We review our recent experiment on the Terabit-class coherent optical communication using a photonics integrated circuit-based optical amplifier. The 25.6-Tb/s 16-channel wavelength-division multiplexed (WDM) transmission (over 81-km fiber) proved the potential of such on-chip amplification for future coherent applications.
A silicon optical electro-absorption modulator (EAM) operating at a high speed and low voltage was achieved by using a Schottky diode in the C-band (1530 nm ~ 1570 nm). The optical modulation is demonstrated by the intensity change of guiding light due to the free-carrier absorption in the semiconductor to change its absorption coefficient, not conventional interference effects. The proposed EAM has lateral metal-semiconductor (MS) junctions that aid in maximizing the free carrier injection and extraction by a Schottky contact on the rib waveguide center. The rib waveguide structure of the modulator on the standard 220-nm silicon-on-insulator (SOI) platform has an etch depth of 80 nm and a width of 450 nm for the single-mode operation. The center of the rib waveguide is lightly doped with 1015 cm-3 indium, where light is mostly confined. The sides are heavily doped with 1020 cm-3 indium to contribute to the optical absorption change in the center. The depletion width in the middle region was drastically changed by a Schottky contact with bias. This design allowed a high overlap between the optical mode and carrier density variations in the center of the waveguide. To achieve a high speed operation, the travelling-wave type electrodes were designed to allow copropagation of electrical and optical signals along the waveguide. The measured results demonstrated a broad operational wavelength range of 40 nm with a uniform 3.9 dB modulation depth for a compact 25 μm modulation length with 1 Vpp driving voltage. The travelling-wave type electrodes enabled the modulator operating up to 26 GHz with 12 GHz of 3-dB electrooptic bandwidth, experimentally.
We discuss the extension of Laguerre-Gaussian (LG) mode sorters to higher spatial mode counts. LG mode sorters based on multi-plane light conversion were recently demonstrated. The device consist of a cascade of phase planes separated by free-space propagation which performs a spatial decomposition in the Laguerre-Gaussian basis. Whereby an incoming beam, described by a basis of N LG modes is mapped onto a Cartesian array of N Gaussian spots in the output plane. Each spot in the array contains a particular LG spatial component of the original beam. Previously, LG mode sorters have been demonstrated supporting as many as 325 modes using 7 planes. In this paper we present a design for a device that supports 1035 modes corresponding with the first 45 degenerate mode groups using 14 planes. At the centre wavelength, the device has a theoretical insertion loss of 2.10dB. The lowest loss LG mode is -1.65dB and the highest loss LG mode is -3.22dB. The average crosstalk over all modes is 12.75dB. The worst-case mode has a crosstalk of 9.20dB.
Multi-plane light conversion is a method of performing spatial basis transformations using cascaded phase plates separated by Fourier transforms or free-space propagation. In general, the number of phase plates required scales with the dimensionality (total number of modes) in the transformation. This is a practical limitation of the technique as it relates to scaling to large mode counts. Firstly, requiring many planes increases the complexity of the optical system itself making it difficult to implement, but also because even a very small loss per plane will grow exponentially as more and more planes are added, causing a theoretically lossless optical system, to be far from lossless in practice. Spatial basis transformations of particular interest are those which take a set of spatial modes which exist in the same or similar space, and transform them into an array of spatially separated spots. Analogous to the operation performed by a diffraction grating in the wavelength domain, or a polarizing beamsplitting in the polarization domain. Decomposing the Laguerre-Gaussian, Hermite-Gaussian or related bases to an array of spots are examples of this and are relevant to many areas of light propagation in free-space and optical fibre. In this paper we present our work on designing multi-plane light conversion devices capable or operating on large numbers of spatial modes in a scalable fashion.
Multi-plane light conversion is a method of performing spatial basis transformations using cascaded phase plates separated by Fourier transforms or free-space propagation. In general, the number of phase plates required scales with the dimensionality (total number of modes) in the transformation. This is a practical limitation of the technique as it relates to scaling to large mode counts. Firstly, requiring many planes increases the complexity of the optical system itself making it difficult to implement, but also because even a very small loss per plane will grow exponentially as more and more planes are added, causing a theoretically lossless optical system, to be far from lossless in practice. Spatial basis transformations of particular interest are those which take a set of spatial modes which exist in the same or similar space, and transform them into an array of spatially separated spots. Analogous to the operation performed by a diffraction grating in the wavelength domain, or a polarizing beamsplitting in the polarization domain. Decomposing the Laguerre-Gaussian, Hermite-Gaussian or related bases to an array of spots are examples of this and are relevant to many areas of light propagation in free-space and optical fibre. In this paper we present our work on designing multi-plane light conversion devices capable or operating on large numbers of spatial modes in a scalable fashion.
Silicon photonics has undergone significant development in the last decade with some commercial successes for optical transceivers in telecommunication and data center applications. Here, we review and discuss the most successful silicon photonics devices which have been already implemented in the products, the remaining device challenges in the coming 400G transceivers, and the future of silicon photonics.
We have tuned the lasing wavelength of a quantum dot laser diode (QDLD) by a thermal treatment. The InGaAs QDLD
structure for 980 nm wavelength applications was grown by molecular beam epitaxy using the Stranski-Krastanov
growth mode. The room temperature photoluminescence (PL) of a QDLD showed the ground state (GS) and excited
state (ES) at the wavelengths at 993 and 946 nm, respectively. The 100 μm-wide and 4 mm-long broad area QDLD
showed the lasing wavelength of 963 nm attributed to the ES of QDs with higher gain. After the thermal treatment at
800 °C for 3 minutes with 300 nm-thick SiO2 capping layers, the PL intensity of the GS increased, which caused the
enhanced GS gain. The enhanced GS gain is thought to the attribution to the decreased carrier trapping due to the
defects quenching. As a result, we could control the lasing wavelength of the QDLD from a wavelength of 963 nm to a
wavelength of 980 nm. Moreover, the performances of these QDLDs have been discussed. This post-growth technique
can be used to enhance the performances of the optoelectronic devices based on quantum dot.
We demonstrated the room temperature lasing of GaAs-based 1.3 μm quantum-dot laser diode (QDLD) grown by atomic layer epitaxy (ALE). The active region of a QDLD consists of 3-stacked InAs quantum-dots (QDs) in an In0.15Ga0.85As quantum well (dots-in-a-well: DWELL), which was grown by molecular beam epitaxy (MBE). For advanced performances of QDLD, the high-growth-temperature spacer layer and p-type modulation doping were applied to QDLD active region. We fabricated ridge waveguide structure LDs which had 10 ~ 50 μm ridge width with several cavity lengths and applied a high reflection (HR) coating on one-sided mirror facet. The threshold current density was 95 A/cm2 under a pulsed operation and 247 A/cm2 under a CW operation, respectively. The lasing wavelength was 1.31 μm under a pulsed operation condition and 1.32 μm under a CW operation at room temperature. The QDLD showed a simultaneous lasing and a state switching to the higher-order state. The lasing wavelength switching from the ground state to the excited state depends on the cavity length, the injection current and operating temperature.
We have investigated the characteristics of GaAs-based 1.3 μm quantum-dot laser diode (QDLD) with Al0.7Ga0.3As cladding layers. The active region of QDLD consists of 3-stacked InAs quantum-dots (QDs) in an In0.15Ga0.85As quantum well (dots-in-a-well: DWELL), which was grown by molecular beam epitaxy (MBE). For advanced performances of QDLD, the high-growth-temperature spacer layer and p-type modulation doping were applied to QDLD active region. We fabricated ridge waveguide structure LDs which had 10 ~ 50 μm ridge width with several cavity lengths and applied a high reflection (HR) coating on one-sided mirror facet. The threshold current density was 155 and 95 A/cm2 for a 2000 μm-long as-cleaved and a 1500 μm-long HR coated LDs, respectively. The lasing wavelength was 1.31 μm from the ground state transition, under a pulsed operation condition (0.1%) at room temperature. The QDLD showed simultaneous lasing at 1.31 μm and 1.23 μm from the ground state (GS) and the excited state (ES), respectively. The lasing wavelength switching from the GS to the ES depends on the cavity length, the injection current and operating temperature.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.