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In this paper, we designed the offset frequency locking and active frequency stabilization system for the continuous-wave (CW) and electro-optical Q-switched RF-excited waveguide CO2 lasers to provide an ideal light source for coherent radar. The CW laser is used as a local laser, and the pulsed laser is used as a main laser, which can produce Q-switched and cavity-dumped laser synchronously. A closed-loop laser frequency control system was used to stabilize the Q-switched laser at the gain curve center frequency and to lock the two lasers at a selected heterodyne frequency. The system includes two parts: 1) pulsed laser frequency stabilization and 2) offset frequency locking. The frequency stabilization part can keep the Q-switched laser oscillating at the peak of the gain curve by measuring the pulse build-up time continuously and controlling the cavity length. The offset frequency locking circuits keep the heterodyne frequency around the selected frequency by measuring the frequency of the beat signals and controlling the CW laser cavity length. In the experiment, the long-term frequency shift of the pulse laser was measured to be less than ±16 MHz and the offset frequency fluctuation was less than ±2 MHz when the frequency control system was in a closed-loop operation. [ABSTRACT FROM AUTHOR]

The concept of nonautonomous soliton dispersion management pertaining to the propagation of chirped nonautonomous Raman colored solitons through a dispersion oscillating fiber in the presence of an electrooptic phase modulator and also by taking into consideration the effect due to self-induced Raman scattering on the propagation of optical solitons when the soliton amplitude does not vary significantly during self-scattering, has been studied. The amplitudes and speeds of these nonautonomous solitons, during the propagation and after the interaction are no longer found to be the same as those prior to the interaction. Moreover, intense soliton pulse amplification has been obtained, which forms the main results of this paper. In the context of Bose-Einstein condensates, the aforementioned scenario has also been interpreted as the dynamics of the condensates with linear and quadratic external potentials in an optical trap. [ABSTRACT FROM AUTHOR]

Semiconductor lasers tend to generate excess intensity noise called the optical feedback noise in addition to the quantum noise. A noise reduction method using an electric positive and negative feedback loop between an optical detector and a semiconductor laser was demonstrated in this paper. The electric positive feedback was set in a high-frequency region, reducing the optical feedback noise, while the electric negative feedback was set in a frequency range lower than the positive-feedback frequency, resulting in the suppression of the quantum noise (optical shot noise). Noise reduction over 100-MHz frequency region and a reduction ability superior to that obtained by the superposition of high-frequency current were confirmed. [ABSTRACT FROM AUTHOR]

A proposal for a silicon-based elastic polarization converter consisting of dual microring resonators and a phase shifter is presented and theoretically investigated. By utilizing a microring resonator for polarization splitting, a phase shifter for phase con- trolling, and another microring resonator for TE- and TM-polarized light combination, this proposed polarization converter can realize polarization conversions between any two linear, circular, and elliptic polarization states. The proposed scheme is also designed and numerically studied by performing the 3-D full vectorial film mode matching method and coupled mode theory. Simulation results show that the capacity factor of polarization conversion is wavelength-dependent and can be high up to 1 when the polarization converter operates at the resonance condition of the microring resonators. Finally, the linear-circular polarization conversion performances are also analyzed. [ABSTRACT FROM AUTHOR]

Theoretical results on the extinction ratio (ER) improvement in ultralong semiconductor optical amplifiers (UL-SOAs) are presented indicating a Bogatov-like effect in the saturated section. Starting from general nonlinear gain equations, an analytic description of the Bogatov-like effect is derived in terms of gain coefficients. These equations are used to explain the results of fully numerical simulations. The data signal's ER improves because of a two-step process. First, the data signal cross-gain modulates the additionally injected CW signal. Second, due to this inverse modulation, the data signal's states are differently amplified via the Bogatov-like effect. Since the ER improvement is caused by the fast intraband effects, this simple scheme has the potential for high-speed regeneration. [ABSTRACT FROM AUTHOR]

InGaN--GaN multiple-quantum-well (MQW)-based photodetectors, with a detection edge at 450 nm and a high responsivity, have been fabricated and characterized. We show that the performance of MQW-based photodetectors strongly depends on a proper device design, i.e., number of QWs, and barrier and blocking layer thickness and doping level. Namely, the responsivity can be varied in the ~1 to ~100 mA/W range in similar structures and with the same number of QWs. These results support a model where the photocurrent increase is due to the improvement of collection efficiency caused by a change in transport mechanism for carriers photogenerated in the QWs. The transport mechanism depends on the location of the QWs in relation to the depletion region. [ABSTRACT FROM AUTHOR]

Using the Maxwell-Bloch equations, we have studied dynamics associated with an electro-optically tunable laser modulated by a sinusoidal signal with a frequency near the cavity free spectral range. We find that frequency modulation (FM) modelocking may occur when a higher order FM mode acquires the lowest threshold. For short-cavity lasers, the pulse waveform in modelocking is complicated, and unlike the simple Gaussian shape suggested by previous studies. In order to explain instability observed in laser FM operation, we develop a linear stability analysis for the lasing FM mode. Our analysis shows that this type of instability is attributed to mode competition and to laser relaxation dynamics. We then confirm the analytic results with numerical simulations. [ABSTRACT FROM AUTHOR]

We present a set of modeling, sensitivity analysis, and design optimization methods for photonic crystal structures based on Wannier basis field expansion and efficient matrix analysis techniques. We develop the sensitivity analysis technique to analyze both refractive index perturbations and dielectric boundary shift perturbations. Our modeling method is ∼1000x faster than finite-difference time-domain (FDTD) for searching through a large number of similar device designs. We show that our optimization techniques, relying on the efficiency of the modeling and sensitivity analysis methods, enable systematic global and local optimizations of integrated optical components. We show that our design method can be controlled to favor designs without high-energy build-ups, potentially making them more fabrication-error tolerant. We present design examples and verify our designs with FDTD calculations. [ABSTRACT FROM AUTHOR]

A 1534-nm fiber laser pumped Er:YAG laser action at room temperature has been demonstrated with high efficiency at two emission wavelengths: 1645 and 1617 nm. Multiwatt continuous-wave power was demonstrated at both wavelengths and active electrooptic Q-switch operation with >90% Q-switch efficiency was achieved at 1645 nm. Etalon tuned wavelength selection showed excellent agreement with theoretical analysis. [ABSTRACT FROM AUTHOR]

The dynamics of a short-cavity, electrooptically tunable microchip laser is studied using the Maxwell-Bloch equations for a unidirectional ring cavity. Within this model, the electrooptic tuning medium is treated rigorously by a wave propagation equation and the electrooptic tuning is equivalent to introducing a time varying perturbation to the boundary condition. With the help of an approximate analytic solution as well as numerical simulations, we find that the laser relaxation does not pose limitations to the intracavity frequency modulation bandwidth. Instead, the bandwidth is a sensitive function of the cavity length and also of the fraction of the cavity length taken up by the electrooptic section. In addition, under large-signal sinusoidal modulation, the numerical solutions reveal complicated dynamical behaviors when the modulation frequencies are near the cavity free spectral range. [ABSTRACT FROM AUTHOR]

We analyze the influence of parameter mismatch between emitter and receiver systems on the bit error rate of an optical chaos communication scheme. Intensity hyperchaosis generated in the system by semiconductor lasers with electrooptical feedback. We find analytical predictions for the dependence of the bit error rate with the amplitude of the various mismatches and the statistical properties of the hyperchaotic carrier. A good concordance is found with numerical and experimental results. [ABSTRACT FROM AUTHOR]

Based on extensive numerical calculations, quantum-dot (QD) amplifiers are predicted to offer higher output power and lower noise figure compared to bulk as well as quantum well amplifiers. The underlying physical mechanisms are analyzed in detail, leading to the identification of a few key requirements that QD amplifiers should meet in order to achieve such superior linear characteristics. The existence of a highly inverted wetting layer or barrier region, acting as a carrier reservoir, is central to this performance enhancement. It is shown that amplified spontaneous emission acts to decrease the inversion of the wetting layer stats, thus helping to quench the gain of these states, which might otherwise dominate. [ABSTRACT FROM AUTHOR]

A dielectric graded-phase mirror was developed to change the intensity distribution of the fundamental mode in an Nd:YAG laser resonator to a top-hat profile. A super-Gaussian mode of the sixth order was generated by means of a graded-phase mirror with a simple ring-shaped phase step on a spherical reflector. The depth of the ring on the mirror was 90 nm. The graded- phase mirror was manufactured with an ordinary vapor deposition technique using an appropriate mask. Laser experiments with CW and repetitively pulsed diode-laser pumping were performed and compared. Slope efficiencies up to 19% were achieved. The experimental results are in excellent agreement with the theory. [ABSTRACT FROM AUTHOR]

Describes an electrooptical traveling-phase grating with periodic domain inversion and its application to ultrafast unidirectional beam deflection. Application of Raman-Nath diffraction in separating input light to many diffracted beams; Parameters of electrooptic traveling phase grating.

Presents a numerical analysis of the operating characteristics of Tetrahertz Optical Asymmetric Demultiplexer (TOAD) devices. Advantages of the TOAD topology; Physical mechanisms behind the operation of TOAD; Reduction of reflected and switched amplitude modulations in negative frequency-detuned TOAD topology.

Develops an optical intensity modulator based on a novel electrooptic (EO) polymer with a high mubeta chromophore. Advantages of EO polymers over inorganic materials; Optical characteristics of poled polymers in terms of EO coefficient r33; Efficacy of the polymer and near optimum poling scheme for high-speed intensity modulator design.

Describes a phase shifter for a low-loss Mach-Zehnder interferometric (MZI) switch. Electrooptic device; Requirements for an MZI space switch; First-principle model for calculating electro-refraction; Design tool for predicting device performance in complicated layer structures; Detailed layer structure of chopped quantum well samples; Minimal achievable dimensions.

Presents a novel electrooptic phase modulator featuring lens modulation. Application to the electrooptic chirping compression method for ultrashort optical pulse generation; Diagram showing the basic structure of electrooptic lens modulation; Suitability for negative and positive group delay dispersion.

Studies the acoustooptic interaction of guided optical waves and surface acoustic waves in multilayered structures of dimensions of the order of those seen in multiple-quantum well structures. Details on the procedure used in this study; Indications from the results of the study; Discussion on the effects of device parameters.

Presents a study which examines the different types of intersubband EO modulation schemes and their suitability for practical realization. Information on the use of first-order pertubation theory; Details on the study done on structures that maximize the electrooptic susceptibility of a particular origin; Discussion on the suitability of the various schemes for practical realizations.

Measures the optical frequency response of epitaxial lift-off on quartz substrates to 140 GHz. Information on the use of electrooptic sampling and heterodyne techniques; What the picosecond sampling measurements establish; Details on the advantages of these lift-off devices.

Presents the results on carrier transport in shallow multiple-quantum-well at various bias voltages. Role the drift of holes play in determining the response times; Details on the sample structures and characteristics used.

Reports on the development of a frequency stabilization scheme for CO2 lasers, using external modulation via an electrooptic modulator (EOM). Information on a laser sideband which is generated by the EOM; Detection of the saturation signal of an OsO4.

Demonstrates an electrooptic modulator that is sensitive to the polarization state of transmitted light, using the intrinsic optical anisotropy of biaxially strained [110]-oriented GaAs-InxGa1-xAs multiple quantum wells. How the ellipticity and direction of polarization of a linearly polarized input pulse are modulated; Use of sensitive ellipsometric measurements to determine operating wavelength, contrast ratio, optical bandwidth and tunability of modulator.

Presents a numerical investigation on the method for ultrashort-pulse (USP) generation in excimer lasers employing fast mode locking (FML) with the use of an electrooptic deflector (EOD). Principle of operation and schematic diagram for laser with FML; Reasons for the laser with a sine-wave-driven EOD and with a square-wave-driven EOD to be considered in the investigations; Conclusions.