{"69360":{"#nid":"69360","#data":{"type":"news","title":"Researchers Take Step Toward Faster Communication","body":[{"value":"\u003Cp\u003EBy using electromagnetic waves instead of electrical current for switching, researchers have operated an optical modulator at terahertz frequencies - an accomplishment that could one day facilitate data transmission rates in the trillions of bits per second.\u003C\/p\u003E\n\u003Cp\u003EThe work represents a key step toward a new generation of optical communication systems that would be as much as 100 times faster than current technology, bringing closer such applications as real-time telemedicine and movies on demand.  While operating their terahertz modulator, the research team observed an effect that is well known in atomic physics - but until now hadn\u0027t been seen in the semiconductor materials that make up optical modulators.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022This is just one piece, but potentially a very important piece, of a very high bit-rate optical communication system for telecommunications and other applications,\u0022 said David Citrin, an associate professor in the School of Electrical and Computer Engineering at the Georgia Institute of Technology.  \u0022The point of the experiment was to show that we can operate a modulator at terahertz frequencies, though we are still a long way from a practical device.\u0022\n\u003C\/p\u003E\n\u003Cp\u003ESupported by the National Science Foundation, the research was reported in the October 28, 2005 issue of the journal \u003Cem\u003EScience\u003C\/em\u003E.\n\u003C\/p\u003E\n\u003Cp\u003EExisting telecommunication systems depend on modulators to encode data onto beams of light that then can be carried long distances by optical fibers.  Modulators work by rapidly changing their reflectivity, which varies the intensity of light beams passing through them.  These variations correspond to the ones and zeroes that are the language of digital communication.  \n\u003C\/p\u003E\n\u003Cp\u003EModulators are also used as switches to reroute data streams by alternately reflecting light or allowing it to pass.\n\u003C\/p\u003E\n\u003Cp\u003EBut most current modulators have a drawback - they cannot operate faster than the electronic circuitry used to control them.  To boost data speeds, researchers have been seeking alternative control technologies.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022Conventional optical modulators use a voltage change to alter the properties of a material which changes the reflectivity,\u0022 Citrin explained.  \u0022Electrically switched systems are just too slow to go much beyond where we are now.  But by using very high frequency electromagnetic energy to modulate the signal, the hope is that we can generate signals that have much higher data rates than what we can achieve with today\u0027s electrical circuits.\u0022\n\u003C\/p\u003E\n\u003Cp\u003ETo gain those higher rates, Citrin and colleagues at the University of California, Santa Barbara and the NASA Ames Research Center used very high-frequency waves from a free-electron laser to control the modulator.  These electromagnetic waves consist of an oscillating electric field and have the advantage of being able to move through free space without the need for circuitry.   \n\u003C\/p\u003E\n\u003Cp\u003E\u0022In principal, you can modulate light much more quickly than you can switch electrical current,\u0022 said Citrin, a theoretician who has been working as part of the team for more than a decade.  \u0022Instead of connecting the modulator to an electrical circuit, we placed it into the beam of the free-electron laser, a unique research facility at the University of California Santa Barbara.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EBecause terahertz oscillation is difficult to measure directly with existing technology, the researchers used indirect means to verify the modulation speed.\n\u003C\/p\u003E\n\u003Cp\u003EBefore this approach can lead to faster communication systems, the modulation must be optimized - and the remainder of the system advanced to terahertz speeds.  \n\u003C\/p\u003E\n\u003Cp\u003EFor example, researchers will have to develop inexpensive and convenient sources of the electromagnetic energy they use for switching.  Another challenge will be to optimize the bit depth - the difference in light intensity that represents ones and zeros.  And to minimize energy requirements, they must reduce the amount of power required to operate such a system.  Finally, the other components of a communications system will also have to advance to terahertz operation\n\u003C\/p\u003E\n\u003Cp\u003EThe research team, which included S.G. Carter, V. Birkedal, C.S. Wang, L.A. Coldren, A. V. Maslov and Mark Sherwin in addition to Citrin - also wants to understand the science of the modulation system.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022There is a lot of interesting science going on into how the modulation works,\u0022 Citrin said.  \u0022We want to understand the issues that influence the ultimate limits of the modulation rate.  If we can really understand the physics, we should be able to understand the limits not only of the modulate rates, but also the modulation depth and what are the weakest fields we might be able to use.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EAs part of the \u0022signature\u0022 of terahertz operation, the researchers observed an effect known as the Autler-Townes Splitting.  The effect is well-known in atomic physics, but the \u003Cem\u003EScience\u003C\/em\u003E paper was the first report of it in the semiconductor quantum wells which are part of the modulator.\n\u003C\/p\u003E\n\u003Cp\u003EThe splitting occurs when the devices are driven to operate at high frequencies, and its signature is a \u0022double-peak\u0022 in the reflectivity of the quantum wells.  \n\u003C\/p\u003E\n\u003Cp\u003E\u0022This is an interesting physical effect that can change the optical properties of the medium from reflective to transparent,\u0022 Citrin explained.  \u0022That may have its own interest for many other applications as well.\u0022\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\nGeorgia Institute of Technology\u003Cbr \/\u003E\n75 Fifth Street, N.W., Suite 100\u003Cbr \/\u003E\nAtlanta, Georgia  30308  USA\u003C\/strong\u003E\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EMedia Relations Contact\u003C\/strong\u003E: John Toon (404-894-6986); E-mail: (\u003Ca href=\u0022mailto:john.toon@edi.gatech.edu\u0022\u003Ejohn.toon@edi.gatech.edu\u003C\/a\u003E)\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003ETechnical Contact\u003C\/strong\u003E: David Citrin (\u003Ca href=\u0022mailto:david.citrin@ece.gatech.edu\u0022\u003Edavid.citrin@ece.gatech.edu\u003C\/a\u003E)\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\n\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":[{"value":"Terahertz optical modulator could permit data rates in trillions of bits per second"}],"field_summary":[{"value":"By using electromagnetic waves instead of electrical current for switching, researchers have operated an optical modulator at terahertz frequencies - an accomplishment that could one day facilitate data transmission rates in the trillions of bits per second.","format":"limited_html"}],"field_summary_sentence":[{"value":"Researchers demonstrate terahertz modulation"}],"uid":"27303","created_gmt":"2005-12-24 01:00:00","changed_gmt":"2016-10-08 03:03:34","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2005-12-26T00:00:00-05:00","iso_date":"2005-12-26T00:00:00-05:00","tz":"America\/New_York"},"extras":[],"hg_media":{"69361":{"id":"69361","type":"image","title":"Free electron laser","body":null,"created":"1449177252","gmt_created":"2015-12-03 21:14:12","changed":"1475894606","gmt_changed":"2016-10-08 02:43:26"},"69362":{"id":"69362","type":"image","title":"Free electron laser","body":null,"created":"1449177252","gmt_created":"2015-12-03 21:14:12","changed":"1475894606","gmt_changed":"2016-10-08 02:43:26"}},"media_ids":["69361","69362"],"related_links":[{"url":"http:\/\/sbfel3.ucsb.edu\/","title":"University of California, Santa Barbara Free Electron Laser Facility"},{"url":"http:\/\/www.ece.gatech.edu\/faculty\/","title":"School of Electrical and Computer Engineering"},{"url":"http:\/\/www.ece.gatech.edu\/faculty\/fac_profiles\/bio.php?id=22","title":"David Citrin"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"135","name":"Research"}],"keywords":[{"id":"3748","name":"communication"},{"id":"7679","name":"Modulation"},{"id":"1143","name":"optical"},{"id":"7678","name":"Terahertz"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cstrong\u003EJohn Toon\u003C\/strong\u003E\u003Cbr \/\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\u003Ca href=\u0022http:\/\/www.gatech.edu\/contact\/index.html?id=jt7\u0022\u003EContact John Toon\u003C\/a\u003E\u003Cbr \/\u003E\u003Cstrong\u003E404-894-6986\u003C\/strong\u003E","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}