Wideband and continuously-tunable fractional photonic Hilbert transformer based on a single high-birefringence planar Bragg grating.

Zijing Zhang,Yu Yu,Meng Huang,Yuan Gao,Li Shen,James C Gates,Minming Zhang,Peter G.R Smith,Matthew T Posner,Deming Liu,Zhenggang Lian,Binchen Cai,Chaotan Sima,Bolan Liu

doi:10.1364/oe.26.020450

Abstract

We propose and experimentally demonstrate wideband and continuously tunable fractional-order photonic Hilbert transformers (FrHT). These are realized by a single apodized planar Bragg grating within a high-birefringence planar substrate. The fractional order of the FrHT is continuously tuned and precisely controlled by changing the polarization state of the input light. The experimental characterization demonstrates an operating bandwidth up to 120 GHz with amplitude ripples below 3 dB. The optical phase shift response is directly measured to verify the proposed tuning property, demonstrating transform orders of around 1, 0.7, and 0.5. This approach is simple, stable, and compact compared to other existing methods and has great potential in the fields of ultrafast all-optical signal processing.

Highlights

Integrated microelectronic circuits have penetrated into every aspect of the field of signal processing, in optical fiber telecommunication systems
One route uses integrated optical chips to realize photonic Hilbert transforms (PHTs) or Fractional Hilbert Transforms (FrHTs) [1] that can be applied to single sideband modulation or the image edge filtering [2]
An amplified spontaneous emission (ASE) light source operating in the telecommunications C-band (15301570 nm) is used to monitor the device reflection spectral response, as shown in the Fig. 5

Summary

Introduction

Integrated microelectronic circuits have penetrated into every aspect of the field of signal processing, in optical fiber telecommunication systems. The fractional order of Hilbert transformers have provided additonal functionality as they offer control over the phase of a signal, and the signal can be interpreted or encoded [2,3]. These are of particular importance in the field of microwave photonics where processing bandwidths above tens of GHz are extremely challenging. The reconfigurable ring structure devices in InP-InGaAsP substrates [11] provide excellent and multifunctional optical processing, including integrator, fractional differentiator as well as around 50 GHz (0.4nm) bandwidth FrHT, but confront considerable fabrication challenges as well as relatively high cost. This kind of FrHT devices has strong potential in applications of secure communication systems

Operation principle

Device concept

Device fabrication and characterization

Results and discussion

Conclusion