A Mach-Zehnder electro-optic modulator

Abstract

The invention relates to a Mach-Zehnder electro-optical modulator, comprising first and second couplers, a first waveguide arm, a second waveguide arm, a third waveguide arm, a fourth waveguide arm, and first and second silicon nitride waveguides; the first silicon nitride waveguide and the second silicon nitride waveguide both comprise a first curved portion, a straight portion, and a second curved portion connected in sequence; the first coupler is respectively connected to one end of the first waveguide arm and one end of the second waveguide arm; the first silicon nitride waveguide is connected to the other end of the first waveguide arm through the first curved portion and to one end of the third waveguide arm through the second curved portion; the second silicon nitride waveguide is connected to the other end of the second waveguide arm through the first curved portion and to one end of the fourth waveguide arm through the second curved portion; the other end of the third waveguide arm is connected to the second coupler; the other end of the fourth waveguide arm is connected to the second coupler through a phase changer; the invention can reduce the active region capacitance of the modulator and improve the high frequency performance of the modulator.

Description

Technical Field

[0001] The invention relates to the field of integrated optoelectronic devices, in particular to a Mach-Zehnder electro-optic modulator. Background Art

[0002] At present, the most common silicon-based electro-optic modulator is based on the carrier dispersion effect to achieve the modulation function. According to the optical structure, it can be mainly divided into Mach-Zehnder Interference (MZI) modulator and Micro Ring Resonant (MRR) modulator. The working principle of the MZI modulator is that when a beam of light is coupled into the incident waveguide, the incident light is divided into two parts by the optical beam splitter, and enters the upper and lower modulation arms respectively. After a certain distance, it is output through the optical beam combiner, and the light fields of the upper and lower arms are superimposed. When the refractive index or length of one of the arms is changed, the phase difference between the two arms changes accordingly, and the output light field changes after the coherent superposition between the two arms; while the working principle of the MRR modulator is to change the refractive index of the waveguide through different electrical structures so as to achieve the change of the spectrum. Although the MRR modulator has the advantages of high modulation rate and small size, this type of modulator needs to make a compromise between energy efficiency and optical bandwidth, and is greatly affected by process errors and environmental factors. MZI has good process tolerance and stability, so the mainstream in the market is MZI electro-optical modulator. However, this type of modulator is large in size, so reducing the size of MZI modulator, improving modulation efficiency and high-frequency performance of the device is the core of the development of this type of modulator.

[0003] The existing Mach-Zehnder modulator simply shortens the length of the entire modulator without improving its high-frequency performance. At the same time, this solution will increase the microwave loss of the traveling wave electrode and have a negative impact on the performance of the device. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a Mach-Zehnder electro-optic modulator, which can reduce the capacitance of the active region of the modulator and improve the high-frequency performance of the modulator.

[0005] The technical solution adopted by the present invention to solve the technical problem is: to provide a Mach-Zehnder electro-optic modulator, including a first coupler, a second coupler, a first waveguide arm arranged on a first PN junction, a second waveguide arm arranged on a second PN junction, a third waveguide arm arranged on a third PN junction, a fourth waveguide arm arranged on a fourth PN junction, a first silicon nitride waveguide and a second silicon nitride waveguide; the P region of the first PN junction is connected to the P region of the second PN junction;

[0006] The first silicon nitride waveguide and the second silicon nitride waveguide each include a first curved portion, a straight portion, and a second curved portion connected in sequence;

[0007] The first coupler is connected to one end of the first waveguide arm and one end of the second waveguide arm respectively;

[0008] The first silicon nitride waveguide is connected to the other end of the first waveguide arm through its first bend, and is connected to one end of the third waveguide arm through its second bend;

[0009] The second silicon nitride waveguide is connected to the other end of the second waveguide arm through its first bend, and is connected to one end of the fourth waveguide arm through its second bend;

[0010] The other end of the third waveguide arm is connected to the second coupler; the other end of the fourth waveguide arm is connected to the second coupler through a phase changer.

[0011] A DC electrode is provided at the connection between the second PN junction and the third PN junction, and the DC electrode is located between the first waveguide arm and the second waveguide arm; a signal electrode is provided in the N region of the third PN junction, and a ground electrode is provided in the N region of the fourth PN junction.

[0012] The N region of the first PN junction is connected to the P region of the third PN junction through a first gate metal, and the straight portion of the first silicon nitride waveguide is located in the first gate metal.

[0013] The N region of the second PN junction is connected to the P region of the fourth PN junction through a second gate metal, and the straight portion of the second silicon nitride waveguide is located in the second gate metal.

[0014] The first waveguide arm, the second waveguide arm, the third waveguide arm and the fourth waveguide arm are parallel to each other.

[0015] The first waveguide arm, the second waveguide arm, the third waveguide arm and the fourth waveguide arm are all silicon waveguides.

[0016] The phase changer is a heater, and the heater is made of titanium nitride.

[0017] The DC electrode, the signal electrode and the ground electrode are all made of aluminum.

[0018] The first coupler and the second coupler are both multi-mode interference couplers.

[0019] Beneficial Effects

[0020] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art: the Mach-Zehnder electro-optic modulator of the present invention shortens the device length while shortening the required traveling wave electrode length in disguise, and can reduce the active area capacitance of the modulator, further improving the high-frequency performance of the device; the process of the present invention is based on CMOS technology, with low processing difficulty and easy promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a top view of a Mach-Zehnder electro-optic modulator according to an embodiment of the present invention;

[0022] Figure 2 is a schematic diagram of the three-dimensional structure of a Mach-Zehnder electro-optic modulator according to an embodiment of the present invention;

[0023] Figure 3 Schematic diagram of a cross-section of a Mach-Zehnder electro-optic modulator according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0025] The embodiment of the present invention relates to a Mach-Zehnder electro-optic modulator, see Figure 1 and Figure 2, including a first coupler 5, a second coupler 6, a first waveguide arm 1 arranged on a first PN junction, a second waveguide arm 2 arranged on a second PN junction, a third waveguide arm 3 arranged on a third PN junction, a fourth waveguide arm 4 arranged on a fourth PN junction, a first silicon nitride waveguide and a second silicon nitride waveguide; the P region of the first PN junction is connected to the P region of the second PN junction; the first silicon nitride waveguide and the second silicon nitride waveguide each include a first curved portion 7, a straight portion 8 and a second curved portion 9 connected in sequence; the first silicon nitride waveguide and the second silicon nitride waveguide are S-shaped; a DC electrode 11 is arranged at the connection between the second PN junction and the third PN junction, and the DC electrode 11 is located between the first waveguide arm 1 and the second waveguide arm 2; a signal electrode 12 is arranged in the N region of the third PN junction , the N region of the fourth PN junction is provided with a ground electrode 13; the first coupler 5 is respectively connected to one end of the first waveguide arm 1 and one end of the second waveguide arm 2; the first silicon nitride waveguide is connected to the other end of the first waveguide arm 1 through its own first bend 7, and is connected to one end of the third waveguide arm 3 through its own second bend 9; the second silicon nitride waveguide is connected to the other end of the second waveguide arm 2 through its own first bend 7, and is connected to one end of the fourth waveguide arm 4 through its own second bend 9; the other end of the third waveguide arm 3 is connected to the second coupler 6; the other end of the fourth waveguide arm 4 is connected to the second coupler 6 through a phase changer 14, and the phase changer 14 in this embodiment is a heater made of TiN (titanium nitride).

[0026] Further, the N region of the first PN junction is connected to the P region of the third PN junction through a first gate metal 10 , and the straight portion 8 of the first silicon nitride waveguide is located in the first gate metal 10 .

[0027] Furthermore, the N region of the second PN junction is connected to the P region of the fourth PN junction through a second gate metal 10 , and the straight portion 8 of the second silicon nitride waveguide is located in the second gate metal 10 .

[0028] Furthermore, the P regions of the first PN junction, the second PN junction, the third PN junction and the fourth PN junction are all composed of P-type heavily doped silicon region 18 and P-type doped silicon region 17 , and the N regions are all composed of N-type heavily doped silicon region 15 and N-type doped silicon region 16 .

[0029] Furthermore, the first waveguide arm 1 , the second waveguide arm 2 , the third waveguide arm 3 and the fourth waveguide arm 4 are parallel to each other; the first waveguide arm 1 , the second waveguide arm 2 , the third waveguide arm 3 and the fourth waveguide arm 4 are all silicon waveguides.

[0030] Furthermore, the DC electrode 11, the signal electrode 12, the ground electrode 13 and the gate metal 10 are all made of aluminum.

[0031] Furthermore, the first coupler 5 and the second coupler 6 are both multimode interference couplers (Multimode interference coupler, MMI).

[0032] The principle of the Mach-Zehnder electro-optic modulator of this embodiment is described in detail below:

[0033] The Mach-Zehnder electro-optic modulator of this embodiment is embedded in silicon dioxide (S i O2), the Mach-Zehnder electro-optic modulator consists of a passive area and an active area. The light is divided into two beams through the first coupler 5 and passes through the modulation area, and the downlink light (i.e., the path connecting the fourth waveguide arm 4 and the second coupler 6) is heated by the phase changer 14 to generate a certain phase difference with the uplink light (i.e., the path connecting the third waveguide arm 3 and the second coupler 6). Finally, the two are combined into one beam of light again through the second coupler 6. Figure 1 It can be seen that after the two light beams are modulated for the first time through the active region, they are coupled into the silicon nitride S-type waveguide (i.e., the first silicon nitride waveguide and the second silicon nitride waveguide) to change the direction of light propagation. Since silicon nitride is an insulating material, the light is not modulated in silicon nitride and is simply transmitted. Finally, the light is coupled into the silicon waveguide (i.e., the third waveguide arm 3 and the fourth waveguide arm 4) again and enters the active region to be modulated again. Figure 1 It can be seen from the transmission direction of the optical path that the propagation direction of the light remains in a straight line when it is modulated. Therefore, compared with the Michelson modulator, this embodiment will not have a situation where the optical path is opposite to the transmission direction of the loaded signal because the phase matching condition is maintained.

[0034] Figure 3 The cross-sectional schematic diagram of the Mach-Zehnder electro-optic modulator is shown. Since the device adopts the GS push-pull loading signal method, the PN junctions on the same side of the DC electrode 11 need to be in the same direction. The device uses two gate metals 10 to achieve this requirement. From the cross-sectional diagram, it can be seen that the first PN junction, the second PN junction, the third PN junction, and the fourth PN junction formed by silicon waveguide doping are in series connection between high-frequency signals, so the capacitance of the entire PN junction structure will be greatly reduced, which is conducive to the improvement of the high-frequency performance of the entire device.

[0035] It can be seen that the Mach-Zehnder electro-optic modulator of the present invention shortens the device length while shortening the required traveling wave electrode length in disguise, and can also reduce the active region capacitance of the modulator, further improving the high frequency performance of the device.

Claims

1. A Mach-Zehnder electro-optic modulator, characterized in that: The invention comprises a first coupler (5), a second coupler (6), a first waveguide arm (1) arranged on a first PN junction, a second waveguide arm (2) arranged on a second PN junction, a third waveguide arm (3) arranged on a third PN junction, a fourth waveguide arm (4) arranged on a fourth PN junction, a first silicon nitride waveguide and a second silicon nitride waveguide; the P region of the first PN junction and the P region of the second PN junction are connected; The first silicon nitride waveguide and the second silicon nitride waveguide each comprise a first curved portion (7), a straight portion (8) and a second curved portion (9) connected in sequence; The first coupler (5) is respectively connected to one end of the first waveguide arm (1) and one end of the second waveguide arm (2); The first silicon nitride waveguide is connected to the other end of the first waveguide arm (1) via its first bent portion (7), and is connected to one end of the third waveguide arm (3) via its second bent portion (9); The second silicon nitride waveguide is connected to the other end of the second waveguide arm (2) via its first bent portion (7), and is connected to one end of the fourth waveguide arm (4) via its second bent portion (9); The other end of the third waveguide arm (3) is connected to the second coupler (6); the other end of the fourth waveguide arm (4) is connected to the second coupler (6) via a phase changer (14); A DC electrode (11) is provided at the connection between the second PN junction and the third PN junction, and the DC electrode (11) is located between the first waveguide arm (1) and the second waveguide arm (2); a signal electrode (12) is provided in the N region of the third PN junction, and a ground electrode (13) is provided in the N region of the fourth PN junction; the N region of the first PN junction is connected to the P region of the third PN junction via a first gate metal (10), and the straight portion (8) of the first silicon nitride waveguide is located in the first gate metal (10); the N region of the second PN junction is connected to the P region of the fourth PN junction via a second gate metal (10), and the straight portion (8) of the second silicon nitride waveguide is located in the second gate metal (10).

2. The Mach-Zehnder electro-optic modulator according to claim 1, characterized in that: The first waveguide arm (1), the second waveguide arm (2), the third waveguide arm (3) and the fourth waveguide arm (4) are parallel to each other.

3. The Mach-Zehnder electro-optic modulator according to claim 1, characterized in that: The first waveguide arm (1), the second waveguide arm (2), the third waveguide arm (3) and the fourth waveguide arm (4) are all silicon waveguides.

4. The Mach-Zehnder electro-optic modulator according to claim 1, characterized in that: The phase changer (14) is a heater, and the heater is made of titanium nitride.

5. The Mach-Zehnder electro-optic modulator according to claim 1, characterized in that: The DC electrode (11), the signal electrode (12) and the ground electrode (13) are all made of aluminum.

6. The Mach-Zehnder electro-optic modulator according to claim 1, characterized in that: The first coupler (5) and the second coupler (6) are both multi-mode interference couplers.

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