The reduction of optical loss for integrated photonics I/O is an important area of active research. Edge coupling (end-firing) is a key I/O technology, having advantages over grating couplers in terms of spectral bandwidth and lower insertion loss1. Low-loss edge coupling into silicon waveguides will be critical to datacenters and telecommunications systems in order to help accommodate the aggressive growth of data analytics applications2. In this work, we investigate the coupling losses from optical fiber (SMF-28) into on-chip silicon waveguides using silicon nitride edge couplers with varying chip facet angles. The expected losses were simulated using Three Dimensional Finite-Difference Time-Domain (3D-FDTD) modelling and measured experimentally to close the design-fabrication loop. The chips were produced within a state-of-the-art 300 mm CMOS foundry, using edge couplers from the foundry Process Design Kit (PDK). During optimization of the photolithography and dry etching process, the facet angle deviation from 90° was minimized. Insertion loss of the SiN edge coupler was investigated via transmission measurements utilizing both cleaved fibers and fiber V-grooves. Facet angles varied from approximately 75°–90° were tested for insertion loss and trends were consistent with the 3D-FDTD modelling. Measurements were performed over a range of 1450–1650 nm using a tunable laser source and optical power meter. In addition, facet insertion loss was isolated by using propagation loss data from an in-line testing tool that measured silicon waveguides propagation losses, on wafer and in the same wavelength band.
An RF-Photonic phased array antenna beamformer was previously demonstrated using cascaded fiber Bragg gratings with 1 x 2 couplers for true-time-delay beamforming. This work's focus is to design, build, and test an integrated Si-photonic beamforming circuit to replace the fiber-optics system, allowing for chip-scale beamformers with low size, weight, power, and cost. Several metastructure waveguides were designed to provide a strong slowlight effect near their transmission band edge. By tuning the wavelength near the band edge, tunable optical truetime delay is achieved. We report the design, simulation, fabrication and test of these high-contrast metastructure waveguides to provide group velocity variation against wavelength near the band-edge. Wavelength-tunable delay was verified using both an interferometric approach using an integrated Mach-Zehnder interferometer, and using a direct measurement of the true-time delay of an RF signal modulated onto a C-band optical carrier. We have also designed an integrated photonic beamforming circuit for a small array, including photodetectors, fabricated by AIM Photonics. Experimental test results for those integrated photonic circuits will be discussed. We will continue to improve our integrated photonic circuit to pursue larger array implementation. The goal is to further integrate this photonic circuit with an RF phase array antenna and demonstrate the scan of an RF beam by optical control.
In this work, we have designed a novel Si based 1-dimensional high contrast meta-structure waveguide that has slow light effect as well as phase tunability using p-n junction. The goal is to use such waveguide to design active optical devices such as high frequency modulators and tunable filters for analog RF-photonics or data communication applications. The Si ridge waveguide has a pair of high contrast grating wings adhered to the waveguide core in the center. Grating bars at two sides of the waveguide are doped P and N-type respectively, while a p-n junction region is formed in the middle of the waveguide core. By applying a voltage to bias the p-n junction, one can sweep the free carriers to change the effective index of the waveguide as well as the dispersion property of the grating. This metastructure Si waveguide is ideal in the design of high frequency optical modulators since the slow light effect can reduce the modulator waveguide length, increase the modulation efficiency as well as compensate other nonlinearity factors of the modulator for analog applications.
Silicon photonic system, integrating photonic and electronic signal processing circuits in low-cost silicon CMOS
processes, is a rapidly evolving area of research. The silicon electroabsorption modulator (EAM) is a key photonic
device for emerging high capacity telecommunication networks to meet ever growing computing demands. To replace
traditional large footprint Mach-Zehnder Interferometer (MZI) type modulators several small footprint modulators are
being researched. Carrier-injection modulators can provide large free carrier density change, high modulation efficiency,
and compact footprint. The large optical bandwidth and ultra-fast transit times of 130nm HBT devices make the carrierinjection
HBT-based EAM (HBT-EAM) a good candidate for ultra-high-speed optical networks.
This paper presents the design and 3D full-wave simulation results of a traveling wave electrode (TWE) structure to
increase the modulation speed of a carrier-injection HBT-EAM device. A monolithic TWE design for an 180um ultra
compact carrier-injection-based HBT-EAM implemented in a commercial 130nm SiGe BiCMOS process is discussed.
The modulator is electrically modeled at the desired bias voltage and included in a 3D full-wave simulation using CST
software. The simulation shows the TWE has a S11 lower than -15.31dB and a S21 better than -0.96dB covering a
bandwidth from DC-60GHz. The electrical wave phase velocity is designed close to the optical wave phase velocity for
optimal modulation speed. The 3D TWE design conforms to the design rules of the BiCMOS process. Simulation results
show an overall increase in modulator data rate from 10Gbps to 60Gbps using the TWE structure.
Silicon-based electro-optic (EO) modulator is an indispensable building block for integrated lightwave circuits. In this
paper, we report an EO modulator that incorporates a heterojunction bipolar transistor (HBT) with Ge composition
graded base. The emitter is n-type doped silicon with a doping concentration of 1021/cm3. The width of the emitter strip
is 0.2μm and the thickness of the emitter layer is 0.16μm. The base has a thickness of 40nm with varying Ge
composition from zero at the emitter-base junction side to 20% at the base-collector junction side. Raised extrinsic base
is incorporated for base contact. The intrinsic base is p-type doped with a concentration of 4×1019/cm3. The HBT is
biased at VCE = 0.5 V whereas VBE is switched between -1.0V and 1.0V. The carrier distribution at "ON" state of the EO
modulator and the transient analysis are performed by MEDCI simulation. The changes of the refractive indices of the
HBT are computed from the carrier density in all regions, and then the refractive index map is imported into an optical
mode solver (RSoft BeamProp). The HBT EO modulator that supports only one optical mode is ideal, but a trade-off
between modal property and device speed is observed. For current design, we achieved a π-phase modulation length of
less than 600μm, and a switching delay less than 62ps.
In this paper, we compare the power consumption of a "line-of-sight" free space optical (FSO) link and a radio frequency
(RF) data link. We investigate a 2.5 Gbps line-of-sight FSO interconnection, which consists of a vertical cavity surface
emitting laser (VCSEL) driver (MAX3795), a VCSEL laser diode (LD), a PIN photodiode (PD), a transimpedance
amplifier (MAX3864), and a limiting amplifier (MAX3746). It is shown that the total power consumption is about 370.6
mW in simple NRZ on-off keying (OOK) modulation format. Different lens configurations are discussed in terms of the
integration/setup efforts and the beam controlling effects. A 250 Kbps commercial radio frequency (RF) link comprised
in Tmote sky module (Moteiv Corporation) is explored to compare with the FSO link. The average power supplied to the
radio transceiver is about 50.76 mw. The estimated energy consumption for the aforementioned RF link is 2.03×10-4
mJ/bit, while the end-to-end FSO consumes 1.48×10-7 mJ/bit. This paper provides design outlines from the aspect of the
power consumption of FSO and RF wireless communication technologies for distributed sensor network applications.
A multi-giga bits circuit-level model of a thin film metal-semiconductor-metal photodetector (MSM PD) for high speed optical receiver (Rx) was obtained using the RF measurement technique and widely used optimization routines in simulation tool such as ADS and SPICE. On-wafer measurement-based modeling technique was employed to exactly characterize DUTs in this paper. On-wafer calibration standard structures such as NiCr 50 Ω of load, short, and open were also fabricated and optimized using laser trimming for exact measurements. The obtained circuit-level model shows good agreement with measured s-parameters and wide eye open up to 20Gbps.
Recent progress toward implementing high-density, optical-digital building blocks necessary to accomplish efficient, end-to-end optical interconnect architecture on low cost FR-4 boards has been demonstrated. The optical interconnect system consists of fabricating an optical buffer layer separating board metallurgy from the optical lightwave circuit layer, and implementing optical links between embedded lasers and detectors. We will show an example of 1310 nm light from an edge emitting distributed-feedback or Fabry-Perot laser operating at 10 Gb/s being guided to the photo-detector by a polymer waveguide. Both lasers and detector are embedded in the waveguide and all construction is built on a low-cost FR-4 board with 3 levels of metallurgy.
Photodetectors (PDs) are an important active device in optoelectronic integrated circuits (OEICs), and, for shorter haul interconnections where circuit (e.g. transimpedance amplifier (TIA)) noise may be the dominant noise in receivers, metal-semiconductor-metal photodiodes (MSM PDs) are attractive due to their low capacitance per unit area compared to PIN photodetectors and the ease of monolithic integration with field effect transistors (FETs). Inverted-MSM PDs (I-MSM PDs), which are thin film MSM PDs with the fingers on the bottom of the device, have demonstrated higher responsivities compared to conventional MSM PDs while maintaining small capacitance per unit area, low dark current (~nA), and high speed. However, the modeling of MSM PDs and I-MSM PDs for insertion into circuit simulators for integrated PD/TIA modeling has not been reported. In this paper, an accurate high-frequency equivalent circuit-level model of thin film I-MSM PDs is obtained using an on-wafer measurement-based modeling technique. This circuit-level model of MSM PDs can be used for capacitance sensitive preamplifier design for co-optimization with widely used simulators (ADS and HSPICE). The obtained circuit-level model shows good agreement with measured s-parameters.
Linear statistical models have been generated to predict the performance of metal-semiconductor-metal (MSM) PDs for multi-gigabit optical interconnections. The models estimate the bandwidth and responsivity of the MSM PDs based on the input factors: absorbing layer thickness, detector size, finger widths and finger gaps. The design of experiments (DOE) approach was employed to obtain the necessary data to construct the models.
Numerous samples were fabricated so that multiple devices measurements could serve to both construct and verify the linear statistical models. The MSM PDs were fabricated from material with structure InAlAs/InAlGaAs/InGaAs (2000Å, 3000Å or 5000Å, absorbing layer)/InAlAs. The MSM interdigitated fingers were photolithographically defined with finger gaps and widths varying as DOE parameters. A benzocyclobutene (BCB, Cyclotene 35) layer was spin-coated onto all of the samples as isolation from the probing pads.
In the bandwidth analysis, the detector size (S) and material thickness (T) were investigated with a fixed finger width (1 μm) and gap (1 μm). Taking the measured results of these detectors in the design matrix, and using least square regression, the model equations were derived as: Bandwidth (GHz) = 12.87 - 0.065S - 3T - 0.02ST. After these equations were developed, predictive calculated results from these equations were then further used to predict and compare measured results on devices that were not used in the statistical model. This leads to an average deviation between predicted and measured bandwidth of less than 5%. In the responsivity analysis, the predictive calculation leads to an average deviation less than 11%.
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.