dB Extinction Ratio Research Articles

Integrated Optoelectronic Devices on Silicon

ABSTRACTSilicon (Si) has been the dominating material platform of microelectronics over half century. Continuous technological advances in circuit design and manufacturing enable complementary metal-oxide semiconductor (CMOS) chips with increasingly high integration complexity to be fabricated in an unprecedently scale and economical manner. Conventional Si-based planar lightwave circuits (PLCs) has benefited from advanced CMOS technology but only demonstrate passive functionalities in most circumstances due to poor light emission efficiency and weak major electro-optic effects (e.g., Pockels effect, the Kerr effect and the Franz–Keldysh effect) in Si. Recently, a new hybrid III-V-on-Si integration platform has been developed, aiming to bridge the gap between Si and III-V direct-bandgap materials for active Si photonic integrated circuit applications. Since then high-performance lasers, amplifiers, photodetectors and modulators, etc. have been demonstrated. Here we review the most recent progress on hybrid Si lasers and high-speed hybrid Si modulators. The former include distributed feedback (DFB) lasers showing over 10 mW output power and up to 85 oC continuous-wave (cw) operation, compact hybrid microring lasers with cw threshold less than 4 mA and over 3 mW output power, and 4-channel hybrid Si AWG lasers with channel space of 360 GHz. Recently fabricated traveling-wave electro-absorption modulators (EAMs) and Mach-Zehnder interferometer modulators (MZM) on this platform support 50 Gb/s and 40 Gb/s data transmission with over 10 dB extinction ratio, respectively.

Hybrid dielectric-loaded plasmonic waveguide and wavelength selective components for efficiently controlling light at subwavelength scale

We analyze and design a hybrid dielectric-loaded plasmonic waveguide (HDLW) featuring a long propagation length and strong field confinement, for efficient control and confinement of light in the subwavelength area of λ2/160. The HDLW is then used to build compact wavelength selective components of high optical performance, including ring resonators (RR) and add-drop filters (ADF). In particular, we demonstrate RRs having a small ring radius of 2 μm, a low transmission loss of 0.8 dB, a high extinction ratio of 21 dB, and a free spectral range of 66 nm. Moreover, an ADF with a ring radius of 2 μm features a 12 dB extinction ratio, a transmission loss of 0.9 dB, and a channel isolation level of 10 dB at the resonant wavelength. The compact footprint and superior performance of these plasmonic components make them promising building blocks for future nanoscale electronic-photonic integrated circuits for data communication and sensing applications.

Simultaneous all-optical digital comparator and dual-directional half-subtractor for two-input 40 Gbit/s DPSK signals employing SOAs

A module of simultaneous implementation of all-optical digital comparator and dual-directional half-subtractor is proposed. Proof-of-concept experiment is performed at 40 Gbit/s employing the four-wave mixing and cross gain modulation in three parallel semiconductor optical amplifiers. All output results with over 10 dB extinction ratios, clear and wide open eye diagrams, are obtained without using assistant/holding light beam. All-optical half-adder can also be obtained by adjusting the phase shifter of delay interferometer in the proposed module because of its inherent reconfigurability and flexibility. The module would be a promising digital logic elementary circuit in all-optical networks and computing systems.

100-mW linear polarization single-frequency all-fiber seed laser for coherent Doppler lidar application

A compact short-cavity fiber laser configured with Er 3+/Yb 3+ highly co-doped phosphate glass fiber with stable linear polarization and single frequency output is proposed and investigated experimentally. The fiber laser is composed of a high-reflectivity fiber Bragg grating (HRFBG) and a polarization-maintaining fiber Bragg grating (PMFBG) with the matched wavelengths at 1540.3 nm, which aims at one of the center wavelengths of the atmospheric transmission windows and may be used as the local oscillator (LO) of the coherent Doppler lidar (CDL). The output power of the laser reaches more than 114-mW, the signal-to-noise ratio is larger than 70 dB and the laser linewidth is about 4.1-kHz. Moreover, the linear polarization with 40.5 dB extinction ratio, the power fluctuation of less than ± 0.25% and the frequency fluctuation of less than ± 80 MHz are also obtained. Compared with the DFB fiber laser, the proposed fiber laser is more suitable for the CDL applications.

Scalable 3D dense integration of photonics on bulk silicon

We experimentally show vertically stacked, multi-layer, low-temperature deposited photonics for integration on processed microelectronics. Waveguides, microrings, and crossings are fabricated out of 400°C PECVD Si3N4 and SiO2 in a two layer configuration. Waveguide losses of ~1 dB/cm in the L-band are demonstrated using standard processing and without post-deposition annealing, along with vertically separated intersections showing -0.04 ± 0.002 dB/cross. Finally 3D drop rings are shown with 25 GHz channels and 24 dB extinction ratio.

Dual-LP_11 mode 4x4 MIMO-OFDM transmission over a two-mode fiber

We report successful transmission of dual-LP(11) mode (LP(11a) and LP(11b)), dual polarization coherent optical orthogonal frequency-division multiplexing (CO-OFDM) signals over two-mode fibers (TMF) using all-fiber mode converters. Mode converters based on mechanically induced long-period grating with better than 20 dB extinction ratios are realized and used for interfacing single-mode fiber transmitter and receivers to the TMF. We demonstrate that by using 4×4 MIMO-OFDM processing, the random coupling of the two LP(11) spatial modes can be successfully tracked and equalized with a one-tap frequency-domain equalizer. We achieve successful transmission of 35.3 Gb/s over 26-km two-mode fiber with less than 3 dB penalty.

40 Gbit/s 2-to-1 photonic data selector via XGM and FWM in two SOAs

A simple design of a 2-to-1 photonic data selector is proposed and has been experimentally demonstrated at 40 Gbit/s, employing four-wave mixing and cross-gain modulation in two parallel semiconductor optical amplifiers. All output signals with over 10 dB extinction ratios, clear and wide open eyes, are obtained without additional input.

A Compact and Highly Efficient Silicon-Based Asymmetric Mach—Zehnder Modulator with Broadband Spectral Operation

An asymmetric Mach—Zehnder electro-optic modulator is demonstrated by using a silicon-based p-i-n diode embedded in compact 200 μm long phase shifters. The measured figure of merit VπL = 0.23 V ·mm shows highly efficient modulation by the device, and an open eye-diagram at 3.2 Gbit/s confirmed its fast electro-optic response. Integrated with the grating coupler, the device exhibits a broad operational wavelength range of 70 nm with a uniform 18 dB extinction ratio covering the C-band and part L-band of optical communication.

Femtosecond laser fabrication of birefringent directional couplers as polarization beam splitters in fused silica

Integrated polarization beam splitters based on birefringent directional couplers are demonstrated. The devices are fabricated in bulk fused silica glass by femtosecond laser writing (300 fs, 150 nJ at 500 kHz, 522 nm). The birefringence was measured from the spectral splitting of the Bragg grating resonances associated with the vertically and horizontally polarized modes. Polarization splitting directional couplers were designed and demonstrated with 0.5 dB/cm propagation losses and -19 dB and -24 dB extinction ratios for the polarization splitting.

Bragg grating-based optical switching in a bismuth-oxide fiber with strong χ^(3)-nonlinearity

We report the first experimental demonstration of Bragg grating-based nonlinear switching in a bismuth-oxide single-mode fiber. Exploiting the strong χ3-nonlinearity of this fiber in a cross-phase modulation scheme, we change the transmission of a probe near the grating stop band from 90 % to 20 %, a 6.5 dB extinction ratio, at powers as low as 55 W. This is an 18-fold improvement in the switching power compared to the best demonstrations in silica. The experimental results agree well with numerical simulations.

High extinction ratio 10 Gbit/s silicon optical modulator

High speed and high extinction ratio silicon optical modulator using carrier depletion is experimentally demonstrated. The phase-shifter is a 1.8 mm-long PIPIN diode which is integrated in a Mach Zehnder interferometer. 8.1 dB Extinction Ratio at 10 Gbit/s is obtained simultaneously with optical loss as low as 6 dB.

Ultra-efficient 10Gb/s hybrid integrated silicon photonic transmitter and receiver

Using low parasitic microsolder bumping, we hybrid integrated efficient photonic devices from different platforms with advanced 40 nm CMOS VLSI circuits to build ultra-low power silicon photonic transmitters and receivers for potential applications in high performance inter/intra-chip interconnects. We used a depletion racetrack ring modulator with improved electro-optic efficiency to allow stepper optical photo lithography for reduced fabrication complexity. Integrated with a low power cascode 2 V CMOS driver, the hybrid silicon photonic transmitter achieved better than 7 dB extinction ratio for 10 Gbps operation with a record low power consumption of 1.35 mW. A received power penalty of about 1 dB was measured for a BER of 10(-12) compared to an off-the-shelf lightwave LiNOb3 transmitter, which comes mostly from the non-perfect extinction ratio. Similarly, a Ge waveguide detector fabricated using 130 nm SOI CMOS process was integrated with low power VLSI circuits using hybrid bonding. The all CMOS hybrid silicon photonic receiver achieved sensitivity of -17 dBm for a BER of 10(-12) at 10 Gbps, consuming an ultra-low power of 3.95 mW (or 395 fJ/bit in energy efficiency). The scalable hybrid integration enables continued photonic device improvements by leveraging advanced CMOS technologies with maximum flexibility, which is critical for developing ultra-low power high performance photonic interconnects for future computing systems.

Forty Gb/s hybrid silicon Mach-Zehnder modulator with low chirp

We demonstrate a hybrid silicon modulator operating up to 40 Gb/s with 11.4 dB extinction ratio. The modulator has voltage-length product of 2.4 V-mm and chirp of -0.75 over the entire bias range. As a switch, it has a switching time less than 20 ps.

40 Gbit/s four-input photonic digital priority encoder employing three parallel semiconductor optical amplifiers

A novel design of a four-input photonic priority encoder is proposed. A proof-of-concept experiment is performed at 40 Gbit/s based on cross-gain modulation in three parallel semiconductor optical amplifiers. All output results with over 10 dB extinction ratios and clear open eye diagrams are obtained without any additional input light beam.

Integrated hybrid silicon triplexer

We demonstrate an integrated triplexer on silicon with a compact size of 1mm by 3.5mm by utilizing a selective area wafer bonding technique. The wavelength demultiplexer on the triplexer chip successfully separates signals at wavelengths of 1310 nm, 1490 nm and 1550 nm with more than 10 dB extinction ratio. The measured 3 dB bandwidth of the integrated laser and photodetectors are 2 GHz and 16 GHz, respectively. Open eye diagrams are also measured for the integrated photodetector up to 12.5 GHz PRBS inputs.

On-Chip All-Optical Passive 3.55 Gbit/s NRZ-to-PRZ Format Conversion Using a High-Q Silicon-Based Microring Resonator

We report the experimental result of all-optical passive 3.55 Gbit/s non-return-to-zero (NRZ) to pseudo-return-to-zero (PRZ) format conversion using a high-quality-factor (Q-factor) silicon-based microring resonator notch filter on chip. The silicon-based microring resonator has 23800 Q-factor and 22 dB extinction ratio (ER), and the PRZ signals has about 108ps width and 4.98 dB ER.

Compact terahertz wave polarizing beam splitter

We designed a compact terahertz (THz) wave polarizing beam splitter based on a periodic bilayer structure, which operates over a wide THz wavelength range. Within a short length (about 1 mm), this polarizing beam splitter separates THz wave TE- and TM-polarized modes into orthogonal output waveguides. Results of simulations with the finite-element method show that 99.99% of the TE-polarized THz wave is deflected by the periodic bilayer structure (with 39.9 dB extinction ratio), whereas 99.58% of the TM-polarized THz wave propagates through the structure (with a 23.7 dB extinction ratio). Tolerance analysis reveals a large tolerance to fabrication errors.

Microfiber-probe-based ultrasmall interferometric sensor

We report an ultrasmall microfiber-probe-based reflective interferometer for highly sensitive liquid refractive index measurement. It has a 3.5 microm micronotch cavity fabricated by focused ion beam micromachining. A sensitivity of 110 nm/RIU (refractive index unit) in liquid is achieved with over 20 dB extinction ratio. Theoretical analysis shows this kind of device is a hybrid of Fabry-Perot and modal interferometers. In comparison with normal fiber interferometers, this probe sensor is very compact, stable, and cheap, offering great potentials for detecting inside sub-wavelength bubbles, droplets, or biocells.

Monolithic electro‐optically modulated vertical cavity surface emitting laser with 10 Gb/s open‐eye operation

AbstractA vertical‐cavity surface‐emitting laser with a monolithically integrated electro‐optical modulator (EOM VCSEL) is fabricated using metal‐organic vapor phase epitaxy. 3 dB extinction ratio of the modulator at a very low power consumption and open‐eye operation of the EOM VCSEL at 10 Gb/s is demonstrated. The modulation of the 845 nm output is temperature‐stable up to 85 °C. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Wavelength-tunable silicon microring modulator

We present a wavelength-tunable, compact, high speed and low power silicon microring modulator. With a ring radius of 5 microm, we demonstrate a modulator with a high speed of 12.5 Gbps and a driving voltage of 3 V to achieve approximately 6 dB extinction ratio in high speed measurement. More importantly, tunability of the resonant wavelength is accomplished by means of a microheater on top of the ring, with an efficiency of 2.4 mW/nm (2.4 mW is needed to tune the resonant wavelength by 1 nm). This device aims to solve the narrow bandwidth problem of silicon microcavity modulators and increase the data bandwidth in optical interconnect systems.