Hiromasa Ito

Optical frequency domain ranging by a frequency-shifted feedback laser

This paper describes the theoretical and experimental study of a new technique for optical frequency domain ranging (OFDR) by a frequency-shifted feedback (FSF) laser. In conventional OFDR, a frequency chirped single-mode laser is used as a light source to convert a distance into a beat frequency, and a tradeoff exists between measurement range and resolution. The FSF laser output consists of periodically generated chirped frequency components whose chirp rate is faster than 100 PHz/s (P=10/sup 15/), By use of the FSF laser, the tradeoff is removed and long-distance high-resolution OFDR is realized In the experiment, a distance of 18.5 km was measured with a resolution of 20 mm.

A new method for measurement of group velocity dispersion of optical fibers by using a frequency-shifted feedback fiber laser

A new method for the measurement of the group velocity dispersion (GVD) in optical fibers, based on optical frequency domain reflectometry (OFDR), is proposed and demonstrated. Frequency chirped light is used as a light source, which allows the dispersion to be determined from changes in the frequency chirp rate. Accurate measurement of the average dispersion, at a single terminal, in fibers up to several tens of kilometers, is accomplished using a frequency-shifted feedback fiber laser as a light source.

Improvement of Diffraction Properties in Waveguide-Type Acoustooptic Modulator Driven by Surface Acoustic Wave

A waveguide-type acoustooptic modulator (AOM) driven by a surface acoustic wave (SAW) in a tapered crossed-channel waveguide on a 128°-rotated Y-cut LiNbO3 substrate has been proposed for an optical wavelength of 1.55 µm. In this study, to improve the diffraction properties of the waveguide-type AOM, the dependences of the diffraction properties on the relative position of the SAW beam for the diffraction region were simulated using a beam-propagation method (BPM) and measured. By decreasing SAW beam width, although the input voltage needed to obtain the maximum diffraction efficiency increased, diffraction efficiency improved to 84% from the previous value of 65%. Furthermore, to obtain a lower driving voltage, the utilization of a unidirectional transducer was investigated for the AO interaction on a planar optical waveguide at an optical wavelength of 0.633 µm.

Monolithically Integrated Tandem Waveguide-Type Acoustooptic Modulator Driven by Surface Acoustic Waves

A waveguide-type acoustooptic modulator (AOM) using coplanar AO coupling due to a surface acoustic wave (SAW), that is, Bragg diffraction, in a tapered crossed-channel proton-exchanged (PE) optical waveguide on a 128°-rotated Y-cut LiNbO3 substrate for an optical wavelength of 1.55 µm has been proposed. In this study, a monolithically integrated tandem waveguide-type AOM driven by SAW was designed and fabricated. The structure considered was a 2×4 optical switch, in which the input ports of two second 1×2 switches were connected to the two output ports of the first 2×2 switch on the same substrate. An interdigital transducer (IDT) with a period length of 32 µm and an overlap length of 2 mm was fabricated in the first and second stages of the AO interaction region. Diffraction efficiency was measured at a driving frequency of approximately 120 MHz. A diffraction efficiency of approximately 90% was obtained for each stage. When both stages were driven at the same frequency, a peak diffraction efficiency of 63% was obtained. Furthermore, the optical frequency shifts for the sum of two driving frequencies and the difference frequency ranging from DC to 5 MHz were observed.

Novel PMD measurement method based on OFDR using a frequency-shifted feedback fiber laser

We propose a new method to measure polarization mode dispersion (PMD) in optical fibers based on optical frequency domain reflectometry technique. In this method the PMD is directly determined from the beat frequency generated by interference between lights from the Fresnel reflection at the end of the device under test, which makes the measurement at single end of the device possible. An automated PMD measurement system is demonstrated on polarization maintaining fibers with a frequency-shifted feedback fiber laser as a light source.

Frequency-Shifted Feedback Fiber Laser Oscillation with Monolithically Integrated Tandem Waveguide-Type Acoustooptic Modulator Driven by Surface Acoustic Waves

Frequency-shifted feedback fiber laser oscillation and optical frequency domain ranging using a monolithically integrated tandem acoustooptic modulator driven by surface acoustic waves (SAWs) were demonstrated. The linear relationships between the beat frequency change and the optical path difference in the Mach–Zehnder interferometer with three slopes were obtained by combining the upward and downward frequency shifts in the first and second SAWs.

Long distance measurement with high spatial resolution by optical frequency domain reflectometry using a frequency-shifted feedback fiber laser

Summary form only given. Optical ranging is important in various fields, such as the characterization of an optical network, fiber optic sensors, and so on. To implement these applications, a spatial resolution better than 1 cm over an operating range of tens of kilometers is desirable. Such performance, however, has not yet been demonstrated, as far as we know. We demonstrate long distance measurement by an optical frequency domain reflectometry (OFDR) using a frequency-shifted feedback (FSF) fiber laser, and achieve a spatial resolution of 0.4 cm at an operating range of 20 km.

Modification of Surface-Acoustic-Wave-Driven Tandem Acoustooptic Frequency Shifter for Improvement of Diffraction Properties

A modification of the waveguide shape of the monolithically integrated tandem waveguide-type acoustooptic frequency shifter (AOFS) was investigated analytically and experimentally to improve its diffraction properties. The simulated diffraction properties were improved by decreasing the vertex angle of the tapered waveguide. The analytically obtained maximum doubly diffracted beam power increased from 0.43 in the previous AOFS to 0.55. The diffraction properties of a fabricated tandem AOFS were measured and compared with the analytical results.