• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.4
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• pp.336-342
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• 2003

In this paper, a new differential detector is introduced, in which a solar cell is used to reduce the low frequency interference from environmental optical noise. The solar cell also supplies electrical power to the detector circuit using the optical noise power. The DC voltage from the solar cell is used as a power supply to the detector, and the AC voltage is used to reduce the optical noise in a photodiode with the differential detection method. The signal to noise ratio was improved by about 20 dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.8
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• pp.891-897
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• 2003

In this paper, a circular orthogonal polarizer is newly fabricated and used in a differential detector to reduce the optical noise in a wireless optical interconnection. The orthogonal polarizer is composed of two semicircular polarizers whose transmission axes are orthogonal each other, The orthogonal polarizer is driven by a motor and matched to the signal polarization in order to reduce the optical noise interference. The noise power was reduced by about 20 dB using a differential detector with the orthogonal polarizer.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.3
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• pp.365-371
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• 2000

In this paper, we introduce a noise reduction method using polarizers in a wireless optical interconnections. If we use polarizers in a differential detector, the noise reduction capability is improved. In a case that two optical signal beams of similar wavelength are overlapped in space and crosstalk is a serious problems, we can detect each channel separately without crosstalk using two orthogonal polarizers. This method is very simple and easy to use.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.2
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• pp.228-233
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• 2000

In this paper, we introduce a differential detection method using approximate average noise detection, which improves the noise reduction efficiency in a wireless optical interconnection. Approximate average noise detection reduces the output voltage fluctuation that may result from the instantaneous change of the coupling coefficients with the movement of some objects or human beings. This method is very useful for noise reduction in an environment with optical noise whose spatial distribution varies instantaneously.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.5 s.96
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• pp.494-500
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• 2005

In this paper, optical noise is reduced by a differential detector with an optical fiber coupler in an optical wireless system. An $1\times2$ optical fiber coupler divides the received optical signal by 2 equally, and connects them to the two photodiodes in a differential detector. The output voltage variation due to the abrupt change of optical noise distribution in space disappears because the two photodiodes effectively detect the optical signal at the same point. The signal to noise ratio in a differential detector with a fiber coupler was 8 dB higher than in a single photodiode with an optical filter.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.4 s.95
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• pp.410-417
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• 2005

In this paper, optical noise is reduced by a differential detector with a plastic optical fiber bundle in a wireless optical interconnection. A plastic optical fiber bundle divides the received optical signal equally and connects it to two photodiodes. In this configuration two photodiodes effectively detect the optical signal at one point, and the output voltage variation due to the abrupt change of optical noise distribution in space disappears. The signal to noise ratio in a differential detector with a fiber bundle was improved to be $10\;\cal{dB}$ higher than in a single photodiode with an optical filter.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.6
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• pp.599-604
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• 2002

In this paper, a digital potentiometer is used as a load resistor of a wireless optical differential detector with a polarizer, to improve the noise reduction capability. In this structure, the noise voltages of the two photodiodes are made equal by controlling a digital potentiometer and the optical noise is cancelled out. With a digital potentiometer, the signal to noise ratio is enhanced by about 23 dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.1
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• pp.96-102
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• 2004

In this paper, optical noise is reduced by a differential detector, which is composed of a beam splitter and two photodiodes whose spectral responses are different each other. In this configuration, the automatic gain control circuit is not required for noise cancellation because the noise intensities at the two photodiodes are kept equal by a beam splitter. The signal to noise ratio in a differential detector with a beam splitter was improved to be 14 ㏈ higher than in a single photodiode with optical filtering.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.5
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• pp.560-567
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• 2011

In this paper, we reduced the optical noise interference using polarizers in a visible light communication system. In a transmitter, two light-emitting diodes(LEDs) are modulated synchronously by the original and the reversed signals of the transmitted data, and the two LED lights are radiated through orthogonal polarizers. In a receiver, two optical signals are detected through orthogonal polarizers and differentially amplified to remove the optical noise. In an environment that noise light from a fluorescent lamp is much stronger than the signal, the receiver with orthogonal polarizers removed the 120 Hz noise, and synchronous light transmission of the original and the reversed signals using two LEDs reduced the illumination flickering to about one-eighth that using one LED.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.1
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• pp.54-62
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• 1999

In this paper, we investigated the signal-to-noise ratio improvement in a differential detector, which is a function of the optical noise coupling ratio and the differential gain ratio. A differential detector consists of two photodiodes and a differential amplifier. The differential detector reduced the noise component and improved the signal-to-noise ratio by about 20 dB when the differential gain ratio equals to the optical noise coupling ratio. The differential detector is very effective in removing the environmental optical noise or interference from an adjacent optical channel. This method is also effective when the noise wavelength is similar to the signal.