Diffraction characteristics of general dielectric planar (slab) gratings and surface-relief (corrugated) gratings are reviewed. Applications to laser-beam deflection, guidance, modulation, coupling, filtering, wavefront reconstruction, and distributed feedback in the fields of acoustooptics, integrated optics, holography, and spectral analysis are discussed. An exact formulation of the grating diffraction problem without approximations (rigorous coupled-wave theory developed by the authors) is presented. The method of solution is in terms of state variables and this is presented in detail. Then, using a series of fundamental assumptions, this rigorous theory is shown to reduce to the various existing approximate theories in the appropriate limits. The effects of these fundamental assumptions in the approximate theories are quantified and discussed.

Analysis and applications of optical diffraction by gratings

We present a theoretical study of the effect of radiation losses on the mode selectivity of DFB lasers with second-order gratings. For a second-order grating, interference of the radiation due to first-order diffraction of oppositely propagating guided waves cancels the radiation loss at one of the edges of the spectrum gap. This provides threshold gain discrimination of order 10 cm-1against one of the two dominant modes occurring near the edges of the gap. This should allow fabrication of DFB lasers with properties that are nearly independent of the positions of the facets relative to the grating corrugations, which are uncontrolled. By applying antireflection coatings to the two ends, differential quantum efficiencies close to those of conventional Fabry-Perot lasers should be achievable.

Second-order distributed feedback lasers with mode selection provided by first-order radiation losses

Recent progress in the dynamic single-mode (DSM) semiconductor lasers in the wavelength of 1.5-1.6\mu m are reviewed and the basic principle of DSM operation is given. Study of the DSM laser is originated for application to the wide-band optical-fiber communication in the lowest loss wavelength region of 1.5 to 1.65 μm. A DSM laser consists of a mode-selective resonator and a transverse-mode-controlled waveguide, such as the narrow-striped distributed-Bragg-reflector (DBR) laser, so as to maintain a fixed axial mode under the rapid direct modulation. The technology of monolithic integration for optical circuits is applied to realize some of DSM lasers. Structures, static and dynamic characteristics of lasing wavelength, output power, and reliability of the art DSM lasers are reviewed. The dynamic Spectral width of 0.3 nm, the output power of a few milliwatts, and the reliability over a few thousand hours are reported for experimental DSM lasers.

Dynamic single-mode semiconductor lasers with a distributed reflector

Semiconductor lasers with stable longitudinal single‐mode operation are essential for optical fiber communication systems. Distributed feedback (DFB) lasers are effective to obtain a stable longitudinal single‐mode operation; however, stability is not enough mainly because of the spatial hole‐burning effect. A corrugation‐pitch‐modulated (CPM) structure was proposed to improve the stability of longitudinal single‐mode operation in distributed feedback lasers. CPM‐DFB lasers have a unique corrugation structure to suppress the spatial hole‐burning effect. This structure was obtained by a newly developed corrugation fabrication method, a photomask self‐interference method. It is confirmed that the CPM‐DFB lasers operate in a stable longitudinal single‐mode by suppressing the spatial hole‐burning effect. This structure is also suitable for narrowing the spectral linewidth for use in coherent optical fiber communication systems. Narrow spectral linewidth lasers with a CPM structure have achieved the narrowest ...

Spectral characteristics of distributed feedback semiconductor lasers and their improvements by corrugation‐pitch‐modulated structure

Lasing characteristics of InGaAsP/InP distributed feedback (DFB) lasers in the 1.5 μm range were studied theoretically and experimentally. Wave propagation in five-layer DFB waveguides were analyzed to estimate the effect of the structural parameters on threshold conditions. A brief consideration on designing a low threshold laser and its lasing wavelength was made. DFB buried heterostructure lasers with fundamental grating emitting at 1.53 μm were prepared by liquid phase epitaxial techniques. CW operation was confirmed in the temperature rangeof -20° to 58°C, and a CW threshold current was as low as 50 mA at room temperature. A stable single longitudinal mode operation was observed both in dc condition and in modulated condition by a pseudorandom pulse current at 500 Mbits/s. No significant increase in the threshold current was observed after 1400 h continuous CW operation at 20°C.

1.5 &#181;m range InGaAsP/InP distributed feedback lasers

Fabrication and lasing characteristics of InGaAsP/InP distributed‐feedback injection lasers are described. An InGaAsP active layer, a p‐InP clad layer, and an n‐InGaAsP cap layer are successively grown on an InP substrate with a 0.32‐μm periodic corrugation. The diodes emit at a wavelength of 1.1 μm up to 170 K under pulsed operation. Single longitudinal mode oscillation and a small temperature dependence of the lasing wavelength of 0.054 nm/K are obtained in these diodes.

T. Fukuzawa

Papers

InGaAsP/InP distributed‐feedback injection lasers fabricated by one‐step liquid phase epitaxy