Abstract-A noise reduction scheme for long haul fiber amplitude modulation (AM) systems is proposed and analyzed. Such systems suffer from intensity noise which results from interference between the (twice) Rayleigh scattered light and the directly transmitted beam. This interference converts the fundamental phase noise of the laser to intensity noise. We show that a strong phase modulation of the output of the laser beam causes large reduction of the detected signal noise in the vicinity of the detected signal components.

Improved stability against electrical dc bias drift has been demonstrated in LiNbO3 electro-optic modulators by replacing the commonly used SiO2 buffer layer with indium tin oxide (ITO), a transparent conductor. The long term drift of the modulators having an ITO buffer layer with a sheet resistivity of ∼20 Ω/⧠ is less than 0.3% in 8 h. The mechanism of the dc drift phenomenon is discussed using an electrical equivalent circuit model of the modulator.

The conversion of laser phase noise to intensity fluctuation noise in optical fibers due to mixing with Rayleigh scattered light is considered. A theory combining the laser quantum phase dynamics and the statistical scattering in the fiber leads to simple expressions for the spectral densities of the intensity fluctuations in a number of generic cases. These are compared with experiments involving distributed feedback semiconductor lasers and low-loss fibers with lengths up to 20 km.

It was experimentally observed that low-frequency intensity noise in 1.3 μm semiconductor lasers can be translated to high frequencies through beating with a high-frequency modulation signal, thus imposing a maximum achievable signal/noise ratio. An analysis of this effect using a formalism developed for treating intermodulation distortion yields good agreement with the experimental results.

High performance, compact planar lightwave circuit based triplexers have been built and tested. The triplexers utilize lasers, photodiodes and filters that have been adapted to enable passive optical assembly of the triplexer, 02005 Optical Society o f America OCIS codes: (130.3120) integrated optics devices (230.0250) optoelectronics ' IntroductionPassive optical networks (PONS) are beginning to be mass deployed in high speed Fiber to the Home (FTTH) access networks. These networks utilize bidirectionaI optical modules that allow downstream and upstream traffic to share a single fiber. In the case where voice, data, and video services are provided on the access network, the optical module on the subscriber side is a triplexer that has two downstream receivers and one upstream laser. The most widely used waveIength plan uses the band from 1550-1560 nm for downstream video, 1480-1500 nm for downstream data, and 1260-1360 nm for upstream data. A triplexer typically consists of a data photodiode and transimpedance amp, a video photodiode, a 13 10 nm band laser and monitor photodiode, and WDM filters to separate the various optical wavelengths. Proper operation of the triplexer requires a high level of optical isolation from the WDM filters as well as effective suppression of stray light. Because every subscriber has a triplexer as part of the Optical Network Termination (ONT) equipment, cost is also an extremely important parameter for triplexers.In this paper we describe a pIanar lightwave circuit (PLC) based triplexer that achieves high levels of performance fiom a compact design that is built entirely using passive optical assembly methods. Planar Lightwave Circuit Triplexer Design . .A PLC based optical triplexer can be viewed as being built from five distinct functional elements. The optical waveguide network provides optical connectivity between the other main elements. The remaining four elements are the Iaser, PDs (3 per triplexer), the WDM filters (two per triplexer), and the optical fiber. A challenge in designing a PLC based ttiplexer is the design of the interfaces between the optical waveguides and these other elements. In this section, we describe ow designs for the key elements and the interfaces. The optical waveguide network used in the triplexer is primarily based on silica waveguides formed on a silicon substrate [ 1 ,a]. The Filter yA Laser Data. PD MPD