Optical devices based on silicon photonic technology are very important as supporting current and future communication
systems in terms of their scale of integration and productivity. Although various devices have been proposed and realized
using silicon photonics technology, this paper describes an optical path switch combining a large number of 2×2-unit-switches
loaded with electrical heaters on a Mach-Zehnder interferometer (MZI). We have been developed 8×8 and
32×32 optical matrix switches, which employ a path-independent-insertion-loss (PILOSS) configuration that has a
feature of the same device count on the any path of the connection. The PILOSS structure has a feature of Strictly-nonblocking,
which can connect any input port to any output port without changing existing connections when making a
new connection.
Each heater of the optical switch is driven by pulse-width-modulation (PWM) generated by a Field Programmable Gate
Array (FPGA). The calibration of the pulse width according to the 2×2-unit switch state (Cross or Bar) is performed on
all of the MZIs in advance, and the values are stored in a table of the FPGA. Separately, Cross / Bar state tables
corresponding to the connection pattern of the optical input port and output port are prepared, and the pulse width
switching according to the state table is simultaneously performed based on a switching command from the upper layer
controller.
It takes a certain amount of time to change the heater temperature of the MZI arm for switching. However, it is possible
to shorten the switching time by applying a signal named “Turbo pulse” for a short term at the transition. When the
temperature is raised by the heater, the switching can be speeded-up by applying a continuous high-level voltage to the
heater temporarily. Even in the case of the temperature drops, the switching time can be accelerated by applying a
continuous high-level voltage to the heater on the other arm of the MZI. The switching time, which was actually 30μs
without Turbo pulse, could be reduced to 2.5 μs with Turbo pulse.
The fabricated silicon photonics switch chip was mounted to the chip-carrier, assembled on a printed circuit board, and
housed in a 19-inch wide 1-rack unit (RU) height blade. In addition to measuring the various characteristics of the device
in our laboratory, it has also been installed and operated at the telecommunication carrier's collocation space to confirm
long-term operation in the field. This shows that the technology related to the large-scale silicon photonics devices
shown here can be adopted to practical use.
Intra-datacenter traffic is growing more than 20% a year. In typical datacenters, many racks/pods including servers are interconnected via multi-tier electrical switches. The electrical switches necessitate power-consuming optical-to- electrical (OE) and electrical-to-optical (EO) conversion, the power consumption of which increases with traffic. To overcome this problem, optical switches that eliminate costly OE and EO conversion and enable low power consumption switching are being investigated. There are two major requirements for the optical switch. First, it must have a high port count to construct reduced tier intra-datacenter networks. Second, switching speed must be short enough that most of the traffic load can be offloaded from electrical switches. Among various optical switches, we focus on those based on arrayed-waveguide gratings (AWGs), since the AWG is a passive device with minimal power consumption. We previously proposed a high-port-count optical switch architecture that utilizes tunable lasers, route-and-combine switches, and wavelength-routing switches comprised of couplers, erbium-doped fiber amplifiers (EDFAs), and AWGs. We employed conventional external cavity lasers whose wavelength-tuning speed was slower than 100 ms. In this paper, we demonstrate a large-scale optical switch that offers fast wavelength routing. We construct a 720×720 optical switch using recently developed lasers whose wavelength-tuning period is below 460 μs. We evaluate the switching time via bit-error-ratio measurements and achieve 470-μs switching time (includes 10-μs guard time to handle EDFA surge). To best of our knowledge, this is the first demonstration of such a large-scale optical switch with practical switching
time.
Deployment of digital coherent transmission technologies to metro networks drives the use of higher-order modulation formats such as PDM-16QAM and downsizing of optical transceivers. A narrow-linewidth (<300 kHz) tunable laser with high output power (>+17 dBm) is very attractive for such purposes, not only because it can compensate for the modulation loss increase caused by a high-peak-to-average ratio of the electrical driving signal of higher-order modulation formats, but also because it can be shared between transmitter and receiver saving the foot-print and power dissipation. This paper reviews the Tunable Distributed Amplification — Chirped Sampled Grating — Distributed Reflector (TDA-CSG-DR) laser being developed for metro application.
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