150 GHz of thermo-optic tuning in direct UV written silica-on-silicon planar Bragg grating

Abstract

An integrated direct UV written apodised planar Bragg grating reflector with 154 GHz (1.23 nm) of thermo-optic tuning in the C-band and a response speed 31 GHz/ms is demonstrated. The degree and speed of tuning of the fabricated device indicates potential application in dynamic optical networks, as an optical add-drop multiplexer.Introduction: An optical add-drop multiplexer (OADM) is a fundamental device in dense wavelength division multiplexing (DWDM) networks. Control over the spectral response of an OADM is essential as small amounts of spectral degradation can drastically degrade their filtering performance; this is especially true for filter misalignments and cascaded operations [1]. Selectively adding or dropping particular wavelengths to and from a network can be attained using Bragg gratings, which can be tuned using electro-optic, thermo-optic or strain-optic means. The majority of literature covering tuned Bragg gratings describes devices in fibre [2,3]. However, fibre based devices do not posses the integration advantages associated with planar technology.Thermo-optic tuning is widely used in integrated optics [4,5] and has been applied to several materials including silicon-on-insulator [6,7] and polymers [8]. The largest tuning ranges reported have been in materials with large thermo-optic coefficients. Polymers give 20 nm tuning [8] and silicon-on-insulator 18 nm tuning [7]. While alternative material systems offer large tuning ranges, there is an advantage in using silica-on-silicon technology as it is well established in telecom networks where it is used for AWGs, splitters and thermo-optic switches [9]. In addition, direct UV written devices can be spectrally engineered to give apodised gratings with small bandwidths (typically ,1 nm). Also, when tuning over only one channel spacing large tuning ranges are not essential. Typically channel spacings in DWDM networks are often 50 GHz, corresponding to 0.4 nm at 1550 nm wavelengths.This Letter demonstrates thermo-optic tuning of a silica-on-silicon direct UV written planar Bragg grating. The device presented can tune 154 GHz, corresponding to a wavelength shift of 1.23 nm at 1550 nm, which is over three times a typical DWDM channel spacing.Investigation of the response time shows that a shift of 31 GHz can be achieved in 1.02 ms. In this device individual adjacent gratings located 1 mm from the heating filament do not show any response, demonstrating that multiple gratings can be tuned on one chip without affecting others.

Integrated reconfigurable photonic filters based on interferometric fractional Hilbert transforms

“…Bulk heating experiments show that α + ς is approximately 10 pm/K in silica-on-silicon substrate in the 1550 nm wavelength region. This provides a tuning range of 154 GHz and a response speed of 31 GHz/ms [17]. In this work the thermal tuning of the micro heaters exhibits similar behaviors during the experiments.…”

“…It has been previously demonstrated that silica-on-silicon planar Bragg gratings fabricated by direct UV writing technique can be thermally tuned [17]. It shows that the phase shift ΔλB caused by thermal tuning is proportional to Bragg wavelength λB and can be expressed as :…”

Planarised optical fiber composite using flame hydrolysis deposition demonstrating an integrated FBG anemometer

“…Additionally a Bragg grating was defined away from bridge structure to monitor thermal fluctuations for the bulk chip. Both Bragg gratings were fabricated using direct UV writing (DUW) after the fiber was bound to the wafer [25][26][27] using FHD. FHD silica soot was formed through burning precursors of SiCl 4 , PCl 3 and BCl 3 at flow rates of 139, 31 and 70 sccm respectively, using the torch configuration illustrated in Fig.…”

High-Speed Interferometric FBG Interrogator With Dynamic and Absolute Wavelength Measurement Capability

“…In the next evolution of the system, we propose that the MZI is miniaturised by incorporating it onto a silicon photonics platform [12]. This should improve stabilisation and reduce the time taken to thermally tune the path difference to within tens of milliseconds [13].…”