Wavelength tunable laser

Abstract

To obtain an optical device and a wavelength variable laser having a novel, more improved configuration, for example, capable of further reducing light loss and more suitably processing stray light.SOLUTION: An optical device includes: a multimode interference waveguide having, for example, a first end in a first direction and a second end in a direction opposite to the first direction; a first port deviating in a second direction from the center in the second direction crossing the first direction in the first end; a second port positioned in a side opposite to the first port relative to the center in the second direction in the first end; a third port positioned in the center in the second direction in the second end; and two fourth ports deviating to both sides in the second direction relative to the third port in the second end. The multimode interference waveguide is configured such that an inphase component of light inputted to the first port and the second port is coupled to the third port, and a reversed phase component inputted to the first port and the second port is coupled to the two fourth ports.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to wave a variable-length laser.

Background Art

[0002] Conventionally, a wavelength-variable laser equipped with a ring resonator has been known (for example, Patent Document 1). In Patent Document 1, a 2×2 multimode interference waveguide (MMI) is provided at the junction between a linear waveguide and a ring waveguide.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In this type of optical device, it is more preferable that the optical loss due to processing errors in the multimode interference waveguide is smaller. Further, it is preferable to have a configuration that can suitably process stray light generated in the multimode interference waveguide.

[0005] Therefore, one of the problems of the present invention is to obtain an optical device and a wavelength-variable laser having a novel configuration that is more improved, for example, capable of further reducing optical loss or more suitably processing stray light.

Means for Solving the Problems

[0006] The optical device of the present invention includes, for example, a multimode interference waveguide having a first end in a first direction and a second end in the direction opposite to the first direction, a first port at the first end that is offset in the second direction from the center of the second direction intersecting the first direction, a second port at the first end that is located on the opposite side of the first port from the center of the second direction, a third port at the second end that is located in the center of the second direction, and two fourth ports at the second end that are offset on both sides of the second direction from the third port, wherein the multimode interference waveguide is configured such that the in-phase components of light input to the first port and the second port are coupled to the third port, and the out-of-phase components of light input to the first port and the second port are coupled to the two fourth ports.

[0007] The optical device may include an optical processing unit that is optically connected to the fourth port.

[0008] The optical device may include a third connecting waveguide, one end of which is optically connected to the first port and the other end of which is optically connected to the second port.

[0009] The optical device may include a first multimode interference waveguide as the multimode interference waveguide, a second multimode interference waveguide as the multimode interference waveguide provided at a distance from the first multimode interference waveguide in the opposite direction to the second direction, a first waveguide optically connected to the first port of the first multimode interference waveguide, a curved first connecting waveguide optically connecting the third port of the first multimode interference waveguide and the third port of the second multimode interference waveguide, a curved second connecting waveguide optically connecting the first port of the second multimode interference waveguide and the second port of the first multimode interference waveguide, and a second waveguide optically connected to the second port of the second multimode interference waveguide.

[0010] The optical device may include a first optical processing unit that is optically connected to both the fourth port of the first multimode interference waveguide that is closer to the second multimode interference waveguide, and the fourth port of the second multimode interference waveguide that is closer to the first multimode interference waveguide.

[0011] The optical device may include a second optical processing unit that is optically connected to both the fourth port of the first multimode interference waveguide that is furthest from the second multimode interference waveguide, and the fourth port of the second multimode interference waveguide that is furthest from the first multimode interference waveguide.

[0012] The tunable laser of the present invention comprises one or more of the optical devices, for example, as filters or mirrors. [Effects of the Invention]

[0013] According to the present invention, improved and novel optical devices and tunable lasers can be obtained. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is an illustrative and schematic plan view of an optical device according to the first embodiment. [Figure 2] Figure 2 is an illustrative and schematic plan view of the optical device according to the second embodiment. [Figure 3] Figure 3 is an exemplary and schematic plan view of a tunable laser according to the third embodiment. [Figure 4] Figure 4 is an exemplary and schematic plan view of a tunable laser according to the fourth embodiment. [Figure 5] Figure 5 is an exemplary and schematic plan view of a tunable laser according to the fifth embodiment. [Figure 6] Figure 6 is an exemplary and schematic plan view of a tunable laser according to the sixth embodiment. [Figure 7]FIG. 7 is an exemplary and schematic plan view of a wavelength tunable laser according to the seventh embodiment. [Figure 8] FIG. 8 is an exemplary and schematic plan view of a wavelength tunable laser according to the eighth embodiment. [Figure 9] FIG. 9 is an exemplary and schematic plan view of a wavelength tunable laser according to the ninth embodiment. [Figure 10] FIG. 10 is an exemplary and schematic plan view of a wavelength tunable laser according to the tenth embodiment. BEST MODE FOR CARRYING OUT THE INVENTION

[0015] Exemplary embodiments of the present invention are disclosed below. The configurations of the embodiments shown below, as well as the operations and results (effects) brought about by the configurations, are examples. The present invention can also be realized by configurations other than those disclosed in the following embodiments. Further, according to the present invention, it is possible to obtain at least one of various effects (including derivative effects) obtained by the configuration.

[0016] The plurality of embodiments shown below have the same configuration. Therefore, according to the configuration of each embodiment, the same operations and effects based on the same configuration can be obtained. Further, in the following, the same reference numerals are given to those same configurations, and redundant descriptions may be omitted.

[0017] In this specification, ordinal numbers are given for convenience in distinguishing parts, directions, etc., and do not indicate priorities or orders.

[0018] Also, in each figure, the D1 direction is represented by arrow D1, the D2 direction is represented by arrow D2, and the Z direction is represented by arrow Z The D1 direction, the D2 direction, and the Z direction intersect each other and are orthogonal to each other.

[0019] [First Embodiment] Figure 1 is a plan view of the optical device 10 of the first embodiment. The optical device 10 has a multimode interferential waveguide 11 and a plurality of waveguides 12 and 14 that are optically connected to the multimode interferential waveguide 11 via a plurality of ports p1 to p4. Waveguides 12 are connected to ports p1, p2 and p3, respectively, and waveguides 14 are connected to the two ports p4, respectively.

[0020] The multimode interfering waveguide 11 has an end 11a in the D1 direction and an end 11b in the opposite direction to the D1 direction. The D1 direction is an example of a first direction. End 11a is an example of a first end, and end 11b is an example of a second end.

[0021] The multimode interfering waveguide 11 has a port p1 at its end 11a that is offset in the D2 direction from the center in the D2 direction. The D2 direction intersects with the D1 direction and is an example of a second direction. Port p1 is an example of a first port.

[0022] The multimode interfering waveguide 11 has a port p2 at its end 11a that is offset from the center in the D2 direction in the opposite direction to the D2 direction. Port p2 is located on the opposite side of port p1 from the center in the D2 direction of end 11a. Port p2 is an example of a second port.

[0023] The multimode interfering waveguide 11 has a port p3 located at the center in the D2 direction at its end 11b. Port p3 is an example of a third port.

[0024] The multimode interference waveguide 11 of this embodiment is configured as a 1x2 multimode interference waveguide 11 that outputs light input from ports p1 and p2 to port p3. Through diligent studies using simulations and experiments, the inventors have found that the 1x2 multimode interference waveguide 11 is less sensitive to optical loss due to processing errors compared to the 2x2 multimode interference waveguide. This is thought to be because, for specifications corresponding to light of the same wavelength, the width in the D2 direction of the 2x2 multimode interference waveguide is narrower than that of the 1x2 multimode interference waveguide, and therefore the effect of processing errors in that width becomes greater. According to one study by the inventors, in a 2x2 multimode interference waveguide, optical loss increases significantly (for example, by about 0.6 dB) when the processing error is ±50 nm, whereas in a 1x2 multimode interference waveguide with almost the same specifications, the increase in optical loss can be suppressed to a lower level (for example, by about 0.2 dB) even when the processing error is ±100 nm.

[0025] Although this has the advantage of suppressing optical loss, in a 1x2 multimode interference waveguide 11, it is known that in response to optical input from ports p1 and p2, out-of-phase components arrive on both sides of the D2 direction at end 11b, and these out-of-phase components are reflected inside the multimode interference waveguide 11, contributing to stray light. Stray light can also be called unwanted light.

[0026] Therefore, the multimode interference waveguide 11 of this embodiment has ports p4 offset on both sides in the D2 direction from port p3 at end 11b. Port p4 is an example of a fourth port. Stray light can be appropriately processed from the waveguide 14 connected to port p4.

[0027] For the multimode interferential waveguide 11, specifications such as the length in the D1 direction, the width in the D2 direction, the shape of the sides in both directions of the D2 direction, and the shape of the ends 11a and 11b in the D1 direction are set so that light input to ports p1 and p2 in the same phase couples to port p3, and light input to ports p1 and p2 in opposite phases couples to the two ports p4.

[0028] As explained above, the multimode interferential waveguide 11 of this embodiment has the advantage of suppressing optical loss due to processing errors compared to a 2x2 multimode interferential waveguide. Furthermore, because the multimode interferential waveguide 11 of this embodiment has a more robust configuration, it offers advantages such as reducing individual differences (variations) in the characteristics of the optical device 10, and improving yield by allowing for larger tolerances.

[0029] [Second Embodiment] Figure 2 is a plan view of the ring resonator 10A of the second embodiment. The ring resonator 10A is an example of an optical device.

[0030] As shown in Figure 2, the ring resonator 10A comprises two multimode interference waveguides 11-1 and 11-2, waveguides 12-1 and 12-2 (12) optically connected to each of these two multimode interference waveguides 11-1 and 11-2, and waveguides 13-1 and 13-2 (12) optically connecting these two multimode interference waveguides 11-1 and 11-2, thus forming a ring resonator.

[0031] Furthermore, the ring resonator 10A is equipped with optical processing units 15-1, 15-2 (15) that process stray light from the multimode interference waveguides 11-1, 11-2.

[0032] The two multimode interference waveguides 11-1 and 11-2 have the same configuration as in the first embodiment described above. Furthermore, the two multimode interference waveguides 11-1 and 11-2 have the same specifications, including the length in the D1 direction, the width in the D2 direction, the side shapes on both sides in the D2 direction, the shapes of the ends 11a and 11b in the D1 direction, and the number and position of ports p1 to p4.

[0033] These two multimode interfering waveguides 11-1 and 11-2 are both arranged parallel to each other in an orientation extending in the D1 direction and aligned in the D2 direction. Multimode interfering waveguide 11-2 is spaced apart from multimode interfering waveguide 11-1 in the opposite direction in the D2 direction. Multimode interfering waveguide 11-1 is an example of a first multimode interfering waveguide, and multimode interfering waveguide 11-2 is an example of a second multimode interfering waveguide.

[0034] The overall configuration of the ring resonator 10A in this embodiment, which includes two multimode interference waveguides 11, a plurality of waveguides 12, and a plurality of optical processing units 15, has a configuration that is symmetrical with respect to a center line (not shown) that passes through the center in the D2 direction and extends in the D1 direction.

[0035] Waveguide 12-1(12) is optically connected to port p1 of the multimode interference waveguide 11-1. Waveguide 12-1 is an example of a first waveguide. Laser light Li is input to the multimode interference waveguide 11-1 via waveguide 12-1 and port p1.

[0036] Waveguide 13-1(12) optically connects port p3 of multimode interference waveguide 11-1 and port p3 of multimode interference waveguide 11-2, and is curved in an arc shape with a substantially constant radius of curvature. Waveguide 13-1 is an example of a first connecting waveguide.

[0037] Waveguide 13-2(12) optically connects port p1 of multimode interference waveguide 11-2 and port p2 of multimode interference waveguide 11-1, and is curved in an arc shape with a substantially constant radius of curvature. The radius of curvature of waveguide 13-2 is set to be slightly smaller than that of waveguide 13-1. Waveguide 13-2 is an example of a second connecting waveguide.

[0038] Waveguide 12-2(12) is optically connected to port p2 of the multimode interference waveguide 11-2. Waveguide 12-2 is an example of a second waveguide. The laser beam Lo is output from the multimode interference waveguide 11-2 via port p2 and waveguide 12-1.

[0039] Furthermore, the multimode interference waveguides 11-1 and 11-2 are optically connected to the optical processing units 15-1 and 15-2 via waveguides 14-1 and 14-2 (14) connected to port p4.

[0040] Optical processing units 15-1 and 15-2 process stray light from multimode interference waveguides 11-1 and 11-2, respectively. Optical processing unit 15-1 is, for example, a slab waveguide, and can process stray light by diffusing it and leaking it to the outside, or by scattering light to the outside from the uneven shape formed at the boundary with the outside. Optical processing unit 15-2 is, for example, a bulk semiconductor or a slab waveguide, and can reduce the power density of stray light by diffusing it two-dimensionally or three-dimensionally before leaking it to the outside of the optical processing unit 15-2.

[0041] As is clear from Figure 2, the optical processing unit 15-1 is optically connected to the two multimode interference waveguides 11-1 and 11-2 via two ports p4 of the two multimode interference waveguides 11-1 and 11-2 that are close to each other, and via waveguide 14-1. The optical processing unit 15-1 is an example of a first optical processing unit.

[0042] Furthermore, the optical processing unit 15-2 is optically connected to the two multimode interference waveguides 11-1 and 11-2 via two separate ports p4 and waveguide 14-2 of the two ports p4 of the two multimode interference waveguides 11-1 and 11-2. The optical processing unit 15-2 is an example of a second optical processing unit.

[0043] In other words, in the ring resonator 10A, the optical processing unit 15-1 is shared for processing stray light from the two multimode interference waveguides 11-1 and 11-2, and the optical processing unit 15-2 is also shared for processing stray light from the two multimode interference waveguides 11-1 and 11-2. This configuration offers advantages such as a simpler and more compact device configuration compared to a configuration in which each of the four ports p4 has its own separate optical processing unit 15.

[0044] Waveguides 14-1 and 14-2 (14) can also be called waste optical waveguides. The extension direction at each port p4 of waveguides 14-1 and 14-2 forms an acute angle with the opposite direction to the D1 direction. Therefore, stray light reflection can be suppressed at each port p4. In addition, the radius of curvature of waveguide 14-1 is smaller than that of waveguides 13-1 and 13-2. Here, waveguide 14-1 can be set to have a smaller radius of curvature while suppressing the increase in stray light leakage due to bending loss by gradually decreasing the radius of curvature as it moves away from port p4 along the clothoid curve.

[0045] According to this embodiment, the configuration of waveguides 14-1, 14-2 (12) and optical processing units 15-1, 15-2 (15) allows stray light recovered from multimode interference waveguides 11-1, 11-2 to be reflected at a greater distance, making it less likely to return to the ring resonator. This suppresses the adverse effects of stray light on the main light in the ring resonator.

[0046] [Third Embodiment] Figure 3 is a plan view of the laser device 100 according to the third embodiment. As shown in Figure 3, the laser device 100 includes a DBR unit 20, a ring resonator 10A, a gain unit 30, an optical amplifier 40, and a waveguide 102.

[0047] The laser device 100 is a semiconductor laser element and is an example of a tunable laser. The laser device 100 is provided on a semiconductor laminated substrate 101. The semiconductor laminated substrate 101 is configured to have a predetermined function, such as a waveguide, by stacking multiple semiconductor layers on a semiconductor substrate.

[0048] The DBR section 20, the ring resonator 10A, the gain section 30, the optical amplifier 40, and the waveguide 102 are all made of InP-based semiconductor material.

[0049] The DBR section 20 has a waveguide (not shown) that includes a distributed Bragg reflector type sampled grating (SG-DBR). The DBR section 20 is an example of a reflector and may also be referred to as the first reflector.

[0050] The ring resonator 10A has the same configuration as the ring resonator 10A of the second embodiment described above. The ring resonator 10A functions as a mirror whose reflection characteristics change periodically with respect to the wavelength of light input from the waveguide 102. The ring resonator 10A is an example of a filter or mirror, and an example of a second reflector.

[0051] The gain section 30 has a waveguide (not shown) made of an active layer.

[0052] Furthermore, the optical amplifier 40 has a waveguide (not shown) made of an active layer.

[0053] In the above configuration, the active layer has a multiple quantum well (MQW) structure made of, for example, a GaInAsP-based semiconductor material or an AlGaInAs-based semiconductor material. The passive waveguide is made of, for example, an i-type GaInAsP-based semiconductor material with a bandgap wavelength of 1300 nm. The waveguide in the SG-DBR configuration is made of, for example, a GaInAsP-based semiconductor material or an AlGaInAs-based semiconductor material, and portions with different refractive indices are periodically arranged to form a diffraction grating.

[0054] Microheaters (not shown) are provided in the DBR section 20 and the ring resonator 10A, respectively. The microheaters are so-called resistive heating elements and generate heat in response to the supply of current. The microheaters are equipped with wiring structures such as electrodes and conductive layers for supplying current.

[0055] The DBR section 20 and the ring resonator 10A constitute a laser resonator. The DBR section 20 has a comb-shaped reflection peak with periodic frequency intervals corresponding to the reciprocal of the period of the diffraction grating. The DBR section 20 and the ring resonator 10A have different periods, and the configuration allows for coarse tuning of the laser light frequency using a method called the vernier type. When the microheater heats the DBR section 20, the refractive index of the DBR section 20 changes, causing the comb-shaped reflection peak to shift in the frequency axis direction. Similarly, when the microheater heats the ring resonator 10A, the refractive index of the ring resonator 10A changes, causing the comb-shaped reflection peak to shift in the frequency axis direction.

[0056] The gain section 30 is located between the DBR section 20 and the ring resonator 10A. In other words, the ring resonator 10A is located on the opposite side of the gain section 30 from the DBR section 20. The gain section 30 is provided with a pair of electrodes (not shown) spaced apart from each other. By applying a voltage to the pair of electrodes, current flows through the gain section 30, and an optical amplification effect is obtained. This causes laser oscillation.

[0057] The optical amplifier 40 is located on the opposite side of the DBR section 20 from the gain section 30 and the ring resonator 10A, and is positioned between the DBR section 20 and the end section 101a, which serves as the laser beam output end. By applying a voltage to the optical amplifier 40 via electrodes (not shown), a current flows through the optical amplifier 40, and an optical amplification effect is obtained. The optical amplifier 40 optically amplifies the laser light output from the DBR section 20 by laser oscillation.

[0058] The laser device 100 outputs laser light L amplified by the optical amplifier 40 from its end 101a. The laser light L emitted from the end 101a is the light emitted from the laser device 100.

[0059] In the laser device 100, the ring resonator 10A has the same configuration as in the second embodiment and also has the same multimode interference waveguides 11-1, 11-2(11) as in the first embodiment. Therefore, the laser device 100 of this embodiment provides the effects of both the first and second embodiments.

[0060] [Fourth Embodiment] Figure 4 is a plan view of the laser device 100A according to the fourth embodiment. As can be seen by comparing Figure 4 with Figure 3, in this embodiment, a multimode interference waveguide 11, similar to that in the above embodiment, is provided as a coupler that optically couples the two waveguides 12-1 and 12-2 extending from the ring resonator 10A with waveguide 102. In this case, the same effects as in the above embodiment can be obtained with this coupler.

[0061] [Fifth Embodiment] Figure 5 is a plan view of the laser device 100B of the fifth embodiment. As shown in Figure 5, the laser device 100B of this embodiment, like the laser device 100 of the third embodiment, includes a DBR unit 20, a ring resonator 10A, a gain unit 30, an optical amplifier 40, and a waveguide 102.

[0062] However, in this embodiment, the gain unit 30 is optically connected to waveguide 12-1 extending from the ring resonator 10A, and the DBR unit 20 and optical amplifier 40 are optically connected to another waveguide 12-2 extending from the ring resonator 10A. The gain unit 30, ring resonator 10A, DBR unit 20, and optical amplifier 40 are arranged in this order from end face 101c2 to end face 101c1 of the semiconductor laminated substrate 101, and are optically connected via waveguide 102. In addition, end face 101c1 is coated with a relatively low reflectivity coating, and end face 101c2 is coated with a relatively high reflectivity coating. In this case, with respect to the gain unit 30, the ring resonator 10A and DBR unit 20 function as vernier-type oscillation wavelength selective filters, the DBR unit 20 functions as a forward reflector, and end face 101c2 functions as a rear reflector. In this configuration, the laser light output from the components between the end face 101c2, which functions as the laser unit, and the DBR unit 20 is amplified by the optical amplifier 40, and laser light L1 is output from the end 101a as output light. On the other hand, a weaker laser light L2 is output from the end 101b of the end face 101c2 than laser light L1. Laser light L2 may be used as a monitor light.

[0063] The laser device 100B of this embodiment is equipped with a ring resonator 10A and a multimode interference waveguide 11 similar to those in the above embodiment. Therefore, the same effects as those in the above embodiment can be obtained with this embodiment as well.

[0064] [Sixth Embodiment] Figure 6 is a plan view of the laser device 100C of the sixth embodiment. The laser device 100C has the same configuration as the laser device 100B of the fifth embodiment described above. However, as will be clear from comparing Figure 6 with Figure 5, in this embodiment, a loop mirror 50 is provided as a rear reflector instead of the coating on the end face 101c2.

[0065] The loop mirror 50 has a multimode interfering waveguide 11. In the multimode interfering waveguide 11, two ports opposite to waveguides 12 and 14 are optically connected via a U-shaped waveguide 16. This configuration, having a multimode interfering waveguide 11 and waveguide 16, functions as a mirror. Waveguide 16 is an example of a third connecting waveguide.

[0066] Furthermore, the multimode interference waveguide 11 has the same configuration as in the above embodiment. That is, the multimode interference waveguide 11 is configured such that when in-phase components of light are input to the two ports (first port and second port) to which waveguide 16 is connected, these in-phase components are coupled to the port (third port) to which waveguide 12 is connected, and when out-of-phase components of light are input to the two ports (first port and second port) to which waveguide 16 is connected, these out-of-phase components are coupled to the two ports (fourth port) to which waveguide 14 is connected. Although not shown, the end of waveguide 14 opposite to the multimode interference waveguide 11 may be optically connected to the optical processing unit 15.

[0067] The laser device 100C of this embodiment also includes a ring resonator 10A, a multimode interference waveguide 11, and a waveguide 14, similar to those in the above embodiment. Therefore, the same effects as those in the above embodiment can be obtained with this embodiment as well.

[0068] [Seventh Embodiment] Figure 7 is a plan view of the laser device 100D of the seventh embodiment. As shown in Figure 7, the laser device 100D of this embodiment includes two ring resonators 10A, a gain unit 30, an optical amplifier 40, a broadband mirror 60, and a waveguide 102.

[0069] The broadband mirror 60 has, for example, multiple mirror sections that reflect laser light for each different wavelength band. The broadband mirror 60 can be fabricated by etching on the semiconductor laminated substrate 101. In this case, the broadband mirror 60 may also be called an etched mirror.

[0070] In this embodiment, the gain unit 30, two series-connected ring resonators 10A, a broadband mirror 60, and an optical amplifier 40 are arranged in this order from end face 101c2 to end face 101c1 and are optically connected via a waveguide 102. End face 101c1 is coated with a relatively low reflectivity coating, while end face 101c2 is coated with a relatively high reflectivity coating. In this configuration, the two ring resonators 10A function as vernier-type oscillation wavelength selective filters for the gain unit 30, the broadband mirror 60 functions as a forward reflector, and end face 101c2 functions as a rear reflector. In this configuration, the laser light output from the components between end face 101c2 (which functions as the laser unit) and the broadband mirror 60 is amplified by the optical amplifier 40, and laser light L1 is output as output light from end 101a. On the other hand, a weaker laser light L2 is output from end 101b of end face 101c2. Furthermore, in order to utilize the vernier effect, the circumference lengths of the two ring resonators 10A are set to slightly different lengths.

[0071] The laser device 100D of this embodiment also includes a ring resonator 10A and a multimode interference waveguide 11 similar to those in the above embodiment. Therefore, the same effects as those in the above embodiment can be obtained with this embodiment as well.

[0072] [Eighth Embodiment] Figure 8 is a plan view of the laser device 100E of the eighth embodiment. The laser device 100E has the same configuration as the laser device 100D of the seventh embodiment. However, as will be clear from comparing Figure 8 with Figure 7, in this embodiment, a loop mirror 50 is provided as a rear reflector instead of the coating on the end face 101c2. The loop mirror 50 has the same configuration as the sixth embodiment.

[0073] The laser device 100E of this embodiment also includes a ring resonator 10A and a multimode interference waveguide 11 similar to those in the above embodiment. Therefore, the same effects as those in the above embodiment can be obtained with this embodiment as well.

[0074] [Ninth Embodiment] Figure 9 is a plan view of the laser device 100F according to the ninth embodiment. As shown in Figure 9, the laser device 100F of this embodiment includes two ring resonators 10A, a gain unit 30, an optical amplifier 40, a broadband mirror 60, and a waveguide 102.

[0075] In this embodiment, two ring resonators 10A and a gain unit 30 are arranged in series from end face 101c2 to end face 101c1 and are optically connected via a waveguide 102. End face 101c1 is coated with a relatively low reflectivity coating, and end face 101c2 is coated with a relatively high reflectivity coating. In this case, with respect to the gain unit 30, end face 101c1 functions as a front reflector, the two ring resonators 10A function as a vernier-type oscillation wavelength selective filter, and end face 101c2 functions as a back reflector. In this configuration, the laser light L1 generated and amplified by the components between end face 101c2 and end face 101c1, which function as the laser unit, is output as output light from end 101a. On the other hand, a weaker laser light L2 is output from end 101b of end face 101c2 than the laser light L1.

[0076] The laser device 100F of this embodiment also includes a ring resonator 10A and a multimode interference waveguide 11 similar to those in the above embodiment. Therefore, the same effects as those in the above embodiment can be obtained with this embodiment as well.

[0077] [Tenth Embodiment] Figure 10 is a plan view of the laser device 100G of the tenth embodiment. As shown in Figure 10, the laser device 100G of this embodiment includes two ring resonators 10A, a multimode interference waveguide 11, a gain unit 30, and a waveguide 102.

[0078] In the multimode interference waveguide 11, the two ports opposite to waveguides 12 and 14 are optically connected via a U-shaped waveguide 102 (16). This configuration, having the multimode interference waveguide 11 and waveguide 16, functions as a mirror. The two ring resonators 10A are optically connected in series via waveguide 16.

[0079] The multimode interference waveguide 11 is optically connected to the gain unit 30 via waveguide 102(12) on the opposite side of waveguide 16. Although not shown, the end of waveguide 14 opposite to the multimode interference waveguide 11 may be optically connected to the optical processing unit 15.

[0080] In this case, with respect to the gain section 30, the end face 101c1 functions as a forward reflector, the two ring resonators 10A function as a vernier-type oscillation wavelength selective filter, and the mirror having the multimode interference waveguide 11 and waveguide 16 functions as a rear reflector. In this configuration, the laser light L1 generated and amplified by the components including the gain section 30, the multimode interference waveguide 11, and the two ring resonators 10A, which function as the laser section, is output as output light from the end face 101a.

[0081] The laser device 100G of this embodiment also includes a ring resonator 10A, a multimode interference waveguide 11, and a waveguide 14, similar to those in the above embodiment. Therefore, the same effects as those in the above embodiment can be obtained with this embodiment as well.

[0082] Although embodiments of the present invention have been illustrated above, these embodiments are merely examples and are not intended to limit the scope of the invention. The above embodiments can be implemented in various other forms, and various omissions, substitutions, combinations, and modifications can be made without departing from the spirit of the invention. Furthermore, each configuration, shape, and other specifications (structure, type, orientation, model, size, length, width, thickness, height, number, arrangement, position, material, etc.) can be modified as appropriate. [Explanation of symbols]

[0083] 10…Optical devices 10A... Ring resonator (optical device) 11…Multimode Interferential Waveguide 11-1…Multimode Interferential Waveguide (First Multimode Interferential Waveguide) 11-2…Multimode Interferential Waveguide (Second Multimode Interferential Waveguide) 11a...End (first end) 11b...End (second end) 12... Waveguides 12-1... Waveguide (First Waveguide) 12-2...Waveguide (second waveguide) 13-1... Waveguide (First connecting waveguide) 13-2... Waveguide (Second connecting waveguide) 14, 14-1, 14-2… Waveguides (waste optical waveguides) 15…Optical Processing Unit 15-1…Optical Processing Unit (First Optical Processing Unit) 15-2…Optical Processing Unit (Second Optical Processing Unit) 16… Waveguide (Third connecting waveguide) 20...DBR section 30... Gain section 40…Optical amplifier 50… Loop mirror (optical device) 100, 100A~100G... Laser device (tunable laser) 101… Semiconductor multilayer substrate 101a, 101b...ends 101c1,101c2...end face 102... Waveguide D1…direction (first direction) D2…direction (second direction) L, L1, L2, Li, Lo... Laser light p1...Port (First Port) p2...port (second port) p3...port (third port) p4...port (fourth port) Z…direction

Claims

1. A multimode interfering waveguide having a first end in a first direction and a second end in the opposite direction to the first direction, At the first end, a first port is located offset in the second direction from the center of the second direction that intersects the first direction, At the first end, a second port is located on the opposite side from the first port with respect to the center in the second direction, At the second end, a third port located in the center of the second direction, At the second end, there are two fourth ports offset to both sides in the second direction relative to the third port, A waste optical waveguide optically coupled to one of the fourth ports, wherein the radius of curvature gradually decreases along a clothoid curve as it moves away from the fourth port, An optical processing unit optically connected to one of the fourth ports via the aforementioned waste optical waveguide, A third connecting waveguide, one end of which is optically connected to the first port and the other end of which is optically connected to the second port, An optical device having, The multimode interference waveguide is a 1x2 multimode interference waveguide configured such that the in-phase components of light input to the first and second ports are coupled to the third port, and the out-of-phase components of light input to the first and second ports are coupled to the two fourth ports. The fourth angular difference between the extension direction of the waste optical waveguide at the connection point with the fourth port and the direction opposite to the first direction is acute, A tunable laser comprising one or more optical devices as filters or mirrors, wherein the fourth angular difference is greater than the third angular difference between the direction of extension of the waveguide optically connected to the third port at the connection point and the direction opposite to the first direction.

2. A multimode interfering waveguide having a first end in a first direction and a second end in the opposite direction to the first direction, At the first end, a first port is located offset in the second direction from the center of the second direction that intersects the first direction, At the first end, a second port is located on the opposite side from the first port with respect to the center in the second direction, At the second end, a third port located in the center of the second direction, At the second end, there are two fourth ports offset to both sides in the second direction relative to the third port, A waste optical waveguide optically coupled to one of the fourth ports, wherein the radius of curvature gradually decreases along a clothoid curve as it moves away from the fourth port, An optical processing unit optically connected to one of the fourth ports via the aforementioned waste optical waveguide, The first multimode interference waveguide, which is the multimode interference waveguide, A second multimode interference waveguide is provided at a distance from the first multimode interference waveguide in the direction opposite to the second direction, and the second multimode interference waveguide is provided at a distance from the first multimode interference waveguide in the direction opposite to the second direction. The first waveguide is optically connected to the first port of the first multimode interference waveguide, A curved first connecting waveguide is formed by optically connecting the third port of the first multimode interfering waveguide and the third port of the second multimode interfering waveguide, A curved second connecting waveguide is formed by optically connecting the first port of the second multimode interfering waveguide to the second port of the first multimode interfering waveguide, A second waveguide optically connected to the second port of the second multimode interference waveguide, An optical device having, The multimode interference waveguide is a 1x2 multimode interference waveguide configured such that the in-phase components of light input to the first and second ports are coupled to the third port, and the out-of-phase components of light input to the first and second ports are coupled to the two fourth ports. The fourth angular difference between the extension direction of the waste optical waveguide at the connection point with the fourth port and the direction opposite to the first direction is acute, A tunable laser comprising one or more optical devices as filters or mirrors, wherein the fourth angular difference is greater than the third angular difference between the direction of extension of the waveguide optically connected to the third port at the connection point and the direction opposite to the first direction.

3. The optical device is The tunable laser according to claim 2, further comprising a first optical processing unit optically connected to both the fourth port of the first multimode interferential waveguide that is closer to the second multimode interferential waveguide, and the fourth port of the second multimode interferential waveguide that is closer to the first multimode interferential waveguide.

4. The optical device is The tunable laser according to claim 2 or 3, further comprising a second optical processing unit optically connected to both the fourth port of the first multimode interferential waveguide that is furthest from the second multimode interferential waveguide, and the fourth port of the second multimode interferential waveguide that is furthest from the first multimode interferential waveguide.

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