Reduction of laser diode intensity noise in optical beam defection systems

Delft University of Technology

Reduction of laser diode intensity noise in optical beam defection systems

Bijster, Roy; Sadeghian Marnani, Hamed; van Keulen, Fred

Publication date 2016

Document Version Final published version

Citation (APA)

Bijster, R., Sadeghian Marnani, H., & van Keulen, F. (2016). Reduction of laser diode intensity noise in optical beam defection systems. Poster session presented at 13th International Workshop on

Nanomechanical Sensing, Delft, Netherlands. Important note

To cite this publication, please use the final published version (if applicable). Please check the document version above.

Copyright

Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons. Takedown policy

Please contact us and provide details if you believe this document breaches copyrights. We will remove access to the work immediately and investigate your claim.

This work is downloaded from Delft University of Technology.

Reduction of laser diode intensity noise

in optical beam deflection systems

Roy Bijster

, Hamed Sadeghian

, Fred van Keulen

1Structural Optimization and Mechanics, Delft University of Technology

2Nano-Opto-Mechanical Instruments (NOMI) group, TNO

laser diode

Single mode fiber

photo

diode 26 dB spectrumanalyzer

50 Ω _acquisitiondata low pass filter + current controller signal generator

Download the poster and abstract to your

phone! sample position sensitive detector laser diode Intensity fluctuations introduce noise here.

A mplitude ( A.U .) 3 1 -1 0 1 Time (A.U.)

The higher harmonics also excite the laser diode!

Frequency (GHz) Noise Power (dBm) 0 Generator Measurement 4 3 2 1 0 -100 Modulation Frequency (MHz) 0 500 1000 Intensity Noise (mW) 0 1 2 3 Unfiltered Low-pass filter

Modulation increases the noise up to 500x ?!

Problem

Is high frequency injection the solution?

TEM₀₀ TEM₁₁ TEM₂₂

0 0.5 1

Normalized center shift (-) 0 1 Nor maliz ed PSD sig nal (-)

Method

Results

The culprit

Modehopping

A change in mode shape causes a change in PSD output, w/o moving

the laser! We need a single mode. Noise spectrum

Average power

100-1000 MHz

DC signal

A low-pass filter after the signal generator helps a bit.

A mplitude ( A.U .) 3 1 -1 0 1 Time (A.U.)

Conclusion

Is high frequency injection the solution?

Not in this application, because

1) higher harmonics from the signal generator also excite the laser diode;

2) mode hopping and the superposition of transverse modes introduce additional noise at the position sensitive detector.

This implies the use of a single mode fiber, but this interferes with the action of the

high frequency injection.

Injection of a high frequency signal, excites the laser in a

multimode state. Mode partition then reduces the total noise.

6 μW with no modulation

TEM₃₃