CN113078956B - Terahertz multiband coherent receiving system based on phase grating - Google Patents

Abstract

The invention discloses a phase grating-based terahertz multi-band coherent receiving system, which is characterized in that it includes two subsystems, a phase grating signal coupling system and a low-temperature off-axis parabolic mirror back coupling system. The phase grating signal coupling system is composed of a multi-band local oscillator signal source and a reflective phase grating; the low-temperature off-axis parabolic mirror back coupling system is composed of a refrigerator, a low-temperature off-axis parabolic mirror and a superconducting HEB mixer. The present invention modulates the wavefront phases of the incident signals in multiple bands through a reflective phase grating, and finally reflects and outputs them at the same angle, and couples the local oscillator signals in multiple bands to the chip side of the superconducting HEB mixer, without the need for additional The stage optical splitter is cascaded to couple the multi-band local oscillator signal source, and at the same time, there is no need for the super-hemispherical lens to couple the local oscillator signal, which not only reduces the system complexity, but also realizes the natural isolation of the local oscillator signal and the detection signal, and reduces the signal loss. Finally, a highly integrated multi-band coherent receiving system based on a single mixer is realized.

Description

Terahertz multi-band coherent receiving system based on phase grating

technical field

The invention relates to the technical field of astronomical observation, in particular to a terahertz multi-band coherent receiving system based on a phase grating.

Background technique

The terahertz band is rich in fine spectral lines of molecules, atoms and ions, and is an important band for the study of cosmic evolution, stars and galaxies. High-resolution spectral line observation can not only detect the intensity of spectral lines, but also distinguish the spectral information of spectral lines, which provides an important scientific means for us to systematically study the characteristics of motion and temperature in astrophysical processes. Based on the multi-band coherent receiver system, multi-spectral observations for different fingerprint spectral lines are of great significance for in-depth understanding and understanding of important scientific issues such as the evolution of the universe, the journeys of stars and galaxies.

In astronomical observation research above 1 THz, superconducting electron (HEB) mixers are widely used in international advanced astronomical observation facilities. For example, the SOFIA airborne infrared observatory jointly developed by NASA and Germany's DLR, and the GUSTO balloon observatory jointly developed by NASA and the Netherlands SRON are based on superconducting HEB array detectors and cover different observations such as 1.9 THz, 2.5 THz and 4.7 THz. band. The superconducting HEB mixer is based on the superconducting thin film and planar antenna technology working at low temperature, and can realize high-sensitivity signal detection covering a broadband range of 1-5 THz. For multi-band collaborative observation, the same ultra-broadband superconducting HEB mixer covers different observation bands, and has special advantages such as redundancy guarantee for balloon observatories and unattended radio astronomy observation facilities such as space or polar regions.

Although a single superconducting HEB detector can cover the above-mentioned multiple observation bands, due to the limitation of the frequency tuning capability of the local oscillator pump signal (semiconductor frequency doubling link and quantum cascade laser), multiple sets of fingerprint spectra are required for multiple fingerprints respectively. The local oscillator signal source in the line observation band. The key technical challenge of the multi-band coherent receiver system based on a single mixer lies in the efficient multi-band local oscillator signal distribution technology. The LO signal of the traditional multi-band coherent receiving system couples the multi-band LO signal to the mixer through multiple optical splitters (usually of types such as Mylar, Kapton thin film, and wire grid). Multiple sets of local oscillator signal sources need to be coupled in cascade with multiple optical splitters, which inevitably increases the transmission loss of the local oscillator signal and increases the complexity of the system.

SUMMARY OF THE INVENTION

The technical purpose of the present invention is to provide a highly integrated terahertz multi-band coherent receiving system based on a phase grating, which can reduce the signal loss and overcome the shortcomings of the existing multi-band coherent receiving systems.

The technical scheme provided by the present invention is:

A phase grating-based terahertz multi-band coherent receiving system, characterized in that it includes two subsystems, a phase grating signal coupling system and a low-temperature off-axis parabolic mirror back-coupling system, wherein:

The phase grating signal coupling system is composed of a local oscillator signal source and a reflective phase grating, and the local oscillator signal source further includes a 1.9 THz local oscillator signal source, a 2.5 THz local oscillator signal source and a 4.7 THz local oscillator signal source;

The low-temperature off-axis parabolic mirror back-coupling system consists of a refrigerator, a low-temperature off-axis parabolic mirror and a superconducting HEB mixer, and the low-temperature off-axis parabolic mirror and the superconducting HEB mixer are all installed in the dewar of the refrigerator , the superconducting HEB mixer is located on the side of the low-temperature off-axis parabolic mirror;

A local oscillator signal incident window and a detection signal incident window are arranged on the Dewar side wall of the refrigerator;

The superconducting HEB mixer includes a mixer chip and a hyperhemispherical lens for detecting the signal to be measured, and the mixer chip is mounted on the back of the hyperhemispherical lens;

The signal to be tested is coupled to the mixer chip from the front side through the super-hemispherical lens;

The 1.9THz, 2.5THz and 4.7THz local oscillator signals respectively emitted by the 1.9 THz local oscillator signal source, the 2.5 THz local oscillator signal source and the 4.7 THz local oscillator signal source are coupled to the surface of the reflective phase grating based on different incident angles, The reflection-type phase grating adjusts the wavefront phase of the incident signal, and reflects the reflected signals of the three bands from the same angle. On the arc-shaped reflective surface of the parabolic mirror, after being re-reflected by the low-temperature off-axis parabolic mirror, the local oscillator signal is coupled to the mixer chip from the back, and is mixed with the signal to be measured in the superconducting HEB mixer.

On the basis of the above scheme, the improved or preferred technical scheme also includes:

Further, the 1.9 THz local oscillator signal source preferably adopts a 1.9 THz semiconductor frequency doubling signal source; the 2.5 THz local oscillator signal source preferably adopts a 2.5 THz quantum cascade laser; the 4.7 THz local oscillator signal source preferably adopts a 4.7 THz Quantum Cascade Laser.

Further, the reflective phase grating is designed by the Gerchberg-Saxton phase inversion algorithm, so that the local oscillator signals of multiple bands with different incident angles are reflected and output from the same angle.

Further, the incident angle of the 4.7 THz local oscillator signal is 20 degrees, the incident angle of the 2.5 THz local oscillator signal is 28 degrees, and the incident angle of the 1.9 THz local oscillator signal is 32 degrees; the reflection angles of the local oscillator signals of the three bands are Unified to 25 degrees.

Further, the cryogenic off-axis parabolic mirror adopts a 90-degree off-axis parabolic mirror.

Further, the refrigerator is a 4K closed-loop refrigerator.

Beneficial effects:

The terahertz multi-band coherent receiving system based on the phase grating of the present invention modulates the wavefront phases of the incident signals in multiple bands through the reflective phase grating, and finally reflects and outputs the same angle. The low-temperature off-axis parabolic mirror in the machine couples the multi-band local oscillator signal to the chip side of the superconducting HEB mixer, without the need for a multi-stage optical splitter to cascade the multi-band local oscillator signal source, and no frequency mixing. Instead, the multi-band LO signal is directly back-coupled to the superconducting HEB micro-bridge through the off-axis parabolic mirror, which not only reduces the system complexity, but also realizes the The natural isolation of the detection signal reduces the loss of the detection signal, and finally realizes a highly integrated multi-band coherent receiving system based on a single mixer.

Description of drawings

1 is a system block diagram of an embodiment of the present invention;

FIG. 2 is a schematic diagram of the signal coupling principle of the terahertz multi-band phase grating in an embodiment of the present invention;

FIG. 3 is a schematic diagram of a back-coupling principle of a low-temperature off-axis parabolic mirror in an embodiment of the present invention.

Detailed ways

In order to clarify the technical solution and working principle of the present invention, the present invention will be further introduced below with reference to the accompanying drawings and embodiments.

The invention is a phase grating-based terahertz multi-band coherent receiving system, comprising two subsystems: a phase grating signal coupling system and a low-temperature off-axis parabolic mirror back coupling system:

The phase grating signal coupling system is composed of a local oscillator signal source and a reflective phase grating, and the local oscillator signal source further includes a 1.9 THz local oscillator signal source 1, a 2.5 THz local oscillator signal source 2 and a 4.7 THz local oscillator signal source 3;

The low-temperature off-axis parabolic mirror back-coupling system is composed of a refrigerator, a low-temperature off-axis parabolic mirror 5 and a superconducting HEB mixer 6, and the low-temperature off-axis parabolic mirror 5 and the superconducting HEB mixer 6 are both installed in the Inside the Dewar of the refrigerator, the superconducting HEB mixer 6 is located beside the cryogenic off-axis parabolic mirror 5 .

In this embodiment as shown in Figures 1 to 3:

The refrigerator adopts a 4K closed-loop refrigerator. On the two mutually perpendicular Dewar side walls, at the positions corresponding to the arc-shaped reflecting surfaces of the low-temperature off-axis parabolic mirror 5, there are respectively a local oscillator signal entrance window and a Detection signal entrance window;

Each local oscillator signal source is specifically composed of a 1.9 THz semiconductor frequency doubling signal source (microwave frequency signal source and semiconductor frequency doubling link), a 2.5 THz quantum cascade laser and a 4.7 THz quantum cascade laser, which are used to generate 1.9 THz, 2.5 Local oscillator signals in three bands of THz and 4.7 THz;

The low-temperature off-axis parabolic mirror 5 adopts a 90-degree off-axis parabolic mirror with a 0.5-inch reflection focal length of 15 mm;

The superconducting HEB mixer includes a mixer chip 62 and a super-hemispherical lens 61 for detecting the signal to be measured. The front of the super-hemispherical lens 61 is a spherical surface and the back is a plane. The center portion of the back of the hemispherical lens 62 .

Working principle: 1.9 THz, 2.5 THz, 4.7 THz three-band local oscillator signals from 1.9 THz local oscillator signal source 1, 2.5 THz local oscillator signal source 2 and 4.7 THz local oscillator signal source 3 respectively, based on different incident angles Coupling to the surface of the reflective phase grating 4, the reflective phase grating 4 reflects the three-band reflected signals from the same angle by adjusting the wavefront phase of the incident signal, and the output reflected signal then passes through the local oscillator signal incident window , projected onto the arc-shaped reflective surface of the low-temperature off-axis parabolic mirror 5 located in the refrigerator, and after the re-reflection of the low-temperature off-axis parabolic mirror 5, the local oscillator signal is coupled to the mixer chip to realize back-coupling , and the forward-coupled signal to be tested is mixed in the superconducting HEB mixer 6 .

In this implementation, the 90-degree off-axis parabolic mirror can realize the natural isolation of the local oscillator signal and the signal to be measured while realizing efficient local oscillator signal coupling.

work process:

As shown in Figure 2, the steps of coupling the multi-band local oscillator signal by the phase grating signal coupling system are as follows:

(11) Simultaneously activate the 1.9 THz semiconductor frequency doubling signal source, the 2.5 THz quantum cascade laser and the 4.7 THz quantum cascade laser to generate the local oscillator signal in the corresponding band;

(12) Coupling the 1.9 THz, 2.5 THz and 4.7 THz local oscillator signals to the reflective phase grating at incident angles of 32 degrees, 28 degrees and 20 degrees respectively, the incident angles refer to the propagation direction of the incident signal and the vertical line of the grating the included angle;

(13) The reflective phase grating modulates the wavefront phases of the incident signals in the three bands, and finally reflects and outputs the local oscillator signals in the three bands through a uniform angle of 25 degrees;

As shown in Figure 3, the steps of signal coupling of the low-temperature off-axis parabolic mirror back-coupling system are as follows:

(21) The local oscillator signals of the three bands are coupled to the 90-degree off-axis parabolic mirror through the local oscillator signal incident window of the 4K closed-loop refrigerator;

(22) The off-axis parabolic mirror couples and converges the local oscillator signal to the chip side of the superconducting HEB mixer to achieve efficient coupling of multi-band local oscillator signals;

At the same time, the superconducting HEB mixer realizes the detection of the signal to be measured through the super-hemispherical lens;

The forward coupled test signal and the backward coupled local oscillator signal are mixed in a superconducting HEB mixer.

During the above process:

It can be designed through the Gerchberg-Saxton phase inversion algorithm to achieve incident angles of 20 degrees (4.7 THz band), 28 degrees (2.5 THz band) and 32 degrees (1.9 THz band), and the reflection angles are unified to 25 degrees (1.9, 2.5 , 4.7 THz band) reflective phase grating.

The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above-mentioned embodiments, and the descriptions in the above-mentioned embodiments and the description are only to illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have Various changes and improvements. The claimed scope of the present invention is defined by the appended claims, description and their equivalents.

Claims (6)

1. a terahertz multi-band coherent receiving system based on phase grating, is characterized in that, comprises two subsystems of phase grating signal coupling system and low temperature off-axis parabolic mirror back coupling system, wherein: The phase grating signal coupling system is composed of a local oscillator signal source and a reflective phase grating, and the local oscillator signal source further includes a 1.9 THz local oscillator signal source, a 2.5 THz local oscillator signal source and a 4.7 THz local oscillator signal source; The low-temperature off-axis parabolic mirror back-coupling system consists of a refrigerator, a low-temperature off-axis parabolic mirror and a superconducting HEB mixer, and the low-temperature off-axis parabolic mirror and the superconducting HEB mixer are all installed in the dewar of the refrigerator , the superconducting HEB mixer is located on the side of the low-temperature off-axis parabolic mirror; A local oscillator signal incident window and a detection signal incident window are arranged on the Dewar side wall of the refrigerator; The superconducting HEB mixer includes a mixer chip and a hyperhemispherical lens for detecting the signal to be measured, and the mixer chip is mounted on the back of the hyperhemispherical lens; The signal to be tested is coupled to the mixer chip from the front side through the super-hemispherical lens; The 1.9THz, 2.5THz and 4.7THz local oscillator signals respectively emitted by the 1.9 THz local oscillator signal source, the 2.5 THz local oscillator signal source and the 4.7 THz local oscillator signal source are coupled to the surface of the reflective phase grating based on different incident angles, The reflection-type phase grating adjusts the wavefront phase of the incident signal, and reflects the reflected signals of the three bands from the same angle. On the arc-shaped reflective surface of the parabolic mirror, after being re-reflected by the low-temperature off-axis parabolic mirror, the local oscillator signal is coupled to the mixer chip from the back, and is mixed with the signal to be measured in the superconducting HEB mixer. 2. a kind of terahertz multi-band coherent receiving system based on phase grating according to claim 1, is characterized in that: The 1.9 THz local oscillator signal source is a 1.9 THz semiconductor frequency doubling signal source; The 2.5 THz local oscillator signal source is a 2.5 THz quantum cascade laser; The 4.7 THz local oscillator signal source is a 4.7 THz quantum cascade laser. 3. a kind of terahertz multi-band coherent receiving system based on phase grating according to claim 1, is characterized in that: The reflective phase grating is designed by the Gerchberg-Saxton phase inversion algorithm, so as to realize the reflection and output of local oscillator signals of multiple bands with different incident angles from the same angle. 4. a kind of phase grating-based terahertz multi-band coherent receiving system according to claim 3, is characterized in that: The incident angle of the 4.7 THz local oscillator signal is 20 degrees, the incident angle of the 2.5 THz local oscillator signal is 28 degrees, and the incident angle of the 1.9 THz local oscillator signal is 32 degrees; The reflection angles of the local oscillator signals of the three bands are uniformly 25 degrees. 5. a kind of phase grating-based terahertz multi-band coherent receiving system according to claim 1, is characterized in that: The cryogenic off-axis parabolic mirror adopts a 90-degree off-axis parabolic mirror. 6. a kind of phase grating-based terahertz multi-band coherent receiving system according to claim 1, is characterized in that: The refrigerator is a 4K closed-loop refrigerator.

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