Quadruple frequency-based scheme for realizing base station passive full duplex millimeter wave RoF link

[0022] Specific implementation method

[0023] The working wavelength of the laser is λ, the present invention takes 1552.5nm (193.1THz) as an example, and the downlink millimeter wave signal rate is f D The present invention takes 40GHz as an example, the corresponding frequency of the lithium niobate Mach-Zehnder modulator is 10GHz, the DC bias voltage is 0, the peak-to-peak voltage of the RF local oscillator is 8V, and the resulting spectrum is as figure 2 Shown. The second sideband is separated by an FBG with a center wavelength of 1552.12nm and a bandwidth of 30GHz, and a binary NRZ baseband signal with a rate of 5Gbit/s is loaded onto the sideband through an intensity modulator with a response rate of 5GHz, and adjusted by a polarization controller After the polarization direction is made parallel, the optical coupler is combined, and the spectrum measured by the spectrometer is as image 3 Shown. In the base station, the optical millimeter wave signal and the optical carrier are separated by the MZI with a delay difference of 25 ps between the two arms. The optical millimeter wave signal and the optical carrier spectrum output from the two ports of the MZI are as follows Figure 4 Shown. Before transmission through optical fiber, a photodetector with a response frequency of 50GHz converts a 40GHz optical millimeter wave signal into an electrical signal. Its radio frequency spectrum and eye diagram are as follows Image 6 Shown. by Image 6 The radio frequency spectrum can be seen: the photocurrent is mainly composed of baseband signals and 40GHz millimeter wave signals, the latter is what we need. In order to verify the performance of the optical millimeter wave signal, a 40GHz local oscillator signal is used to coherently demodulate the 40GHz photocurrent signal, and the demodulated baseband signal eye diagram is as follows Figure 7 Shown.

[0024] The generated optical millimeter wave signal is injected into a standard single-mode fiber, and after 40km transmission and amplified to 10dBm by an erbium-doped fiber amplifier (EDFA), the eye pattern of the radio frequency signal is coherently demodulated by the 40GHz photocurrent 5Gbit/s baseband signal eye diagram such as Figure 8 , Picture 9 Shown. It can be seen from the eye diagram that although the fiber dispersion has a certain degree of degradation to the signal quality, after 40km of fiber transmission, the opening of the eye diagram can still ensure the correct detection of the signal.

[0025] In the uplink, the reserved optical carrier (1552.5nm) is intensity modulated by the uplink baseband signal (binary NRZ) at a rate of 5Gbit/s. The spectrum and eye diagram in the back-to-back case are as follows Picture 10 Shown. The eye pattern of the 5Gbit/s uplink baseband signal after 40km uplink transmission to the central station is as follows Picture 11 Shown. It can be seen from the eye diagram that the openness of the eye diagram can still ensure correct signal detection.

[0026] In summary, the present invention uses a conventional lithium niobate Mach-Zehnder modulator to simultaneously generate 4 times the frequency downlink optical millimeter wave signal and uplink optical carrier at the central station, and simultaneously realizes single-carrier modulation of the signal. To reduce the influence of fiber link dispersion, this solution not only reduces the frequency requirements of the optical modulator and RF local oscillator in the optical millimeter wave generating equipment, but also the generated optical millimeter wave signal has good long-distance (~40km) transmission performance. Migrating the uplink light source in the base station to the central station greatly simplifies the structure of the base station without additional downlink bandwidth. The invention is simple and easy to implement, and requires low component frequency requirements, which greatly reduces the difficulty and cost of implementing a Gbit/s broadband millimeter wave full-duplex RoF link.

[0027] In a word, the above-mentioned embodiment is only an example of the present invention, and is not only used to limit the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art, the content disclosed in the present invention is also Several equivalent deformations and replacements can be made, and the frequency range of the millimeter wave is not limited to the 40 GHz in the above example. These equivalent deformations and replacements and adjustment of the frequency range should also be regarded as the protection scope of the present invention.