A single-modulator multi-wavelength comb modulation method based on dispersion mapping

Abstract

The application relates to a single-modulator multi-wavelength optical comb modulation method based on dispersion mapping. A multi-wavelength optical carrier is generated by using an optical frequency comb, time-gated optical pulses with a limited time length are formed, and different wavelengths are separated in the time domain through a dispersion medium, so that a single modulator can be used, time division multiplexing is combined, optical signals in each time slot are modulated, and multi-wavelength independent data information loading is realized. The method does not need to configure an independent modulator for each wavelength, has the advantages of simple structure and low system complexity, and is suitable for optical comb communication and a multi-channel optical transmission system.

Description

Technical Field

[0001] This invention relates to the fields of optical communication and photonics technology, specifically to a single modulator multi-wavelength optical comb modulation method based on dispersion mapping, applicable to multi-channel optical transmission systems based on optical frequency combs and multi-carrier signal modulation in wavelength division multiplexing optical communication systems. Background Technology

[0002] With the rapid development of information technologies such as cloud computing, big data, and artificial intelligence, the requirements for transmission capacity and system energy efficiency in data center interconnection and access networks are constantly increasing, driving optical communication systems towards high spectral efficiency, high integration, and low power consumption. Wavelength Division Multiplexing (WDM) technology, by transmitting multiple data streams in parallel on different wavelengths, is undoubtedly an important means of realizing high-capacity optical communication.

[0003] However, in traditional WDM systems, each wavelength channel is usually implemented by an independent laser and modulator. That is, each optical carrier needs to be configured with a corresponding electro-optic modulator to load the data signal. As the number of channels continues to increase, the number of light sources and modulators required in the system will inevitably increase significantly. This not only leads to an extremely complex system structure, high power consumption and a significant increase in cost, but also puts forward stringent requirements on the consistency and stability between multiple channels.

[0004] In recent years, optical frequency combs, as a light source capable of providing equally spaced multi-wavelength optical carriers, have been widely used in multi-channel optical communication systems due to their high coherence and frequency stability. In particular, microcavity-based optical comb devices can generate multiple equally spaced comb teeth in a single device, providing a unified light source for multi-wavelength transmission, thereby simplifying the system structure to a certain extent.

[0005] In existing optical communication systems based on optical combs, it is still necessary to first separate each comb tooth using a wavelength division multiplexer, and then modulate each tooth using an independent modulator before multiplexing the output. In other words, this method still ultimately requires multiple modulators, only reducing the complexity of the carrier generation part.

[0006] To reduce the number of modulators, some solutions in the industry have attempted to use a single modulator to uniformly modulate multi-wavelength signals. However, since optical signals of different wavelengths often overlap in time, a single modulator simply cannot achieve independent data loading for each wavelength signal, which easily leads to severe inter-channel crosstalk and thus affects the overall system performance.

[0007] Dispersive media can introduce wavelength-dependent group delays, causing different wavelength signals to have different time delays during propagation, thus realizing a frequency-to-time mapping relationship. Combined with time gating, the optical comb signal is confined to a limited time range, and the dispersion effect is used to completely separate different comb teeth in the time domain, enabling independent modulation of different wavelength signals at different times by a single modulator.

[0008] Therefore, a single modulator multi-wavelength optical comb modulation method based on dispersion mapping is proposed to reduce system complexity and achieve efficient modulation of multi-channel signals. Detailed Implementation

[0009] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0010] This invention provides a single modulator multi-wavelength optical comb modulation system based on dispersion mapping. Its core physical mechanism is to utilize the frequency correlation group delay provided by the dispersion medium to demultiplex the broadband optical frequency comb signal in the time domain, thereby allowing the independent loading of multi-channel data to be completed using a single low-speed modulator.

[0011] The core components involved in this embodiment include: a microcavity soliton optical frequency comb generator, a programmable optical filter (such as a WaveShaper), a high-speed Mach-Zehnder modulator (MZM), a commercial single-mode dispersion-compensating fiber (DCF), and a multi-channel arbitrary waveform generator (AWG), etc. The system of this invention mainly includes an optical frequency comb light source module, a time-gated module, a dispersion mapping module, and a single electro-optic modulator module.

[0012] like Figure 1 The system block diagram shown illustrates that the optical frequency comb light source module is used to generate multi-wavelength continuous optical signals. A microcavity generates a broadband frequency comb with a hyperbolic secant square envelope. To ensure consistent channel signal-to-noise ratio and simplify system clock management, a WaveShaper is used to extract the wavelengths required for wavelength division multiplexing modulation.

[0013] The time-gating module is used to periodically truncate continuous multi-wavelength optical comb signals into pulse sequences. The modulator of this module employs an RF bandwidth greater than the modulation information and a relatively large extinction ratio to obtain steep pulse edges. The AWG injects a rectangular electrical pulse sequence with a preset repetition period and a preset low duty cycle. The high-level duration of the rectangular electrical pulses precisely matches the target modulation time slot width of a single channel, while maintaining a low-level deep cutoff state for the remaining time periods within the period. Figure 2 As shown in (b), Figure 2 In (a), the multi-wavelength carriers are periodically truncated according to preset time slots to extract highly overlapping pulse sequences within a specific time window. That is, the total number of multiplexed channels in the system is... The single-channel target modulation time slot is The repetition period of the electrical pulses injected by the synchronization control module is... Boundary conditions must be met: This parameter setting ensures that each wavelength has sufficient expansion space in the time domain, and fundamentally avoids cross-cycle aliasing of pulses from adjacent periods after dispersion mapping.

[0014] The dispersion mapping module is the core component for achieving uniform separation of multiple wavelengths in the time domain. To precisely control the evolution of the broadband optical frequency comb in the dispersive medium, this invention comprehensively considers center wavelength dispersion, dispersion slope (dispersion rate of change), and higher-order dispersion effects. The physical evolution of the system's frequency-time mapping is modeled and calculated with high precision based on the following theoretical equations: First, calculate the equation for the linear change of dispersion with wavelength: Secondly, the dispersion coefficients are converted into second-order dispersion parameters: Finally, calculations were performed based on higher-order Taylor expansions to determine the difference between different wavelengths and the center wavelength. The precise time delay equation: in, The dispersion coefficient is the center wavelength. The rate of change of dispersion, This is the offset relative to the center wavelength. The third-order dispersion coefficient, The length of the optical fiber. It is the speed of light in a vacuum.

[0015] Based on the aforementioned group delay evolution equation, while maintaining a preset wavelength interval across all channels, a dispersive medium with specific dispersion parameters is configured to generate a relative group delay difference between adjacent wavelength pulses whose absolute value is precisely equal to the target modulation time slot of a single channel, thereby accurately matching the system's target modulation rate. After passing through this dispersion mapping module, as shown... Figure 2 As shown in (c), the multi-wavelength pulse sequences that were originally highly overlapping in the time domain are spaced out at equal intervals, wherein the arrival interval of each time slot is synchronized with the target modulation time slot.

[0016] In addition, to further reduce the size and insertion loss of the dispersion module and improve the linearity of dispersion mapping, the dispersion mapping module can also use a chirped fiber Bragg grating (CFBG) instead of a single-mode dispersion compensation fiber.

[0017] Specifically, the overlapping optical pulse sequence is input into the CFBG through an optical circulator. By precisely designing the chirp period of the CFBG core refractive index, the CFBG can not only provide an equivalent second-order cumulative dispersion that precisely matches the target modulation rate, but also simultaneously provide higher-order dispersion compensation to offset the nonlinear group delay deviation caused by the frequency-to-wavelength conversion.

[0018] Since the light pulses of each wavelength have been completely separated in time, a single modulator can process signals of different wavelengths in sequence, avoiding time-domain crosstalk.

[0019] Based on the above system architecture, the specific steps of the single modulator multi-wavelength optical comb modulation method based on dispersion mapping provided by this invention are as follows:

[0020] Step 1: Multi-wavelength carrier extraction and power equalization. Turn on the microcavity optical frequency comb generator, extract wavelengths using the WaveShaper programmable optical filter, and perform amplitude flattening equalization.

[0021] Step 2: Time-gated pulse generation. A high extinction ratio intensity modulator is used as a time gate to truncate the continuous optical signal into periodic overlapping optical pulses.

[0022] Step 3: Precise mapping of dispersion frequency to time. Overlapping optical pulses are injected into the dispersion-compensating fiber. The dispersion effect is used to make the multi-wavelength signals equidistantly expand in the time domain according to the higher-order group delay evolution equation, forming non-overlapping serial time slots.

[0023] Step 4: Serial Synchronous Modulation. The unfolded optical pulse sequence is fed into the modulator, enabling each channel to load independent data without crosstalk.

[0024] Step 5: Direct Transmission. The modulated multi-wavelength signal output from the single electro-optic modulator is directly coupled into the single-mode transmission fiber optic link. This multi-carrier signal is treated as a standard wavelength division multiplexing (WDM) signal in subsequent transmission, requiring no additional demultiplexing processing. Attached Figure Description Figure 1 This is a schematic diagram of the structure of a single modulator multi-wavelength optical comb modulation system based on dispersion mapping according to the present invention. Figure 2 This is a schematic diagram illustrating the time-domain changes of multi-wavelength optical signals after time gating and dispersion mapping in a single-modulator multi-wavelength optical comb modulation method based on dispersion mapping according to the present invention. Figure 2 (a) is a schematic diagram of the overlapping transmission of multiple wavelength continuous optical carriers in the time domain; Figure 2 (b) is a schematic diagram of periodic multi-wavelength overlapping optical pulses formed after time gating; Figure 2(c) is a schematic diagram of how multiple wavelength overlapping optical pulses are sequentially separated in the time domain to form serial time slots after dispersion mapping.

Claims

1. A single-modulator multi-wavelength optical comb modulation method based on dispersion mapping, characterized by mainly... The process includes: A. Multi-wavelength continuous optical signals are generated by an optical frequency comb light source module; B. The continuous optical signal enters the time-gated module and is periodically truncated into a multi-wavelength overlapping pulse sequence under the modulation of an arbitrary waveform generator, and the truncation process satisfies the time-domain boundary condition formula: ; C. The multi-wavelength overlapping pulse sequence enters the dispersion mapping module, which uses frequency-correlated group delay to achieve equidistant separation of different wavelength comb teeth in the time domain. The mapping process follows a higher-order group delay evolution equation: After time-domain separation, each wavelength component forms a serial independent time-slot sequence, which enters the single electro-optic modulator module in sequence. The single electro-optic modulator module performs independent data loading on each wavelength component at different times. D. The modulated multicarrier signal is directly coupled into the optical fiber link and transmitted as a wavelength division multiplexed signal.

2. The method as described in claim 1, characterized in that, The time-gating module employs a high-speed intensity modulator with a RF bandwidth greater than the single-channel target modulation rate and a high extinction ratio to obtain steep pulse edges and suppress optical field leakage during the shutdown period. Furthermore, the truncation process satisfies the time-domain boundary condition formula: .

3. The method as described in claim 1, characterized in that, The dispersion mapping module utilizes the frequency correlation group delay provided by the dispersion medium to cause different time delays in the propagation of multi-wavelength optical pulses that were originally highly overlapping in the time domain. This transforms the signal state from time aliasing to an interleaved, non-aliased, independent time slot state, ensuring that a time-division independent modulation window is provided for the single electro-optic modulator on the time axis.

4. The method as described in claim 1, characterized in that, The electro-optic modulator module uses a time-division multiplexing method to sequentially load independent data for multiple channels within a single modulation cycle.

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