FORTH-experiments Nikos Katsarakis, Tamara Gundogdu, Eirini Tsiapa Heraklion, July 2004

Issues addressed during the last months SRR studies: propagation in different orientations, single vs. double rings, square vs. non-square unit cell, SRRs with four cuts Improve the transmittance of 1D LH structures: Address the origin of losses 2-D structures 1-D SRR structures at ~6THz

SRR studies ax=5mm ay=3.63mm az =2.1-9.6mm l=3mm t=w=d=0.33mm

SRR study: a. Electric response at ω0 First experimental demonstration of the electric response of the SRRs [Appl. Phys. Lett. 84, 2943 (2004)] λ~ 20 u. c. ωm ω0

SRR study: b. single vs. double rings Note that for the single ring ωm is shifting a bit higher while ω0 is almost constant.

SRR study: c. square vs. non-square unit cell Note how ω0 is changing due to the cut-wire effect: as the cut-wire length increases ω0 goes to zero frequency.

SRR study: d. propagation in different orientations The incident electric field E couples unexpectedly to the magnetic resonance of the SRR when the EM waves propagate perpendicular to the SRR plane and E is parallel to the gap-bearing sides of the SRR

SRR study: e. SRRs with four cuts at the corners (1) E along the short period λ ~ 2 u.c.

e. SRRs with four cuts at the corners (2) E along the long period

e. SRRs with four cuts at the corners (3) E along the long period λ ~ 2 u.c.

e. SRRs with four cuts at the corners (4) E along the short period

Conclusions The SRRs exhibit resonant electric response in addition to their resonant magnetic response. Single rings behave the same as double rings: For the single ring ωm is shifting a bit higher while ω0 is almost constant compared to the original double ring model. The incident electric field E couples unexpectedly to the magnetic resonance of the SRR when the EM waves propagate perpendicular to the SRR plane and E is parallel to the gap-bearing sides of the SRR. Symmetric SRR structures were tested (four-cut design) but one needs smaller cuts in order to really shift ωm to lower frequencies below ω0.

Transmittance in 1-D LH structures at ~10 GHz ax=5mm ay=3.63mm az =2.1-9.6mm l=3mm t=w=d=0.33mm

(a) Measured transmission spectra for in-plane CMMs composed of SRRs and continuous wires (solid line), SRRs-only structures (dotted line) and wires-only structures (dashed line). The latter two identify ωm and ωp. The width of the continuous wires is 0.5 mm. The inset shows the unit cell of the in–plane CMM (SRRs plus wires) as well as the electric field orientation and polarization; (b) In‑plane CMM solid curve redrawn to show that the same threshold is exhibited (at ωp΄) as in the non-magnetic structure consisting of closed-SRRs and wires (dotted-dashed line). Thus the transmission peak in the CMM curve is actually RH and not LH; the dip in the CMM spectrum corresponds to the SRR stop band, shifted due to the presence of the wires. (submitted to Phys. Rev. B)

(a) Measured transmission spectra for in-plane CMMs (solid line), SRRs-only structures (dotted line) and wires-only structures (dashed line). The width of the continuous wires has been increased to 1 mm; (b) The coincidence of the CMM solid curve with the closed-SRRs plus wires (dotted-dashed) curve determines the effective plasma frequency, ωp΄, which is now well above the CMM transmission peak, identified as left-handed.

Measured transmission spectra for off-plane CMMs composed of SRRs and continuous wires (solid line), SRRs-only structures (dotted line) and structures consisting of closed-SRRs and wires (dotted-dashed line). The width of the continuous wires is 1 mm. The inset shows the unit cell of the off–plane CMM (SRRs plus wires) as well as the electric field orientation and polarization. The frequencies ωm = ωm΄ and ωp΄ are well separated and the CMM peak is clearly LH.

Number of unit cells in the propagation direction: SRRs

Number of unit cells in the propagation direction: LH CMMs (1)

Number of unit cells in the propagation direction: LH CMMs (2)

Effect of the continuous wires width on the transmittance of LH CMM peaks (1)

Effect of the continuous wires width on the transmittance of LH CMM peaks (2)

Varying the distance between the rings in the SRRs: how it affects the transmittance of the LH peaks (1)

Varying the distance between the rings in the SRRs: how it affects the transmittance of the LH peaks (2)

Varying the distance between the rings in the SRRs: how it affects the transmittance of the LH peaks (3)

Varying the distance between the boards in the direction perpendicular to the SRRs: how it affects the transmittance of the LH peaks

2-D structures Increased losses due to the perpendicular boards: need to reduce the number of boards and u.c. in the propagation direction.

1-D structures at ~6THz Structures fabricated by George Constandinides

Conclusions (1) Major conclusion: The new criterion proposed by Koschny et al. for identifying if a peak is really LH or not was experimentally demonstrated for the first time (submitted to PRB on February 2004). We were therefore able to demonstrate a real LH structure with a moderate transmittance of -10dB which was later drastically improved for circular SRRs by the group of Ekmel Ozbay. The transmittance of the LH peak increases by decreasing the number of u.c. in the propagation direction. (after the paper of Boeing using 3 u.c. in the propagation direction). For rectangular SRRs with 6 u.c. in the propagation direction we have achieved a transmittance of ~ -7dB. Increasing the width of the off-plane continuous wires leads to a decrease in the transmittance. Decreasing the distance between the rings leads to a shift of ωm to lower freq. and decreases the transmittance due to enhanced losses in the region between the rings. The LH peak can be tuned by varying the distance between the boards: the closer ω΄m and ω΄p the higher the transmittance.

Conclusions (2) The 2-D SRR structures show a dip which is deeper than in the 1-D SRRs, however, in the CMMs there is no peak due to the losses generated by the presence of a lot of boards in the plane perpendicular to the propagation: We probably have to decrease the numbers of the boards and of the u.c. For the THz structures we can see two different transmission spectra corresponding -needs more studies- to the two polarizations of E with respect to the SRR. It is possible that the observed dip corresponds to the electric coupling to the magnetic resonance discussed earlier.

Future issues on LH CMMs Study the THz structure Fabricate 2-D CMMs with high transmittance Investigate the reason of the drop in the transmittance for symmetric CMMs Compare perhaps circular with rectangular SRRs: Why is there more transmittance in the first case? ?