Silicon-based integrated optically adjustable delay line based on optical phased array

Abstract

A silicon- and optical phased array-based integrated optically adjustable delay line, comprising, an optical phased array transmitting unit, a slab waveguide transmitting unit, and an optical phased array receiving unit that are sequentially arranged. By the optical phase control transmitting unit, the phase difference between channels is regulated and controlled via a phase shifter to change a far-field interference light spot and form a wave beam with directivity to regulate and control an incident angle of an optical signal entering the slab waveguide, thus changing the propagation path length of the optical signal. Finally, the optical signal is received by a corresponding optical phased array receiving unit to obtain different delay amounts. Large adjustable delay amount is realized and the delay line has the advantages of simple structure and control and high integration level with high application value in optical communication and microwave photonic and optical signal processing.

Claims

1. A silicon-based and an optical phased array-based integrated optically adjustable delay line, comprising an optical phased array transmitting unit (101) comprising an output end, a slab waveguide transmitting unit (102) comprising a first end and a second end, and an optical phased array receiving unit (103); wherein the output end of the optical phased array transmitting unit (101) is connected with the first end of the slab waveguide transmitting unit (102), and the second end of the slab waveguide transmitting unit (102) is connected with the optical phased array receiving unit (103); the optical phased array transmitting unit (101) is sequentially composed of a coupler, a cascaded beam splitting structure, and a phase shifter phase array; and the optical phased array receiving unit (103) is sequentially composed of a phase shifter phase array, a cascaded beam splitting structure, and a coupler.

2. The integrated optically adjustable delay line according to claim 1, wherein the optical phased array transmitting unit (101) and the optical phased array receiving unit (103) are arranged symmetrically with respect to the slab waveguide transmitting unit (102) or at the same side of the slab waveguide transmitting unit (102).

3. The integrated optically adjustable delay line according to claim 1, wherein the optical phased array transmitting unit (101) transmits a wave beam having directivity by beam forming and is connected to the first end of the slab waveguide transmitting unit (102); an input light beam larger than a total reflection critical angle is constrained to be transmitted in the slab waveguide transmitting unit (102); the other end of the slab waveguide transmitting unit (102) is connected to the optical phased array receiving unit (103); and according to an optical path reversibility principle, the second end of the slab waveguide transmitting unit (102) receives an optical signal transmitted from a specific angle in the slab waveguide transmitting unit (102) so as to complete a connection of the optical path from the input to the output.

4. A method for adjusting light delay using the integrated optically adjustable delay line of claim 1, comprising regulating a phase difference between channels by the phase shifter phase array of the optical phased array transmitting unit (101) or the optical phased array receiving unit (103) to change a far-field interference light spot and forming a wave beam with directivity, changing an angle of a light beam of the optical phased array transmitting unit (101) or the optical phased array receiving unit (103), changing a length of a propagation path of the light beam in the slab waveguide; and adjusting the light delay.

5. The integrated optically adjustable delay line according to claim 1, wherein an input coupler of the optical phased array of the optical phased array transmitting unit (101) or the optical phased array receiving unit (103) adopts a grating coupler or an inverse taper, and an external signal that is an input and output through the coupler in the optical phased array transmitting unit (101) or the optical phased array receiving unit (103) adopts horizontal coupling or vertical coupling to realize a connection between an external optical signal and a planar optical waveguide; and the horizontal coupling adopts a lens, and an inverted cone spot-size converter on a chip, and the vertical coupling adopts a planar optical fiber, and a grating coupler on the chip.

6. The integrated optically adjustable delay line according to claim 1, wherein the cascaded beam splitting structure of the optical phased array transmitting unit (101) is a beam splitter that employs a cascaded multimode interference coupler, a cascaded Y-beam splitter, or a star coupler.

7. The integrated optically adjustable delay line according to claim 1, wherein the phase shifter of the optical phased array transmitting unit (101) or of the optical phased array receiving unit (103) adopts a phase shifter based on a free carrier dispersion effect or a phase shifter based on a thermo-optic effect.

8. The integrated optically adjustable delay line according to claim 1, wherein the optical phased array has a sub-wavelength spaced antenna density to enable a large angular range of non-aliased light beam deflection, and the transmit array uses a curved waveguide array, a waveguide array of different widths, or a photonic bandgap structure containing metamaterials to enable coupling suppression between transmit units.

9. The integrated optically adjustable delay line according to claim 1, wherein the optical phased array receiving unit comprises a mirror image structure with the optical phased array transmitting unit, and uses different array size, sub-channel number, sub-channel phase adjusting principle, beam combining device, output coupler, or a combination thereof from the optical phased array transmitting unit.

10. A method for increasing receiving efficiency or receiving integrated of the optically adjustable delay line according to claim 1, comprising increasing an array size of a receiver or the number of sub-channels in the optical phased array receiving unit (103).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the structure of the optical phased array transmitter/receiver arranged oppositely to each other in one embodiment of the present invention.

(2) FIG. 2 shows the structure of the optical phased array transmitter/receiver arranged at the same side in another embodiment of the present invention.

(3) FIG. 3A shows the vertical grating coupler in the present invention; and FIG. 3B shows the inverted cone coupler used in the optical phased array in the embodiment of the present invention and cross-section view of the inverted cone coupler along the dotted lines.

(4) FIG. 4 shows the multimode interference coupler and the cascaded beam splitting structure for the optical phased array in the embodiment of the present invention

(5) FIG. 5 is shows the metal microheater based phase shifter in accordance with the optical phased array in the embodiment of the present invention.

(6) FIG. 6 shows the waveguide array antenna in the embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(7) The present invention is described in further detail with reference to the accompanying drawings and embodiments, yet they do not limit the scope of protection.

(8) The silicon-based and an optical phased array-based integrated optically adjustable delay line of the present invention comprises an optical phased array transmitting unit (101) comprising an output end, a slab waveguide transmitting unit (102) comprising a first end and a second end, and an optical phased array receiving unit (103); wherein the output end of the optical phased array transmitting unit (101) is connected with the first end of the slab waveguide transmitting unit (102), and the second end of the slab waveguide transmitting unit (102) is connected with the optical phased array receiving unit (103); the optical phased array transmitting unit (101) is sequentially composed of a coupler, a cascaded beam splitting structure, and a phase shifter phase array; and the optical phased array receiving unit (103) is sequentially composed of a phase shifter phase array, a cascaded beam splitting structure, and a coupler.

(9) In the integrated optically adjustable delay line of the present invention, the optical phased array transmitting unit (101) and the optical phased array receiving unit (103) are arranged symmetrically with respect to the slab waveguide transmitting unit (102) or at the same side of the slab waveguide transmitting unit (102).

(10) The optical phased array transmitting unit (101) transmits a wave beam having directivity by beam forming and is connected to the first end of the slab waveguide transmitting unit (102); an input light beam larger than a total reflection critical angle is constrained to be transmitted in the slab waveguide transmitting unit (102); the other end of the slab waveguide transmitting unit (102) is connected to the optical phased array receiving unit (103); and according to an optical path reversibility principle, the second end of the slab waveguide transmitting unit (102) receives an optical signal transmitted from a specific angle in the slab waveguide transmitting unit (102) so as to complete a connection of the optical path from the input to the output. The principle of light path reversibility refers to that, if light starts from point A and can reach point B in the medium, then when light starts from point B, it can go back to point A through the same path. Further, the specific angle refers to the angle of light that can be transmitted in the slab waveguide. The beam steering angle of 101 and 103 is the same specific angle.

(11) The present invention further provides a method for adjusting light delay using the integrated optically adjustable delay line, comprising the steps of regulating a phase difference between channels by the phase shifter phase array of the optical phased array transmitting unit (101) or the optical phased array receiving unit (103) to change a far-field interference light spot and forming a wave beam with directivity, changing an angle of a light beam of the optical phased array transmitting unit (101) or the optical phased array receiving unit (103), changing a length of a propagation path of the light beam in the slab waveguide; and adjusting the light delay.

(12) In the integrated optically adjustable delay line of the present invention, an input coupler of the optical phased array of the optical phased array transmitting unit (101) or the optical phased array receiving unit (103) adopts a grating coupler or an inverse taper, and an external signal that is an input and output through the coupler in the optical phased array transmitting unit (101) or the optical phased array receiving unit (103) adopts horizontal coupling or vertical coupling to realize a connection between an external optical signal and a planar optical waveguide; and the horizontal coupling adopts a lens, and an inverted cone spot-size converter on a chip, and the vertical coupling adopts a planar optical fiber, and a grating coupler on the chip.

(13) In the present invention, the cascaded beam splitting structure of the optical phased array transmitting unit (101) is a beam splitter that employs a cascaded multimode interference coupler, a cascaded Y-beam splitter, or a star coupler.

(14) In the present invention, the phase shifter of the optical phased array transmitting unit (101) or of the optical phased array receiving unit (103) adopts a phase shifter based on a free carrier dispersion effect or a phase shifter based on a thermo-optic effect.

(15) In the present invention, the optical phased array has a sub-wavelength spaced antenna density to enable a large angular range of non-aliased light beam deflection, and the transmit array uses a curved waveguide array, a waveguide array of different widths, or a photonic bandgap structure containing metamaterials to enable coupling suppression between transmit units.

(16) In the present invention, the optical phased array receiving unit comprises a mirror image structure with the optical phased array transmitting unit, and uses different array size, sub-channel number, sub-channel phase adjusting principle, beam combining device, output coupler, or a combination thereof from the optical phased array transmitting unit.

(17) The present invention further provide a method for increasing receiving efficiency or receiving integrated of the optically adjustable delay line comprises increasing an array size of a receiver or the number of sub-channels in the optical phased array receiving unit (103).

(18) As shown in FIGS. 1 and 2, an integrated adjustable delay line based on an optical phased array is mainly divided into three parts according to functional characteristics: an optical phased array transmitting unit (101), a slab waveguide transmitting unit (102) and an optical phased array receiving unit (103); the optical phased array transmitting unit (101) is sequentially composed of a coupler, a cascaded light splitting structure and a phase shifter phase array from left to right, respectively represented by “a coupler, a light splitter 1×N and a multi-channel waveguide with a fixed phase difference ΔΦ” in the unit (101) of FIG. 1. The optical phased array receiving unit (103) is sequentially composed of a phase shifter phase array, a cascaded light splitting structure and a coupler from left to right. The component structures are the same as the component structures in the optical phased array transmitting unit, but arranged in different orders.

(19) First, an optical signal is required to be coupled into an input waveguide of the optical phased array by a vertical grating coupler/inverse taper shown in FIG. 3A to 3B.

(20) Next, the input waveguide performs N-channel uniform beam splitting via a cascaded beam splitting structure shown in FIG. 4.

(21) Then, the N paths of optical signals are subjected to phase adjustment by a phase shifter phase modulation array shown in FIG. 5. The phase modulation array is mainly used for effectively adjusting the phases of the N paths of light beams output by a beam splitter (phase modulation) to generate a fixed phase difference ΔΦ among channels of the waveguide array. Effective deflection of far-field diffraction main lobe light beams is realized by adjusting the phase difference among the channels, changing angular distribution of a far-field interference pattern to form a wave beam with directivity so as to change the angle of the transmitting/receiving wave beam of the optical phased array.

(22) After that, a light beam directionally transmitted in a certain direction is obtained by the output of the waveguide array antenna shown in FIG. 6 and enters the waveguide to perform multiple total reflection transmission according to a specific total reflection angle. At the end of the waveguide transmission, the light beam is received by the optical phased array receiving unit, with the principle same as that of the phased array transmitting unit, except that the optical path is reversed.

(23) FIG. 3A is the overall structure diagram of the vertical grating coupler, including the grating, a section of straight waveguide, and a section of taper waveguide; and the inset is the grating structure, and FIG. 3B is the schematic diagram showing the three-dimensional structure diagram of the taper. Based on the above solution, the vertical grating coupler adopts the structure as shown in FIG. 3A in order to couple an optical signal into a transmission waveguide, wherein a silicon waveguide has a height of 220 nm, an etched grating has a height of 70 nm, a formed grating period is 630 nm, a duty ratio is 50%, and there are 27 grating periods. The silicon waveguide in the grating has a width of 12 μm and a length of 30 μm. In order to effectively transition the mode of a wide waveguide to a single-mode waveguide (500 nm wide), a segmented tapered (tapered) waveguide transition is required. The length of the tapered waveguide obtained by optimization is 200 μm. An optical fiber is incident at an angle of 8° and achieves good spot-size matching with the waveguide, so that high coupling efficiency is realized. Alternatively, the optical coupling can be also realized with an inverse taper, as shown in FIG. 3B. The silicon waveguide is also 220 nm in height. The waveguide tip width is around 120 nm and tapered to a single-mode waveguide (500 nm wide). Light is horizontally coupled to the inverse taper from a lens fiber. FIG. 3B also shows the cross-sectional view of the inverse taper.

(24) Based on the above solution, an optical splitter is adopted as shown in FIG. 4. It is composed of 15 1×2 MMI couplers arranged as a four-stage binary tree structure and has 16 optical paths.

(25) Based on the solution, the phase shifter adopts the metal microheater based phase shifter shown in FIG. 5, and air trenches are etched between adjacent waveguides so as to restrain thermal crosstalk between the waveguides and further reduce phase crosstalk between the waveguides. The metal used is titanium nitride (TiN), because the resistivity of the TiN metal is high, the TiN metal is suitable for generating heat as a heat source, the heat is conducted to a silicon waveguide by silicon oxide, and the effective refractive index of the waveguide is changed to generate a phase shift. In order to ensure that sufficient phase shift is generated, the TiN is designed to have a width of 2 μm and a thickness of 120 nm, and the length of the phase shifter is 400 μm. A strip single-mode silicon waveguide is arranged right below the TiN microheater. After voltage is applied to the 16-channel phase shifter, different phase shift amounts can be realized, so that the deflection angle of a light beam transmitted from the waveguide array antenna is finally controlled.

(26) On the basis of the above solution, the waveguide output antenna adopts the structure as shown in FIG. 6. In order to transition the array waveguide from a wider pitch to a narrower pitch, the structure of two S-shaped transition sections has been designed in the present invention. It can be seen that an initial OPA pitch is 50.5 μm which is transited to an output array spacing of 3.3 μm by the first S-shaped transition (shown in an upper inset of FIG. 6), and is further shrunken to an array spacing of 0.8 μm by the second specially designed S-bend (shown in a lower inset of FIG. 6). The conventional design has an array spacing of 2.5 μm, and the spacing (much greater than a half wavelength) is limited by the optical coupling between the silicon waveguides, so that there are side lobes in the far field, limiting the effective deflection angle range of the main lobe light beam. By the subsequent design that a section of S-shaped waveguide bend transitions to an array spacing of only 0.8 μm, we have realized theoretically that there is no side lobe in the far field, and the scanning angle range of the main lobe beam is unlimited.

(27) On the basis of the solution, different heat can be generated in the TiN microheater by adjusting the external voltage of the optical phased array transmitting unit, so that the effective refractive index of the waveguide is changed to generate a phase shift, regulating the angle of an optical signal entering the waveguide and changing the propagation optical path of the optical signal, and different delay amounts are generated. Specifically, the invention can realize large adjustable delay amount, has the advantages of simple structure and control and high integration level. It has potential application value in the fields of signal processing, microwave photonics, optical communication and the like.

(28) It will be readily understood by those skilled in the same field of research or industry that the foregoing description are embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made in the spirit and principles of the invention shall be covered by the protection of the invention.