System for optical spectral amplitude code division multiple access communication

Abstract

A system for optical spectral amplitude code division multiple access communication using unipolar double-weighted codes, comprising: a code generation unit configured to generate MDW-ZCC (Modified Double Weight and Zero Cross-Correlation)-based codes for SAC-OCDMA (Spectral Amplitude Coding-Optical Code Division Multiple Access), wherein the code generation unit is configured to generate optimal autocorrelation and cross-correlation values; an encoding unit connected to the code generation unit and configured to encode transmitter information using the MDW-ZCC codes; a decoder unit configured to decode received optical signals, the decoder unit comprising a single photodiode detection unit (SPD) and a direct detection unit (DD); a signal analysis unit configured to implement a Gaussian approximation for estimating the bit error rate (BER) from eye diagrams of BER and Q-factor; and a performance evaluation unit configured to measure the performance metrics Q-factor and bit error rate.

Description

FIELD OF THE INVENTION

[0001] The present disclosure relates to a system for spectral amplitude code division multiplexing (SAC-OCDMA) optical communication. More specifically, the present invention relates to a SAC-OCDMA-based system with unipolar codes and a double weighting design. The system is configured to generate the code design for SAC-OCDMA, decode the code, reduce noise, and estimate the bit error rate and Q-factor. BACKGROUND OF THE INVENTION

[0002] Optical Code Division Multiple Access (OCDMA) is a multiplexing technique in which each user of a communication channel is assigned a distinct optical code by the transmitter. OCDMA systems leverage the advantages of fiber optic technology, including high security, extremely high bandwidth, low attenuation, and long-distance transmission capabilities.

[0003] The main challenge in OCDMA systems is the suppression of multiple access interference (MAI) and phase-induced intensity noise (PIIN), which significantly degrade system performance. Current OCDMA systems are divided into coherent systems with bipolar codes (-1, +1), which require additional components, and non-coherent systems with unipolar codes (0, +1), which simplify the infrastructure but complicate the system architecture.

[0004] Spectral amplitude coding (SAC) offers efficient solutions for reducing MAI and PIIN effects by leveraging low-cost non-coherent broadband sources and zero-cross-correlation (ZCC) codes. However, existing code sequences such as modified frequency hopping codes, MQC, and Hadamard codes are not suitable for multimedia applications with diverse quality of service requirements.

[0005] Therefore, there is a need for an improved OCDMA system that addresses these limitations while maintaining optimal performance metrics such as quality factor and bit error rate in SAC-OCDMA approaches.

[0006] In view of the previous discussion, it is clear that there is a need for a system for optical spectral amplitude code division multiplexing communication. Summary of the invention

[0007] The present disclosure relates to a system for optical spectral amplitude code division multiplexing (SPX-ZCC) communication. The present invention relates to a system for optical spectral amplitude code division multiplexing (SPX-ZCC) communication using unipolar double-weighted codes. The system comprises a code generation unit for generating modified double-weighted zero-cross correlation (MDW-ZCC) codes, a decoder unit using single-photodiode (SPD) and direct detection (DD) techniques, a signal analysis unit using Gaussian approximation for BER estimation, and a performance evaluation unit for measuring system metrics. The system effectively reduces noise interference while ensuring optimal performance in fiber optic communication applications.

[0008] An object of the present disclosure is to provide a system for optical spectral amplitude code division multiple access communication.The system comprises: a code generation unit for generating MDW-ZCC (Modified Double Weight and Zero Cross-Correlation)-based codes for SAC-OCDMA (Spectral Amplitude Coding-Optical Code Division Multiple Access), the code generation unit generating optimal autocorrelation and cross-correlation values; an encoder unit connected to the code generation unit for encoding transmitter information using the MDW-ZCC codes; a decoder unit for decoding received optical signals, the decoder unit comprising an SPD (Single Photodiode) detection unit and a DD (Direct Detection) unit; a signal analysis unit implementing a Gaussian approximation to estimate the bit error rate (BER) from eye diagrams of BER and Q-factor; and a performance evaluation unit for measuring Q-factor and bit error rate.

[0009] Another object of the present disclosure is to provide a system for spectral amplitude code division multiplexed optical communication.

[0010] Another object of the present disclosure is to develop an optical CDMA system that generates MDW-ZCC codes with optimal autocorrelation and cross-correlation properties, thereby significantly reducing multiple access interference and phase-induced intensity noise compared to conventional systems.

[0011] Another object of the present disclosure is to implement a low-cost detection system using single photodiode and direct detection techniques that eliminates the need for complex balanced receivers while maintaining superior signal quality and reducing system implementation costs.

[0012] Another objective of the present disclosure is to provide accurate performance evaluation capabilities through Gaussian approximation techniques that enable precise estimation of bit error rate and Q-factor metrics, thus facilitating reliable system optimization and performance comparison with existing OCDMA systems.

[0013] To further clarify the advantages and features of the present disclosure, the invention will be explained in more detail with reference to specific embodiments illustrated in the accompanying drawings. These drawings illustrate only typical embodiments of the invention and are therefore not to be considered as limiting its scope. The invention will be described and explained in more detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE CHARACTERS

[0014] These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings, in which like characters represent like parts throughout. Fig. 1 shows a block diagram of a system for spectral amplitude code division multiplexed optical communication according to an embodiment of the present disclosure; Fig. 2 shows a block diagram of a workflow of the system according to an embodiment of the present disclosure. Fig. 3 shows a block diagram of the SPD technique for a SAC-OCDMA system according to an embodiment of the present disclosure.

[0015] Those skilled in the art will also appreciate that the elements in the drawings are shown for convenience and are not necessarily to scale. For example, the flowcharts illustrate the method by key steps to enhance understanding of aspects of the present disclosure. Furthermore, with respect to device construction, one or more components of the device may be represented in the drawings by conventional symbols. The drawings may show only the specific details relevant to understanding embodiments of the present disclosure in order not to clutter the drawings with details that would be readily apparent to those skilled in the art from the present description. DETAILED DESCRIPTION:

[0016] To facilitate understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and will be clearly described. However, the scope of the invention is not limited thereby. Changes and further modifications to the illustrated system, as well as further applications of the principles of the invention, are possible, as would normally occur to one skilled in the art to which the invention pertains.

[0017] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be limiting thereof.

[0018] References in this specification to "one aspect," "another aspect," or similar language mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Therefore, the language "in one embodiment," "in another embodiment," and similar language throughout this specification may or may not refer to the same embodiment.

[0019] The terms "comprises," "comprising," or other variations thereof are intended to cover non-exclusive inclusion, such that a process or method comprising a list of steps may include not only those steps, but also additional steps not expressly listed or inherent in that process or method. Likewise, the statement "comprises" for one or more devices, subsystems, elements, structures, or components does not exclude, without further limitation, the existence of other devices, subsystems, elements, structures, components, or additional devices, subsystems, elements, structures, or components.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. The systems, methods, and examples provided herein are for illustrative purposes only and should not be considered limiting.

[0021] Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0022] Fig. 1 shows a block diagram of a system (100) for optical spectral amplitude code division multiplexing communication according to an embodiment of the present disclosure;

[0023] According to Fig. 1, the system (100) comprises: a code generation unit (102) configured to generate MDW-ZCC (Modified Double Weight and Zero Cross-Correlation)-based codes for SAC-OCDMA (Spectral Amplitude Coding-Optical Code Division Multiple Access), wherein the code generation unit (102) is configured to generate optimal autocorrelation and cross-correlation values; an encoding unit (104) connected to the code generation unit (102) and configured to encode transmitter information using the MDW-ZCC codes; a decoding unit (106) configured to decode received optical signals, wherein the decoding unit (106) comprises an SPD detection unit (106a) and a DD (Direct Detection) unit (106b); a signal analysis unit (108) configured to implement a Gaussian approximation for estimating the bit error rate (BER) from eye diagrams of BER and Q-factor;and a performance evaluation unit (110) configured to measure the performance metrics Q-factor and bit error rate;

[0024] In one embodiment, the code generation unit (102) is configured to utilize MDW-ZCC to generate codes for the SAC-OCDMA system. Code construction is performed by implementing mathematical recursive equations, without requiring step-by-step programming. The code generation unit (102) is also configured to generate double-weighted codes, with all chips occurring in pairs. This reduces system implementation costs and filtering requirements. All generated codewords have ZCC, which increases system performance and completely suppresses multi-access interference (MAI). The system (100) is configured for fiber optic communication applications requiring high bandwidth, low attenuation, and long-haul transmission.

[0025] In one embodiment, the encoder unit (104) is configured to use broadband incoherent light sources including light-emitting diodes (LEDs) to enable a low-cost implementation with reduced complexity.

[0026] In one embodiment, the single photodiode detection unit (SPD) (106a) comprises a decoder and a subtractive decoder (S-decoder), wherein the decoder uses low-cost fiber Bragg grating (FBG) filters with the same spectral response as the encoder but from different interferers, wherein the S-decoder uses only frequency bins, wherein the decoder first decodes the received signal and then transmits the output to the S-decoder, wherein for the target user the output signal is either zero or contains frequency bins of interference after optical removal, wherein the single photodiode detection unit (SPD) transmits the signal from the optical to the electrical domain, and wherein the single photodiode detection unit (SPD) eliminates both PIIN and MAI before converting the received signal to the electrical domain.

[0027] In one embodiment, the direct detection unit (106b) comprises a decoder and detector set, wherein the direct detection mechanism uses non-overlapping wavelengths that are unique to each user and transmitted to the photodiode at the receiver. When detecting non-overlapping wavelengths, PINN is eliminated, thereby improving performance and reducing receiver complexity.

[0028] In one embodiment, the signal analysis unit (108) is configured to calculate the noise variance consisting of optical beat interference (OBI), relative intensity noise (RIN), shot noise, and thermal noise components, and the signal analysis unit (108) is configured to implement a Gaussian approximation to determine the BER and SNR of the system.

[0029] In one embodiment, the performance evaluation unit (110) is configured to compare system performance with three-dimensional single weight zero cross-correlation (3D-SWZCC) code, two-dimensional spectral / spatial cyclic shift (2D-SSCS) and permutation matrix zero cross-correlation (PM-ZCC) code systems.

[0030] In one embodiment, the system (100) is configured to accommodate multiple concurrent users with shorter code lengths and weights while maintaining optimal BER performance.

[0031] The present invention provides a comprehensive system for optical spectral amplitude code division multiple access (OCDMA) communication that solves the fundamental challenges of existing OCDMA systems. The system architecture includes a sophisticated code generation unit specifically configured to generate modified dual-weight and zero-cross-correlation codes through mathematical recursive equations. This eliminates complex step-by-step programming procedures. This code generation approach ensures optimal autocorrelation and cross-correlation values ​​while providing flexibility for varying user numbers and code weights.

[0032] The decoder unit represents a significant advance in OCDMA detection technology by integrating single-photodiode detection components with direct detection techniques. This configuration utilizes fiber Bragg grating filters combined with single-photodiode components to effectively detect non-overlapping optical pulses. The system also includes a subtractive decoder component that utilizes frequency ranges of different interferers, thus eliminating interfering signals in the optical domain before the optical-to-electrical conversion occurs.

[0033] The signal analysis unit implements advanced Gaussian approximation techniques for comprehensive noise analysis and performance evaluation. It calculates noise variance components such as optical beat noise, relative intensity noise, shot noise, and thermal noise, enabling precise system performance evaluation. Direct detection technology specifically eliminates phase-induced intensity noise and multiple access interference by utilizing non-overlapping, user-specified wavelengths, significantly improving overall system performance.

[0034] The system supports multiple concurrent users with shorter code lengths and weights while maintaining an optimal bit error rate. The implementation utilizes broadband incoherent light sources, including light-emitting diodes, for a cost-effective implementation with reduced complexity compared to coherent systems. The performance evaluation unit enables comprehensive comparison with existing systems, including three-dimensional single-weight zero-cross-correlation codes, two-dimensional spectral / spatial cyclic shift systems, and permutation matrix zero-cross-correlation code systems.

[0035] The dual-weighted design ensures that all chips are arranged in pairs, reducing system implementation costs and filtering requirements. This approach provides superior performance for fiber optic communication applications requiring high bandwidth, low attenuation, and long-distance transmission. This makes the system particularly suitable for modern optical communication networks.

[0036] Fig. 2 illustrates a block diagram of a system workflow according to an embodiment of the present disclosure.

[0037] According to Fig. 2, the SAC (Spectral Amplitude Coding) system is configured as a highly effective solution for reducing the effects of multiple access interference (MAI) and the resulting intensity noise. The SAC-OCDMA system architecture incorporates MAI mitigation capabilities through broadband incoherent sources, including light-emitting diodes (LEDs), enabling cost-effective implementation with reduced complexity. The system tackles the challenging task of code family construction with comprehensive features. The system's code generation unit utilizes optimal cross-correlation and autocorrelation qualities to reduce phase-induced intensity noise (PIIN) and multiple user interference (MUI). The system's detection components achieve significant MAI removal effectiveness through non-overlapping chip elimination techniques.The system architecture accommodates different numbers of concurrent users through shorter code lengths and weights while maintaining strong BER performance.

[0038] The architecture of the system process is in Fig. 2. The system first includes a modified double weighting combined zero cross-correlation (MDW-ZCC) code generation unit for constructing the SAC-OCDMA system, which is configured to generate optimal autocorrelation and cross-correlation values. The system implements a direct detection (DD) component for decoding transmitted information. The DD component of the system is configured to reduce various types of noise, including signal-to-noise degradation, optical beat interference (OBI), PIIN, and receiver noise. The system then applies Gaussian approximation analysis to the decoded information. The Gaussian approximation component of the system is configured to estimate the BER from the eye diagram analysis of the BER and Q-factor parameters.

[0039] The SAC-OCDMA system continues to address the challenges of code family selection, with the development of suitable variable weight (VW) or constant weight (CW) codes remaining an important aspect of system design. Previous system implementations have not sufficiently addressed the key parameter of chip-1 position in code sequences, which affects system performance. The system features a spectral coding architecture for OCDMA applications that supports various service classes through the proposed combination of MDW and ZCC (MDW-ZCC). The system offers several advantages, including acceptable code length, simple and powerful mathematical code generation capabilities, and modifiable ZCC properties. By selecting the detection technique based on optical code qualities, the system contributes significantly to higher code quality.

[0040] The MDW-ZCC code generation unit combines two separate code approaches, MDW and ZCC, and integrates their potential advantages into the system architecture. The system utilizes dual weights for MDW code construction, with all chips occurring in pairs. This reduces system implementation costs and filtering requirements. The ZCC component of the system ensures that all generated codewords retain ZCC properties, resulting in improved system performance and complete MAI suppression. Similar to other ZCC code systems, the system utilizes DD detection for DW-ZCC implementation. This eliminates the need for additional filters in the lower arms of the symmetric receiver, resulting in further system cost savings. The system's code construction is based on a recursive model, where code generation with specific weight requirements requires code generation with appropriate weight parameters.This offers advantages for DW-ZCC over conventional ZCC systems. The system addresses the performance degradation associated with larger code lengths, which are uncalculable using conventional formulas, while ZCC systems have restrictive requirements. The system allows for variable user numbers and code weights for the proposed DW-ZCC implementation. ZCC systems, in contrast, are better suited for wavelength optical networks (WONs) with low user numbers. The system generates shorter code lengths than ZCC-generated codes, except for certain user numbers where the performance of both codes is equivalent. The system's DW-ZCC code construction implements fully mathematical recursive equations, without the need for step-by-step programming or procedural implementations. Once the user numbers are determined, the system simplifies individual codeword construction for each user.The system eliminates the need for preceding codewords or code matrix dependencies and provides features that are particularly useful for modifying encoder / decoder components.

[0041] The system addresses the challenges of signal transmission detection in the presence of system noise and performance-affecting parameters for optical CDMA applications. Optical performance is ensured by a code-specific detector design that enables easy decoding of transmitted information. System analysis utilizes single photodiode (SPD) and direct detection (DD) components. The DD implementation of the system includes received signals with non-overlapping spectral components, thus providing unique approaches for individual users required for diode detector functionality. The system utilizes fiber Bragg grating (FBG) filter components in combination with single photodiode components for non-overlapping optical pulse detection.The technical performance of the system takes into account system noise influences and turbulence, including signal-to-noise ratio, effective received power, phase-induced intensity noise, receiver noise, optical beat interference (OBI), and relative intensity noise. The implementation of DD detection improves the system's performance, thus enabling noise suppression.

[0042] Fig. 3 shows a block diagram of the SPD technique for a SAC-OCDMA system according to an embodiment of the present disclosure.

[0043] Fig.Figure 3 shows the system's decoding architecture, which consists of a decoder and a subtractive decoder (s-decoder). The decoder uses low-cost FBG filters with identical spectral responses to the encoder components, while the s-decoder exclusively uses frequency ranges of various interferers. The decoder first processes the received signals and then transmits the decoder output to the s-decoder. The system generates either zero output signals or frequency ranges of interfering signals after optical removal for selected users. The system transfers signals from the optical to the electrical domain via individual photodiode components. The SPD approach eliminates both PIIN and MAI before converting the received signal to the electrical domain. This enables simultaneous system access for significantly more users while improving system performance.The system architecture diagram illustrates the implementation of SPD technology. The system enables the use of individual photodiodes by suppressing interference signals in the optical domain. Through this technology implementation, the system reduces shot noise generation and optical-to-electrical conversion processing at the receiver end. The system implements SAC with SPD detection for any fixed in-phase cross-correlation code through simple S-decoder spectral distribution modification, depending on the SAC code structure.

[0044] The DD implementation requires a decoder and a detector set, unlike other techniques that require two sets of inputs for the receivers. The detection mechanism operates on non-overlapping wavelengths. The system selects the non-overlapping wavelengths unique to each user and transmits them to the photodiode components of the receivers. The system eliminates the need for subtractors because the wavelengths are detected by individual photodetector components. The system eliminates PIIN when non-overlapping wavelengths are detected. The system thus improves performance and reduces receiver complexity. The DD implementation eliminates the need for power dividers, two photodiodes, and subtractors at each user decoder compared to symmetric detection systems. The system achieves lower costs through reduced component consumption.

[0045] The system uses critical parameters such as BER and Q-factor to evaluate system efficiency. It examines BER performance calculations for three OCDMA receiver types: receivers using Multiple Access Interference Cancellation (MAIC) and Manchester coding, receivers using MAIC approaches, and simple receivers. The system calculates BER and signal-to-noise ratio (SNR) using Gaussian approximation techniques. The photodetector components determine thermal and shot noise parameters. The system demonstrates doubly weighted ZCC performance in SAC-OCDMA environments through an eye diagram analysis in terms of BER and Q-factors. The system determines BER and SNR using a Gaussian approximation to analyze system performance. The system excludes PIIN due to ZCC characteristics and lack of spectral overlap between different users, while including shot and thermal noise in the analysis.The system uses the proposed DD-based Gaussian approach for accurate BER estimation. The system estimates the BER using eye diagram analysis of the BER and Q-factor parameters and utilizes simulation capabilities.

[0046] In one embodiment, the system implementation requires novel code testing based on various performance verification parameters. The three-user SAC-OCDMA system with Zero Frequency Division (ZFD) code functions is tested based on parameters such as distance or fiber length, effective source power, and data rate. The first implementation of the system uses MDW-ZCC code with different data rates. The system tests the BER and eye diagram parameters, respectively. The system's performance is evaluated using Python software version 3.8.0. The system runs on Ubuntu with 4 GB of DDR3 memory. It uses an Intel Core i5 processor running at 3.5 GHz and a simulation time of 200 seconds. Detailed specifications are shown in the system configuration table.

[0047] The system performance evaluation demonstrates comprehensive performance across multiple operating parameters and data rates. The SAC system with MDW-ZCC code architecture demonstrates excellent performance characteristics through eye diagram analysis, showing clear relationships between amplitude and bit period at various data transmission rates from 1 Gbps to 4 Gbps. The system maintains optimal eye openings at different bit rates, indicating robust performance for simultaneous multi-user communication at high data rates. However, the system performance analysis shows that performance degradation occurs with increasing data rates, which is typical for higher-frequency optical communication systems. The amplitude performance demonstrates stable operation with time variations between 0 and 1 second, while amplitude variations range from -1 to +1, ensuring acceptable signal integrity for optical transmission applications.The Q-factor analysis shows that system performance degradation occurs at bit periods above 5 Gbps per network user. This corresponds to Q-factor values ​​below the minimum threshold of 3 dB required for acceptable BER performance. The quality factor values ​​range between 1 and 3 and indicate satisfactory system operation within the specified parameters. Using the MDW-ZCC code implementation, the system demonstrates excellent performance at 155 Mbps across various bit periods, with optimal eye diagram openings achieved through proper filter implementation. The system eliminates interference between adjacent filter channels, confirming that the impact of chip-1 position on system performance is successfully mitigated.The evaluation of the multi-user system demonstrates consistent eye quality across multiple active users with Q-factor values ​​between 1 and 5 dB, indicating robust performance even at high data rates of up to 8 Gbps. The system successfully detects and recovers important signals at bit rates of 155 Mbps with operating parameters of 1.2 nm. Distance-based performance analysis shows that the system supports maximum transmission distances of 25 kilometers using SAC-OCDMA with MDW-ZCC code and direct detection techniques. The BER performance varies with transmission distance, starting at 0.35 for 5-kilometer distances and gradually increasing to 0.85 at maximum transmission distances of 25 kilometers. The system exhibits acceptable performance over this distance range, making it suitable for mid-range optical communications applications.Data rate correlation analysis shows an inverse relationship between Q-factor performance and increasing data rate. As the data rate increases from 1.0 to 2.4 Gbit / s, the corresponding Q-factor values ​​decrease from 8.25 to 6.50, demonstrating predictable system behavior under various operating conditions. The system exhibits optimal Q-factor performance characteristics suitable for the requirements of high-speed optical communications. Receive power analysis shows improved system performance at increased receive powers. The system operates effectively over receive power ranges from -35 dBm to 0 dBm, with BER performance improving significantly with increasing receive power. This property confirms the system's capabilities for sensitivity optimization and energy efficiency for practical optical communications implementations.

[0048] A comparative performance analysis with existing systems, including three-dimensional single weight zero cross-correlation (3D-SWZCC) codes, two-dimensional spectral / spatial cyclic shift (2D-SSCS), and permutation matrix zero cross-correlation (PM-ZCC) codes, demonstrates superior system performance. The proposed system achieves lower BER values ​​compared to existing methods, thus confirming improved system performance. The signal-to-noise ratio (SNR) performance analysis shows improved performance compared to permutation matrix zero cross-correlation PM-ZCC codes and two-dimensional spectral / spatial cyclic shift systems. A comparative Q-factor analysis with existing MDW, PM-ZCC codes, and two-dimensional multidiagonal (2D-MD) codes shows higher performance values, thus confirming the superior operating characteristics of the proposed system.

[0049] In one embodiment, system validation utilizes Python simulation software for comprehensive performance modeling and experimental verification. Critical performance criteria such as eye diagram analysis, BER evaluation, and Q-factor assessment confirm system efficiency across multiple operating parameters, including bit rate, operating wavelength, receiver noise temperature, and various system components. The system demonstrates a performance improvement of approximately 3% over existing methods while maintaining shorter code weights. Performance parameter tests regarding data rate, distance, and received power confirm robust system operation, which is suitable for advanced optical communications applications.

[0050] The present invention relates to a comprehensive spectral amplitude coding system with optical code division multiple access (CDMA). It utilizes modified double-weighted and zero-cross-correlation codes for optimal autocorrelation and cross-correlation performance. The system integrates single-photodiode and direct detection techniques for effective decoding of transmitter information and noise rejection. The implementation of the Gaussian approximation enables precise estimation of the bit error rate through eye diagram analysis of the BER and Q-factor parameters. The performance evaluation of the system confirms its superior capabilities compared to existing systems and lays the foundation for future three-dimensional code implementations using m-sequence codes in spectral / temporal / spatial OCDMA domains with integrated encoder and decoder designs for efficient 3D bipolar mode operation.

[0051] The drawings and the foregoing description illustrate examples of embodiments. Those skilled in the art will recognize that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be separated into multiple functional elements. Elements of one embodiment may be added to another embodiment. For example, the order of the processes described herein may be changed and is not limited to the manner described herein. Furthermore, the actions of a flowchart need not be performed in the order shown; nor do all actions need to be performed. Also, actions that are not dependent on other actions may be performed in parallel with the other actions. The scope of the embodiments is in no way limited by these specific examples.Numerous variations, whether explicitly stated in the specification or not, such as differences in structure, dimensions, and use of materials, are possible. The scope of the embodiments is at least as broad as indicated in the following claims.

[0052] Advantages, further benefits, and solutions to problems have been described above with reference to specific embodiments. However, the advantages, advantages, solutions to problems, and any components that may result in or enhance an advantage, advantage, or solution are not to be construed as critical, required, or essential features or components of any or all of the claims. REFERENCES 100 A system for spectral amplitude code division multiple access optical communication. 102 Code generation unit 104 Encoder unit 106 Decoder unit 106a Single photodiode detection unit (Spd) 106b Direct detection unit (Dd) 108 Signal analysis unit 110 Performance Evaluation Unit 202 Modified Double Weighting and Zero Cross-Correlation (Mdw-Zcc) 204 Direct detection technique (Dd) 206 Gaussian approximation 208 Ber estimate 210 Eye diagram of Ber and Q-factor 212 Decoding the transmitter information 214 Signal-to-noise ratio 216 Phase-induced intensity noise 218 Optical Beat Interference (Obi) 220 - Receiver noise 222 Reduce Noise 224 Building Regulations for Sac-Ocdma 226 Best possible autocorrelation and cross-correlation 302 Received signal 304 Optical Adder 306 Optical Subtractor 308 Edition

Claims

[1] A system for optical spectral amplitude code division multiple access communication using unipolar double-weighted codes, comprising: a code generation unit configured to generate MDW-ZCC (Modified Double Weight and Zero Cross-Correlation)-based codes for SAC-OCDMA (Spectral Amplitude Coding-Optical Code Division Multiple Access), wherein the code generation unit is configured to generate optimal autocorrelation and cross-correlation values; an encoding unit connected to the code generation unit and configured to encode transmitter information using the MDW-ZCC codes; a decoder unit configured to decode received optical signals, the decoder unit comprising a single photodiode detection unit (SPD) and a direct detection unit (DD); a signal analysis unit configured to implement a Gaussian approximation for estimating the bit error rate (BER) from eye diagrams of BER and Q-factor; and a performance evaluation unit configured to measure the performance metrics Q-factor and bit error rate. [2] The system of claim 1, wherein the code generation unit is configured to use MDW-ZCC to construct codes for the SAC-OCDMA system, wherein the code construction is performed by implementing mathematical recursive equations without requiring step-by-step programming. [3] The system of claim 2, wherein the code generation unit is further configured to generate double-weighted codes, with all chips occurring in pairs, thereby reducing system implementation costs and filtering requirements, and wherein all generated codewords are ZCC, resulting in improved system performance and complete suppression of multi-access interference (MAI), the system being configured for fiber optic communication applications requiring high bandwidth, low attenuation, and long-distance transmission capabilities. [4] The system of claim 1, wherein the encoder unit is configured to use broadband incoherent light sources comprising light-emitting diodes (LEDs) to enable a low-cost implementation with reduced complexity. [5] The system of claim 1, wherein the single photodiode detection unit (SPD) comprises a decoder and a subtractive decoder (S-decoder), the decoder using low-cost fiber Bragg grating (FBG) filters with the same spectral response as the encoder but from different interferers, the S-decoder using only frequency bins, the decoder first decoding the received signal and then transmitting the output to the S-decoder, wherein for the target user the output signal is either zero or contains frequency bins of interference after optical removal, the single photodiode detection unit (SPD) transmits the signal from the optical to the electrical domain, and the single photodiode detection unit (SPD) eliminates both PIIN and MAI before converting the received signal to the electrical domain. [6] The system of claim 1, wherein the direct detection unit comprises a decoder and detector set, wherein the direct detection mechanism uses non-overlapping wavelengths that are unique to each user and are communicated to the photodiode at the receiver, wherein upon detection of non-overlapping wavelengths, PINN is eliminated, thereby improving performance and reducing receiver complexity. [7] The system of claim 1, wherein the signal analysis unit is configured to calculate the noise variance consisting of optical beat interference (OBI), relative intensity noise (RIN), shot noise, and thermal noise components, and wherein the signal analysis unit is configured to implement a Gaussian approximation to determine the BER and SNR of the system. [8] The system of claim 1, wherein the performance evaluation unit is configured to compare system performance with three-dimensional Single Weight Zero Cross-Correlation (3D-SWZCC) code, two-dimensional Spectral / Spatial Cyclic Shift (2D-SSCS) and Permutation Matrix Zero Cross-Correlation (PM-ZCC) code systems. [9] The system of claim 1, wherein the system is configured to accommodate multiple concurrent users with shorter code lengths and weights while maintaining optimal BER performance.

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