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Published on: September 8, 2017
Effective reflectivity of hyperbolic microlenses.
Applied Optics
|September 8, 2010
Summary
Hyperbolic microlenses reflect significant optical power back into semiconductor lasers, causing frequency shifts. A dielectric coating reduces this reflectivity and frequency shift by over tenfold.
Area of Science:
- Optics and Photonics
- Semiconductor Lasers
- Optical Fiber Coupling
Background:
- Hyperbolic microlenses offer superior power coupling into single-mode optical fibers compared to other designs.
- Reflectivity from optical components can negatively impact semiconductor laser stability and performance.
- Understanding and mitigating back-reflection is crucial for laser applications.
Purpose of the Study:
- To quantify the effective reflectivity of a hyperbolic microlens at peak coupling.
- To investigate the impact of this reflectivity on semiconductor laser frequency stability.
- To evaluate the effectiveness of a dielectric coating in reducing microlens reflectivity and its effects.
Main Methods:
- Characterization of hyperbolic microlens effective reflectivity using optical power measurements.
- Analysis of lasing frequency shifts in a distributed Bragg reflector (DBR) laser under microlens illumination.
- Measurement of laser frequency stability before and after applying a two-layer dielectric coating.
Main Results:
- The hyperbolic microlens exhibited a back-reflection of approximately -40 dB at peak coupling.
- This reflectivity induced a 3.7 GHz peak-to-peak shift in the laser's lasing frequency.
- The two-layer dielectric coating reduced the frequency shift by over an order of magnitude, corresponding to ~ -60 dB reflectivity.
Conclusions:
- Hyperbolic microlenses, despite their coupling efficiency, can introduce significant back-reflection into semiconductor lasers.
- Dielectric coatings are effective in mitigating the detrimental effects of microlens reflectivity on laser frequency stability.
- The findings provide valuable insights for the design of optical systems employing microlenses with semiconductor lasers.
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