CN113281844A

CN113281844A - Multi-mode interference coupler based on near-zero refractive index array resonance

Info

Publication number: CN113281844A
Application number: CN202110562248.7A
Authority: CN
Inventors: 董国艳; 郑姝慧
Original assignee: University of Chinese Academy of Sciences
Current assignee: University of Chinese Academy of Sciences
Priority date: 2021-05-21
Filing date: 2021-05-21
Publication date: 2021-08-20

Abstract

A multimode interference coupler based on near-zero refractive index array resonance is characterized in that a near-zero refractive index resonator is manufactured by utilizing a periodic medium array, a reflecting device is arranged on a radial emergent end face of the resonator, and when light enters from the end face of the array in a vertical mode, severe standing wave resonance is excited in the resonator; when resonance occurs, the field energy is not transmitted along the incident direction, and the light energy is converted into transverse traveling waves to be radiated outwards, so that the multimode interference light coupling function is realized. The 1 multiplied by 2N multi-mode interference coupler can be realized according to different resonance modes; a 2 x 1 coupler can be realized under fundamental mode resonance; the coupler realizes an on function when the phase difference of the two beams of light is even times of pi, and realizes an off function when the phase difference of the two beams of light is odd times of pi. The invention has compact structure, small size, easy processing and flexible and adjustable performance.

Description

Multi-mode interference coupler based on near-zero refractive index array resonance

Technical Field

The invention relates to a multimode interference coupler based on near-zero refractive index array resonance, belonging to the technical field of optical communication.

Background

The dynamic regulation of light plays an important role in the micro-nano integrated optical circuit, and the optical coupler for optical interconnection and optical power distribution has wide application requirements in optical communication and integrated optical circuits. As one of the most indispensable components for light manipulation, a multi-mode interference (MMI) coupler has been used in various applications of light splitting, beam combining, directional coupling, optical switching from microwave to visible light, and the like. A conventional MMI coupler is an optical rectangular waveguide with overall dimensions on the order of a few μm wide and tens of μm long. Due to the complex behavior of the internal light, a mathematical model and an equation cannot be directly used for solving, and the application and development of the light loss, the large size and the complex structural design in the micro-nano integrated optical circuit are hindered.

The photonic crystal has unique photonic band gap and photonic local characteristics, can flexibly and effectively control the motion of photons, and has a well-developed optical frequency band processing technology along with the miniaturization of an optical system and the development of an integration technology. The theory of photonic band gap and nonlinear frequency conversion has been exploited to construct a variety of functional optical switching devices. Nonlinear effects are introduced into waveguides, microcavities or other defects, but the defect states undoubtedly increase the manufacturing difficulty and increase the processing cost.

In order to solve the above problems, a new optical coupling method suitable for micro-nano optical circuit integration is urgently needed to be found.

Disclosure of Invention

Aiming at the problems that the traditional MMI coupler is too large in device size, complex in structural design and not suitable for a micro-nano integrated optical path, the invention provides the multi-mode interference coupler which is compact in structure, small in size, easy to adjust, good in robustness and high in energy conversion efficiency based on the near-zero refractive index photonic band edge resonance effect.

The invention discloses a multimode interference coupler based on near-zero refractive index array resonance, which adopts the following technical scheme.

The coupler is characterized in that a periodic medium array is used for manufacturing a near-zero refractive index resonator, a reflecting device is arranged on a radial emergent end face of the resonator, when light enters from a direction perpendicular to the array end face (the end face of the periodic medium array), severe standing wave resonance is excited in the resonator, when the resonance occurs, field energy does not propagate along the incident direction, and the incident light energy is converted into transverse traveling waves to radiate outwards, so that the multi-mode interference light coupling function is realized.

The propagation wavelength lambda in the coupler is greater than the transmission wavelength lambda in the air₀The side length L of the resonator is an integer multiple of the half propagation wavelength λ/2, i.e., L ═ N λ/2 and N ═ 1,2,3.

According to the coupler, the field energy in the resonator is divided into N parts by the node line according to different resonance modes (orders), and 2N outgoing beams are generated from two symmetrical transverse ports due to structural symmetry, so that the beam splitting function of the 1X 2N multimode interference coupler is realized.

In the coupler, under the condition of fundamental mode resonance, two beams of identical coherent light are controlled to be relatively incident and enter the resonator perpendicular to two transverse end surfaces, resonance is excited, field energy is converted into light beams emergent along the radial direction, the two beams of incident light are combined into one emergent light, and the beam combining function of the 2X 1 interference coupler is realized.

The coupler realizes the function of transmitting light on when the phase difference of the two beams of incident light is even times of pi, and realizes the function of transmitting light off when the phase difference of the two beams of light is odd times of pi.

The design scheme of the novel multi-mode interference coupler based on near-zero refractive index array resonance provided by the invention can be applied to a wide frequency range from microwave to light wave by scaling the size according to the scalar invariance principle, has the advantages of compact structure, small size, easiness in processing and flexible and adjustable performance, and provides a new method for designing a micro-nano integrated optical path optical interconnection device.

Drawings

FIG. 1 is a schematic diagram of a multimode interference coupler according to the present invention; wherein (a) is a 1 × 2 multimode interference coupler and (b) is a 2 × 1 multimode interference coupler.

FIG. 2 is a field profile of a multimode interference coupler of the present invention; wherein (a) is the field pattern of the square lattice array based 1 × 4 multimode interference coupler of example 2, (b) is the field pattern of the square lattice array based 1 × 6 multimode interference coupler of example 3, and (c) is the field pattern of the triangular lattice array based 1 × 4 multimode interference coupler of example 4.

Fig. 3 is a diagram of the on-off state transmission spectrum of a 2 × 1 multimode interference coupler composed of a square lattice array of example 5.

Detailed Description

The multimode interference coupler based on near-zero refractive index array resonance of the invention utilizes periodic medium arrays (squares, triangles and the like) to manufacture a near-zero refractive index resonator, a reflecting device is arranged on the radial emergent end face of the resonator, and when light is vertical to the radial emergent end face of the resonatorWhen the array is incident on the end face, the resonator excites violent standing wave resonance. The propagation wavelength lambda in the coupler is greater than the transmission wavelength lambda in the air₀The side length of the near-zero index resonator is about an integer multiple L of a half propagation wavelength N λ/2 (N1, 2, 3.). When resonance occurs, the field energy is static along the incident direction and does not propagate, and the incident light energy is converted into transverse traveling waves to radiate outwards, so that the multimode interference optical coupling function is realized. According to the difference of resonance modes (orders), the field energy in the resonator is divided into N parts by the node line, and because of the structural symmetry, one beam of light is incident from a radial port and generates 2N outgoing beams from two symmetrical transverse ports, so that the 1X 2N multimode interference coupler is realized, as shown in FIG. 1 (a). Under the condition of fundamental mode resonance, two beams of identical coherent light can be controlled to be vertically incident into the resonator relatively on two transverse end faces, the fundamental mode resonance is excited and converted into a beam of light emergent along the radial direction, the two beams of incident light are combined into one beam of emergent light, and therefore the 2 x 1 multimode interference coupler is realized, as shown in fig. 1 (b). When the phase difference of the two beams of light is even times of pi, the on function is realized, and when the phase difference of the two beams of light is odd times of pi, the off function is realized.

Example 1

The radius r is 3.3mm, the lattice constant a is 13.75mm, and the relative dielectric constant epsilon_r10, magnetic permeability mu_rThe dielectric cylinder of 1 constitutes a 10 × 10 two-dimensional square photonic crystal array to form a near-zero refractive index resonator. Light is perpendicularly incident into the photonic crystal resonator body. When the light source frequency f is 12.53GHz, 1 × 2 3dB splitting is achieved, as shown in fig. 1(a), where a maximum transmittance value of 94.05% and an additional loss value of 0.27dB can be achieved.

Example 2

With the same crystal structure as in example 1, when the size of the photonic crystal array is 12 × 10, the maximum amount of light flux is achieved at the second resonance frequency f of 12.71GHz, the transmittance is 95.32%, the additional loss is 0.21dB, the field distribution is as shown in fig. 2(a), one horizontal incident light beam resonates first in the photonic crystal array, and the incident light energy is divided into four light beams which are symmetrical up and down, thereby realizing the 1 × 4 type multimode interference coupler function.

Example 3

With the same crystal structure as in example 1, when the photonic crystal array size is 15 × 10, the best coupling effect can be achieved at the second resonance frequency f of 12.77GHz, the transmittance is 93.09%, the additional loss is 0.31dB, the field pattern is as shown in fig. 2(b), and one light is divided into six light beams which are vertically symmetric, and the 1 × 6 type multimode interference coupler function can be achieved.

Example 4

The two-dimensional triangular lattice photonic crystal is used for manufacturing a square array, and the structural parameters are that the radius r is 3mm, the lattice constant a is 13.04mm, and the dielectric constant epsilon_r8.35, permeability μ_rThe radial incident end face of the array has 9 dielectric columns, and the two transverse emergent end faces are composed of 5 dielectric columns, as shown in fig. 2(c), so that the 1 × 4 type multimode interference coupler function is realized at the fundamental frequency f of 14.94GHz, the maximum transmittance is 94.36%, and the additional loss is 0.25 dB.

Example 5

With the same crystal structure as in example 1, in the 9 × 9 photonic crystal multimode interference coupler, as shown in fig. 1(b), the phase difference between the two incident lights is an even multiple of pi, and the phase difference is in an "on" state, and the broadband transmission spectrum obtained after the combination is shown in a solid black line in fig. 3, the maximum value of the total transmittance is 92.51% and the additional loss is 0.34dB at the 0-order resonance frequency f of 12.6GHz, and the function of the 2 × 1 type multimode interference coupler is realized. The dotted line in fig. 3 shows that the two beams are off when the phase difference is odd times pi, the resonant frequency shows that the transmissivity is at least 4.61%, and the extinction ratio of the optical switch is 13.02 dB.

Claims

1. A multimode interference coupler based on near-zero refractive index array resonance is characterized in that:

a periodic medium array is used for manufacturing a near-zero refractive index resonator, a reflecting device is arranged on the radial emergent end face of the resonator, when light enters from the end face of the array perpendicularly, severe standing wave resonance is excited in the resonator, when the resonance occurs, field energy does not propagate along the incident direction, and the incident light energy is converted into transverse traveling waves to radiate outwards, so that the multi-mode interference light coupling function is realized.

2. The near-zero index array resonance-based multimode interference coupler of claim 1, wherein: the propagation wavelength lambda in the coupler is greater than the transmission wavelength lambda in the air₀。

3. The near-zero index array resonance-based multimode interference coupler of claim 1, wherein: the side length L of the resonator is an integral multiple of the transmission half wavelength lambda/2.

4. The near-zero index array resonance-based multimode interference coupler of claim 1, wherein: according to the coupler, according to different resonance modes, the field energy in the resonator is divided into N parts by the node line, and 2N outgoing light beams are generated from two symmetrical transverse ports due to structural symmetry, so that the beam splitting function of the 1X 2N multimode interference coupler is realized.

5. The near-zero index array resonance-based multimode interference coupler of claim 1, wherein: the coupler controls two beams of same coherent light to be relatively incident and enter the resonator perpendicular to two transverse end faces under the condition of fundamental mode resonance, resonance is excited, field energy is converted into light beams emergent along the radial direction, the two beams of incident light are combined into one emergent light, and the beam combination function of the 2 x 1 interference coupler is realized.

6. The near-zero index array resonance-based multimode interference coupler of claim 1, wherein: the coupler realizes the function of transmitting light on when the phase difference of the two beams of incident light is even times of pi, and realizes the function of transmitting light off when the phase difference of the two beams of light is odd times of pi.