CN108227079A - A kind of high-precision N-bit adjustable light delays - Google Patents

Abstract

The present invention provides a kind of high-precision N bit adjustable light delays, are mainly made of optical switch chip, collimator lens array, free space time delay module, input-output optical fiber pigtail, pedestal.Wherein optical switch chip is integrated for the array of multiple optical switch elements, and free space time delay module realizes the integration of multistage delay unit, and the efficient coupling of the two is realized by lens array, ps grades of step-lengths, the adjustable light delay of 10 more than bit finally can be achieved.The present invention have many advantages, such as delay precision it is high, with it is roomy, small, light-weight, be easy to technique realization, be very suitable for the application in the fields such as Optical Controlled Phased Array Antenna system, particularly airborne, spaceborne radar.

Description

A high-precision N-bit dimmable delayer

technical field

The invention relates to the technical field of optoelectronic devices, in particular to a high-precision tunable optical delayer.

Background technique

In a phased array radar system, the configuration of the phase shifter of the traditional electrical domain phased array antenna is related to the frequency of the microwave signal, which makes the instantaneous bandwidth very narrow. In order to realize the large instantaneous bandwidth of the phased array radar, the technology of True Time Delay should be used instead of the electric domain phase shifter. The traditional TTD is composed of waveguide or coaxial cable. This method of directly delaying the microwave signal is limited by the density of the electrical circuit. The time delay network constructed is bulky and heavy, and the signal loss is high. Both in terms of performance and engineering. Not practical. The microwave signal is modulated onto the light, and the optical waveguide is used as the delay circuit, that is, the optical true delay technology (OTTD). The device has the advantages of small size, light weight, wide bandwidth, stable transmission, and no mutual radiation interference. It is a microwave photon important field of study.

In order to make the scanning direction of the antenna adjustable, the delay length of the optical delayer must be adjustable; and in order to ensure the high resolution of the antenna scanning angle, the tuning step of the optical delayer should be small enough. In order to meet the high-band radar application, for the step-by-step dimmable delayer, the delay step generally needs to reach the ps level. At this time, it can be considered as a "quasi-continuous" dimmable delayer.

At present, there are many implementation schemes for the adjustable optical delay device, mainly including "optical switch + delay line", optical resonant cavity, chirped grating, photonic crystal, etc. Optical resonators, chirped gratings, and photonic crystals can achieve continuous tuning of optical delay, but they all belong to resonant structures. The performance of optical signal delay is limited by the inherent delay-bandwidth product of the resonant structure itself, and their bandwidths are relatively Narrow, can not meet the application requirements of broadband radar. The "optical switch + delay line" scheme can achieve large bandwidth, but it is a step-by-step adjustable optical delay technology. In order to meet high-band radar applications, it must have a sufficiently small delay step and a sufficiently high delay accuracy.

The "optical switch + fiber delay" solution is a classic step-by-step adjustable optical delay technology, but due to the limitation of optical fiber processing accuracy, the delay accuracy can only be about 0.01ns, which is only suitable for low-frequency band applications such as S-band, and Limited by the volume and weight of discrete optical fiber devices, it is difficult to achieve integration and miniaturization of the device, which limits its application in airborne/spaceborne and other fields.

An emerging technology is the on-chip adjustable optical delay technology of "optical switch + optical waveguide delay". Its delay accuracy can reach below 0.1 ps, which can meet the delay accuracy requirements of high-band radar applications. There are still some problems in implementation. If submicron-scale small-sized waveguides are used, there are problems such as large waveguide optical transmission loss, low coupling efficiency between chips and optical fibers, difficulty in precise control of delay paths, and high sensitivity of chip performance to process; For large-sized waveguides, the bending radius of the waveguide is relatively large, and the number of bits of the delayer that can be realized is small, which cannot meet the application requirements. In addition, for the multi-bit optical delayer integrated on the chip, due to the temperature dependence of the refractive index of the material, the delay variation caused by the temperature change is easily equal to or even exceeds the delay step, so the device must have a temperature control measures. In short, the current on-chip integrated "optical switch + optical waveguide delay" dimmable delay technology is still far from being practical.

Contents of the invention

The purpose of the present invention is to address the deficiencies of the prior art, and propose a high-precision dimmable delayer, whose delay tuning step length can reach 1ps, and the delay accuracy can reach 0.1ps, and has large bandwidth and small size at the same time. , fast tuning speed, easy process implementation and other advantages, can meet the application requirements of optically controlled phased array broadband radar.

The technical scheme disclosed by the present invention is as follows:

Using binary "optical switch + optical delay" topology, the device is mainly composed of optical switch chip, collimating lens array, free space delay module, input and output optical fiber Pigtail, and base. For an N-bit adjustable optical delayer, the optical switch chip needs to contain N+1 optical switch units, and the free space delay module needs to construct N free space delay units, and the delay units at each level include two delay units The channels are respectively connected to the two input/output ports of the optical switch unit, and the delay length difference between the two delay channels in each stage of delay unit increases by a factor of 2. The optical signal is input by the optical fiber, and the delay path is selected when passing through the first optical switch unit, and a certain delay channel entering the first-level delay unit is selected, and then the second-level delay channel is selected through the second optical switch unit , and so on, until passing through the Nth delay channel, and then switching to the output end through the N+1th optical switch unit, and the optical signal is output from the optical fiber after being delayed.

The optical switch can use electro-optic effect, thermo-optic effect, plasma dispersion effect, etc. to realize "on" and "off" state control, and can be based on silicon-based SOI (Silicon On Insulator) materials, organic polymer materials, etc. The optical switch chip has two possible configurations: one is that the N+1 optical switch units are all 2×2 optical switches; the other is that the first and N+1th optical switches are 1×2 optical switches, and the rest All 2×2 optical switches. All the optical switch units in the optical switch chip are arranged side by side to form an array. In order to facilitate the processing of the lens array, the input/output waveguides of the optical switch array are generally distributed at equal intervals, or at integer multiples of the minimum interval.

In order to increase the return loss, the end face of the input/output waveguide of the chip can be polished vertically or horizontally, and the input/output optical waveguide and the normal line of the end face of the chip can also be inclined at a certain angle during chip design.

The free space delay module includes two parts, which are respectively placed at both ends of the optical switch chip, and the adjacent delay units are respectively located in the two parts of the delay module. Each delay unit is composed of two delay paths, and the delay difference between the two paths increases by 2 times with the number of stages. Each time-delay path is turned back by two reflectors, so as to be sent to the next-level optical switch. The design of the delay length is achieved by designing the position of the mirrors. All the mirrors are attached to the substrate with position markings through high-precision patch and glue bonding process to form an integrated delay module.

The lens array adopts equidistant lens design, and the distance thereof is equal to the minimum distance between the input/output ends of the optical switch. All lenses of the lens array can be designed with the same focal length, or a lens array with non-uniform focal length, so that the coupling efficiency of each lens can better match the corresponding optical path, which depends on the trade-off between coupling efficiency and process complexity.

The input and output optical fiber pigtail is a fiber pigtail with a self-focusing lens. The self-focusing lens is coupled with a collimating lens array and a chip waveguide, and the input and output of optical signals are realized through the optical fiber.

The base is a base mounting platform designed for optimal coupling optical paths and reliable fixed connections of components such as optical switch chips, collimating lens arrays, free space delay modules, input and output optical fiber Pigtails, etc. Low material, its mechanical structure should also have low temperature sensitivity. Optical switch chips, collimating lens arrays, mirrors and substrates, input and output optical fiber pigtails and other components are bonded together with the base through glue curing to keep their relative positions fixed. The collimating lens array is located on both sides of the optical switch chip, and collimates the light spots emitted by the waveguide of the chip. The input and output optical fiber Pigtail is fixed on the substrate of the reflector by glue bonding and coupled with the collimating lens.

The advantages of the present invention are: compared with the traditional "optical switch + optical fiber delay" adjustable optical delay device, the delay step and delay accuracy are greatly improved, and the volume is small and the weight is light, so that it can be used in the optical control phase Controlled array radar systems, especially in the field of airborne and spaceborne radars, have strong applicability; compared with the on-chip integrated "optical switch + optical waveguide delay" adjustable optical delay device, the process feasibility is much stronger, and The optical delay length is not affected by temperature changes.

Description of drawings

Fig. 1 is a schematic diagram of the topology structure of the adjustable light delay used in the present invention.

Fig. 2 is a schematic structural diagram of an example of a 9-bit optical delay device disclosed in the present invention.

Fig. 3 is a schematic diagram of the arrangement of the optical switch array disclosed in the present invention.

Fig. 4 is a schematic diagram of the vertical oblique polishing process on the end face of the chip optical waveguide disclosed in the present invention.

Fig. 5 is a schematic diagram of Example 1 of the horizontal oblique polishing of the end surface of the chip optical waveguide disclosed in the present invention.

Fig. 6 is a schematic diagram of Example 2 of the horizontal oblique polishing of the end face of the chip optical waveguide disclosed in the present invention.

Fig. 7 is a schematic diagram of the inclined design of the chip optical waveguide disclosed in the present invention.

FIG. 8 is a schematic diagram of Example 1 of a delay path of a free-space unit disclosed in the present invention.

FIG. 9 is a schematic diagram of Example 2 of the free-space unit delay path disclosed in the present invention.

Fig. 10 is a schematic diagram of a lens array disclosed in the present invention.

Fig. 11 is a schematic structural view of the base platform disclosed by the present invention.

Detailed ways

Below by specific embodiment and in conjunction with accompanying drawing, the present invention is described in detail:

The invention proposes a novel adjustable optical delay device of "optical switch + free space optical delay", which adopts a binary topology structure. As shown in Figure 1, the optical delay units at all levels have two delay channels, and the difference between the delay lengths of the two is ΔL, 2ΔL, 4ΔL...2 ^n-1 ΔL, where n is the number of bits of the delayer , ΔL is the tuning step of the delayer. The 1st and N+1th optical switches in the figure can also be replaced by 2×2 optical switches.

FIG. 2 shows a schematic structural diagram of an example of a 9-bit optical delay device disclosed by the present invention. In the figure, 1 is an optical switch chip, which is composed of 10 2×2 optical switch arrays, 2 is a collimating lens array, 3 is a mirror, 4 is a mirror base platform, and 5 is an input/output optical fiber Pigtail. As shown in Figure 2, the 2×2 optical switch unit can switch between two transmission states of "straight-through" and "crossover", and realize the delay channel selection through the state switching of each level of optical switch unit. A series of reflectors and a substrate platform constitute two free-space optical delay modules, which are respectively located on both sides of the optical switch chip. The optical switch chip and the free-space optical delay module realize efficient coupling through a collimating lens array. The input/output optical fiber Pigtail is respectively coupled to the output ends of the first-stage and last-stage optical switch units through a collimating lens. Thus, for the 9-bit optical delayer in this example, by controlling the transmission state control of each stage of optical switch unit, an adjustable delay with ΔL as the step size and ²⁹ steps can be realized.

The layout of the optical switch array is shown in Figure 3. The spacing a in the figure is the center-to-center distance between two input/output waveguides of the same 2×2 optical switch unit, and the spacing b is the center-to-center distance between adjacent input/output waveguides of adjacent optical switch units. In order to facilitate the processing of the collimating lens array, all optical switch units should be arranged at equal intervals, and the intervals a and b in the figure should satisfy the integer multiple relationship, wherein the smaller interval is the center-to-center distance of adjacent lenses in the lens array. The simplest case is given in this example, that is, a=b, which is also equal to the center-to-center distance of adjacent lenses of the lens array. The present invention does not impose any restrictions on the control mechanism and chip material of the optical switch. For example, the control mechanism can be thermo-optic effect, electro-optic effect, plasma dispersion effect, MEMS, etc., and the chip material can be silicon (including SOI), organic polymer, etc. In this example, SOI material is used, and the switching technology based on the plasma dispersion effect is adopted.

In order to increase the return loss, the incident light of the chip waveguide and the normal line of the chip end surface can be designed to have a certain angle, which is called oblique incidence. An angle should also be maintained. There are various implementation schemes for the inclination angle, including vertical oblique polishing and horizontal oblique polishing of the chip end face, or maintaining the inclination angle between the optical waveguide and the normal line of the chip end face during chip design.

Fig. 4 shows a schematic diagram of an example of performing vertical oblique polishing on the end face of the waveguide of the optical switch chip. In the figure, 1 is the chip substrate material, 2 is the optical waveguide layer of the chip, 3 is the vertical oblique polishing angle of the chip, and 4 is the lens array. In this example, the vertical oblique polishing treatment is inclined at the top narrow at the bottom and wide at the bottom, or it can be obliquely polished at the top wide and narrow at the bottom. Both end faces of the chip coupled with the lens array can be processed with vertical oblique polishing, and only the end face of the chip coupled with the input/output optical fiber can be processed with vertical oblique polishing.

FIG. 5 shows a schematic diagram of an example of performing horizontal oblique polishing on the end face of the waveguide of the optical switch chip. In the figure, 1 is the chip, 2 is the lens array, 3 is the optical waveguide in the chip, and 4 is the horizontal oblique polishing angle of the chip. The dotted line in the figure indicates the optical path. The two end faces of the chip coupled with the lens array can be horizontally inclined polished, and only the end face of the chip coupled with the input/output optical fiber can be horizontally inclined polished.

FIG. 6 is a schematic diagram of another example of performing horizontal oblique polishing on the end face of the waveguide of the optical switch chip. In the figure, 1 is the chip, 2 is the lens array, 3 is the optical waveguide in the chip, and 4 is the horizontal oblique polishing angle of the chip. The dotted line in the figure indicates the optical path. The chip polishing method is the same as the example shown in Figure 5, except that the individual lens units of the lens array in this example are designed in a tilted manner, so the optical path coupled to the free space is different.

Fig. 7 shows a schematic diagram of an example of a chip optical waveguide tilt design. In the figure, 1 is a chip, 2 is a lens array, and 3 is an optical waveguide in the chip, and the dotted lines in the figure indicate the optical path. In this example, the chip is not subjected to oblique polishing treatment, but the input/output optical waveguide and the normal line of the chip end face form a certain oblique angle during chip design. In this example, the optical waveguides at both ends of the chip are tilted, and only the end coupled with the input/output optical fiber can be tilted.

Fig. 8 shows a schematic diagram of an example of a free-space unit delay path. One of the optical delay loops is: the optical signal is output through the upper output end of the i-th (1≤i≤N) optical switch unit, coupled to the free space through the lens, and the optical path reflection is realized through the mirror of the free space optical delay module. folded, and then coupled to the drop output end of the i+1th optical switch unit through a lens. Another optical delay loop is: an optical signal is output from the drop output end of the i-th optical switch, and coupled to the add input end of the i+1-th optical switch after passing through the optical path in the free-space optical delay module. For simplicity, this example assumes that all reflectors are at a 45° angle to the incident light. As shown in the figure, four symmetrically placed mirrors form two optical paths, and their optical paths are L1 and L2 respectively. The optical path difference between L1 and L2 is the adjustable delay length of the delay unit at this stage. As mentioned above, the adjustable delay lengths of adjacent delay units increase by 2 times. In the design, the optical path difference of the delay units L1 and L2 at each stage needs to be precisely controlled to meet the requirement of binary increment, but the absolute length of L1 or L2 does not need to be strictly controlled. The length of L1 and L2 is not important, as long as the process can be realized. This example gives a relatively simple example, that is, each stage of delay unit is L2 longer than L1.

FIG. 9 shows a schematic diagram of another example of a free-space unit delay path. One of the optical delay loops is: the optical signal is output through the upper output end of the i-th optical switch unit, coupled to the free space through the lens, and the optical path is refracted through the mirror of the free space optical delay module, and then coupled to the The add output end of the i+1th optical switch unit. Another optical delay loop is: the optical signal is output from the drop output end of the i-th optical switch, and is coupled to the drop input end of the i+1-th optical switch after passing through the optical path in the free space optical delay module. .

Fig. 10 is a schematic diagram of a collimator lens array disclosed in the present invention. As shown in FIG. 10 , the collimating lenses are arranged at a certain distance in the same direction, and the distance between the lenses corresponds to the distance between the channels of the waveguide chip. Corresponding to the waveguide pitch of the optical switch chip, FIG. 10 shows an example of a lens array with uniform center-to-center distances. The central axes of all the lenses are parallel to each other in the arrangement direction, the spherical surface of the lens is on the same side, and the aspheric surface is on the other side. All lenses of the lens array can be designed with the same focal length, or a lens array with non-uniform focal length, so that the coupling efficiency of each lens can better match the corresponding optical path, which depends on the trade-off between coupling efficiency and process complexity. For the lens array design with the same focal length of all lenses, because different lenses correspond to different optical lengths, and the coupling efficiency is also different when the optical lengths are not equal. In order to make the coupling efficiency difference between the maximum optical path and the minimum optical path small enough, the spot diameter of the lens should be selected large enough.

Fig. 11 is a schematic structural view of the base platform disclosed by the present invention. As shown in FIG. 11 , 1 is a platform base, 2 is an optical switch array chip, 3 is a collimating lens array, and 4 is a free-space optical delay module. The base platform can be made of metal or non-metal material. The center of the platform is the waveguide chip placement area, and the two ends are respectively the lens array placement area and the free space delay module placement area. The planes of each area are kept parallel, and the heights of each plane are different according to the height difference of the waveguide chip, lens array and delay module. In order to make the temperature stability of the overall device higher, the optical switch chip, the free space optical delay module, and the lens array should choose the same substrate material, or materials with similar thermal expansion rates.

The above embodiments have described the present invention in detail, and those skilled in the art can make various changes to the present invention according to the above description. Therefore, some details in the embodiments shall not be construed as limiting the present invention, and the scope of the present invention shall be defined by the appended claims as the protection scope of the present invention.

Claims (15)

1. A high-precision N-bit (N≥1) adjustable optical delay device, mainly composed of an optical switch chip, a free space optical delay module, a lens array, an input/output optical fiber Pigtail, and a base, is characterized in that: a) The N-bit adjustable optical delay device includes N-level adjustable optical delay units, each optical delay unit includes 2 optical delay circuits, and the optical path difference of the 2 optical delay circuits constitutes the Adjustable light delay length of the light delay unit. The optical path difference of the N adjustable light delay units satisfies the relationship of 2 ⁰ ΔL, 2 ¹ ΔL...2 ^N-1 ΔL, where ΔL represents the step size of the adjustable light delay. b) The optical switch chip includes N+1 optical switch units, and the N+1 optical switch units are arranged side by side from top to bottom, wherein the first optical switch unit is coupled to the input optical fiber, and the first optical switch unit is connected to the output optical fiber The N+1th optical switch unit is coupled and connected, the first optical switch unit is a 2×2 or 1×2 optical switch, and the N+1th optical switch unit is a 2×2 or 2×2 optical switch unit 1 optical switch, and the remaining N-1 optical switch units are all 2×2 optical switches. c) The 2×2 optical switch includes 2 input terminals and 2 output terminals, which are respectively the upper input terminal, the lower input terminal, the upper channel output terminal, and the lower channel output terminal, and the 1×2 optical switch includes 1 input terminal and 2 output terminals, of which the 2 output terminals are respectively the upper channel output terminal and the lower channel output terminal. road input. The upper path refers to a port near the upper side among the two input ends or output ends, and the lower path refers to a port near the lower side among the two input ends or output ends. d) The two optical delay loops of the i-th stage (1≤i≤N) adjustable optical delay unit, the circuit construction method is that the optical signal in one of the optical delay loops passes through the i-th optical switch An output terminal of the unit is output, coupled to the free space through a lens, and the optical path is refracted through the mirror of the free space optical delay module, and then coupled to an input terminal of the i+1th optical switch unit through the lens, and the other The optical signal in an optical delay loop is output from the other output end of the i-th optical switch, and is coupled to the other input end of the i+1-th optical switch after passing through the optical path in the free-space optical delay module. e) The free space optical delay is composed of two optical delay modules, which are respectively placed on both sides of the optical switch chip, and the optical delay units of all levels are interleaved in the two delay modules. f) The optical delay module is composed of a series of reflectors and substrate materials, and the adjustable optical delay lengths at various levels are realized through the arrangement design of the reflectors. g) The optical input/output waveguide of the optical switch chip and the free-space optical delay module are coupled through a lens array. h) The optical switch chip, the free space optical delay module, the lens array, the input/output optical fiber Pigtail and other components are optimally coupled to each other and fixed relative to each other through the mechanical structure of the base. 2. The i-th stage adjustable optical delay unit according to claim 1, characterized in that: the optical signal in one of the optical delay loops is output through the upper output end of the i-th optical switch unit, and is coupled to In the free space, the optical path is refracted through the mirror of the free space optical delay module, and then coupled to the lower input end of the i+1th optical switch unit through the lens, and the optical signal in the other optical delay circuit is transmitted from the i The output of the drop output port of the first optical switch is coupled to the top input port of the i+1th optical switch after the optical path in the free space optical delay module is reflected. 3. The i-th stage adjustable optical delay unit according to claim 1, characterized in that: the optical signal in one of the optical delay loops is output through the upper output end of the i-th optical switch unit, and is coupled to In the free space, the optical path is refracted through the mirror of the free space optical delay module, and then coupled to the upper input end of the i+1th optical switch unit through the lens, and the optical signal in the other optical delay circuit is transmitted from the ith The output of the drop output end of the optical switch is coupled to the drop input end of the i+1th optical switch after the optical path in the free-space optical delay module is refracted. 4. The optical delay unit according to claim 1, wherein the delay circuit can be constructed by adjacent optical switch units + free space delay, or by spaced optical switch units + free space delay. 5. The N-level adjustable optical delay unit as claimed in claim 1 only needs to form the optical path differences of N lengths unequal as claimed in claim 1, but the optical path differences are constructed for all levels of optical delay units The order of precedence is not limited. 6. The optical switch chip according to claim 1, which can be realized by thermo-optic effect, electro-optic effect, plasma dispersion effect, or MEMS physical mechanism, and can be realized based on silicon or organic polymer materials. 7. The optical switch chip according to claim 1, wherein the return loss is increased by performing vertical oblique polishing on the end face of the waveguide of the chip. 8. The optical switch chip according to claim 1, wherein the waveguide end face of the chip is polished horizontally to increase the return loss. 9. The optical switch chip according to claim 1, characterized in that: the input/output waveguide of the chip is designed to be inclined at a certain angle to the normal line of the end face of the chip. 10. The lens array according to claim 1, wherein each lens unit adopts non-uniform or uniform focal length. 11. The free-space time-delay module according to claim 1, wherein the accurate positioning of the reflector is realized by etching and forming position marking lines on the substrate. 12. The base and free-space delay module substrate according to claim 1, characterized in that temperature-sensitive materials and mechanical structures are avoided. 13. The input/output optical fiber pigtail according to claim 1, characterized in that it is an optical fiber pigtail with a self-focusing lens. 14. The optical delay device according to claim 8, wherein each lens unit of the lens array adopts an inclined design. 15. The optical delay device according to claim 9, characterized in that each lens unit of the lens array adopts an inclined design.