We propose a compact polarization diversity optical circuit using silica waveguides and photonic crystal waveplates. By setting these circuits at the front and rear of the silicon optical devices, the polarization dependence of the silicon devices can be suppressed. Photonic crystals can be produced artificially using nanolithography, so that the retardation and orientation of the photonic crystal waveplate can be locally varied on a single chip. This enables to dramatically reduce the size of the polarization diversity circuit, which consists of a 1x2 multimode interference (MMI) coupler, two arm waveguides with quarter-waveplates (QWPs), a 2x2 MMI coupler, and output waveguides with half-waveplates (HWPs). The input light, including the transverse electric (TE) and transverse magnetic (TM) modes, is split by the 1x2 MMI coupler. The optical axes of the two QWPs, spaced 125 μm apart, are set to be orthogonal to each other, so that the phases of the TE modes in the two arm waveguides differ by 90 degrees, and those of the TM modes differ by -90 degrees. The TE mode and the TM mode are separated at the outputs of the 2x2 MMI coupler, and the polarization of the light at one of the outputs is aligned to that at the other output by the HWP. In this paper, we designed a 4x8 polarization diversity circuit for a 4x4 silicon optical switch.
Processing ultra-fast optical signals without optical/electronic conversion is in demand and time-to-space conversion has
been proposed as an effective solution. We have designed and fabricated an arrayed-waveguide grating (AWG) based
optical spectrum control circuit (OSCC) using silica planar lightwave circuit (PLC) technology. This device is composed
of an AWG, tunable phase shifters and a mirror. The principle of signal processing is to spatially decompose the signal’s
frequency components by using the AWG. Then, the phase of each frequency component is controlled by the tunable
phase shifters. Finally, the light is reflected back to the AWG by the mirror and synthesized. Amplitude of each
frequency component can be controlled by distributing the power to high diffraction order light. The spectral controlling
range of the OSCC is 100 GHz and its resolution is 1.67 GHz.
This paper describes equipping the OSCC with optical coded division multiplex (OCDM) encoder/decoder functionality.
The encoding principle is to apply certain phase patterns to the signal’s frequency components and intentionally disperse
the signal. The decoding principle is also to apply certain phase patterns to the frequency components at the receiving
side. If the applied phase pattern compensates the intentional dispersion, the waveform is regenerated, but if the pattern
is not appropriate, the waveform remains dispersed. We also propose an arbitrary filter function by exploiting the
OSCC’s amplitude and phase control attributes. For example, a filtered optical signal transmitted through multiple
optical nodes that use the wavelength multiplexer/demultiplexer can be equalized.
We present a novel Brillouin time domain analysis configuration for monitoring parallel fiber networks. By employing branch length manipulation, the new probe pulse arrangement improves the system dynamic range compared with a previously reported approach that uses a single pair of pump and probe pulses. This technique is promising in parallel fiber sensing that enhances the system reliability.
We have proposed an optical spectrum control circuit that realizes various kinds of signal processing in the optical
domain using a silica-based planar lightwave circuit including arrayed-waveguide gratings. In order to obtain a flat
transmission spectrum required for processing an optical signal that has a continuous spectrum, the number of the
spectral output waveguides is set more than the number of waveguides in the waveguide array. In this study, we
demonstrated a phase error compensation and obtained the flat transmission spectrum with ripples below 0.9 dB. We
also demonstrated a tunable bandwidth operation as an example of the spectral amplitude control and a variable pulse
delay operation as an example of the spectral phase control, respectively. In the tunable bandwidth operation, the passband
characteristic of the minimum bandwidth of 5-GHz and tunable pass-band characteristics with different center
frequencies with about 20-dB extinction ratio were obtained. In the variable delay operation, pulse delays equal to
calculated values could be observed with some phase settings.
Silica waveguide planar lightwave circuit (PLC) technology is very useful for fabricating compact and high performance
optical devices for optical communication. Wavelength multiplexers and optical switches for ROADM and OXC are still
being developed to improve performance further. New devices for an advanced modulation format can also be fabricated
with PLC technology.
We review the athermalization techniques that have been proposed for AWGs and discuss the advantages and disadvantages provided by each approach. We then describe our recent progress on the design and fabrication of a silica-based athermal AWG with a 1.5%-▵ waveguide and report its compactness and excellent optical characteristics including its extremely low insertion loss.
We review recent progress on optical switches that employ silica-based planar lightwave circuits (PLC) including a 16 x 16 matrix switch, a 1 x 128 switch, an 8-channel 1 x 8 switch array, and a 32-channel 2 x 2 switch array. These switches are composed of silica-based waveguides and have a solid-state structure with no moving parts, thus they exhibit low insertion loss, high repeatability, and excellent long-term reliability. We also describe IC-on-PLC technology, where IC chips are integrated on the PLC surface for higher functionality and greater compactness. We report the results of reliability tests on the PLC switches, and show that they can put to practical use.
Silica-based planar lightwave circuits (PLC) are key components of functional devices designed for use in optical fiber communication systems because, compared with bulk optics devices, they offer compactness, excellent stability and reliability in addition to high functionality. This talk reviews the current status of PLC development. The fabrication process, basic characteristics, packaging and reliability are presented, many device applications are described, and experimental results related to optical switches, interleave filters, chromatic/polarization dispersion compensators, gain spectrum equalizers and wavelength multiplexers are reported. Finally, the history of PLC development is summarized, and future target devices are described along with the kind of development needed for such devices designed for use in the next generation of optical communication systems.
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