The fastest multichannel fibre optic digital correlator

This research work was supported by a Paul Instrument Fund grant (September 1993 - October 1995). The aim was to implement an optoelectronic configuration [1-3,6,8-10] of a clipped correlator, based on an original idea of prof. D. A. Jackson and J. D. C. Jones [0]. Ryan Harding has studied for a PhD on this project and added his excellent computing expertise and patience in fusing fibre.

The aim was to expand the number of channels and the speed of a previous version, 8 channel, 10 ns correlator built in Kent. The research was very challenging in terms of high speed Electronics. We designed and build very fast photodetector modules on PTFE board (amplifiers up to 45 dB, 4.5 GHz), 85 ps step recovery diode shapers, high speed powerful distributors (based on GaAs powerful transistors, logical circuits using GaAs ICs (125 ps) and switchable delay line blocks (0.2 ns). The PTFE boards where produced either outside using state of the art gold plating and metallic through holes or in house using a milling machine for microwave circuits, specially purchased to assist this research. As the majority of electronic circuits in the correlator used surface mount components, the work was very demanding in terms of miniaturisation, adjustment and maintenance.

At the end of the project, an original hybrid configuration of the fastest multichannel digital correlator with 0.25 ns lag time and 640 channels [1] was completed. The remarkable high speed was achieved with a relatively low cost by an in house design and implementation of very fast electronic AND gates based on double-gate GaAs transistors [6]. We have also shown [2] how the Fibre Optic Digital Correlator configuration (potentially very fast but rigid in terms of channel bin) could be used in tandem with an electronic clipped correlator (versatile in terms of channel bin but potentially slower) for extended versatility in terms of delays and number of channels for time bins over 10 ns.

We have practically demonstrated the retrieval of signal from noise up to 2 GHz (fastest reported so far in a multichannel configuration and highly appreciated by the participants at the OSA Conference "Photon correlation and scattering '96" [9].

A comparative analysis of the fiber fixed delay correlator and the clipped electronic correlator is presented in [5] and we have shown that this configuration does not necessarily need a derandomiser to recover a periodic signal burried in noise [1].

We have experimentally demonstrated that a self-pulsating laser with optoelectronic feedback can be used [4] for the adjustment of the delays.

We have devised two altered versions of the correlator which could act as a multichannel time of flight analyser for time-resolved imaging and investigation of human tissue, as babies heads and breast tissue (unpublished results).

Connecting the fibre array multimode coupler to the derandomiser

Connecting the fibre array multimode coupler to the derandomiser

The photo shows the 16 ST terminated multimode fibres connected to the APDs of the 16 real time channels

The photo shows the 16 ST terminated multimode fibres connected to the APDs of the 16 real time channels

0. D. A. Jackson and J.D.C.Jones, "Proposed topologies for a fiber-optic-based 1GHz clipped digital correlator, Opt Lett, 11, (1991), pp. 824-826

Journals

  1. A. Gh.Podoleanu, R. K. Harding, D. A. Jackson, "Practical implementation of a high-speed multichannel correlator with fiber-optic delays", Appl. Opt. (1997), Vol. 36, No.30, pp.7523-7530.
  2. A. Gh.Podoleanu, D. A. Jackson, "Comparative Studies of an Electronic Clipped Correlator and an Optical Fiber Fixed Delays Correlator", Opt. Engineering, 35, (6), pp.1565-1572, (1996).
  3. A. Gh.Podoleanu, R. K. Harding, D. A. Jackson, "Low Cost High-speed Multichannel Fiber-Optic Correlator", Opt. Lett., vol.20, pp. 112-114, (1995).
  4. A. Gh.Podoleanu, R. K. Harding, D. A. Jackson, "Delay Measurements Using a Self-pulsating Laser with Optoelectronic Feedaback2, Meas.Sci.Technol., 6, pp. 371-375, (1995).
  5. A. Gh. Podoleanu, D. A. Jackson, "Simple Very Low Cost High Speed 2 Input AND Gate", Rev. Sci. Instrum.66 (9), pp. 4698-4702, (1995)
  6. A. Gh. Podoleanu, D. A. Jackson, "Combined Electronic Clipped Correlator and Fibre-Optic Correlator", Electron Lett., vol.31, No.17, pp. 1492-1494, (1995).
  7. S. S. G. Pasca, A. Gh. Podoleanu L. I. Plesea, "One Counter Photon Arrival Timer", Measurement Science and Technology, vol.4, pp. 1404-1409, (1993).
  8. A.Gh.Podoleanu R. K. Harding D.A.Jackson 40-channel 1-nanosecond Digital Fiber Optic Correlator Intern. Conf. on Applic. Of Photon Technology (ICAPT'96), G.A.Lambropoulos ed., Montreal Canada, 29 July-1 Aug. 1996.
  9. A.Gh.Podoleanu, D.A.Jackson, "160-Channel 0.5 nanosecond Hybrid Digital Correlator Based Upon Fiber Optic Delay Lines", Technical Digest of Photon Correl. & Scatter., OSA Confer., Aug. 21-24, Capri, pp. FB3-3/111-113, 1996.
  10. A.Gh.Podoleanu, R.K.Harding and D.A.Jackson Very Fast Optoelectronic Correlator 6th Joint EPS-APS Intern. Conf. on Physics Computing 94, R. Gruber, M. Tomassini eds., Lugano, Aug. 22-26, pp. 531-534, (1994).

 

Staff Involved