JP7409642B2 - Optical resonator and optical pulse generator using the same - Google Patents

Description

The present invention relates to an optical resonator and an optical pulse generator using the same, and more particularly to an optical resonator that operates in whispering gallery mode and an optical pulse generator using the same.

Whispering gallery mode optical resonators formed from dielectric materials have been studied. Whispering gallery mode is an eigenmode of light that orbits near the surface of a sphere, circular disk, etc., and it is possible to confine light in a minute area.

Whispering gallery mode optical resonators can be obtained by etching or laser reflow processing a spheroid rotated around the short axis of the ellipse (for example, see Patent Document 1), or a SiO ₂ film on a silicon wafer. A toroidal cavity type silica disk (for example, see Non-Patent Document 1) is known.

In these optical resonators, the circumferential side of the spheroid or silica disk is curved with a predetermined curvature. Light that enters the optical resonator and resonates with a specific whispering gallery mode circulates along the circumference with curved side walls and is amplified by interference.

In recent years, optical frequency comb light sources in which narrow linewidth optical spectra are arranged at equal intervals on the frequency axis have been put into practical use. Among optical frequency comb light sources, this configuration uses a thinly tapered air-clad waveguide to input continuous laser light into a whispering gallery mode optical resonator, and generates four-wave mixing light to obtain optical frequency comb light output. is known (for example, see Patent Document 2). Such optical frequency comb light sources are being applied to optical communications, distance measurement, and the like because they are small, easy to integrate, and have a high repetition frequency.

A method has been proposed in which a whispering gallery mode microcavity is manufactured using a dielectric crystal using a precision cutting machine (see, for example, Non-Patent Document 2). In this document, a microcavity is formed that has a triangular cross-sectional shape when cut along a plane perpendicular to the plane of light circulation (or a plane including the central axis of circulation).

Patent No. 3941856 Patent No. 5619344

D.K. Armani et al., "Ultra-high-Q toroid microcavity on a chip", Nature Vol. 421 pp. 925-928 (2003) Y. Nakagawa et al., "Dispersion tailoring of a crystalline whispering gallery mode microcavity for a wide-spanning optical Kerr frequency comb"', J Opt. Soc. Amer. B Vol. 33 pp. 1913-1920 (2016)

In order to generate an optical frequency comb using a whispering gallery mode optical resonator, it is necessary to simultaneously have high optical confinement performance (high Q value) and anomalous dispersion.

In addition to the above requirements, it is known that the repetition frequency of an optical frequency comb light source matches the free spectral range (FSR) of a whispering gallery mode optical resonator, which increases the repetition frequency. Therefore, there is a need for smaller resonators. For example, in order to realize an optical pulse train with a repetition frequency of 100 GHz used in optical communication in a whispering gallery mode optical resonator made of magnesium fluoride (MgF ₂ ), the distance (radius) from the center of the optical resonator to the outer periphery must be needs to be 350 μm.

In order to miniaturize the whispering gallery mode optical resonator with curved side walls of Patent Document 1, Patent Document 2, and Non-Patent Document 1, the diameter of the resonator is reduced, and the optical communication wavelength band (light wavelength from 1500 nm to 1600 nm) is reduced. ) makes it difficult to maintain anomalous dispersion. Also in Non-Patent Document 2, the microcavity with a triangular cross section has normal dispersion.

The present invention has been made in view of the above circumstances, and includes a whispering gallery mode optical resonator that is miniaturized and maintains the anomalous dispersion necessary for generating an optical frequency comb over the used wavelength band; The purpose of the present invention is to provide an optical pulse generator using the present invention.

Optical resonators operating in whispering gallery mode are
It has a rotationally symmetrical body made of optical crystal,
The main body has a light confinement part along the outer periphery,
The optical confinement portion has a trapezoidal cross-sectional shape that projects in a direction away from the central axis when cut along a plane that includes the central axis of rotation,
The length (L1) of the upper base of the trapezoid is 2 μm or more and less than 7 μm (2 μm≦L1<7 μm),
The size from the central axis to the top base of the main body is a size that provides a free spectral spacing of 100 GHz or more.

A whispering gallery mode optical resonator is realized which is miniaturized and maintains the anomalous dispersion necessary for generating an optical frequency comb over the used wavelength band. By using this optical resonator, an optical frequency comb light source that generates optical pulses at a repetition frequency of 100 GHz or higher is realized.

FIG. 3 is a diagram showing the dependence of the dispersion state on the resonator size of a conventional whispering gallery mode resonator. FIG. 1 is a schematic diagram of an optical pulse generator using an optical resonator according to an embodiment. FIG. 2 is an external view of an optical resonator according to an embodiment. 4 is an enlarged cross-sectional view showing a trapezoidal structure of an optical confinement portion of the optical resonator of FIG. 3. FIG. It is an example (simulation result) of the optical spectrum of the optical frequency comb generated using the optical resonator of embodiment. In the optical resonator of the embodiment, it is an electric field distribution diagram when the inclination angle θ of the trapezoid is fixed at 20 degrees and the length (L1) of the upper base is changed. In the optical resonator of the embodiment, it is an electric field distribution diagram when the inclination angle θ of the trapezoid is fixed at 0 degrees and the length (L1) of the upper base is changed. It is a figure showing the optimal range of inclination angle theta in an optical resonator of an embodiment. In the optical resonator of the embodiment, it is a schematic diagram illustrating a range in which a single mode and anomalous dispersion occur when L1 and the inclination angle θ are changed in the cross-sectional shape of the optical confinement portion. It is a modification of the optical pulse generator using the optical resonator of the embodiment.

Before explaining the specific configuration of the optical resonator of the embodiment, we will explain the problems that occur when applying a conventional whispering gallery mode optical resonator to DWDM (Dense Wavelength Division Multiplexing) with a wavelength spacing of 100 GHz. Let me explain this point in more detail.

FIG. 1 is a diagram showing the resonator size dependence of the dispersion state of a conventional whispering gallery mode resonator. In the whispering gallery mode resonators of Patent Documents 1, 2 and Non-Patent Document 1, the cross-sectional shape of the outer periphery when cut along a plane perpendicular to the optical circulation plane is a circular arc or It becomes U-shaped. We investigate the dispersion state when a whispering gallery mode optical resonator with an arcuate cross-sectional shape is made of optical crystal.

As described above, in order to generate an optical frequency comb using a whispering gallery mode optical resonator, it is necessary to simultaneously satisfy high optical confinement performance (high Q value) and anomalous dispersion. Anomalous dispersion refers to dispersion in which the refractive index or effective refractive index of a medium increases as the wavelength increases. The dispersion is expressed by group velocity dispersion (picosecond ² /km), and when the group velocity dispersion is positive, it is normal dispersion, and when it is negative, it is anomalous dispersion. In order to generate an optical frequency comb with equally spaced peaks using a whispering gallery mode optical resonator, anomalous dispersion must be maintained over the wavelength band used.

On the other hand, in order to increase the repetition frequency of the optical frequency comb to be generated to 100 GHz or higher, the size of the optical resonator may be reduced. In the case of a MgF ₂ optical resonator, the radius R will be 350 μm or less if a repetition frequency of 100 GHz or higher is to be achieved. In conventional spheroidal or toroidal silica resonators, the vertical cross section of the outer periphery of the optical resonator is a circular arc, so assuming the radius of curvature of the arc is 25 μm, calculate the dispersion of an optical resonator with radius R = 350 μm. do.

As a result of the calculation, as shown in FIG. 1, it is found that normal dispersion occurs in the optical wavelength range of 1500 nm to 1550 nm used in optical communications.

By increasing the radius R of the optical resonator, anomalous dispersion is maintained in the optical communication band, but increasing the radius R decreases the FSR and lowers the optical frequency comb repetition frequency.

The following embodiments provide an optical resonator that operates in whispering gallery mode, maintains a size that has an FSR corresponding to a repetition frequency of 100 GHz or more, and satisfies anomalous dispersion conditions over an optical communication wavelength band. do.

<Basic structure>
FIG. 2 is a schematic diagram of the optical pulse generator 100 using the optical resonator 201 of the embodiment. The optical pulse generator 100 is used as an optical frequency comb light source.

The optical pulse generator 100 includes a laser diode 202 that outputs light of a single wavelength, an optical waveguide 203 that propagates the light output from the laser diode 202, and an optical resonator 201 that is placed close to the optical waveguide 203. has.

The optical waveguide 203 has a narrow tapered region at an optical coupling portion 205 to the optical resonator 201 . As an example, a tapered optical fiber whose diameter is reduced to 1 μm or less from a 125 μm diameter optical fiber or an air-clad waveguide can be used. The optical waveguide 203 is close to the optical resonator 201 at its narrowed portion. Evanescent waves seep out from the tapered portion of the optical waveguide 203 and are coupled to the adjacent optical resonator 201, so that light of a single wavelength is input into the optical resonator 201.

Of the light input to the optical resonator 201, the light that resonates with the whispering gallery mode of the optical resonator 201 is confined within the optical resonator 201 by circulating in the circumferential direction while being totally reflected on the inner surface. . At this time, light of a new wavelength is generated inside the optical resonator 201 due to four-wave mixing (FWM) due to the interaction between the optical crystal forming the optical resonator 201 and the incident light. As a result, an optical frequency comb is obtained. In the case of normal dispersion, no FMW gain occurs, so light of a new wavelength is not generated.

As will be described later, the optical resonator 201 of the embodiment exhibits anomalous dispersion over the used wavelength band (for example, optical communication wavelength band). When the optical frequency comb reaches a predetermined power, the optical frequency comb is recombined from the optical resonator 201 to the optical waveguide 203 and output.

<Configuration of optical resonator>
FIG. 3 shows an example of the configuration of the optical resonator 201 according to the embodiment. 3A shows a flange type optical resonator 201A, and FIG. 3B shows a disk type optical resonator 201B. The optical resonators 201A and 201B are formed of photodielectric optical crystals that are transparent to the wavelength used.

As the optical crystal, CaF ₂ crystal, BaF ₂ crystal, SrF ₂ crystal, MgF ₂ crystal, etc. can be used. Among these, CaF ₂ crystal, BaF ₂ crystal, and SrF ₂ crystal have opposite refractive index changes due to thermo-optic effect and optical Kerr effect, but they can be used by controlling the optical frequency comb generation process. In the embodiment, whispering gallery mode optical resonators 201A and 201B are fabricated using MgF ₂ crystal.

As mentioned above, the radius R for obtaining 100 GHz FSR using MgF ₂ crystal is 350 μm, but when using an optical crystal made of another material, the radius R for obtaining 100 GHz FSR changes. . No matter which crystal material (dielectric material) is used, the radius R is designed so that the FSR spacing is 100 GHz or closer.

In FIG. 3A, the optical resonator 201A has a rotationally symmetrical shape with respect to the central axis 301. In FIG. The optical resonator 201A is made from an optical crystal rod, and has a cylinder 211 and a flange 212 protruding from the outer periphery of the cylinder 211. The flange 212 has a flat side surface 215 along the outer periphery and a surface 213 extending from the side surface 215 toward the surface of the cylinder 211. The flange 212 becomes an optical confinement part of the optical resonator 201A, and light circulates along the side surface 215 of the flange 212.

Although the surface 213 is formed as an inclined surface in FIG. 3A, it may be a horizontal surface perpendicular to the central axis 301, as described later. When the surface 213 is an inclined surface, the cross-sectional shape of the flange 212 becomes a trapezoid when cut along a surface perpendicular to the light orbiting surface (or a surface including the central axis of rotation 301). When the surface 213 is a horizontal surface, the cross-sectional shape of the flange becomes a rectangle when cut along a surface perpendicular to the light orbiting surface (or a surface including the central axis of rotation 301).

Here, a trapezoid is defined as "a quadrilateral with a pair of parallel sides facing each other," and since a rectangle also has a pair of parallel sides, it is included in the trapezoid.

In FIG. 3B, the optical resonator 201B has a rotationally symmetrical shape with respect to the central axis 301. In FIG. The optical resonator 201B has a disk-shaped main body, and has a top surface 214T, a bottom surface 214B, a side surface 215 serving as the outermost circumference, and a surface 213 extending from the side surface 215 toward the top surface 214T and the bottom surface 214B. The side surface 215 and the surface 213 constitute an optical confinement section 216 that extends from the top surface 214T and the bottom surface 214B toward the outer circumferential side (in the direction away from the central axis 301). The optical resonator 201B is manufactured, for example, by using a chip cut out from a wafer and adjusting the shape of the side surface 215 and the surface 213 extending from the side surface 215.

Although the surface 213 is formed as an inclined surface in FIG. 3B, it may be a horizontal surface perpendicular to the central axis 301, as will be described later. In this case, the optical confinement section 216 has a flange structure that extends horizontally from the outer periphery of the cylinder, as shown in FIG. 3A.

When the surface 213 is an inclined surface, the cross-sectional shape of the light confinement section 216 becomes a trapezoid when cut along a surface perpendicular to the light orbiting surface (or a surface including the central axis of rotation 301). When the surface 213 is a horizontal surface, the cross-sectional shape of the light confinement section 216 is rectangular when cut along a surface perpendicular to the light orbiting surface (or a surface including the central axis of rotation 301).

The optical resonators 201A and 201B can be manufactured using, for example, a precision cutting machine used in Non-Patent Document 2. The whispering gallery mode optical resonator having the configuration disclosed in Patent Document 1, Patent Document 2, and Non-Patent Document 1 has a shape in which the side wall along the outer periphery is curved at a predetermined curvature due to its structure and manufacturing process. . In the embodiment, a trapezoidal cross-sectional shape is achieved using precision processing technology.

FIG. 4 shows a cross-sectional structure of the optical resonator 201 taken along a plane including the central axis of rotation 301. It is inside the flange 212 that the light circulates. The cross-sectional shape of the flange 212 is an isosceles trapezoid in this example. The side surface 215 of the flange 212, that is, the side farther from the central axis 301 in the cross section, becomes the upper base of the trapezoid. The length of the upper base of the trapezoid is L1, and the length of the lower base is L2. The upper and lower bases of the trapezoid are parallel to the central axis 301. Let h be the distance between the upper base and the lower base, that is, the height of the trapezoid. The height h of the trapezoid corresponds to the amount of protrusion of the flange 212 from the surface of the cylinder 211.

The inclination angle of the surface 213 forming the trapezoidal cross section is assumed to be θ. The inclination angle θ is defined as the angle obtained by subtracting 90 degrees from the interior angle at the upper base. When the inclination angle θ is 0 degrees, the cross-sectional shape of the flange 212 is rectangular.

From the viewpoint of ease of precision processing, the vertical cross-sectional shape of the optical confinement part may be an isosceles trapezoid as shown in FIG. 4, but as long as the conditions for optical confinement are maintained and the conditions for obtaining anomalous dispersion are satisfied. It does not necessarily have to be an isosceles trapezoid. Details of the optical confinement conditions and the anomalous dispersion conditions will be described later with reference to FIGS. 6 to 9.

The radius R of the optical resonator 201 is the distance from the central axis of rotation 301 to the upper base of the trapezoid, that is, the outermost side surface 215 of the flange 212 or the optical confinement part 216.

The light propagates in the circumferential direction while being totally reflected on the inner surface of the flange 212, thereby being confined in the optical resonator 201 in a whispering gallery mode. By precision machining, the inclination angle θ between the side surface 215 and the surface 213 of the flange 212 is formed to a desired dimension, thereby obtaining high optical confinement performance (high Q value) and anomalous dispersion characteristics.

FIG. 5 shows the calculation results of the optical spectrum of an optical frequency comb generated using a whispering gallery mode optical resonator whose flange 212 has a trapezoidal cross-sectional shape. In this calculation, MgF ₂ is used as the material of the optical resonator 201, the radius R of the optical resonator 201 is 350 μm, the length L1 of the upper base of the trapezoid in cross section is 5 μm, the height h is 10 μm, and the slope on both sides of the upper base is The angle θ is set to 20 degrees.

Optical frequency combs have been obtained at 100 GHz intervals over a wide wavelength band from 1510 nm to 1590 nm, centered at 1550 nm.

In order for the optical pulse generator 100 to function as a narrowly spaced optical frequency comb light source with a repetition frequency of 100 GHz or more, the optical resonator 201 must have a high Q and a radius R of 350 μm or less (in the case of MgF ₂ crystal). In addition, whispering gallery mode must be single landscape mode. The single transverse mode is a TEM00 mode in which the light intensity distribution is large at the center of the spot and becomes smaller toward the periphery in a Gaussian distribution. Multiple transverse modes other than single transverse mode are not preferred because the coherence of the output light decreases. Therefore, we will investigate the optimal range of the trapezoidal cross-sectional shape to achieve a single transverse mode and anomalous dispersion.

<Optimum range of trapezoidal cross-sectional shape>
FIG. 6 shows the electric field distribution when the optical confinement part of the optical resonator 201 of the embodiment has a trapezoidal cross-sectional shape.

The trapezoidal structure in the circumferential cross section, which becomes the optical confinement part in the whispering gallery mode optical resonator, can confine the light without spreading it in the direction parallel to the central axis 301, and does not affect the dispersion of the mode. It is necessary to have a sufficient height h (see FIG. 5). The height h is required to be several times the mode or wavelength of light, and in the optical communication wavelength band, the height h is approximately 5 μm or more. Considering ease of fabrication, the appropriate range for the height h is 5 to 15 μm, and the optimal value is around 10 μm.

In FIG. 6, the radius R of the optical resonator 201 is set to 350 μm, the height h of the trapezoid is set to 10 μm, the inclination angle θ of the surface 213 is set to 20 degrees, and the length L1 of the upper base is set to 2 μm, 3 μm, 5 μm, and 7 μm. The electric field distribution is calculated by changing the electric field.

When the length L1 of the upper base is 2 μm, 3 μm, or 5 μm, a single transverse whispering gallery mode exists. When the length L1 of the upper base is 7 μm or more, a plurality of whispering gallery modes that are different transverse modes may exist in the trapezoidal light confinement portion. This is called multimode. Under multimode conditions, the smooth optical frequency comb spectrum shown in FIG. 5 cannot be obtained.

Although the whispering gallery mode exists even when the length L1 of the upper base is 2 μm or less, normal dispersion occurs in the communication wavelength band, and an optical frequency comb cannot be obtained.

As a result, in order to make a single whispering gallery mode with anomalous dispersion exist in an optical confinement section with a trapezoidal cross section, the length range of the upper base needs to be 2 μm or more and less than 7 μm. be.

In FIG. 7, the radius R of the optical resonator 201 is set to 350 μm, the height h of the trapezoid is set to 10 μm, the inclination angle θ of the surface 213 is set to 0 degrees, and the length L1 of the upper base is set to 2 μm, 3 μm, 5 μm, and 7 μm. This is the electric field distribution when changed.

Even when the inclination angle θ of the surface 213, that is, the inclination angle of the side extending from the upper base of the trapezoid, is 0 degrees, the light is confined without spreading in the direction parallel to the central axis 301, and the mode dispersion is not affected. It must have a sufficient height h. The range of the height h is 5 to 15 μm as in the case of FIG. 6, and in the electric field distribution calculation, h is set to 10 μm.

When the inclination angle θ is 0 degrees, if the length L1 of the upper base is less than 2 μm, the light cannot be confined in the optical confinement region, so a whispering gallery mode suitable for generating an optical frequency comb cannot be obtained. . When the length L1 of the upper base is 7 μm or more, a plurality of whispering gallery modes exist in the optical confinement portion, and the smooth optical frequency comb spectrum shown in FIG. 5 cannot be obtained.

As a result, in order to have a single whispering gallery mode with anomalous dispersion in an optical confinement section with a rectangular cross section, when the tilt angle θ is 0 degrees, the length range of the upper base must be smaller than 2 μm. It needs to be large and less than 7 μm.

FIG. 8 is a diagram showing the optimum range of the tilt angle θ in the whispering gallery mode optical resonator of the embodiment. An optical resonator 201 with a radius R of 350 μm was formed of MgF ₂ , the length L1 of the upper base of the trapezoidal section of the optical confinement section was fixed at 5 μm, the height h of the trapezoid was fixed at 10 μm, and the inclination angle θ was varied. shows the group velocity dispersion when

The group velocity dispersion β ₂ is given by equation (1).

ここで、Ｒは光共振器２０１の半径、ｖlはｌ（エル）番目の縦モード、ｍは共鳴間のモード間隔である。ｌ番目の縦モードｖlは、たとえば、有限要素法で計算することができる。

Here, R is the radius of the optical resonator 201, vl is the l-th longitudinal mode, and m is the mode spacing between resonances. The l-th longitudinal mode vl can be calculated using the finite element method, for example.

When the inclination angle θ is 0 degrees (the vertical cross section is rectangular), the anomalous dispersion is large. When the tilt angle θ is 20 degrees and 40 degrees, anomalous dispersion is obtained over the wavelength band of optical communication. When the inclination angle θ is 60 degrees, normal dispersion occurs on the wavelength side shorter than 1550 nm.

From this calculation result, in order to generate an optical frequency comb, it is desirable that the inclination angle θ is 0 degrees or more and less than 60 degrees. Considering the difficulty of precision machining, it is more desirable that the inclination angle θ is larger than 0 degrees. In order to reliably maintain anomalous dispersion over the entire communication wavelength band, it is more desirable that the tilt angle θ is 40 degrees or less.

FIG. 9 illustrates the range in which a single mode and anomalous dispersion occur when the upper base length L1 and the inclination angle θ of the cross-sectional shape of the optical confinement section are changed in the whispering gallery mode optical resonator of the embodiment. FIG. The horizontal axis is the length L1 of the upper base, and the vertical axis is the inclination angle θ.

When the length L1 of the upper base is smaller than 2 μm, a cutoff region A exists in which no single transverse mode exists. When the length L1 of the upper base is 7 μm or more, the multimode region B is reached. The length L1 of the upper base of the trapezoid is set within a range where optical confinement can be achieved in a single transverse mode.

The inclination angle θ is determined depending on whether or not anomalous dispersion can be obtained. When the inclination angle θ becomes 60 degrees or more, normal dispersion occurs.

The appropriate trapezoidal range for obtaining anomalous dispersion and a single transverse mode is that when the inclination angle θ is greater than 0 degrees and less than 60 degrees, the length L1 of the upper base is 2 μm or more and less than 7 μm, and the inclination angle θ is less than 7 μm. At 0 degrees, the length L1 of the upper base is greater than 2 μm and less than 7 μm.

Regarding the height h of the trapezoidal cross section, that is, the distance between the upper base and the lower base, as h becomes smaller, it becomes difficult to confine light in a direction parallel to the center line. The range of h is preferably several times the wavelength. In the optical communication wavelength band, h is preferably 5 μm or more. Considering ease of processing, h is set to 5 μm to 15 μm.

<Modified example of optical pulse generator>
FIG. 10 shows a modification of the optical pulse generator using the optical resonator 201 of the embodiment. The optical pulse generator 100A includes a laser diode 202 that outputs light of a single wavelength, an optical waveguide 203 that propagates the light output from the laser diode 202, and an optical resonator 201 disposed close to the optical waveguide 203. has.

Similar to the optical pulse generator 100 of FIG. 2, the optical waveguide 203 is a narrow tapered waveguide, and is coupled to the optical resonator 201 at the tapered region. The optical resonator 201 has the above-mentioned optical confinement section having a trapezoidal cross section. The optical confinement section has a side surface 215 located at the outermost periphery of the optical resonator 201 and a surface 213 extending from the side surface toward the central axis.

The optical pulse generator 100A includes, for example, a thermoelectric cooler (TEC) as a temperature control section. In the example of FIG. 10, a TEC1 that controls the wavelength of the laser diode 202 and a TEC2 that controls the center wavelength of the whispering gallery mode of the optical resonator 201 are provided. The light source 206 may be configured by the laser diode 202 and the TEC1.

In the optical resonator 201, an optical frequency comb is generated from input single wavelength light, and the optical frequency comb is output from the optical waveguide 203.

Similar to the optical pulse generator 100 in FIG. 2, one small optical pulse generator 100A can simultaneously output multiple channels of light at a frequency interval of 100 GHz. Compared to a conventional wavelength division multiplex communication configuration in which a plurality of single wavelength laser diodes corresponding to the number of channels and a TEC corresponding to each laser diode are arranged, the optical pulse generators 100 and 100A of the embodiment , it is possible to realize a light source system that is small and has low power consumption.

Generally, it is considered to reduce the diameter of the resonator in order to increase the repetition frequency of the optical frequency comb, but if the diameter of the resonator is reduced, it becomes difficult to satisfy the conditions for anomalous dispersion. In the embodiment, by optimizing the cross-sectional shape of the optical confinement section, a resonator size that provides a repetition frequency of 100 GHz or more satisfies the conditions for anomalous dispersion and a single transverse mode.

The optical resonator 201 (including 201A and 201B) of the embodiment can be applied not only as a WDM light source but also as a high repetition frequency optical pulse light source in an optical signal processing circuit or the like.

100, 100A Optical pulse generator 201, 201A, 201B Optical resonator 202 Laser diode 203 Optical waveguide 205 Optical coupling section 206 Light source 211 Cylinder 212 Flange (optical confinement section)
213 Surface 214T Top surface 214B Bottom surface 215 Side surface 216 Optical confinement section 301 Central axis L1 Length of upper base of trapezoid L2 Length of lower base of trapezoid R Radius θ Inclination angle (one side)
h height

Claims (5)

An optical resonator operating in whispering gallery mode,
It has a rotationally symmetrical body made of optical crystal,
The main body has a light confinement part along the outer periphery,
The optical confinement portion has a trapezoidal cross-sectional shape that projects in a direction away from the central axis when cut along a plane that includes the central axis of rotation,
The material of the optical crystal is _MgF2 , the radius from the central axis of the main body to the outer periphery is 350 μm, and the inclination angle of the side connecting the upper and lower bases of the trapezoid is greater than 0 degrees and 60 degrees. and the length of the upper base is greater than 2 μm and less than 7 μm,
optical resonator. The height of the trapezoid is 5 μm or more and 15 μm or less,
The optical resonator according to claim 1. the trapezoid is an isosceles trapezoid;
The optical resonator according to claim 1 or 2. The optical resonator according to any one of claims 1 to 3,
a single wavelength laser diode,
a tapered optical waveguide that inputs output light from the single wavelength laser diode into the optical resonator;
An optical pulse generator having: The tapered optical waveguide is disposed close to the optical resonator in a region with the most constricted diameter.
The optical pulse generator according to claim 4.

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