Hitless and gridless reconfigurable optical add drop (de)multiplexer based on looped waveguide sidewall Bragg gratings on silicon

Abstract

Reconfigurable optical add-drop filters in future intelligent and software controllable wavelength division multiplexing networks should support hitless wavelength switching and gridless bandwidth tuning. The hitless switching implies that the central wavelength of one channel can be shifted without disturbing data transmissions of other channels, while the gridless tuning means that the filter bandwidth can be adjusted continuously. Despite a lot of efforts, very few integrated optical filters simultaneously support the hitless switching of central wavelength and the gridless tuning of bandwidth. In this work, we demonstrate a hitless add-drop filter with gridless bandwidth tunability on the silicon-on-insulator (SOI) platform. The filter comprises the two identical multimode anti-symmetric waveguide Bragg gratings (MASWBG) which are connected to a loop. The phase apodization technique is utilized to weaken the intrinsic sidelobe interference of grating-based devices. By sequentially manipulating central wavelengths of the two MASWBGs with the thermo-optical effect, we can reconfigure the spectral response of the filter gridlessly and hitlessly. Specifically, the central wavelength of the device is shifted by 14.5 nm, while its 3 dB bandwidth is tuned from 0.2 nm to 2.4 nm. The dropping loss and the sidelobe suppression ratio (SLSR) are dependent on the bandwidth selected. Measured variation ranges of dropping loss and SLSR are from -1.2 dB to -2.5 dB and from 12.8 dB to 21.4 dB, respectively. The hitless wavelength switching is verified by a data transmission measurement at a bit rate of 25 Gbps.

Silicon and silicon nitride based bilayer polarization-insensitive optical filter

“…In order to suppress the sidelobes, the lateral-shift apodization [7][8] is introduced. The lateral shift of corrugation of the gratings are modulated with a Gaussian function of the position z in the propagation direction.…”

“…An ideal WDM filter requires a flat-passband and broad bandwidth. The Bragg grating filter [6][7][8][9] is a promising candidate due to its unique feature of flat-top response, but it still faces the problem of polarization sensitivity. In the long-range optical fiber transmission system, the polarization of the light signal becomes random.…”

Inverse design of the multimode Bragg grating based on time-domain layer peeling method

“…The ADC work as mode (de)multiplexers including two tapered waveguides [17], waveguide widths of the adiabatic directional couplers are chosen to be ω1 = 0.6 µm, ω2 = 0.45 µm, ω3 = 1.2 µm, and ω4 = 0.1 µm, the coupling length and the gap are 200 µm and 0.12 µm. The width of a multimode waveguide in the filter is chosen to be 1.2 µm to support TE1 mode, as well as to get a large feature size.…”

“…However, the single-mode waveguide grating still cannot overcome the insertion loss of signal separation and the too small feature size. However, multimode waveguide Bragg gratings (MWBGs) can achieve lossless separation of reflected signal and incident signal, the wider multimode waveguide is easy to achieve a smaller coupling coefficient without too small feature size [16,17]. Although many efforts have been done, the LP algorithm suitable for multimode Bragg gratings still needs to be demonstrated.…”

Elimination of the zeroth order for four-port power separation by T-ridge metamaterial

“…At present, gratings are widely used in fiber-optic communications [6][7][8], lasers [9][10][11][12], optical image processing [13][14][15] and optical sensors [16][17][18][19]. Moreover, sub-wavelength grating structures are expected to have important applications in the fields of polarizers [20,21], wave plates [22] and spatial-optical couplings [23]. Gratings with different structures can achieve various functions under different incident conditions [24][25][26][27], and many researchers are working on this.…”