• Korean Journal of Optics and Photonics
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• v.13 no.5
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• pp.373-376
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• 2002

An asymmetrical directional coupler with two nonidentical fibers has, for the first time, been proposed and analyzed for an EDFA gain flattening filter (GFF). The characteristics of the transmission spectra of the GFFs have been theoretically investigated for the core spacings, the coupling lengths and the fiber parameters of the asymmetrical directional coupler. The analytical results show that an EDFA gain spectrum with flatness of ~7 ㏈ can be flattened to within $\pm$0.75 ㏈ over a bandwidth of 30 nm by using the asymmetrical directional coupler-based GFF.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.8A
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• pp.626-632
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• 2003

In this paper, forward-wave -3㏈ directional coupler with finite-thickness conductor and asymmetrical coupled lines are designed and experimentally verified using mode-matching based design methodology. Most of studies published in the literatures about the coupled lines are mainly concentrated on the adjustment of coupling amount by changing various geometric configurations. The analysis results in this paper show that thicker metalization requires reduced coupler length in the forward-wave directional coupler composed of asymmetrical coupled lines. Several forward-wave directional -3 ㏈ couplers with finite metalization thickness composed of asymmetrical coupled microstrip lines have been designed in the 5 ㎓ based on proposed design method. The measured data show -4.05㏈∼-4.09㏈ coupling at center frequency which is very closed to design value. The tight coupling has been implemented with accurate design methodology which take mentalization thickness into account.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.9
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• pp.1949-1956
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• 1997

The mode parameters of asymmetrical coupled microstrip lines on composite substrates are derived by using closed form expression. A 10 dB directional couplers, where the center frquency is 1.8 GHZ, are fabricated on a single-layer substrate and on compsite substrates respectively. It is shown that coupler on a single-layer substrate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.1
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• pp.81-88
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• 1997

Wavelength tunable, narrowbandwidth wvelength filters in compound semiconductor have been modeled, fabricated, and characterized. In order to obtain a narrow bandpass characteristics at 1.55.$\mu$m, a highly asymmertrical directional coupler structure composed of a strongly guided ridge waveguide and a weakly guided strip-loaded waveguide was used. The optimized filter structure modeling has been obtained by using the spectral index method, effective index method, and the coupled mode theory. Operation at a center wavelength a 1.537.mu.m with a bandwidth of 1.8nm and transfer efficiency of 50-70% is experimentally achieved. For the purpose of center wavelength tuning, the carrier injection in p-n diode structure has been theoretically investigated. It has been found that the tuning range of nanometer can be easily obtained by moderate amount carrier injection. We also found that the bandwidth becomes broad as the center wavelength tuning increases.