Showing papers on "Extinction ratio published in 1977"

LiNbO 3 TE-TM mode converter using collinear acoustooptic interaction

Abstract: A highly efficient TE-TM mode conversion device utilizing the acoustooptic effect has been demonstrated. Mode conversion has been made by an acoustic surface wave propagating collinearly with an optical guided wave. The maximum mode conversion, although the fraction was restricted to 70 percent, has been obtained with an acoustic power of only 55 mW (electrical input 0.55 W). Effective interaction length of the present device is limited to 5 mm due to optical and/or acoustic inhomogeneity of the waveguides. For selecting TE and TM waves, a polarizer is constructed monolithically and the extinction ratio is improved by up to 21 dB. Performance characteristics of a tunable optical filter of this type of the mode conversion are also discussed.

Metal-clad waveguide as cutoff polarizer for integrated optics

Abstract: Propagation constants, attenuation, and field distributions of optical modes in dielectric waveguides clad by a thin metal layer are calculated. It is shown that by reducing the metal thickness, the attenuation of optical modes reduces in such a way that short metal-clad devices become possible even in thin guides with thicknesses near cutoff. As an application, a cutoff polarizer in symmetrical waveguides has been built by depositing a small thin silver stripe on the surface of the guide. By this structure the TE 0 mode is coupled out into the substrate, whereas the TM 0 mode is transmitted with very low losses. The best extinction ratio measured is 18 dB. The polarizer can be used as a TE 0 mode coupler into symmetrical waveguides as well.

Efficient intensity modulation in a Ti-diffused LiNbO3 branched optical waveguide device

Abstract: By careful design of the Y-junctions and bends of a Ti-diffused LiNbO3 branched waveguide modulator, an efficient intensity modulator has been realised. The halfwave voltage is 2.0 V, the extinction ratio is ?18 dB and the loss between the input and output channel waveguides is approximately 5 dB at 0.633 ?m.

An 800 Mbit/s optical transmission experiment using a single-mode fiber

Abstract: It has been confirmed by a preliminary transmission experiment that a repeater spacing at 800 Mbits/s can be lengthened up to 7.3 km, by using a combination of a low-loss single-mode fiber and a well designed AlGaAs laser. The laser is modulated by a signal current superimposed on a dc bias current above the threshold. This modulation scheme avoids the spectrum broadening of the laser at the cost of extinction ratio degradation. A discrepancy of about 13 dB exists between the measured and the calculated error-rate performance curves. The major part of the discrepancy, 10 dB, is due to the extinction ratio degradation.

GaAlAs Schottky directional‐coupler switch

Abstract: Electro‐optic metal‐gap directional‐coupler switches have been fabricated in GaAlAs waveguide structures. A very thin GaAs cap facilitates the electroplating of Schottky barriers without significantly increasing the optical attenuation at wavelengths near 8600 A, making this type of device suitable for integration with a GaAs laser source on a common chip. The performance of the switch was investigated at 1.06 m. A 17‐dB extinction ratio in the coupled channel was measured at a reverse‐bias voltage of 25 V.

Reduced depth polarizer for integrated optics

Abstract: Taking advantage of the different cut-off thickness of the two fundamental modes in an optical waveguide, a polarizing structure has been realized. It consists of a narrow stripe (∼100 μm) of reduced diffusion depth in an ion-exchanged waveguide. The TE0-mode passes the polarizer with negligible losses, whereas the TM0-mode is forced to couple out into the substrate. The extinction ratio is better than −16 dB.

One Gigabit Wideband Modulator

Abstract: An exploratory development of a 1 Gbps single-pass single-unit (unmultiplexed) modulator for use with a mode-locked and frequency-doubled neodymium YAG laser in a space laser communication system was conducted for the Air Force Avionics Laboratory. The modulator was to operate at data rates up to 1 Gbps with a 0.53 micrometer laser input. The performance goals were (1) a static extinction ratio of 100 to 1 or greater, (2) a worst case dynamic extinction ratio of 30 to 1 or greater with a 1 Gbps pseudorandom code input, (3) 100% depth of modulation, and (4) at least 80% transmission of the beam input power statically. This effort consisted of a 1 Gbps 0.53 micrometer modulator and driver in breadboard form used as a laboratory tool to demonstrate the feasibility of this modulator design concept. The modulator development utilized lithium tantalate crystals in four different configurations. The modulator drivers were designed with both thin film hybrid and discrete component input stages with the dual output stage using only discrete components. Various modulator and modulator driver combinations were used in the dynamic performance evaluations. The performance of the best modulator and modulator driver, met most of the design goals. The modulator driver had 20 volts ±1 volt outputs with timing inaccuracies of ≤ ±175 ps including PN generator timing inaccuracies of ≤ ±70 ps. The driver had rise times between 400 ps and 500 ps. The modulator had two 10mm long lithium tantalate crystals tapered in the c-axis in order to reduce the switching voltage by 20% which resulted in a dc half-wave switching voltage of 19.8 volts at 0.53 pm wavelength. This modulator had a static extinc-tion ratio of 90:1 and a worst case dynamic extinction ratio of ≥ 22.4:1 with a 1 Gbps pseudorandom code. The depth of modulation was 100% since the driver applied full half-wave switching voltage to the modulator. The modulator (crystals only - single pass) transmitted 81.5% of the beam input power statically.