| EPSRC Reference: |
GR/J17753/01 |
| Title: |
OPTICAL PREFILTERING IN SUBCARRIER MULTIPLEXED OPTICAL SYSTEMS |
| Principal Investigator: |
Greenhalgh, Dr P |
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| Department: |
Sch of Engineering & Digital Arts |
| Organisation: |
University of Kent |
| Scheme: |
Standard Research (Pre-FEC) |
| Starts: |
01 September 1993 |
Ends: |
31 August 1996 |
Value (£): |
162,443
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Summary on Grant Application Form |
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The primary objective of this research programme is to evaluate optical prefiltering as a practical technique for real optical subcarrier multiplexed (SCM) systems. A secondary objective is to identify specific areas of communication where the benefits of prefiltering are best suited.Progress:Our efforts to date have followed our original programme of work closely. This has allowed us to reach some firm conclusions about the application of optical prefiltering to optical communication systems. The research started with a thorough analysis of the optimum configuration for both the optical transmitter and receiver. Optical prefiltering as a scheme works best when as much power as possible is present in the modulation sidebands. This can be achieved using an externally modulated source with the Mach-Zender external modulator biassed at a transmission minima rather than the half power point which is usual for conventional applications of external modulation. This produces a modulated optical source which is analogous to double sideband suppressed carrier electrical systems with no power remaining at the original optical carrier frequency. This increases the power in the required optical sideband by 3dB. It also minimises the amount of second harmonic distortion introduced into the system due to the non-linear transfer function of the modulator. These theoretical predictions were confirmed experimentally. [1] The analysis also allowed a direct comparison of detection sensitivity with an optimised conventional SCM receiver. The results of this work suggest that prefiltering has an inherent signal-to-noise ratio disadvantage compared to the best electronic SCM receivers unless more involved sub-subcarrier modulation formats are considered. Then optical prefiltering can compete favourably with conventional receivers. [2]In conclusion we believe that optical prefiltering can provide some real advantages over other techniques in situations where there are relatively few SCM channels with very wide channel spacing. This circumstance will allow the baseband detection benefits of optical prefiltering to be most evident. Also optical prefiltering is relatively insensitive to fibre dispersion. Under direct modulation even small amounts of fibre dispersion can introduce intermodulation products between subcarriers if the modulated optical signal is conventionally demultiplexed. This is not the case with prefiltered systems. Work is continuing on investigating possible applications of prefiltering considering the benefits identified above. Also novel methods of generating optical subcarriers separated from the original optical carrier by more than 10GHz are being developed. [1] P.A. Greenhalgh, A..P Foord & P.A. Davies. 'Signal Distortion in Optically Prefiltered Subcarrier Systems.' Optical Networks and Their Enabling Technologies, July 12 1994, PP 76 - 77, Lake Tahoe, Nevada, USA. [2] A.P. Foord, P. A. Davies & P.A. Greenhalgh. 'Optical Demultiplexing for Subcarrier Multiplexed Systems.' Submitted to joint special issue of MTT/JLT.
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Key Findings |
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This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
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Potential use in non-academic contexts |
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This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
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Impacts |
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| Description |
This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk |
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Sectors submitted by the Researcher |
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This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
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| Project URL: |
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| Further Information: |
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| Organisation Website: |
http://www.kent.ac.uk |