Optical Frequency Comb Generator

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					              Ongoing development                                                                   Contact
The existing version of the OFCG is fully operational. Due                 If you are interested and would like further information
                                                                                                                                             Optical Frequency
to the high sensitivity of the OFCG to temperature and
vibration, suitable packaging is required. Currently the
                                                                           regarding any aspect of the Optical Frequency Comb
                                                                           Generator please contact us directly. The OFCG can be
                                                                                                                                              Comb Generator
packaging solution for OFCG is being designed to allow                     custom-designed to operate with different comb line
operation in less well-controlled environments. A first pre-               spacings, spans and tuning step-sizes. Please consult us     Technical information on optical and
prototype has been built and successfully tested. Stable                   with your requirements.                                       microwave properties of an Optical
operation over several hours has been achieved.
                                                                                                                                            Frequency Comb Generator
                                                                           Dr. Pengbo Shen, Dr. Salavat R. Magazov, Dr. Nathan J.       developed by the Photonics Group at
                                                                           Gomes, Prof. Phil A. Davies                                         the University of Kent
                                                                                                                                       An Optical Frequency Comb generator has been developed
                                                                           Dept. of Electronics
                                                                                                                                       in the Photonics Group of the University of Kent by
                                                                           University of Kent
                                                                                                                                       Pengbo Shen as part of the international ALMA radio
                                                                                                                                       astronomy project. A fully functional pre-prototype has
                                                                           Kent CT2 7NT
                                                                                                                                       been built and is operational in our laboratory. Currently it
                                                                           United Kingdom
                                                                                                                                       is undergoing packaging development and will be available
                                                                           ofcgee@kent.ac.uk                                           as a finished product in the very near future.

  First packaging solution for OFCG “optics box” – suitable for 19” rack
                                                                           More information can also be found in the following,
The second version is being developed now, which should                    selected publications:
result in a shorter warm up period and resolve some other
general packaging problems which have arisen. We are                       1. P. Shen, N.J. Gomes, P.A. Davies, W.P. Shillue, P.G.
ensuring that the OFCG will be easy to use and maintain,                      Huggard, B.N. Ellison, ‘Fiber ring based optical
and will provide easy access to user serviceable parts.                       frequency comb generator with comb line spacing
                                                                              tunability’, LEOS Summer Topical Meeting, Digest, San    Here we present the technical characteristics of the OFCG
                                                                              Diego CA, USA, July 2005, pp. 69-70                      – demonstrating its optical, terahertz and microwave
                                                                           2. P. Shen, N.J. Gomes, P.A. Davies, ‘Generation of 2 THz   properties.
                                                                              Span Optical Comb in a Tunable Fibre Ring Based
                                                                              Optical    Frequency     Comb      Generator’,   IEEE
                                                                              International Topical Meeting on Microwave Photonics,
                                                                              Proceedings, Victoria BC, Canada, October 2007, paper
                                                                              TH-1.2                                                                  Photonics Group
                                                                           3. P. Shen, N.J. Gomes, P.A. Davies, P.G. Huggard, B.N.
                                                                              Ellison, ‘Analysis and Demonstration of a Fast Tunable
                                                                              Fibre-Ring-Based Optical Frequency Comb Generator’,
                                                                              Journal of Lightwave Technology, vol. 25, no. 11,
                                                                              November 2007
                    OFCG operation                                                                                                                               Terahertz and microwave parameters
The reference laser light is injected into the ring where it is                                                                                                  It is possible to generate accurate and stable millimetre and
modulated by the electro-optic phase modulator.                                                                                                                  sub-millimetre wave signals at any frequency within the
Recirculation around the ring generates a wide comb span                                                                                                         comb span range, dependent on the availability of a
of frequencies separated by the modulator’s drive                                                                                                                suitable, high-frequency photodetector.
frequency. The EDFA overcomes insertion losses and
provides high-Q operation (but the ring does not oscillate).
The cavity mode spacing is currently tuned to 12.5 MHz,
allowing the generation of any frequency defined to this
step size. The cavity modes, defined by the fibre ring
effective length, must be stabilised to the reference laser
wavelength and the microwave reference source.
                                                                                                                                                                  90 GHz beatnote produced by the OFCG and its measured phase noise
                                                                                                    Optical comb with over 2 THz span for 10 dB power envelope

                                                                           The comb lines are concentrated within one CWDM                                                                                          DWDM applications
                                                                                                                                                                 The OFCG can be used to generate reference wavelengths
                                                                           The produced comb is flat over a wide range with good                                 in dense wavelength division multiplexing systems.
                                                                           power output.                                                                         Another possible application is the simultaneous
                                                                                                                                                                 distribution of a clock signal on multiple wavelengths. In
                                                                           The comb generator can be tuned to different RF and                                   our experiment, the comb was passed through a DWDM
                                                                           optical references. Also, rapid tuning of the RF reference (at                        filter and then detected by a PIN photodiode. Each DWDM
                                                                           0.5 GHz steps each second) while maintaining the locking                              channel contained 7-8 strong optical lines which generate
                                                                           conditions has been demonstrated. The comb maintains its                              clock pulses for each channel.
                                                                           profile apart from a slight increase in slope due to the
                                                                           reduction of the phase modulator efficiency at higher
Block diagram of the OFCG – PC: polarization controllers, TFF: thin film   frequency.

                                                                                                                                                                   Relative magnitude, (linear scale))
   filter, EDF: Erbium doped fibre, PD: photodiode, LNA: low-noise                                                                                                                                       Ch24
                               amplifier                                                                                                                                                                 Ch25
                                                                           Drive Frequency (GHz)

                  Optical parameters                                                                                                                                                                     Ch27
The presently generated comb contains 200 lines at 10 GHz                                                                                                                                                Ch29
spacing, providing a 2 THz span within a 10 dB bandwidth.                                          10
Over a 3 dB bandwidth the comb contains 1500 lines                                                                                                                                                       Ch32
(1.5 THz span).                                                                                                                                                                                          Ch33

                                                                                                    8                                                                                                    Ch34

                                                                                                                                                                                                                0     100       200        300       400       500
                                                                                                                                                                                                                                Time, ps
                                                                                                                                                                                                   12-channel pulse train produced by filtering of the OFCG output
                                                                                                   1553    1554     1555 1556 1557            1558     1559
                                                                                                                      Wavelength (nm)
                                                                                 Fast RF reference stepping from 6 GHz to 12.5 GHz in 0.5 GHz steps at
                                                                                                              1 sec intervals

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Description: Optical Frequency Comb Generator