Electro-optic Transmitter Research Articles

A 37-Gb/s Monolithically Integrated Electro-Optical Transmitter in a Silicon Photonics 250-nm BiCMOS Process

In this paper, the design of a monolithically integrated electro-optical transmitter is studied. The circuit was realized in an electro-photonic 250-nm technology which integrates a silicon photonics Mach-Zehnder modulator (MZM) and an electrical BiCMOS driver on the same chip. The circuit reaches on-off keying data rates up to 37 Gb/s, thus being, to the best of the authors' knowledge, the fastest monolithically integrated electro-optical transmitter in the literature (in terms of symbol rate). We show that by employing a high-swing, open-collector electrical driver, a compact MZM assembly with short-length phase shifters (2 mm) can be realized, while still reaching a high extinction ratio (ER) of 7.6 dB (at 35 Gb/s). The open-collector design approach allowed to increase the data rate while reducing the DC power consumption. In this work, we prove that one of the main drawbacks of MZM-based transmitters, namely their large chip footprint, can be overcome without sacrificing the speed, ER or the power consumption of the transmitter.

A 50–20 Gb/s, 80 mW Photonic Receiver With 59–70 dBΩ Gain and 12.3–8.2 pA/√Hz Input-Referred Noise

This letter presents the design and measurements of a monolithically integrated photonic receiver manufactured in 0.25 μm SiGe BiCMOS electro-photonic technology. The receiver consists of an on-chip germanium photodiode directly connected to the transimpedance amplifier (TIA). An on-chip, low-noise feedback loop compensates the dc photocurrent. The circuit provides a maximum bandwidth of 35.6 GHz at a gain of 59.2 dBQ with a noise of 12.34 pA/√(Hz) while consuming only 80 mW. In combination with a 20 GHz, 1550 nm electro-optical transmitter, a maximum data rate of 50 Gb/s at a bit error rate of less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> was measured. To the best of the authors' knowledge, this is the fastest error-free detected data rate reported for a monolithically integrated photonic receiver. Additionally, the feedback resistor of the TIA can be tuned via a MOSFET allowing error-free operation at 20 Gb/s with a sensitivity of only -13 dBm. In this setting the input-referred noise is only 8.16 pA/√(Hz).

CMOS and plasmonics get close

Electro-optic transmitters with high bandwidth can be created by monolithically integrating bipolar CMOS electronics with plasmonics.

A monolithic bipolar CMOS electronic–plasmonic high-speed transmitter

To address the challenge of increasing data rates, next-generation optical communication networks will require the co-integration of electronics and photonics. Heterogeneous integration of these technologies has shown promise, but will eventually become bandwidth-limited. Faster monolithic approaches will therefore be needed, but monolithic approaches using complementary metal–oxide–semiconductor (CMOS) electronics and silicon photonics are typically limited by their underlying electronic or photonic technologies. Here, we report a monolithically integrated electro-optical transmitter that can achieve symbol rates beyond 100 GBd. Our approach combines advanced bipolar CMOS with silicon plasmonics, and addresses key challenges in monolithic integration through co-design of the electronic and plasmonic layers, including thermal design, packaging and a nonlinear organic electro-optic material. To illustrate the potential of our technology, we develop two modulator concepts—an ultra-compact plasmonic modulator and a silicon-plasmonic modulator with photonic routing—both directly processed onto the bipolar CMOS electronics. The monolithic integration of electronic and plasmonic technologies can be used to create electro-optic transmitters capable of symbol rates beyond 100 GBd.

A Sub-pJ/Bit, Low-ER Mach–Zehnder-Based Transmitter for Chip-to-Chip Optical Interconnects

Designing high-speed and low-power interconnects is a challenge for high performance computing applications, while silicon photonics can provide attractive solutions to perform high-density communications. This paper presents an electro-optic transmitter operating at 20 Gbps (gigabit per second), as a first step toward the demonstration of chip-to-chip optical links. The architecture is based on a dual-drive Mach-Zehnder interferometer co-integrated with a 55-nm CMOS driver. Design optimizations and trade-offs analysis enable low-energy and negligible bit error rate ( $BER ) transmission at 20 Gbps, by exploring a firstly reported low extinction ratio (ER) modulator. A wire-bonding board assembly is then carried out to co-integrate hybrid transmitter. Co-simulations are presented and show good agreement with experiments. Combined with an adequate MZM bias, this solution achieves a minimal energy consumption of 0.9 pJ/bit while ensuring a sufficiently large ER of 0.73 dB for chip-to-chip interconnects applications.

Experimental Investigation of Link Impairments in Pilot Tone Aided Superchannel Transmission

We investigate the performance of single-pilot-tone locked frequency comb-based superchannel transmission for distances up to 1200km. In our scheme, electro-optic transmitter and receiver combs are locked by leaving one of the transmitter carriers unmodulated and regenerating the receiver comb via optical injection locking. This approach significantly reduces carrier offsets and therefore leads to reduced digital signal processing complexity. We experimentally assess how transmission impairments such as noise added by optical amplifiers and fiber nonlinearities affect the quality of the comb regeneration. Our results show that while the operating conditions are more stringent at longer distances, the single pilot is robust to impairments. At optimal launch power, similar performance with respect to an intradyne receiver is observed, showing that the optical pilot tones can be co-transmitted with data channels even at distances spanning hundreds of kilometer. The total superchannel spectral efficiency (throughput), including the pilot tone and guardbands, is 9.6 bits/s/Hz (12 Tbit/s) after 480 km and 8.4 bits/s/Hz (10.5 Tbit/s) after 960km.

Design and Analysis of an Electro-Optic Type Pressure Transmitter Using Bellows as Primary Sensor

In process industries, an optical transmitting system has a great impact especially for long distance transmission through inflammable and hazardous areas. A combination of bellows and Mach-Zehnder Interferometer (MZI)-based pressure transmitting system has been proposed in this paper. This novel approach is capable to transmit pressure reading to a remote location using an electro-optic modulation in the MZI. The proposed system is the hybrid type and consists of two sections. First part is the electrical type which is responsible for transmission of measured information in an electrical domain (primary) and a second section is designed for transmission of measured information in an optical domain (secondary). Primary part is the combination of bellows, a Hall probe sensor, and a signal conditioning circuit, and the second part consists of the MZI with three electrodes. The pressure is directly applied to the bellows. The magnet is placed at the top of the Bellows and the variation of the magnet positions is sensed by the Hall probe sensor. The response of the Hall probe sensor, in terms of millivolt range, is not capable to perform the electro-optic modulation in the MZI, so it is further amplified by an instrumentation amplifier and a calibrating circuit. The output from the signal conditioning circuit is fed to the MZI so that the intensity of light which is propagating in the MZI is modulated due to the electro-optic effect. Transmission of the optical signal is very much beneficial for the inflammable industry to prevent the sparking like situation. The operation of the system has been explained with the help of derived theoretical equations. The experiment has been done and the performance of the system along with the experimental results is reported in this paper. The proposed system is linear and provides good repeatability with the applied pressure.

Design of an inductive pickup type displacement transducer using an electro‐optic effect of lithium‐niobate‐based Mach–Zehnder interferometers

In this study, an improved inductive pickup coil and an electro-optic type displacement transmitter has been proposed. A modified differential inductance bridge network has been used to generate electrical signals and Mach–Zehnder interferometer (MZI) converts an electrical signal into an optical signal. The sensitivity of the sensor part of the transducer is very good because of two parallel magnetic paths for the inductive pickup. The theoretical equations explaining the operation of the transducer are derived. The proposed transducer is tested experimentally to obtain the static characteristics. The characteristics of the MZI-based displacement transmitter have been observed by using PC-based Opt wave Opti-BPM.v.9 simulation software in the linear zone. The experimental and simulated results are reported in this study. Very good linear characteristics of the transducer with adjustable sensitivity have been observed. The transmitter output in the form of normalised intensity of light is also found to be linearly related with displacement. The theoretical equations derived in this are found to support the experimental characteristics to a very good extent.

RF and Thermal Considerations of a Flip-Chip Integrated 40+ Gb/s Silicon Photonic Electro-Optic Transmitter

We demonstrate a flip-chip integrated electro-optic transmitter incorporating a high-swing CMOS driver and silicon photonic Mach–Zehnder modulator, and discuss the RF and thermal characteristics of the assembly. The transmitter showed a dynamic extinction ratio of 8 dB, which is the highest to date for 40+ Gb/s-class transmitters using CMOS drivers with silicon modulators. The input reflection coefficient of the module was mostly determined by the input electrical lines, solder bumps, and driver, while the electro-optic transfer function was mostly set by the Mach–Zehnder modulator. Despite the high power consumption of the driver and modulator (553 mW) and the close proximity between the electronic and photonic dies, the thermal simulations show that heat can be efficiently sunk from the bottom side of the silicon photonic die.

Flip-chip integrated silicon Mach-Zehnder modulator with a 28nm fully depleted silicon-on-insulator CMOS driver.

We present a silicon electro-optic transmitter consisting of a 28nm ultra-thin body and buried oxide fully depleted silicon-on-insulator (UTBB FD-SOI) CMOS driver flip-chip integrated onto a Mach-Zehnder modulator. The Mach-Zehnder silicon optical modulator was optimized to have a 3dB bandwidth of around 25 GHz at -1V bias and a 50 Ω impedance. The UTBB FD-SOI CMOS driver provided a large output voltage swing around 5 Vpp to enable a high dynamic extinction ratio and a low device insertion loss. At 44 Gbps, the transmitter achieved a high extinction ratio of 6.4 dB at the modulator quadrature operation point. This result shows open eye diagrams at the highest bit rates and with the largest extinction ratios for silicon electro-optic transmitter using a CMOS driver.

Insights Into Silicon Photonics Mach–Zehnder-Based Optical Transmitter Architectures

Mach–Zehnder-based modulator architectures lend themselves to the realization of high-data-rate Silicon Photonics transmitters. In this work the challenges set by the integration of such devices on silicon are analyzed in depth. The two main alternative electronic driver architectures, namely multistage and travelling wave, are compared with focus to power efficiency. This is, in fact, a key parameter when considering the stringent requirements of standard module form factors. A 25 Gbps multistage and a 56 Gbps travelling wave modulator have been realized. Each electro-optical transmitter is obtained by the 3D assembly of an electronic IC on top of a photonic IC through copper pillars. STMicroelectronics PIC25G Silicon Photonics platform has been adopted for the fabrication of optical devices, while 65 nm CMOS and 55 nm BiCMOS technologies are exploited to realize the electronic drivers. A 30% better power efficiency compared to Silicon Photonics state-of-the-art at similar data rates and comparable extinction ratio performance has been demonstrated in both cases. Since packaging is also a crucial aspect for Silicon Photonics high volume production, experiments on bare dice as well as on packaged chips are reported.

A High-Speed Fully-Integrated POF Receiver With Large-Area Photo Detectors in 65 nm CMOS

This paper describes the design of a multi-gigabit fiber-optic receiver with integrated large-area photo detectors for plastic optical fiber applications. An integrated 250 μm diameter non-SML NW/P-sub photo detector is adopted to allow efficient light coupling. The theory of applying a fully-differential pre-amplifier with a single-ended photo current is also examined and a super-Gm transimpedance amplifier has been proposed to drive a C PD of 14 pF to multi-gigahertz frequency. Both differential and common-mode operations of the proposed super-Gm transimpedance amplifier have been analyzed and a differential noise analysis is performed. A digitally-controlled linear equalizer is proposed to produce a slow-rising-slope frequency response to compensate for the photo detector up to 3 GHz. The proposed POF receiver consists of an illuminated signal photo detector, a shielded dummy photo detector, a super-Gm transimpedance amplifier, a variable-gain amplifier, a linear equalizer, a post amplifier, and an output driver. A test chip is fabricated in TSMC's 65 nm low-power CMOS process, and it consumes 50 mW of DC power (excluding the output driver) from a single 1.2 V supply. A bit-error rate of less than 10-12 has been measured at a data rate of 3.125 Gbps with a 670 nm VCSEL-based electro-optical transmitter.

A traffic-handling comparison of centralized and distributed ATM switching systems

This paper describes a geographically distributed ATM switching architecture that exploits new possibilities offered by lightwave technology. Small modules that provide both an access and an ATM switching function are distributed over some extended geographical area and connected to a passive optical medium. Each module is equipped with some small number of electrooptic transmitters and receivers that provide access to the medium. Assignment of wavelengths to transmitter/receiver pairs create logical that are wavelength-multiplexed onto the medium, thus creating a logical connection diagram among the modules. Advantages of the lightwave-based distributed architecture are the huge bandwidth of the medium, a high degree of modularity to facilitate growth, high reliability, and the ability to provide clear channels among modules. On the other hand, if the externally offered flow of ATM cells among modules is too uniform, then each module may be capable of supporting only a fraction of the load that could be carried by any port of a fully connected centralized ATM switch with output queueing. Fortunately, under the much more realistic assumption of nonuniform traffic, the independence between the logical connection diagram and the physical topology of the medium can be exploited by reconfiguring the connection diagram to the nonuniformity of the cell traffic. Simulation results show that, as the nonuniformity becomes larger, the reconfiguration technique allows the traffic-handling capability of a distributed switch to match that of a centralized switch. >

IBM Enterprise Systems multimode fiber optic technology

This paper describes the first implementation of optical fiber technology for the I/O channel connections of the IBM Enterprise Systems Connection (ESCON™) Architecture™. The ESCON optical link line rate is 200 megabits per second and is capable of transmission over distances of 3 km. The link is composed of a serializer, electro-optic transmitter, duplex fiber optic cable, electro-optic receiver, and deserializer. The serializer and deserializer respectively perform the conversions from parallel to serial and serial to parallel formats. The clock which is used to retime the serial data in the deserializer is extracted from the encoded serial signal using a phase-locked loop (PLL) technique. The optical link technology selected to achieve the data processing system requirements is InGaAsP/InP 1300-nm LED, InGaAsP/InP PIN photodiode, and multimode optical fiber. A duplex fiber jumper cable is designed with a rugged, low-profile, polarized connector, with a unique protective cap which recedes as it is mated. The optical link loss budget is determined by dividing the link into two major categories: available optical power and cable plant loss. The link design ensures that the minimum available power is greater than the maximum cable plant loss. The design parameters and trade-offs of the optical link are discussed in this paper. Unique measurement techniques and tools to ensure reliable and consistent link performance are described.