CN106506090B - A kind of optical heterodyne regulator control system of Terahertz ultra-wideband communications waveform - Google Patents

Abstract

The invention discloses an optical heterodyne control system for terahertz ultra-broadband communication waveforms, which includes a high repetition frequency pulse laser source, a programmable pulse shaper, a continuous laser, a dual-parallel Mach-Zehnder modulator, a coupler, and a terahertz transmitter The present invention adopts the heterodyne frequency mixing method of continuous light and pulsed light to photoelectrically generate terahertz pulse sequences, dual parallel Mach-Zehnder modulators modulate continuous light to realize the modulation of terahertz communication pulses, and programmable pulse shapers in the optical domain Shaping optical pulses to design terahertz pulse shapes; this scheme can realize the modulation of terahertz high-speed pulse communication signals.

Description

An optical heterodyne control system for terahertz ultra-wideband communication waveforms

technical field

The invention belongs to the field of wireless communication, and in particular relates to an optical heterodyne control system for terahertz ultra-wideband communication waveforms.

Background technique

In order to solve the problem of limited spectrum resources and capacity in existing wireless communication systems, terahertz communication has received extensive attention in recent years. The terahertz frequency band usually refers to 0.1-10THz, and the communication bandwidth is much larger than that of microwave and millimeter waves. The terahertz communication system based on the photoelectric method can carry data information up to tens to hundreds of gigabits (Gbps).

Terahertz communication methods mainly include continuous terahertz carrier modulation and terahertz pulse modulation. The continuous terahertz wave carrier is generally generated by means of photo-mixing two continuous lasers, and the modulation of the terahertz communication signal is realized by modulating one of the continuous lasers. The common photoelectric generation methods of terahertz pulses are ultrashort light pulses irradiating nonlinear crystals and femtosecond pulses exciting photoconductive antennas. Both the nonlinear effect and the photoconductive effect require high optical peak power, which greatly exceeds the damaged optical power of the photoelectric modulator, so the repetition frequency of femtosecond pulses is usually very low (50-100MHz), and it is not conducive to the detection of terahertz signals. optical modulation.

A common terahertz pulse transmitting and receiving system consists of a femtosecond laser, an optical chopper, a beam splitter (BS), a THz transmitter (THz emitter), and a receiver (THz detector). Through the principle of instantaneous photoconductive switching (photoconductive switching), when the photocurrent changes with time, the magnitude of the photocurrent generated corresponds to the time differential of the incident laser beam intensity, thereby converting femtosecond laser pulses into broadband terahertz pulses.

The patent with the publication number CN 104155825 A discloses a method and device for generating high-energy terahertz pulses. Specifically, a beam of high-energy femtosecond pulses is evenly divided into two or more beams, and they are respectively incident on In the ZeTn crystal, the terahertz pulses are generated in the crystal through the femtosecond pulse light rectification process, and the coherently synthesized terahertz pulses can be obtained by adjusting the time delay so that the generated terahertz pulses reach the detector at the same time. The repetition rate of this method is relatively low, and it is not conducive to the optical modulation of terahertz signals.

Contents of the invention

The invention provides an optical heterodyne control system for terahertz ultra-broadband communication waveforms, which adopts the heterodyne frequency mixing method of continuous light and pulsed light to realize the generation of terahertz pulses and realize the modulation of terahertz high-speed pulse communication signals.

An optical heterodyne control system for terahertz ultra-broadband communication waveforms, including a high repetition rate pulsed laser source, a programmable pulse shaper, a continuous laser, a dual-parallel Mach-Zehnder modulator (DPMZM), a fiber delay line, a coupler, Terahertz transmitter (UTC-PD); the programmable pulse shaper performs waveform shaping on the high repetition rate optical pulse source, and sends the shaped pulse signal to the coupler; the dual parallel Mach-Zehnder modulator The continuous laser is modulated, and the modulated optical signal is sent to the coupler through the fiber delay line, and the coupler couples the shaped pulse signal and the modulated optical signal to the terahertz transmitter to generate a terahertz pulse.

The high repetition rate pulsed laser source is used to emit a pulse source with a high repetition rate (≥10GHz) in the 1550nm optical communication band.

The high repetition rate pulsed laser source is a tunable semiconductor laser or fiber laser.

The programmable pulse shaper performs waveform shaping on an optical pulse source with a high repetition frequency f ₀ . The pulse source appears as a comb-like spectrum with a frequency interval of f ₀ in the frequency domain, and the shape of the pulse can be designed through fine shaping of the spectrum.

The programmable pulse shaper performs amplitude and phase processing on the high repetition frequency comb spectrum line-by-line. Through the line-by-line processing of the optical pulse source spectrum in the frequency domain, the pulse time-domain waveform can be flexibly regulated and designed in the optical domain, such as Gaussian, parabolic, and Lorentzian. According to the Fourier transform correspondence between the time-domain waveform and the frequency-domain spectrum, for example, when the output comb spectrum of the programmable pulse shaper presents a Gaussian envelope, the pulse is a Gaussian pulse with a repetition frequency f ₀ in the time domain.

The time interval of time-domain pulses corresponding to the high repetition frequency f ₀ is T.

The continuous laser generates continuous steady-state optical signals.

The dual-parallel Mach-Zehnder modulator is composed of two sub-Mach-Zehnder modulators (MZM) and a main Mach-Zehnder modulator, wherein the two sub-Mach-Zehnder modulators are embedded in the two sub-MZMs of the main Mach-Zehnder modulator. on a modulation arm. The dual-parallel Mach-Zehnder modulator modulates the digital baseband signal on the two sub-Mach-Zehnder modulators, and realizes the quadrature phase control of the input continuous laser through the main Mach-Zehnder modulator, so that the quadrature phase shift key can be realized. control (QPSK) and other complex modulation methods.

The optical fiber delay line adopts an adjustable delay control line for 1550nm optical communication based on optical fiber.

The fiber delay line is used to adjust the time when the digital signal arrives at the coupler to realize the synchronization between the digital signal and the optical pulse, and one bit digital signal corresponds to N pulses.

The coupler couples the two 1550nm band optical signals connected to the input end of the coupler together and outputs them together.

The terahertz emitter uses an antenna-integrated single-line carrier photodetector. Compared with the traditional photodetector, the terahertz emitter only has high-speed moving electrons as the carriers in the excited state, so it has ultra-fast skin Second-level photon response speed and ultra-large bandwidth.

In the time domain, each digital bit will modulate N pulses at the same time, and the center frequency of the generated terahertz pulse is determined by the center wavelength difference between the shaped pulse signal and the modulated continuous optical signal. For example, when the center wavelength of the shaped pulsed light is 2.4 nm different from that of the continuous laser, the center frequency of the generated terahertz pulse is 300 GHz.

In general, the terahertz transmitting antenna is a small-aperture antenna with two electrode structures, dipole (Dipole) or bow-tie (Bow-Tie). In the time domain, the terahertz radiation electromagnetic wave is the first order of the transient photocurrent in the detector differential. Therefore, the shape design of terahertz radiation pulses is flexibly handled by optical pulse filter shaping.

Modulation formats of terahertz pulses (such as OOK, BPSK, QPSK, etc.) are realized by the simple way of modulating continuous light.

The working engineering of the optical heterodyne control system of terahertz ultra-wideband communication waveform is as follows:

The programmable pulse shaper performs waveform shaping on the high repetition frequency optical pulse source, and the Mach-Zehnder modulator performs relatively low-speed (f ₀ /N) modulation on the continuous laser, and the shaped pulse source and the modulated continuous optical signal are coupled through a coupler Together, the terahertz emitter is irradiated to generate a terahertz pulse. Under the optical heterodyne mixing mechanism, one light pulse will correspondingly generate a terahertz pulse.

The invention adopts the heterodyne frequency mixing mode of continuous light and pulse light to photoelectrically generate terahertz modulation pulse sequence. The regulation of terahertz pulses is carried out in the optical domain. The modulation of terahertz communication pulses is realized by modulating continuous light. The shape of terahertz pulses is designed by shaping optical pulses in the optical domain by a programmable pulse shaper. This scheme can realize the modulation of terahertz high-speed pulse communication signals.

Compared with other terahertz pulse transmitting and receiving systems, the present invention has the following advantages:

(1) The center frequency of the terahertz pulse is determined by the center wavelength difference of two heterodyned lasers, which is simple and easy to control.

(2) The terahertz time-domain pulse waveform is flexibly designed in the optical domain through a programmable pulse shaper.

(3) Pulse encoding is realized by modulating continuous light, which can realize high-speed communication of terahertz pulses.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Figure 2 is a QPSK modulated terahertz waveform.

Detailed ways

In order to describe the present invention more specifically, the technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1, the optical heterodyne control system for terahertz ultra-wideband communication waveforms includes a high repetition rate pulsed laser source, a programmable pulse shaper, a continuous laser, a dual-parallel Mach-Zehnder modulator, a fiber delay line, and a coupler , Terahertz transmitter.

The pulsed laser source adopts a high repetition rate pulse source in the 1550nm optical communication band, such as a 10GHz repetition rate, and can also obtain a higher repetition rate through optical time division multiplexing, such as 40GHz or even higher.

The programmable pulse shaper adopts a 10GHz resolution 1550nm band programmable optical processor based on solid-state liquid crystal-on-silicon technology, and performs amplitude and phase processing line-by-line for high repetition frequency spectrum. According to the Fourier transform correspondence between the time domain waveform and the frequency domain spectrum, through fine processing of the frequency domain spectrum, the output frequency domain envelope shape of the optical processor is designed, such as Gaussian, parabolic, Lorentzian, etc. Regulate the pulse waveform on the domain. Terahertz time-domain radiated electromagnetic wave is the first-order differential of the corresponding waveform. Therefore, the shape of the terahertz pulse is determined by the shape of the optical pulse designed in the optical domain. For example, the first-order differential of a Gaussian optical pulse is a Gaussian monocycle (Gaussian monocycle) .

The continuous laser adopts the commonly used 1550nm band wavelength tunable semiconductor laser or fiber laser for optical communication.

The optical fiber delay line adopts an adjustable delay control line for 1550nm optical communication based on optical fiber.

The dual-parallel Mach-Zehnder modulator uses a commercial DPMZM modulator with a low RF bandwidth (less than 10GHz) in the 1550nm band to modulate the continuous laser with a binary digital signal of f ₀ /N, where N is an integer. The modulated continuous laser is delayed through the fiber delay line to synchronize digital bits and optical pulses (one bit corresponds to N pulses). After the 3dB fiber coupler, the synchronously modulated continuous laser light and the shaped pulsed light are combined into one path and sent to the antenna-integrated terahertz transmitter. At present, the response bandwidth of UTC-PD commercialized by NTT in Japan can reach 1.5THz, and the transmission power at 300GHz frequency is as high as 0dBm. In addition, the UTC-PD developed by UCL in the UK and IEMN in France also has quite good performance in bandwidth and responsivity.

Under the heterodyne mixing mechanism of the terahertz transmitter, the center wavelength difference of the two paths of light will determine the terahertz center frequency. Hertz pulse center frequency is 300GHz. Meanwhile, under the condition that one bit digital signal and N optical pulses are synchronized, N pulses will be modulated by the same bit, thus having the same terahertz pulse shape, amplitude and phase.

Figure 2 illustrates the terahertz waveform of QPSK modulation. The 00 and 11 waveforms radiated by the antenna are mutually opposite Gaussian second-order differential (doublet) pulses, and the 01 and 10 are mutually opposite Gaussian monocycle pulses (monocycle ). Therefore, encoding of high-speed terahertz communication pulses can be realized by modulating continuous light at low speed and avoiding the use of large-bandwidth modulators.

The above-mentioned specific embodiments have described the technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned are only the most preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, supplements and equivalent replacements made within the scope shall be included in the protection scope of the present invention.

Claims (5)

1. a kind of optical heterodyne regulator control system of Terahertz ultra-wideband communications waveform, it is characterised in that：Including high repetitive frequency pulsed Lasing light emitter, programmable pulse reshaper, continuous wave laser, double parallel MZ Mach-Zehnder, fibre delay line, coupler with And terahertz transmitter；The programmable pulse reshaper carries out pulse waveform shaper to high repeat frequency pulsed laser source, And the pulse signal of shaping is transported to coupler；The double parallel MZ Mach-Zehnder adjusts continuous wave laser System, and the optical signal of modulation is transported to coupler through fibre delay line, the coupler is by the pulse signal and tune of shaping It is irradiated to terahertz transmitter after the optical signal coupling of system, generates terahertz pulse；

Frequency >=10GHz of the clock of the high repeat frequency pulsed laser source transmitting.

2. the optical heterodyne regulator control system of Terahertz ultra-wideband communications waveform as described in claim 1, which is characterized in that described High repeat frequency pulsed laser source is semiconductor laser with tunable or optical fiber laser.

3. the optical heterodyne regulator control system of Terahertz ultra-wideband communications waveform as described in claim 1, which is characterized in that described Double parallel MZ Mach-Zehnder is made of two sub- MZ Mach-Zehnders and a main MZ Mach-Zehnder, In two sub- MZ Mach-Zehnders be embedded in two modulation arms of main MZ Mach-Zehnder.

4. the optical heterodyne regulator control system of Terahertz ultra-wideband communications waveform as described in claim 1, which is characterized in that described Fibre delay line uses the 1550nm optic communications adjustable delay control line based on optical fiber.

5. the optical heterodyne regulator control system of Terahertz ultra-wideband communications waveform as described in claim 1, which is characterized in that described Terahertz transmitter is the uniline carrier photodetector that antenna integrates.