We review the history of research on the surface emitting laser or vertical cavity surface emitting laser (VCSEL). Then, some of important technologies are introduced and future prospect will be discussed.

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Long-wavelength vertical-cavity surface-emitting lasers (VCSELs) are required as light sources for next-generation optical communications. In this review, technical issues concerning fabrication of long-wavelength VCSELs are discussed, and approaches to make a breakthrough regarding these issues are presented.

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Vertical-cavity surface-emitting lasers (VCSELs) are used in optical transceivers for local area networks (LANs) and interconnections with data rates of around 1Gbps, such as Gigabit Ethernet, Fibre Channel, and so on. In these systems, the transmission distance more than 500m is available by using 50 μEm core multimode fiber . In this paper, basic technologies of VCSEL-based data transmissions are introduced . Transverse mode characteristics of the oxide-confined VCSELs are also reviewed. Transverse mode can be controlled by adjusting the refractive index confinement effect and applying excess loss to higher order mode selectively . Currently, standardization of 10Gbps LANs and interconnections is in progress. High speed VCSELs and VCSEL arrays are candidates for the short reach applications.

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The technical issues involved in applying vertical-cavity surface-emitting lasers (VCSELs) to optical interconnections and optoelectronic processing systems are discussed from the viewpoint of system applications. We review the parallel optical links and switching smart pixel chips as application examples and discuss the VCSEL requirements on system applications.

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Red-light surface-emitting lasers are expected to be applied as compact light sources for optical data links employing plastic optical fibers. InGaAlP red VCSELs have been successfully fabricated. One ofthe important subjects respecting InGaAlP VCSELs is improvement in temperature characteristics. Reduction of the active region diameter is advantageous in that threshold current is reduced, resulting in a reduction of heat generation. It is also effective for the reduction of thermal resistance, due to the heat dissipation through the upper and side regions. The control of such transverse structure is very important for obtaining high-performance VCSELs. Excellent temperature characteristics were obtained for 666-nm VCSELs with a protonimplanted planar structure.

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We propose a micromachined VCSEL and an optical filter with a strain control layer, which enables wavelength tuning induced by local heating in a cantilever structure. We present a possibility of a large tuning range of over 100nm. Experimentally, we demonstrate both negative tuning and positive tuning of micromachined GaAlAs/GaAs filters. Also, we demonstrate a temperature insensitive filter with a temperature coefficient of 0.01 nm/K and a 4×4 multi-wavelength filter array in addition with wavelength trimming of over 20nm.

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Vertical-cavity surface-emitting laser (VCSEL) arrays are promising light sources for laser-printer applications. Two types of the raster output scanning (ROS) systems with VCSEL array for the laser printer are introduced, and VCSEL arrays for each ROS systems are shown. Also demonstrated are the properties of the VCSEL arrays. From viewpoint of high-speed and high-resolution printer applications, high optical output power is required for single- and fundamental-transverse mode VCSELs. For the requirement, thetransversemode-controlled VCSELs with output aperture by metal electrode are shown to achieve the outputpower as high as 3.4 mW at 780nm. For reproducibility and uniformity of the device performance, the oxidation process of AlAs which confines a current injection is in-situ monitored via optical reflectivity from the VCSEL substrate.

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Possibility of phase conjugation (PC) of solid-state laser radiation via Brillouin Enhanced Four-Wave Mixing (BEFWM) has been shown experimentally. Correction of various types of optical aberration introduced into incoming signal has been observed. PC-fidelity has been estimated to be equal to 0.62. Principle of operation of a multifunctional telescope system using BEFWM effect for correction for priary mirror aberration is briefly described.

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We present a technique of photorefractiveffects for white-light incoherent-to-coherent conversion and oneway image transmission through a thick turbulent medium. A high resolution photorefractive incoherent-tocoherent optical converter was realized even for white light transmission by applying the same technique as we used in incoherent laser beam transmission. Analogical reconstructed laser images with high-fidelity were obtained, correcting the image blurring due to the thick turbulent medium.

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