In this paper we describe both the 1310 and 1550 nm VCSEL development work at Honeywell using both InP and GaAs substrates, and using both MOCVD and MBE. We describe the material systems, the designs, the growth techniques, and the promising results obtained and compare them to the needs of the communications industry. InGaAsN quantum well based VCSELs have been demonstrated to 1338 nm lasing at temperatures up to 90 C. Continuous wave InP based 1550 nm VCSELs have also been demonstrated.
Recently VCSEL technology has been emerging outside data communications. VCSEL's unique characteristics of low power consumption, high efficiency, circular beam spot, and low manufacturing cost make it a good candidate to replace LEDs or edge-emitting diode lasers in optical sensors. Optical sensors based on VCSEL technology in industrial applications have been studied in Honeywell. Traditional interruption type and Moire fringes type VCSEL sensors have demonstrated high resolution, simple design and lower cost in both transmission and reflection operation modes. Convergent and retroreflective VCSEL sensors were also studied. A safety circuit was added to control the VCSEL output power within the Class I laser limit. Other potential VCSEL sensors such as a VCSEL light curtain device, dual-beam linear encoder, dynamic Moire optical torque sensor would also be discussed in the presentation.
A transient photo-electric current was investigated in photorefractive crystals of Sr1-xBaxNb2O6 (SBN) and Bi12TiO20 (BTO) as a response to a step-like modulation of the light grating phase. Different dependencies of the photocurrent relaxation time on the grating period were observed for SBN and BTO crystals. It is explained theoretically taking into consideration kinetics of the photoexcitation of carriers, charge transfer and trapping. A number of important parameters characterizing the crystals are estimated.
We analyze recording of gratings by orthogonally polarized waves-modes of birefringent crystal which are coupled by nonlinear interaction, photogalvanic current in photorefractive crystals, or by anisotropy of two-photon absorption in semiconductors. Different schemes of polarization grating recording (four-beam, two-beam, single-beam) are discussed.
Holographic gratings recorded in BaTiO3 with five different wavelengths have been studied. Using the knowledge of grating formation developed in this way, we have visualized infrared images in BaTiO3 with two different two-wave mixing configurations.
Multimode fibers destroy the shape, phase, and polarization of laser beams passing through them. We show how to correct for those problems on line using devices which combine a photorefractive double phase conjugate mirror (DPCM) and a local reference beam holographic wave coupling (LRHWC).
The problems of image transmission via distorting media have been discussed in literature and different methods have been suggested to solve these problems which include phase conjugation by four-wave mixing. Image by phase conjugation requires it to pass twice through the distortion. It is a major disadvantage in the practical field where the picture information is to be transmitted from one place to the other. In this paper we present our results of image transmission in transmission and reflection geometries. We have demonstrated the abilities of performing optical processing using two-wave and four-waving mixing of one- way phase conjugation with ferroelectric crystal BaTiO3.
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