Measurement of visual index in tunnels using automatic gain controlled laser diodes and a homodyne detection scheme
✍ Scribed by Jongtaek Park; Donghyun Seo; Bonjeong Koo; Youngil Park
- Publisher
- Elsevier Science
- Year
- 2004
- Tongue
- English
- Weight
- 290 KB
- Volume
- 233
- Category
- Article
- ISSN
- 0030-4018
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✦ Synopsis
A visual index measurement scheme that can be applied to a tunnel environment is proposed. To check the ventilation condition, a relative visibility is measured using a laser diode (LD) with wavelength of 880 nm. The LD is modulated with a 10 kHz sinusoidal signal to be used for a homodyne detection, which helps avoiding environmental noises. Both an automatic power control (APC) and an automatic gain control (AGC) circuits are adopted for stabilizing the optical source. Measurements are done in bidirectional ways and then averaged. Final results show that the proposed scheme works well even in harsh conditions.