CN108761648A - A kind of three ports light rings of hybrid integrated - Google Patents

Abstract

The invention discloses a hybrid integrated three-port optical circulator, which is composed of five polarization beam splitters, two polarization conversion components composed of a half-wave plate and an optical rotation plate, and a single-mode optical waveguide, wherein the PBS uses an integrated optical Technology preparation, and the single-mode optical waveguide between the PBS is grooved transversely, and the polarization conversion component is inserted, so that the optical signal is transmitted in a loop between the three ports. In addition, the central wavelength of the half-wave plate in the polarization conversion component is shifted from 1310nm to 1285nm, which improves the minimum isolation of the optical circulator in the 1260nm-1340nm working band and optimizes the isolation performance of the entire bandwidth. By adopting the hybrid integrated optical technology, the present invention realizes the miniaturization and integration of the device under the premise of ensuring the isolation of the optical circulator, and can be conveniently connected with other integrated optical devices, and the manufacturing process is also simplified to meet the data requirements. Requirements for WDM single-fiber bidirectional transmission modules in the center.

Description

A Hybrid Integrated Three-Port Optical Circulator

technical field

The invention belongs to the field of optical communication, and more specifically relates to a hybrid integrated three-port optical circulator.

Background technique

In the optical fiber communication system, the transmission of reverse light will bring instability to the device and the system. The optical circulator is a non-reciprocal device with multi-port input and output, which makes the optical signal only circulate along a fixed path. It is widely used in optical communication subsystems such as single-fiber bidirectional transmission systems, dispersion compensation units, wavelength blockers, channel equalizers, and wavelength selective switches.

The vigorous development of Internet applications has promoted the large-scale construction of data centers, and high-speed data transmission between data center servers can only be realized through optical fiber interconnection technology. Optical fiber interconnection technology has gone through the stages of multi-mode optical fiber parallel transmission, single-mode optical fiber parallel transmission and single-mode optical fiber wavelength division multiplexing transmission. In order to further save optical fiber resources, data center users put forward the requirement of wavelength division multiplexing single-fiber bidirectional transmission, realize the separation of receiving and receiving optical signals through optical circulators, and require its working band to cover 1260-1340nm.

Traditional optical circulators use displacement crystals and wedge wedges as discrete devices, which are larger in size and require more devices, cannot be easily integrated into the transceiver module, and have a narrow operating bandwidth. Compared with telecommunication applications, data center optical interconnection technology puts forward broadband requirements for optical circulators. The former requires 40nm bandwidth of 1530-1570nm, and the latter requires 80nm bandwidth of 1260-1340nm. The optical circulator is integrated in the optical transceiver module, so there is a demand for miniaturization of the optical circulator.

Compared with the existing discrete optical circulator, the optical waveguide device has the advantages of small size, simple process and low cost. The present invention designs a miniaturized optical circulator through the hybrid integration of optical waveguide devices and discrete devices, and optimizes its working bandwidth so that it can meet the requirements of wavelength division multiplexing and single-fiber bidirectional transmission in data centers. module requirements.

Contents of the invention

Aiming at the defects of the prior art, the object of the present invention is to provide a hybrid integrated three-port optical circulator, aiming to solve the problems of traditional optical circulators with large volume, low integration, narrow working bandwidth, and inconvenient use in data centers. question.

The invention provides a hybrid integrated three-port optical circulator, comprising: an optical waveguide chip, a first polarization conversion component and a second polarization conversion component; five polarization beam splitters (PBS1-PBS5) are integrated on the optical waveguide chip ), the first end of the first polarization beam splitter PBS1 is used as the optical signal input end T1 of the three-port optical circulator, and the third end of the second polarization beam splitter PBS2 is used as the optical signal transmission end T2 of the three-port optical circulator, The first end of the third polarizing beam splitter PBS3 serves as the optical signal output end T3 of the three-port optical circulator; the second end of the first polarizing beam splitter PBS1 is connected to the first polarizing beam splitter through the first polarization conversion component The first end of the four polarization beam splitter PBS4, the third end of the first polarization beam splitter PBS1 is connected to the first end of the fifth polarization beam splitter PBS5 through the first polarization conversion component; The second end of the third polarization beam splitter PBS3 is connected to the second end of the fourth polarization beam splitter PBS4 through the first polarization conversion component, and the third end of the third polarization beam splitter PBS3 is connected through the The first polarization conversion component is connected to the second end of the fifth polarization beam splitter PBS5; the third end of the fourth polarization beam splitter PBS4 is connected to the second polarization through the second polarization conversion component The first end of the beam splitter PBS2 and the third end of the fifth polarization beam splitter PBS5 are connected to the second end of the second polarization beam splitter PBS2 through the second polarization conversion component.

When working, when the optical signal is transmitted from the T1 port to the T2 port, the incident random polarized light is divided into TE polarized light and TM polarized light by PBS1, after passing through the first polarization conversion component, the polarization state of TE polarized light and TM polarized light remains remain unchanged, enter PBS4 and PBS5 respectively, and then pass through the second polarization conversion component. When it reaches the T3 port, the incident random polarized light is divided into TE polarized light and TM polarized light by PBS2. After passing through the second polarization conversion component, the two beams undergo polarization transformations of TE→TM and TM→TE respectively, and then pass through PBS4 and TM respectively. PBS5 is transmitted to the lower part of the first polarization conversion component, and the polarization conversion of TM→TE and TE→TM occurs again, and finally the two paths of TE and TM polarized light are combined by PBS3 and output from the T3 port.

Furthermore, each polarization beam splitter is connected to the first polarization conversion component or the second polarization conversion component through a single-mode optical waveguide.

Furthermore, a first notch and a second notch are provided in the lateral direction of the single-mode optical waveguide connecting each polarization beam splitter, and the first polarization conversion component is inserted into the first notch, and the first notch Two polarization conversion components are inserted into the second groove.

Furthermore, in the single-mode optical waveguide, the waveguide width of the first waveguide at the position where the first notch or the second notch is provided is greater than the waveguide width of the second waveguide at other positions.

Furthermore, a transition is made between the first waveguide and the second waveguide through a tapered region.

Furthermore, the structure of the first polarization conversion component and the second polarization conversion component are the same; and both the first polarization conversion component and the second polarization conversion component are used to realize the The direction is rotated by 90 degrees; when the light passes from the other side, the polarization direction is not rotated.

Furthermore, the first polarization conversion component includes: a Faraday rotator and a half-wave plate; the Faraday rotator is closely attached to the half-wave plate, the Faraday rotator is connected to PBS1 and PBS3, and is close to T1 and T3 ports, and the half-wave plate is connected to PBS4 It is connected to PBS5 and is close to the T2 port; the Faraday rotator is used to rotate the polarization state of the optical signal by 45 degrees, and the half-wave plate is used to make the polarization state of the light mirror deflect around its fast axis.

Furthermore, the center wavelength of the half-wave plate is 1285nm. In order to expand the working bandwidth of the optical circulator, the present invention designs the center wavelength of the half-wave plate to be 1285nm, which is shifted to the short wavelength by 25nm compared with 1310nm used by the traditional optical circulator. Through this optimized design, the minimum isolation of the optical circulator in the working band is improved.

Through the above technical scheme conceived by the present invention, compared with the prior art, due to the use of hybrid integration technology, the displacement crystal and angle wedge pair in the traditional optical circulator are replaced by optical waveguide devices, and optical rotators are inserted into the grooves. A polarization conversion component composed of a half-wave plate and a half-wave plate, and redesigning the center wavelength of the half-wave plate can make the entire optical circulator miniaturized and integrated, while reducing manufacturing costs and simplifying the manufacturing process. Overall isolation of 1260-1340nm operating bandwidth.

Description of drawings

Fig. 1 is the hybrid integrated optical circulator structure provided by the embodiment of the present invention, wherein the optical signal is transmitted from the T1 port to the T2 port;

Fig. 2 is the hybrid integrated optical circulator structure provided by the embodiment of the present invention, wherein the optical signal is transmitted from the T2 port to the T3 port;

Fig. 3 is the polarization beam splitter (PBS) structure based on optical waveguide technology;

Figure 4 is a 3dB coupler structure based on optical waveguide technology, where (a) is a directional coupler, and (b) is a multimode interference coupler;

Figure 5 is the structure of the interference arm in PBS, where (a) is the three-dimensional structure diagram of the first arm, (b) is the three-dimensional structure diagram of the second arm, (c) is the cross-sectional view of the first arm, (d) the second arm cross-sectional view;

Figure 6 shows the structure of the polarization conversion component based on discrete device technology, (a) shows the incident situation of TE polarized light, and (b) shows the incident situation of TM polarized light;

Fig. 7 is a schematic diagram of tapering treatment at the connection between the groove and the single-mode optical waveguide;

Fig. 8 is the isolation optimization curve in the working band, wherein (a) represents the curve before optimization, and (b) represents the curve after optimization;

Explanation of reference numerals: 1 is the first notch, 2 is the second notch, 3 is the first polarization conversion component, 4 is the second polarization conversion component, 5 is the first arm, 6 is the second arm, 7 is the second One 3dB coupler, 8 is the second 3dB coupler, 9 is the first single-mode optical waveguide, 10 is the second single-mode optical waveguide, 11 is the planar optical waveguide, 12 is the single-mode optical waveguide, 13 is the tapered area, 14 for a wide waveguide.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The present invention proposes a hybrid integrated three-port optical circulator, as shown in Figure 1, it consists of five polarization beam splitters (PBS1-PBS5), two grooves (1, 2), and two polarization conversion components (3, 4) and a single-mode optical waveguide connecting each component, in which the PBS is prepared on an optical waveguide chip by integrated optical technology, and the polarization conversion component is composed of a Faraday rotator and a half-wave plate of discrete device technology, as shown in Fig. The middle black thick line represents the single-mode optical waveguide. In the transverse direction of the single-mode optical waveguides connecting each PBS, two grooves cutting off the single-mode optical waveguides are made, and two polarization conversion components are respectively inserted into the grooves. The T1 port is an optical signal input port, the T2 port is an optical signal transmission port, and the T3 port is an optical signal output port.

Figure 1 shows the situation where the optical signal is transmitted from the T1 port to the T2 port. The incident random polarized light is divided into TE polarized light and TM polarized light by PBS1 (the electric field vibration direction is perpendicular to the incident plane called TE polarized light, and the electric field vibration direction is within the incident plane. is called TM polarized light.), after passing through the first polarization conversion component 3, the polarization states of TE and TM polarized light remain unchanged, enter PBS4 and PBS5 respectively, and then pass through the second polarization conversion component 4, the polarization state remains unchanged, Finally, the two paths of TE and TM polarized light are combined by PBS2 and output from T2 port. Figure 2 shows the situation where the optical signal is transmitted from the T2 port to the T3 port. The incident random polarized light is divided into TE and TM polarized light by PBS2. After passing through the second polarization conversion component 4, the two beams of light undergo TE→TM and TM→TE respectively. Then the polarization conversion of TM and TE is transmitted to the lower part of the first polarization conversion component 3 through PBS4 and PBS5 respectively, and the polarization conversion of TM → TE and TE → TM occurs again, and finally these two paths of TE and TM polarized light are combined by PBS3, from T3 port output.

The structure of the polarization beam splitter (PBS) is shown in Figure 3. It is an optical waveguide device composed of two 3dB couplers (7, 8) and a pair of interference arms (5, 6). The optical signal is input from the C1 port , output from ports C2 and C3, and port C4 is deprecated. The input light is divided into two beams by the 3dB coupler 7, the two asymmetric arms have different waveguide widths, the width of the first arm 5 is W1, the width of the second arm 6 is W2, the TE and TM light in the first arm 5 The effective refractive indices are n _1TE and n _1TM , and the effective refractive indices of TE and TM light in the second arm 6 are n _2TE and n _2TM , respectively. The transmission of asymmetric arms makes TE and TM light accumulate different phase differences respectively. After passing through the 3dB coupler 7, the two beams of TE and TM polarized light entering the two arms have an initial phase difference of π/2. When the asymmetric arm reaches the 3dB coupler 8, the phase difference of the two TE polarized lights increases by 2mπ (m is an integer), that is, the total phase difference is 2mπ+π/2; the phase difference of the two TM polarized lights increases (2n+1) π (n is an integer), that is, the total phase difference is 2nπ+3π/2. Excluding the phase difference of 2π integer multiples, the accumulated phase difference of TE and TM polarized light is π. According to the working principle of the 3dB optical coupler, the TE and TM polarized light will be output from the two ports of the 3dB coupler 8 respectively to realize polarization separation. bundle function. In order to satisfy the above phase relationship, the incident light wavelength λ, the arm length L of the asymmetric interference arm and the equivalent refractive index should satisfy the following relationship:

(n _1TE -n _2TE )·L=mλm is an integer

(n _1TM -n _2TM )·L=(n+1/2)λn is an integer

Figure 4 shows the structure of the 3dB coupler. There are two implementations, one is the directional coupler in (a), and the other is the multimode interference coupler realized by using a flat optical waveguide in (b). The function of both is to divide the input light equally and output it from two ports. There is a certain phase difference between the two output lights, such as a directional coupler, and the phase difference is π/2.

The specific structure and cross-section of the two arms in the polarizing beam splitter are shown in Figure 5, (a) is the three-dimensional structure diagram of the first arm, (b) is the three-dimensional structure diagram of the second arm, and (c) is the cross-section of the first arm Fig. (d) Cross-sectional view of the second arm. The length and section height of the optical waveguides in the two arms are the same, but the width of the first arm is W1, and the width of the second arm is W2. The effective refractive index of TE and TM polarized light is different in the optical waveguides of different widths.

Figure 6 shows a polarization conversion assembly composed of a 45-degree Faraday rotator (shaded square) and a half-wave plate (white square). (a) shows the incident light in TE mode, and (b) shows the incident light in TM mode. The Faraday rotator rotates the polarization state of light by 45 degrees, and the direction of rotation depends on the direction of the applied magnetic field. The function of the half-wave plate is to deflect the polarization direction of light around its fast axis as a mirror image. The angle between the fast axis angle and the x-axis direction is designed to be 22.5 degrees, and the deflection direction depends on the distance between the polarization direction of the incident light and the fast axis direction. Relationship. Therefore, the combined function of the Faraday rotator and the half-wave plate is that when the light passes through one side, the polarization direction is deflected by 90 degrees; when the light passes through the other side, the polarization direction does not deflect.

Fig. 7 shows the tapered region structure at the junction of the single-mode optical waveguide 12 and the groove 1. Since the single-mode optical waveguide is cut off by the transverse groove, in order to reduce the transmission loss of the optical signal in the groove and re-enter the optical waveguide on the other side When the coupling loss occurs, the truncated single-mode optical waveguide needs to increase the waveguide width at the port position, and make a transition connection between the narrow waveguide 12 and the wide waveguide 14 through the tapered region 13 to reduce the loss. There is also a similar structure at the connection between the single-mode optical waveguide and the groove 2 .

Figure 8 shows the isolation curve on the bandwidth of 1260nm～1340nm, the abscissa is the wavelength, and the ordinate is the isolation, where (a) is the curve before optimization, the center wavelength of the half-wave plate is 1310nm, it can be seen that the center isolation is very High, the minimum isolation over the entire bandwidth is 44.2dB. (b) is the isolation curve after optimizing the half-wave plate. The center wavelength of the half-wave plate is 1285nm, the entire curve becomes flat, and the minimum isolation is increased to 46.0dB.

It is easy for those skilled in the art to understand that the above content is a further detailed description of the present invention in conjunction with specific embodiments, and it cannot be assumed that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deductions or substitutions can be made, which should be deemed to be included in the protection scope of the present invention.

Claims (9)

1. A hybrid integrated three-port optical circulator is characterized in that, comprising: an optical waveguide chip, a first polarization conversion assembly (3) and a second polarization conversion assembly (4); Five polarization beam splitters (PBS1～PBS5) are integrated on the optical waveguide chip, the first end of the first polarization beam splitter PBS1 is used as the optical signal input end T1 of the three-port optical circulator, and the second polarization beam splitter The third end of the device PBS2 is used as the optical signal transmission end T2 of the three-port optical circulator, and the first end of the third polarization beam splitter PBS3 is used as the optical signal output end T3 of the three-port optical circulator; The second end of the first polarization beam splitter PBS1 is connected to the first end of the fourth polarization beam splitter PBS4 through the first polarization conversion component (3), and the first end of the first polarization beam splitter PBS1 The third end is connected to the first end of the fifth polarization beam splitter PBS5 through the first polarization conversion component (3); The second end of the third polarization beam splitter PBS3 is connected to the second end of the fourth polarization beam splitter PBS4 through the first polarization conversion component (3), and the second end of the third polarization beam splitter PBS3 The third end is connected to the second end of the fifth polarization beam splitter PBS5 through the first polarization conversion component (3); The third end of the fourth polarization beam splitter PBS4 is connected to the first end of the second polarization beam splitter PBS2 through the second polarization conversion component (4), and the fifth end of the polarization beam splitter PBS5 The third end is connected to the second end of the second polarization beam splitter PBS2 through the second polarization conversion component (4). 2. The three-port optical circulator according to claim 1, wherein, during operation, when the optical signal is transmitted from the T1 port to the T2 port, the incident random polarized light is divided into TE polarized light and TM polarized light by PBS1, After passing through the first polarization conversion component, the polarization states of TE polarized light and TM polarized light remain unchanged, and enter PBS4 and PBS5 respectively, and then pass through the second polarization conversion component. TM polarized light is combined by PBS2 and output from T2 port; When the optical signal is transmitted from the T2 port to the T3 port, the incident random polarized light is divided into TE polarized light and TM polarized light by PBS2, and after passing through the second polarization conversion component, the two beams of light undergo TE→TM and TM→TE polarization respectively Transformed, and then passed through PBS4 and PBS5 respectively, transmitted to the lower part of the first polarization conversion component, and the polarization conversion of TM→TE and TE→TM occurs again, and finally the two paths of TE and TM polarized light are combined by PBS3 and output from the T3 port . 3. The three-port optical circulator according to claim 1, wherein each polarization beam splitter is connected to the first polarization conversion assembly (3) or the second polarization conversion assembly (4) through a single-mode optical waveguide . 4. The three-port optical circulator as claimed in claim 3, characterized in that, a first groove (1) and a second groove (2) are arranged in the lateral direction of the single-mode optical waveguide connecting each polarization beam splitter , and the first polarization conversion component (3) is inserted into the first groove (1), and the second polarization conversion component (4) is inserted into the second groove (2). 5. The three-port optical circulator according to claim 4, characterized in that, in the single-mode optical waveguide, the waveguide width of the first waveguide at the first groove (1) or the second groove (2) is provided greater than the waveguide width of the second waveguide at other locations. 6 . The three-port optical circulator according to claim 5 , wherein a transition is made between the first waveguide and the second waveguide through a tapered region. 7. The three-port optical circulator according to any one of claims 1-6, wherein the first polarization conversion component (3) and the second polarization conversion component (4) have the same structure; and Both the first polarization conversion component (3) and the second polarization conversion component (4) are used to realize that when the light passes through one side, the polarization direction is rotated by 90 degrees; when the light passes through the other side, the polarization direction No rotation occurs. 8. The three-port optical circulator according to claim 7, wherein the first polarization conversion component (3) comprises: a Faraday optical rotator and a half-wave plate; the Faraday optical rotator and the half-wave plate are closely attached, The Faraday rotator is connected to the first polarization beam splitter PBS1 and the third polarization beam splitter PBS3 and is close to the T1 and T3 ports; the half-wave plate is connected to the fourth polarization beam splitter PBS4 and the fifth polarization beam splitter PBS5 and is close to T2 port; the Faraday rotator is used to rotate the polarization state of the optical signal by 45 degrees, and the half-wave plate is used to make the polarization state of the light mirror deflect around its fast axis. 9. The three-port optical circulator according to claim 8, wherein the central wavelength of the half-wave plate is 1285 nm.