplitude and phase characteristics and allow designing compact filters, modulators, and delay elements. A basic configuration of the ERRs with two rings coupled in a point-to-point manner is discussed under two operating conditions. An ERR-based microring modulator shows a high operation speed up to 30 GHz. ERRs with distributed coupling are briefly described as well.

We demonstrate tunable time-slot interchange of 40 Gbits/s optical data packets using a conversion-dispersion-based tunable optical delay element. Odd and even data packets are extracted from an input signal, delayed relative to one another in a highly dispersive medium, and then multiplexed back together. Tunability is demonstrated by operating with two different packet lengths, 182 and 288 bits/packet, and a bit error rate of <10(-9) is achieved.

A compact silicon coupled-ring modulator structure is proposed. Two rings are coupled to each other, and only one of these rings is actively driven and over-coupled to a waveguide, which enables high modulation speed. The resultant notch filter profile is steeper than that of the single ring and has exhibited a smaller resonance shift and lower driving electrical power. Simulation results include: (i) potentially 60-Gb/s non-return-to-zero (NRZ) data modulation and over 20-dB extinction ratio can be achieved by shifting the active ring by a 20 GHz resonance shift, (ii) the frequency chirp of the modulated signals can be adjusted by varying the coupling coefficient between the two rings, and (iii) dispersion tolerance at 0.5-dB power penalty is extended from 18 to 85 ps/nm, for a 40-Gb/s NRZ signal.

Silicon microring resonators are proposed to achieve ultrasmall differential quadrature phase-shift keying modulators and demodulators operated at 20 Gb/s, which may require a dramatically reduced chip size. The modulators are characterized in terms of the carrier transit time and misalignment of the driving signals, while the demodulation performance is analyzed in terms of the bandwidth and frequency detuning of the demodulator. A bit-error rate of <10(-9) is achieved using all microring-based devices in the back-to-back case.

We experimentally demonstrate all-optical 2(7)-1 pseudorandom bit sequence data multiplexing using wavelength conversion, interchannel chromatic dispersion, and intrachannel dispersion compensation. Bit-rate tuning capability is demonstrated with 10-20 and 20-40 Gbits/s multiplexing, achieving a bit-error rate <10(-9) for both rates.

An ultra-small silicon-based microring modulator and filter were proposed to generate and demodulate NRZ DPSK at 10 Gb/s. In this paper, we analyze performance dependencies of the modulator and demodulator under different operating conditions, such as variable laser linewidth, phase shift, demodulator offset and receiver bandwidth. Data quality of the microring-based DPSK transceiver can be optimized with eye-opening improvement of up to 7 dB. Transmission performance of the all-microring-based DPSK signal over a 70-km single mode fiber is compared to that of DPSK using a Mach-Zehnder modulator and a delay-line interferometer.

We present the results of a comprehensive analysis optimizing the performance of DPSK systems with increased FSR and narrow optical filtering, establishing improved chromatic dispersion tolerance of NRZ-DPSK by 20%, RZ-DPSK by 71% and CSRZ-DPSK by 74% approximately. Transmitting a 40Gb/s signals on a spectrally efficient 50GHz DWDM grid still exhibit improvements of 7% for NRZ-DPSK, 37% for RZ-DPSK and 22% for CSRZ-DPSK, relative to a typical DPSK receiver. The optimized delay and optical filtering scale with the amount of chromatic dispersion. We also demonstrate the impact of limited transmitter bandwidth on optimal optical filtering and bit delay parameters.

A novel photonic crystal fiber featured by concentric cores is proposed to induce dispersion controllability by photosensitivity. Chromatic dispersion can be changed from -1827 to 72 ps/nm/km with refractive index modulation of 4 x 10(-4) produced in Ge-doped regions in the fiber. Effective mode area of inner mode is as small as 6.4 mum(2). The proposed fiber enables to achieve quasi-phase-matched nonlinear parametric interaction in a single piece of photonic crystal fiber, by periodically alternating dispersion and compensating for phase mismatching caused by the dispersion.

We experimentally demonstrate a transmission scheduling algorithm to avoid congestion collapse in O-CDMA networks. Our result shows that transmission scheduling increases the performance of the system by orders of magnitude.

We demonstrate chromatic dispersion (CD) and polarization mode dispersion (PMD) monitoring techniques via simulation and experiment for 2- and 4-level intensity-modulated as well as phase-modulated optical systems. Degree of polarization (DOP) measurement for monitoring PMD up to 100-ps and clock tone measurement for monitoring CD up to 720-ps/nm are demonstrated in 10-Gsymbol/s non-return-to-zero (NRZ) and return-to-zero (RZ) systems. Analysis on dynamic range and monitoring window shows that careful consideration and characterization are necessary when applying these monitoring techniques to multi-level systems.

We have experimentally demonstrated two novel pulse position modulation techniques, namely Double Pulse Position Modulation (2-PPM) and Differential Pulse Position Modulation (DPPM) in Time-Wavelength OCDMA systems that will operate at a higher bit rate compared to traditional OOK-OCDMA systems with the same bandwidth. With 2-PPM technique, the number of active users will be more than DPPM while their bit rate is almost the same. Both techniques provide variable quality of service in OCDMA networks.

Ultra-small modulator and demodulator for 10 Gb/s differential phase-shift-keying (DPSK), using silicon-based microrings, are proposed. A single-waveguide microring modulator with over-coupling between ring and waveguide generates a DPSK signal, while a double-waveguide microring filter enables balanced DPSK detection. These modulator and demodulator are characterized. A trade-off between pattern dependence of the Duobinary signal and alternate-mark inversion signal power in demodulator design is discussed. Power penalty of the proposed approach is 0.8 dB relative to baseline using conventional modulation and demodulation techniques.

10 Gb/s non-return-to-zero (NRZ) on-off keyed (OOK) optical data packets are synchronized and time-multiplexed using a 26-ns tunable all-optical delay line. The delay element is based on wavelength conversion in periodically poled lithium niobate (PPLN) waveguides, inter-channel chromatic dispersion in dispersion compensating fiber (DCF) and intra-channel dispersion compensation with a chirped fiber Bragg grating (FBG). Delay reconfiguration time is measured to be less than 300 ps.

Optical differential phase shift keying is normally demodulated in a delay-line interferometer with a 1-bit delay such that the free-spectral-range of the demodulator is equal to the transmitted bitrate. We show using Karkunen-Loeve expansion simulation that free-spectral-range optimization leads to increased chromatic dispersion tolerances. The optimized delay inversely scales with the amount of chromatic dispersion such that a delay slightly shorter than the bit period increases tolerances with no adverse effect on the polarization-mode-dispersion tolerance or frequency offset penalty at the receiver.

We present an optical multipath error correction technique for differentially encoded modulation formats such as differential-phase-shift-keying (DPSK) and differential polarization shift keying (DPolSK) for fiber-based and free-space communication. This multipath error correction method combines optical and electronic logic gates. The scheme can easily be implemented using commercially available interferometers and high speed logic gates and does not require any data overhead therefore does not affect the effective bandwidth of the transmitted data. It is not merely compatible but also complementary to error correction codes commonly used in optical transmission systems such as forward-error-correction (FEC). The technique consists of separating the demodulation at the receiver in multiple paths. Each path consists of a Mach-Zehnder interferometer with a different integer bit delay used in each path. Some basic logic operations follow and the three paths are compared using a simple majority vote algorithm. Experimental results show that the scheme improves receiver sensitivity by 1.5 dB at BER of 10(-3),in back-to-back configuration. Numerical results indicate a 1.6 dB improvement in the presence of Chromatic Dispersion for a 25% increase in tolerance for a 3dB penalty from +/-1220 ps/nm to +/-1520 ps/nm. and a 0.35 dB improvement for back-to-back operation.

We demonstrate an optical half-subtracter and half-adder module that performs simultaneous bit-wise subtraction and addition of two 5 Gbit/s RZ data streams. We generate Borrow (/X*Y) and Difference/Sum (X plus sign in circleY, or XOR) outputs using cross-gain modulation (XGM) in two parallel SOAs. Taking advantage of the gain saturation inherent to SOAs, we generate two signals, /X*Y, and X*/Y, and combine them using a passive optical coupler to generate the XOR Difference/Sum output. We use difference-frequency-generation-based lambda-conversion in a PPLN waveguide to generate the Carry (X*Y) output. The PPLN waveguide allows bit-synchronous wavelength shifting, is wide-bandwidth, and offers no intrinsic chirp. Our module uses three active elements to perform simultaneous half-subtraction and addition, and carries a maximum power penalty of 1.0 dB.

We demonstrate, via simulation and experiment, slowing down of a phase-modulated optical signal. A 10.7-Gb/s NRZ-DPSK signal can be delayed by as much as 42 ps while still achieving error free via broadband SBS-based slow light. We further analyze the impact of slow-light-induced data-pattern dependence on both constructive and destructive demodulated ports. By detuning the SBS gain profile, we achieve 3-dB Q-factor improvement by the reduction of pattern dependence. Performance comparison between NRZ-DPSK and RZ-DPSK shows that robustness to slow-light-induced pattern dependence is modulation format dependent.

We demonstrate an all-optical half adder for bit-wise addition of two serial data streams that simultaneously generates Sum and Carry outputs. The module performs the required XOR and AND operations using only two nonlinear optical elements. Difference Frequency Generation in a periodically poled lithium niobate waveguide serves as the AND gate and cross-gain modulation in a semiconductor optical amplifier is employed to generate the XOR output. Error free operation for RZ data is reported.

We report on an all-optical XNOR-gate using simultaneous Four-Wave Mixing (FWM) and Cross-Gain Modulation (XGM) in a semiconductor optical amplifier (SOA). FWM generates the bitwise AND output corresponding to the two input data streams while XGM is used to generate the NOR output. These two outputs are combined using a coupler to obtain the final XNOR output. Error-free operation for RZ data with <2dB power-penalty is reported.

We propose and demonstrate a simple technique for the measurement of the magnitude and sign of the chirp parameter of electro-optic modulators, using phase comparison between two optically filtered vestigial sidebands generated from 10-GHz sinusoidal signals. We show the analytical, simulation, and experimental results of this approach.