阅读说明：本技术 可调谐激光源和包括可调谐激光源的光转向装置 (Tunable laser source and light steering device comprising a tunable laser source ) 是由 申东宰 边铉一 申昶均 于 2020-11-05 设计创作，主要内容包括：提供了一种可调谐激光源,其包括：多个光波导；至少三个光谐振器,设置在所述多个光波导之间并与所述多个光波导光耦合,所述至少三个光谐振器具有不同的长度；以及至少一个光放大器,设置在所述多个光波导中的至少一个上,其中,所述至少三个光谐振器中的第一光谐振器的第一长度与所述至少三个光谐振器中的第二光谐振器的第二长度的比不是整数。(There is provided a tunable laser source comprising: a plurality of optical waveguides; at least three optical resonators disposed between and optically coupled with the plurality of optical waveguides, the at least three optical resonators having different lengths; and at least one optical amplifier disposed on at least one of the plurality of optical waveguides, wherein a ratio of a first length of a first optical resonator of the at least three optical resonators to a second length of a second optical resonator of the at least three optical resonators is not an integer.)

1. A tunable laser source, comprising:

a plurality of optical waveguides;

at least three optical resonators disposed between and optically coupled with the plurality of optical waveguides, the at least three optical resonators having different lengths; and

at least one optical amplifier disposed on at least one of the plurality of optical waveguides,

wherein a ratio of a first length of a first optical resonator of the at least three optical resonators to a second length of a second optical resonator of the at least three optical resonators is not an integer.

2. The tunable laser source of claim 1, wherein the at least three optical resonators comprise:

a first ring resonator having a first circumference;

a second ring resonator having a second circumference greater than the first circumference; and

a third ring resonator having a third perimeter that is greater than the second perimeter.

3. The tunable laser source of claim 2, wherein a first ratio of the third perimeter to the first perimeter or a second ratio of the third perimeter to the second perimeter is not an integer.

4. The tunable laser source of claim 3, wherein the first ratio of the third perimeter to the first perimeter or the second ratio of the third perimeter to the second perimeter is a rational number having at least two bits after a decimal point.

5. The tunable laser source of claim 3, wherein the first ratio of the third perimeter to the first perimeter or the second ratio of the third perimeter to the second perimeter is an irrational number.

6. The tunable laser source of claim 2, wherein the difference between the first perimeter and the second perimeter is 1% to 10% of the first perimeter.

7. The tunable laser source of claim 2, further comprising a controller disposed at the first, second, and third ring resonators, respectively, the controller configured to adjust refractive indices of the first, second, and third ring resonators, respectively.

8. The tunable laser source of claim 2, further comprising at least one optical delay line disposed on at least one of the plurality of optical waveguides.

9. The tunable laser source of claim 2, further comprising at least one optical delay line disposed on at least one of the first, second, and third ring resonators.

10. The tunable laser source of claim 2, further comprising a fourth ring resonator optically coupled to the third ring resonator,

wherein a size of the fourth ring resonator is equal to a size of the third ring resonator.

11. The tunable laser source of claim 2, further comprising at least one phase shifter disposed on at least one of the plurality of optical waveguides.

12. The tunable laser source of claim 2, further comprising at least one monitoring device disposed on at least one output port of at least one of the plurality of optical waveguides.

13. The tunable laser source of claim 2, wherein the tunable laser source forms a closed loop resonator.

14. The tunable laser source of claim 2, wherein the tunable laser source forms a fabry-perot resonator.

15. The tunable laser source of claim 14, further comprising grating mirrors or sagnac mirrors disposed at both ends of the fabry-perot resonator.

16. A light redirecting device comprising:

a tunable laser source; and

a steering device configured to steer a laser beam incident from the tunable laser source,

wherein the tunable laser source comprises:

a plurality of optical waveguides;

at least three optical resonators disposed between and optically coupled with the plurality of optical waveguides, the at least three optical resonators having different lengths; and

at least one optical amplifier disposed on at least one of the plurality of optical waveguides,

wherein a ratio of a first length of a first optical resonator of the at least three optical resonators to a second length of a second optical resonator of the at least three optical resonators is not an integer.

17. The light redirecting device of claim 16, wherein the at least three optical resonators comprise: a first ring resonator having a first circumference; a second ring resonator having a second circumference greater than the first circumference; and a third ring resonator having a third perimeter greater than the second perimeter; and

a first ratio of the third perimeter to the first perimeter or a second ratio of the third perimeter to the second perimeter is not an integer.

18. The light redirecting apparatus of claim 16, wherein the tunable laser source further comprises at least one monitoring device disposed on at least one output port of at least one of the plurality of optical waveguides.

19. The light redirecting device of claim 16, further comprising a one-dimensional antenna array disposed in the light output portion of the redirecting apparatus.

20. The light redirecting device of claim 16, further comprising a detector configured to detect the laser beam redirected by the redirecting apparatus.

21. A tunable laser source, comprising:

a plurality of optical waveguides;

at least three optical resonators disposed between and optically coupled with the plurality of optical waveguides, the at least three optical resonators having different lengths; and

at least one optical amplifier disposed on at least one of the plurality of optical waveguides,

wherein a ratio of a first length of a first optical resonator of the at least three optical resonators to a second length of a second optical resonator of the at least three optical resonators is not an integer, an

Wherein at least one of the at least three optical resonators is disposed on one side of the at least one optical amplifier and at least two of the at least three optical resonators are disposed on an opposite side of the at least one optical amplifier.

Technical Field

Example embodiments of the present disclosure relate to tunable laser sources and light turning devices including tunable laser sources.

Background

Light sources are important components in integrated optical circuits in which optical elements are integrated. Light sources can be divided into single wavelength types and variable wavelength types (tunable types), and in particular, there is increasing interest in tunable laser sources as light sources for light-turning devices such as light detection and ranging (LiDAR) devices. When a single-wavelength light source is used as the light source of the light redirecting means, for two-dimensional optical scanning, an antenna array in which antennas are arranged two-dimensionally is required. However, when a tunable light source is used as the light source of the light turning device, two-dimensional optical scanning may be performed using an antenna array in which antennas are arranged one-dimensionally.

Disclosure of Invention

One or more example embodiments provide a tunable laser source and a light redirecting device that includes the tunable laser source.

Additional aspects will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the example embodiments.

According to an aspect of an example embodiment, there is provided a tunable laser source comprising: a plurality of optical waveguides; at least three optical resonators disposed between and optically coupled with the plurality of optical waveguides, the at least three optical resonators having different lengths; and at least one optical amplifier disposed on at least one of the plurality of optical waveguides, wherein a ratio of a first length of a first optical resonator of the at least three optical resonators to a second length of a second optical resonator of the at least three optical resonators is not an integer.

The at least three optical resonators may include a first ring resonator having a first circumference, a second ring resonator having a second circumference greater than the first circumference, and a third ring resonator having a third circumference greater than the second circumference.

A first ratio of the third perimeter to the first perimeter or a second ratio of the third perimeter to the second perimeter may not be an integer.

A first ratio of the third perimeter to the first perimeter or a second ratio of the third perimeter to the second perimeter may be a rational number having two or more bits after the decimal point.

A first ratio of the third perimeter to the first perimeter or a second ratio of the third perimeter to the second perimeter may be irrational.

The difference between the first circumference and the second circumference may be 1% to 10% of the first circumference.

The tunable laser source may further include a controller disposed on the first, second, and third ring resonators, respectively, the controller configured to adjust refractive indices of the first, second, and third ring resonators, respectively.

The tunable laser source may further comprise at least one optical delay line disposed on at least one of the plurality of optical waveguides.

The tunable laser source may further include at least one optical delay line disposed on at least one of the first, second, and third ring resonators.

The tunable laser source may further include a fourth ring resonator optically coupled to the third ring resonator, wherein a size of the fourth ring resonator is equal to a size of the third ring resonator.

The tunable laser source may further include at least one phase shifter disposed on at least one of the plurality of optical waveguides.

The tunable laser source may further comprise at least one monitoring device disposed on at least one output port of at least one of the plurality of optical waveguides.

The tunable laser source may form a closed loop resonator.

The tunable laser source may form a fabry-perot resonator.

The tunable laser source may further include grating mirrors or sagnac mirrors disposed at both ends of the fabry-perot resonator.

According to an aspect of another exemplary embodiment, there is provided a light redirecting apparatus including a tunable laser source, and a redirecting device configured to redirect a laser beam incident from the tunable laser source, wherein the tunable laser source includes: a plurality of optical waveguides; at least three optical resonators disposed between and optically coupled with the plurality of optical waveguides, the at least three optical resonators having different lengths; and at least one optical amplifier disposed on at least one of the plurality of optical waveguides, wherein a ratio of a first length of a first optical resonator of the at least three optical resonators to a second length of a second optical resonator of the at least three optical resonators is not an integer.

The at least three optical resonators may include a first ring resonator having a first circumference, a second ring resonator having a second circumference greater than the first circumference, and a third ring resonator having a third circumference greater than the second circumference, and a first ratio of the third circumference to the first circumference or a second ratio of the third circumference to the second circumference may not be an integer.

The tunable laser source may further comprise at least one monitoring device disposed on at least one output port of at least one of the plurality of optical waveguides.

The light redirecting means may further comprise a one-dimensional antenna array disposed in the light output portion of the redirecting device.

The light redirecting device may further comprise a detector configured to detect the laser beam redirected by the redirecting apparatus.

According to an aspect of another example embodiment, there is provided a tunable laser source comprising: a plurality of optical waveguides; at least three optical resonators disposed between and optically coupled with the plurality of optical waveguides, the at least three optical resonators having different lengths; and at least one optical amplifier disposed on at least one of the plurality of optical waveguides, wherein a ratio of a first length of a first optical resonator of the at least three optical resonators to a second length of a second optical resonator of the at least three optical resonators is not an integer, and wherein at least one optical resonator of the at least three optical resonators is disposed on one side of the at least one optical amplifier and at least two optical resonators of the at least three optical resonators are disposed on an opposite side of the at least one optical amplifier.

Drawings

The above and/or other aspects, features and advantages of the exemplary embodiments will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a tunable laser source according to an example embodiment;

fig. 2A, 2B and 2C are views illustrating optical loss differences according to a circumference ratio of a ring resonator of the tunable laser source illustrated in fig. 1;

FIG. 3 illustrates a tunable laser source according to another example embodiment;

FIG. 4 illustrates a tunable laser source according to another example embodiment;

FIG. 5 illustrates a tunable laser source according to another example embodiment;

FIG. 6 illustrates a tunable laser source according to another example embodiment;

FIG. 7 illustrates a tunable laser source according to another example embodiment;

FIG. 8 illustrates a tunable laser source according to another example embodiment;

FIG. 9 illustrates a tunable laser source according to another example embodiment;

FIG. 10 illustrates a tunable laser source according to another example embodiment;

FIG. 11 shows a tunable laser source according to another example embodiment; and

FIG. 12 illustrates a light redirecting device according to an example embodiment.

Detailed Description

Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, example embodiments may take different forms and should not be construed as limited to the descriptions set forth herein. Accordingly, the exemplary embodiments are described below merely by referring to the drawings to explain various aspects. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. Expressions such as "at least one of …" when following a list of elements modify the entire list of elements rather than modifying individual elements in the list. For example, the expression "at least one of a, b and c" should be understood to include only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b and c.

Hereinafter, example embodiments will be described with reference to the accompanying drawings. In the drawings, the size of elements may be exaggerated for clarity of illustration. The example embodiments described herein are for illustrative purposes only, and various modifications may be made therein.

In the following description, when an element is referred to as being "on" or "over" another element, it may be directly on the upper, lower, left or right sides of the other element while being in contact with the other element or may be on the upper, lower, left or right sides of the other element without being in contact with the other element. Unless otherwise mentioned, terms in the singular may include the plural. It will be further understood that the terms "comprises" and/or "comprising," when used herein, specify the presence of stated features or elements, but do not preclude the presence or addition of one or more other features or elements.

An element referred to by a definite article or an indicative word may be construed as one or more elements, even if it is in the singular. Unless explicitly described in terms of sequence or otherwise, the operations of the method may be performed in an appropriate order and are not limited to the order described.

In the present disclosure, terms such as "unit" or "module" may be used to denote a unit having at least one function or operation, and implemented in hardware, software, or a combination of hardware and software.

Furthermore, the line connections or connection means between the elements depicted in the figures represent functional connections and/or physical or circuit connections by way of example and, in practical applications, they may be replaced or implemented by various other functional, physical or circuit connections.

The examples or exemplary terms are used herein only to describe technical ideas and should not be taken as limiting purposes unless defined by the claims.

Fig. 1 shows a tunable laser source 100 according to an example embodiment. Fig. 1 shows a tunable laser source 100 of the on-chip type, in which all components are integrated on a substrate 110. The tunable laser source 100 may be, for example, a tunable laser diode.

The tunable laser source 100 shown in fig. 1 may generally form a closed-loop resonator. Referring to fig. 1, a tunable laser source 100 may include: a plurality of optical waveguides 111, 112 and 113, three or more optical resonators R1, R2 and R3 arranged between the optical waveguides 111, 112 and 113, and one or more optical amplifiers 121 and 122 disposed on the optical waveguides 111, 112 and 113.

The optical waveguides 111, 112, and 113, the three or more optical resonators R1, R2, and R3, and the one or more optical amplifiers 121 and 122 may be integrated on the substrate 110 by a semiconductor process. Here, the substrate 110 may be a semiconductor substrate such as a silicon substrate, but the substrate 110 is not limited thereto.

The optical waveguides 111, 112, and 113 may include a first optical waveguide 111, a second optical waveguide 112, and a third optical waveguide 113 separated from each other. The first, second, and third optical waveguides 111, 112, and 113 may be arranged side by side, but are not limited thereto. The first optical waveguide 111, the second optical waveguide 112, and the third optical waveguide 113 may include, for example, silicon. However, this is merely an example, and the first, second, and third optical waveguides 111, 112, and 113 may include various other materials.

The three or more optical resonators R1, R2, and R3 may include a first ring resonator R1, a second ring resonator R2, and a third ring resonator R3. For example, the first ring resonator R1 may be disposed between the first optical waveguide 111 and the second optical waveguide 112. Here, the first ring resonator R1 may be physically separated from the first and second optical waveguides 111 and 112, but may be optically coupled to the first and second optical waveguides 111 and 112. The first ring resonator R1 may be physically separated from the first and second optical waveguides 111 and 112 by about 0.1 μm to about 1 μm, but the embodiment is not limited thereto.

The second ring resonator R2 may be disposed between the second optical waveguide 112 and the third optical waveguide 113. Here, the second ring resonator R2 may be physically separated from the second and third optical waveguides 112 and 113, but may be optically coupled to the second and third optical waveguides 112 and 113. The second ring resonator R2 may be physically separated from the second and third optical waveguides 112 and 113 by about 0.1 μm to about 1 μm, but the embodiment is not limited thereto.

The third ring resonator R3 may be disposed between the first optical waveguide 111 and the third optical waveguide 113. Here, the third ring resonator R3 may be physically separated from the first optical waveguide 111 and the third optical waveguide 113, but may be optically coupled to the first optical waveguide 111 and the third optical waveguide 113. The third ring resonator R3 may be physically separated from the first and third optical waveguides 111 and 113 by about 0.1 μm to about 1 μm, but the embodiment is not limited thereto.

Each of the first, second, and third ring resonators R1, R2, and R3 may have a circular shape or various other ring shapes. The first, second, and third ring resonators R1, R2, and R3 may have different lengths, for example, different circumferences. For example, the first ring resonator R1 may have a first circumference L1, the second ring resonator R2 may have a second circumference L2 larger than the first circumference L1, and the third ring resonator R3 may have a third circumference L3 larger than the second circumference L2. For example, each of the first, second, and third ring resonators R1, R2, and R3 may have a circumference of about several tens of micrometers (μm) or about several hundreds of micrometers (μm). However, the embodiment is not limited thereto, and each of the first, second, and third ring resonators R1, R2, and R3 may have various other circumferences.

The difference between the first perimeter L1 and the second perimeter L2 may depend on a variable wavelength range. For example, the difference between the first perimeter L1 and the second perimeter L2 may be about 1% to about 10% of the first perimeter L1. However, the embodiments are not limited thereto. Further, as described later, when the ratio L3/L1 of the third circumference L3 to the first circumference L1 or the ratio L3/L2 of the third circumference L3 to the second circumference L2 is designed as a number other than an integer, mode selectivity can be improved.

The controllers 151, 152, and 153 may be disposed near the first, second, and third ring resonators R1, R2, and R3, respectively, to adjust refractive indexes of the first, second, and third ring resonators R1, R2, and R3. For example, a first controller 151 configured to adjust the refractive index of the first ring resonator R1 may be disposed near the first ring resonator R1, a second controller 152 configured to adjust the refractive index of the second ring resonator R2 may be disposed near the second ring resonator R2, and a third controller 153 configured to adjust the refractive index of the third ring resonator R3 may be disposed near the third ring resonator R3. In the example shown in fig. 1, the controllers 151, 152, and 153 are disposed inside the ring resonators R1, R2, and R3. However, the embodiment is not limited thereto, and various modifications may be made to the positions of the controllers 151, 152, 153.

The first controller 151, the second controller 152, and the third controller 153 may control refractive indexes of the first, second, and third ring resonators R1, R2, and R3, respectively, so that a resonance wavelength comb of each of the first, second, and third ring resonators R1, R2, and R3 may be horizontally moved along a wavelength axis to realize a variable wavelength, as described later.

For example, the controllers 151, 152, and 153 may include: a heating element configured to change refractive indices of the ring resonators R1, R2, and R3 by heating the ring resonators R1, R2, and R3; an electrode element configured to change the refractive index of the ring resonators R1, R2, and R3 by applying an electric field around the ring resonators R1, R2, and R3; or a piezoelectric element configured to change the refractive index of the ring resonators R1, R2, and R3 by deforming the ring resonators R1, R2, and R3.

The one or more optical amplifiers 121 and 122 may include a first optical amplifier 121 and a second optical amplifier 122 disposed on the optical waveguides 111, 112, and 113. In the example shown in fig. 1, the first optical amplifier 121 is disposed on the first optical waveguide 111, and the second optical amplifier 122 is disposed on the third optical waveguide 113. However, the embodiment is not limited thereto, and the number and the position of the optical amplifiers may be variously determined. The first and second ring resonators R1 and R2 may be disposed at one side of the first and second optical amplifiers 121 and 122, and the third ring resonator R3 may be disposed at the other side of the first and second optical amplifiers 121 and 122.

The first optical amplifier 121 and the second optical amplifier 122 may be configured to amplify light and also configured to generate light. Each of the first optical amplifier 121 and the second optical amplifier 122 may include, for example, a semiconductor optical amplifier. For example, a semiconductor optical amplifier may be formed by depositing a layer of material comprising a III-V semiconductor or a II-VI semiconductor over an optical waveguide comprising silicon. However, the embodiment is not limited thereto, and each of the first and second optical amplifiers 121 and 122 may include an ion-doped amplifier.

The light generated by at least one of the first optical amplifier 121 and the second optical amplifier 122 may be amplified while propagating clockwise or counterclockwise through the first, second, and third ring resonators R1, R2, and R3 in the closed-loop resonator shown in fig. 1, and may then be output at a desired resonance wavelength. Fig. 1 shows an example in which the amplified laser beam L is output to the outside through the main output port of the first optical waveguide 111.

In general, the ring resonator has a resonance wavelength comb including resonance wavelengths arranged at intervals determined depending on the circumference of the ring resonator. When a plurality of ring resonators having different circumferences are combined with each other, a plurality of resonance wavelength combs having different intervals are generated, and of these resonance wavelength combs, only a first oscillation mode in which a first resonance wavelength is arranged can be selected to oscillate a single-mode laser beam. Further, by adjusting the refractive index of the at least one ring resonator, the at least one resonant wavelength comb can be horizontally moved along the wavelength axis, and thus a second oscillation mode in which the second resonant wavelength is arranged can be selected instead of the first oscillation mode, thereby realizing a tunable laser source.

In tunable laser sources, high mode selectivity is required for stable single mode oscillations. The mode selectivity may be determined by an optical gain difference or an optical loss difference between an oscillation mode as the most advantageous oscillation mode and a competition mode as the second most advantageous oscillation mode. Assuming that the optical gain is independent of wavelength, the mode selectivity can be determined by the optical loss difference between the oscillating mode and the competing mode.

In the oscillation mode, all resonant wavelengths are aligned, while in the competition mode, at least some resonant wavelengths are misaligned. Therefore, an optical loss difference occurs between the oscillation mode and the competition mode, and as the optical loss difference increases, the mode selectivity may increase.

The mode selectivity of the tunable laser source 100 of the example embodiment may be improved by adjusting the first circumference L1 of the first ring resonator R1, the second circumference L2 of the second ring resonator R2, and the third circumference L3 of the third ring resonator R3.

As described above, the first, second, and third ring resonators R1, R2, and R3 may have first, second, and third circumferences L1, L2, and L3, respectively. Here, when the ratio L3/L1 of the third circumference L3 of the third ring resonator R3 to the first circumference L1 of the first ring resonator R1 or the ratio L3/L2 of the third circumference L3 of the third ring resonator R3 to the second circumference L2 of the second ring resonator R2 are designed as a number other than an integer, the mode selectivity of the tunable laser light source 100 can be improved as described later.

Fig. 2A to 2C are views illustrating optical loss differences according to the circumferential ratios of the ring resonators R1, R2, and R3 of the tunable laser source 100 shown in fig. 1. In the example shown in fig. 2A to 2C, the difference between the first circumference L1 of the first ring resonator R1 and the second circumference L2 of the second ring resonator R2 is 1% to 10% of the first circumference L1.

Fig. 2A shows a wavelength comb of the first, second, and third ring resonators R1, R2, and R3, and a wavelength comb of a combination of the first, second, and third ring resonators R1, R2, and R3 when the third circumference L3 of the third ring resonator R3 is twice the first circumference L1 of the first ring resonator R1, wherein the ratio L3/L1 of the third circumference L3 to the first circumference L1 is 2.

Fig. 2B shows a wavelength comb of the first, second, and third ring resonators R1, R2, and R3, and a wavelength comb of a combination of the first, second, and third ring resonators R1, R2, and R3 when the third circumference L3 of the third ring resonator R3 is three times the first circumference L1 of the first ring resonator R1, wherein the ratio L3/L1 of the third circumference L3 to the first circumference L1 is 3.

Fig. 2C shows a wavelength comb of the first, second, and third ring resonators R1, R2, and R3, and a wavelength comb of a combination of the first, second, and third ring resonators R1, R2, and R3 when the third circumference L3 of the third ring resonator R3 is 2.5 times the first circumference L1 of the first ring resonator R1, wherein a ratio L3/L1 of the third circumference L3 to the first circumference L1 is 2.5.

Referring to fig. 2A to 2C, the optical loss difference Δ H3 between the oscillation mode and the competition mode when the ratio L3/L1 of the third circumference L3 to the first circumference L1 is 2.5 is greater than the optical loss difference Δ H1 when the ratio L3/L1 of the third circumference L3 to the first circumference L1 is 2 and the optical loss difference Δ H2 when the ratio L3/L1 of the third circumference L3 to the first circumference L1 is 3.

In the simulation experiment, the optical loss difference was measured while changing the ratio L3/L1 of the third circumference L3 of the third ring resonator R3 to the first circumference L1 of the first ring resonator R1. In the simulation experiment, the difference between the first circumference L1 of the first ring resonator R1 and the second circumference L2 of the second ring resonator R2 was set to 1% to 10% of the first circumference L1.

When only the first and second ring resonators R1 and R2 are combined with each other, the optical loss difference between the oscillation mode and the competition mode is measured as low as about 11dB to about 14 dB. This indicates that the mode selectivity may be relatively low when only two ring resonators are used.

When the ratio of the third circumference L3 to the first circumference L1, L3/L1, was set to 2 and 3, the optical loss difference between the oscillation mode and the competition mode was measured to be about 12dB to about 16 dB. This shows that when the ratio L3/L1 of the third circumference L3 to the first circumference L1 is set to an integer in the tunable laser source 100 including three ring resonators R1, R2, and R3, the mode selectivity of the tunable laser source 100 can be as low as the case where only two ring resonators are used.

When the ratio L3/L1 of the third circumference L3 to the first circumference L1 was set to 2.5, the optical loss difference between the oscillation mode and the competition mode was measured to be about 16dB to about 20 dB. This shows that when the ratio L3/L1 of the third circumference L3 to the first circumference L1 is set to a non-integer in the tunable laser source 100 including the three ring resonators R1, R2, and R3, the mode selectivity of the tunable laser source 100 can be improved as compared with the case where the ratio L3/L1 is an integer.

When the ratio L3/L1 of the third circumference L3 to the first circumference L1 is set to 2.25 and 2.75, the optical loss difference between the oscillation mode and the competition mode is measured to be about 24dB to about 28 dB. When the ratio of the third circumference L3 to the first circumference L1, L3/L1, was set to 2.225 and 2.275, the optical loss difference between the oscillation mode and the competition mode was measured to be about 32dB to about 37 dB.

These results show that the mode selectivity of the tunable laser source 100 is further improved when the ratio L3/L1 of the third circumference L3 to the first circumference L1 of the tunable laser source 100 including three ring resonators, R2 and R3 is set to a rational number having two or more bits after a decimal point. Furthermore, these results show that the mode selectivity improves with increasing number of bits after decimal point. Therefore, when the ratio L3/L1 of the third circumference L3 to the first circumference L1 of the tunable laser source 100 including the three ring resonators R1, R2, and R3 is set as an irrational number, the tunable laser source 100 can have improved mode selectivity.

Although the above description has been given only with respect to the ratio L3/L1 of the third circumference L3 of the third ring resonator R3 to the first circumference L1 of the first ring resonator R1, the above description may be applied to the ratio L3/L2 of the third circumference L3 of the third ring resonator R3 to the second circumference L2 of the second ring resonator R2. For example, when the ratio L3/L2 of the third circumference L3 of the third ring resonator R3 to the second circumference L2 of the second ring resonator R2 is designed to be a non-integer, the mode selectivity can be improved.

Tunable laser sources used in light-redirecting devices, such as light detection and ranging (LiDAR) devices, may have a large coherence length when the spectral linewidth in the oscillating mode of the tunable laser source is small, and in such cases, the tunable laser source may be capable of remote detection. Since the spectral line width in the oscillation mode of the resonator is approximately inversely proportional to the square of the total length of the resonator, the spectral line width decreases as the total length of the resonator increases.

The tunable laser source 100 of the exemplary embodiment may include one or more optical delay lines 130 disposed on the optical waveguides 111, 112, and 113 to reduce the spectral linewidth in the oscillation mode. Fig. 1 shows an example in which one optical delay line 130 is provided on the first optical waveguide 111. However, the embodiment is not limited thereto, and the number and position of the optical delay lines 130 may be variously determined. The optical delay line 130 may have a function of reducing a spectral line width in an oscillation mode by increasing the total length of the entire resonator as a closed-loop resonator. The optical delay line 130 may comprise, for example, a spiral waveguide.

Tunable laser source 100 may also include one or more phase shifters 140 disposed on optical waveguides 111, 112, and 113. In this case, when the phase of the entire resonator, which is a closed-loop resonator, is different from the phases of the ring resonators R1, R2, and R3, the phase shifter 140 may compensate for the phase difference. Although fig. 1 shows an example in which one phase shifter 140 is disposed on the third optical waveguide 113, the number and position of the phase shifters 140 may be determined differently.

As described above, the tunable laser source 100 of the example embodiment includes three ring resonators having different circumferences, for example, the first ring resonator R1, the second ring resonator R2, and the third ring resonator R3, and the ratio L3/L1 of the third circumference L3 of the third ring resonator R3 to the first circumference L1 of the first ring resonator R1 or the ratio L3/L2 of the third circumference L3 of the third ring resonator R3 to the second circumference L2 of the second ring resonator R2 may be adjusted to a non-integer to improve the mode selectivity of the tunable laser source 100 and thus achieve a stable single oscillation mode.

Further, the total length of the entire resonator can be increased by providing one or more optical delay lines 130 on the optical waveguides 111, 112, and 113, and thus the spectral line width in the oscillation mode can be reduced. Furthermore, all components of the tunable laser source 100 may be integrated on a single substrate (e.g., substrate 110), and thus the tunable laser source 100 may be implemented as an on-chip device.

Fig. 3 shows a tunable laser source 200 according to another example embodiment. The tunable laser source 200 shown in fig. 3 is identical to the tunable laser source 100 shown in fig. 1, except for the position of the optical delay line 230.

Referring to fig. 3, the tunable laser source 200 may include one or more optical delay lines 230 disposed in a plurality of ring resonators R1, R2, and R3 including a first ring resonator R1, a second ring resonator R2, and a third ring resonator R3. Here, the optical delay line 230 may include, for example, a spiral waveguide. Fig. 3 shows an example in which one optical delay line 230 is provided in the third ring resonator R3. However, the embodiment is not limited thereto, and the optical delay line 230 may be disposed in the first ring resonator R1 or the second ring resonator R2. In addition, the number and positions of the optical delay lines 230 may be determined differently.

Even when the optical delay line 230 provided in the ring resonators R1, R2, and R3 of the tunable laser source 200 is shorter than the optical delay line 130 provided on the optical waveguides 111, 112, and 113 of the tunable laser source 100 shown in fig. 1, the spectral line width in the oscillation mode of the tunable laser source 200 can be reduced as much as the spectral line width in the oscillation mode of the tunable laser source 100. Accordingly, the tunable laser source 200 may have a smaller size than the tunable laser source 100 shown in FIG. 1.

Fig. 4 shows a tunable laser source 300 according to another example embodiment. Tunable laser source 300 shown in FIG. 4 is the same as tunable laser source 100 shown in FIG. 1, except for monitoring devices 171 through 175.

Referring to FIG. 4, the tunable laser source 300 may include one or more monitoring devices including a first monitoring device 171, a second monitoring device 172, a third monitoring device 173, a fourth monitoring device 174, and a fifth monitoring device 175. In this case, one or more monitoring devices 171 to 175 may be disposed on auxiliary output ports of the plurality of optical waveguides 111, 112 and 113 other than the main output ports of the optical waveguides 111, 112 and 113, wherein the amplified laser beam L is output through the main output ports of the optical waveguides 111, 112 and 113. The one or more monitoring devices 171 to 175 may measure the amount of light output from the auxiliary output ports of the optical waveguides 111, 112, and 113 to monitor the wavelength alignment between the first ring resonator R1, the second ring resonator R2, and the third ring resonator R3. Although fig. 4 shows an example in which five monitoring devices 171 to 175 are provided, the embodiment is not limited thereto, and the number of monitoring devices 171 to 175 may be determined differently.

In fig. 4, one end of the first optical waveguide 111, both ends of the second optical waveguide 112, and both ends of the third optical waveguide 113 may correspond to auxiliary output ports. Further, the other end of the first optical waveguide 111 may correspond to a main output port through which the amplified laser beam L is output.

The first and second monitoring devices 171 and 172 may be disposed at both ends of the third optical waveguide 113, and the third and fourth monitoring devices 173 and 174 may be disposed at both ends of the second optical waveguide 112. Further, a fifth monitoring device 175 may be disposed at one end of the first optical waveguide 111. Each of the first to fifth monitoring devices 171 to 175 may include, for example, a photodiode.

The first and second monitoring devices 171 and 172 may monitor the wavelength alignment between the second and third ring resonators R2 and R3, and the third and fourth monitoring devices 173 and 174 may monitor the wavelength alignment between the first and second ring resonators R1 and R2. In addition, the fifth monitoring device 175 may monitor the wavelength alignment between the first ring resonator R1 and the third ring resonator R3.

As described above, since the monitoring devices 171 to 175 are provided on the auxiliary output ports of the optical waveguides 111, 112, and 113 to monitor the wavelength alignment between the ring resonators R1, R2, and R3, on-chip control is possible.

Tunable laser source 300 may include one or more optical delay lines 130 disposed on optical waveguides 111, 112, and 113.

Fig. 5 shows a tunable laser source 400 according to another example embodiment. The tunable laser source 400 shown in fig. 5 is identical to the tunable laser source 300 shown in fig. 4, except for the position of the optical delay line 230. Referring to fig. 5, the tunable laser source 400 may include one or more optical delay lines 230 disposed in the plurality of ring resonators R1, R2, and R3.

Fig. 6 shows a tunable laser source 500 according to another example embodiment. The tunable laser source 500 shown in fig. 6 may generally form a closed-loop resonator.

Referring to fig. 6, the first optical waveguide 511, the second optical waveguide 512, and the third optical waveguide 513 are disposed apart from each other, and four ring resonators, for example, a first ring resonator R1, a second ring resonator R2, a third ring resonator R3, and a fourth ring resonator R4, are disposed between the first optical waveguide 511, the second optical waveguide 512, and the third optical waveguide 513.

The first ring resonator R1 may be disposed between the first optical waveguide 511 and the second optical waveguide 512, and the second ring resonator R2 may be disposed between the second optical waveguide 512 and the third optical waveguide 513. Here, the first and second ring resonators R1 and R2 may be physically separated from the first, second, and third optical waveguides 511, 512, and 513, but may be optically coupled with the first, second, and third optical waveguides 511, 512, and 513.

The third ring resonator R3 may be disposed between the first optical waveguide 511 and the third optical waveguide 513. Here, the third ring resonator R3 may be physically separated from the first and third optical waveguides 511 and 513, but may be optically coupled to the first and third optical waveguides 511 and 513.

The fourth ring resonator R4 may be disposed between the first optical waveguide 511 and the third optical waveguide 513 adjacent to the third ring resonator R3. Here, the fourth ring resonator R4 may be physically separated from the third ring resonator R3, but may be optically coupled with the third ring resonator R3. In addition, the fourth ring resonator R4 may be physically and optically separated from the first optical waveguide 511 and the third optical waveguide 513.

In an example embodiment, similar to the optical delay lines 130 and 230 described above, the fourth ring resonator R4 may have a function of reducing a spectral line width by increasing the total length of the entire resonator as a closed-loop resonator. The fourth ring resonator R4 may have the same size and resonance wavelength as the third ring resonator R3. Accordingly, the light resonated in the third ring resonator R3 may be resonated in the fourth ring resonator R4, thereby increasing the overall length of the entire resonator and reducing the spectral line width of the laser beam output from the tunable laser source 500.

The first, second, and third ring resonators R1, R2, and R3 may have different circumferences from one another. For example, the first ring resonator R1 may have a first circumference L1, the second ring resonator R2 may have a second circumference L2 larger than the first circumference L1, and the third ring resonator R3 may have a third circumference L3 larger than the second circumference L2.

The difference between the first circumference L1 and the second circumference L2 may be about 1% to about 10% of the first circumference L1, but the embodiment is not limited thereto. Further, when the ratio of the third circumference L3 to the first circumference L1, L3/L1 or the ratio of the third circumference L3 to the second circumference L2, L3/L2 is designed as a number other than an integer, mode selectivity can be improved.

The first controller 551, the second controller 552, the third controller 553, and the fourth controller 554 may be disposed near the first ring resonator R1, the second ring resonator R2, the third ring resonator R3, and the fourth ring resonator R4 to adjust refractive indices of the first ring resonator R1, the second ring resonator R2, the third ring resonator R3, and the fourth ring resonator R4. Here, each of the controllers 551, 552, 553, and 554 may include, for example, a heating element, an electrode element, or a piezoelectric element.

One or more optical amplifiers 521 and 522 may be disposed on the first, second, and third optical waveguides 511, 512, and 513. In the example shown in fig. 6, a first optical amplifier 521 is provided on the first optical waveguide 511, and a second optical amplifier 522 is provided on the third optical waveguide 513. Here, the first and second ring resonators R1 and R2 may be disposed at one side of the first and second optical amplifiers 521 and 522, and the third and fourth ring resonators R3 and R4 may be disposed at the other side of the first and second optical amplifiers 521 and 522.

At least one phase shifter 540 may also be disposed on the first, second, and third optical waveguides 511, 512, and 513. Fig. 6 shows an example in which one phase shifter 540 is disposed on the third optical waveguide 513, but the embodiment is not limited thereto and the number and position of the phase shifters 540 may be variously determined.

FIG. 7 illustrates a tunable laser source 600 according to another example embodiment. The tunable laser source 600 shown in FIG. 7 is the same as the tunable laser source 500 shown in FIG. 6, except for the monitoring devices 571-575.

Referring to fig. 7, one or more monitoring devices, for example, a first monitoring device 571, a second monitoring device 572, a third monitoring device 573, a fourth monitoring device 574, and a fifth monitoring device 575, may be disposed on the first optical waveguide 511, the second optical waveguide 512, and the third optical waveguide 513. For example, one or more monitoring devices 571 to 575 may be provided on the auxiliary output ports of the first optical waveguide 511, the second optical waveguide 512 and the third optical waveguide 513.

A first monitoring device 571 and a second monitoring device 572 may be disposed at both ends of the third optical waveguide 513 to monitor wavelength alignment between the second ring resonator R2 and the third ring resonator R3. Third and fourth monitoring devices 573 and 574 can be disposed at both ends of the second optical waveguide 512 to monitor wavelength alignment between the first and second ring resonators R1 and R2. Further, a fifth monitoring device 575 may be provided at one end of the first optical waveguide 511 to monitor the wavelength alignment between the first ring resonator R1 and the third ring resonator R3.

FIG. 8 illustrates a tunable laser source 700 according to another example embodiment. The tunable laser source 700 shown in fig. 8 may generally form a fabry-perot resonator.

Referring to fig. 8, a first optical waveguide 711, a second optical waveguide 712, a third optical waveguide 713, and a fourth optical waveguide 714 are disposed apart from each other, and a first ring resonator R1, a second ring resonator R2, and a third ring resonator R3 are disposed between the first optical waveguide 711, the second optical waveguide 712, the third optical waveguide 713, and the fourth optical waveguide 714.

The first ring resonator R1 may be disposed between the first optical waveguide 711 and the second optical waveguide 712, the second ring resonator R2 may be disposed between the second optical waveguide 712 and the third optical waveguide 713, and the third ring resonator R3 may be disposed between the third optical waveguide 713 and the fourth optical waveguide 714. Here, the first, second, and third ring resonators R1, R2, and R3 may be physically separated from the first, second, third, and fourth optical waveguides 711, 712, 713, and 714, but may be optically coupled with the first, second, third, and fourth optical waveguides 711, 712, 713, and 714. For example, the first, second, and third ring resonators R1, R2, and R3 may be physically separated from the first, second, third, and fourth optical waveguides 711, 712, 713, and 714 by about 0.1 μm to about 1 μm, but the embodiment is not limited thereto.

The first, second, and third ring resonators R1, R2, and R3 may have different circumferences from one another. For example, the first ring resonator R1 may have a first circumference L1, the second ring resonator R2 may have a second circumference L2 larger than the first circumference L1, and the third ring resonator R3 may have a third circumference L3 larger than the second circumference L2.

The difference between the first circumference L1 and the second circumference L2 may be about 1% to about 10% of the first circumference L1, but the embodiment is not limited thereto. Further, when the ratio of the third circumference L3 to the first circumference L1, L3/L1 or the ratio of the third circumference L3 to the second circumference L2, L3/L2 is designed as a number other than an integer, mode selectivity can be improved. The first control section 751, the second control section 752, and the third control section 753 may be disposed near the first ring resonator R1, the second ring resonator R2, and the third ring resonator R3 to adjust refractive indices of the first ring resonator R1, the second ring resonator R2, and the third ring resonator R3.

One or more optical amplifiers 720 may be disposed on the first optical waveguide 711, the second optical waveguide 712, the third optical waveguide 713, and the fourth optical waveguide 714. Fig. 8 shows an example in which one optical amplifier 720 is provided on the first optical waveguide 711. Here, the first, second, and third ring resonators R1, R2, and R3 may be disposed at one side of the optical amplifier 720.

At least one optical delay line 730 may be disposed on the first optical waveguide 711, the second optical waveguide 712, the third optical waveguide 713, and the fourth optical waveguide 714. Fig. 8 shows an example in which one optical delay line 730 is provided on the first optical waveguide 711. The optical delay line 730 may have a function of reducing a spectral line width in an oscillation mode by increasing the total length of the entire resonator as a fabry-perot resonator. The optical delay line 730 may comprise, for example, a spiral waveguide. At least one phase shifter 740 may be further disposed on the first optical waveguide 711, the second optical waveguide 712, the third optical waveguide 713, and the fourth optical waveguide 714. Fig. 8 shows an example in which one phase shifter 740 is provided on the first optical waveguide 711.

The first and second grating mirrors 781 and 782 may be disposed at both ends of the entire resonator as a fabry-perot resonator. For example, the first grating mirror 781 may be disposed at one end of the first optical waveguide 711, and the second grating mirror 782 may be disposed at one end of the fourth optical waveguide 714. Each of the first and second grating mirrors 781 and 782 may be a highly reflective mirror on which a grating pattern is periodically arranged at predetermined intervals. Here, the period of the grating pattern may be related to the wavelength of light propagating in the first optical waveguide 711, the second optical waveguide 712, the third optical waveguide 713, and the fourth optical waveguide 714, and may be, for example, about 100nm to about 500 nm. However, the embodiments are not limited thereto.

The light generated by the optical amplifier 720 may be amplified while reciprocating between the first and second grating mirrors 781 and 782 by the first, second, and third ring resonators R1, R2, and R3, and then may be output at a desired resonance wavelength. Fig. 8 shows an example in which the amplified laser beam L is output to the outside through the main output port of the fourth optical waveguide 714.

The tunable laser source 700 of the example embodiment includes three ring resonators having different circumferences, for example, a first ring resonator R1, a second ring resonator R2, and a third ring resonator R3, and a ratio L3/L1 of a third circumference L3 of the third ring resonator R3 to a first circumference L1 of the first ring resonator R1 or a ratio L3/L2 of a third circumference L3 of the third ring resonator R3 to a second circumference L2 of the second ring resonator R2 may be adjusted to be non-integer to improve mode selectivity and thus achieve a stable single oscillation mode.

Further, the total length of the entire resonator can be increased based on one or more optical delay lines 730 disposed on the first optical waveguide 711, the second optical waveguide 712, the third optical waveguide 713, and the fourth optical waveguide 714, and thus the spectral line width in the oscillation mode can be reduced. Furthermore, all components of the tunable laser source 700 may be integrated on a single substrate (e.g., substrate 110), and thus the tunable laser source 700 may be implemented as an on-chip device.

The above description has given the case where the first grating mirror 781 and the second grating mirror 782 are respectively provided at both ends of the fabry-perot resonator. However, the embodiments are not limited thereto. For example, Sagnac mirrors (Sagnac mirrors) may be provided at both ends of the fabry-perot resonator.

FIG. 9 illustrates a tunable laser source 800 according to another example embodiment. The tunable laser source 800 shown in fig. 9 is the same as the tunable laser source 700 shown in fig. 8 except for the position of the optical delay line 830.

Referring to fig. 9, at least one optical delay line 830 may be disposed in a plurality of ring resonators R1, R2, and R3 including a first ring resonator R1, a second ring resonator R2, and a third ring resonator R3. Fig. 9 shows an example in which one optical delay line 830 is provided in the third ring resonator R3. Thus, the tunable laser source 800 may be smaller than the tunable laser source 700 shown in FIG. 8.

FIG. 10 illustrates a tunable laser source 900 according to another example embodiment. The tunable laser source 900 shown in fig. 10 is the same as the tunable laser source 700 shown in fig. 8, except for the monitoring devices 971 to 977.

Referring to FIG. 10, tunable laser source 900 can include one or more monitoring devices, such as first 971, second 972, third 973, and fourth 974, fifth 975, sixth 976, and seventh 977 monitoring devices. In this case, one or more monitoring devices 971 to 977 may be disposed on auxiliary output ports of the plurality of optical waveguides 711, 712, 713, and 714 other than the main output ports of the optical waveguides 711, 712, 713, and 714, where the amplified laser beam L is output through the main output ports of the optical waveguides 711, 712, 713, and 714. Fig. 10 shows an example in which first to seventh monitoring devices 971 to 977 are provided on auxiliary output ports of the first optical waveguide 711, the second optical waveguide 712, the third optical waveguide 713, and the fourth optical waveguide 714.

In fig. 10, one end of the fourth optical waveguide 714 may correspond to a main output port through which the amplified laser beam L is output. Further, both ends of the first optical waveguide 711, both ends of the second optical waveguide 712, both ends of the third optical waveguide 713, and the other end of the fourth optical waveguide 714 may correspond to auxiliary output ports.

A first monitoring device 971 and a second monitoring device 972 may be disposed at both ends of the first optical waveguide 711, and a third monitoring device 973 and a fourth monitoring device 974 may be disposed at both ends of the second optical waveguide 712. Further, a fifth monitoring device 975 and a sixth monitoring device 976 may be provided at both ends of the third optical waveguide 713, and a seventh monitoring device 977 may be provided at the other end of the fourth optical waveguide 714. Each of the first to seventh monitoring devices 971 to 977 may include, for example, a photodiode.

The third monitoring device 973 and the fourth monitoring device 974 may monitor the wavelength alignment between the second ring resonator R2 and the third ring resonator R3, and the fifth monitoring device 975 and the sixth monitoring device 976 may monitor the wavelength alignment between the second ring resonator R2 and the third ring resonator R3. In addition, the first monitor device 971, the second monitor device 972, and the seventh monitor device 977 may monitor the wavelength alignment between the first ring resonator R1 and the third ring resonator R3.

Tunable laser source 900 may include one or more optical delay lines 730 disposed on optical waveguides 711, 712, 713, and 714.

Fig. 11 shows a tunable laser source 1000 according to another example embodiment. The tunable laser source 1000 shown in fig. 11 is the same as the tunable laser source 900 shown in fig. 10, except for the position of the optical delay line 830. Referring to fig. 11, the tunable laser source 1000 may include one or more optical delay lines 830 disposed on the plurality of ring resonators R1, R2, and R3.

Each of the tunable laser sources described in the above example embodiments may be used as a light source for a light-redirecting device, such as a LiDAR. Fig. 12 shows a light redirecting device 2000 according to an example embodiment.

Referring to fig. 12, the light-diverting apparatus 2000 of an example embodiment may include a tunable laser source 2100, a diverting device 2200 configured to divert light in a desired direction, a detector 2300 configured to detect the diverted light, and a driver 2400. The driver 2400 may include a driving circuit configured to drive the tunable laser source 2100, the steering device 2200, and the detector 2300.

The tunable laser source 2100 may be one of the tunable laser sources 100 to 1000 of the above-described exemplary embodiments.

The steering apparatus 2200 may steer the laser beam incident from the tunable laser source 2100 in a desired direction. Further, when the light is turned to and reflected from the object by the turning device 2200, the detector 2300 may detect the reflected light.

The steering apparatus 2200 may include: a plurality of optical waveguides 2210 configured to divide a laser beam incident from the tunable laser source 2100 into a plurality of laser beams and emit the laser beams; and a plurality of modulation units provided on the optical waveguide 2210 to modulate the phase of the laser beam. An antenna array 2220 in which antennas are arranged in one dimension is provided in the light output portion of the steering device 2200.

Two-dimensional optical scanning may be performed using a tunable laser source 2100 and a steering apparatus 2200. For example, optical scanning may be performed in a first direction (y-axis direction in fig. 12) by controlling the phase of the laser beam using the steering apparatus 2200, and optical scanning may be performed in a second direction (x-axis direction in fig. 12) perpendicular to the first direction by controlling the wavelength of the laser beam using the tunable laser source 2100. As described above, when the tunable laser source 2100 is used as the light source of the light redirecting device 2000, two-dimensional optical scanning is possible even in the case where the antenna array 2220 of the redirecting apparatus 2200 is arranged in one-dimensional form.

When a single wavelength light source is used as a LiDAR light source, the antennas of the turning section are arranged in two dimensions for two-dimensional optical scanning. However, in this case, since a large number of antennas, for example, 10000 or more antennas, are required in each product, it is difficult to manufacture the product. In addition, optical loss, reduction in control time, and the like may occur. However, when a tunable laser source according to an example embodiment is used as a LiDAR light source, two-dimensional optical scanning is possible even where the antennas of the steering device are arranged in a one-dimensional fashion, thereby reducing the number of antennas required for two-dimensional optical scanning and facilitating commercialization. Further, compared with the case of using a single-wavelength light source, light loss, an increase in control time, and the like can be reduced.

The tunable laser sources 100 to 1000 described in the above exemplary embodiments may be variously used as light sources of an integrated optical circuit in which optical elements are integrated. For example, in addition to being used in the light redirecting device 2000 described above, the tunable laser sources 100 to 1000 may also be used in various fields including depth sensors and three-dimensional sensors. Further, the tunable laser sources 100 to 1000 may be used as light sources for optical connection in data centers, for example, light sources for Wavelength Division Multiplexing (WDM) optical communication.

As described above, according to one or more of the above exemplary embodiments, the tunable laser light source includes three ring resonators, for example, a first ring resonator, a second ring resonator, and a third ring resonator having different lengths, and a ratio of the length of the third ring resonator to the length of the first ring resonator or a ratio of the length of the third ring resonator to the length of the second ring resonator is designed to be a number other than an integer, thereby improving mode selectivity and realizing a stable single oscillation mode.

According to an exemplary embodiment, the tunable laser source comprises one or more optical delay lines arranged on the optical waveguide, thereby increasing the overall length of the overall resonator and reducing the spectral linewidth in the oscillation mode. Furthermore, all components of the tunable laser source may be integrated on a single substrate by semiconductor processes, and thus the tunable laser source may be implemented as an on-chip tunable laser source.

According to an example embodiment, the tunable laser source includes one or more monitoring devices disposed on the output ports of the optical waveguides to monitor wavelength alignment between the ring resonators to enable on-chip control.

According to an example embodiment, when a tunable laser source is used as a LiDAR light source, two-dimensional optical scanning is possible even where the antennas of the steering device are arranged in a one-dimensional fashion, thereby reducing the number of antennas required for two-dimensional optical scanning and facilitating commercialization. Although the exemplary embodiments have been described, the exemplary embodiments are for illustrative purposes only, and various modifications may be made therefrom by those skilled in the art.

It should be understood that the example embodiments described herein should be considered in descriptive sense only and not for purposes of limitation. The description of features or aspects in each example embodiment should typically be considered as other similar features or aspects that may be used in other embodiments. Although the illustrative embodiments have been described with reference to the accompanying drawings, those skilled in the art will understand that various changes in form and details may be made therein without departing from the spirit and scope defined by the appended claims.