Simon Ayotte

Experimental verification and capacity prediction of FE-OCDMA using superimposed FBG

This paper presents the experimental demonstration and simulation results of a frequency-encoded optical code-division multiple-access (FE-OCDMA) system using broad-band incoherent source, superimposed fiber Bragg gratings for encoding/decoding of unipolar m-sequence codes, and balanced detection. The bit-error rate is measured for up to four simultaneous users at 155 and 622 Mb/s. Exploiting the excellent match between simulation and experiment, the paper concludes with a prediction of the potential capacity of an optimized FE-CDMA system.

Analysis of the spectral efficiency of frequency-encoded OCDMA systems with incoherent sources

This paper presents the spectral efficiency of frequency-encoded (FE) optical code-division multiple-access (OCDMA) systems with incoherent sources. The spectral efficiency of five code families compatible with FE-OCDMA is calculated as a function of the number of users. Analytical equations valid in the limiting case of Gaussian noise are also developed for the bit-error rate and the spectral efficiency. Among the code families considered, the modified quadratic congruence code leads to the maximum achievable spectral efficiency.

Label Stacking in Photonic Packet-Switched Networks With Spectral Amplitude Code Labels

Label stacking is used for hierarchical addressing to reduce the size of lookup tables and to increase the speed of the routing process. We propose an optical label stacking using spectral-amplitude codes (SAC) as labels to accomplish ultrafast packet forwarding. We discuss the advantages of this label architecture compared to other proposals in the literature and present experimental results. We experimentally examine two types of optical packets, one with separable SAC labels and the other one with SAC-encoded payloads. In the first case, the SAC label is a collection of spectral tones modulated at the packet rate (low rate), and the payload is on a separate wavelength modulated at the data rate (fast rate). In the second case, the payload data modulates the collection of wavelengths that constitute the code. We implement a network with two forwarding nodes, and we transmit the packets with two labels in the label stack over 80 km of fiber and measure the bit error rate (BER) after two hops. We achieve error-free transmission (BER<10 -9) for the packets with SAC labels and SAC-encoded payload at payload bit rates of 10 and 2.5 Gb/s, respectively. This is the first experimental demonstration of optical label stacking to our knowledge

Experimental comparison of coherent versus incoherent sources in a four-user /spl lambda/-t OCDMA system at 1.25 Gb/s

In optical code-division multiple access (OCDMA), the optical bandwidth is accessed simultaneously by multiple users, leading to beat noise in photodetection. The choice of the optical source can have important impact on that noise. In this paper, we compare two optical sources, a broad-band erbium-doped fiber source and a multilaser source. Experimental results for a wavelength-time OCDMA system are presented for up to four simultaneous users. Bit-error-rate curves are measured at 1.25 Gb/s with a chip rate of 10 Gchip/s. It is shown that the multilaser source outperforms the broad-band source for the design parameters of this system.

Ultrafast Forwarding Architecture Using a Single Optical Processor for Multiple SAC-Label Recognition Based on FWM

We propose and demonstrate a novel ultrafast label processor that can recognize multiple spectral amplitude coded (SAC) labels using four wave mixing (FWM) sideband allocation and selective optical filtering. Our proposed solution favors hardware simplicity over bandwidth efficiency in order to achieve ultra- fast label recognition at reasonable cost. Our implementation, unlike all other optical label processing techniques, does not require time gating, envelope detectors, or serial-to-parallel converters. Labels are transmitted simultaneously with the payload, improving temporal efficiency at the expense of spectral efficiency. Note that bandwidth efficiency can be improved through a frequency management scheme that uses irregular spacing of wavelengths for payload and label, a complexity overhead in management similar to that in long-haul networks employing irregular spacing of carriers to avoid FWM products. We present two experiments of the single processor for ultrafast forwarding using first optoelectronic and then all-optical switches. In the first experiment, we use 10 SAC labels with minimum bin separation of 25 GHz, 10 Gb/s variable-length data packets, and forward packets over 200 km using electrooptical switches. In the second experiment, all-optical switching at 40 Gb/s is demonstrated using a SAC family for up to 36 labels. We present details on the families of spectral codes for label recognition, using unequally spaced frequency bins. A code family with weight 2 and length 9 uniquely identifies 36 labels. Hardware complexity is moderate compared with short-pulse code labels (mode-locked laser) techniques. Two stable tunable lasers are required for label generation of this code family; all other hardware is commercial, off-the-shelf components such as semiconductor optical amplifiers, array waveguide gratings, optoelectronic switches, and photodetectors.

Experimental demonstration of frequency-encoded optical CDMA using superimposed fiber Bragg gratings

We propose and demonstrate a novel scheme for frequency-encoded optical code division multiple access (FE-OCDMA). Eight-wavelength superimposed fiber Bragg gratings (SFBGs) are used to encode four channels at 155 Mb/s. Multiple access interference suppression is achieved using M-sequence codes with balanced detection.

Ultra-narrowband fiber Bragg gratings for laser linewidth reduction and RF filtering

We review the improved performances of a narrow linewidth laser using negative electrical feedback obtained through advances on narrowband FBG filters. Noteworthy, the tolerance of the laser to vibrations is significantly improved. As an extension of this work, these narrow filters are proposed for filtering optical signals in RF photonics systems.

Balanced Detection of Correlated Incoherent Signals: A Statistical Analysis of Intensity Noise With Experimental Validation

We study the balanced detection of broadband incoherent optical signals-signals characterized by high-intensity noise. We consider signals generated from a single incoherent source with two types of correlation: identical spectra, but delayed in time, and overlapping, nonidentical spectra but zero time delay. Our statistical analysis yields equations for the probability density function (pdf) of the balanced detector output for partially correlated input signals based on easily measured system parameters (power spectral densities in one case, relative time delay in the other). Using analytical tools we derive expressions for output pdfs giving extremely good prediction of measured pdfs for signals with correlation coefficient up to 95%. The analytic expressions can be used to characterize system performance, in particular, bit error rate for communications systems.

Increasing the Capacity of SAC-OCDMA: Forward Error Correction or Coherent Sources?

We consider three different strategies for maximizing the capacity while minimizing the cost of spectral amplitude coding optical code-division multiple access (SAC-OCDMA): incoherent sources, multilaser sources and forward error correction (FEC). Due to their low cost and wide optical bandwidth, incoherent sources are often considered for SAC-OCDMA. Such sources exhibit reduced spectral efficiency due to their intensity-noise- limited performance. For single user systems, coherent sources offer greater spectral efficiency and improved performance; this is not necessarily the case for OCDMA. Even coherent sources are ultimately intensity noise limited in SAC-OCDMA due to the beating of coherent signals from different users overlapping in bandwidth. The intensity noise in coherent systems can be eliminated by having the center frequencies of spectral bins be offset from nominal values by a unique differential amount for each user. This requirement, however, leads to exacting requirement for source quality control and stability, and thus greater cost. We examine via simulation how system performance is affected for coherent sources under various assumptions about the precision of frequency offsets during manufacture. Finally, we examine the effectiveness of FEC in combating intensity noise in a cost effective manner. We find that coherent sources must have precise frequency placement to outperform FEC combined with incoherent sources. FEC systems work best in networks with low statistical utilization, while multilaser systems work best under high load.

Low-cost, Scalable Optical Packet Switching Networks with Multi-Wavelength Labels

We propose a self-forwarding packet-switched optical network with bit-parallel multi-wavelength labels. We experimentally demonstrate transmission of variable-length optical packets over 80 km of fiber and switching over a 1x4 multistage switch with two stages.