This paper reports the radiation performance results of several new product types designed for high radiation environments. The products tested include radiation hardened highly birefringent (HiBi) passive products for polarised applications and radiation tolerant active erbium doped fiber products for amplifiers.
Radiation hardened, short beatlength HiBi fiber products have been developed for high accuracy polarisation maintaining (PM) gyros and sensors at both 1310nm and 1550nm operation in the space environment. The fibers have been tested up to 5kGy (500krad) – levels which could be expected in extreme, extra-terrestrial space environments. Results show a consistently low Radiation Induced Attenuation (RIA) of <7dB/km at 5kGy, giving a RIA value of 1.37×10-2 dB/km/krad at 1550nm for this product range.
Radiation tolerant EDF AstroGain™ fibers are intended for use in multichannel amplifiers in optical intersatellite communications. The structure of the fibers have been designed to deliver an accelerated recovery of radiation damage through photo-annealing using only the residual energy already available in an amplifier using a 980nm pumping regime. These products have been tested up to 200Gy (20krad) – levels which can be expected in Earth orbit environments over a 20-30 mission lifetime. Results show up to 100% recovery under continuous use for dose rates of 0.11rad/hr. It has also been demonstrated through analysis of the optical spectral output that this effect reverses the gain tilt, or spectral narrowing, induced by radiation damage through the C and L band. These combined fiber characteristics allow performance stability of the amplifier over the lifetime of the space mission.
We report on the rapid prototyping platform, developed at Fibercore, for producing spun multicore fiber (MCF) which maintains the high-specification and quality of a large-scale manufacturing process adding the versatility to fully customize fiber for specific applications. Such MCF has been produced by using an ultrasonic drill to accurately position the core holes in the cladding glass, achieving <0.4µm accuracy in fiber. Cross-talk between cores has been minimized by implementing high numerical aperture cores of 0.20, with levels less than -55dB over 400m. Additionally, the high level of germanium doping also allows fiber Bragg gratings (FBGs) to be written into each core without the need for hydrogen loading. Finally, in order to enable distinction between any potential twist and strain in the fiber from the bend under measurement, a permanent twist has been introduced in the fiber by spinning the preform whilst it is being drawn. The manufacturing cycle time for the fiber is 8 days, allowing rapid prototyping and repeat development cycles to be tested over a short period of time when creating new fiber designs.
The design of an optical fiber to give optimized sensing and lifetime performance for downhole fiber optic seismic sensors is presented. The SM1500SC(7/80)P is designed with an 80μm cladding diameter, pure silica core, high numerical aperture, high cut off wavelength and a polyimide coating to achieve outstanding performance when used in a coiled deployment state and operating in high temperature and hydrogen rich environments.
Fibercore have developed AstroGainTM fiber optimized for multichannel amplifiers used in optical satellite
communications and control. The fiber has been designed to take full advantage of the photo-annealing effect that results
from pumping in the 980nm region. The proprietary trivalent structure of the core matrix allows optimum recovery
following radiation damage to the fiber, whilst also providing a market leading Erbium Doped Fiber Amplifier (EDFA)
efficiency. Direct measurements have been taken of amplifier efficiency in a multichannel assembly, which show an
effective photo-annealing recovery of up to 100% of the radiation induced attenuation through excitation of point
Proc. SPIE. 5248, Semiconductor Optoelectronic Devices for Lightwave Communication
KEYWORDS: Switches, Coarse wavelength division multiplexing, Switching, Waveguides, Networks, Wavelength division multiplexing, Control systems, Telecommunications, Local area networks, Standards development
This paper describes the current status of Coarse Wavelength Division Multiplexing (CWDM), and then progresses to discuss how it may evolve in networking applications in the future. As WDM can enhance not only transmission but also networking systems, the paper reports a potentially low cost WDM based access node architecture, particularly suited for routing optical data packets on nanosecond timescales. The scheme is cascadable and involves the use of a simple semiconductor optical amplifier (SAO) based add-drop switch. Preliminary results concerning the operation of the add-drop switches under multi-wavelength operation are reported.
This paper demonstrates channel selection under embedded microprocessor control within an optical heterodyne receiver. The receiver is for use in a coherent multi-channel system demonstrator having ten channels occupying a total wavelength bandwidth of 0. 8 nm at 1 560nm. . The local oscillator laser in the receiver has to have a sufficiently large continuous wavelength tuning range achieved by electronic methods to ensure that all channels can be received and tuned rapidly. It is demonstrated that a twosegment DFB laser can used to achieve this. Use of computer control of the bias currents and temperature of the laser combined with the flexibility of the tuning method adopted has allowed an adaptive method of channel acquisition and lock to be built. Computer control of other features of the receiver simplifies design and allows relatively straightforward incorporation of infra-red remote control LCD display of date/time/channel information and allows laser ageing effects i. e. long-term drift of wavelength with constant operating conditions to be compensated for.
Laser phase noise manifests itself as a degradation in SNR or BER in coherent optical communication systems. Real systems, particularly those employing phase modulation, often require sub-megahertz linewidth sources to perform satisfactorily. Experimental laboratory systems offer greater flexibility in their realisation and in this paper a novel technique is described to reduce the effective linewidth of semiconductor lasers, which is appropriate to such laboratory experiments.