Showing papers by "Takuro Fujii published in 2018"
TL;DR: In this paper, the III-V membrane thickness is increased to 350nm, which is close to the calculated critical thicknesses, and a direct modulation with a 50-Gbit/s non return to zero signal is demonstrated by increasing bias current up to 10mA.
Abstract: High demand exists for low operating energy optical links that use wavelength division multiplexing technologies in datacenter networks. Thus, we fabricate a directly modulated membrane distributed-reflector laser with low operating energy on a thermally oxidized silicon (Si) substrate. Because we use epitaxial growth to bury an active region on a directly bonded InP-based membrane, it needs to be kept within a critical thickness, which is related to the growth temperature and the thermal expansion coefficients of materials. In previous studies, we used 250-nm-thick structures, causing relatively large series resistance that limited device performance on such aspects as energy cost and output power. In this study, we increase the III–V membrane thickness to 350 nm, which is close to the calculated critical thicknesses. We achieve the same high crystal quality of multiquantum-wells found in our previous studies. The fabricated laser shows a differential resistance of 72 Ω and thermal resistance of 982 K/W. Thanks to a reduction in bias voltage, the laser can be directly modulated at 25.8 Gbit/s with an energy cost of 97 fJ/bit. In addition, due to a reduction in heat generation, direct modulation with a 50-Gbit/s non return to zero signal is demonstrated by increasing bias current up to 10 mA.
36 citations
11 Mar 2018
TL;DR: A driver modulator sub-assembly for beyond 100-GBd CDM is fabricated by employing an optimized electrode and a co-designed driver IC that exhibits an ultra-high bandwidth exceeding 67 GHz, which is sufficient for practical implementation.
Abstract: We fabricated a driver modulator sub-assembly for beyond 100-GBd CDM by employing an optimized electrode and a co-designed driver IC. The sub-assembly exhibits an ultra-high bandwidth exceeding 67 GHz, which is sufficient for practical implementation.
28 citations
12 Apr 2018
TL;DR: In this paper, the photonic-crystal waveguide reverse-biased photodetectors (PDs) were used for high-speed optical receivers, and they achieved 40 Gbit/s with high responsivity (0.88 A/W).
Abstract: Generally, reverse-biased photodetectors (PDs) are used for high-speed optical receivers. The forward voltage region is only utilized in solar-cells, and this photovoltaic operation would not be concurrently obtained with high efficiency and high speed operation. Here we report that photonic-crystal waveguide PDs enable forward-biased high-speed operation at 40 Gbit/s with keeping high responsivity (0.88 A/W). Within our knowledge, this is the first demonstration of the forward-biased PDs with high responsivity. This achievement is attributed to the ultracompactness of our PD and the strong light confinement within the absorber and depleted regions, thereby enabling efficient photo-carrier generation and fast extraction. This result indicates that it is possible to construct a high-speed and ultracompact photo-receiver without an electrical amplifier nor an external bias circuit. Since there is no electrical energy required, our estimation shows that the consumption energy is just the optical energy of the injected signal pulse which is about 1 fJ/bit. Hence, it will lead to an ultimately efficient and highly integrable optical-to-electrical converter in a chip, which will be a key ingredient for dense nanophotonic communication and processors.Generally, reverse-biased photodetectors (PDs) are used for high-speed optical receivers. The forward voltage region is only utilized in solar-cells, and this photovoltaic operation would not be concurrently obtained with high efficiency and high speed operation. Here we report that photonic-crystal waveguide PDs enable forward-biased high-speed operation at 40 Gbit/s with keeping high responsivity (0.88 A/W). Within our knowledge, this is the first demonstration of the forward-biased PDs with high responsivity. This achievement is attributed to the ultracompactness of our PD and the strong light confinement within the absorber and depleted regions, thereby enabling efficient photo-carrier generation and fast extraction. This result indicates that it is possible to construct a high-speed and ultracompact photo-receiver without an electrical amplifier nor an external bias circuit. Since there is no electrical energy required, our estimation shows that the consumption energy is just the optical energy of th...
12 citations
TL;DR: This report marks an important step towards realizing a nanolaser diode with a high cavity-QED effect, which is promising for use with on-chip densely integrated laser sources in photonic networks-on-chip combined with CMOS processors.
Abstract: Few-cell point-defect photonic crystal (PhC) nanocavities (such as LX and H1 type cavities), have several unique characteristics including an ultra-small mode volume (Vm), a small device footprint advantageous for dense integration, and a large mode spacing advantageous for high spontaneous-emission coupling coefficient (β), which are promising for energy-efficient densely-integratable on-chip laser light sources enhanced by the cavity QED effect. To achieve this goal, a high quality factor (Q) is essential, but conventional few-cell point-defect cavities do not have a sufficiently high Q. Here we adopt a series of modified designs of LX cavities with a buried heterostructure (BH) multi-quantum-well (MQW) active region that can achieve a high Q while maintaining their original advantages and fabricate current-injection laser devices. We have successfully observed continuous-wave (CW) lasing in InP-based L1, L2, L3 and L5 PhC nanocavities at 23°C with a DC current injection lower than 10 μA and a bias voltage lower than 0.9 V. The active volume is ultra-small while maintaining a sufficiently high confinement factor, which is as low as ~10−15 cm3 for a single-cell (L1) nanocavity. This is the first room-temperature current-injection CW lasing from any types of few-cell point-defect PhC nanocavities (LX or H1 types). Our report marks an important step towards realizing a nanolaser diode with a high cavity-QED effect, which is promising for use with on-chip densely integrated laser sources in photonic networks-on-chip combined with CMOS processors.
12 citations
TL;DR: In this paper, a new multicore fiber (MCF) receptacle for space division multiplexing (SDM) based transceiver applications was proposed, in which a compact fiber-bundle type fan-in/fan-out device was integrated for directly connecting MCF to LDs and PDs.
Abstract: We describe a new multicore fiber (MCF) receptacle for space division multiplexing (SDM) based transceiver applications, in which we integrated a compact fiber-bundle type fan-in/fan-out device for directly connecting MCF to LDs and PDs. We design the length of the fan-out fibers taking their bending stress into account to achieve a configuration with a smaller footprint. With the proposed receptacle, we develop a 100 Gb/s SDM transmitter based on a four-channel, 1.3 μm membrane laser array on Si, in which spot-size convertor (SSC) using inverse taper InP and SiON waveguides is integrated. Since the core size of SiON waveguide is much smaller than that of MCF, we utilize different fibers with optimized modal fields at each connection point and introduce thermally-expanded-core (TEC) fusion splicing to realize a low-loss connection between them. We achieve a pluggable connection between the lasers and 125 μm-cladding 4-core MCF in an LC connector. The developed receptacle maintained satisfactory laser characteristics including sufficient output power and clear eye openings for directly modulated 28 Gb/s NRZ signals. We also achieve an error-free transmission at a bit-error rate of less than 10−12 with a 500-m MCF transmission link for all 4 channels with simultaneous 4-channel operation.
11 citations
TL;DR: 20-μm-long twin-mirror membrane distributed-reflector (DR) lasers for chip-to-chip optical interconnects are demonstrated and single-mode lasing in a λ/4-phase shifted DFB mode at room temperature is achieved.
Abstract: We demonstrate 20-μm-long twin-mirror membrane distributed-reflector (DR) lasers for chip-to-chip optical interconnects. The lasers employ distributed Bragg reflectors (DBRs) at both ends of a 20-μm-long λ/4-phase shifted distributed feedback (DFB) section. We achieve single-mode lasing in a λ/4-phase shifted DFB mode at room temperature with a threshold current of 0.39 mA. The lasing wavelength remains stable while the injected current is varied, and it is determined by the λ/4 phase-shifted DFB. The modulation current efficiency is 11.4 GHz/mA1/2, which is measured by using relative intensity noise spectra. We also demonstrate the direct modulation of the DR lasers at a bit rate of 25.8 Gbit/s with an energy cost of 163 fJ/bit.
10 citations
13 May 2018
TL;DR: In this article, a nanocavity-based modulator is closely integrated with a nano-photodetector to form an ultracompact O-E-O converter.
Abstract: A nanocavity-based modulator is closely integrated with a nano-photodetector to form an ultracompact O-E-O converter. The femto-joule energy operation proves the opto-electronic integrability with a femto-farad capacitance, for the first time.
8 citations
11 Mar 2018
TL;DR: Heterogeneous integration of lasers and 200-nm-thick Si waveguides is the key to realizing high-performance transmitters.
Abstract: Heterogeneous integration of lasers and 200-nm-thick Si waveguides is the key to realizing high-performance transmitters. A 500-μm-long DFB laser on Si waveguide exhibits 4.6-mW fiber coupled output power at 25°C and lasing up to 130°C.
8 citations
11 Mar 2018
TL;DR: DMT transmissions are reported by directly modulating a single-mode membrane laser grown on an InP/SiO2/Si substrate, requiring only 28.2 mW for driving.
Abstract: We report DMT transmissions of 120-Gbps over 10-km SSMF (for SD-FEC) and 100-Gbps over 2-km (for HD-FEC), by directly modulating a single-mode membrane laser grown on an InP/SiO 2 /Si substrate, requiring only 28.2 mW for driving.
6 citations
11 Mar 2018
TL;DR: A multicore-fiber LC receptacle with a compact fan-in/fan-out as a new transceiver interface for connecting LDs and PDs and achieves low-loss coupling with the receptacle between a 4-core MCF and a laser array.
Abstract: We describe a multicore-fiber LC receptacle with a compact fan-in/fan-out as a new transceiver interface for connecting LDs and PDs. We achieve low-loss coupling with the receptacle between a 4-core MCF and a laser array.
5 citations
11 Mar 2018
TL;DR: A low-power compact 4-channel transmitter consisting of a 65-nm CMOS cascode shunt LD driver and flip-chip-bonded 1.3-μm LD-array-on-Si achieves 25-Gbps 2-km-long SSMF error-free operation for each channel.
Abstract: A low-power compact 4-channel transmitter consisting of a 65-nm CMOS cascode shunt LD driver and flip-chip-bonded 1.3-μm LD-array-on-Si achieves 25-Gbps 2-km-long SSMF error-free operation for each channel, with power consumption of 1.37 mW/Gbps.
30 Oct 2018
TL;DR: In this paper, an InP-based photonic-crystal laser is integrated with a Si waveguide by using direct bonding and buried regrowth technologies on an SOI substrate.
Abstract: An InP-based photonic-crystal laser is integrated with a Si waveguide by using direct bonding and buried regrowth technologies on an SOI substrate. The fabricated device exhibits a threshold current of 24 pA and a 7.3-fJ/bit energy cost in direct modulation of a 10-Gbit/s NRZ signal.
01 Sep 2018
TL;DR: 70-Gbps NRZ, 112- Gbps PAM-4, and 100-GMbps PAM -8 are demonstrated by directly-modulating an O-band membrane laser-on-silicon, over a 2-km single-mode fiber link under low-complexity nonlinear equalization.
Abstract: 70-Gbps NRZ, 112-Gbps PAM-4, and 100-Gbps PAM-8 are demonstrated by directly-modulating an O-band membrane laser-on-silicon, over a 2-km single-mode fiber link under low-complexity nonlinear equalization. The laser was driven at a bias of only 11.5-mA with power consumption ~7x times lower than conventional DMLs.
01 Jan 2018
11 Mar 2018
TL;DR: Eight-channel 56-Gbit/s PAM-4 direct modulations are demonstrated using a 1.3-μm WDM transmitter, consisting of membrane lasers and a SiN AWG filter.
Abstract: Eight-channel 56-Gbit/s PAM-4 direct modulations are demonstrated using a 1.3-μm WDM transmitter, consisting of membrane lasers and a SiN AWG filter. Direct bonding, epitaxial regrowth, and low-temperature SiN deposition are employed for integration on Si.
01 Jan 2018
TL;DR: In this paper, a III-V/Si MOS capacitor Mach-Zehnder modulator with an ultrahigh-efficiency phase shifter, which consists of n-type InGaAsP and p-type Si, is presented.
Abstract: A high-efficiency and low-loss Mach-Zehnder modulator on a Si platform is a key component for meeting the demand for high-capacity, low-cost and low-power optical transceivers in future optical fiber links. We report a III-V/Si MOS capacitor Mach-Zehnder modulator with an ultrahigh-efficiency phase shifter, which consists of n-type InGaAsP and ptype Si. The main advantage of this structure is a large electron-induced refractive index change and low free-carrier absorption loss of the n-type InGaAsP. The heterogeneously integrated InGaAsP/Si MOS capacitor structure is fabricated by using the oxygen plasma assisted bonding method. The fabricated device shows VπL of 0.09 Vcm, a value over three-times smaller than that of the conventional Si MOS capacitor Mach-Zehnder modulator, without an increase in the insertion loss. This clearly indicates that the proposed III-V/Si MOS capacitor Mach-Zehnder modulator overcomes the performance limit of the Si Mach-Zehnder modulator.
30 Oct 2018
TL;DR: In this paper, a 1.3-μm membrane laser on Si for datacom applications was developed, which achieved lasing at up to 95°C and direct modulation up to 40Gbit/s at 25°C.
Abstract: We have developed energy-efficient 1.3-μm membrane lasers on Si for datacom applications. We employ InGaAlAs-based MQWs as an active material to improve the temperature characteristics and modulation speed. We achieved lasing at up to 95°C and direct modulation up to 40-Gbit/s at 25°C.
30 Oct 2018
TL;DR: In this paper, a photonic crystal (PhC) laser with extremely short active regions (420 nm∼1260 nm) was developed, which achieved 4-μΛ threshold currents and 1-fJ/bit operating energies with active regions consisting of 3 and 2 QWs, respectively.
Abstract: We have developed photonic crystal (PhC) lasers, in which extremely short active regions (420 nm∼1260 nm) are embedded with an InP PhC slab. 4-μΛ threshold currents and 1-fJ/bit operating energies were achieved with 840-nm-long and 1260-nm-long active regions consisting of 3 and 2 QWs, respectively.
14 Nov 2018
TL;DR: The device is directly modulated by a 10-Gbit/s NRZ signal with a $10.5-\mu A$ bias current, resulting in an energy cost of 1 fJ/bit.
Abstract: We have fabricated InP-based photonic-crystal lasers using ultra-compact embedded active region $(1.26 \times 0.25\times 0.15\ \mu m^{3})$ . The device is directly modulated by a 10-Gbit/s NRZ signal with a $10.5-\mu A$ bias current, resulting in an energy cost of 1 fJ/bit.
14 Nov 2018
TL;DR: Low-temperature-deposited hydrogen-free SiN waveguides enable us to construct the Mach-Zehnder interferometer on a Si platform.
Abstract: A Mach-Zehnder modulator with $300-\mu m$ -Iong membrane InGaAsP phase shifters shows V, L of 0.3 Vcm and 40-Gbit/s NRZ modulations in the C band. Low-temperature-deposited hydrogen-free SiN waveguides enable us to construct the Mach-Zehnder interferometer on a Si platform.
01 Jul 2018
TL;DR: In this article, a heterogeneously integrated metaloxide-semiconductor capacitor Mach-Zehnder modulator with an n-type InGaAsP layer was presented.
Abstract: A heterogeneously integrated metal-oxide-semiconductor capacitor Mach-Zehnder modulator with an n-type InGaAsP layer shows V π L of 0.09 Vcm. It overcomes the V π L limit of conventional Si modulators without degrading the optical loss.
29 Jul 2018
TL;DR: In this article, the authors demonstrate membrane III-V/Si integrated devices with fiber-coupled power of 4.6 mW using a laser diode coupled to a 0.2-μm-thick Si waveguide.
Abstract: We demonstrate membrane III-V/Si integrated devices. An InGaAsP/Si metal-oxide-semiconductor capacitor Mach-Zehnder modulator shows small V π L (0.09 Vcm), and a laser diode coupled to a 0.2-μm-thick Si waveguide shows a fiber coupled power of 4.6 mW.
30 Oct 2018
TL;DR: In this paper, a 32-Gbit/s direct modulation of Si waveguide integrated membrane buried heterostructure laser with 500-μm-long cavity, whose cavity consists of a multiple phase-shift grating to suppress the spatial hole burning effect.
Abstract: We have demonstrated 32-Gbit/s direct modulation of Si waveguide integrated membrane buried heterostructure laser with 500-μm-long cavity, whose cavity consists of a multiple phase-shift grating to suppress the spatial hole burning effect. The optical output power was 9 mW at a stage temperature of 25 C.
TL;DR: In this article, a membrane buried heterostructure with a lateral p-i-n junction on SiO2/Si substrate enables tight confinement of carriers and photons simultaneously, which enables energy-efficient lasers.
Abstract: A membrane buried heterostructure with a lateral p-i-n junction on SiO2/Si substrate enables tight confinement of carriers and photons simultaneously, which enables us to achieve energy-efficient lasers.
14 Nov 2018
TL;DR: SDM transmissions based on DMT and a 4-channel membrane DML-array-on-Si are reported with ∼6× power reduction compared to conventional DMLs.
Abstract: We report SDM transmissions based on DMT and a 4-channel membrane DML-array-on-Si. By simultaneously modulating all lasers, 200G (KP4-FEC) and 400G (SD-FEC) are demonstrated over 425-m MCF with ∼6× power reduction compared to conventional DMLs.
11 Mar 2018
TL;DR: A directly-modulated membrane-laser array exhibiting a low, VCSEL-like operating energy is reported.
Abstract: We present a III-V/Si integration technology that employs epitaxially-grown active layers on an InP/SiO 2 /Si substrate for low-cost fabrication of PICs. Based on it, a directly-modulated membrane-laser array exhibiting a low, VCSEL-like operating energy is reported.
01 Jan 2018
TL;DR: In this article, a high-modulation-efficiency Mach-Zehnder modulator (MZM) on an Si platform is presented, in which the n-InGaAsP, p-Si, and SiO2 film are used for constructing the MOS capacitor.
Abstract: High-capacity optical transmitters with reduced size, cost, and power consumption are required to meet growing bandwidth requirements of network systems. A high-modulation-efficiency Mach-Zehnder modulator (MZM) on an Si platform is a key piece of equipment for these transmitters. Si-MZMs have been widely reported; however their performance is limited by the material properties of Si. To overcome the performance limitations of Si MZMs, we have integrated III-V materials on Si substrate and developed a heterogeneously integrated III-V/Si metal oxide semiconductor (MOS) capacitor phase shifter for constructing ultra-high efficient MZM, in which the n-InGaAsP, p-Si, and SiO2 film are used for constructing the MOS capacitor. The fabricated MZM with the MOS capacitor exhibited a VπL of 0.09 Vcm and insertion loss of ~2 dB. 32-Gbps modulation of the MZM was also demonstrated.