Arbitrary waveform generation attracts a lot of interests in recent years because of its widely applications in many different fields. We have proposed and experimentally demonstrate two on-chip pulse shaper schemes for microwave and optical arbitrary waveform generation. These schemes are all fabricated on
the silicon-on-insulator (SOI) chips for its compactness and capability to integrate with electronics. The
two schemes based on finite impulse response (FIR). By thermally controlling the amplitude and phase
of each path, we can obtain different applications of arbitrary waveform generation. The pulse shaper of optical arbitrary waveform generation can be a programmable filter with central wavelength tunable,
bandwidth tunable and passband shape variable functions, and a high-order differentiator which may
obtain the first-order, second-order and third-order differentiations likewise. It can also implement several typical optical waveforms, such as the square waveform, triangular waveform, sawtooth waveform and Gaussian waveform. The pulse shaper for microwave arbitrary waveform generation can
obtain several microwave waveforms with the central frequency at 125GHz. Comparing with the proposed schemes by frequency shaping and frequency-to-time mapping, our schemes do not require any spectral dispersers or large dispersion mediums. And all units in our schemes are broad-band devices, so there is no bandwidth limitation in our schemes.
We propose and demonstrate optical true time delay using tapered SOI contradirectional couplers with single sidewallmodulated
Bragg gratings. The contradirectional couplers consist of two tapered rib waveguides with different width,
and the Bragg gratings are modulated in the inner sidewall of the wider one. The optical signal is launched from the wide
waveguide and coupled to the narrow waveguide through the Bragg gratings structure. Along the direction of light
propagation, the waveguide width varies linearly, so the reflection wavelength is different at different positions.
Therefore, linear delay line can be realized within the grating passband using the present structure. In the simulation,
grating period is 310nm and grating number is 2400, corresponding to the grating length of 744μm. Using 2.5D FDTD
simulation, the current structure can realize optical group delay of 20ps within bandwidth of 18nm. The proposed device
is fabricated on a 220nm SOI chip with Electron Beam Lithography (EBL) and Inductively Coupled Plasma (ICP)
etching. In the experiment, continuous light is modulated by 10GHz radio-frequency signal and travel through the chip,
which is finally detected by the oscilloscope. By adjusting the wavelength of input light, group delay of different
wavelength are recorded by the oscilloscope. The experimental results show that group delay of 28ps is realized within
the bandwidth of 20nm. In the end, the drift of the reflection spectrum and delay lines under different temperature are
analyzed. The reflection spectrum drifts 0.1nm/°C and causes redshift of the corresponding delay line.