We demonstrate the automatic thermal alignment of photonic components within an integrated optical switch. The WDM optical switch involves switching elements, wavelength de-multiplexers, interleavers and monitors each one needing independent control. Our system manages rerouting of channels coming from four different directions, each carrying 12, 200GHz spaced, wavelengths into eight add/drop ports. The integrated device includes 12 interleavers, which can act either as optical de-interleavers to split the optical signal into odd and even channels or as optical interleavers that recombine the odd and even channels coming from the switching matrix. Integrated Ge photodiodes are placed in key positions within the photonic integrated circuit (PIC) are serve for monitoring. An electronic integrated circuit (EIC) drives the photonic elements by means of dedicated heating circuits (824 on-board heater control cells, 768 for the switching elements and 56 for the interleavers and the mux/de-mux) and reads out the Ge diodes photocurrent through TIAs. We applied a stochastic optimization algorithm to align the spectral response of the interleavers to the ITU grid. We exploit the thermo-optic effect to shift the interleavers pass-band in a desired spectral position. The interleavers are provided with dedicated metallic heaters that can be operated in order to tune the interleaver response, which is typically misaligned due to fabrication inaccuracies. The experimental setup is made of a tunable laser coupled with one input port of optical switch. The optimization algorithm is implemented via a software to drive the EIC till finding the best heating configuration (on the two branches of the interleaver) on the basis of the monitor diode-feedback. This way, the even and odd wavelengths input in the interleaver are directed toward the wanted lines within the switching matrix. Our method has been used for aligning the micro-ring based switching elements in the PIC as well. In that case, the integrated Ge photodiodes have been used to align the photonic components in the PIC in order to enable different pathways for the routing or the broadcasting operation of the optical switch. With no bias applied to the heaters of the switching elements, the optical signal is expected to be maximum at the through port. When the micro-ring heaters are biased, the feedback controller finds the best set of heating values that minimize the optical power at the through port of the switching node. This way, the optical signal is coupled in the drop port and the node is enabled for switching. The algorithm, implemented in LabVIEW, converges over multiple instances and it is robust against stagnation. This work aims at enabling the automatic reconfiguration/restoration of the whole WDW optical switch.
We report a white-light Mach-Zehnder interferometry method for an accurate measurement of spectral distribution of the
chromatic dispersion coefficient of very short optical waveguides over a wavelength range of 1520~1560 nm. The
chromatic dispersion curve of a 7.6 mm long silicon nano-waveguide of 400 nm width and 250 nm height was
successfully measured by confirming the method with standard single-mode fibers up to 3 cm length, for which its total
chromatic dispersion is as small as 0.51 fs/nm. This method will be very useful for determination of chromatic dispersion
profile of compact nanowaveguide devices.
Recently, we developed a wavelength converter, a 16-arrayed electro-optic (EO) Mach-Zehnder (MZ) modulator, polarization adjustable and athermal arrayed waveguide gratings (AWGs), and a wavelength channel selector by using all polymers. We designed and fabricated periodically poled nonlinear optical (NLO) polymer waveguides for the wavelength converter. Difference-frequency generation (DFG) process with a quasi-phase-matching (QPM) scheme was used. An all polymer-based wavelength channel selector composed of 16-channel EO polymer modulator array between two polymer AWGs is proposed and fabricated using chip-to-chip bonding of the three optical polymeric waveguide devices. For this, the 16-arrayed polymeric optical modulator and AWGs are respectively fabricated using EO and low-loss optical polymers. For these two-typed devices, we have synthesized new side chain NLO polymers and used low-loss optical polymers, designed and developed by ZenPhotonics, Inc. The developed these photonic devices were discussed in details from materials to packaging.