Terahertz optical delay device and method based on multi-reflection White cavity

Abstract

The invention belongs to the technical field of measurement, and particularly relates to a terahertz optical delay device and method based on a multi-reflection White cavity, the terahertz optical delay device is used for pulse equivalent sampling in terahertz time-domain spectroscopy detection, and the delay device comprises a movement mechanism, a movable concave mirror, two fixed concave mirrors and an optical base, the movable concave mirror and the two fixed concave mirrors form a multi-reflection White cavity, the movable concave mirror is driven by the movement mechanism to move in a reciprocating mode to change the cavity length, then the propagation path of an optical signal in the cavity is changed, time delay is generated, by means of the White cavity, multi-reflection of an optical path can be achieved in the small size, and time delay is reduced. Therefore, the endoscope can achieve a large time delay range with a small reciprocating motion distance, and the frequency resolution, the thickness measuring range and the spectrum scanning rate of the terahertz time-domain spectroscopy system are increased.

Description

Technical Field

[0001] The invention belongs to the field of measurement technology, and in particular relates to a terahertz optical delay device and method based on a multi-reflection White cavity. Background Art

[0002] In the terahertz time-domain spectroscopy system, a femtosecond laser is used to excite a photoconductive antenna to generate a terahertz time-domain pulse signal, whose pulse width is in the picosecond range and the repetition frequency is usually in the hundreds of megahertz. For transient terahertz time-domain pulse signals, the traditional method based on the Nyquist sampling theorem has a sampling frequency in the terahertz range, which is technically difficult to achieve. Therefore, an equivalent sampling method that exchanges space for time is adopted, and piezoelectric ceramics and voice coil motors are used in space to achieve femtometer interval movement, control femtosecond pulses to complete the sequential sampling of picosecond terahertz pulses, and reconstruct them into complete terahertz time-domain pulses. This method is equivalent sampling, which requires the use of a high-precision optical delay structure to achieve.

[0003] The traditional optical delay structure consists of a mobile platform and a corner cube prism. The mobile platform drives the corner cube prism to move to change the optical path, thereby changing the time delay. In order to achieve a larger delay magnitude, the traditional method requires the platform to move a long distance and the reciprocating frequency to be slow, which limits the scanning time of each terahertz time-domain pulse signal. At the same time, the structure is complex and not easy to integrate into the system. Summary of the invention

[0004] In view of the above situation, the present invention provides a terahertz optical delay device and method based on a multiple reflection White cavity. The optical signal can be transmitted by multiple reflections in the cavity, and the motion mechanism drives the mobile concave mirror to perform reciprocating motion. A larger delay range can be achieved through a smaller moving distance. The delay device provided by the present invention can broaden the scanning range of terahertz time-domain pulses, improve the spectral resolution of such technology when detecting material composition or the range when used for thickness measurement, and at the same time, the increase in the reciprocating motion frequency can also achieve rapid scanning of terahertz time-domain pulse signals.

[0005] The technical solution adopted by the present invention is to provide a terahertz optical delay device based on a multiple reflection White cavity, including a motion mechanism, a White cavity delay mechanism, an optical signal transmitting end, an optical signal receiving end and an optical base. The White cavity delay mechanism includes a movable concave mirror, a first fixed concave mirror and a second fixed concave mirror. The White cavity delay mechanism relies on the motion mechanism to drive the movable concave mirror to move back and forth to realize optical delay scanning. The motion mechanism realizes reciprocating motion by piezoelectric ceramics, voice coil motors, magnetic levitation motors or stepping motors.

[0006] The first fixed concave mirror and the second fixed concave mirror are installed in parallel at the first end of the optical base, and the first fixed concave mirror and the second fixed concave mirror are flush with each other. A motion mechanism is installed at the second end of the optical base, and a mobile concave mirror is installed on the motion mechanism, and the center of curvature of the mobile concave mirror is located in the middle of the first fixed concave mirror and the second fixed concave mirror. The optical signal transmitting end is installed on the first side of the mobile concave mirror, and the optical signal receiving end is installed on the second side of the mobile concave mirror. The number of reflections N in the White cavity delay mechanism is changed by changing the incident position of the optical signal, the incident angle of the optical signal, the angle of the first fixed concave mirror, or the angle of the second fixed concave mirror.

[0007] Preferably, the light signal is incident and emitted by the first fixed concave mirror and the second fixed concave mirror, and the light signal is transmitted back and forth in the White cavity delay mechanism. The relationship between the optical path and the White cavity delay mechanism is L=2(N+1)d, where L is the optical path, N is the number of reflections, and d is the cavity length of the White cavity delay mechanism. When the terahertz time-domain spectrum delay line is scanned, the light signal delay is a step value, and the relationship between the delay change and the cavity length change of the White cavity delay mechanism is ΔT=(2(N+1)Δd) / c, where Δd is the cavity length change of the White cavity delay mechanism during the movement of the moving concave mirror, c is the speed of light, ΔT is the delay change of the device, and N is the number of reflections.

[0008] Preferably, the light signal is incident on the first side of the movable concave mirror and enters the White cavity delay mechanism, and after multiple reflections, is emitted from the second side of the movable concave mirror, and the emission position of the light signal is symmetrically distributed with the incident position of the light signal.

[0009] Preferably, within the reciprocating motion range of the motion mechanism, the number of reflections N is a constant.

[0010] A second aspect of the present invention provides a time delay method of a terahertz optical time delay device based on a multi-reflection White cavity, which comprises the following steps:

[0011] S1: Set the reciprocating distance of the mobile concave mirror;

[0012] S2: The optical signal transmitting end transmits a light beam to the outside;

[0013] S3: The light beam is transmitted through multiple reflections in the White cavity delay mechanism;

[0014] S4: The optical signal receiving end receives the light beam;

[0015] S5: The mobile concave mirror moves back and forth, and the transmission distance of the multi-reflected light beam in the White cavity delay mechanism changes back and forth, realizing optical delay.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The present invention can realize rapid scanning of terahertz time-domain spectroscopy;

[0018] 2. The present invention realizes optical delay based on multiple reflection White cavity, and the light beam can be transmitted over long distances in a narrow space;

[0019] 3. The present invention introduces a motion mechanism and a movable concave mirror into the multiple reflection White cavity, so that a larger delay range can be obtained through a smaller moving range;

[0020] 4. The motion mechanism of the present invention moves within a small range, which can increase the scanning frequency of the spectrum;

[0021] 5. The present invention has the characteristics of small size, light weight, good stability and simple and compact structure;

[0022] 6. The present invention can be extended to the fields of optical coherence tomography, optical time domain effect measurement and autocorrelator technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of the optical delay mechanism of the present invention;

[0024] Figure 2 It is a working schematic diagram of the optical delay mechanism of the present invention;

[0025] Figure 3 It is a flow chart of the working process of the present invention;

[0026] Figure 4 is the first embodiment of the present invention; and

[0027] Figure 5 This is the second embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to fully describe the technical content, structural features, objectives and effects of the present invention, the following will be described in detail with reference to the accompanying drawings.

[0029] The present invention provides a terahertz optical delay device based on a multi-reflection White cavity, such as Figure 1 and Figure 2 As shown, it includes a motion mechanism 1, a White cavity delay mechanism 8, an optical signal transmitting end 6, an optical signal receiving end 7 and an optical base 5. The White cavity delay mechanism 8 includes a movable concave mirror 2, a first fixed concave mirror 3 and a second fixed concave mirror 4. The White cavity delay mechanism 8 relies on the motion mechanism 1 to drive the movable concave mirror 2 to move back and forth to realize optical delay scanning. The motion mechanism 1 realizes reciprocating motion by piezoelectric ceramics, voice coil motors, magnetic levitation motors or stepping motors.

[0030] The first fixed concave mirror 3 and the second fixed concave mirror 4 are installed in parallel at the first end of the optical base 5, and the first fixed concave mirror 3 and the second fixed concave mirror 4 are flush with each other. The second end of the optical base 5 is installed with a motion mechanism 1, and the motion mechanism 1 is installed with a mobile concave mirror 2, and the center of curvature of the mobile concave mirror 2 is located in the middle of the first fixed concave mirror 3 and the second fixed concave mirror 4. The optical signal transmitting end 6 is installed on the first side of the mobile concave mirror 2, and the optical signal receiving end 7 is installed on the second side of the mobile concave mirror 2. The number of reflections N in the White cavity delay mechanism 8 is changed by changing the incident position of the optical signal, the incident angle of the optical signal, the angle of the first fixed concave mirror 3 or the angle of the second fixed concave mirror 4.

[0031] The optical signal is incident and emitted by the first fixed concave mirror 3 and the second fixed concave mirror 4, and the optical signal is transmitted back and forth in the White cavity delay mechanism 8. The optical path and the White cavity delay mechanism 8 have the following relationship: L=2(N+1)d, where L is the optical path, N is the number of reflections, d is the cavity length of the White cavity delay mechanism 8, and when the terahertz time-domain spectrum delay line is scanned, the optical signal delay is a step value. The relationship between the delay change and the cavity length change of the White cavity delay mechanism 8 is ΔT=(2(N+1)Δd) / c, where Δd is the cavity length change of the White cavity delay mechanism 8 during the movement of the mobile concave mirror 2, c is the speed of light, ΔT is the delay change of the device, and N is the number of reflections.

[0032] The light signal enters the White cavity delay mechanism 8 from the first side of the movable concave mirror 2, and after multiple reflections, it is emitted from the second side of the movable concave mirror 2, and the emission position of the light signal is symmetrically distributed with the incident position of the light signal. Within the reciprocating range of the moving mechanism 1, the number of reflections N is constant.

[0033] A second aspect of the present invention provides a time delay method of a terahertz optical time delay device based on a multi-reflection White cavity, such as Figure 3 As shown, it includes the following steps:

[0034] S1: Set the reciprocating distance of the mobile concave mirror 2;

[0035] S2: The optical signal transmitting end 6 transmits a light beam to the outside;

[0036] S3: The light beam is reflected and transmitted multiple times in the White cavity delay mechanism 8;

[0037] S4: The optical signal receiving end 7 receives the light beam;

[0038] S5: The moving concave mirror 2 moves back and forth, and the transmission distance of the multi-reflected light beam in the White cavity delay mechanism 8 changes back and forth, thereby realizing optical delay.

[0039] Specifically, the movable concave mirror 2 of the present invention, the first fixed concave mirror 3 and the second fixed concave mirror 4 constitute a multiple reflection White cavity delay mechanism 8. The motion mechanism 1 drives the movable concave mirror 2 to perform reciprocating motion. The optical path in the cavity changes during the motion, thereby achieving time delay. The optical base 5 is responsible for support and load-bearing.

[0040] like Figure 2 As shown, when the present invention is working, the optical signal emitted by the optical signal transmitting end 6 is transmitted into the cavity of the White cavity delay mechanism 8, and after multiple reflections between the movable concave mirror 2 and the first fixed concave mirror 3 and the second fixed concave mirror 4, it is output to the optical signal receiving end 7. When the moving mechanism 1 performs reciprocating motion, the optical path between the optical signal transmitting end 6 and the optical signal receiving end 7 changes, that is, the delay changes. The center of curvature of the movable concave mirror 2 falls in the middle position of the first fixed concave mirror 3 and the second fixed concave mirror 4, and the center of curvature of the first fixed concave mirror 3 and the second fixed concave mirror 4 is near the movable concave mirror 2. The optical signal is incident from the outside of the cavity of the White cavity delay mechanism 8 and is emitted from the cavity after multiple reflections.

[0041] Embodiment 1, the present invention is based on three concave mirrors to form a White cavity delay mechanism 8, realizes compact multiple reflections of optical signals, and realizes optical path change by using a motion mechanism 1 to drive the cavity mirror and change the cavity length of the White cavity delay mechanism 8, thereby realizing optical delay. It can be applied to terahertz time-domain spectrometers to realize equivalent sampling and signal reconstruction for terahertz time-domain pulse signals, improve the range of thickness measurement in time-domain systems, and improve the frequency resolution of material composition analysis functions. During the use of terahertz time-domain spectroscopy, such as Figure 4 As shown, the specific process is as follows, including that the laser output femtosecond laser is split into a pump beam and a detection beam by a fiber coupler, wherein the pump beam is incident on the photoconductive antenna at the transmitting end to radiate terahertz waves, and the terahertz waves enter the photoconductive antenna at the receiving end after spatial transmission; the detection beam is incident on the photoconductive antenna at the receiving end after being delayed by the White cavity delay mechanism 8 after multiple reflections, and equivalent sampling is achieved by relying on the reciprocating motion of the motion mechanism 1 of the White cavity that reflects multiple times, that is, terahertz spectrum scanning.

[0042] Embodiment 2, the present invention can also be applied to autocorrelation systems, such as Figure 5 As shown, the specific process is as follows, including the femtosecond laser output light beam; adjusting the beam splitter to divide the laser pulse into two beams; adjusting the optical path to ensure that the two beams overlap in space and time in the nonlinear crystal; in the nonlinear crystal, the two beams generate a signal related to the pulse width through the second harmonic; the delay line moves back and forth to change the time delay of the two beams, completing the complete pulse autocorrelation signal scan.

[0043] In addition, the multi-reflection White cavity delay line of the present invention can be applied to optical time domain detection, radar calibration, optical coherence tomography detection and optical network time division multiplexing system, and has application value.

[0044] The above are preferred implementation modes of the present application, which are not intended to limit the protection scope of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principles of this technology, and these improvements and modifications should also be regarded as the protection scope of the present application.

Claims

1. A terahertz optical delay device based on a multi-reflection White cavity, characterized in that: It includes a motion mechanism, a White cavity delay mechanism, an optical signal transmitting end, an optical signal receiving end and an optical base. The White cavity delay mechanism includes a mobile concave mirror, a first fixed concave mirror and a second fixed concave mirror. The White cavity delay mechanism relies on a motion mechanism to drive the mobile concave mirror to move back and forth to realize optical delay scanning. The motion mechanism realizes reciprocating motion by piezoelectric ceramics, voice coil motors, magnetic suspension motors or stepper motors. The first fixed concave mirror and the second fixed concave mirror are installed in parallel at the first end of the optical base, and the first fixed concave mirror and the second fixed concave mirror are flush with each other; a motion mechanism is installed at the second end of the optical base, a movable concave mirror is installed on the motion mechanism, and the center of curvature of the movable concave mirror is located at a middle position between the first fixed concave mirror and the second fixed concave mirror; The optical signal transmitting end is installed on the first side of the movable concave mirror, and the optical signal receiving end is installed on the second side of the movable concave mirror; The number of reflections N in the White cavity delay mechanism is changed by changing the incident position of the light signal, the incident angle of the light signal, the angle of the first fixed concave mirror or the angle of the second fixed concave mirror.

2. The terahertz optical delay device based on a multi-reflection White cavity according to claim 1, characterized in that: The optical signal is incident and emitted by the first fixed concave mirror and the second fixed concave mirror, and the optical signal is transmitted back and forth in the White cavity delay mechanism. The relationship between the optical path and the White cavity delay mechanism is L=2(N+1)d, where L is the optical path, N is the number of reflections, and d is the cavity length of the White cavity delay mechanism. When the terahertz time-domain spectrum delay line is scanned, the optical signal delay is a step value, and the relationship between the delay change and the cavity length change of the White cavity delay mechanism is ΔT=(2(N+1)Δd) / c, where Δd is the cavity length change of the White cavity delay mechanism during the movement of the mobile concave mirror, c is the speed of light, ΔT is the delay change of the device, and N is the number of reflections.

3. The terahertz optical delay device based on a multi-reflection White cavity according to claim 1, characterized in that: The optical signal is incident from the first side of the movable concave mirror into the White cavity delay mechanism, and after multiple reflections, is emitted from the second side of the movable concave mirror, and the emission position of the optical signal is symmetrically distributed with the incident position of the optical signal.

4. The terahertz optical delay device based on a multi-reflection White cavity according to claim 3, characterized in that: When the moving mechanism is within the reciprocating motion range, the number of reflections N is a constant.

5. A time delay method using the terahertz optical time delay device based on a multi-reflection White cavity according to any one of claims 1 to 4, characterized in that: It includes the following steps: S1: Set the reciprocating distance of the mobile concave mirror; S2: The optical signal transmitting end transmits a light beam to the outside; S3: The light beam is transmitted through multiple reflections in the White cavity delay mechanism; S4: The optical signal receiving end receives the light beam; S5: The mobile concave mirror moves back and forth, and the transmission distance of the multi-reflected light beam in the White cavity delay mechanism changes back and forth, realizing optical delay.

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