Sébastien Blais

Optical ultrawideband monocycle pulse generation based on cross-gain modulation in a semiconductor optical amplifier

A novel method for generating ultrawideband (UWB) monocycle pulses based on cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) is proposed and experimentally demonstrated. Thanks to the XGM in the SOA, a pair of polarity-reversed optical Gaussian pulses is generated at the output of the SOA, to which a Gaussian pulse pump and a continuous-wave probe are applied. The two polarity-reversed optical pulses are then time delayed by two cascaded fiber Bragg gratings to introduce a time delay difference. A UWB monocycle pulse with a full width at half-maximum of 48 ps and a fractional bandwidth of 188% is generated at the output of a high-speed photodetector.

Optical Single Sideband Modulation Using an Ultranarrow Dual-Transmission-Band Fiber Bragg Grating

A novel and simple optical single sideband with carrier (SSB+C) modulation scheme implemented using an ultranarrow dual-transmission-band superstructured equivalent phase shift (EPS) fiber Bragg grating (FBG) is presented. The FBG with two ultranarrow transmission bands is created by introducing two EPSs in its structure during the fabrication process. The use of EPSs instead of true phase shifts allows the reduction of the stringent requirement for accurate phase shifts during the fabrication process. An experimental setup using the EPS FBG to implement SSB+C modulation is demonstrated. The performance of the SSB filter is studied by analyzing the eye diagrams and bit-error-rate measurements

Ultrafast and Precise Interrogation of Fiber Bragg Grating Sensor Based on Wavelength-to-Time Mapping Incorporating Higher Order Dispersion

An interrogation scheme based on wavelength-to-time mapping to achieve ultrafast, high-precision, and large dynamic range interrogation of fiber Bragg grating (FBG) sensors is proposed and experimentally demonstrated. The wavelength-to-time mapping, also called temporal self-imaging effect, is realized in the optical domain, using a dispersive element that has a large group velocity dispersion. For a practical dispersive element, higher order dispersions exist, which makes the wavelength-to-time mapping nonlinear. Thus, an interrogation system based on wavelength-to-time mapping without considering the high-order dispersion would reduce the interrogation accuracy. In this paper, for the first time to the best of our knowledge, a mathematical model that incorporates higher order dispersion to achieve an accurate wavelength-to-time mapping is developed, which is then verified by a numerical simulation. An FBG-based strain sensor interrogated based on the developed wavelength-to-time mapping scheme is experimentally investigated. The system has a sampling speed of 48.6 MHz, a dynamic range as large as 20 nm, and a sensing accuracy as high as 0.87 ¿¿ for a single-shot measurement.

Photonic True-Time Delay Beamforming Based on Superstructured Fiber Bragg Gratings With Linearly Increasing Equivalent Chirps

A photonic true-time delay beamforming system for phased array antennas based on superstructured fiber Bragg gratings (SFBGs) with linearly increasing equivalent chirps is proposed and demonstrated. The theory behind SFBGs with equivalent chirps is detailed and a closed-form equation for the equivalent dispersion is presented for the first time. Array factors, calculated based on the experimentally measured time delays are shown for different wavelengths of the photonic beamformer. An analysis of the errors present in the group delay responses of the fabricated SFBGs is also presented.

Tunable Photonic Microwave Bandpass Filter With Negative Coefficients Implemented Using an Optical Phase Modulator and Chirped Fiber Bragg Gratings

A continuously tunable photonic microwave bandpass filter with positive and negative coefficients implemented using an optical phase modulator and chirped fiber Bragg gratings (FBGs) is proposed and experimentally demonstrated. The positive and negative coefficients are generated through optical phase-modulation to intensity-modulation conversion by reflecting the phase-modulated optical carrier from linearly chirped FBGs (LCFBGs) with positive and negative dispersions. The tunability of the filter is realized by changing the wavelength of the optical carrier such that it is reflected at different physical locations in the LCFBGs. A two-tap microwave bandpass filter with a free spectral range tunable from 1.14 to 4.55 GHz is experimentally demonstrated.

Tunable Photonic Microwave Filter Using a Superstructured FBG With Two Reflection Bands Having Complementary Chirps

A tunable photonic microwave bandpass filter using a superstructured fiber Bragg grating (SFBG) with two reflection bands having complementary chirps is proposed. Being different from a regular chirped FBG, which is usually fabricated using a chirped phase mask with a fixed chirp rate, the SFBG with complementary chirps is fabricated using a uniform phase mask and a chirped sampling function. The chirp rate of the sampling function can be designed to realize specific equivalent chirp rates that are complementary in the 1st-order and the 1st-order reflection bands of the SFBG. An SFBG with complementary chirps is fabricated and characterized. The use of the SFBG to implement a photonic tunable microwave filter with a negative coefficient is experimentally demonstrated.

All-Optical Bandpass Microwave Filter Based on a Superstructured Fiber Bragg Grating with Equivalent Chirp

An all-optical bandpass microwave filter that is implemented using an optical phase modulator and equivalent-chirped superstructured fiber Bragg gratings (SFBGs) to generate negative coefficients is presented in this paper. It is well known that SFBGs, also called sampled FBGs, contain many Fourier orders in their spectrum. By appropriately chirping the period of the sampling function of the SFBG, it is possible to achieve an equivalent chirp in the +1 and the -1 orders. This method allows the fabrication of FBGs with different equivalent chirp rates by using a single uniform phase mask. While other methods to create chirped FBGs require multiple phase masks or variable tension on the optical fiber during the FBG writing process, the use of SFBGs eases the requirements for the fabrication of specific phase and amplitude responses. This is achieved by tailoring the sampling function of the SFBG instead of the Bragg period of the phase mask. In this paper, a two-tap all-optical bandpass microwave filter is demonstrated by using an equivalent-chirped SFBG. The negative coefficients of the filter are realized by exploiting the characteristics of the phase-modulation-to-intensity-modulation (PM-IM) conversion in the CFBG.

Optical single sideband modulation based on superstructure grating for a remotely controlled phased array antenna system

A single sideband (SSB) modulation scheme using a superstructure fiber Bragg grating (FBG) for a remotely controlled photonic true time-delay (TTD) beamforming system is presented in this paper. Photonic true time-delay (TTD) is considered a promising technique for wideband phased array antennas, as it allows beam steering of the antenna without the beam squint problem. For remotely controlled phased array antennas, the dispersive properties of a single mode fiber induce a power penalty at discrete RF frequencies when a double sideband (DSB) modulation scheme is used. The SSB modulation scheme is an effective way to eliminate this power penalty as only one sideband is transmitted and thus no beating is possible upon the recovery of the electrical signal by a photodetector. This paper presents for the first time a theoretical model as well as experimental results of a SSB modulation scheme based on a superstructure grating with two phase shifts. The true-time delay system considered utilizes a discrete uniform Bragg prism which allows discrete beam steering capabilities for the phased array antenna.

Single sideband modulation scheme employing an equivalent phase shifted fiber Bragg grating for a remotely controlled photonic true time-delay beamforming system

A single sideband (SSB) modulation scheme using a fiber-based equivalent phase shifted Bragg grating for a remotely controlled photonic true time-delay (TTD) beamforming module is presented in this paper. Photonic TTD is considered a promising technique for wideband phased array antennas (PAA) as it allows beam steering of the antenna without the beam squint problem. For remotely controlled phased array antennas, the dispersive properties of a single mode fiber induce a power penalty at higher RF frequencies when a double sideband (DSB) modulation scheme is used. The SSB modulation scheme is an effective way to eliminate this power penalty as only one sideband is transmitted and thus there is no cancellation between the two signals generated by beating the upper sideband with the optical carrier and the lower sideband with the optical carrier at a photodetector. This paper presents for the first time experimental results of a SSB modulation scheme using an equivalent phase shifted fiber Bragg grating. The true-time delay system considered utilizes a discrete uniform fiber Bragg grating prism which allows discrete beam steering capabilities for the phased array antenna.

Effects of chromatic dispersion in a waveguide Bragg grating prism based true time-delay beamforming module

Phased array antennas (PAAs) is an enabling technology in high-performance radars and wireless communications systems. The technique of photonic true time-delay (TTD) beamforming for these antennas has been studied intensively for the last few years and is considered as a key technique for wideband applications. In this paper, the effects of chromatic dispersion on a photonic TTD beamforming module are presented for the first time. The simulation results consider a true time-delay (TTD) beamforming network using a Bragg grating prism (BGP) on Ge-doped silica-on-silicon planar integrated optical waveguide. The effect of chromatic dispersion is considered on a true time-delay module using chirped Bragg gratings to introduce the time delays