# Topological Berry Antenna on a Silicon Chip for Terahertz Wireless Communication

Sonu Kumar, Ridong Jia, Yi Ji Tan, Thomas Caiwei Tan, Pascal Szriftgiser, G Arun Kumar, Guillaume Ducournau, Arokiaswami Alphones, Ranjan Singh

► To cite this version:

Sonu Kumar, Ridong Jia, Yi Ji Tan, Thomas Caiwei Tan, Pascal Szriftgiser, et al. Topological Berry Antenna on a Silicon Chip for Terahertz Wireless Communication. Advanced Photonics Research, inPress, 10.1002/adpr.202500123. hal-05131748

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# Topological Berry Antenna on a Silicon Chip for Terahertz Wireless Communication

Sonu Kumar, Ridong Jia, Yi Ji Tan, Thomas Caiwei Tan, Pascal Szriftgiser, G. Arun Kumar, Guillaume Ducournau, Arokiaswami Alphones,* and Ranjan Singh*

Nonzero Berry curvature is central to the existence of topological edge states in electronic and photonic valley-Hall systems. While manipulating the Berry curvature in condensed matter systems is challenging, valley-Hall topological photonics offer unprecedented control, where the broken spatial inversion symmetry alters the Berry curvature. Herein, an all-silicon Berry antenna is presented, using a continuously varying geometry corresponding to a gradual change in Berry curvature. The on-chip topological edge mode with a tunable field extent is achieved to enhance effective antenna aperture, creating a high-gain on-chip photonic antenna with perfectly planar wavefronts. Experimentally, a maximum gain of 17 dBi that supports 20 Gbps chip-to-chip wireless communication is demonstrated, with active optical tunability of the antenna gain with modulation depths of 8 dBi. This Berry antenna paves the way for the development of complementary metal-oxide-semiconductor (CMOS) compatible topological Berry devices, with potential applications in integrated micro-/nanophotonics, next-generation wireless communications (6G to Xth generation), and terahertz detection and ranging.

## 1. Introduction

Studies on photonic topological edge state have attracted considerable attention owing to the robust propagation under a class of geometric deformations.[1,2] The topological nature of such systems is usually characterized using Berry curvature, defined as the curl of Berry connection in momentum space.[3-5] In topological photonic crystals, such as valley photonic crystals (VPCs), obtaining a nonzero Berry curvature can be achieved by breaking spatial inversion symmetry, giving rise to valley edge states on the domain wall of these symmetry-breaking bulks.[1,3,6] The all-dielectric VPC platform has already enabled numerous efficient on-chip devices[6-8] including topological lasers,[9] waveguides,[10] power splitters,[11] routers,[12] and antennas.[7,13] While conventional VPCs with homogeneous topology (Berry curvature) has been widely demonstrated, combining VPC bulk with different Berry curvature distributions, however, is barely discussed that can provide a new degree of freedom to control the edge states.[14,15]

S. Kumar, A. Alphones
School of Electrical and Electronic Engineering
Nanyang Technological University
Singapore 639798, Singapore
E-mail: ealphones@ntu.edu.sg

R. Jia, Y. J. Tan, T. C. Tan, R. Singh
Division of Physics and Applied Physics
School of Physical and Mathematical Sciences
Nanyang Technological University
Singapore 637371, Singapore
E-mail: rsingh3@nd.edu

R. Jia, Y. J. Tan, T. C. Tan, R. Singh
Center for Disruptive Photonic Technologies
The Photonics Institute
Nanyang Technological University
Singapore 639798, Singapore

<figure><img src="image_2.png" /></figure>

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adpr.202500123.

© 2025 The Author(s). Advanced Photonics Research published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

DOI: 10.1002/adpr.202500123

P. Szriftgiser
Laboratoire de Physique des Lasers
Atomes et Molécules
PhLAM
UMR 8523
Univ. Lille
CNRS
F-59000 Lille, France

G. A. Kumar
Department of Electronics and Communications Engineering
National Institute of Technology
Warangal 506004, India

G. Ducournau
Institut d'Electronique
Microelectronique et Nanotechnologie
UMR 8520
IEMN
Univ. Lille
CNRS
F-59000 Lille, France

R. Singh
Department of Electrical Engineering
University of Notre Dame
Notre Dame, IN 46556, USA
Recent works have shown that tuning the profiles of valley edge modes can be achieved by varying the size of the holes and pillars.[14,16,17] However, the inherent topological property of these tuning remains elusive, as well as an approach to continuously manipulate the Berry curvature, which potentially further enhances the field extent aiming at applications such as on-chip planar wavefront propagation and radiation.

To address, our work demonstrates the design of a topological Berry device through the gradual cascading of various Berry curvatures. The tunable mode extent significantly enhances the radiation aperture of our on-chip topological antenna, producing a perfect planar wavefront that is crucial for long-range wireless communication.[18,19] Traditional antenna systems on the CMOS platform often exhibit limited gain, necessitating bulky 3D lenses,[20,21] which restrict its integration capabilities. In contrast, aperture antennas can achieve higher gain due to their larger planar wavefronts with the potential to exclude the bulky components.[22–26] However, the requirement of large flaring angle and the nonuniform phase front make it challenging to design an aperture antenna with broad planar wavefront.[22–26] This results in limited coverage distance in free space radiation. On the other hand, conventional phase compensation and wavefront flattening techniques require prior knowledge of phase profile and intensive optimization to achieve uniform phase profile and planar wavefront.[24–27] These challenges can be addressed using the concept of manipulating Berry curvature in VPCs. Additionally, the lack of tunability of the realized gain is another challenge for the on-chip aperture antennas, which is essential for applications such as gain modulation and on-off switching in wireless networks.

In this work, a VPC-based Berry antenna (BA) is demonstrated with an enhanced antenna aperture and gain performance surpassing the current antenna designs through simply tuning the geometrical perturbation.[14] The spatial inversion symmetry breaking creates a topological bandgap in VPC, of which the width determines the transverse field extent of the edge mode.[15] The zigzag VPC interfaces support two types of waveguiding modes, symmetric (even) and antisymmetric (odd),[28,29] where the even mode is utilized for achieving the uniform planar wavefront.[29] Experimental validation of the proposed antenna in the terahertz (THz) wireless testbed shows a maximum gain of 17 dBi and a gain density (maximum gain per unit aperture length) of 2.2, which can be improved to 4.85 based on our numerical analysis. We further demonstrate 20 Gbps chip-to-chip wireless data communication over a distance of 15 cm. A photoexcitation is also employed to demonstrate the active tunability of our BA, with a tuning range of 8 dBi in the realized antenna gain, that also showcases the robustness of the topological devices. Our BA serves as a promising solution for high-data-rate applications in 6G to XG wireless communication and terahertz detection and ranging (TEDAR).

## 2. Discussion

The proposed BA is fabricated on a high-resistivity (>10 kΩ cm) silicon platform, as shown in Figure 1a. It consists of three regions: the waveguiding region (marked as P-Q in Figure 1a), the region with varying Berry curvatures (Q-R), and the impedance-matching region (R-S), all fabricated in a single step through the deep reactive ion-etching (DRIE)

technique (Experimental Section). The waveguide and the varying Berry curvature region comprise the interfaces of two mirrored VPC bulks, supporting a robust topological edge state. The mode profile exhibits uniform field extension along the y direction in the P-Q region and a gradual field extension in the Q-R region when the Berry curvatures increase. The final region (R-S) is a graded refractive index buffer (GRIB) with the effective refractive index varying along the x direction, which is used to gradually match the VPC mode to the wave in free space while preserving the planar wavefront of the selected VPC waveguide mode.

The bulk VPC structure consists of unit cells in a honeycomb lattice, which comprises altered triangular air holes with side lengths $l_1$ and $l_2$, as illustrated in Figure 1a. The spatial inversion symmetry breaking ($l_1 \neq l_2$) lifts the Dirac degeneracy point, forming a bandgap at the K(K') valleys. Figure 1b depicts the Berry curvature at the lower band of the transverse-electric (TE) mode when symmetry breaking strength is $\delta = 0.3a$, where $\delta = l_1 - l_2$. The Berry curvatures are nonzero with opposite signs at K and K' valleys. The variation of Berry curvature at K'-valley point is also highlighted in Figure 1a. The peak value of the Berry curvature increases with the reduction of $\delta$ values from 0.3a to 0.05a over 18 unit cells. The width of the topological bandgap is also decreased, resulting in the extended spatial mode profile along y direction. This field extension enhances the radiating aperture width, as shown by the simulated field profile in Figure 1c by the real part of the y component of the electric field. The Berry curvature increases in linear steps for $\delta$ from 0.3a to 0.05a. Versatile Berry curvature variations give rise to various Berry antenna performances, which are detailed in Section S1, Supporting Information.

The simulated photonic band diagram versus different $\delta$ is presented in Figure 2a. A larger bandgap is achieved with the larger $\delta$ ($\delta_i = 0.3a$), which decreases with the smaller $\delta$ ($\delta_i = 0.05a$). Figure 2b illustrates two types of VPC interfaces, type I and type II interfaces, formed by mirrored bulks along y direction. The y-component electric field of the valley mode in type I possesses an antisymmetric phase profile (odd-mode) about the interface, while for type II, it is a symmetric phase profile (even mode). Type II interface is selected to design our BA with a single central beam radiation due to its uniform phase along the radiating aperture (y axis) (Figure S2, Supporting Information). The dispersion curve of the edge states in type II interface for different $\delta$ is plotted in Figure 2c, illustrating nearly identical group velocities (slopes of the solid lines). The unit cells with varying $\delta$ correspond to different calculated valley Chern numbers as:[30]

$$C_v = \frac{1}{2\pi} \int_{HBZ} \Omega(\vec{k}) \, d^2\vec{k} \quad (1)$$

where $\Omega(\vec{k})$ represents the Berry curvature, and the integration area is selected near the K' valley using an area of half of the first Brillouin zone. For smaller perturbation with $\delta_i = 0.05a$, corresponding to the bandgap of around 5 GHz, the valley Chern number at K' is 0.45. As $\delta$ value increases to $\delta_i = 0.3a$ and a bandgap of 28 GHz, the valley Chern number is modified to 0.22.

Figure 2d illustrates the numerical results of the valley Chern number and group velocities versus the change of geometric
<figure><img src="image_3.png" /><figcaption>**Figure 1.** On-chip THz Berry antenna with various Berry curvatures. a) Schematic of on-chip THz BA with nearly planar wavefront radiation, consisting of three regions: waveguide region (marked as P-Q), varying Berry curvature region (Q-R), and impedance matching region (R-S). A tapered coupler is employed to efficiently couple the TE mode THz wave from the rectangular waveguide to the VPC waveguide. The inversion symmetry breaking in the waveguide region is uniform as $\delta = l_1 - l_2 = 0.3a$ ($l_1$ and $l_2$ are the side lengths of the triangular air holes). The Berry curvature gradually varies in the Q-R region across 18 unit cells, where mode extension along the transverse y-axis direction increases. The respective Berry curvatures near K' valley are highlighted with $\delta_i = 0.3a$, $\delta_m = 0.18a$, and $\delta_l = 0.05a$. The graded refractive index buffer (GRIB) in the R-S region efficiently matches the planar wavefront from VPC to free space. The aperture length (Q-S) is $l_a$. The inset sample picture shows the dimensions of the Berry antenna sample. b) Berry curvature of the VPC bulk with $\delta = 0.3a$ in the first-Brillouin zone. c) The gradually increased field extension in the Q-R region, indicated by the simulated electric field $Re(E_y)$.</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>**Figure 2.** Tuning Berry curvatures and topological mode extensions. a) Band structure of VPC eigenmodes with varying $\delta$ values. The topological bandgap is lifted from the degeneracy point at K' as $\delta$ increases from zero (dashed) to nonzero (colormap). b) The mode profiles of the two types of VPC interfaces, type I and type II, supporting odd and even topological edge states, respectively, as indicated by the simulated $Re(E_y)$. c) The dispersion curve of the type II interface, showcased when $\delta_i = 0.3a$, $\delta_m = 0.18a$, and $\delta_l = 0.05a$. d) The decreased valley Chern numbers and near-constant group velocities (0.24 $C_o$ at 302 GHz) versus increasing bandgap widths. e) Mode extension of edge state over different $\delta$. A larger extension is achieved for $\delta = 0.05a$, whereas $\delta = 0.3a$ gives rise to a more confined mode. f) The power flow (arrow) in the varying Berry curvature region, indicating the attenuated back reflection and scattering. The sample image of this region is shown in the inset.</figcaption></figure>
parameter δ. The valley Chern number varies from 0 to 1/2 for the employed asymmetry perturbations. The group velocity (v<sub>D</sub> = dω/dk) of the edge state remains nearly identical for different δ values, in a narrow range from 0.24C<sub>o</sub> to 0.32C<sub>o</sub> calculated at f = 302 GHz. The simulated field profiles of the edge states in type II interfaces are shown in Figure 2e for δ = 0.3a, 0.18a, and 0.05a. The structure supports the edge state with varying mode profiles along the y direction. The seamless cascading of these edge states is illustrated in Figure 2f, where the valley vortex modes in the varying Berry curvature region minimize the scattering loss and back-reflection. The Dirac Hamiltonian describing the symmetry perturbations in varying Berry curvature regions is detailed in Section S3, Supporting Information.

In **Figure 3a**, the y component of the electric field distribution of the BA chip is highlighted over its effective width dimension (w). The value of w = 12.2 mm is determined where the maximum electric field amplitude (|E_y|) along the transverse (y-axis) direction surpassing 87% of maximum (Section S4, Supporting Information). The waveguide portion incorporates an Ω-like path with four 60° sharp corners, highlighting robust wave propagation with significantly reduced bending loss, facilitating chip miniaturization and efficiency. Figure 3b presents the phase profile of the on-chip even modes with minimal phase changes (<15°) along y direction, highlighted at the waveguiding

region (x<sub>δl</sub>), the varying Berry curvature region (x<sub>δi</sub>), and the BA boundary (x<sub>a</sub>). This is distinct from a conventional flaring antenna case where physical flaring introduces a cylindrical wavefront, as compared in **Table 1** with state-of-the-art aperture antenna designs. The employed GRIB ensures the perfect matching of the planar wavefront from the varying Berry curvature region to free space (Section S5, Supporting Information).

To experimentally validate the proposed concept, a Keysight-
Virginia Diodes Inc. (VDI)-based terahertz testbed operating in
the WR2.8 band (260–400 GHz) is employed to excite the BA and
characterize the radiation, as depicted in Figure 3c. A BA without
edge mode flaring, with a uniform δ = 0.3a across the entire
structure, is employed as a comparison reference. Gain calcula-
tions over different distances for both the flared and non-flared
BAs (at f = 304 GHz and f = 312 GHz) distinguish the far-field
and near-field regions (Section S6, Supporting Information).
The far-field starts at a distance of ≈20 cm for the flared BA
and 10 cm for the non-flared BA, as observed in Figure 3d.
The antenna gain spectra are thereby showcased at a far-field dis-
tance of D = 40 cm, as plotted in Figure 3e. The flared BA
achieved an enhanced gain of 17 dBi at f = 302 GHz (blue) com-
pared to the non-flared antenna with a maximum gain of around
10.1 dBi (red), with an improvement of 6.9 dBi due to the aper-
ture enhancement from our manipulation in Berry curvature

<figure><img src="image_5.png" /><figcaption>**Figure 3.** Berry antenna characterization with enhanced radiation gain. a) The simulated field profile of Re(E_y) for the entire Berry antenna with Ω shape waveguide path. b) The phase of E_y at the start (x_δi) and end edges (x_δl) of the varying Berry curvature region and at BA chip edge (x_a). The phase variation is nearly constant (<15°) along the y direction. c) THz gain measurement testbed with BA at the transmitter end and WR2.8 horn at the receiver end. The gain is measured at a far-field distance of D = 40 cm. The receiver is placed on a rotating mount to measure the 2D-radiation pattern over different angles. d) The measured gain over different distances for both flared and non-flared BA at f = 304 GHz and f = 312 GHz, respectively. e) The realized gain of both BA over the frequencies measured at a distance of 40 cm. The flared BA antenna achieves a gain of 17 dBi, 6.9 dBi higher than that of the non-flared BA. f) The measured reflection coefficients for both the flared and non-flared BA, showing a magnitude below −10 dB within the 3 dB gain bandwidth (blue region).</figcaption></figure>
<table><caption>Table 1. Comparison table of our topological Berry antenna chip with state of the art.</caption><thead><tr><th>Reference</th><th>Platform</th><th>Applied technique</th><th>Frequency (f<sub>o</sub>) (GHz)</th><th>Gain density<sup>a)</sup></th><th>Aperture length [λ<sub>o</sub>]<sup>b)</sup></th><th>Peak realized gain (dBi)</th><th>Total efficiency [%]</th><th>Wavefront flattening required<sup>h)</sup></th><th>Inherent planar wavefront</th><th>Topological protection</th><th>Active photoexcitation</th><th>chip-to-chip data communication<sup>i)</sup></th></tr></thead><tbody><tr><td>[20]</td><td>Metal</td><td>Holey substrate integrated waveguide</td><td>40 (low)</td><td>1.95</td><td>6.13</td><td>12</td><td>NA</td><td>Yes</td><td>No</td><td>No</td><td>No</td><td>No</td></tr><tr><td>[18]</td><td>CMOS</td><td>Patch + lens</td><td>470</td><td>0.11</td><td>284.9<sup>c)</sup></td><td>33.6<sup>d)</sup></td><td>69</td><td>NA</td><td>NR<sup>c)</sup></td><td>No</td><td>No</td><td>No</td></tr><tr><td>[17]</td><td>CMOS</td><td>Slot + lens</td><td>220</td><td>0.32</td><td>42.4<sup>c)</sup></td><td>14</td><td>31</td><td>NR</td><td>NR</td><td>No</td><td>No</td><td>No</td></tr><tr><td>[35]</td><td>CMOS</td><td>Leaky slot lens</td><td>400</td><td>0.33</td><td>80.6<sup>c)</sup></td><td>27</td><td>25</td><td>NR</td><td>NR</td><td>No</td><td>No</td><td>No</td></tr><tr><td>[22]</td><td>dielectric</td><td>PhCs</td><td>340</td><td>0.9</td><td>20.9</td><td>19<sup>e)</sup></td><td>NR<sup>f)</sup></td><td>Yes</td><td>No</td><td>No</td><td>No</td><td>6</td></tr><tr><td>[23]</td><td>dielectric</td><td>PhCs</td><td>275</td><td>3.58</td><td>4.2</td><td>14</td><td>NA<sup>g)</sup></td><td>Yes</td><td>No</td><td>No</td><td>No</td><td>No</td></tr><tr><td>This work</td><td>dielectric</td><td>Berry curvature modification</td><td>302</td><td>2.2</td><td>7.7</td><td>17</td><td>86</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td><td>20</td></tr></tbody></table>

(Section S7, Supporting Information). The slight difference in the bandwidths between the flared and non-flared BAs results from the thickness variation across the fabricated samples.

We further introduce a gain density parameter g<sub>d</sub> to calibrate our improvement of the aperture antenna gain as expressed as:

$$g_d = \frac{G}{l_a} \qquad (2)$$

where G represents the peak gain from the antenna and l<sub>a</sub> is the aperture length of the flaring region (Figure 1). The proposed fabricated BA exhibits a gain density of 2.2 for an aperture length of 7.7 λ. Although this is lower than the value reported in ref. [26] simulation results show that g<sub>d</sub> of the proposed work can be improved to 4.85 (Section S8, Supporting Information). This can be the highest value in comparison to the state-of-the-art literature. Additionally, the total efficiency achieved through BA is over 90% for -2 dB realized gain bandwidth and over 86% within the -3 dB gain bandwidth. Furthermore, to assess the perfect matching of the structure with the free space, the reflection coefficients at the input port of both flared and non-flared BAs are measured using a vector network analyzer (VNA), as shown in Figure 3f. It is noteworthy that both antennas exhibit an identical bandwidth of reflection coefficient, indicating that the continuous variation of Berry curvature leads to minimal back reflection. The measured 2D-radiation pattern of the flared BA (red) in the E plane (θ = 90°) at f = 308 GHz is plotted in Figure 4a, which matches the simulation result (blue). A 2 dBi decrease in φ = 0° is observed, mainly attributed to fabrication imperfection. In contrast, the radiation pattern of the non-flared BA (yellow) exhibits a wider beam in the E plane with a reduced peak gain. Furthermore, the measured 3D radiation patterns are illustrated in Figure 4b,c for the flared and non-flared BAs, respectively. The peak gain is obtained in the direction of φ = 0°, θ = 90°.

To demonstrate the feasibility of employing the BA to THz data links, wireless data communication is presented using the pair of flared BAs, as shown in Figure 4d. The setup utilizes the arbitrary waveform generator (AWG) for the in-phase and quadrature-phase (IQ) modulation (Figure S6, Supporting Information). The optical signal is transformed into the terahertz signal using a uni-traveling carrier-photodiode (UTC-PD). The modulated terahertz signal is then radiated into the free space using the BA as the transmitter and received by another BA at a distance of D = 15 cm. Here, D = 15 cm is selected based on the power sensitivity requirements of the measurement setup. The transmitted signal is modulated using the 16 quadrature amplitude modulation (QAM) technique.

As depicted in Figure 4e, the BA wireless link demonstrates a data rate of 20 Gbps (5 Gbaud) with an error vector magnitude (EVM) of ≈9%, realized at a relative power of 0 dB for the over-the-air transmission. Compared to the direct reference connection, a power penalty of 34 dB is observed through the over-the-air transmission for this 20 Gbps data rate and the 9% EVM. This penalty is confirmed by the VNA measurements of a flared BA pair at the same distance. The achieved chip-to-chip data rate of the proposed BA is also compared with state-of-the-art works, including CMOS[31–33] and dielectric[7,25] platforms in Section S9, Supporting Information, showing that our proposed design achieves the highest data rate of 20 Gbps for the maximum distance of 15 cm through a single-channel wireless communication. Furthermore, the link budget is also calculated for the flared BA using the experimentally measured power. The power transmission spectrum closely matches the gain plot of the flared BA. Our data-communication experiment highlights the signal transmission enhancement using the BAs, leveraging the planar wavefront of the edge mode with long field extent. Additionally, the robustness of the BA with defect and disorder has also been analyzed (Section S10, Supporting Information).

Active modulation of realized gain of the BA is achieved with tunable photoexcitation when employing laser pumping, as illustrated in Figure 5a. The silicon BA chip absorbs the light with the

<footnote>a)Gain/aperture length. b)Including lens and rod. c)2D aperture area (λ<sub>o</sub><sup>2</sup>) of 3D lens. d)Directivity. e)With aperture flaring + dielectric rod. f)Not required. g)Not available.</footnote>

<footnote>h)Wavefront flattening required. i)In Gbps.</footnote>
<figure><img src="image_6.png" /><figcaption>**Figure 4.** High-gain performance and long-distance wireless data communication enhanced by Berry antenna. a) The 2D radiation patterns for both flared and non-flared BA in E plane (θ = 90°). b,c) The measured 3D radiation patterns for (b) the flared BA and (c) the non-flared BA. d) The THz wireless data communication testbed. The IQ-modulated THz signal is radiated into the free space by transmitter BA and is received by BA at the receiver end. UTC–PD: uni-traveling carrier–photodiode. LO: local oscillator. RTO: real-time oscilloscope. e) The wireless data communication between the flared BAs wireless link, achieving a data rate of 20 Gbps over a distance of 15 cm and an EVM of 9% for the relative power of 0 dB. The inset shows the received 16 QAM constellation diagrams. f) The budget analysis of the wireless communication link between flared BAs.</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>**Figure 5.** Active optical tuning of Berry antenna. a) Measurement configuration for phototuning BA with different laser pumping locations. b) Modulation of realized antenna gain with pump fluence of 622.2 W cm⁻² at different locations along the interface of BA. c) Modulated antenna gain results using lower pump fluence of 60.24 W cm⁻². d) Realized gain modulation using pump fluence 622.2 W cm⁻² at locations 6-unit-cell from the interface. e) Gain modulation with different pump fluence at location A¹. f) Gain modulation at *f* = 304 GHz versus different pump fluences.</figcaption></figure>
pumping photon energy *E* exceeding the silicon bandgap (*E*<sub>g</sub> = 1.1 eV) where the free carriers are generated.[34] Various pumping locations, including waveguiding (A), flaring (B, C, D), and matching regions (E), are chosen for photoexcitation using the continuous wave laser with wavelength 525 nm (*E* = 2.36 eV). To ensure uniform light illumination on a single unit cell, a small beam size of 0.45 mm and a maximum fluence power of 622.2 W cm<sup>-2</sup> are employed (gain modulation with lower power of 60.24 W cm<sup>-2</sup> at the 6-unit cells from the interface is shown in Figure S9, Supporting Information). Figure 5b illustrates the results with maximum realized gain modulation of around 8 dBi versus optical pumping at fluence power of 622.2 W cm<sup>-2</sup> applied along the interface, particularly at location A<sup>1</sup>. The modulation decreases as the pumping location moves toward positive *x* direction (B<sup>1</sup>, C<sup>1</sup>, D<sup>1</sup>, and E<sup>1</sup>), as shown in Figure 5b,c. This indicates that the topological mode intensity is highest at the waveguide interface and diminishes along the *x* direction in the flaring region due to mode extension to the transverse y-axis direction (Figure S3, Supporting Information). Thus, robustness of BA to defects is enhanced as we move toward *x* direction of BA. As the strength of the topological mode profile decays toward the *y* direction, the level of gain modulation decreases due to the lower magnitude of terahertz waveguide mode, as observed from Figure 5d when pumping is performed at the 6-unit cells from the interface. Figure 5e demonstrates the active photo-tunability of the antenna gain versus pumping fluence employed at point A<sup>1</sup>. The results of *G* of the flared BA is shown in Figure 5f at 304 GHz, highlighting the active tuning range over 8 dBi. This opens up the application potential of the Berry device for wireless on-off amplitude modulation and power profile tuning for different radiation beams using active optical approaches.

## 3. Conclusion

In summary, we demonstrate the Berry antenna and its optical active control on a silicon chip through manipulating the geometry of the topological photonic crystal achieving various Berry curvatures on a single chip, which enables an enhanced antenna aperture and radiation gain with planar wavefront. Experimentally, we have achieved an antenna gain to a maximum value of 17 dBi with topological protection, significantly outperforming conventional aperture antennas. Our photo-tuning experiment on the Berry antenna realized modulation depths up to 8 dBi in the gain performance. Furthermore, a 20 Gbps chip-to-chip wireless data communication link is achieved using our BA designs over distance of 15 cm. Our proposed BA design demonstrates a promising approach for aperture antennas, opening up the potential for designing topological photonics with continuously varying Berry curvatures, such as cascaded Berry filters, sensors, and couplers, aiming at 6G to XG wireless and TEDAR applications.

## 4. Methods

### 4.1. Numerical Simulation

The analysis of VPC bulk topology focuses on the TE mode, which involves calculating the band diagram of the bulk unit cell and type I and II edge states using the 2D finite-element method

simulation in COMSOL Multiphysics software. The 3D model of the BA is simulated in CST Microwave Studio using the time-domain solver. Additionally, MATLAB is used for further data processing and analysis.

### 4.2. Silicon Chip Fabrication

For the experimental realization of the BA, the samples were fabricated on a 4-inch high-resistivity (>10 kΩ cm) silicon wafer with a 220 µm thickness and a 2 µm thick silicon dioxide deposited on top. A 1.5 µm thickness AZ 5214 E photoresist was spin-coated and the Berry antenna structures were patterned using photo-lithography. DRIE is applied to etch the silicon to form triangular and circular holes with different aspect ratios.

## 5. Experimental Section

**Gain Measurement of BA:** The BA characterization was done using the Keysight-VDI terahertz measurement setup. For the measurement at the terahertz band of frequencies, a Keysight millimeter-wave signal generator was employed to generate a radiofrequency signal (at $f_{RF}$). Utilizing the VDI frequency extender module (WR2.8SGX), the frequency was upconverted from the 260–400 GHz frequency band ($18 \times f_{RF}$). The upconverted signal was applied through a WR2.8 rectangular waveguide (WR3.4 for radiation pattern and data communication measurement) to the BA using a silicon taper connected to the BA. On the receiver end, a WR2.8 diagonal horn antenna (WR3.4 for radiation pattern measurements), mounted on a rotational stage, was used to receive the signal. This was directly connected to the VDI extender module to downconvert the signal. The downconverted signal was then received by the Keysight spectrum analyzer for further analysis. The LabVIEW was used to precisely control the measurement system, including the signal generator, signal analyzer, and rotating motor for calculating antenna gain and radiation pattern in both the E and H planes.

**Chip-to-Chip Wireless Data Communication:** Inter-chip wireless data communication was conducted in the photonics-based terahertz generation testbed. This testbed utilized two laser sources operating in optical C-band, with a frequency difference of around 300 GHz, to generate coherent optical signals for data transmission. For IQ modulation, one of the lasers was modulated using the AWG. The combined modulated output signal was then amplified using the erbium-doped fiber amplifier to a desired level before fed into the UTC–PD. The UTC–PD converted the optical signal to a terahertz electrical signal. Subsequently, this modulated terahertz electrical signal was coupled into the BA through the WR3.4 rectangular waveguide using TE mode. The BA on the transmitter end radiated the modulated terahertz signal into the free space, which was received by the BA connected at the receiver end. The received terahertz signal was coupled into the rectangular waveguide and fed into the sub-harmonic mixer to convert the signal from terahertz to intermediate frequency. The signal was then amplified using the SHF810 broadband amplifier to evaluate the constellation and EVM response on the 70 GHz RTO.

## Supporting Information

Supporting Information is available from the Wiley Online Library or from the author.

## Acknowledgements

All the authors acknowledge the research funding support from the National Research Foundation (NRF), Singapore (grant no. NRF-CRP23-2019-0005). The authors also thank the IEMN characterization service for the access to various instruments and infrastructure support used
during the device characterization. The test of experimental testbed at IEMN was supported by the "France2030" programs, PEPR (Programmes et Equipements Prioritaires pour la Recherche), CPER Wavetech. The PEPR is operated by the Agence Nationale de la Recherche (ANR), under the grants ANR-22-PEEL-0006 (FUNTERA, PEPR "Electronics") and ANR-22-PEFT-0006 (NF-SYSTERA, PEPR 5G and beyond—Future Networks). The Contrat de Plan Etat-Region (CPER) WaveTech is supported by the Ministry of Higher Education and Research, the Hauts-de-France Regional council, the Lille European Metropolis (MEL), the Institute of Physics of the French National Centre for Scientific Research (CNRS), and the European Regional Development Fund (ERDF).

## Conflict of Interest

The authors declare no conflict of interest.

## Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

## Keywords

Berry antenna, Berry curvature manipulation, chip-to-chip wireless communication, photonic topological insulator, silicon photonics, terahertz 6G to Xth-generation (XG) wireless communications, topological antenna, terahertz topological photonic integrated circuit

Received: April 29, 2025

Published online:

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