OSEM Sensor Development

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OSEM Sensor Development University of
Birmingham David Hoyland Senior Electronics
Design Engineer Astrophysics and Space Research
Group
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• Overview
• Currently Investigating two possible solutions
• - Opto-electronic (Shadow) Detectors
• - Review of evolution of BIPM design
• - Developing current BIPM design.
• - Sub-miniature Interferometer Approach
• - Development of NPL quadrature interferometer.
  
• - Feasibility of integration into OSEM envelope

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Opto-Electronic Detectors - BIPM Designs

• Scheme A (George Gillies circa 1980)
• LED Source.
• Opaque Object, either spherical or cylindrical
• Low sensitivity to rotation
• Some optical power obscured and scattered by the
  object.

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Opto-Electronic Detectors - BIPM Designs

• Scheme B, C (Developed from Scheme A by Clive
  Speake (B), Alain Picard(C))
• LED Source (B), Laser Diode Source (C).
• Multimode Fibre Feed (B), Monomode Fibre Feed
  (C).
• Lens 2 fixed to the moving object.
• Photodiode dimensions chosen to accommodate
  Laser beam profile

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Opto-Electronic Detectors - Development

• Development of the BIPM Scheme C is being
  undertaken at UoB to assess feasibility for LIGO
• We predicted a maximum sensitivity of 1?10-11
  mHz1/2 should be achievable.
• Sensitivity fundamentally constrained by
  photodiode characteristics or coupled laser
  power, and dynamic range.
• Further development to resolve the following
  issues
• Laser diode speckle (spatial stability), and
  beam format
• Optimum laser power
• Source pointing stability
• This will enable us to find the best optical
  configuration, as well as
• Identify the optimal source choice e.g. LED,
  SLD, VCSEL, Pig-tailed SLD etc.
• Define custom photodiode fabrication options.

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Sub miniature Interferometer Approach
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Design Approach

• Development of this Interferometer is being
  undertaken at UoB to assess feasibility for LIGO
• Outputs 1 and 2 from PBS2 provide two quadrature
  fringe signals.
• A DSP is utilised to count the fringes and fit
  ellipse parameters in real time.
• - Development is taking place in collaboration
  with colleagues at UCSD
• - 100KHz sampling limits max velocity of
  proof-mass to 15 mms-1.
• - Dynamic range limited only by numeric range of
  the processor.
• - Also able to track ellipse parameter changes
  over a pre-defined timescale.
• - A sensitivity of 5?10-13 mHz1/2 has been
  demonstrated which is effectively independent of
  dynamic range and laser power
• - Output position data is in digital domain
  (floating point?) IMPLICATIONS??
• Further design and testing should help to resolve
  the following issues
• - Source coherence length
• - Optimisation of optical design via Gaussian
  beam propagation analysis

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Interferometer Image
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Schedule / Plan
Development of the Opto-electronic
(non-interferometric) position sensor - Design
and testing July 2003 October 2003 Development
of the interferometric position sensor - Design
and testing October 2003 December
2003 Consider trade-offs between identified
viable methods, December 2003 - Cost /
Performance - Interface to LIGO system -
Manufacturability