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Ultra-Fast Wavelength-Hopping Optical CDMA Principal Investigator: Eli Yablonovitch; Co-PI’s: Prof. Rick Wesel, Prof. Bahram Jalali, Prof. Ming Wu Electrical Engineering Department, University of California, Los Angeles CA Objectives Approach Accomplishments To create an Optical Code Division Multiplexing system that: That is more secure than a WDM optical communications system using conventional time domain codes. That suffers little or no capacity degradation compared to a WDM system. That is ultimately scalable to 100 simultaneous users running at 10Gbits/sec each. That is usable for both free-space optical as well as fibers That will be reasonably close in hardware cost compared to a WDM system. We will encode individual bits in a wavelength-time matrix, that is programmed by provably secure algorithms, and that hops with every bit period. Have distinguished the advantages and dis-advantages between direct sequence spread spectrum and frequency hopping. Designed a system for secure wavelength hopping OCDMA.

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t carrier + - Amplitude Modulation freq

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Coherent Communication (homodyne detection) signal(t) carrier wave local oscillator signal(t) cos t 2 signal(t) cos t Transmitter Receiver

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Direct Sequence Spread Spectrum: carrier wave cos t code(t) signal(t) Transmitter signal(t) code(t) “noisy” carrier 1 time chip local oscillator cos t code(t) local code generator Receiver cos t 2 code(t) 2 signal(t)

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1 t 1 1 direct sequence PN code data PN data TcTc TbTb c(t)c(t) t t d(t)d(t) s ds (t) d(t)d(t) c(t)c(t) direct sequence encoding Figure 2a Figure 2b

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Frequency Hopping Spread Spectrum 1. Time Division - TDMA 2. Wavelength Division - WDMA 3. Code Division - CDMA OCDMA Time Wavelength TDM Time Wavelength WDM Time Wavelength

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CDMA or Spread-Spectrum Seemingly wasteful of bandwidth channels Codes are orthogonal, N channels N codes Channel capacity is unchanged! Secret Covert Jamming resistant Multi-path or speckle resistant Self-managed network - users pick codes at random Orthogonality Condition:

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Direct Sequence (homogeneous broadening) Frequency Hopping (inhomogeneous) first patented by Hedy Lamarr (actress) in 1941 Used by Secret Service (U.S.) Military radios Cellular telephones: Subtle optimization competition between TDMA and CDMA About 50% of US cellphones use CDMA, including particularly the Sprint PCS network. World-Wide Generation 3.0 Cellphone standard will be CDMA.

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Dispersion-Limited Signal Propagation Distance TDM CDM WDM = dispersion coefficient M = # of channels (length of code)

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The basic idea: wavelength-time matrix OCDMA Time Wavelength TDM Time Wavelength WDM Time Wavelength Legend: 1 2 user1, user2

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Generate hopping patterns 1. Bob chooses secret primes p and q and computes n = pq. 2. Bob chooses integer e which is prime to (p-1)(q-1). 3. Bob computes d with de mod (p-1)(q-1) Bob makes n and e public, and keeps p, q, d secret. 5. Alice encrypts m as c m e mod n, and sends c to Bob over a public channel. 6. Bob decrypts by computing m c d mod n. 7. Both Bob and Alice use m as a seed and feed it in to Advanced Encryption Standard (AES) encoder to generate a string of random numbers. 8. That string is fed back into to AES encoder to generate a 2nd string, etc., etc. 9. Both Bob and Alice use the string of random numbers to fill the wavelength-time matrix, using modular arithmetic. 10. Bob and Alice generate the hopping patterns according to the wavelength-time matrix, using a different modular arithmetic RSA public key algorithm AES encoder Seed S k-1 SkSk }

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Fill the wavelength-time matrix Random numbers: Time Wavelength 232 mod 64 = mod 63 = mod 62 = mod 61 = 51 Time y k = N mod (64-k), k = 0, 1, … 63 “The pattern never repeats” Then randomly fill the next matrix using a continuation of the random string.

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Define users from wavelength-time matrix Time Wavelength Time Wavelength User1User2 User k: numbers with N mod 8 = k-1, k = 1, 2, …, 8

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High level of security in the case with only one user

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Overall system design using electronic switches Pattern generator Data 1 Data 2 Data 3 Data 4 Hopping pattern 4:1 Fiber Space Division Switch + small buffer Modulator 1:4 Data 1 Data 2 Data 3 Data 4 Detector Space Division Switch + small buffer Transmitter Receiver

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The first milepost demo of 4x2.5Gbps: transmitter Pattern generator 16X16 Switch 155MHz Data 2.5Gbps Data User 1 User 2 User 3 User 4 Hopping pattern 4:1 Modulator Fiber 1:16 16:1 2.5Gbps 16X16 Switch 16X16 Switch 16X16 Switch de-SerializerSerializer 1:16 16:1

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Hopping pattern 1:4 Detector Fiber Detector Data User 1 16X16 Switch 155MHz 1:16 16:1 16X16 Switch 16X16 Switch 16X16 Switch 16:1 Data User 2 Data User 3 Data User 4 Pattern generator de-SerializerSerializer 1:16 16:1 The first milepost demo of 4x2.5Gbps: receiver

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Switching Fabrics In general, the implementation of an NXN switch need NlogN 2X2 switches. For an NXN rearrangeable permutation switch, the number of 2X2 swithes is at least log(N!), which is approximately equal to NlogN N+log(2 N)/2. For N=16, log(N!) = Network implementing 16X16 using 56 2X2 switches.

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Overall system design using LiNbO 3 optical switches Pattern generator Hopping pattern 1:4 Data 1 4:1 Fiber 16X16 LiNbO 3 Space Division Switch Modulator Data 1 1:4 Modulator Data 2 1:4 Modulator Data 3 1:4 Modulator Data 4 1:4 4:1 OE EO OE EO 16X16 LiNbO 3 Space Division Switch 1:4 4:1 OE Data 2 Data 3 Data 4 1:4 Bit time division demultiplexer 4:1 Bit interleaving time division multiplexer

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Availability of components: 2X2 switch VSC Gbits/sec Dual 2x2 Crosspoint Switch Features Up to 2.5GHz Clock, 2.5Gb/s NRZ Data Bandwidth Output Jitter <40ps Peak-to-Peak Output Skew <50ps Single 3.3V Power Supply Industry Standard 44 Pin PQFP Packaging Switch configuration time < 1ns

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Availability of components: de-Serializer and Serializer VSC :1 Serializer Features: 2.5Gb/s Operation +3.3V Single Supply Operation VSC8164 1:16 de-Serializer Features: 2.5Gb/s Operation +3.3V Single Supply Operation

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Since the wavelength-hopping occurs in the time domain, the initial implementation requires only time-encoded WDM hardware. Four OCDMA channels at 10 Gbit/sec requires only 4 WDM channels, that can be implemented in Coarse WDM hardware, time encoded by a Silicon chip. 100 simultaneous OCDMA users (out of 1000 subscribers) can be implemented at the expense of more WDM hardware, and would require Dense WDM. Component count can be reduced, and spectral efficiency increased, by using chirped sources and time gating in Silicon to fill-in the spectral guard bands: ReceiverTransmitter

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Fast wavelength-hopping OCDMA is compatible with conventional WDM components, allowing early technology demonstrations. Rapid Summary of Mile-Posts: demonstration of the wavelength time concept using discrete conventional off-the-shelf WDM components Gbit/sec is expected to lead rapidly to 4 10Gbit/sec, using conventional components. 100 simultaneous users, out of 1000 subscribers should be feasible, but would require a large number of Dense WDM components. Time chirped hardware would lead to more efficient use of components, and more efficient spectral packing of the optical channels, and the inter- channel spaces. Critical Milestones, (Go/No Go decision) at 15 months: 1. Deliver Fiber System of Two OCDMA 2.5Gbit/sec. 2. Validate Si-Ge time gating chip design for >4 users at higher speed.

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Progression of FWH-OCDMA capabilities as a function of hardware progress: Initial Demonstrations Using Conventional WDM components: 1. Four OCDMA 2.5Gbit/sec. (15 month deliverable) 2. Ultimately Ten OCDMA 10Gbit/sec. All components are off-the-shelf, except for fast time-gating logic that implements the hopping code in Si-Ge logic technology. Later Demonstrations Using Chirped WDM hardware: 1. In this later phase, we will demonstrate an Optical-CDMA transmitter with four wavelengths and four parallel electro-absorption modulators, duplicating the coarse WDM result; four OCDMA 10Gbit/sec. 2. Increase the number of parallel optical channels, that will require large numbers of modulators and photo-detectors on-chip.

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... WDM DEMUX 1 … N 2 transmitted signal WDM MUX d(t)d(t) c(t)c(t) wavelength select s ds (t) hop pattern generator Figure 6 Multi-wavelength source...

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output data MUX DEMUX... MUX DEMUX... i0 or i1 threshold device 3-dB splitter (A) wavelength select hop pattern generator c(t)c(t) i1 or i0 wavelength select hop pattern generator c(t)c(t) Figure 7

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