Alexandre Simard

Bragg gratings operating in reflection are versatile filters that are an important building block of photonic circuits but, so far, their use has been limited due to the absence of CMOS compatible integrated circulators. In this paper, we propose to introduce two identical Bragg gratings in the arms of a Mach-Zehnder interferometer built with multimode interference 2 x 2 couplers to provide a reflective filter without circulator. We show that this structure has unique properties that significantly reduce phase noise distortions, avoid the need for thermal phase tuning, and make it compatible with complex apodization functions implemented through superposition apodization. We experimentally demonstrate several Bragg grating filters with high quality reflection spectra. For example, we successfully fabricated a 4 nm dispersion-less square-shaped filter having a sidelobe suppression ratio better than 15 dB and an in-band phase response with a group delay standard deviation of 2.0 ps. This result will enable the fabrication of grating based narrowband reflective filters having sharp spectral responses, which represents a major improvement in the filtering capability of the silicon platform.

ABSTRACT form only given. Monolithic multiwavelength lasers are of great interest for many applications. They can be used as low-cost and compact multiwavelength sources for optical broadcasting in passive optical networks, for upconversion of multiple radio-over-fiber signals, for on-chip and inter-chip interconnections, and for mm or THz-wave generators. Several technologies and designs have been proposed to fabricate multiwavelength laser sources; however, the laser line spacing usually cannot be actively controlled. In this work, we propose a novel multiwavelength laser structure based on superimposed Bragg gratings on multiquantum well AlGalnAs-InP. This laser exhibits a comb of modes with a frequency spacing that can be tuned over 17 GHz.

Tunable millimeter wave generation using a dual-band fiber ... Y. Kim, AD Simard, P. Chrétien, and S. LaRochelle Centre d'optique, photonique et laser (COPL), Department of Electrical and Computer Engineering, Université Laval, Québec, Canada, G1V 0A6 larochel@gel. ...

Bandpass filters with square shape amplitude responses and well-controlled dispersion characteristics are achieved by accurate apodization of Bragg grating structures in silicon-on-insulator waveguides. For these devices, precise tailoring of their frequency response typically requires low coupling coefficients and relatively long on-chip propagation lengths. These challenges are addressed by implementing apodization by phase-modulation and using wider strip waveguides to reduce phase noise. This design approach is demonstrated with a dispersion-less narrowband filter and a chirped bandpass filter.

ABSTRACT Integrated optical filters with flexible and precisely tailored spectral responses are required for many applications in communication and sensing. Integrated Bragg gratings (IBG) in silicon-on-insulator (SOI) waveguides can provide these filtering characteristics on a low-cost platform but a major drawback is the need for long grating structures to obtain elaborate spectral responses, which can pose problem when small footprints are desired. A mean to overcome this problem is to fabricate IBGs in spiral-waveguides (Fig. 1-a)). As a result, the footprint of the device is drastically reduced. However, the curvature modifies the waveguide effective index and distorts the grating spectrum. In this work, we design and fabricate IBGs in spiral waveguides using 193 nm deep UV photolithography and successfully avoid this distortion by adding a phase term, Ω(z), to compensate the effective index perturbation, δn(R(z)), caused by the curvature profile, R(z).

ABSTRACT We show static and dynamic operation of a tunable, all-optical dual-stage swapper for spectral amplitude labels based on cross-gain modulation in semiconductor optical amplifiers in fiber ring lasers. 24dB switching on/off ratios are obtained.

ABSTRACT As data traffic increases on telecommunication networks, optical communication systems must adapt to deal with this increasing bursty traffic. Packet switched networks are considered a good solution to provide efficient bandwidth management. We recently proposed the use of spectra amplitude codes (SAC) to implement all-optical label processing for packet switching and routing. The implementation of this approach requires agile photonic components including filters and lasers. In this paper, we propose a reconfigurable source able to generate the routing codes, which are composed of two wavelengths on a 25 GHz grid. Our solution is to use a cascade of two chirped fibre Bragg gratings (CFBG) in a semiconductor fibre ring laser. The wavelength selection process comes from distributed phase shifts applied on the CFBG that is used in transmission. Those phase shifts are obtained via local thermal perturbations created by resistive chrome lines deposited on a glass plate. The filter resonances are influenced by four parameters: the chrome line positions, the temperature profile along the fibre, the neighbouring heater state (ON/OFF) and the grating itself. Through numerical modeling, these parameters are optimized to design the appropriate chrome line pattern. With this device, we demonstrate successful generation of reconfigurable SAC codes.

ABSTRACT Spectral responses of gratings in SOI are extracted using time windowing to eliminate parasitic reflections. Filtering high spatial frequencies of the phase profile, obtained by layer peeling, allows examination of the wafer thickness uniformity.

ABSTRACT Phase-sensitive photonic devices fabricated in silicon-on-insulator platform can have their response significantly modified by wafer height fluctuations. In this letter, we demonstrate a novel metrology technique for measuring on-chip thickness variations using long integrated chirped Bragg gratings. Thickness variations are recovered from the measurement of the complex transmission and reflection spectra using an inverse scattering algorithm. With 1-cm long sidewall gratings on 1.2- $mu text{m}$ wide waveguides, we measure waveguide height variations with nanometer-scale precision and tens of micrometer of longitudinal resolution. The results are confirmed by atomic force microscopy measurements.

A multiwavelength laser based on a super-structured Bragg grating is designed and fabricated on multiquantum well AlGaInAs-InP. This laser exhibits phase locking via mutual injection of the neighboring cavities assisted by four wave mixing. We present optical and electrical characterization of its emission regimes showing a complex dynamic behavior. More specifically, this paper focuses on a pulsed regime with a quasi-continuous tunable repetition rate from 32 GHz to 49 GHz.

1. Introduction In recent years, much research efforts has been devoted to the development of multiwavelength fiber lasers for applications to Wavelength Division Multiplexing (WDM) systems [1], optical fiber sensors [2] and so forth. Some of these applications require a dense ...

A major issue in the fabrication of integrated Bragg grating filters in highly confined waveguides is the average effective index fluctuations caused by waveguide dimension variations. Lateral variations are caused by the sidewall roughness created during the etching process while vertical variations are coming from the wafer silicon layer thickness non-uniformity. Grating spectral distortions are known to result solely from the low spatial frequency components of these variations. As a result, in this work, we present an experimental method to quantify such relevant spatial components by stitching a hundred high-resolution scanning electron microscope images. Additionally, we propose two techniques to reduce, in the design, the phase noise impact on integrated Bragg gratings without relying on fabrication process improvements. More specifically, we show that the use of hybrid multimode/singlemode waveguides reduce by more than one order of magnitude the effect of sidewall roughness on integrated Bragg gratings while we show that the fabrication of ultra-compact gratings in spiral waveguides mitigate the impact of the silicon layer thickness variations.

Over the last two decades, many filters requiring custom spectral responses were obtained from photo-inscribed fiber Bragg gratings because of the flexibility inherent to this technology. However, Bragg gratings in silicon waveguides have the potential to provide faster and more efficient tuning capabilities when compared to optical fiber devices. One drawback is that Bragg gratings filters with elaborate spectral amplitude and phase responses often require a long interaction length, which is not compatible with current integration trends in CMOS compatible photonic circuits. In this paper, we propose to make Bragg gratings in spiral-shaped waveguides in order to increase their lengths while making them more compact. The approach preserves the flexibility of regular straight grating structures. More specifically, we demonstrate 2-mm long gratings wrapped in an area of 200 µm x 190 µm without any spectral degradation due to waveguide curvature. Furthermore, we interleave three spiral waveguides with integrated gratings thereby tripling the density and demonstrate good phase compensation for each of them. Finally, we show that this approach is compatible with phase-apodization of the grating coupling coefficient.

ABSTRACT An accurate control of the apodization profile is still an issue for integrated Bragg grating filters fabricated in silicon-on-insulator because of the high modal confinement of these waveguides. In this letter, we present two fabrication-friendly apodization techniques that are compatible with deep UV lithography and can be used in mass-production of photonic-integrated circuits. These techniques are reliable even for weak effective index modulation amplitude, thus opening the door to the fabrication of long and elaborate grating structures.