Fig. 1. Scheme of the proposed integrated grating-assisted contradirectional couplers.

Fig. 2. (a) Simulated transmission spectra and (b) group-delay spectra for chirped Bragg gratings with different apodization filters applied. L=710.4  μm, wg=50  nm, w1=570  nm, w2=470  nm, Δw=20  nm, gap=180  nm.

Fig. 3. (a) Measured transmission spectra of different grating periods with w1=570  nm, w2=470  nm, and Δw=20  nm. (b) Measured transmission spectra of different grating periods with w1=600  nm and w2=500  nm. (c) Measured transmission spectra of different Δw with w1=570  nm, w2=470  nm, and Λ=296  nm. (d) Measured transmission spectra of unapodized and asymmetric apodized Bragg gratings with w1=570  nm, w2=470  nm, Λ=296  nm, and Δw=20  nm. (e) SEM image of apodized Bragg gratings. (d) SEM image of unapodized Bragg gratings.

Fig. 4. (a) Schematic of type I and type II heaters. (b) Spectral drift as a function of the applied voltage of the two types of heaters. Micrographs of (c) type I and (d) type II heaters.

Fig. 5. Experimental setup of the time-delay measurement. TLS, tunable laser source; PC, polarization controller; RF, radio frequency; IM, intensity modulator; EDFA, erbium-doped fiber amplifier; ATT, attenuator; OSC, oscilloscope.

Fig. 6. Measured spectral responses of (a) unapodized and (b) asymmetric apodized fabricated devices. Measured group delay lines of (c) unapodized and (d) asymmetric apodized fabricated devices.

Fig. 7. 10 GHz optical waveforms with different wavelengths after passing through the apodized device. Gray dot curves represent input waveforms; red curves represent delayed waveforms.

Fig. 8. (a) Schematic of a novel structure combining the grating-assisted contradirectional couplers with an ultra-compact reflector. (b) Measured spectral responses and (c) group delay lines of the fabricated device at different voltages. (d) Micrograph of the fabricated device.

Fig. 9. 5 GHz optical waveforms with different wavelengths after passing through the gratings with an ultra-compact reflector. Gray dot curves represent input waveforms; red curves represent delayed waveforms.