CN114740568A

CN114740568A - Array waveguide grating and manufacturing method thereof, transceiver and optical communication system

Info

Publication number: CN114740568A
Application number: CN202110025612.6A
Authority: CN
Inventors: 陈文君; 孙旭; 郜定山
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2021-01-08
Filing date: 2021-01-08
Publication date: 2022-07-12
Also published as: JP2024502168A; KR20230121923A; WO2022148327A1

Abstract

The application discloses an arrayed waveguide grating and a manufacturing method thereof, a transceiver and an optical communication system, and belongs to the field of optical communication. The arrayed waveguide grating includes: the device comprises a first waveguide, a pre-broadening device, a first coupler, an array waveguide, a second coupler and a second waveguide; the first waveguide is used for inputting n paths of optical signals to the first coupler, the first coupler is used for coupling the n paths of optical signals to the m waveguides for transmission, the second coupler is used for coupling the optical signals transmitted on the m waveguides to the p waveguides for transmission, and the second waveguide is used for outputting the p paths of optical signals; the pre-broadening device is located between the first waveguide and the first coupler or between the second coupler and the second waveguide, the region where the pre-broadening device is located is provided with sub-wavelength gratings arranged along the extending direction of the pre-broadening device, and the pre-broadening device is used for adjusting the flatness of the top end of the output spectrum of the arrayed waveguide grating. The method and the device can reduce insertion loss caused by wavelength deviation of the optical signal.

Description

Array waveguide grating and manufacturing method thereof, transceiver and optical communication system

Technical Field

The present disclosure relates to the field of optical communications, and in particular, to an arrayed waveguide grating, a method for manufacturing the arrayed waveguide grating, a transceiver, and an optical communications system.

Background

An Arrayed Waveguide Grating (AWG) is a core device in Wavelength Division Multiplexing (WDM) technology.

The AWG comprises a first waveguide, a first star coupler, an array waveguide, a second star coupler and a second waveguide which are connected in sequence; the optical signal passing through the arrayed waveguide forms a gaussian spectrum (also referred to as a gaussian spectrum), so that the spectrum of the optical signal output through the AWG is a gaussian spectrum, and a 3dB bandwidth (which refers to a frequency range defined when a highest point of the power spectral density falls to 1/2 of the power spectral density) of the gaussian spectrum is small, and when the optical signal is transmitted based on the AWG having a small 3dB bandwidth, a wavelength shift (also referred to as a wavelength drift) of the input optical signal easily causes a large insertion loss (simply referred to as an insertion loss, also referred to as a device insertion loss).

Disclosure of Invention

The embodiment of the application provides an arrayed waveguide grating, a manufacturing method thereof, a transceiver and an optical communication system. The technical scheme is as follows:

in a first aspect, there is provided an arrayed waveguide grating comprising: the waveguide array comprises a first waveguide, a pre-broadening device, a first coupler, an array waveguide, a second coupler and a second waveguide. The array waveguide comprises m waveguides, the first waveguide comprises n waveguides, the second waveguide comprises p waveguides, m is a positive integer larger than 1, n and p are both positive integers, and n and p are different.

The first waveguide is used for inputting n paths of optical signals to the first coupler, the first coupler is used for coupling the n paths of optical signals to the m waveguides for transmission, the second coupler is used for coupling the optical signals transmitted on the m waveguides to the p waveguides for transmission, and the second waveguide is used for outputting the p paths of optical signals. The first coupler and/or the second coupler may be a star coupler. The star coupler is a slab waveguide with a rowland circle structure (also called free-propagation region). The Rowland circle structure is used for reducing diffraction distortion and realizing uniform distribution of optical power.

The pre-broadening device is located between the first waveguide and the first coupler or between the second coupler and the second waveguide, the region where the pre-broadening device is located is provided with sub-wavelength gratings arranged along the extending direction of the pre-broadening device, and the pre-broadening device is used for adjusting the flatness of the top end of the output spectrum of the arrayed waveguide grating. For example, the sub-wavelength grating is arranged in the region where the pre-widening device is located, that is, the sub-wavelength grating is arranged on the pre-widening device, or the sub-wavelength grating is arranged in the region surrounded by the boundary of the pre-widening device.

According to the AWG provided by the embodiment of the application, the pre-broadening device with the sub-wavelength grating structure is additionally arranged between the first waveguide and the first coupler or between the second coupler and the second waveguide, and the pre-broadening device is used for adjusting the flatness of the top end of the output spectrum of the AWG, so that the flat-top spectrum is finally output from the AWG, and the 3dB bandwidth of the flat-top spectrum is larger, so that the insertion loss caused by the wavelength shift of an optical signal can be effectively reduced. In addition, the AWG can resist the wavelength deviation of optical signals, an additional wavelength control system is not needed, the manufacturing cost is reduced, and the structural complexity of the AWG is reduced.

The grating parameters of the grating include a grating period, which is a distance between two adjacent slits of the grating, and/or a duty cycle, which is a ratio of a width of a gap between adjacent slits in the grating to the grating period. A sub-wavelength grating refers to a grating having a grating period less than the operating wavelength. In the sub-wavelength grating, the value range of the grating period is [0.1um, 1um ], and the value range of the duty ratio is (0, 1).

In the embodiment of the present application, the sub-wavelength grating structure on the pre-broadening device can be of various types. The sub-wavelength grating structure on the pre-broadening device can be divided into two types provided by the following first optional example and second optional example according to the arrangement direction; the sub-wavelength grating structure on the pre-widening device can be divided into two types provided by the following third alternative example and fourth alternative example according to the grating parameter division.

In a first alternative example, the sub-wavelength grating on the pre-widening device is a one-dimensional sub-wavelength grating, that is, the arrangement direction of the sub-wavelength grating is only one direction.

In a second alternative example, the sub-wavelength grating on the pre-broadened device is a two-dimensional sub-wavelength grating (also referred to as a 3D sub-wavelength grating). In the AWG, the sub-wavelength grating on the pre-widening device is a two-dimensional sub-wavelength grating, that is, the arrangement direction of the sub-wavelength grating on the pre-widening device has two directions.

In a third alternative example, the sub-wavelength grating is a uniform grating. The uniform grating is a grating with fixed grating period and fixed duty ratio.

In a fourth alternative example, the sub-wavelength grating is a non-uniform grating. The non-uniform grating is a grating with a grating period and a duty ratio which are not fixed values; i.e. the non-uniform grating is a grating having at least two grating periods and/or a grating having at least two duty cycles. By way of example, the non-uniform grating may be a graded grating, which refers to a grating having a grating period that gradually increases or decreases.

In practical implementation, the foregoing first to fourth alternative examples may be combined as appropriate. For example, the sub-wavelength grating on the pre-broadening device is a one-dimensional sub-wavelength grating and is a uniform grating. Or the sub-wavelength grating on the pre-broadening device is a two-dimensional sub-wavelength grating and is a uniform grating. Or the sub-wavelength grating on the pre-broadening device is a one-dimensional sub-wavelength grating and is a non-uniform grating. Or the sub-wavelength grating on the pre-broadening device is a two-dimensional sub-wavelength grating and is a non-uniform grating. Or the sub-wavelength grating on the pre-broadening device is a two-dimensional sub-wavelength grating, one group of sub-wavelength gratings is a uniform grating, and the other group of sub-wavelength gratings is a non-uniform grating.

It should be noted that, in the foregoing embodiments, the slits of the sub-wavelength grating are illustrated as stripe slits, and in practical implementation, the slits of the sub-wavelength grating may be slits of other shapes, such as curved slits; the sub-wavelength grating may have slits of equal or different lengths.

Before the AWG is manufactured, grating parameters of the sub-wavelength grating may be determined, and the AWG may be manufactured based on the determined grating parameters. Thereby achieving top flattening of the AWG output spectrum. In one implementation, the flatness of the top end of the output spectrum of the AWG is correlated with the grating parameters of the sub-wavelength grating. The grating parameters of the sub-wavelength grating can be determined by the flatness of the top end of the output spectrum of the AWG to be manufactured. In another implementation, the equivalent refractive index of the AWG is related to grating parameters of the sub-wavelength grating, and the equivalent refractive index of the AWG is related to the flatness of the top end of the output spectrum of the AWG. The grating parameters of the sub-wavelength grating can be determined by the equivalent refractive index of the AWG to be fabricated. Under the condition that the grating period is not changed, the larger the duty ratio is, the larger the equivalent refractive index of the AWG is; under the condition of unchanged duty ratio, the larger the grating period is, the larger the equivalent refractive index of the AWG is.

In an alternative implementation, the pre-widening device is of an axisymmetric structure, and the symmetry axis of the pre-widening device is parallel to the extending direction of the pre-widening device. The axisymmetric pre-broadening device is convenient to manufacture, and can form a symmetric double-peak light field, so that the top end of the output spectrum of the AWG is flat, and the situation of top end inclination is avoided.

The first waveguide is of an axisymmetric structure, and the symmetry axis of the pre-widening device is aligned with the symmetry axis of the first waveguide. The first waveguide, being axisymmetric, is convenient to manufacture and is capable of forming a symmetrical gaussian-type spectrum. The alignment of the symmetry axis of the pre-widening device with the symmetry axis of the first waveguide 1 facilitates a stable transmission of the optical signal. In practical implementations, the axis of symmetry of the pre-widening device may not be aligned with the axis of symmetry of the first waveguide.

The pre-stretching device is a Multimode interference (MMI) device, the MMI device is a rectangular structure, and the sub-wavelength grating is arranged on the MMI device, namely on the rectangular surface of the MMI device. In fig. 7, the pre-widening device is a Y-shaped structure (also referred to as a Y-branch structure), and the sub-wavelength grating is disposed in a region surrounded by the boundary of the Y-shaped structure. In the embodiment of the present application, the pre-widening device can also be other structures capable of adjusting the flatness of the top end of the output spectrum of the AWG, such as other structures capable of generating a bimodal optical field.

In a second aspect, a transmitter is provided, comprising: a light source, a modulator, and an arrayed waveguide grating as in any of the first aspects; the light source and the modulator are sequentially connected with the array waveguide grating, and n is larger than p; the light source is used for outputting optical signals, and the modulator is used for modulating received optical signals to obtain optical signals with multiple wavelengths and inputting the optical signals with the multiple wavelengths to the arrayed waveguide grating.

In a third aspect, a receiver is provided, including: an arrayed waveguide grating according to any one of the first aspect and a plurality of receivers; the array waveguide grating is respectively connected with a plurality of receivers, and n is smaller than p; the receiver is used for receiving the optical signal output by the arrayed waveguide grating.

In a fourth aspect, an optical communication system is provided, including: a transmitter as in the second aspect, a receiver as in the third aspect, and optical fibers connected to the transmitter and the receiver, respectively.

In a fifth aspect, a method for manufacturing an arrayed waveguide grating is provided, including:

providing a substrate; manufacturing a first waveguide, a pre-broadening device, a first coupler, an array waveguide, a second coupler and a second waveguide on a substrate; the array waveguide comprises m waveguides, the first waveguide comprises n waveguides, the second waveguide comprises p waveguides, m is a positive integer larger than 1, n and p are both positive integers, and n and p are different; the first waveguide is used for inputting n paths of optical signals to the first coupler, the first coupler is used for coupling the n paths of optical signals to the m waveguides for transmission, the second coupler is used for coupling the optical signals transmitted on the m waveguides to the p waveguides for transmission, and the second waveguide is used for outputting the p paths of optical signals; the pre-broadening device is located between the first waveguide and the first coupler or between the second coupler and the second waveguide, the region where the pre-broadening device is located is provided with sub-wavelength gratings arranged along the extending direction of the pre-broadening device, and the pre-broadening device is used for adjusting the flatness of the top end of the output spectrum of the arrayed waveguide grating.

Since the grating parameters of the sub-wavelength grating are related to the flatness of the top of the output spectrum of the AWG and the equivalent refractive index of the AWG, the determination of the grating parameters can be performed using the following two alternative implementations.

In an alternative implementation, before fabricating the first waveguide, the pre-widening device, the first coupler, the arrayed waveguide, the second coupler, and the second waveguide on the substrate, the method further comprises: determining grating parameters of the sub-wavelength grating based on the flatness of the top end of the output spectrum of the arrayed waveguide grating to be manufactured, the grating parameters including a grating period and/or a duty cycle.

In another alternative implementation, before the first waveguide, the pre-widening device, the first coupler, the arrayed waveguide, the second coupler, and the second waveguide are fabricated on the substrate, the method further comprises: determining grating parameters of the sub-wavelength grating based on the equivalent refractive index of the arrayed waveguide grating to be manufactured, wherein the grating parameters comprise grating period and/or duty ratio.

The AWG provided by the embodiment of the application has the advantages that the flatness of the top end of the output spectrum of the AWG is higher due to the pre-broadening device with the sub-wavelength grating, and the insertion loss caused by the wavelength deviation of optical signals in the AWG can be reduced. And since the flatness of the top end of the output spectrum of the AWG is adjusted using the output spectrum of the AWG. And an additional thermal regulation device is not required, so that the complexity of the AWG is reduced, the power consumption of the AWG is reduced, and the insertion loss caused by temperature drift is avoided.

The AWG provided by the embodiment of the application is matched with the pre-broadening device by adjusting the grating parameters of the sub-wavelength grating so as to adjust the flatness of the top end of the output spectrum of the AWG, and is high in design freedom degree and compatibility, and suitable for different substrate materials and optical waveguide materials. Moreover, by arranging the pre-broadening device with the sub-wavelength grating, the size of the whole AWG is hardly increased, the manufacturing cost is low, and the miniaturization of the AWG can be realized.

Drawings

Fig. 1 is a schematic diagram of the spectrum of one optical signal output by a conventional AWG;

fig. 2 is a schematic structural diagram of an AWG provided in an embodiment of the present application;

fig. 3 is a schematic structural diagram of another AWG provided by an embodiment of the present application;

fig. 4 is a schematic diagram illustrating an operation principle of a first coupler according to an embodiment of the present application;

fig. 5 is a schematic diagram illustrating an operation principle of a second coupler according to an embodiment of the present application;

fig. 6 is a schematic diagram of an AWG operating principle provided by an embodiment of the present application;

fig. 7 is a schematic partial structural diagram of an AWG provided in an embodiment of the present application;

fig. 8 is a schematic partial structural view of another AWG provided in an embodiment of the present application;

fig. 9 is a schematic diagram of another AWG operating principle provided by the embodiments of the present application;

fig. 10 is a schematic partial structural view of an AWG provided in an embodiment of the present application;

fig. 11 is a partial structural schematic diagram of an AWG provided in an embodiment of the present application;

fig. 12 is a schematic cross-sectional view of an AWG provided in an embodiment of the present application;

fig. 13 is a schematic diagram of the output spectrum of the AWG provided by an embodiment of the present application;

fig. 14 is a schematic structural diagram of a transmitter provided in an embodiment of the present application;

fig. 15 is a schematic structural diagram of another transmitter provided in the embodiment of the present application;

fig. 16 is a schematic structural diagram of a receiver according to an embodiment of the present application;

fig. 17 is a schematic structural diagram of an optical communication system according to an embodiment of the present application;

fig. 18 is a schematic flow chart of a method for manufacturing AWG according to an embodiment of the present application.

Detailed Description

To make the principles and technical solutions of the present application clearer, the following detailed description of embodiments of the present application will be made with reference to the accompanying drawings.

The conventional AWG includes a first waveguide, a first star coupler, an arrayed waveguide, a second star coupler, and a second waveguide connected in sequence. Fig. 1 is a schematic diagram of a spectrum (also called output spectrum) of one optical signal output by a conventional AWG, which is a gaussian spectrum. In the diagram, the horizontal axis represents wavelength in micrometers (μm) or nanometers (nm), and the vertical axis represents power transmittance in decibels (dB) (the vertical axis may also represent optical power in milliwatts (mw) or decibel-milliwatts (dBm)). The power transmittance is a ratio of output optical power to input optical power of the optical signal. As shown in fig. 1, the gaussian spectrum is mainly due to the gaussian optical field generated by the optical signal passing through the arrayed waveguide. The top of the Gaussian spectrum is convex, and the 3dB bandwidth is small. The 3dB bandwidth is typically only around 40% of the overall bandwidth of the gaussian. When an optical signal is transmitted based on an AWG having a small 3dB bandwidth, if the wavelength of the input optical signal is unstable, a small wavelength shift may cause a decrease in optical power, resulting in a large insertion loss (referred to as insertion loss). Referring to the spectrum diagram shown in fig. 1, the wavelength shift refers to the shift of the wavelength of the optical signal from the wavelength corresponding to the position with the maximum power transmittance to the wavelength corresponding to the other position. If the insertion loss needs to be reduced, a wavelength control system is added to control the wavelength of the input optical signal, and the wavelength control system increases the manufacturing cost of the AWG and increases the structural complexity of the AWG.

Fig. 2 and fig. 3 are schematic structural diagrams of two AWG10 provided in the embodiments of the present application. The flatness of the top end of the output spectrum of the AWG is high, and the wavelength range corresponding to the 3dB bandwidth can be enlarged, so that the insertion loss caused by the wavelength deviation of the optical signal in the AWG is reduced, and a wavelength control system does not need to be additionally arranged. As shown in fig. 2 and 3, the AWG10 includes: a first waveguide 101, a pre-widening device 102, a first coupler 103, an arrayed waveguide 104, a second coupler 105 and a second waveguide 106.

The arrayed waveguide 104 includes m waveguides, the first waveguide 101 includes n waveguides, the second waveguide 106 includes p waveguides, m is a positive integer greater than 1, n and p are both positive integers, and n and p are different. Fig. 2 illustrates an example where m is 10, n is 1, and p is 5, and fig. 3 illustrates an example where m is 10, n is 5, and p is 1. The number of m, n and p is not limited in the embodiments of the present application.

The first waveguide 101 is used to input n optical signals to the first coupler 103, and the second waveguide 106 is used to output p optical signals.

The first coupler 103 is used for coupling the n optical signals to the m waveguides for transmission. Fig. 4 is a schematic diagram illustrating an operation principle of a first coupler according to an embodiment of the present application. As shown in fig. 4, for the first coupler 103, each of the n optical signals is input from the first waveguide 101, enters a coupling region (i.e., a rowland circle) of the first coupler 103, and then diverges by the coupling region and simultaneously enters m waveguides. The first coupler 103 is used to distribute the power of each of the n optical signals to m waveguides, and fig. 4 is described by taking n as 1 and m as 5 as examples, but the specific values of n and m are not limited. For example, if an optical signal with a wavelength of 1550nm enters the coupling region of the first coupler 103, the optical signal with the wavelength enters m waveguides of the arrayed waveguide 104 at the same time.

The arrayed waveguide 104 is used for transmission of an optical signal by the principle of multi-beam interference. In the arrayed waveguide 104, adjacent waveguides have a fixed length difference, and by introducing a certain optical path difference, the transmission of m optical signals through the arrayed waveguide 104 forms different wavefront inclinations, and the m optical signals are focused at different positions of the second coupler 105, so as to be received by different waveguides in the second waveguide 106 through the second coupler 105.

The second coupler 105 is used for coupling the optical signals transmitted on the m waveguides to the p waveguides for transmission. Fig. 5 is a schematic diagram illustrating an operation principle of a first coupler according to an embodiment of the present application. As shown in fig. 5, with the second coupler 105, after the m optical signals are emitted from the arrayed waveguide 104 having a fixed length difference, diffraction occurs at a coupling region (i.e., a rowland circle) of the second coupler 105, and are focused at p positions to be output from p waveguides of the second waveguide 106, respectively. In the coupling region of the second coupler 105, the optical signals with the same wavelength are focused at the same position in the coupling region, and the optical signals with different wavelengths are focused at different positions in the coupling region, so that the second coupler 105 can realize the function of splitting, that is, the wavelengths of the optical signals entering the p waveguides of the second waveguide 106 are different from each other. In fig. 5, the example where m is 5 and p is 3 is given, and it is assumed that the second coupler 105 outputs 3 optical signals having different wavelengths, and the optical signals have wavelengths λ 1 to λ 3, respectively, but specific values of m, p, and λ are not limited.

The first coupler 103 and/or the second coupler 105 may be a star coupler. The star coupler is a slab waveguide with a rowland circle structure (also called free-propagation region). The Rowland circle structure is used for reducing diffraction distortion and realizing uniform distribution of optical power.

As shown in fig. 2, the pre-widening device 102 is located between the first waveguide 101 and the first coupler 103, and the pre-widening device 102 forms a transition region between the first waveguide 101 and the first coupler 103. The widths of the first waveguide 101, the pre-widening device 102 and the first coupler 103 vary, for example, gradually become larger or smaller. Alternatively, as shown in fig. 3, the pre-widening device 102 is located between the second coupler 105 and the second waveguide 106, and the pre-widening device 102 forms a transition region between the second coupler 105 and the second waveguide 106. The widths of the second coupler 105, the pre-widening device 102 and the second waveguide 106 vary, e.g., gradually increase or gradually decrease.

As shown in fig. 2 or fig. 3, the pre-widening device 102 is provided with a sub-wavelength grating 1021 arranged along an extending direction (i.e., a length direction) r1 of the pre-widening device 102, and a width direction r2 of the pre-widening device 102 is perpendicular to the extending direction r1 of the pre-widening device 102. The pre-widening device 102 and the sub-wavelength grating 1021 may be fabricated by the same patterning process. For example, the sub-wavelength grating is arranged in the region where the pre-widening device is located, that is, the sub-wavelength grating is arranged on the pre-widening device, or the sub-wavelength grating is arranged in the region surrounded by the boundary of the pre-widening device.

The pre-broadening device 102 is used to adjust the flatness of the top end of the output spectrum of the AWG 10. The flatness of the top of the output spectrum refers to the degree of variation in the amplitude of the power transmittance with the variation in the wavelength of the optical signal. Among them, the smaller the amplitude variation of the power transmittance, the higher the flatness. Through the adjustment of the pre-broadening device 102, the AWG10 can output a flat-top spectrum, and the 3dB bandwidth of the flat-top spectrum can be greatly improved, so that the wavelength range corresponding to the 3dB bandwidth is effectively increased, and the insertion loss caused by the instability of the input optical signal is reduced to a certain extent.

According to the AWG provided by the embodiment of the application, the pre-broadening device with the sub-wavelength grating structure is additionally arranged between the first waveguide and the first coupler or between the second coupler and the second waveguide, and is used for adjusting the flatness of the top end of the output spectrum of the AWG, so that the flat-top spectrum is finally output from the AWG, and the 3dB bandwidth of the flat-top spectrum is larger, so that the insertion loss caused by the wavelength shift of optical signals can be effectively reduced.

Moreover, the AWG can resist the wavelength deviation of optical signals, so that an additional wavelength control system is not required to be arranged, the manufacturing cost is reduced, and the structural complexity of the AWG is reduced.

In the present embodiment, the pre-widening device 102 is capable of forming a double humped optical field (also referred to as a double humped optical field or a humped optical field). The bimodal light field refers to a light field having two peaks (also called peaks) and one valley (also called valley) located between the two peaks. Fig. 6 is a schematic diagram of an operating principle of an AWG10 according to an embodiment of the present application. Fig. 6 schematically depicts the change process of the optical field w corresponding to the optical signal in fig. 2 during the optical signal passes through the first waveguide 101, the pre-widening device 102 and the first coupler 103. The optical field of the optical signal input from the first waveguide 101 is a gaussian optical field, and after the optical signal passes through the pre-widening device 102, the optical field of the optical signal input to the first coupler 103 becomes a double-peak optical field.

In an alternative, the pre-widening device 102 forms a bimodal optical field by the self-image principle. Self-imaging, also called self-imaging, is a characteristic of multimode waveguides, by which the input optical field distribution reproduces N-fold images of the input optical field at periodic intervals along the optical signal propagation direction of the waveguide (N is a positive integer). Along the transmission direction of the optical signal of the multimode waveguide, different equally divided optical fields, such as 1 to 2 optical fields (i.e., a bimodal optical field), 1 to 3 optical fields (i.e., a trimodal optical field), or 1 to 4 optical fields (i.e., a quadrapodal optical field), may respectively appear at different positions. In the present embodiment, the pre-widening device 102 is a multimode waveguide. The length of the pre-widening device 102 ensures that a 1/2 optical field appears at the output of the pre-widening device 102. Fig. 7 is a schematic partial structural diagram of an AWG according to an embodiment of the present application. In fig. 7, the pre-widening device 102 is a Multimode interference (MMI) device, which forms a double peak optical field by the self-image principle.

In another alternative, the pre-widening device 102 forms a bimodal optical field by the principle of power division. The pre-widening device 102 based on the power division principle is a power division structure, which divides the power of an input optical signal into two equal parts and outputs the two divided optical signals through two branch waveguides. When the distance between the two branch waveguides is short, the optical fields of the optical signals of the two branches form a double-peak optical field due to the superposition of edge energy. Fig. 8 is a partial schematic structural view of another AWG provided in the embodiment of the present application. In fig. 8, the pre-widening device 102 has a Y-shaped structure (also referred to as a Y-branch structure) including one main path waveguide a1 and two branch waveguides a2 connected to the main path waveguide a 1. The Y-shaped structure forms a double-peak light field through a power equal division principle.

In the embodiment of the present application, the pre-widening device 102 can also be other structures capable of adjusting the flatness of the top end of the output spectrum of the AWG, such as other structures capable of generating a bimodal optical field. The embodiment of the present application does not limit this.

Illustratively, as shown in fig. 2 and 3, the pre-widening device 102 is an axisymmetric structure, and the axis of symmetry of the pre-widening device 102 is parallel to the extending direction r1 of the pre-widening device 102. The axisymmetric pre-broadening device 102 is easy to manufacture and is capable of forming a symmetric double peak optical field such that the top of the output spectrum of the AWG10 is flat without tip tilt.

In the embodiment of the present application, the first waveguide 101 may also be an axisymmetric structure, and the symmetry axis of the pre-widening device 102 is aligned with the symmetry axis of the first waveguide 101. The axisymmetric first waveguide 101 is convenient to manufacture and is capable of forming a symmetric gaussian-type spectrum. The alignment of the symmetry axis of the pre-stretching device 102 with the symmetry axis of the first waveguide 101 facilitates the power equalization of the two protrusions (i.e., the two peaks) of the bimodal optical field, thereby ensuring the symmetry of the bimodal optical field. In practical implementation, the first waveguide 101 may also be a non-axisymmetric structure.

Fig. 9 schematically shows a schematic diagram of the superposition of the bimodal optical field output by the pre-broadening device 102 and the gaussian optical field output by the arrayed waveguide 104 for one optical signal. Because the concave part of the double-peak light field and the convex part of the Gaussian light field can be mutually offset, the flatness of the top end of the light field of the light signal finally output from the AWG10 is higher, the light field is called a flat-top light field, and the corresponding output spectrum is the flat-top spectrum. In fig. 9, the horizontal axis of each optical field diagram indicates the width of the waveguide through which the optical signal passes, and the vertical axis indicates the magnetic field strength corresponding to the optical signal, and the unit is a.u., which indicates a unit of one relative value, and may be an arbitrarily set unit. Fig. 9 does not depict two coordinate axes of each light field schematic.

Grating refers to an optical device consisting of a large number of parallel slits (or lines). The grating parameters of the grating include the grating period and/or the duty cycle. Wherein the grating period, also called grating constant, refers to the distance between two slits adjacent to the grating, which can be represented by the distance between the same sides of the two slits. The grating period may be equal to the sum of the width of one slit of the grating and the width of the gap between the slit and the other slit. The duty cycle is the ratio of the width of the gap between adjacent slits in the grating to the grating period. As shown in fig. 7, fig. 7 is labeled by taking the grating period a as the distance between the right sides of the two slits and b as the width of the slit gap (i.e., the width of the region between the two slits) as an example.

A sub-wavelength grating refers to a grating having a grating period that is less than the operating wavelength. For example, the grating period of the sub-wavelength grating provided in the embodiment of the present application ranges from [0.1um, 1um ], and the duty ratio ranges from (0, 1). In an AWG, the operating wavelength refers to the wavelength of the optical signal supported by the AWG. For example, if the output of the AWG has one optical channel, the operating wavelength refers to the wavelength of the optical signal corresponding to the one optical channel. If the output end of the AWG has a plurality of optical channels, the optical signal passing through the AWG is a plurality of optical signals corresponding to the plurality of optical channels. The operating wavelength then refers to the specified wavelength of the plurality of optical signals. For example, the specified wavelength is a center wavelength, any wavelength, a minimum wavelength, a maximum wavelength, an average wavelength, or the like.

The placement of the sub-wavelength grating on the pre-stretched device 102 may be different for different types of pre-stretched devices 102. Illustratively, in fig. 7, the pre-widening device 102 is an MMI device having a rectangular structure, and the sub-wavelength grating is disposed on the MMI device, i.e., on a rectangular surface of the MMI device. In fig. 8, the pre-widening device 102 is a Y-shaped structure (also called Y-branch structure), and the sub-wavelength grating is disposed in the region enclosed by the boundary of the Y-shaped structure, i.e., between the two branch waveguides a 2.

In the present embodiment, the sub-wavelength grating structure 1021 on the pre-broadside device 102 may be of various types. The sub-wavelength grating structure 1021 on the pre-widening device 102 can be divided into two types provided by the following first alternative example and second alternative example according to the arrangement direction; the sub-wavelength grating structure 1021 on the pre-widening device 102 can be divided into two types as provided in the third and fourth alternative examples described below, according to the grating parameter division.

In a first alternative example, the sub-wavelength grating on the pre-widening device 102 is a one-dimensional sub-wavelength grating, that is, the sub-wavelength grating has only one arrangement direction. The structure of the sub-wavelength grating on the pre-broadening device 102 is shown in fig. 2, 3, 7 or 8.

In a second alternative example, the sub-wavelength grating on the pre-widening device 102 is a two-dimensional sub-wavelength grating (also referred to as a 3D sub-wavelength grating). Fig. 10 is a schematic partial structure diagram of an AWG according to an embodiment of the present application. In the AWG, the sub-wavelength grating on the pre-widening device 102 is a two-dimensional sub-wavelength grating, that is, the arrangement direction of the sub-wavelength grating on the pre-widening device 102 has two directions. Then, as shown in fig. 10, in addition to the sub-wavelength grating arranged along the extending direction r1 of the pre-widening device 102, the pre-widening device 102 is further provided with a sub-wavelength grating arranged along another direction r2, and the another direction r2 is perpendicular to the extending direction r1 of the pre-widening device 102. In this way, the sub-wavelength grating arranged along the extending direction of the pre-widening device 102 and the sub-wavelength grating arranged along the other direction form a grid-like grating structure. In an alternative implementation, the slits of the sub-wavelength grating arranged along the extending direction r1 of the pre-widening device 102 and the sub-wavelength grating arranged along the other direction r2 are arranged on the surface of the pre-widening device, and each grid of the grid-shaped grating is a block-shaped body which is convex relative to the surface of the pre-widening device.

In a third alternative example, the sub-wavelength grating is a uniform grating. The uniform grating is a grating with a fixed grating period and a fixed duty ratio, and the structure of the uniform grating is shown in fig. 2, fig. 3, fig. 7, fig. 8 or fig. 10. As shown in fig. 7, the duty cycle of the grating refers to the ratio of the width b of the slit gap to the grating period a, i.e. b/a.

In a fourth alternative example, the sub-wavelength grating is a non-uniform grating. The non-uniform grating is a grating with a grating period and a duty ratio which are not fixed values; i.e. the non-uniform grating is a grating having at least two grating periods and/or a grating having at least two duty cycles. Fig. 11 is a schematic partial structural diagram of an AWG according to an embodiment of the present application. In the AWG, the sub-wavelength grating on the pre-broadening device 102 is a non-uniform grating. By way of example, the non-uniform grating may be a graded grating, which refers to a grating having a grating period that gradually increases or decreases.

In practical implementation, the foregoing first to fourth alternative examples may be combined as appropriate. For example, the sub-wavelength grating on the pre-widening device 102 is a one-dimensional sub-wavelength grating and is a uniform grating. Alternatively, the sub-wavelength grating on the pre-widening device 102 is a two-dimensional sub-wavelength grating and is a uniform grating. Alternatively, the sub-wavelength grating on the pre-widening device 102 is a one-dimensional sub-wavelength grating and is a non-uniform grating. Alternatively, the sub-wavelength grating on the pre-widening device 102 is a two-dimensional sub-wavelength grating and is a non-uniform grating. Alternatively, the sub-wavelength gratings on the pre-widening device 102 are two-dimensional sub-wavelength gratings, one group of sub-wavelength gratings is uniform gratings, and the other group of sub-wavelength gratings is non-uniform gratings.

It should be noted that, in the foregoing embodiments, the slits of the sub-wavelength grating are taken as the slits distributed along a straight line as an example, and in actual implementation, the slits of the sub-wavelength grating may be slits with other shapes, such as curved slits; the sub-wavelength grating may have slits of equal or different lengths. Any sub-wavelength grating that can achieve the flatness adjustment function of the top end of the output spectrum of the pre-broadening device 102 is within the scope of the present embodiments.

In the embodiment of the present application, the width of the pre-widening device 102 (which is r2 in the direction shown in fig. 2, 3 or 10) determines the position of the double peak light field, the equivalent refractive index of the pre-widening device 102 affects the depth of the depression in the double peak light field, and generally, the equivalent refractive index of the pre-widening device 102 is inversely related to the depth of the double peak light field. That is, the smaller the equivalent index of the pre-broadening device 102, the deeper the dip of the bimodal optical field. It should be noted that the equivalent refractive index of the pre-widening device refers to the equivalent refractive index of the region where the pre-widening device is located. For example, when the pre-widening device is an MMI, the area where the pre-widening device is located is the area surrounded by the boundary of the MMI; when the pre-widening device is a Y-shaped structure, the area where the pre-widening device is located is an area surrounded by the boundary of the Y-shaped structure. If the pre-broadening device 102 does not have a sub-wavelength grating. For example, the pre-broadened device is an MMI device without a sub-wavelength grating, since the width and the equivalent refraction of the MMI device are fixed. The MMI device cannot accurately regulate and control the amplitude distribution of a double-peak light field generated by a double self-imaging effect, and in the double-peak light field output by the MMI device, the light field between two image points (namely two peaks) can be overlapped and integrally lifted, so that the sunken degree of the middle region (namely the sunken region) of the light field is insufficient, and the sunken depth does not meet the requirement of flattening the output spectrum of the AWG. Therefore, using a pre-broadening device 102 without a sub-wavelength grating does not allow the top of the output spectrum of AWG10 to reach the target flatness. The sub-wavelength grating may affect the equivalent refractive index of the pre-broadening device (e.g., decrease the equivalent refractive index of the pre-broadening device), which may in turn adjust the depth of the depression in the bimodal optical field, thereby affecting the shape of the output spectrum of AWG 10. By setting the sub-wavelength grating, the pre-broadening device 102 can be assisted to adjust the equivalent refractive index of the pre-broadening device, so as to adjust the flatness of the top end of the output spectrum of the AWG10, thereby achieving the target flatness of the top end of the output spectrum of the AWG10 on the premise of ensuring that the pre-broadening device 102 has a certain width.

Thus, prior to fabrication of AWG10, the grating parameters of the sub-wavelength grating may be determined, and then the AWG10 may be fabricated based on the determined grating parameters. Thereby achieving top flattening of the output spectrum of AWG 10. Wherein the grating parameters comprise a grating period and/or a duty cycle. In one implementation, the flatness of the top end of the output spectrum of the AWG10 is related to the grating parameters of the sub-wavelength grating. The grating parameters of the sub-wavelength grating can be determined by the flatness of the top end of the output spectrum of the AWG10 to be fabricated. In another implementation, the equivalent refractive index of the AWG10 (or the equivalent refractive index of the pre-broadening device) is related to the grating parameters of the sub-wavelength grating, and the equivalent refractive index of the AWG is related to the flatness of the top end of the output spectrum of the AWG. Under the condition that the grating period is not changed, the larger the duty ratio is, the larger the equivalent refractive index of the AWG is; under the condition of constant duty ratio, the larger the grating period is, the larger the equivalent refractive index of the AWG is. The grating parameters of the sub-wavelength grating can be determined by the equivalent refractive index of the AWG10 to be fabricated. The specific processes of the two implementation modes can refer to the processes of the subsequent method embodiments.

It should be noted that the AWG10 provided in the embodiment of the present application may further include a substrate (also referred to as a substrate base plate), on which an AWG pattern (pattern) is disposed, the AWG pattern including: a first waveguide 101, a pre-widening device 102, a first coupler 103, an arrayed waveguide 104, a second coupler 105 and a second waveguide 106. The material of the substrate may be different and the material of the AWG pattern may be different for different manufacturing scenarios. For example, the material of the substrate may be lithium niobate (LiNbO3), a group iii-v semiconductor compound, silicon dioxide (SiO2), silicon (Si), Polymer (Polymer), glass, or the like. The optical waveguide material used to make the AWG pattern may be silicon (Si), silicon nitride (SiN), silicon oxynitride (SiON), or silicon dioxide.

Optionally, the AWG10 may also include other layers of material. For example, the AWG10 may also include a first protective layer positioned on a side of the AWG pattern proximate the substrate; and/or a second protective layer located on a side of the AWG pattern adjacent to the substrate. The first protective layer and the second protective layer are used for protecting the AWG pattern so as to improve the service life of the AWG pattern. Illustratively, the materials of the first protective layer and the second protective layer are both silicon dioxide. Fig. 12 is a schematic cross-sectional view of an AWG10 provided by an embodiment of the present application. The AWG10 includes a substrate 107, a first protective layer 108, an AWG pattern M including the first waveguide 101, the pre-widening device 102, the first coupler 103, the arrayed waveguide 104, the second coupler 105, and the second waveguide 106 in the foregoing embodiments, and a second protective layer 109. The pre-broadening device 102 has a sub-wavelength grating 1021 disposed thereon.

For the convenience of the reader, the following description will take the structure of an actual AWG as an example. Assuming that the arrayed waveguide in the AWG includes 16 waveguides (also called 16 channels), adjacent waveguides have a length difference of 100(GHz), that is, a channel spacing of 100 gigahertz (GHz), the channel spacing refers to a ratio of a wavelength corresponding to a peak of an output spectrum of the adjacent waveguide to a frequency spacing. The material of the AWG pattern is silicon nitride, and the thickness of the silicon nitride layer is 80 nanometers (nm). And the AWG further comprises a first protective layer and a second protective layer disposed on both sides of the AWG pattern. The first protective layer and the second protective layer are made of silicon dioxide. The width of each of the first waveguide, the second waveguide, and the arrayed waveguide is 3.5 microns. The n waveguides of the first waveguide have a pitch of 8 microns at the connection with the first coupler and the p waveguides of the second waveguide have a pitch of 8 microns at the connection with the second coupler. The m waveguides of the arrayed waveguide are each 10 microns apart at the connection with the first coupler and the second coupler. m 145, n 1, p 16. The first and second couplers each have a rowland circular structure with a diameter of 1.823 mm. A pre-widening device with a one-dimensional sub-wavelength grating is arranged between the first waveguide and the first coupler, and the pre-widening device is an MMI.

Fig. 13 is a schematic diagram of the output spectrum of the AWG provided by an embodiment of the present application, which includes spectra corresponding to 16 waveguides (also referred to as output channels) included in the second waveguide. In the graph of the output spectrum, the horizontal axis represents wavelength in μm, and the vertical axis represents power transmittance in dB. Due to the introduction of the sub-wavelength grating, the superposition of two bulges of a double-peak light field is effectively blocked, so that the sinking degree is larger. As shown in fig. 13, the spectral flatness of each of the second waveguides was good in the obtained output spectrum. For example, for a single optical signal, the 0.5dB bandwidth (referring to the frequency range defined by the 0.5dB drop from the highest point of the power spectral density) is 46GHz, the 1dB bandwidth is 53GHz, the 1dB bandwidth (referring to the frequency range defined by the 1dB drop from the highest point of the power spectral density) is 53% of the channel spacing, and the 3dB bandwidth is obviously greater than 53% of the channel spacing. Therefore, the 3dB bandwidth of the obtained flat-top spectrum can be greatly improved, and the insertion loss caused by the instability of the input optical signal is effectively reduced.

According to the AWG provided by the embodiment of the application, the flatness of the top end of the output spectrum of the AWG is higher due to the pre-broadening device with the sub-wavelength grating, the insertion loss caused by the wavelength deviation of an optical signal in the AWG can be reduced, the influence of the preparation error on the performance of the AWG device can be reduced, and the stability of the AWG device is improved.

In the related art, an AWG including a thermal modulation device disposed at an input end of the first waveguide, the thermal modulation device reducing a wavelength shift of the input optical signal by heating the first waveguide, is also proposed. But would increase the complexity of the AWG and increase the power consumption of the AWG. And temperature drift may also introduce insertion loss. The AWG provided by the embodiment of the application adjusts the flatness of the top end of the output spectrum of the AWG by using the output spectrum of the AWG. And an additional thermal regulation device is not required, so that the complexity of the AWG is reduced, the power consumption of the AWG is reduced, and the insertion loss caused by temperature drift is avoided.

In addition, the AWG provided by the embodiment of the application adjusts the flatness of the top end of the output spectrum of the AWG by adjusting the grating parameters of the sub-wavelength grating and matching with the pre-broadening device, has high design freedom degree and high compatibility, and can be applied to different substrate materials and optical waveguide materials. Moreover, by arranging the pre-broadening device with the sub-wavelength grating, the size of the whole AWG is hardly increased, the manufacturing cost is low, and the miniaturization of the AWG can be realized.

Fig. 14 and fig. 15 are schematic structural diagrams of two transmitters (also referred to as optical transmitters) 20 provided in the embodiments of the present application, respectively. The transmitter 20 includes: a light source 201, a modulator 202, and an AWG 203. The AWG203 may be any of the AWG10 provided by the embodiments of the present application.

In fig. 14 and 15, a light source 201, a modulator 202, and an AWG203 are connected in this order. Wherein, in the AWG203, the first waveguide includes a number n of waveguides greater than the number p of waveguides included in the second waveguide. For example, p is 1. In this way, the AWG203 multiplexes the plurality of optical signals into one optical signal.

In fig. 14 and 15, the light source 201 is configured to output an optical signal, and the modulator 202 is configured to modulate the received optical signal to obtain an optical signal with multiple wavelengths, and input the optical signal with multiple wavelengths to the AWG 203.

In an alternative implementation, as shown in fig. 14, the transmitter 20 includes a light source 201 and one or more modulators 202. The optical signal of a fixed wavelength output by the optical source 201 is modulated by one or more modulators 202 to obtain an optical signal of multiple wavelengths. In another alternative implementation, as shown in fig. 15, the transmitter 20 includes a plurality of light sources 201 and a plurality of modulators 202, and the plurality of light sources 201 are connected to the plurality of modulators 202 in a one-to-one correspondence. Different light sources 201 have different wavelengths, and the optical signal of a fixed wavelength output by each light source 201 is modulated by a corresponding modulator 202. The plurality of modulators 202 output optical signals of a plurality of wavelengths, and thereby input optical signals of a plurality of wavelengths to the AWG 203.

According to the transmitter provided by the embodiment of the application, the pre-broadening device with the sub-wavelength grating structure is additionally arranged between the first waveguide and the first coupler or between the second coupler and the second waveguide of the AWG, and the pre-broadening device is used for adjusting the flatness of the top end of the output spectrum of the AWG, so that the flat-top spectrum is finally output from the AWG, and the 3dB bandwidth of the flat-top spectrum is larger, so that the insertion loss caused by the wavelength shift of an optical signal can be effectively reduced, and the insertion loss of the transmitter is further reduced.

And because the insertion loss of the AWG is smaller, an additional wavelength control system is not needed, the manufacturing cost is reduced, and the size of the transmitter is reduced.

Fig. 16 is a schematic structural diagram of a receiver 30 according to an embodiment of the present disclosure. The receiver 30 includes: AWG301 and multiple receivers 302. The AWG301 may be any of the AWG10 provided by embodiments of the present application.

In fig. 16, the AWG301 is connected to a plurality of receivers 302, respectively, and the receivers 302 are configured to receive optical signals output from the AWG 301. In the AWG301, the first waveguide includes a number n of waveguides smaller than the number p of waveguides included in the second waveguide, and n is 1 as an example. Thus, one optical signal is demultiplexed into multiple optical signals by the AWG 301. As an example, AWG301 outputs a plurality of optical signals, which are input to different receivers 302, respectively.

According to the receiver provided by the embodiment of the application, the pre-broadening device with the sub-wavelength grating structure is additionally arranged between the first waveguide and the first coupler or between the second coupler and the second waveguide of the AWG, and the pre-broadening device is used for adjusting the flatness of the top end of the output spectrum of the AWG, so that the flat-top spectrum is finally output from the AWG, and the 3dB bandwidth of the flat-top spectrum is larger, so that the insertion loss caused by the wavelength shift of an optical signal can be effectively reduced, and the insertion loss of the receiver is further reduced.

And because the insertion loss of the AWG is smaller, an additional wavelength control system is not needed, the manufacturing cost is reduced, and the volume of the receiver is reduced.

Fig. 17 is a schematic structural diagram of an optical communication system 40 according to an embodiment of the present application. The optical communication system includes: a transmitter 401, a receiver 402, and an optical fiber 403 connected to the transmitter 401 and the receiver 402, respectively. The transmitter 401 may be the transmitter 20 in the previous embodiment; the receiver 402 may be the receiver 30 in the previous embodiment.

Fig. 18 is a schematic flow chart of a method for manufacturing AWG according to an embodiment of the present application. The manufacturing method comprises the following steps:

s501, determining grating parameters of the sub-wavelength grating, wherein the grating parameters comprise a grating period and/or a duty ratio.

As mentioned before, since the grating parameters of the sub-wavelength grating are related to the flatness of the top of the output spectrum of the AWG and the equivalent refractive index of the AWG, the determination of the grating parameters can be performed in the following two alternative implementations.

In a first alternative implementation, the grating parameters of the sub-wavelength grating are determined based on the flatness of the top end of the output spectrum of the AWG to be manufactured.

The higher the flatness of the top end of the output spectrum of the manufactured AWG, the smaller the insertion loss of the AWG due to the wavelength shift of the optical signal. Thus, before the AWG is manufactured, the grating parameters of the sub-wavelength grating can be determined based on the desired flatness of the top end of the output spectrum of the AWG. For example, a worker may employ simulation software to continually adjust grating parameters to observe changes in the flatness of the top end of the output spectrum of the AWG obtained by simulation. When the top of the output spectrum of the AWG obtained by simulation is approximately horizontal, the corresponding grating parameters are determined as those required for manufacturing the AWG. The concave degree of the double-peak light field is accurately regulated and controlled by adjusting the grating period and/or the duty ratio of the sub-wavelength grating, so that the input field distribution required by the AWG spectrum planarization design is met, and the required planarization of the AWG spectrum is realized.

As mentioned above, under the condition that the grating period is not changed, the larger the duty ratio is, the larger the equivalent refractive index of the AWG is; under the condition of unchanged duty ratio, the larger the grating period is, the larger the equivalent refractive index of the AWG is. The equivalent refractive index of the pre-broadening device is inversely related to the sinking degree of the double-peak light field, and correspondingly, the equivalent refractive index of the AWG is inversely related to the sinking degree of the double-peak light field under the condition that other parameters are not changed. Then, for example, before manufacturing the AWG, a worker may employ simulation software to keep the grating period constant and gradually decrease the duty cycle of the sub-wavelength grating. For example, the worker may start with a duty cycle of 1 (or 0.99) and gradually decrease the duty cycle. Thus, the equivalent refractive index of the AWG is gradually decreased (the equivalent refractive index of the pre-broadening device is also gradually decreased), and the degree of depression of the bimodal optical field is gradually increased. The staff can observe that the flatness of the output spectrum of the AWG is gradually increased, if the flatness reaches the maximum value, the duty ratio of the sub-wavelength grating is continuously reduced, so that the equivalent refractive index of the AWG is continuously reduced (the equivalent refractive index of the pre-broadening device is also gradually reduced), the depression degree of the double-peak light field is continuously increased, and the staff can observe that the flatness of the output spectrum of the AWG is gradually reduced. Therefore, the operator can record the corresponding relationship between the duty ratio of the sub-wavelength grating and the flatness of the output spectrum, find the flatness of the turning point (i.e. the turning point of increasing and decreasing) where the flatness turns after finding that the flatness of the output spectrum of the AWG is increased and decreased first, and then query the corresponding relationship based on the target flatness to determine the target duty ratio.

For another example, before the AWG is manufactured, the operator may also adjust the grating period by using simulation software to keep the duty cycle constant. Alternatively, the duty cycle and the grating period are adjusted simultaneously. The process of determining the grating parameters may refer to the process of determining the target duty ratio, which is not described in detail in this embodiment of the present application.

In a second alternative implementation, the grating parameters of the sub-wavelength grating are determined based on the equivalent refractive index of the AWG to be manufactured.

The higher the flatness of the top end of the output spectrum of the manufactured AWG, the smaller the insertion loss of the AWG due to the wavelength shift of the optical signal. The flatness of the top end of the output spectrum of the AWG is different, and the equivalent refractive index of the AWG is different. Thus, before the AWG is manufactured, the equivalent refractive index of the AWG can be determined based on the desired flatness of the top end of the output spectrum of the AWG. And determining the grating parameters of the sub-wavelength grating based on the equivalent refractive index of the AWG. For example, a worker may set a target flatness of the top end of the output spectrum (e.g., which may be determined based on the method provided in the first alternative implementation described above) and convert the target flatness of the top end of the output spectrum to a target equivalent refractive index of the AWG. Then, the simulation software is adopted to continuously adjust the grating parameters so as to observe the change of the equivalent refractive index of the AWG obtained by simulation. When the equivalent refractive index of the AWG obtained by simulation is equal to or approximate to the target equivalent refractive index, the corresponding grating parameters are determined as the grating parameters required for manufacturing the AWG. Since the equivalent refractive index of the pre-broadening device also affects the equivalent refractive index of the AWG, the flatness of the top end of the output spectrum can also be translated into the target equivalent refractive index of the pre-broadening device. Then, the simulation software is adopted to continuously adjust the grating parameters so as to observe the change of the equivalent refractive index of the pre-broadening device obtained by simulation. When the equivalent refraction rate of the pre-broadening device obtained by simulation is equal to or approximate to the target equivalent refraction rate, the corresponding grating parameters are determined as the grating parameters required for manufacturing the AWG.

It is worth noting that since the equivalent refractive index of the pre-broadening device affects the flatness of the top end of the output spectrum, which in turn is affected by the material and thickness, before the AWG is manufactured, the staff can also determine the target material and target thickness by adjusting the material and thickness of the pre-broadening device, so as to use the target material and target thickness in the manufacturing process for the AWG.

S502, providing a substrate.

By way of example, the substrate material may be lithium niobate, a group iii-v semiconductor compound, silicon nitride, silicon dioxide, silicon, a polymer, glass, or the like.

S503, manufacturing a first waveguide, a pre-broadening device, a first coupler, an array waveguide, a second coupler and a second waveguide on the substrate.

The array waveguide comprises m waveguides, the first waveguide comprises n waveguides, the second waveguide comprises p waveguides, m is a positive integer larger than 1, n and p are both positive integers, and n and p are different. The first waveguide is used for inputting n paths of optical signals to the first coupler, the first coupler is used for coupling the n paths of optical signals to the m waveguides for transmission, the second coupler is used for coupling the optical signals transmitted on the m waveguides to the p waveguides for transmission, and the second waveguide is used for outputting the p paths of optical signals; the pre-broadening device is located between the first waveguide and the first coupler or between the second coupler and the second waveguide, the region where the pre-broadening device is located is provided with sub-wavelength gratings which are arranged along the extending direction of the pre-broadening device, and the pre-broadening device is used for adjusting the flatness of the top end of the output spectrum of the AWG.

The first waveguide, the pre-widening device, the first coupler, the arrayed waveguide, the second coupler, and the second waveguide may be fabricated by one or more patterning processes (also referred to as photolithography processes). Illustratively, the manufacturing process includes: forming an optical waveguide material layer on a substrate by adopting a deposition, coating or sputtering process; performing a patterning process on the optical waveguide material layer once to obtain an AWG pattern, wherein the AWG pattern comprises: the waveguide array comprises a first waveguide, a pre-broadening device, a first coupler, an array waveguide, a second coupler and a second waveguide. Optionally, other structures may also be included in the aforementioned AWG pattern. The one-time composition process comprises the following steps: photoresist coating, exposure, development, etching and photoresist stripping. For example, in the patterning process, the etching process may be performed by a dry etching process.

Illustratively, the optical waveguide material may be silicon, silicon nitride, silicon oxynitride, or silicon dioxide.

In practical implementation, other material layers can be manufactured on the substrate according to practical situations. For example, the first protective layer may also be formed by a deposition, coating or sputtering process before the AWG pattern is fabricated on the substrate; alternatively, after the AWG pattern is fabricated on the substrate, a second protective layer may also be formed by deposition, coating, or sputtering process. The first protective layer and the second protective layer are used for protecting the AWG pattern so as to improve the service life of the AWG pattern. Illustratively, the materials of the first protective layer and the second protective layer are both silicon dioxide.

According to the manufacturing method of the AWG provided by the embodiment of the application, the pre-broadening device with the sub-wavelength grating structure is added between the first waveguide and the first coupler or between the second coupler and the second waveguide of the AWG, and the pre-broadening device is used for adjusting the flatness of the top end of the output spectrum of the AWG, so that the flat-top spectrum is finally output from the AWG, and the 3dB bandwidth of the flat-top spectrum is larger, so that the insertion loss caused by the wavelength shift of an optical signal can be effectively reduced.

The manufacturing method of the AWG is completely compatible with the traditional AWG manufacturing process, the pre-broadening device with the sub-wavelength grating structure can be synchronously manufactured with other devices in the AWG pattern through one or more composition processes, additional process steps are not needed to be added, the manufacturing process is simple, the implementation is easy, and the manufacturing cost is low.

In this application, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. The term "plurality" means two or more unless explicitly defined otherwise. "A refers to B" and means that A is the same as B or A is simply modified based on B.

It is noted that in the drawings, the sizes of layers and regions may be exaggerated for clarity of illustration. Also, it will be understood that when an element or layer is referred to as being "on" another element or layer, it can be directly on the other element or layer or intervening layers may also be present. In addition, it will be understood that when an element or layer is referred to as being "under" another element or layer, it can be directly under the other element or intervening layers or elements may also be present. In addition, it will also be understood that when a layer or element is referred to as being "between" two layers or elements, it can be the only layer between the two layers or elements, or more than one intermediate layer or element can also be present. Like reference numerals refer to like elements throughout.

It should be noted that: the AWG provided in the above embodiments, the manufacturing method, the transceiver, and the optical communication system embodiments belong to the same concept, and specific implementation processes thereof are described in the device embodiments and are not described herein again.

The above description is intended only to illustrate the alternative embodiments of the present application, and should not be construed as limiting the present application, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. An arrayed waveguide grating, comprising: the device comprises a first waveguide, a pre-broadening device, a first coupler, an array waveguide, a second coupler and a second waveguide;

the array waveguide comprises m waveguides, the first waveguide comprises n waveguides, the second waveguide comprises p waveguides, m is a positive integer larger than 1, n and p are both positive integers, and n and p are different;

the first waveguide is used for inputting n optical signals to the first coupler, the first coupler is used for coupling the n optical signals to the m waveguides for transmission, the second coupler is used for coupling the optical signals transmitted on the m waveguides to the p waveguides for transmission, and the second waveguide is used for outputting p optical signals;

the pre-broadening device is located between the first waveguide and the first coupler or between the second coupler and the second waveguide, a sub-wavelength grating arranged along the extending direction of the pre-broadening device is arranged in the area where the pre-broadening device is located, and the pre-broadening device is used for adjusting the flatness of the top end of the output spectrum of the arrayed waveguide grating.

2. The arrayed waveguide grating of claim 1, wherein the pre-broadening device is further provided with a sub-wavelength grating arranged along a first direction, and the first direction is perpendicular to an extending direction of the pre-broadening device.

3. The arrayed waveguide grating of claim 1 or 2, wherein the sub-wavelength grating is a uniform grating or a non-uniform grating.

4. The arrayed waveguide grating of any one of claims 1 to 3, wherein the flatness of the apex of the output spectrum of the arrayed waveguide grating is related to grating parameters of the sub-wavelength grating, the grating parameters including grating period and/or duty cycle.

5. The arrayed waveguide grating of any one of claims 1 to 3, wherein the equivalent refractive index of the arrayed waveguide grating is related to grating parameters of the sub-wavelength grating, and the equivalent refractive index of the arrayed waveguide grating is related to flatness of the top of the output spectrum of the arrayed waveguide grating, and the grating parameters comprise grating period and/or duty cycle.

6. The arrayed waveguide grating of any one of claims 1 to 5, wherein the pre-stretching device is an axisymmetric structure, and an axis of symmetry of the pre-stretching device is parallel to an extending direction of the pre-stretching device.

7. The arrayed waveguide grating of claim 6, wherein the pre-stretching device is a multimode interference MMI device or a Y-type structure.

8. The arrayed waveguide grating of claim 6, wherein the first waveguide is an axisymmetric structure, and an axis of symmetry of the pre-stretching device is aligned with an axis of symmetry of the first waveguide.

9. A transmitter, comprising: a light source, a modulator and an arrayed waveguide grating according to any one of claims 1 to 8;

the light source, the modulator and the arrayed waveguide grating are sequentially connected, and n is larger than p;

the light source is used for outputting optical signals, and the modulator is used for modulating received optical signals to obtain optical signals with multiple wavelengths and inputting the optical signals with the multiple wavelengths to the arrayed waveguide grating.

10. A receiver, comprising: an arrayed waveguide grating according to any one of claims 1 to 8 and a plurality of receivers;

the arrayed waveguide grating is respectively connected with the plurality of receivers, and n is smaller than p; the receiver is used for receiving the optical signal output by the arrayed waveguide grating.

11. An optical communication system, comprising: a transmitter according to claim 9, a receiver according to claim 10, and optical fibres connected to the transmitter and the receiver respectively.

12. A method of fabricating an arrayed waveguide grating, comprising:

providing a substrate;

manufacturing a first waveguide, a pre-broadening device, a first coupler, an array waveguide, a second coupler and a second waveguide on the substrate;

13. The method of claim 12, wherein prior to fabricating the first waveguide, the pre-widening device, the first coupler, the arrayed waveguide, the second coupler, and the second waveguide on the substrate, the method further comprises:

determining grating parameters of the sub-wavelength grating based on flatness of a top end of an output spectrum of the arrayed waveguide grating to be manufactured, the grating parameters including a grating period and/or a duty cycle.

14. The method of claim 12, wherein prior to fabricating the first waveguide, the pre-stretched device, the first coupler, the arrayed waveguide, the second coupler, and the second waveguide on the substrate, the method further comprises:

determining grating parameters of the sub-wavelength grating based on the equivalent refractive index of the arrayed waveguide grating to be manufactured, wherein the grating parameters comprise grating period and/or duty ratio.