Fotoniske krystaller er metamaterialer, der udgøres af periodiske dielektriske eller metal-dielektriske (nano)strukturer som er designet til at påvirke elektromagnetiske bølgers (EM) udbredelse på den samme måde som det periodiske potential i et halvledende krystal påvirker elektronernes bevægelse ved at definere tilladte og forbudte elektriske energibånd.

Fraværet af tilladte udbredelsesenergibånd indeni strukturen for et interval af bølgelængder kaldes et fotonisk båndgab, som forårsager bemærkelsesværdige optiske fænomener, som bl.a. resulterer i; spontan udsendelse, generering af alle regnbuens farver ud fra infrarødt-lys, højreflekterende spejle som virker i alle retninger og lysleder med lavt tab, og materialer med negativt brydningsindeks.

Fotonisk krystal er grundlæggende set baseret på det fysiske fænomen diffraktion.

• Kvantemekanik
• Optik
• Nanoteknologi
• Kvanteø
• Opal

• Webarchive backup: Ingeniøren nr. -3/1999: Dansk gennembrud i fiberoptik Danske og engelske forskere har sammen bevist, at optisk fiber med huller i kan transportere lys over lange afstande.
• Vejviser: Photonic Crystal and Photonic Band Gap Links Arkiveret 13. oktober 2007 hos Wayback Machine
• Cnet, August 31, 2000, Why photonics? Citat: "...Demand for photonic equipment is skyrocketing. Internet traffic on the backbone networks has been doubling every three months and shows no sign of abating. Companies are laying fiber in just about every cross-country right-of-way they can find. First it was along the railways, and now it's the gas pipelines, sewers and just about any conduit you can think of... "
• November 3, 2000, Sandia LabNews: Cheesecloth-like photonics device bends light with little loss Arkiveret 25. februar 2004 hos Wayback Machine Citat: "...the cheesecloth-like structure can be considered essentially a wire for light...Because of the very small light loss, the technique offers the potential of ultimately replacing electronic chips with faster, cooler photonic chips...two-dimensional crystals are cheaper and far easier to build..."
• Number 646 #1, July 16, 2003, AIP: Photonic Crystal Shifts Energy Arkiveret 6. februar 2004 hos Wayback Machine Citat: "...Shawn Lin and his Sandia colleagues, in the course of their studies of photonic crystals, have seemed to challenge the venerable formulation, made by Max Planck a hundred years ago, of what kind of emission spectrum a body should have..."
• CERN Courier: Photonic crystal makes flat lens Arkiveret 13. april 2004 hos Wayback Machine Citat: "...The key to creating the flat lens lies with the recent advent of materials – photonic crystals – that effectively have a negative index of refraction...the principle could herald a revolution in optics..."
• BBC News: 3 January, 2001, Sea mouse promises bright future Arkiveret 3. februar 2008 hos Wayback Machine Citat: "...The sea mouse, or Aphrodita, has spines that normally appear deep red in colour. But when light falls on a spine perpendicular to its axis, stripes of different colours appear – strong blues and greens..."The simple structure responsible for this effect is a remarkable example of photonic engineering by a living organism."..."These structures may have application in photonic communications, where there is much interest in fabricating photonic crystal fibres with similar morphology."..."