Nobuyuki Yokoyama

Ultra-compact 32 × 32 strictly-non-blocking Si-wire optical switch with fan-out LGA interposer

We demonstrate a 32 × 32 path-independent-insertion-loss optical path switch that integrates 1024 thermooptic Mach-Zehnder switches and 961 intersections on a small, 11 × 25 mm2 die. The switch is fabricated on a 300-mm-diameter silicon-on-insulator wafer by a complementary metal-oxide semiconductor-compatible process with advanced ArF immersion lithography. For reliable electrical packaging, the switch chip is flip-chip bonded to a ceramic interposer that arranges the electrodes in a 0.5-mm pitch land grid array. The on-chip loss is measured to be 15.8 ± 1.0 dB, and successful switching is demonstrated for digital-coherent 43-Gb/s QPSK signals. The total crosstalk of the switch is estimated to be less than -20 dB at the center wavelength of 1545 nm. The bandwidth narrowing caused by dimensional errors that arise during fabrication is discussed.

Low-loss, flat-topped and spectrally uniform silicon-nanowire-based 5th-order CROW fabricated by ArF-immersion lithography process on a 300-mm SOI wafer

We report superior spectral characteristics of silicon-nanowire-based 5th-order coupled resonator optical waveguides (CROW) fabricated by 193-nm ArF-immersion lithography process on a 300-mm silicon-on-insulator wafer. We theoretically analyze spectral characteristics, considering random phase errors caused by micro fabrication process. It will be experimentally demonstrated that the fabricated devices exhibit a low excess loss of 0.4 ± 0.2 dB, a high out-of-band rejection ratio of >40dB, and a wide flatband width of ~2 nm. Furthermore, we evaluate manufacturing tolerances for intra-dies and inter-dies, comparing with the cases for 248-nm KrF-dry lithography process. It will be shown that the 193-nm ArF-immersion lithography process can provide much less excess phase errors of Si-nanowire waveguides, thus enabling to give better filter spectral characteristics. Finally, spectral superiorities will be reconfirmed by measuring 25 Gbps modulated signals launched into the fabricated device. Clear eye diagrams are observed when the wavelengths of modulated signals are stayed within almost passband of the 5th-order CROW.

32×32 strictly non-blocking Si-wire optical switch on ultra-small die of 11×25 mm 2

We demonstrate an ultra-compact 32 × 32 path-independent-insertion-loss optical switch that integrates 1024 thermooptic MZ switches on SOI platform using ArF immersion lithography. On-chip loss of 19.7 dB and estimated crosstalk of -20 dB are achieved.

Ultrahigh-Q photonic crystal nanocavities fabricated by CMOS process technologies

We fabricated photonic crystal high-quality factor (Q) nanocavities on a 300-mm-wide silicon-on-insulator wafer by using argon fluoride immersion photolithography. The heterostructure nanocavities showed an average experimental Q value of 1.5 million for 12 measured samples. The highest Q value was 2.3 million, which represents a record for a nanocavity fabricated by complementary metal-oxide-semiconductor (CMOS)-compatible machinery. We also demonstrated an eight-channel drop filter with 4 nm spacing consisting of arrayed nanocavities with three missing air holes. The standard deviation in the drop wavelength was less than 1 nm. These results will accelerate ultrahigh-Q nanocavity research in various areas.

Evaluation of the phase error in Si-wire arrayed-waveguide gratings fabricated by ArF-immersion photolithography

The phase errors in 100-GHz spacing, 8-ch, Si-wire arrayedwaveguide gratings (AWG) fabricated by ArF-immersion photolithography were measured by the frequency-domain interference method. To our knowledge, this is the first time phase error measurements in a Si-wire AWG have been performed. By comparing the reconstructed transmission spectrum to the directly measured spectrum, the accuracy of this phase error measurement was confirmed. The average phase error in the AWGs on 6 chips was 0.27π radian, and this value is equivalent to a fluctuation in the effective refractive index of 1.1 × 10−4.

A 200-GHz spacing, 17-channel, 1×2 wavelength selective switch using a silicon arrayed-waveguide grating with loopback

A 200-GHz spacing, 17-channel, 1×2 wavelength selective switch was fabricated using silicon wire waveguides. An arrayed-waveguide grating with loopback is used to configure the 1×2 wavelength selective switch. The chip size was only 2.8 mm × 6.5 mm. The minimum and the maximum losses of the wavelength selective switch were 21 dB and 26 dB, respectively. The minimum and the maximum crosstalks were -21 dB and -2 dB, respectively.

Optimum waveguide-core size for reducing device property distribution of Si-wire waveguide devices

We investigated the waveguide-core size distribution of ring resonators fabricated on a 300 mm silicon-on-insulator (SOI) wafer using a CMOS-compatible process featuring ArF immersion lithography. These ring resonators were constructed in a Si-wire waveguide with a standard core size of 400 nm width and 220 nm height. The group refractive indices of the waveguide were derived from the transmission spectra of the ring resonators. From the deviation of these group refractive indices, the waveguide-core width distribution was estimated to be 5 nm, and the waveguide-core height distribution was estimated to be 1 nm. Moreover, the device property distribution of various Si-wire waveguide depended on the estimated fabrication error was calculated. The waveguide core with the smallest device property distribution had a 540 nm width and a 160 nm height, and this waveguide has a device property distribution of 2/3 value compared with the standard core size.

Integrated silicon photonic wavelength-selective switch using wavefront control waveguides

A wavelength selective switch (WSS) can route optical signals into any of output ports by wavelength, and is a key component of the reconfigurable optical add/drop multiplexer. We propose a wavefront control type WSS using silicon photonics technology. This consists of several arrayed waveguide gratings sharing a large slab waveguide, wavefront control waveguides and distributed Bragg reflectors. The structure, design method, operating principle, and scalability of the WSS are described and discussed. We designed and fabricated a 1 × 2 wavefront control type WSS using silicon waveguides. This has 16 channels with a channel spacing of 200 GHz. The chip size is 5 mm × 10 mm. The switching operation was achieved by shifting the phase of the light propagating in each wavefront control waveguide, and by controlling the propagation direction in the shared large slab waveguide. Our WSS has no crossing waveguide, so the loss and the variation in loss between channels were small compared to conventional waveguide type WSSs. The heater power required for switching was 183 mW per channel, and the average extinction ratios routed to Output#1 and Output#2 were 9.8 dB and 10.2 dB, respectively.

Low-loss and flatband silicon-nanowire-based 5th-order coupled resonator optical waveguides (CROW) fabricated by ArF-immersion lithography process on a 300-mm SOI wafer

We present flatband, low-loss and low-crosstalk characteristics of Si-nanowire-based 5th-order coupled resonator optical waveguides (CROW) fabricated by ArF-immersion lithography process on a 300-mm silicon-on-insulator (SOI) wafer. We theoretically specified why phase controllability over Si-nanowire waveguides is prerequisite to attain desired spectral response, discussing spectral degradation by random phase errors during fabrication process. It was experimentally demonstrated that advanced patterning technology based on ArF-immersion lithography process showed extremely low phase errors even for Si-nanowire channel waveguides. As a result, the device exhibited extremely low loss of <0.2dB and low crosstalk of <-40dB without any external phase compensation. Furthermore, fairly good spectral uniformity for all fabricated devices was found both in intra-dies and inter-dies. The center wavelengths for box-like drop channel responses were distributed within 0.4 nm in the same die. This tendency was kept nearly constant for other dies on the 300-mm SOI wafer. In the case of the inter-die distribution where each die is spaced by ~3cm, the deviation of the center wavelengths was as low as ±1.8 nm between the dies separated by up to ~15 cm. The spectral superiority was reconfirmed by measuring 25 Gbps modulation signals launched into the device. Clear eye openings were observed as long as the optical signal wavelengths are stayed within the flat-topped passband of the 5th-order CROW. We believe these high-precision fabrication technologies based on 300-mm SOI wafer scale ArF-immersion lithography would be promising for several kinds of WDM multiplexers/demultiplexers having much complicated configurations and requiring much finer phase controllability.

Annealing Condition Optimization of Sputtered Amorphous Carbon for Large-grain, Multi-layer Graphene

In order to obtain large-grain, multi-layer graphene (MLG), we have investigated the effect of a catalyst and annealing ambient gas on the growth of MLG fabricated by post-annealing sputtered amorphous carbon. Higher quality graphene sheets stacked parallel to the SiO2/Si substrate plane were obtained when using a Co catalyst layer and annealing in N2 ambient gas. Moreover, the grain size of the carbon film was measured to be about 400 nm. By comparing these results with the results obtained with highly oriented pyrolytic graphite (HOPG), we speculated that the grain boundary is one of the reasons why the resistance of our film is still high.