Overview of technology for RF and Digital Optical Communications

Transcription

1 Overview of technology for RF and Digital Optical Communications

2 Structure of talk Day 1 Introduction What is EPIC, How has EPIC evolved Use to show how a research and development capability matched to the targeted manufacturing capability helps reduce time to product. Where is EPIC today. Components etc How has EPIC IMPACTED Communications. (Bring in a CHIP to Pass Around.) Application to RF Communication Day 2 Application to Digital Optical Communications Future application to high capacity Analog to digital.

3 Electronic and Photonic Integrated Circuits (EPIC) Integrated Silicon Photonics involves the realization of optical functions on silicon chips with existing and future Silicon Microelectronic Technology. Has been studied actively since the early 1990 s Research has progressed however, efforts have been smaller than those in silicon micromechanics, and negligible (near zero) compared to silicon microelectronics. Recent work has for the first time applied a full CMOS foundry with its specialized equipment to the problem of Integrated Silicon Photonics. Has allowed us to apply large volume of existing Silicon Microelectronic research to the problem of ISP.

4 Why is Silicon Photonics important to Optical Communications? Integration of photonic components with CMOS electronics CMOS drivers, processors and digital electronic interfaces, Photonic filters, modulators, detectors, waveguides, splitters, optical switches. Size and Power reduction through scale reduction and device efficiency improvement. Lower optical losses, lower power consumption to achieve a specific index change etc. Allows the best of the electronic and photonic component functionality to be employed to demonstrate improved system performance. Integrated Photonic Platforms, In addition to being able to treat an Ultra Wide Band RF signal as an Ultra Narrow Signal, provide added efficiency in their ability to move signals around the chip and preserve their shape and phase.

5 What level of integration is possible and where? LEVEL 1 Die and Package Level Integration LEVEL 2 System level Integration LEVEL 3 Platform Level Integration Integration of Photonic based functions Intra chip optical data routing Application of RF functionality in optical domain Integration of Photonic and Electronic components within a single die Combination of photonic based functional components to build a usable system Photonic based communications, IW, EW, SIGNINT, ECM, and RADAR Photonically reconfigurable antennas Integration of photonic based systems and data links. Application of analog and digital photonic data links. Integration of photonic flight controls and interfaces.

6 HOW WILL THESE TECHNOLOGIES AFFECT FUTURE SYSTEMS AND PRODUCT DEVELOPMENT? CURRENT 0.18mm SOI CMOS HIC Silicon Waveguides Germanium Detectors Silicon Phase Modulators EVOLVING Integrated Optical Sources Integrated Optical Amplifiers

7 Technology: Why are we interested? On Chip optical routing and processing of RF and Microwave Signals is more efficient in terms of control of phase, loss and Size On Chip Signal fidelity Comparison TYPICAL CPW (1mm Thick, G.T. 150mm Wide) 2.0 db/cm, 18GHz BW 3mm Bend Radius (0.25 db/turn Loss) 0.50mm 0.25mm High Index Contrast Waveguide 0.35dB/cm, 100THz BW 1mm Bend Radius (0.1 db/turn Loss) Integrated Photonic Platforms, In addition to being able to treat an Ultra Wide Band RF signal as an Ultra Narrow Signal, provide added efficiency in their ability to move signals around the chip and preserve their shape and phase.

8 Examples of Integrated Devices. Segmented Path Optical Gyroscope Fabricated in our Silicon Photonic Process NIR Image of 1550nm modal propagation through lower coupler on our optical gyroscope Micrograph of Fabricated Gyroscope

9 Waveguide Modulator Detector nfet pfet MIM CAPACITOR Level of Integration Our Silicon Photonic work represents a new system of technologies that enable the monolithic fabrication of a wide range of photonic and electronic components. The Diagram at Right Shows the level of integration that will be included within our next process run PHOTONIC ELECTRONIC BOX 3.0 mm

10 Photocurrent (A) Transmittance (db) Essential Components of our EPIC Technology Optical Waveguides Optical Filters SEM of a-si Waveguides Deposited Waveguide Micrograph of EPIC Filter In R R R R Oxide Underclad Passive output -10 (as fabricated) CMOS Electronics Tuned output Fabricated High Index Contrast waveguides in a rad-hard CMOS foundry with state of the art transmission losses (0.35 db/cm in SOI, 4 db/cm in a-si) Modulators Frequency (THz) Demonstrated fully tunable, integrated optical filters with fine passband resolution (0.6 GHz) and excellent out of band rejection (>45 db) Detectors 70.0µ 60.0µ 71mA photocurrent. 50.0µ 40.0µ 30.0µ 20.0µ Integrated SiGe waveguide detector 10.0µ Photodetector length mm) ( Demonstrated Si ring modulators with lowest reported power to date, <1.0 V at < 1 ma, and modulation speeds of > 6.5 Gbps Demonstrated discrete SiGe detectors with High responsivities and Bandwidths

11 Volts The E in EPIC The E18 Process has worked to demonstrate a stable process for electronic as well as photonic elements Have worked to turn our Rad Hard process into a Process Hard ONE To Date, within our photonic process, we have demonstrated functional: 0.18um N & P FETS capable of operation out to 20GHz 0.8 Bipolar Transistors A wide Range of Passives 0.5 RF waveguides 0.4 Lot NFET V T - linear Upper Spec Target Spec Lower Spec NFET test sites

12 The AS-EPIC Signal Processor Chip Objective To demonstrate the world s first densely integrated Application Specific Electronic Photonic Integrated Circuit (AS-EPIC). Demonstrate the meaningful integration of this technology into an existing product Approach Integrate the best technology to realize our AS-EPIC chip. This involves combining CMOS compatible, low loss, high index contrast (HIC) waveguides and optoelectronic components to form optical filters, modulators, and detectors with associated tuning, driver and TIA electronic circuits. 4.5X Increase IBW 95X Reduction Size 80X 4.5X Reduction Increase IBW in Weight 95X Reduction in Size Power 100X Reduction in Cost

13 Technology: Communications Impact? EPIC technology enable chip scale components that will revolutionize communications RF Communications EPIC Phase I Tunable RF Filter Monolithic: 54 optical elements Digital Optical Communications The integration of photonics and electronics will enable a new generation of inexpensive aerospace components: Digital channelizers for EW/IW systems Photonic beam forming (Butler Matrix) for Radar, MIMO, etc. Integrated laser gyroscope (smaller, lower cost, more accurate) Photo-RF data links for air and space platforms Optical communications (military and commercial- fiber to the home) Photonic clocking for microprocessors Document number 13

14 EPIC Chip Design Elements The BAE SYSTEMS EPIC channelizer represented the most complex, integrated optical component in existence, (With the complication of electronics) The design on the following slides represents a chip with all filters required for an 18 GHz IBW device It embodied: 16 Optical Band Pass Filters (BPF) 32 Germanium Detectors (DET) w/ Integrated Transimpedance Amplifiers (TIA) 8 RF->Optical Modulators 1 Nulling Filter The chip will have integrated electronics to assist with filter control and tuning

15 Layout of the BAE SYSTEM EPIC Channelizer Band Pass Filter Detector ML LASER 2.5GHz Note: Laser 1* frequency is 625MHz Lower than Laser 2. Modulator Laser 1* Band 1 RF (0-10GHz) Laser 1 Band 1 RF (0-10GHz) Modulator Mod Driver Modulator Mod Driver Nulling Filter Control Nulling Filter BPF Control BPF BPF BPF Control BPF BPF BPF Det TIA BPF Det TIA BPF Det BPF Det BPF Det TIA BPF Det TIA BPF Det TIA BPF Det TIA TIA TIA BPF Det TIA BPF Det TIA BPF Det BPF Det Det Det TIA TIA Det Det TIA TIA TIA TIA Band 1 Odd Channels Transimpedance Amplifier Band 1 Even Channels

16 Overview of EPIC RFChannelizer Most Recent BAE SYSTEMS EPIC chip, embodies Electro and Thermo-optic phase control, low loss waveguides, Detectors, Digital CMOS, RF CMOS and Analog CMOS (for control of Thermo-optic devices.)

17 Optical In RF OUT Integration of Germanium Photodiodes with High Speed TIA Balanced Germanium Photodiodes Trans-impedance Amplifier

18 EPIC integrated 0-20GHz Cascaded Modulator Driver Using BAE SYSTEMS EPIC technology 4 types electronic circuitry were successfully integrated: Digital CMOS in the control circuitry (addressing, latching, etc.) Low power precision analog in the DAC circuitry High power analog in the tuning High Frequency analog in the modulator drivers and TIA s document number 18

19 Devices and There Applications

20 Basics of the ISP technologies Technology involving the generation, conduction, manipulation and detection of light in a well defined densely integrated fashion on silicon. Electrons and photons are the basic functional units of electronic and photonics. Electrons propagate along regions of high electrical conductivity, Photons propagate along regions having a high refractive index variation. Photonic waveguides correspond to electrical wires, propagating light from one point to another. Optoelectronic components, such as lasers, detectors, and modulators act as a bridge between photonic and electronic signals Optical amplification boosts attenuated optical signals Compensates for the losses associated with non-ideal components and power splitters. Future Optical transistors and other all-optical components based on nonlinear phenomena will enable extremely fast optical computing, interfacing, and all-optical fiber communications

21 Silicon Waveguides While at visible wavelengths from 200 to 700 nm, Si is highly transparent at near-ir wavelengths from 1.2 to approximately 7 µm Particularly useful as fiber-optic communication, which is usually carried out between 1.3 and 1.7 µm, and especially at λ 1.55 µm has initiated and supported the development of a wide range of critical components such as optical sources, amplifiers, modulators and detectors. Light propagation in a silicon waveguide is based on total internal reflection (TIR) at the outer boundaries of the Si core. The core index n Si 3.45 is surrounded by SiO 2 (n ) the index difference n = n Si - n 0 = 2 Extremely high compared to other waveguide technologies and optical fibers ( n < 0.01).

22 Basic Silicon HIC Waveguide fabrication Key fabrication challenges: Deposition, Etching, Polishing Surface Roughness top & bottom Sidewall Roughness Si SiO2 Silicon Substrate

23 Silicon Waveguide fabrication efficiency Application of CMOS fabrication methodology has numerous advantages, including the lowest possible periodic variation in the sidewall though application of statistically verified process steps. New Waveguide hard mask etch techniques reduce roughness by 30% over reported values, demonstrated unprecedented device uniformity. Hard Mask Si SiO 2 Ridge Waveguide Channel Waveguide

24 Silicon Waveguide fabrication efficiency

25 Physical implementation of Modulator Technology in the EPIC Fabrication Platform, individual modulator technologies Thermo-optic Phase Modulator The refractive Index variation of silicon due to the thermo-optic effect is given by: 1. 86x10 T n 4 MOS based EO Modulator Bias applied across a gate oxide over the modulator induces an accumulation of charge. Modification of the charge density modifies waveguide refractive index profile, the optical phase of light passing through it. Traditional P-i-N EO Modulator Carriers can be injected in a larger area (intrinsic region) in order to maximize the aforementioned overlap, increasing the effective index change. 1 K CoSi Heaters Poly-Silicon Gate N-Implanted Source & Drain N- Implanted Silicon Substrate Silicon Substrate Silicon Substrate Metal 1 HIC Silicon Waveguid e Metal 1 P-Implanted Inversion region Metal 1 P-Implanted

26 Resonant enhancement of modulators A typical Mach Zehnder Interferometer suffers from large nonlinear distortion Limits the dynamic range in precision analog applications. A number of resonantly enhanced configurations have been used to enhance performance. Foremost among them a simple resonator based method of linear transfer curve compensation to attain cancellation of the third-order term. Allows us to extend standard MZI interferometer with an additional nonlinear phase shift incorporated in one or both arms. These resonators in employed in a off resonance condition Its performance does not rely upon high Q resonators and is tolerant to the ring loss and other imperfections. Off-resonance the light effectively traverses the ring just once, Very broad frequency response, unlike designs that use ultrahigh Q modulators having a narrow response of the near the resonance.

27 Resonantly enhanced modulators RF Phase Modulator CARRIER IN COUPLER COUPLER COUPLER MODULATED CARRIER OUT 1 MODULATED CARRIER OUT 2 Figure shows the application of our basic All Pass optical filter to the formation of a singularly resonant linearized modulator.

28 A(z) Comparison of modulator performance TRANSFER FUNCTION VS MODULATION ANGLE (Input carrier frequency is fixed at THz) Linearity of modulation transfer function can be optimized by controlling coupling coefficient. LINEARIZED MODULATION RANGE TYPICAL MODULATION RANGE Shape of MZI transfer function is not modifiable RING Enhanced MZI Standard MZI PHASE DEGREES

29 Various Configurations for Integrated Germanium Detectors P-Epitaxy (SiGe) i-epitaxy (Ge) N-Epitaxy (SiGe) N-Implant (Si) i-epitaxial (Ge) P and N Implants Silicon Silicon Vertically integrated P-i-N Heterojunction Photodiode b) P-Poly (Si) i-epitaxy (Ge) N-Implant (Si) Laterally integrated P-i-N Photodiode c) N+ Implants Silicon P+ and N+ Implants P - -Epitaxial (Ge) P + -Implant Silicon Current Generation Germanium P-i-N Detector a) P - -Epitaxial (Ge) P + -Implant Silicon Laterally integrated PN Photodiode d) Laterally integrated PN Photodiode e)

30 Configurations Used for Germanium Detectors

31 Application to RF Communications

32 RF Communication, Spectral conversion RF SIGNAL SSB - Single Side Band OPTICAL CARRIER 0 FREQUENCY 18 GHz OUTPUT FROM FILTER 625MHz SSB OPTICAL MODULATION of RF SIGNAL 195 FREQUENCY THz FREQUENCY THz Photonic Heterodyne OUTPUT WITH OLO2 Conversion RF OUT at DETECTOR 625MHz Currently Carrier Not Suppressed! FREQUENCY THz FREQUENCY THz FREQUENCY MHz 1250

33 Output power and Phase scale Linearly The output of a TIA shows that the phase and amplitude relationships are preserved in the output beat signature of two modulated optical carriers. Gain in the TIA does not effect this linear relationship.

34 Optical Filters Our demonstrated resonant photonic filter architecture is quite versatile and a variety of applications can be achieved including: 1) narrowband channelizers, 2) single-sideband extraction, 3) optical interference suppression via a high quality notch response, 4) linearized response for optical modulation, 5) arbitrary multi-bandpass response. These channel filters pass a narrow slice of RF spectrum with minimum in-band insertion loss while rejecting out-of band signals. To achieve high selectivity at an arbitrary chosen frequency, a very high quality-factor (Q) tunable filter is needed. Our recent work has allowed us to demonstrate significant progress in the realization of photonic based RF filters fabricated with Q-factors in excess of 10 8

35 Output Filter Operation Filters are implemented in a Mach-Zehnder (MZ), allpass configuration employing a series of ring resonators. This pole/zero filter design requires fewer stages than an all pole filter to: Attain a narrow pass-band response, simplifying tuning of the filter limiting the overall optical loss associated Allows tailoring of the pass-band and stop-band ripple, allowing the the same filter to be dynamically tuned to create a Butterworth, Chebyshev or elliptic filter response. Ring Resonator with tunable coupling and phase variation. A 1 Input 1/2(A 1 -A 2 ) 1/2(A 1 +A 2 ) Phase Shifter Tunable 3dB Coupler A 2 =A 1 * Tunable 3dB Coupler

36 Application of Gain within the Filter Structure Filter Insertion Loss and Gain. Note that much gain can be obtained at ring gain approximately equal to coupling loss of ring. Loss of filter bottoms out at maximum rejection level.

37 Extension of filters to commercially viable ranges. A number of has run comprehensive tests have been performed on a variety of filter configurations Initial results show that a 5 th order filter can be used to achieve a 50MHz bandpass. Results below represent a unit cell having ~25ps center delay with a minimum of 4p phase tunability. These same variables have indicated that we should be able to achieve a minimum 40GHz FSR. 50 MHz filter simulation, transition band response. Filter frequency response showing 40GHz free spectral range.

38 Application to Digital Optic Communications

39 The Long Term Goal, An Optical Transceiver with >1000x reduction in SWAP over conventional technology Optical transceivers are employed in many applications, including as signal repeaters to implement long fiber optic lines Optical transceivers convert noisy inputs on irregular channels to regenerated outputs on standardized channel grids. Many optical transceiver applications drop dramatically in cost when the optical package shrinks and draws less power. BAE Systems goal was to apply EPIC (electronic-photonic integrated circuit) technology to reduce the size, complexity and cost of optical transceivers and related components by several orders of magnitude beyond the current state of the art. Input amp Tunable Dispersion Wavelength demux Compensator Converter mux Output amp DCF DCF DCF DCF O/E/O O/E/O O/E/O O/E/O O/E/O

40 Silicon photonic benefits to Digital optical comms EPIC technologies allow massive integration of components onto a single small piece of silicon. Allows multiple approached to wave division multiplexed (DWDM) optical transceivers (Prism and tuned filter). Work has shown that a complete system that performs optical dispersion compensation and 1R wavelength conversion into a 3R wavelength converter with integrated electronic dispersion compensation can be achieved. EPIC technology, has been used to produce and demonstrated a optical multiplexer and demultiplexer, with a reconfigurable Heterodyne/Homodyne modulation and demodulation data engine. Using EPIC technology BAE Systems made a first attempt has been made to reduce an array of 3R wavelength converters into a single chip, attaining reductions in size, weight and power that far exceed the competitive state of the art.

41 EPIC for correction of Optical Fiber Dispersion error The spectral width of the laser (the carrier of the data) causes the data pulses to spread over long distances The Optical Fiber is a dispersive media. Total dispersion increases with cable length, limiting practical cable lengths Eventually the 0 s and 1 s are not recognizable Dispersion compensation is generally employed to undo effects of the cable length and thus allow longer cables Distance (0 to Gbps) Current Dispersion Compensation Techniques Dispersion Compensation Fiber (DCF) For every km traveled, must go through an equal distance of DCF Fiber gratings Shoebox size

42 Technique for Dispersion Compensation Z- Transform Z-transform model of individual ring with tunable coupler Differential phase of coupler given by y Ring phase given by f Sample time for z-transform given by ring delay T Ring loss given by g (with 0 < g < 1) Each ring is an approximate all-phase filter Pole at z = sin(y/2)gexp(j(f+p/2)) Zero at z = (1/sin(y/2))gexp(j(f+p/2)) H Ring Resonator with tunable coupling and phase variation. j sin( y / 2) ge 1 j sin( y / 2) ge z z jf 1 ( z) jf 1 Input Output Phase Shifter Tunable 3dB Coupler Tunable 3dB Coupler

43 EPIC (Electronic - Photonic Integrated Circuit) based Technique for Dispersion Compensation For dispersion compensation, first a set of all-pass pole-zero pairs is computed such that the overall filter has a desired negative dispersion over the frequency band of interest This can be done by building up an approximately-linear group-delay profile over the frequency-band of interest (from the group delays of the individual pole-zero pairs) Each all-pass filter pole-zero pair is then implemented by an individual ring by tuning both the coupler differential phase and the ring phase Ring Resonator with tunable coupling and phase variation. H k ( ) j sin( y k / 2) ge 1 j sin( y / 2) ge k jf jf k e e k j T j T Input Output Phase Shifter Tunable 3dB Coupler Tunable 3dB Coupler

44 Photonic Analog to Digital

45 BAE s Photonic A/D Attributes All Optical Microwave Input - Digitized Word Optical Pulse Output Digitized Optical Word Converted to Digital Electronic Word by Low Bandwidth, Allows Optical-to-Electronic-Converter (OEC) to be conducted Remotely Not Based on a Circular Argument Used in Hybrid Approaches (Photonic A/D Needed to Replace Speed Limitations of Electronic A/D, So Let s Rely on Electronics for Quantization, and Bit Decoding Which Are the Highest Speed/Bandwidth and Delay Sensitive Areas of an A/D Circuit) Based on Mature Technologies Implemented With Recent Advances in Component Technologies and Performance Sampling Using extension of PACT Developed MLL Sources, Integration into EPIC environment will allow Growth to Higher Linearity Using Nonlinear Device Enabled Linear Optical Sampling Quantization Based on Mature Nonlinear Interferometer Optical Window Or Threshold Comparators. High Bit Count Sensitivity Provided by Recent Material Advances, Engineered Nonlinearity Materials, Resonant Enhancement Techniques, and Photonic Bandgap Structures. Wavelength Quantization Level Encoding, Self Limiting, and Pulsewidth Extension Integrated into Optical Comparator Device (Optical R-S Flip-Flop, Optical One-Shot), or Obtained Using Opti-Optical Wavelength Converters Wavelength Binary Bit Encoding Using Sampled Fiber/Waveguide Bragg Gratings Level Shifting Architecture Enabled by Photonic Integration for High Bit Count Implementation

46 Level Shifting All-Optical Photonic A/D Architecture High Bit Count Design Architecture Which Dramatically Lowers Component Count and Complexity Dependent on Photonic Integrated Circuit Implementation in Order to Meet the Difficult Pulse Overlap and Synchronization Issues for High Sample Rates Dependent on Photonic Analog Equivalent Of A DAC For Adaptive Threshold Setting Benefits from Optical Comparator and Bit Sensitivity Enhancement Developments in Flash Architecture Implementation I thresh (OC3) OC3 Q I thresh (OC2) WDM W W W OEC 1 1 : 4 splitter level 13 input optical delays OC2 Q I thresh (OC1) W WDM Q OC1 I thresh (OC0) W W WDM OEC 1 OEC 0 OC0 Q OEC 1 OC3 optical r-s flip-flop comparator optical coupler W optical attenuator WDM optical wave division multiplexer OEC inverting optical-to-electrical converter

47 Nonlinear Interferometer Threshold Comparator Two Nonlinear Interferometer Optical Gates Combined To Form An R-S Flip-Flop Comparator Set-Reset Extends Pulsewidth And Converts The Doubled-Sided Comparator Intensity Window Response To Be A Single-Sided Threshold Comparator Intensity Response Allows Conventional Transition Detection Logic Based On Nonlinear Interferometer Optical Gates (Inverters, NAND, XOR)

48 Optical R-S Flip-Flop Comparator Implementations Can Provide Times Pulsewidth Extension For Detectability As Well As Threshold Comparison nonlinear phaseshifter reset pulse OC2 bias CW1 out1 ( Q ) dual resonantly enhanced optical comparators OC2 OC1 CW2 nonlinear phaseshifter out2 ( Q ) set pulse OC1 bias Optical R-S Flip-Flop

49 Photonic Transition Detection Logic Flash Quantizers Based On Threshold Or Window Comparators Provide Up To 2 N -1 Level Outputs (Threshold Comparators By Design; Window Comparators By Artifacts Of The Finite Pulse Rise/Fall And Comparator Intensity Response Interaction) Transition Detection Logic Determines The Highest Level Threshold Or Window Exceeded. In Addition It Contains Many Error Detection/Correction Features Once The Highest Level Is Determined, Its Value Is Converted To Binary By A Binary Encoder Square Pulse Shaping Of The Sampling Pulse And Comparator Intensity Response Benefits Both Comparison Methods

50 Discussion