Joji Maeda

Squeezing characteristics analysis of a fundamental-confined second-harmonic generation system by means of a self-consistent method

We discuss quantum-fluctuation characteristics of a second-harmonic generation system that uses an optical resonator to confine only the fundamental field. It was predicted that the available amount of squeezing is limited to 1.76 dB for the fundamental output and 9.54 dB for the second-harmonic output, respectively, irrespective of system parameters. However, these predictions are based on low-order perturbation theory and are unavailable if the nonlinear coupling between the fundamental and the second harmonic becomes large. We consider the spatial evolution of the fields and reveal that the maximum amount of squeezing depends on the cavity loss: Even an arbitrary amount of squeezing is possible for both the fundamental output and the second-harmonic output. We also consider the possibility of parametric oscillation of empty cavity modes pumped by the generated second harmonic and derive the following prediction: In a system that uses a type I phase-matched crystal, the oscillation of the side mode hardly occurs because of sum-frequency generation with the fundamental and scarcely imposes any limitations on squeezing. On the other hand, a system with a type II phase-matched crystal suffers from the oscillation of the polarization mode orthogonal to that of the fundamental input, and squeezing of the second-harmonic output is limited to 3 dB.

Amplitude squeezing from singly resonant frequency-doubling laser

We analyze amplitude squeezing from a singly resonant frequency-doubling laser oscillating at a single frequency. In this laser system, the cavity loss depends on the intensity of the oscillating fundamental field, so that conventional analyses based on a mean-field approximation become invalid in a highly pumped regime. To avoid this inconvenience, we consider spatial evolution of fields both in a laser medium and in a nonlinear crystal. It is predicted for the first time that a combination of excess nonlinearity and modest laser saturation can increase the output noise. We propose novel indices to evaluate the possible noise enhancement and suggest a design rule for squeezed light generation.

Bright squeezing by singly resonant second-harmonic generation: effect of fundamental depletion and feedback.

We analyze the squeezing characteristics of a singly resonant second-harmonic-generation system, in which only the fundamental light is confined in a plain cavity resonator, with consideration for fundamental depletion in a nonlinear crystal. The system was analyzed under the mean-field approximation, which neglects the variation of the field in the crystal, and as much as 9.5 dB of squeezing was predicted in the second-harmonic output. On the basis of the self-consistent method, we analyze the system, which is driven by such an intense fundamental input that the mean-field approximation is not valid, and predict that an arbitrary amount of squeezing will be available in this regime.

Characteristics of All-Optical Ultra-Fast Retiming Switches Using Cascade of Second Harmonic Generation and Difference Frequency Mixing in Periodically Poled Lithium Niobate Waveguides

We numerically calculate the performance of all-optical retiming switches employing the cascaded second-order nonlinear effect in quasi-phase-matched lithium niobate waveguides. A time offset between the signal and clock pulses can improve the timing-jitter transfer characteristics.

Analysis of amplitude squeezing of harmonic generation in a quasi-phase-matched device: effect of stochastic variation of domain length

Amplitude squeezing of the second-harmonic generation in periodically poled quasi-phase-matched devices is analyzed with consideration for errors of the domain length. We show that the amount of squeezing is a complex function of the phase mismatch and of the input power and that it is practically impossible to maintain the perfect quasi-phase matching for an arbitrary input power. For evaluation of the availability of squeezing, we propose a contour map of squeezing that can visualize the tolerance of squeezing for the phase mismatch. It is shown that the effect of domain length error depends on the type of the error; the random duty-cycle error, where the mean domain period is precisely fixed, does not alter the squeezing performance, whereas the random period error, which fluctuates during the domain period, severely alters tuning characteristics. The available amount of squeezing is predicted to be determined by the tuning stability of the device.

Quantum noise analysis of frequency-doubling ring lasers: nonlinearity-induced noise enhancement and its dependence on gain profile

Using a traveling-wave model that can treat the spatial evolution of light fields, quantum noise characteristics of frequency-doubling ring lasers are analyzed under single-frequency operation. Systems under consideration are the discrete system, in which a laser crystal and a nonlinear crystal are separately installed, and the self-doubling system, which is equipped with a nonlinear crystal with laser gain. It is predicted that the unsaturated gain profile does not affect noise characteristics of the discrete system: nonlinear loss-induced noise enhancement (NINE), i.e., an increase of the spontaneous emission noise associated with enlarged gain that compensates the nonlinear loss, manifests itself at a specific operating point regardless of the gain profile. In the self-doubling system, on the other hand, the manifestation of NINE will arise for higher harmonic output compared with that in the discrete system. For the self-doubling system, moreover, the profile of the unsaturated gain causes a significant difference in NINE; because NINE is associated with a large field variation, it is effectively suppressed by configuring the gain profile to be flat or increasing along the direction of laser field propagation.

Characteristics of all-optical ultra-fast gate switches using the cascaded second-order nonlinear effect in quasi-phase matched lithium niobate devices

We numerically analyze switching characteristics of all-optical gate switches using the cascade of second harmonic generation and difference frequency mixing in quasi-phase matched Lithium Niobate devices, and show possibility of efficient ultra-fast operation beyond 1Tbps.

Chaotic Approach to Evaluation of Disturbed Magnetic Surfaces

A circle mapping can approximately reproduce the cross section of magnetic surfaces and the value of the periodic driving force ( K ) at a magnetic island varies with the width of the magnetic island, which suggests the value of K is one of measures for the degradation of magnetic surfaces. The profile of a rotational transform has flat regions at the magnetic islands. The width of the flat region is proportional to the width of the magnetic island. Therefore it may be another measure of the degradation of magnetic surfaces. This method requires less data for the estimation than the usual method of calculating the width of magnetic islands. For collapsed magnetic surfaces that are produced by overlapping of two magnetic islands, the fractal dimension can effectively estimate the degradation of them. The fractal dimensions of cross sections of regular magnetic surfaces and clear magnetic islands are nearly 1, while that of a collapsed magnetic surface is about 1.2 in the present study.

Broadband Wavelength-Tunable Actively Mode-Locked Fiber Ring Laser Using a Bismuth-Oxide-Based Erbium-Doped Fiber

We demonstrate an actively mode-locked fiber ring laser employing a 151-cm-long bismuth-oxide-based erbium-doped fiber. Stable short pulses at 10GHz are obtained with a broadband wavelength tuning range of 66nm covering both the C- and L-bands.

Efficiency map of a quasi-phase-matched device

>As a tool to evaluate the performance of a quasi-phase-matched device, we propose a contour map of conversion efficiency as a function of input power and phase mismatch. We demonstrate, using numerical analyses, that the map reflects the error of domain lengths; the map of a device with random duty cycle error is essentially similar to that of an ideal device. On the other hand, the map of a device with random period error is severely deformed, suggesting the necessity of simultaneous tuning of phase mismatch and input power.