Optical signal inner-circulation delay system based on electro-optic polarization control
The optical signal internal loop delay system with electro-optic polarization modulation uses a ring optical path and an electro-optic polarization modulator to realize multiple loops of optical signals, which solves the problems of non-adjustable optical signal delay, large size and high loss in the existing technology, and realizes flexible delay time adjustment and low-cost optical signal delay effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SOUTH WEST INST OF TECHN PHYSICS
- Filing Date
- 2023-12-01
- Publication Date
- 2026-06-23
AI Technical Summary
Existing optical signal delay technologies have drawbacks such as being non-adjustable, large in size, high in loss, and high in cost, making it difficult to meet the requirements for large delay times.
An internal loop delay system for optical signals based on electro-optic polarization modulation is adopted. The signal light is controlled to rotate and cycle multiple times in the ring optical path through the polarization rotation effect. The ring optical path is constructed by electro-optic polarization modulator, lens, total reflection mirror and other components to realize flexible adjustment and expansion of the delay time.
It achieves low-loss, low-cost, and small-size optical signal delay, can adjust the delay time range, is suitable for large delay time requirements, and can convert continuous light into controllable pulsed light.
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Figure CN117856909B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of optical signal modulation technology and relates to an optical signal inner loop delay system based on electro-optic polarization modulation. Background Technology
[0002] In applications such as fiber optic communication, optical sensing, and heterodyne detection, a certain time delay is typically required for optical signals to load or extract useful information. On the other hand, an important method for extracting useful information from optical signals is to create interference between the signal light and the reference light, and then analyze the characteristics of the interference pattern. To ensure interference formation, the reference light and the signal light need to have temporal coherence. The simplest and most effective implementation is to split the initial signal light into two parts, serving as the reference light and the signal light respectively. However, in some cases, the distance the signal light travels in a complex system exceeds the coherence length of the light source; therefore, a corresponding time delay is also needed for the reference light to maintain good coherence.
[0003] The basic method for achieving time delay in optical signals is to utilize the delay generated by the propagation of the optical signal in a waveguide or space, and to change the delay time by adjusting the transmission distance (strictly speaking, the optical path). This method is simple in structure, easy to implement, and feasible when the required delay time is short (on the order of nanoseconds). However, in most application scenarios, the delay time is much longer than nanoseconds, and the required optical path exceeds or even far exceeds kilometers. Achieving such a time delay may lead to many drawbacks such as large space requirements, high costs, and inconvenient maintenance.
[0004] Currently, the following technologies have been developed to overcome these shortcomings: 1) By using optical fibers of different lengths to transmit multiple optical signals generated by beam splitters, different time delays can be achieved for these optical signals; 2) By using 1×2 couplers to cascade multiple delay fibers of the same length, different time delays can be achieved for these optical signals. This method can effectively reduce the large losses caused by parallel optical beam splitting (e.g., Chinese Patent CN206601507U); 3) By using a vertical-cavity surface-emitting laser (VCSEL) to generate positive phase dispersion in the input optical signal, a delay of optical signals with slower group velocities can be achieved. This method is characterized by its flexible adjustment of the delay time (e.g., Chinese Patent CN202631915U); 4) Optical signal delay methods using fluorescence effects. This method is advantageous for extracting delayed signals in multiple spatial directions (e.g., Chinese Patent CN104660339). While these technologies may excel in certain aspects such as adjustment flexibility, transmission loss, signal distortion, and size and cost, they inevitably have some shortcomings in other aspects. Therefore, in order to make up for the shortcomings of existing technologies, it is necessary and urgent to study an optical signal delay technology that is time-adjustable, has low transmission loss, high signal fidelity, small size, and low cost. Summary of the Invention
[0005] (a) Purpose of the invention
[0006] The purpose of this invention is to address the shortcomings of traditional optical signal delay technologies, such as non-adjustability, large size, and high loss, by proposing an optical signal internal loop delay system based on electro-optic polarization modulation. This system utilizes the polarization rotation effect to control the input signal to rotate and cycle multiple times in the same loop optical path before outputting it. It achieves the delay time that would otherwise require several times the length of an optical fiber with just one delay fiber, aiming to overcome the deficiencies of existing technologies and further expand the delay range.
[0007] (II) Technical Solution
[0008] To address the aforementioned technical problems, this invention provides an optical signal internal loop delay system based on electro-optic polarization modulation, comprising: a signal light source 1, a first polarization beam splitter 2, a first electro-optic polarization modulator 3, a second polarization beam splitter 4, a second electro-optic polarization modulator 5, a third polarization beam splitter 6, a first total reflection mirror 7, a first lens 8, a first fiber collimator 9, a single-mode / multimode fiber 10, a second lens 12, a second fiber collimator 11, and a second total reflection mirror 13.
[0009] The signal light source 1 and the first electro-optic polarization modulator 3 are located on opposite sides of the first polarization beam splitter 2, and the signal light enters the first electro-optic polarization modulator 3 after being reflected by the first polarization beam splitter 2. The reflecting surfaces of the second polarization beam splitter 4 and the first polarization beam splitter 2 are parallel and perpendicular to the third polarization beam splitter 6. The two ends of the single-mode / multimode fiber 10 are respectively fused with a first fiber collimator 9 and a second fiber collimator 11, with the first fiber collimator 9 facing the first lens 8 and the second fiber collimator 11 facing the second lens. 12; A first total reflection mirror 7 is placed at a 45° angle between the first lens 8 and the third polarizing beam splitter 6; a second total reflection mirror 13 is placed at a 45° angle between the second lens 12 and the second polarizing beam splitter 4; a second electro-optic polarization modulator 5 is arranged between the second polarizing beam splitter 4 and the third polarizing beam splitter 6; the second polarizing beam splitter 4, the second electro-optic polarization modulator 5, the third polarizing beam splitter 6, the single-mode / multimode fiber 10, and all total reflection mirrors, lenses, and fiber collimators form a ring optical path.
[0010] The signal light source 1 emits continuous unpolarized light or S-polarized light.
[0011] Among them, the reflecting surfaces of the first polarizing beam splitter 2, the second polarizing beam splitter 4, and the third polarizing beam splitter 6 can fully transmit P light while reflecting S light.
[0012] The focal point of the first lens 8 is located exactly at the waist of the Gaussian beam output by the first fiber collimator 9.
[0013] The focal point of the second lens 12 is located exactly at the waist of the Gaussian beam output by the second fiber collimator 11.
[0014] When an electrical signal with a level greater than a specified value is applied to the first electro-optic polarization modulator 3 and the second electro-optic polarization modulator 5, the polarization direction of the emitted light rotates by 90 degrees, that is, P light becomes S light and S light becomes P light; when the level of the applied electrical signal is lower than the specified value, the polarization direction of the emitted light remains unchanged from the original incident light direction.
[0015] In this configuration, the first electro-optic polarization modulator 3 and the second electro-optic polarization modulator 5 are loaded with the same modulation pulse electrical signal, and the pulse width of the electrical signal is... It is less than the time τ for the signal light to circulate once in the loop optical path, while the pulse interval T is an integer multiple of τ.
[0016] Let L be the spatial optical path length of the annular optical path. air The length of the single-mode / multimode fiber 10 is L. fiber Then the optical path length L is expressed as:
[0017] ,
[0018] In the formula, n is the effective refractive index of the optical fiber, and the time for the signal light to travel one revolution in the loop optical path is:
[0019] ,
[0020] In the formula, c is the speed of light in a vacuum, which is determined by adjusting the length L of the optical fiber. fiber This is used to change the delay time τ of the signal light circulating once in the loop optical path.
[0021] The continuous unpolarized light emitted by the signal light source 1 is split into two beams with mutually perpendicular polarization directions by the first polarization beam splitter. The transmitted P-beam is directly dispersed into the air, while the reflected S-beam enters the first electro-optic polarization modulator 3. If the first electro-optic polarization modulator 3 is in a low-level state, the output is still S-polarized light, which is dispersed into the air by the second polarization beam splitter 4. If it is in a high-level state, it is adjusted by the first electro-optic polarization modulator 3 and outputs P-polarized light. This part of the signal light enters the ring optical path through the second polarization beam splitter 4. For the P-beam entering the fiber optic loop: if the second electro-optic polarization modulator 5 is in a low-level state, it is directly transmitted out from the third polarization beam splitter 6. If the second electro-optic polarization modulator 5 is at a high level, the light is transmitted sequentially through the electro-optic polarization modulator 5, reflected by the third polarization beam splitter 6, reflected by the first total reflection mirror 7, transmitted through the first lens 8, passed through the first fiber collimator 9, single-mode / multimode fiber 10, transmitted through the second fiber collimator 11, transmitted through the second lens 12, reflected by the second total reflection mirror 13, and reflected by the second polarization beam splitter 4, thus propagating in the loop optical path. When the signal light is propagating in the loop optical path, if the electro-optic polarization modulator 5 is always at a low level, the signal light is always in a cyclic propagation state. When the control signal of the electro-optic polarization modulator 5 is at a high level, the light signal, after multiple cycles, is transmitted and output from the third polarization beam splitter 6.
[0022] The switch or level state of the first electro-optic polarization controller 3 and the second polarization controller 5 are controlled simultaneously to achieve adjustable delay optical signal output without background light.
[0023] (III) Beneficial Effects
[0024] The optical signal internal loop delay system based on electro-optic polarization modulation provided by the above technical solution has the following beneficial effects:
[0025] (1) In this invention, the input and output of the ring optical path are realized by a polarizing beam splitter, which can effectively reduce the loss caused by multi-stage beam splitting compared with traditional beam splitters and beam combiners.
[0026] (2) In this invention, the combination structure of lens and fiber collimator can effectively improve the coupling efficiency of signal light transmission from space to single-mode / multimode fiber and from fiber to space.
[0027] (3) In this invention, the input signal is controlled to rotate and cycle multiple times in the loop optical path before being output. The delay time that would otherwise require several times the length of an optical fiber is achieved with a single extended optical fiber. This not only greatly reduces the cost but also facilitates miniaturization and weight reduction.
[0028] (4) In this invention, adjusting the length of the single-mode / multimode fiber and the duration of the high level of the modulation electrical signal can change the repetition frequency and pulse width of the output optical signal respectively, and therefore can also be used to convert continuous light into controllable pulsed light.
[0029] (5) In this invention, the number of times the signal light circulates in the annular optical path can be controlled by the loaded electrical signal, thereby flexibly adjusting the delay time and expanding the range of delay time. Attached Figure Description
[0030] Figure 1 This is a structural diagram of an optical signal internal loop delay system based on electro-optic polarization modulation, according to an embodiment of the present invention.
[0031] Figure 2 This is a schematic diagram illustrating the method for adjusting the optical signal delay time in an embodiment of the present invention.
[0032] Figure 3 This is a schematic diagram illustrating the method of generating pulsed light signals with fixed frequency and delay in an embodiment of the present invention. Detailed Implementation
[0033] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.
[0034] Combination Figure 1 The optical signal internal loop delay system based on electro-optic polarization modulation in this embodiment includes: a signal light source 1, a first polarization beam splitter 2, a first electro-optic polarization modulator 3, a second polarization beam splitter 4, a second electro-optic polarization modulator 5, a third polarization beam splitter 6, a first total reflection mirror 7, a first lens 8, a first fiber collimator 9, a single-mode / multimode fiber 10, a second lens 12, a second fiber collimator 11, and a second total reflection mirror 13.
[0035] The signal light source 1 and the first electro-optic polarization modulator 3 are located on opposite sides of the first polarization beam splitter 2, and the signal light enters the first electro-optic polarization modulator 3 after being reflected by the first polarization beam splitter 2. The reflecting surfaces of the second polarization beam splitter 4 and the first polarization beam splitter 2 are parallel and perpendicular to the third polarization beam splitter 6. The two ends of the single-mode / multimode fiber 10 are respectively fused with a first fiber collimator 9 and a second fiber collimator 11, with the first fiber collimator 9 facing the first lens 8 and the second fiber collimator 11 facing the second lens 1. 2; A first total reflection mirror 7 is placed at a 45° angle between the first lens 8 and the third polarizing beam splitter 6; a second total reflection mirror 13 is placed at a 45° angle between the second lens 12 and the second polarizing beam splitter 4; a second electro-optic polarization modulator 5 is arranged between the second polarizing beam splitter 4 and the third polarizing beam splitter 6; the second polarizing beam splitter 4, the second electro-optic polarization modulator 5, the third polarizing beam splitter 6, the single-mode / multimode fiber 10, and all total reflection mirrors, lenses, and fiber collimators form a ring optical path.
[0036] The signal light source 1 emits continuous unpolarized light or S-polarized light.
[0037] Among them, the reflecting surfaces of the first polarizing beam splitter 2, the second polarizing beam splitter 4, and the third polarizing beam splitter 6 can completely transmit P light while reflecting S light.
[0038] The focal point of the first lens 8 is located exactly at the waist of the Gaussian beam output by the first fiber collimator 9; the focal point of the second lens 12 is located exactly at the waist of the Gaussian beam output by the second fiber collimator 11.
[0039] Among them, the first electro-optic polarization modulator 3 and the second electro-optic polarization modulator 5 are similar to a tunable waveplate. When an electrical signal with a level greater than a specified value is applied to the modulator, the polarization direction of the outgoing light rotates by 90 degrees, that is, P light becomes S light and S light becomes P light; when the level of the applied electrical signal is lower than the specified value, the polarization direction of the outgoing light remains unchanged from the original incident light direction.
[0040] In this circuit, the first electro-optic polarization modulator 3 and the second electro-optic polarization modulator 5 are loaded with the same control pulse electrical signal, and the pulse width ∆T of the electrical signal is less than the time τ for the signal light to circulate once in the annular optical path, while the pulse interval T is equal to an integer multiple of τ.
[0041] If the spatial optical path length of the annular optical path is L air The length of the single-mode / multimode fiber 10 is L. fiber Then the optical path length L can be expressed as:
[0042] ,
[0043] In the formula, n is the effective refractive index of the optical fiber, and the time for the signal light to travel one revolution in the loop optical path is:
[0044] ,
[0045] In the formula, c is the speed of light in a vacuum. In this invention, the speed is mainly achieved by adjusting the length L of the optical fiber. fiber This is used to change the delay time τ of the signal light circulating once in the loop optical path.
[0046] In this embodiment, the continuous unpolarized light emitted by the signal light source 1 is split into two beams with mutually perpendicular polarization directions by the first polarization beam splitter. The transmitted P-beam is directly dispersed into the air, while the reflected S-beam enters the first electro-optic polarization modulator 3. If the first electro-optic polarization modulator 3 is in a low-level state, the output is still S-polarized light, which is dispersed into the air by the second polarization beam splitter 4. If it is in a high-level state, P-polarized light is output after adjustment by the first electro-optic polarization modulator 3, and this part of the signal light enters the annular optical path through the second polarization beam splitter 4. For P-beams entering the fiber optic loop: if the second electro-optic polarization modulator 5 is at a low level, it is directly transmitted through the third polarization beam splitter 6; if the second electro-optic polarization modulator 5 is at a high level, it is transmitted sequentially through the electro-optic polarization modulator 5, reflected by the third polarization beam splitter 6, reflected by the first total reflection mirror 7, transmitted through the first lens 8, transmitted through the first fiber collimator 9, transmitted through the single-mode / multimode fiber 10, transmitted through the second fiber collimator 11, transmitted through the second lens 12, reflected by the second total reflection mirror 13, and reflected by the second polarization beam splitter 4, thus propagating in the loop optical path. When the signal light propagates in the loop optical path, as long as the electro-optic polarization modulator 5 remains at a low level, the signal light can be guaranteed to be in a cyclic propagation state. When the control signal of the electro-optic polarization modulator 5 is at a high level, the optical signal, after multiple cycles, is transmitted and output through the third polarization beam splitter 6.
[0047] Combination Figure 2 This example demonstrates how to achieve adjustable-delay optical signal output without background light by simultaneously controlling the switching (level) states of the first electro-optic polarization controller 3 and the second polarization controller 5. At time 0, the input electrical signal is at a high level V. high (Greater than or equal to the specified peak level), duration Then it becomes low level V low (less than the specified peak level), and It is less than the time τ it takes for the signal light to circulate once in the loop optical path. During this period, the duration is... The pulsed signal light (the optical signal before the delay) enters the loop optical path and becomes S-polarized light, which then propagates within it. At time τ, the input electrical signal is again at a high level V. high After the same duration ∆T, it becomes a low level V. lowDuring this period, the optical signal delayed by time τ (the delayed optical signal) is transmitted and output from the polarization beam splitter prism 6, while a pulse signal light with a duration of ∆T (the pre-delayed optical signal) enters the annular optical path and circulates. By time 3τ, the pulse optical signal (the pre-delayed optical signal) that entered at time τ has circulated twice in the annular optical path. At this point, the control input electrical signal changes from low level to high level V. high Continuing for the same amount of time Then it goes low again V low At high level V high During the duration, an optical signal with a time delay of 2τ (the delayed optical signal) is transmitted and output from the polarization beam splitter 6, while a signal with a duration of... The pulsed light signal (the delayed light signal) enters the loop optical path and is transmitted cyclically. Thus, after time 6τ, the input electrical signal is at a high level V. high During this state, an optical signal with a time delay of 3τ is output. Therefore, by adjusting the electrical signal only at times τ, 3τ, 6τ, ... , Duration after τ When the internal signal is in a high-level state and the other time is in a low-level state, a series of delay times τ, 2τ, 3τ, etc. can be output. The optical signal of mτ.
[0048] Combination Figure 3 By inputting a periodic rectangular pulse electrical signal to simultaneously control the switching states of two electro-optic polarization controllers, a periodic pulse optical signal with a fixed time delay can be generated. The pulse interval of the modulation electrical signal is T = mτ (m is a positive integer), and the pulse width is... < τ, repetition frequency f = 1 / mτ. The input continuous optical signal is modulated and converted into a signal with a fixed delay T. d = mτ and frequency f = 1 / mτ of the pulsed optical signal. Clearly, by changing the pulse interval T of the electrical signal, the number of rotations m of the optical signal in the annular optical path can be adjusted, thereby achieving a wide range of flexible adjustment of the time delay and repetition frequency of the output optical signal.
[0049] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A light signal internal loop delay system based on electro-optic polarization modulation, characterized in that, include: Signal light source (1), first polarization beam splitter (2), first electro-optic polarization modulator (3), second polarization beam splitter (4), second electro-optic polarization modulator (5), third polarization beam splitter (6), first total reflection mirror (7), first lens (8), first fiber collimator (9), single-mode / multimode fiber (10), second lens (12), second fiber collimator (11), and second total reflection mirror (13); The signal light source (1) and the first electro-optic polarization modulator (3) are located on opposite sides of the first polarization beam splitter (2), and the signal light enters the first electro-optic polarization modulator (3) after being reflected by the first polarization beam splitter (2); the reflecting surfaces of the second polarization beam splitter (4) and the first polarization beam splitter (2) are parallel and perpendicular to the third polarization beam splitter (6); the two ends of the single-mode / multimode fiber (10) are respectively fused with a first fiber collimator (9) and a second fiber collimator (11), with the first fiber collimator (9) facing the first lens (8) and the second fiber collimator (11) facing the second lens. (12); A first total reflection mirror (7) is placed at a 45° angle between the first lens (8) and the third polarization beam splitter (6), and a second total reflection mirror (13) is placed at a 45° angle between the second lens (12) and the second polarization beam splitter (4); a second electro-optic polarization modulator (5) is arranged between the second polarization beam splitter (4) and the third polarization beam splitter (6); the second polarization beam splitter (4), the second electro-optic polarization modulator (5), the third polarization beam splitter (6), the single-mode / multimode fiber (10), and all total reflection mirrors, lenses, and fiber collimators form a ring optical path.
2. The optical signal inner loop delay system based on electro-optic polarization modulation as described in claim 1, characterized in that, The signal light source (1) emits continuous unpolarized light or S-polarized light.
3. The optical signal inner loop delay system based on electro-optic polarization modulation as described in claim 2, characterized in that, The reflecting surfaces of the first polarizing beam splitter (2), the second polarizing beam splitter (4), and the third polarizing beam splitter (6) can fully transmit P light and reflect S light.
4. The optical signal inner loop delay system based on electro-optic polarization modulation as described in claim 3, characterized in that, The focal point of the first lens (8) is located exactly at the waist of the Gaussian beam output by the first fiber collimator (9).
5. The optical signal inner loop delay system based on electro-optic polarization modulation as described in claim 4, characterized in that, The focal point of the second lens (12) is located exactly at the waist of the Gaussian beam output by the second fiber collimator (11).
6. The optical signal inner loop delay system based on electro-optic polarization modulation as described in claim 5, characterized in that, When an electrical signal with a level greater than a specified value is applied to the first electro-optic polarization modulator (3) and the second electro-optic polarization modulator (5), the polarization direction of the outgoing light rotates by 90 degrees, that is, P light becomes S light and S light becomes P light; when the level of the applied electrical signal is lower than the specified value, the polarization direction of the outgoing light remains unchanged from the original incident light direction.
7. The optical signal inner loop delay system based on electro-optic polarization modulation as described in claim 6, characterized in that, The first electro-optic polarization modulator (3) and the second electro-optic polarization modulator (5) are loaded with the same modulation pulse electrical signal, and the pulse width of the electrical signal is... It is less than the time τ for the signal light to circulate once in the loop optical path, while the pulse interval T is an integer multiple of τ.
8. The optical signal inner loop delay system based on electro-optic polarization modulation as described in claim 7, characterized in that, Let the spatial optical path length of the annular optical path be L. air The length of the single-mode / multimode fiber (10) is L fiber Then the optical path length L is expressed as: ， In the formula, n is the effective refractive index of the optical fiber, and the time for the signal light to travel one revolution in the loop optical path is: ， In the formula, c is the speed of light in a vacuum, which is determined by adjusting the length L of the optical fiber. fiber This is used to change the delay time τ of the signal light circulating once in the loop optical path.
9. The optical signal inner loop delay system based on electro-optic polarization modulation as described in claim 8, characterized in that, The continuous unpolarized light emitted by the signal light source (1) is split into two beams with mutually perpendicular polarization directions by the first polarization beam splitter. The transmitted P-beam is directly dispersed into the air, while the reflected S-beam enters the first electro-optic polarization modulator (3). If the first electro-optic polarization modulator (3) is in a low-level state, the output is still S-polarized light, which is dispersed into the air by the second polarization beam splitter (4). If it is in a high-level state, it is adjusted by the first electro-optic polarization modulator (3) and outputs P-polarized light. This part of the signal light enters the ring optical path through the second polarization beam splitter (4). For the P-beam entering the fiber optic loop: if the second electro-optic polarization modulator (5) is in a low-level state, it is directly transmitted from the third polarization beam splitter (6); if the second electro-optic polarization modulator (5) is in a high-level state, it is directly transmitted from the third polarization beam splitter (6). When the modulator (5) is at a high level, the signal light is transmitted through the electro-optic polarization modulator (5), reflected by the third polarization beam splitter (6), reflected by the first total reflection mirror (7), transmitted through the first lens (8), transmitted through the first fiber collimator (9), single-mode / multimode fiber (10), second fiber collimator (11), transmitted through the second lens (12), reflected by the second total reflection mirror (13), and reflected by the second polarization beam splitter (4) in sequence, and is transmitted in the ring optical path. When the signal light is transmitted in the ring optical path, when the electro-optic polarization modulator (5) is always at a low level, the signal light is always in a cyclic propagation state. When the control signal of the electro-optic polarization modulator (5) is at a high level, the optical signal that has undergone multiple cycles is transmitted and output from the third polarization beam splitter (6).
10. The optical signal inner loop delay system based on electro-optic polarization modulation as described in claim 9, characterized in that, Simultaneously control the switching or level state of the first electro-optic polarization controller (3) and the second polarization controller (5) to achieve adjustable delay optical signal output without background light.