Toshiharu Tako

Frequency Stabilization of AlGaAs Semiconductor Laser Based on the 85Rb-D2 Line

The frequency of an AlGaAs semiconductor laser was stabilized by using the linear absorption spectrum of the 85Rb-D2 line. By controlling the injection current, the frequency stability of 3.0×10-10σ1.4×10-12 was obtained for 10 msτ500 s. First observation of the saturated absorption spectrum of the 85Rb-D2 line is demonstrated, which can be used as a frequency reference to improve the frequency stability.

Frequency Stabilization of AlGaAs Semiconductor Laser to the Absorption Line of Water Vapor

The absorption spectrum of water vapor in the (2, 1, 1) vibration-rotation band has been observed by using an AlGaAs semiconductor laser around 0.82 µm. The laser frequency was stabilized to one of the absorption lines by controlling the injection current. A frequency stability of 1.9×10-9≧σ≧1.1×10-11 was obtained for 10 ms≦τ≦500 s.

Estimation of the Ultimate Frequency Stability of Semiconductor Lasers

The frequency stabilities of 0.8 µm AlGaAs lasers were estimated by using the Allan variance as a measure of the stability. The contributions of the quantum noise (the spontaneous emission, carrier, and current noise) and additional noise (current source noise and temperature noise) are given. The highest frequency stability of the free-running laser was estimated to be 6.3×10-11 at an integration time of 0.1 s. It is shown that the frequency stability of the stabilized laser is limited by the quantum noise. The estimated results were compared with the experimental results and with the estimated stability of 3.39 µm He–22Ne lasers. The derivations of the spectral width from the frequency stability are also given. The narrowest limit of the spectral width was estimated to be 5.5 MHz (HWHM) for I/Ith=1.3, while the corresponding experimental result was 6.2 MHz for a channeled-substrate planar (CSP)-type laser.

Linewidth Measurement of a Single Longitudinal Mode AlGaAs Laser with a Fabry-Perot Interferometer

Interferometric measurement of the linewidth has been carried out on a single longitudinal mode AlGaAs/GaAs double heterostructure laser by using a Fabry-Perot interferometer with spacers of 30 cm, 3.2 m, and 10 m. The full width at half maximum was estimated to be less than 1 MHz when the current level exceeds 1.15 times the threshold, which was near the estimated theoretical limit.

Frequency Stabilization of AlGaAs DH Lasers

The frequency of AlGaAs DH lasers was stabilized at the resonant frequency of a Fabry-Perot interferometer by controlling the injection current. The interferometer was controlled by a Lamb dip stabilized He-Ne laser at 633 nm. The frequency stability obtained here was 2.0×10-11σ2.1×10-9 for 10 ms τ500 s, where σ and τ represent the square root of the Allan variance and the integration time, respectively.

Frequency Stability Measurement of Feedback Stabilized AlGaAs DH Laser

The frequency of a single longitudinal mode AlGaAs DH laser was stabilized at the resonant frequency of an external Fabry-Perot interferometer by controlling the temperature. The frequency stability was evaluated by using the square root of the Allan variance ?2 and the power spectral density. The following value was obtained: 2.1?10-9???9.6?10-9 for 10ms 10 s.

Nonlinear optical properties of tin-phthalocyanine thin films

Abstract The nonlinear optical properties of evaporated tin–phthalocyanine thin films were investigated through absorption measurement, atomic force microscopy, and transmissivity measurement using a z-scan method. The pyramidal molecules fabricated by vacuum evaporation while applying a high electric field parallel to the substrate had large third-order nonlinear susceptibility of 3.8×10−8 esu.

A Novel Technique for Measuring the Frequency Deviation of Semiconductor Lasers Under Direct Modulation

A novel technique is proposed for measuring the frequency deviation of semiconductor lasers under direct modulation using a Michelson interferometer. This technique is applicable to a wide range of modulation frequency and does not require high-speed photo-detectors. The accuracy of the measurement is not reduced by the spectral line-width of lasers, the misalignment of the optical axes, or the depth of intensity modulation.

Limit of the Frequency Stability in AlGaAs Semiconductor Lasers

A theoretical analysis is presented on the limit of the frequency stability in AlGaAs semiconductor lasers. The theoretical stability is derived taking into account the various limiting factors, which include the quantum noise of the lasers, noise of a photodetector and modulation of the laser frequency. The estimated stability is then compared with the experimental results. It is found that the stability can be improved to the quantum noise level when a Fabry-Perot interferometer is used as a frequency reference, and that the stability is limited not only by the quantum noise but also the noise of a photodetector and frequency modulation when atomic or molecular absorption lines are used.

II Coherence in Semiconductor Lasers

Publisher Summary This chapter discuses the coherence in semiconductor lasers. Theoretical backgrounds and experimental results on temporal coherence in semiconductor lasers are described in the chapter. Techniques to improve coherence and applications to the field of optics are also reviewed. The semiconductor lasers presently available still have a primitive structure for obtaining high temporal coherence. Improvements in coherence require the fabrication of more sophisticated lasers, which are to be connected with external electronic and optical components. The reproducibility and reliability of semiconductor lasers also need improvement at the stage of laser fabrication. Close cooperation between device fabrication and system design is essential to obtain extremely high temporal coherence. Developments of external optical components, such as high-performance optical isolators, optical fibers, fiber couplers, and opto-electronic integrated circuits (OEIC), are required to support efforts to improve coherence. Ultrahigh coherence in semiconductor lasers can be achieved under these conditions, thus giving new applications and impact to optics.