On‐chip integration of laser‐ablated zone plates for detection enhancement of InGaAs bow‐tie terahertz detectors

Abstract

One order of magnitude detection enhancement of bow-tie-shaped InGaAs-based terahertz detectors by on-chip incorporation of the secondary diffractive optics is reported. Zone plates were produced directly on the bottom surface of 500 µm-thick InP substrate using the direct laser write technique after an array of InGaAs detectors was formed on the front surface of the wafer. Measurements of detected signal dependence on the angle of the incident wave were performed at 0.76 THz and compared with finite-difference time-domain simulation results. Good correlation of the results shows that the observed enhancement is indeed caused by the focusing performance of the zone plate rather than by the exceptional sensitivity of the single detector.Introduction: Reduction of dimensions in terahertz (THz) imaging systems is one of the key-issues bridging them to direct and versatile implementation for security, medical and materials science aims [1]. As a rule, preferences are given to the development of compact room temperature THz sources [2] and sensing components [3], while routes to avoid relatively large size optical constituents like parabolic mirrors, splitters, waveguides etc. remain out of the margins of focal interest. Recently, we have demonstrated an option to minimise the size of passive optics by the use of zone plates with integrated crossshaped filters produced by means of the laser direct write technique or etching directly in the metal foil [4].In this Letter, we evidence a further step in the miniaturisation of the THz image recording setup via the on-chip integration of InGaAs-based bow-tie THz detectors [5] and focusing components -zone plates. The top surface of the InP wafer was used to process the InGaAs detector array using the previously reported procedure [5], whereas the bottom metalised surface was structured to provide the focusing elements. Integration of such focusing elements with detectors in a single chip allowed one to increase the signal by at least an order of magnitude, as was predicted by numerical simulations, and hence to benefit from the rigid alignment in the recording array.

Recent Advances in Laser Utilization in the Chemical Modification of Graphene Oxide and Its Applications

“…[ 107 ] Further, it was demonstrated that the fl at optics technology can serve as an effective instrument to integrate THz optics and sensing elements in one chip. [ 108 ] The DLW method was applied to produce the zone plate either in 30 µm-thick steel [ 106 ] or in a 200 nm-thick gold layers deposited on one of the bottom surfaces of an InP wafer with integrated InGaAs bow-tie detectors. [ 108 ] It is reasonable to suppose that graphene can also be an option to squeeze fl at optics into ultrathin dimensions.…”

“…[ 108 ] The DLW method was applied to produce the zone plate either in 30 µm-thick steel [ 106 ] or in a 200 nm-thick gold layers deposited on one of the bottom surfaces of an InP wafer with integrated InGaAs bow-tie detectors. [ 108 ] It is reasonable to suppose that graphene can also be an option to squeeze fl at optics into ultrathin dimensions. Quite recently it was demonstrated computationally that monolayers and multilayers of graphene fabricated into Fresnel zones can operate in the visible and terahertz regimes.…”

Compact room temperature terahertz imaging: Towards on-chip integration

“…In order to resolve the intluences of zone plate focusing performance and the sensitivity of the InGaAs bow-tie sensor itself on its output signal, one needs to vary incident angle. It is shown theoretically [6] that the turn of angle of incidence by 11 0 is quite sufficient to obtain two distinct maxima in the detector plane -the first corresponds to the shifted focus of the zone plate while the other one -to the electric field enhancement by the bow-tie antenna itself. In more details, even without the detector, several open zones are sufficient to increase the amplitude of the electric field in 5.5 times from a 0.9 mean value without the detector and zone plate.…”

“…One deserves noting that the bow-tie antenna shape of the detector itself provides a similar order of magnitude enhancement due to the concentration of the electric field near the tip. When both of these effects coupled combined, an enhancement should increase weil above order of magnitude is obtained near the tip of the contact [6].…”

Terahertz Diffractive Optics—Smart Control over Radiation

“…The last group continued research in applying the diffractive optics for imaging purposes with free electron laser illumination [70] and [71]. The group of Gintaras Valušis described manufacturing of lenses by laser patterning of silicon [72], next used for imaging [73], or used laser ablation to integrate FZP on-chip of detector [74]. They also proposed a manufacturing technique using cross-shaped apertures (being a resonant filter) [75][76][77][78] to select the THz frequencies ( Fig.…”