Terahertz bandwidth photonic Hilbert transformers based on synthesized planar Bragg grating fabrication

Abstract

Terahertz bandwidth photonic Hilbert transformers are proposed and experimentally demonstrated. The integrated device is fabricated via a direct UV grating writing technique in a silica-on-silicon platform. The photonic Hilbert transformer operates at bandwidths of up to 2 THz (~16nm), which is at least ten fold greater bandwidth than any previously reported experimental approaches. Achieving this performance requires detailed knowledge of the system transfer function of the direct UV grating writing technique, this allows improved linearity, and yields THz bandwidth Bragg gratings with improved spectral quality. By incorporating a flat-top reflector and Hilbert grating with a waveguide coupler an ultra wideband alloptical single-sideband filter is demonstrated.

Integrated waveguide Bragg gratings for microwave photonics signal processing

“…The authors emphasize that the operative bandwidth is limited by the available measurement setup only, and that the PHT grating strength and the sideband suppression could be further increased by improving the phase trimming and the scattering methods employed. THz-bandwidth PHTs have been recently reported using improved WBG technology [102].…”

Terahertz-bandwidth photonic fractional Hilbert transformer based on a phase-shifted waveguide Bragg grating on silicon

“…As said before, when reducing the fractional order toward 1, the TBP decreases with δn due to the simultaneous reduction in the quality factor of the central notch and of the maximum bandwidth. To achieve high TBP when P approaches 1 (integer HT), a complex grating apodization is needed, which is similar to the profile reported in previous designs of integer photonic Hilbert transformers [1][2][3]5,6].…”

“…It is important to notice that the resonance depth at the center of the reflection band reaches approximately 40 dB, which represents a 20 dB improvement compared with other integrated photonic Hilbert [11].} transformers demonstrated to date [5,6]. Based on the spectral response measurement in Fig.…”

“…The fastest photonic on-chip HT reported to date offered a bandwidth limited to approximately 200 GHz [5]. Recently, Sima et al [6] demonstrated the first THz-bandwidth 1st-order (integer) photonic Hilbert transformer fabricated in a silica-on-silicon platform. Two main issues, however, can be found in their approach, which is based on a waveguide Bragg grating (WBG) created in glass through a photosensitive process.…”

“…Two main issues, however, can be found in their approach, which is based on a waveguide Bragg grating (WBG) created in glass through a photosensitive process. The UV writing method is limited in terms of the effective index modulation δn or the related coupling strength (<10 −3 ) [6], which, in turn, requires gratings with long lengths (in the order of 1 cm) to achieve the desired performance. In addition, complicated apodization profiles are required, which are not trivial to realize using the UV writing method.…”