Abstract
In Ref. [10], 60-wavelength DFB laser arrays with a π-equivalent phase shift (π-EPS) were designed and fabricated in two wafers. For all the laser arrays, the mean lasing wavelength residuals of 83.3% of the lasers are within ± 0.20 nm, and 93.5% are within ± 0.30 nm. Lasers with a wavelength deviation of > 0.50 nm are less than 1.0% of the total laser count. The single-longitudinal-mode (SLM) yield of lasers from the seven arrays are 98.3%, 100%, 100%, 100%, 98.3%, 93.3% and 100% respectively.
As shown in Fig. 1, the standarddeviationis 0.159 nm, which means 68.26% of the laser wavelengths are lied within ± 0.159 nm. The detailed lasing spectrum of one array was randomly selected. Its wavelength spacing is 0.8 nm.
Figure 1.(Color online) (a) Frequency count of wavelength residual (871 lasers) and (b) measured lasing spectra of one 60-channel array.
From the above experimental results, it can be seen that low-cost high-channel-count and high precision channel spacing MLAs can be obtained by REC technique. It also implies that the two great obstacles to manufacture MLAs for very-large-scale PICs, namely poor wavelength accuracy and the low yield, which have impeded progress for nearly three decades, have been essentially overcome.
An effective and low-cost method is to integrate multi-wavelength laser array (MLA) and switch between wavelengths by turning on/off individual lasers. The DFB lasers are very stable against temperature variations and the speed of electronics is only a few nanoseconds, making it possible to stabilize the wavelength within tens of nanoseconds. The proposed method is an M × N DFB laser matrix shown in Fig. 2. It can cover wide tuning range and the wavelength can be switched quickly by turning on/off individual lasers using high speed switching driving circuit. Because for a wideband fast tunable laser, there are at least 40-wavlength array, the precision PICs will be very important.
Figure 2.(Color online) Schematic of an
Because up to now, both the semiconductor processes and the silicon lasers are very difficult for commercial LS-PICs, another possible way should be pursued, Photonic wire bonding (PWB) is a technique developed at the Karlsruhe Institute of Technology (KIT) of Germany in which photonic waveguides are written with an ultrafast laser into a photoresist material via two-photon lithography[
The combination of LS precision REC laser arrays and PWB may is a good way to LS-PICs, as Fig. 3 shows. The modulators and passive waveguides can be made based on silicon photonics.
Figure 3.(Color online) Schematic of an LS-PICs based on the combination of LS precision REC laser arrays and PWB.
Ruiqin Jin
Ruiqin Jin is a senior editor of Journal of Semiconductors.
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