Semiconductor tunable ring laser, photonic integrated circuit and optoelectronic system

Abstract

The present disclosure relates to a semiconductor tunable ring laser (1) comprising a laser cavity (2) having a closed-loop optical path and an optical filter (3) arranged within the laser cavity. The filter comprises a first MZI-based tunable frequency filter portion (3a) comprising a 1 * 3 MMI input optical splitter (4) providing a first non-zero proportion T1 of optical radiation for wavelength locking and / or power monitoring purposes outside the laser cavity at a first optical output port (7) of the 1 * 3 MMI input optical splitter (4), the first MZI-based tunable frequency filter portion (3a) comprising a first MZI-based tunable frequency filter portion (3a) comprising a first MZI-based tunable frequency filter portion (3a), the first MZI-based tunable frequency filter portion (3a) comprising a first MZI-based tunable frequency filter portion (3a) comprising a first MZI-based tunable frequency filter portion (3a); a second ratio of optical radiation T2 = (1-T1) / 2 is provided at a second optical output port (8) of the 1 * 3 MMI input optical splitter (4), and a third ratio of optical radiation T3 = (1-T1) / 2 is provided at a third optical output port (9) of the 1 * 3 MMI input optical splitter (4). The present disclosure also relates to a PIC (100) comprising a semiconductor tunable ring laser according to the present disclosure, and to an optoelectronic system (200) comprising such a PIC.

Description

Technical Field

[0001] The present disclosure relates to a semiconductor tunable ring laser. The present disclosure also relates to a photonic integrated circuit (PIC) including the semiconductor tunable ring laser according to the present disclosure. The present disclosure also relates to an optoelectronic system including the PIC according to the present disclosure. The optoelectronic system according to the present disclosure can be used, for example, but not limited to, in telecommunications applications, light detection and ranging (LIDAR), or sensor applications. Background Art

[0002] In many optoelectronic systems, such as but not limited to those that can be used in telecommunication applications, light detection and ranging (LIDAR) or sensor applications, semiconductor lasers are key components for generating a stable optical radiation beam with a narrow spectrum. Many different types of semiconductor lasers are known, such as semiconductor tunable ring lasers, which include a laser cavity with a closed loop optical path. An advantage of semiconductor tunable ring lasers over, for example, distributed Bragg reflector lasers or Fabry-Perot lasers is that the laser cavity of a semiconductor tunable ring laser makes on-chip reflectors or facet reflectors unnecessary for achieving stimulated emission of photons. This advantage of semiconductor tunable ring lasers is beneficial for problems related to the design and manufacture of advanced PICs and optoelectronic systems that require reduced complexity.

[0003] In order to maintain a stable lasing wavelength of a known semiconductor tunable ring laser, a control loop is typically required that includes a sensor capable of generating a sensor signal upon which the control loop can act. Typically, the sensor is a light sensor capable of generating a sensor signal based on a small fraction of optical radiation that is separated from the amount of optical radiation that constitutes the main optical output of the semiconductor tunable ring laser and directed toward the sensor. Typically, this small fraction of optical radiation accounts for a few percent of the main optical output of the semiconductor tunable ring laser. Separating this small fraction of optical radiation from the main optical output of the semiconductor tunable ring laser and directing this small fraction of optical power toward the sensor of the control loop for the purpose of stabilizing the lasing wavelength not only results in the main optical output not being fully available for the application using the semiconductor tunable ring laser, but also causes optical losses that reduce the overall efficiency of the semiconductor tunable ring laser.

[0004] Based on the foregoing, there is a need to provide a semiconductor tunable ring laser that has improved overall efficiency despite splitting off a small proportion of the optical radiation and any optical losses associated with lasing wavelength stabilization purposes. Summary of the Invention

[0005] An object of the present disclosure is to provide a semiconductor tunable ring laser with improved overall efficiency, whereby the semiconductor tunable ring laser according to the present disclosure is able to prevent or at least reduce at least one of the above-mentioned and / or other disadvantages associated with known semiconductor tunable ring lasers.

[0006] Another object of the present disclosure is to provide a PIC including the semiconductor tunable ring laser according to the present disclosure.

[0007] Yet another object of the present disclosure is to provide an optoelectronic system comprising the PIC according to the present disclosure.The optoelectronic system according to the present disclosure can be used in, for example but not limited to, telecommunication applications, LIDAR or sensor applications.

[0008] Various aspects of the present disclosure are set out in the accompanying independent and dependent claims. Features of the dependent claims can be combined with features of the independent claims as appropriate, not just in the manner explicitly set out in the claims. Furthermore, all features may be replaced by other technically equivalent features.

[0009] At least one of the above objectives is achieved by a semiconductor tunable ring laser, comprising:

[0010] - a laser cavity having a closed-loop optical path; and

[0011] - an optical filter arranged in the laser cavity and configured as a transmissive filter during use of the semiconductor tunable ring laser, the optical filter comprising:

[0012] A first MZI-based tunable frequency filter section, the first MZI-based tunable

[0013] The harmonic frequency filter section includes:

[0014] o a 1×3 MMI input optical splitter, the 1×3 MMI input optical splitter comprising a first multimode waveguide section, the first multimode waveguide section being provided with:

[0015] o a first optical input port arranged in optical communication with a closed-loop optical path of the laser cavity;

[0016] o a first optical output port configured and arranged to serve as an optical monitoring port of the laser cavity;

[0017] o a second optical output port; and

[0018] oThe third optical output port;

[0019] o a first 2×1 MMI output combiner, the first 2×1 MMI output combiner comprising a second multimode waveguide section, the second multimode waveguide section being provided with:

[0020] oSecond optical input port;

[0021] o a third optical input port; and

[0022] o a fifth optical output port arranged in optical communication with the closed-loop optical path of the laser cavity; and

[0023] o a first optical waveguide structure, the first optical waveguide structure comprising a first optical waveguide arranged to optically interconnect the second optical output port of the 1×3 MMI input optical splitter with the second optical input port of the first 2×1 MMI output combiner, the first optical waveguide structure being configured to optically interconnect the second optical output port of the 1×3 MMI input optical splitter with the second optical input port of the first 2×1

[0024] providing a first optical path length between the second optical input ports of the MMI output combiner; and

[0025] o a second light-guiding structure comprising a second optical waveguide arranged to connect the third optical output port of the 1×3 MMI input optical splitter to the first 2×1

[0026] The third optical input port of the MMI output combiner is optically interconnected, and the second optical guide structure is configured to connect the third optical output port of the 1×3 MMI input optical splitter to the first 2×1

[0027] providing a second optical path length between the third optical input ports of the MMI output combiner, the second optical path length being different from the first optical path length;

[0028] The first multimode waveguide portion of the 1×3 MMI input optical splitter is configured to enable, during use of the semiconductor tunable ring laser, the following:

[0029] a first non-zero proportion T1 of the amount of optical radiation T0 incident on the first optical input port of the 1×3 MMI input splitter, wherein optical radiation appears at the first optical output port of the 1×3 MMI input splitter; and

[0030] A second proportion T2 = (1-T1) / 2 of the optical radiation amount T0 appears at the second optical output port of the 1×3 MMI input optical splitter; and

[0031] A third proportion T3 = (1-T1) / 2 of the optical radiation amount T0 appears at the third optical output port of the 1×3 MMI input optical splitter;

[0032] The optical radiation of the first non-zero ratio T1 is sufficient to achieve wavelength locking and / or power monitoring purposes outside the laser cavity.

[0033] In this way, the semiconductor tunable ring laser according to the present disclosure enables the optical radiation of the first non-zero ratio T1 to be directly tapped out from the laser cavity, rather than tapped out after or outside the laser cavity, as is done in semiconductor tunable ring lasers known in the art, i.e., from the amount of optical radiation that constitutes the main optical output of the semiconductor tunable ring laser. Surprisingly, it was found that tapping out the optical radiation of the first non-zero ratio T1 directly from the laser cavity resulted in a reduction in the total optical loss of the semiconductor tunable ring laser according to the present disclosure, compared to the total optical loss of semiconductor tunable ring lasers known in the art that tapped out the optical radiation of the first non-zero ratio T1 after or outside the laser cavity. Therefore, despite the tapping out of the optical radiation of the first non-zero ratio T1 and any optical losses associated with the purpose of stabilizing the lasing wavelength, the semiconductor tunable ring laser according to the present disclosure still has an improved overall efficiency compared to semiconductor tunable ring lasers known in the art.

[0034] One insight of the present disclosure is that the dimensions of the first multimode waveguide section of the 1x3 MMI input splitter may be configured, for example, such that optical radiation of a first non-zero ratio T1 always appears at the first optical output port of the 1x3 MMI input splitter.

[0035] An advantage of the above insights is that there is no need to include a dedicated optical radiation splitting structure within the laser cavity, the dedicated optical radiation splitting structure being configured and arranged to allow a certain amount of optical radiation to be split off from the cavity for wavelength locking and / or power monitoring purposes outside the laser cavity. Those skilled in the art will appreciate that including a dedicated optical radiation splitting structure would result in additional losses and potentially harmful reflections that would reduce the overall efficiency of the semiconductor tunable ring laser.

[0036] Another advantage of the above insights is that a control loop is no longer required to ensure that a minimum amount of optical radiation is available for wavelength locking and / or power monitoring outside the laser cavity. Therefore, compared to semiconductor tunable ring lasers known in the art, the semiconductor tunable ring laser according to the present disclosure requires fewer components to achieve laser wavelength stabilization. To achieve wavelength locking and / or power monitoring outside the laser cavity, the optical radiation of the first non-zero fraction T1 is sufficient if, for example, it accounts for 1% to 15% of the optical radiation amount T0 incident on the first optical input port of the 1×3 MMI input splitter.

[0037] In an embodiment of a semiconductor tunable ring laser according to the present disclosure, the first multimode waveguide section of the 1×3 MMI input splitter is configured such that the value of the first non-zero ratio T1 is in the range of 0.01 to 0.15. In this manner, during use of the semiconductor tunable ring laser according to the present disclosure, 1% to 15% of the optical radiation incident on the first optical input port of the first MZI-based tunable frequency filter section always appears at the first optical output port of the 1×3 MMI input splitter. Consequently, the maximum transmittance of the closed-loop optical path toward the second and third optical output ports of the 1×3 MMI input splitter and ultimately to the laser cavity can be in the range of 85% to 99%. In an exemplary embodiment of a semiconductor tunable ring laser according to the present disclosure, the first multimode waveguide section of the 1×3 MMI input splitter is configured such that 5% of the optical radiation incident on the first optical input port of the 1×3 MMI input splitter is always available at the first optical output port of the 1×3 MMI input splitter, and 95% of the optical radiation incident on the first optical input port of the 1×3 MMI input splitter is always available at the second and third optical output ports of the 1×3 MMI input splitter.

[0038] In an embodiment of the semiconductor tunable ring laser according to the present disclosure, the optical filter includes a second MZI-based tunable frequency filter portion, the second MZI-based tunable frequency filter portion including:

[0039] a first 1×2 MMI input splitter, the first 1×2 MMI input splitter comprising a third multimode waveguide section, the third multimode waveguide section being provided with:

[0040] a fourth optical input port arranged in optical communication with a fifth optical output port of the first 2×1 MMI output combiner of the first MZI-based tunable frequency filter section, and thereby in optical communication with the closed-loop optical path of the laser cavity;

[0041] a sixth optical output port; and

[0042] · Seventh optical output port;

[0043] The third multimode waveguide section is configured to achieve a 50 / 50 splitting ratio;

[0044] a second 2×1 MMI output combiner, the second 2×1 MMI output combiner comprising a fourth multimode waveguide section, the fourth multimode waveguide section being provided with:

[0045] Fifth optical input port;

[0046] a sixth optical input port; and

[0047] an eighth optical output port arranged in optical communication with the closed-loop optical path of the laser cavity;

[0048] a third optical waveguide structure, the third optical waveguide structure comprising a third optical waveguide arranged to optically interconnect the sixth optical output port of the first 1×2 MMI input splitter with the fifth optical input port of the second 2×1 MMI output combiner, the third optical waveguide structure being configured to provide a third optical path length between the sixth optical output port of the first 1×2 MMI input splitter and the fifth optical input port of the second 2×1 MMI output combiner; and

[0049] a fourth optical waveguide structure, the fourth optical waveguide structure comprising a fourth optical waveguide arranged to optically interconnect the seventh optical output port of the first 1×2 MMI input splitter with the sixth optical input port of the second 2×1 MMI output combiner, the fourth optical waveguide structure being configured to provide a fourth optical path length between the seventh optical output port of the first 1×2 MMI input splitter and the sixth optical input port of the second 2×1 MMI output combiner, the fourth optical path length being different from the third optical path length.

[0050] Due to the first MZI-based tunable frequency filter section and the second MZI-based tunable frequency filter section, the above-described embodiments of the semiconductor tunable ring laser according to the present disclosure have improved frequency tunability. This is advantageous for PICs and optoelectronic systems including the semiconductor tunable ring laser according to the present disclosure. Such PICs and optoelectronic systems can be used, for example, but not limited to, in telecommunications applications, light detection and ranging (LIDAR), or sensor applications.

[0051] In an embodiment of the semiconductor tunable ring laser according to the present disclosure, the filter includes a third MZI-based tunable frequency filter portion, the third MZI-based tunable frequency filter portion including:

[0052] a second 1×2 MMI input splitter, the second 1×2 MMI input splitter comprising a fifth multimode waveguide section, the fifth multimode waveguide section being provided with:

[0053] a seventh optical input port arranged in optical communication with an eighth optical output port of the second 2×1 MMI output combiner of the second MZI-based tunable frequency filter section, and thereby in optical communication with the closed-loop optical path of the laser cavity;

[0054] a ninth optical output port; and

[0055] ·Tenth optical output port;

[0056] The fifth multimode waveguide section is configured to achieve a 50 / 50 splitting ratio;

[0057] a third 2×1 MMI output combiner, the third 2×1 MMI output combiner comprising a sixth multimode waveguide section, the sixth multimode waveguide section being provided with:

[0058] Eighth optical input port;

[0059] A ninth optical input port; and

[0060] an eleventh optical output port arranged in optical communication with the closed-loop optical path of the laser cavity;

[0061] a fifth optical waveguide structure, the fifth optical waveguide being arranged to optically interconnect a ninth optical output port of the second 1×2 MMI input splitter with an eighth optical input port of the third 2×1 MMI output combiner, the fifth optical waveguide structure being configured to provide a fifth optical path length between the ninth optical output port of the second 1×2 MMI input splitter and the eighth optical input port of the third 2×1 MMI output combiner; and

[0062] a sixth optical waveguide structure, the sixth optical waveguide structure comprising a sixth optical waveguide arranged to optically interconnect the tenth optical output port of the second 1×2 MMI input splitter with the ninth optical input port of the third 2×1 MMI output combiner, the sixth optical waveguide structure being configured to provide a sixth optical path length between the tenth optical output port of the second 1×2 MMI input splitter and the ninth optical input port of the third 2×1 MMI output combiner, the sixth optical path length being different from the fifth optical path length.

[0063] Due to the first MZI-based tunable frequency filter section, the second MZI-based tunable frequency filter section, and the third MZI-based tunable frequency filter section, the above-described semiconductor tunable ring laser according to the present disclosure has further improved frequency tunability. Therefore, the PIC and optoelectronic system including the semiconductor tunable ring laser according to the above-described embodiment of the present disclosure can be used for more advanced applications in the fields of, for example, but not limited to, telecommunications, light detection and ranging (LIDAR), or sensors.

[0064] In an embodiment of the semiconductor tunable ring laser according to the present disclosure, the closed-loop optical path of the laser cavity is provided with:

[0065] - a gain section, the gain section comprising:

[0066] o a tenth optical input port arranged in optical communication with an eleventh optical output port of the third 2×1 MMI output combiner of the third MZI-based tunable frequency filter section, and thereby in optical communication with the closed-loop optical path of the laser cavity; and

[0067] o a twelfth optical output port; and

[0068] - a 2×2 MMI output optical splitter, the 2×2 MMI output optical splitter comprising a seventh multimode waveguide section, the seventh multimode waveguide section being provided with:

[0069] o a twelfth optical input port arranged in optical communication with a twelfth optical output port of the gain section, and thereby in optical communication with the closed-loop optical path of the laser cavity;

[0070] o a thirteenth optical input port arranged in optical communication with an optical reflector arranged outside the closed-loop optical path of the laser cavity;

[0071] o a thirteenth optical output port arranged in optical communication with the first optical input port of the 1×3 MMI input splitter of the first MZI-based tunable frequency filter section, and thereby in optical communication with the closed-loop optical path of the laser cavity; and

[0072] o a fourteenth optical output port configured and arranged to enable optical power to be coupled out of the laser cavity for applications other than wavelength locking and / or power monitoring purposes.

[0073] The 2x2 MMI output splitter can be configured to have any suitable splitting ratio, depending on the requirements of the application in which the semiconductor tunable ring laser according to the present disclosure is used.

[0074] In an embodiment of a semiconductor tunable ring laser according to the present disclosure, a first MZI-based tunable frequency filter portion is configured to have a first free spectral range, a second MZI-based tunable frequency filter portion is configured to have a second free spectral range, and a third MZI-based tunable frequency filter portion is configured to have a third free spectral range, wherein the first free spectral range, the second free spectral range, and the third free spectral range are different from each other. In this way, the stability of the semiconductor tunable ring laser according to the present disclosure can be improved.

[0075] In an embodiment of a semiconductor tunable ring laser according to the present disclosure, the semiconductor tunable ring laser is an InP-based tunable ring laser. Those skilled in the art will appreciate that InP-based semiconductor materials are the preferred semiconductor materials for fabricating semiconductor tunable ring lasers, which can be used, for example, but not limited to, telecommunications applications, light detection and ranging (LIDAR), or sensor applications. InP-based technology enables monolithic integration of active components (e.g., light generating optics and / or light absorbing optics) and passive components (e.g., light guiding optics and / or light switching optics) into a PIC on a single die.

[0076] According to another aspect of the present disclosure, a PIC is provided, comprising a semiconductor tunable ring laser according to the present disclosure, wherein the PIC is a hybrid integrated PIC or a monolithic integrated PIC. Based on the foregoing, those skilled in the art will appreciate that the PIC according to the present disclosure can benefit from the advantages provided by the semiconductor tunable ring laser according to the present disclosure.

[0077] The advantage of hybrid integrated PIC is that the semiconductor tunable ring laser can be an InP-based tunable ring laser combined with, for example, silicon-based optoelectronic devices. Therefore, the PIC according to the present disclosure can be used in any field of semiconductor technology, such as silicon photonics.

[0078] Another advantage of the hybrid integrated PIC according to the present disclosure is that the semiconductor tunable ring laser can be replaced. For example, in the event of a laser failure or after a laser breakdown, the semiconductor tunable ring laser may need to be replaced.

[0079] The advantage of monolithically integrated PICs is that both active and passive optoelectronic devices can be integrated on the same semiconductor substrate, such as an InP-based substrate. Furthermore, monolithic integration of active and passive optoelectronic devices can be less cumbersome and may require less die area than hybrid integration of active and passive optoelectronic devices.

[0080] In an embodiment of a PIC according to the present disclosure, the PIC includes an optical radiation monitoring component optically connected to a first optical output port of a 1×3 MMI input splitter of a first MZI-based tunable frequency filter portion of an optical filter of a semiconductor tunable ring laser. The optical radiation monitoring component can be part of a control loop configured and arranged to control the optical performance of the semiconductor tunable ring laser according to the present disclosure. In an exemplary embodiment of the PIC according to the present disclosure, the optical radiation monitoring component includes a wavelength locker configured and arranged to stabilize the lasing wavelength of the semiconductor tunable ring laser according to the present disclosure using optical radiation of a first non-zero ratio T1, wherein the optical radiation of the first non-zero ratio T1 is present at the first optical output port of the 1×3 MMI input splitter of the first MZI-based tunable frequency filter portion of the intracavity filter of the semiconductor tunable ring laser during use of the semiconductor tunable ring laser.

[0081] According to another aspect of the present disclosure, an optoelectronic system including a PIC according to the present disclosure is provided, wherein the optoelectronic system is one of a transmitter, a receiver, a transceiver, a coherent transmitter, a coherent receiver, and a coherent transceiver. The optoelectronic system can be used, for example, but not limited to, in telecommunications, LIDAR, or sensor applications. Based on the foregoing, those skilled in the art will appreciate that any of the aforementioned transmitters, receivers, and transceivers can benefit from the advantages provided by a PIC according to the present disclosure including a semiconductor tunable ring laser according to the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Other features and advantages of the present disclosure will become apparent from the description of exemplary and non-limiting embodiments of semiconductor tunable ring lasers, PICs, and optoelectronic systems according to the present disclosure.

[0083] Those skilled in the art will appreciate that the described embodiments of the semiconductor tunable ring laser, PIC, and optoelectronic system are merely exemplary in nature and should not be construed as limiting the scope of protection in any way. Those skilled in the art will recognize that alternative and equivalent embodiments of the semiconductor tunable ring laser, PIC, and optoelectronic system may be conceived and practiced without departing from the scope of protection of the present disclosure.

[0084] Reference will be made to the accompanying drawings on the accompanying drawings page. The drawings are schematic in nature and are not necessarily drawn to scale. Additionally, like reference numerals designate like or similar parts. In the accompanying drawings:

[0085] Figure 1 shows a schematic top view of a first exemplary and non-limiting embodiment of a semiconductor tunable ring laser according to the present disclosure;

[0086] Figure 2 shows a schematic top view of a second exemplary and non-limiting embodiment of a semiconductor tunable ring laser according to the present disclosure;

[0087] Figure 3 shows a schematic top view of a third exemplary and non-limiting embodiment of a semiconductor tunable ring laser according to the present disclosure;

[0088] Figure 4AFIG4 shows a comparison of the total optical output power of three semiconductor tunable ring lasers A, B, and C known in the art and a semiconductor tunable ring laser E according to the present disclosure, wherein each of these known semiconductor tunable ring lasers includes a conventional 2×2 MMI output optical splitter, which is arranged after or outside the laser cavity to provide optical radiation that can be used for lasing wavelength stabilization. In the semiconductor tunable ring laser E of the present disclosure, the laser cavity is directly split using a 1×3 MMI input optical splitter, and the 1×3 MMI input optical splitter is configured to provide optical radiation with a first non-zero ratio T1 that can be used for lasing wavelength stabilization.

[0089] Figure 4B A comparison of total photogenerated currents of three known semiconductor tunable ring lasers A, B, and C and a semiconductor tunable ring laser E according to the present disclosure is shown, where the total photogenerated current is the sum of the photogenerated current generated by the main light output and the photogenerated current generated by a portion of the light radiation directed to a light sensor of a control circuit for stabilizing the lasing wavelength;

[0090] Figure 5 shows a schematic top view of a first exemplary and non-limiting embodiment of a PIC according to the present disclosure, the PIC including a semiconductor tunable ring laser according to the present disclosure; and

[0091] Figure 6 A schematic top view of a first exemplary and non-limiting embodiment of an optoelectronic system according to the present disclosure is shown, the optoelectronic system including a PIC according to the present disclosure. DETAILED DESCRIPTION

[0092] Figure 1 A schematic top view of a first exemplary and non-limiting embodiment of a semiconductor tunable ring laser 1 according to the present disclosure is shown. The semiconductor tunable ring laser 1 includes a laser cavity 2 having a closed-loop optical path and an optical filter 3 disposed within the laser cavity 2. During use of the semiconductor tunable ring laser 1, the optical filter 3 is configured as a transmissive filter. The optical filter 3 includes a first MZI-based tunable frequency filter section 3a, a second MZI-based tunable frequency filter section 3b, and a third MZI-based tunable frequency filter section 3c disposed in a series configuration within the laser cavity 2. Those skilled in the art will appreciate that the number of MZI-based tunable frequency filter sections is exemplary and non-limiting. Depending on the specific requirements to be met by the semiconductor tunable ring laser, any suitable number is contemplated, such as 1, 2, 3, 4, 5, 6, etc.

[0093] Figure 1The first MZI-based tunable frequency filter portion 3a of the illustrated filter 3 comprises a 1×3 MMI input splitter 4 comprising a first multimode waveguide portion 5 provided with a first optical input port 6, a first optical output port 7, a second optical output port 8, and a third optical output port 9. The first optical input port 6 is arranged to be in optical communication with the closed-loop optical path of the laser cavity 2. The first optical output port 7 is configured and arranged as an optical monitoring port of the laser cavity 2. Figure 1In the first exemplary and non-limiting embodiment of the semiconductor tunable ring laser 1 shown, the first optical output port 7 is arranged to be in optical communication with the wavelength locker 120 of the optical radiation monitoring assembly 110. The second optical output port 8 and the third optical output port 9 are arranged to be in optical communication with the closed-loop optical path of the laser cavity 2. As described above, one insight of the present disclosure is that the dimensions of the first multimode waveguide portion 5 of the 1×3 MMI input optical splitter 4 can be configured, for example, such that a first non-zero proportion T1 of the amount of optical radiation T0 incident on the first optical input port 6 of the 1×3 MMI input optical splitter 4 always appears at the first optical output port 7 of the 1×3 MMI input optical splitter 4, wherein the first non-zero proportion T1 of the optical radiation is sufficient to achieve wavelength locking and / or power monitoring outside the laser cavity 2. Furthermore, the first multimode waveguide section 5 causes a second proportion T2 = (1-T1) / 2 of the optical radiation amount T0 to appear at the second optical output port 8 of the 1×3 MMI input splitter 4, and a third proportion T3 = (1-T1) / 2 of the optical radiation amount T0 to appear at the third optical output port 9 of the 1×3 MMI input splitter 4. In this manner, the optical radiation of the second proportion T2 and the optical radiation of the third proportion T3 remain within the closed-loop optical path of the laser cavity 2. As described above, the first multimode waveguide section 5 of the 1×3 MMI input splitter 4 can be configured such that the value of the first non-zero proportion T1 is within a range of 0.01 to 0.15. In this manner, during use of the semiconductor tunable ring laser 1 according to the present disclosure, 1% to 15% of the optical radiation incident on the first optical input port 6 of the first MZI-based tunable frequency filter section 3a always appears at the first optical output port 7 of the 1×3 MMI input splitter 4. Thus, the maximum transmittance of the closed-loop optical path toward the second optical output port 8 and the third optical output port 9 of the 1×3 MMI input splitter 4 and ultimately to the laser cavity can be in the range of 85% to 99%. In an exemplary embodiment of a semiconductor tunable ring laser according to the present disclosure, the first multimode waveguide portion of the 1×3 MMI input splitter is configured such that 5% of the optical radiation incident on the first optical input port of the 1×3 MMI input splitter is always available at the first optical output port of the 1×3 MMI input splitter, and 95% of the optical radiation incident on the first optical input port of the 1×3 MMI input splitter is always available at the second and third optical output ports of the 1×3 MMI input splitter. Thus, the second fraction T2 of optical radiation and the third fraction T3 of optical radiation will each include 47.5% of the optical radiation incident on the first optical input port of the 1×3 MMI input splitter. Those skilled in the art will appreciate that, for simplicity, any internal optical losses of the 1×3 MMI input splitter are ignored.

[0094] It should be noted that an advantage of the semiconductor tunable ring laser 1 according to the present disclosure is that a control loop for ensuring that a minimum amount of light reaches the wavelength locker 120 is no longer required, because the design can ensure that at least 5% of the optical radiation incident on the first optical input port 6 of the 1×3 MMI input splitter 4 reaches the wavelength locker 120. The wavelength locker 120 is arranged in optical communication with the first optical output port 7 of the 1×3 MMI input splitter 4, and the first optical output port 7 serves as the optical monitoring port of the laser cavity 2.

[0095] The first MZI-based tunable frequency filter section 3a further includes a first 2×1 MMI output combiner 10, which includes a second multimode waveguide section 11 configured to achieve a 50 / 50 combining ratio. The second multimode waveguide section 11 is provided with a second optical input port 12, a third optical input port 13, and a fifth optical output port 14, which is arranged to optically communicate with the closed-loop optical path of the laser cavity 2. The second optical output port 8 of the 1×3 MMI input optical splitter 4 is optically interconnected with the second optical input port 12 of the first 2×1 MMI output combiner 10 via a first optical waveguide structure 15, which includes a first optical waveguide 16. The first optical waveguide 16 is configured to provide a first optical path length between the second optical output port 8 and the second optical input port 12. The third optical output port 9 of the 1×3 MMI input optical splitter 4 is optically interconnected with the third optical input port 13 of the first 2×1 MMI output combiner 10 via a second optical waveguide structure 17. The second optical waveguide structure 17 includes a second optical waveguide 18. The second optical waveguide 18 is configured to provide a second optical path length between the third optical output port 9 and the third optical input port 13. Figure 1In the first exemplary and non-limiting embodiment of the semiconductor tunable ring laser 1 shown, the second optical path length is shorter than the first optical path length because the second optical waveguide 18 is shorter than the first optical waveguide 16. Due to the difference between the first and second optical path lengths, the first MZI-based tunable frequency filter section 3a can be considered an asymmetric MZI-based tunable frequency filter section. Those skilled in the art will appreciate that the above-described embodiment of the difference between the first and second optical path lengths, i.e., by employing the first and second optical waveguide structures 15, 17, respectively including first and second optical waveguides 16, 18 having different lengths, is merely a non-limiting example. Another non-limiting example (not shown) of how to achieve the difference between the first optical path length and the second optical path length is to apply a first optical waveguide structure 15 and a second optical waveguide structure 17, respectively including a first optical waveguide 16 and a second optical waveguide 18 having equal lengths, wherein the first optical waveguide structure 15 also includes an annular structure, which is optically associated with the first optical waveguide 16 so as to establish an annular loading structure, so that the first optical path length provided by the first optical waveguide structure 15 is different from the second optical path length provided by the second optical waveguide structure 17.

[0096] Figure 1 The second MZI-based tunable frequency filter portion 3b of the illustrated optical filter 3 includes a first 1×2 MMI input splitter 19, which includes a third multimode waveguide portion 20 configured to achieve a 50 / 50 splitting ratio. This third multimode waveguide portion 20 is provided with a fourth optical input port 21, a sixth optical output port 22, and a seventh optical output port 23. The fourth optical input port 21 is arranged in optical communication with the fifth optical output port 14 of the first 2×1 MMI output combiner 10 of the first MZI-based tunable frequency filter portion 3a. In this manner, the fourth optical input port 21 is arranged in optical communication with the closed-loop optical path of the laser cavity 2.

[0097] The second MZI-based tunable frequency filter section 3b further includes a second 2×1 MMI output combiner 24, which includes a fourth multimode waveguide section 25 configured to achieve a 50 / 50 combining ratio. The fourth multimode waveguide section 25 is provided with a fifth optical input port 26, a sixth optical input port 27, and an eighth optical output port 28, the eighth optical output port 28 being arranged in optical communication with the closed-loop optical path of the laser cavity 2. The sixth optical output port 22 of the first 1×2 MMI input optical splitter 19 is optically interconnected with the fifth optical input port 26 of the second 2×1 MMI output combiner 24 via a third optical waveguide structure 29 including a third optical waveguide 30. The third optical waveguide 30 is configured to provide a third optical path length between the sixth optical output port 22 and the fifth optical input port 26. The seventh optical output port 23 of the first 1×2 MMI input optical splitter 19 and the sixth optical input port 27 of the second 2×1 MMI output combiner 24 are optically interconnected via a fourth optical waveguide structure 31 including a fourth optical waveguide 32. The fourth optical waveguide 32 is configured to provide a fourth optical path length between the seventh optical output port 23 and the sixth optical input port 27. Figure 1 In the illustrated first exemplary and non-limiting embodiment of the semiconductor tunable ring laser 1, because the fourth optical waveguide 32 is shorter than the third optical waveguide 30, the fourth optical path length is shorter than the third optical path length. Due to the difference between the fourth and third optical path lengths, the second MZI-based tunable frequency filter section 3b can be considered an asymmetric MZI-based tunable frequency filter section. Those skilled in the art will appreciate that the above considerations regarding the manner in which the optical path length difference is established apply mutatis mutandis.

[0098] Figure 1 The third MZI-based tunable frequency filter portion 3 c of the illustrated optical filter 3 includes a second 1×2 MMI input splitter 33, which includes a fifth multimode waveguide portion 34 configured to achieve a 50 / 50 splitting ratio. This fifth multimode waveguide portion 34 is provided with a seventh optical input port 35, a ninth optical output port 36, and a tenth optical output port 37. The seventh optical input port 35 is arranged in optical communication with the eighth optical output port 28 of the second 2×1 MMI output combiner 24 of the second MZI-based tunable frequency filter portion 3 b. In this manner, the seventh optical input port 35 is arranged in optical communication with the closed-loop optical path of the laser cavity 2.

[0099] The third MZI-based tunable frequency filter section 3c further includes a third 2×1 MMI output combiner 38, which includes a sixth multimode waveguide section 39 configured to achieve a 50 / 50 combining ratio. The sixth multimode waveguide section 39 is provided with an eighth optical input port 40, a ninth optical input port 41, and an eleventh optical output port 42, which is arranged to optically communicate with the closed-loop optical path of the laser cavity 2. The ninth optical output port 36 of the second 1×2 MMI input optical splitter 33 and the eighth optical input port 40 of the third 2×1 MMI output combiner 38 are optically interconnected via a fifth optical waveguide structure 43 including a fifth optical waveguide 44. The fifth optical waveguide 44 is configured to provide a fifth optical path length between the ninth optical output port 36 and the eighth optical input port 40. The tenth optical output port 37 of the second 1×2 MMI input optical splitter 33 is optically interconnected with the ninth optical input port 41 of the third 2×1 MMI output combiner 38 via a sixth optical waveguide structure 45 including a sixth optical waveguide 46. The sixth optical waveguide 46 is configured to provide a sixth optical path length between the tenth optical output port 37 and the ninth optical input port 41. Figure 1 In the illustrated first exemplary and non-limiting embodiment of the semiconductor tunable ring laser 1, because the sixth optical waveguide 46 is shorter than the fifth optical waveguide 44, the sixth optical path length is shorter than the fifth optical path length. Due to the difference between the sixth and fifth optical path lengths, the third MZI-based tunable frequency filter section 3c can be considered an asymmetric MZI-based tunable frequency filter section. Those skilled in the art will appreciate that the above considerations regarding the manner in which the optical path length difference is established apply mutatis mutandis.

[0100] according to Figure 1 In the first non-exemplary embodiment of the semiconductor tunable ring laser 1 shown, the closed-loop optical path of the laser cavity 2 is provided with a gain section 47, which includes a tenth optical input port 48 and a twelfth optical output port 49. The tenth optical input port 48 is arranged in optical communication with the eleventh optical output port 42 of the third 2×1 MMI output combiner 38 of the third MZI-based tunable frequency filter section 3 c. In this manner, the tenth optical input port 48 is arranged in optical communication with the closed-loop optical path of the laser cavity 2.

[0101] The closed-loop optical path of the laser cavity 2 is further provided with a 2×2 MMI output splitter 50. This 2×2 MMI output splitter 50 includes a seventh multimode waveguide section 51. This seventh multimode waveguide section 51 is provided with a twelfth optical input port 52. This twelfth optical input port 52 is arranged to optically communicate with the twelfth optical output port 49 of the gain section 47, thereby optically communicating with the closed-loop optical path of the laser cavity 2. The seventh multimode waveguide section 51 is also provided with a thirteenth optical input port 53, a thirteenth optical output port 55, and a fourteenth optical output port 56. The thirteenth optical input port 53 is arranged to optically communicate with an optical reflector 54 arranged outside the closed-loop optical path of the laser cavity 2. The thirteenth optical output port 55 is arranged to optically communicate with the first optical input port 6 of the 1×3 MMI input splitter 4 of the first MZI-based tunable frequency filter section 3a, thereby optically communicating with the closed-loop optical path of the laser cavity 2. The fourteenth optical output port 56 is configured and arranged to enable optical power to be coupled out of the laser cavity 2 for applications other than wavelength locking and / or power monitoring purposes. The 2×2 MMI output splitter 50 can be configured to have any suitable splitting ratio, depending on the requirements of the application in which the semiconductor tunable ring laser 1 according to the present disclosure is used.

[0102] Figure 2 A schematic top view of a second exemplary and non-limiting embodiment of a semiconductor tunable ring laser 1 according to the present disclosure is shown, wherein the semiconductor tunable ring laser 1 includes a laser cavity 2 having a closed-loop optical path and an optical filter 3 arranged in the laser cavity 2. During use of the semiconductor tunable ring laser 1, the optical filter 3 is configured as a transmissive filter. Figure 1 As shown, the filter 3 includes a first MZI-based tunable frequency filter section 3a, a second MZI-based tunable frequency filter section 3b, and a third MZI-based tunable frequency filter section 3c. However, the order in which these three MZI-based tunable frequency filter sections are arranged in series inside the laser cavity 2 is different. Figure 2 In the second exemplary and non-limiting embodiment of the semiconductor tunable ring laser 1 shown, a first MZI-based tunable frequency filter section 3a is disposed between a second MZI-based tunable frequency filter section 3b and a third MZI-based tunable frequency filter section 3c. Those skilled in the art will appreciate that the number of MZI-based tunable frequency filter sections is exemplary and non-limiting. Depending on the specific requirements to be met by the semiconductor tunable ring laser, any suitable number is contemplated, such as 1, 2, 3, 4, 5, 6, and the like.

[0103] according to Figure 2In the second exemplary and non-limiting embodiment of the semiconductor tunable ring laser 1 shown, the fourth optical input port 21 of the first 1×2 MMI input splitter 19 of the second MZI-based tunable frequency filter section 3b is arranged in optical communication with the closed-loop optical path of the laser cavity 2. The eighth optical output port 28 of the second 2×1 MMI output combiner 24 of the second MZI-based tunable frequency filter section 3b is arranged in optical communication with the first optical input port 6 of the 1×3 MMI input splitter 4 of the first MZI-based tunable frequency filter section 3a.

[0104] The fifth optical output port 14 of the first 2×1 MMI output combiner 10 of the first MZI-based tunable frequency filter section 3a is arranged in optical communication with the seventh optical input port 35 of the second 1×2 MMI input splitter 33 of the third MZI-based tunable frequency filter section 3c. The first optical output port 7 of the 1×3 MMI input splitter 4 of the first MZI-based tunable frequency filter section 3a is configured and arranged as an optical monitoring port of the laser cavity 2. Figure 2 In the second exemplary and non-limiting embodiment of the semiconductor tunable ring laser 1 shown, the first optical output port 7 of the 1×3 MMI input splitter 4 of the first MZI-based tunable frequency filter section 3 a is arranged in optical communication with the wavelength locker 120 of the optical radiation monitoring assembly 110 .

[0105] The eleventh optical output port 42 of the third 2×1 MMI output combiner 38 of the third MZI-based tunable frequency filter section 3c is arranged in optical communication with the tenth optical input port 48 of the gain section 47. The thirteenth optical output port 55 of the 2×2 MMI output splitter 50 is arranged in optical communication with the fourth optical input port 21 of the first 1×2 MMI input splitter 19 of the second MZI-based tunable frequency filter section 3b.

[0106] Figure 3 A schematic top view of a third exemplary and non-limiting embodiment of a semiconductor tunable ring laser 1 according to the present disclosure is shown, wherein the semiconductor tunable ring laser 1 includes a laser cavity 2 having a closed-loop optical path and an optical filter 3 arranged in the laser cavity 2. During use of the semiconductor tunable ring laser 1, the optical filter 3 is configured as a transmissive filter. Figure 1 and Figure 2 As shown, the filter 3 includes a first MZI-based tunable frequency filter section 3a, a second MZI-based tunable frequency filter section 3b, and a third MZI-based tunable frequency filter section 3c. However, the order in which these three MZI-based tunable frequency filter sections are arranged in series inside the laser cavity 2 is different. Figure 3The third exemplary and non-limiting embodiment of the semiconductor tunable ring laser 1 is shown, with Figure 1 Compared to the order of the MZI-based tunable frequency filter sections shown in FIG. 1 , the order of the MZI-based tunable frequency filter sections has been reversed. That is, from left to right, the third MZI-based tunable frequency filter section 3 c is followed by the second MZI-based tunable frequency filter section 3 b, which is followed by the first MZI-based tunable frequency filter section 3 a. Those skilled in the art will appreciate that the number of MZI-based tunable frequency filter sections is exemplary and non-limiting. Depending on the specific requirements to be met by the semiconductor tunable ring laser, any suitable number is contemplated, such as 1, 2, 3, 4, 5, 6, etc.

[0107] according to Figure 3 In the third exemplary and non-limiting embodiment of the semiconductor tunable ring laser 1 shown, the seventh optical input port 35 of the second 1×2 MMI input splitter 33 of the third MZI-based tunable frequency filter section 3c is arranged in optical communication with the closed-loop optical path of the laser cavity 2. The eleventh optical output port 42 of the third 2×1 MMI output combiner 38 of the third MZI-based tunable frequency filter section 3c is arranged in optical communication with the fourth optical input port 21 of the first 1×2 MMI input splitter 19 of the second MZI-based tunable frequency filter section 3b. The eighth optical output port 28 of the second 2×1 MMI output combiner 24 of the second MZI-based tunable frequency filter section 3b is arranged in optical communication with the first optical input port 6 of the 1×3 MMI input splitter 4 of the first MZI-based tunable frequency filter section 3a.

[0108] The fifth optical output port 14 of the first 2×1 MMI output combiner 10 of the first MZI-based tunable frequency filter section 3a is arranged in optical communication with the tenth optical input port 48 of the gain section 47. The first optical output port 7 of the 1×3 MMI input splitter 4 of the first MZI-based tunable frequency filter section 3a is configured and arranged as an optical monitoring port of the laser cavity 2. Figure 3 In the third exemplary and non-limiting embodiment of the semiconductor tunable ring laser 1 shown, the first optical output port 7 is arranged to be in optical communication with the wavelength locker 120 of the optical radiation monitoring assembly 110. The thirteenth optical output port 55 of the 2×2 MMI output optical splitter 50 is arranged to be in optical communication with the seventh optical input port 35 of the second 1×2 MMI input optical splitter 33 of the third MZI-based tunable frequency filter section 3c.

[0109] Those skilled in the art will appreciate that each of the three aforementioned exemplary and non-limiting embodiments of the semiconductor tunable ring laser 1 according to the present disclosure is capable of directly splitting the first non-zero fraction T1 of optical radiation from the laser cavity 2, rather than splitting it after or outside the laser cavity as is done in semiconductor tunable ring lasers known in the art, i.e., splitting it from the amount of optical radiation that constitutes the main optical output of the semiconductor tunable ring laser. As described above, despite the splitting of the first non-zero fraction T1 of optical radiation and any optical losses associated with the purpose of stabilizing the lasing wavelength, the semiconductor tunable ring laser 1 according to the present disclosure still has improved overall efficiency compared to semiconductor tunable ring lasers known in the art.

[0110] For each of the three exemplary and non-limiting embodiments of the semiconductor tunable ring laser 1 according to the present disclosure, the first MZI-based tunable frequency filter section 3a is configured to have a first free spectral range, the second MZI-based tunable frequency filter section 3b is configured to have a second free spectral range, and the third MZI-based tunable frequency filter section 3c is configured to have a third free spectral range. The first free spectral range, the second free spectral range, and the third free spectral range are different from each other. In this way, the stability of the semiconductor tunable ring laser 1 according to the present disclosure can be improved.

[0111] In addition, each of the three above-mentioned exemplary and non-limiting embodiments of the semiconductor tunable ring laser 1 according to the present disclosure can be implemented as an InP-based tunable ring laser. As mentioned above, InP-based semiconductor materials are the preferred semiconductor materials for manufacturing semiconductor tunable ring lasers, which can be used for, for example, but not limited to, telecommunications applications, light detection and ranging (LIDAR) or sensor applications. InP-based technology enables the monolithic integration of active components (such as light generating optical devices and / or light absorbing optical devices) and passive components (such as light guiding optical devices and / or optical switching optical devices) in one PIC on a single die.

[0112] As described above, by directly splitting the optical radiation of the first non-zero ratio T1 from the laser cavity 2 at the first optical output port 7 of the 1×3 MMI input optical splitter 4, the use of a lossy coupler disposed after or outside the laser cavity 2, as is done in semiconductor tunable ring lasers known in the art, can be avoided. Wafer probe measurement results show that omitting the aforementioned lossy coupler leads to a reduction in the total optical loss of the semiconductor tunable ring laser 1 according to the present disclosure. Figure 4AA comparison of the total optical output powers of three semiconductor tunable ring lasers A, B, and C known in the art and a semiconductor tunable ring laser E according to the present disclosure is shown, wherein each of these known semiconductor tunable ring lasers includes a conventional 2x2 MMI output splitter, which is arranged after or outside the laser cavity to provide optical radiation that can be used for the purpose of stabilizing the laser wavelength. In the semiconductor tunable ring laser E according to the present disclosure, the laser cavity is directly split using a 1×3 MMI input splitter, which is configured to provide optical radiation with a first non-zero ratio T1 that can be used for the purpose of stabilizing the laser wavelength. Figure 4A It is shown that the optical output power of the semiconductor tunable ring laser E according to the present disclosure is higher than the optical output power of each of the known semiconductor tunable ring lasers A, B, and C. This is not only because the optical radiation with a non-zero ratio T1 separated in the case of the semiconductor tunable ring laser E according to the present disclosure is smaller than the optical radiation with a non-zero ratio T1 separated in the cases of the known semiconductor tunable ring lasers A, B, and C, but also because the total photocurrent of the semiconductor tunable ring laser E (the total photocurrent is the sum of the photocurrent generated by the main light output of the semiconductor tunable ring laser E and the photocurrent generated by the first non-zero ratio T1 of the optical radiation directed to the light sensor of the control circuit for stabilizing the lasing wavelength) is higher than the total photocurrent of each of the known semiconductor tunable ring lasers A, B, and C. This is Figure 4B It is reflected in.

[0113] Reference Figure 4A and 4B Those skilled in the art will appreciate that, compared to the total optical losses of the three known semiconductor tunable ring lasers A, B, and C that branch off the optical radiation of the first non-zero ratio T1 after or outside the laser cavity, branching off the optical radiation of the first non-zero ratio T1 directly from the laser cavity results in a reduced total optical loss of the semiconductor tunable ring laser E according to the present disclosure. Therefore, compared to the three known semiconductor tunable ring lasers A, B, and C, the semiconductor tunable ring laser E according to the present disclosure has improved overall efficiency.

[0114] Figure 5 A schematic top view of a first exemplary and non-limiting embodiment of a PIC 100 according to the present disclosure is shown, the PIC 100 including a semiconductor tunable ring laser 1 according to the present disclosure. The semiconductor tunable ring laser 1 can be considered monolithically integrated with other optoelectronic devices (not shown) of the PIC 100.

[0115] According to an exemplary and non-limiting embodiment of a PIC (not shown), a semiconductor tunable ring laser can be integrated in a hybrid manner with other optoelectronic devices of the PIC. One advantage of implementing a hybrid integration of a semiconductor tunable ring laser according to the present disclosure is that the semiconductor tunable ring laser can be used in any field of semiconductor technology, such as silicon photonics. Another advantage of implementing a hybrid integration of a semiconductor tunable ring laser according to the present disclosure is that the semiconductor tunable ring laser can be replaced. For example, in the event of a laser failure or after a laser breakdown, the semiconductor tunable ring laser may need to be replaced.

[0116] like Figure 5 As shown, the advantage of monolithically integrating the semiconductor tunable ring laser 1 with other optoelectronic devices (not shown) on the same semiconductor substrate is that the monolithic integration of the semiconductor tunable ring laser 1 and other optoelectronic components may be less cumbersome and may require a smaller die area than hybrid integration thereof. Therefore, the cost associated with monolithic integration of active and passive optoelectronic devices may be less than the cost associated with hybrid integration thereof. Furthermore, monolithic integration may allow the PIC 100 to have a smaller footprint. This helps reduce the cost of the PIC.

[0117] PIC 100 may be an InP-based PIC. Those skilled in the art will appreciate that the most common technology platform for PICs (particularly those applicable to telecommunications, LIDAR, or sensor applications) uses wafers comprising InP-based semiconductor materials. InP-based technology enables monolithic integration of active components (e.g., light-generating optics and / or light-absorbing optics) and passive components (e.g., light-guiding optics and / or light-switching optics) into one PIC on a single die.

[0118] Based on the above, those skilled in the art will understand that the PIC 100 according to the present disclosure can benefit from the advantages provided by the semiconductor tunable ring laser 1 according to the present disclosure.

[0119] Figure 6 A schematic diagram of a first exemplary and non-limiting embodiment of an optoelectronic system 200 according to the present disclosure is shown, the optoelectronic system 200 including the PIC 100 according to the present disclosure. The optoelectronic system 200 can be used, for example, but not limited to, in telecommunications, LIDAR, or sensor applications. The optoelectronic system 200 can be, for example, a transmitter, a receiver, a transceiver, a coherent transmitter, a coherent receiver, and a coherent transceiver. Based on the foregoing, those skilled in the art will appreciate that the optoelectronic system 200 according to the present disclosure can benefit from the advantages provided by the PIC 100 according to the present disclosure.

[0120] The present disclosure can be summarized as relating to a semiconductor tunable ring laser 1, which includes a laser cavity 2 having a closed-loop optical path and an optical filter 3 arranged in the laser cavity. The optical filter includes a first MZI-based tunable frequency filter section 3a, which includes a 1×3 MMI input optical splitter 4, which provides optical radiation with a first non-zero ratio T1 at a first optical output port 7 of the 1×3 MMI input optical splitter 4 for wavelength locking and / or power monitoring purposes outside the laser cavity, provides optical radiation with a second ratio T2=(1-T1) / 2 at a second optical output port 8 of the 1×3 MMI input optical splitter 4, and provides optical radiation with a third ratio T3=(1-T1) / 2 at a third optical output port 9 of the 1×3 MMI input optical splitter 4. The present disclosure also relates to a PIC 100 comprising a semiconductor tunable ring laser according to the present disclosure, and an optoelectronic system 200 comprising such a PIC.

[0121] It will be clear to those skilled in the art that the scope of the present disclosure is not limited to the examples discussed above, but that several modifications and changes may be made thereto without departing from the scope of the present disclosure as defined by the appended claims. In particular, combinations of specific features of various aspects of the present disclosure may be made. By adding features described with respect to another aspect of the present disclosure, one aspect of the present disclosure may be further advantageously enhanced. Although the present disclosure has been described and illustrated in detail in the drawings and the specification, such illustrations and descriptions are to be considered merely illustrative or exemplary, and not restrictive.

[0122] The present disclosure is not limited to the disclosed embodiments. Variations of the disclosed embodiments may be understood and effected by those skilled in the art in practicing the claimed invention by studying the drawings, the description, and the appended claims. In the claims, the word "comprising" does not exclude other steps or elements, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the present disclosure.

Claims

1. A semiconductor tunable ring laser (1), comprising: - a laser cavity (2), wherein the laser cavity (2) has a closed-loop optical path; as well as - an optical filter (3), which is arranged in the laser cavity (2) and is configured as a transmission filter during use of the semiconductor tunable ring laser (1), and comprises: A first MZI-based tunable frequency filter section (3a), comprising: o a 1×3 MMI input optical splitter (4), the 1×3 MMI input optical splitter (4) comprising a first multimode waveguide section (5), the first multimode waveguide section (5) being provided with: o a first optical input port (6), the first optical input port (6) being arranged to be in optical communication with the closed-loop optical path of the laser cavity (2); o a first optical output port (7), the first optical output port (7) being configured and arranged as an optical monitoring port of the laser cavity (2); o a second optical output port (8); and o a third optical output port (9); o a first 2×1 MMI output combiner (10), the first 2×1 MMI output combiner (10) comprising a second multimode waveguide portion (11), the second multimode waveguide portion (11) being provided with: o a second optical input port (12); o a third optical input port (13); and o a fifth optical output port (14), the fifth optical output port (14) being arranged in optical communication with the closed-loop optical path of the laser cavity (2); and o a first optical waveguide structure (15), the first optical waveguide structure (15) comprising a first optical waveguide (16), the first optical waveguide (16) being arranged to optically interconnect the second optical output port (8) of the 1×3 MMI input optical splitter (4) with the second optical input port (12) of the first 2×1 MMI output combiner (10), the first optical waveguide structure (15) being configured to provide a first optical path length between the second optical output port (8) of the 1×3 MMI input optical splitter (4) and the second optical input port (12) of the first 2×1 MMI output combiner (10); and o a second optical waveguide structure (17), the second optical waveguide structure (17) comprising a second optical waveguide (18), the second optical waveguide (18) being arranged to optically interconnect the third optical output port (9) of the 1×3 MMI input optical splitter (4) with the third optical input port (13) of the first 2×1 MMI output combiner (10), the second optical waveguide structure (17) being configured to provide a second optical path length between the third optical output port (9) of the 1×3 MMI input optical splitter (4) and the third optical input port (13) of the first 2×1 MMI output combiner (10), the second optical path length being different from the first optical path length; The first multimode waveguide portion (5) of the 1×3 MMI input optical splitter (4) is configured to enable, during use of the semiconductor tunable ring laser (1), a first non-zero proportion T1 of the amount of optical radiation T0 incident on the first optical input port (6) of the 1×3 MMI input optical splitter (4) appears at the first optical output port (7) of the 1×3 MMI input optical splitter (4); A second proportion T2=(1-T1) / 2 of the optical radiation amount T0 appears at the second optical output port (8) of the 1×3 MMI input optical splitter (4); and A third proportion T3=(1-T1) / 2 of the optical radiation amount T0 appears at the third optical output port (9) of the 1×3 MMI input optical splitter (4); The optical radiation of the first non-zero ratio T1 is sufficient to achieve wavelength locking and / or power monitoring purposes outside the laser cavity (2).

2. The semiconductor tunable ring laser (1) according to claim 1, wherein: The first multimode waveguide section (5) of the 1×3 MMI input optical splitter (4) is configured such that the value of the first non-zero ratio T1 is in the range of 0.01 to 0.

15.

3. The semiconductor tunable ring laser (1) according to claim 1, wherein: The optical filter (3) comprises a second MZI-based tunable frequency filter portion (3b), wherein the second MZI-based tunable frequency filter portion (3b) comprises: - a first 1×2 MMI input optical splitter (19), the first 1×2 MMI input optical splitter (19) The invention comprises a third multimode waveguide portion (20), wherein the third multimode waveguide portion (20) is provided with: a fourth optical input port (21) arranged to be in optical communication with the fifth optical output port (14) of the first 2×1 MMI output combiner (10) of the first MZI-based tunable frequency filter section (3a), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); A sixth optical output port (22); and A seventh optical output port (23); The third multimode waveguide section (20) is configured to achieve a 50 / 50 splitting ratio; - a second 2×1 MMI output combiner (24), said second 2×1 MMI output combiner (24) The invention comprises a fourth multimode waveguide portion (25), wherein the fourth multimode waveguide portion (25) is provided with: A fifth optical input port (26); A sixth optical input port (27); and an eighth optical output port (28), the eighth optical output port (28) being arranged in optical communication with the closed-loop optical path of the laser cavity (2); - a third light-guiding structure (29), said third light-guiding structure (29) comprising a third optical waveguide (30), The third optical waveguide (30) is arranged to optically interconnect the sixth optical output port (22) of the first 1×2 MMI input optical splitter (19) with the fifth optical input port (26) of the second 2×1 MMI output combiner (24), and the third optical waveguide structure (29) is configured to provide a third optical path length between the sixth optical output port (22) of the first 1×2 MMI input optical splitter (19) and the fifth optical input port (26) of the second 2×1 MMI output combiner (24); and - a fourth light-guiding structure (31), said fourth light-guiding structure (31) comprising a fourth optical waveguide (32), The fourth optical waveguide (32) is arranged to optically interconnect the seventh optical output port (23) of the first 1×2 MMI input splitter (19) and the sixth optical input port (27) of the second 2×1 MMI output combiner (24), and the fourth optical waveguide structure (31) is configured to provide a fourth optical path length between the seventh optical output port (23) of the first 1×2 MMI input splitter (19) and the sixth optical input port (27) of the second 2×1 MMI output combiner (24), and the fourth optical path length is different from the third optical path length.

4. The semiconductor tunable ring laser (1) according to claim 2, wherein: The optical filter (3) comprises a second MZI-based tunable frequency filter portion (3b), wherein the second MZI-based tunable frequency filter portion (3b) comprises: - a first 1×2 MMI input optical splitter (19), the first 1×2 MMI input optical splitter (19) The invention comprises a third multimode waveguide portion (20), wherein the third multimode waveguide portion (20) is provided with: a fourth optical input port (21) arranged to be in optical communication with the fifth optical output port (14) of the first 2×1 MMI output combiner (10) of the first MZI-based tunable frequency filter section (3a), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); A sixth optical output port (22); and A seventh optical output port (23); The third multimode waveguide section (20) is configured to achieve a 50 / 50 splitting ratio; - a second 2×1 MMI output combiner (24), said second 2×1 MMI output combiner (24) The invention comprises a fourth multimode waveguide portion (25), wherein the fourth multimode waveguide portion (25) is provided with: A fifth optical input port (26); A sixth optical input port (27); and an eighth optical output port (28), the eighth optical output port (28) being arranged in optical communication with the closed-loop optical path of the laser cavity (2); - a third light-guiding structure (29), said third light-guiding structure (29) comprising a third optical waveguide (30), The third optical waveguide (30) is arranged to optically interconnect the sixth optical output port (22) of the first 1×2 MMI input optical splitter (19) with the fifth optical input port (26) of the second 2×1 MMI output combiner (24), and the third optical waveguide structure (29) is configured to provide a third optical path length between the sixth optical output port (22) of the first 1×2 MMI input optical splitter (19) and the fifth optical input port (26) of the second 2×1 MMI output combiner (24); and - a fourth light-guiding structure (31), said fourth light-guiding structure (31) comprising a fourth optical waveguide (32), The fourth optical waveguide (32) is arranged to optically interconnect the seventh optical output port (23) of the first 1×2 MMI input splitter (19) and the sixth optical input port (27) of the second 2×1 MMI output combiner (24), and the fourth optical waveguide structure (31) is configured to provide a fourth optical path length between the seventh optical output port (23) of the first 1×2 MMI input splitter (19) and the sixth optical input port (27) of the second 2×1 MMI output combiner (24), and the fourth optical path length is different from the third optical path length.

5. The semiconductor tunable ring laser (1) according to claim 3, wherein: The optical filter (3) comprises a third MZI-based tunable frequency filter portion (3c), the third MZI-based tunable frequency filter portion (3c) comprising: - a second 1×2 MMI input optical splitter (33), the second 1×2 MMI input optical splitter (33) The invention comprises a fifth multimode waveguide section (34), wherein the fifth multimode waveguide section (34) is provided with: a seventh optical input port (35) arranged to be in optical communication with the eighth optical output port (28) of the second 2×1 MMI output combiner (24) of the second MZI-based tunable frequency filter section (3b), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); A ninth optical output port (36); and A tenth optical output port (37); The fifth multimode waveguide section (34) is configured to achieve a 50 / 50 splitting ratio; - a third 2×1 MMI output combiner (38), the third 2×1 MMI output combiner (38) The invention comprises a sixth multimode waveguide section (39), wherein the sixth multimode waveguide section (39) is provided with: An eighth optical input port (40); A ninth optical input port (41); and an eleventh optical output port (42), the eleventh optical output port (42) being arranged to be in optical communication with the closed-loop optical path of the laser cavity (2); - a fifth light-guiding structure (43), said fifth light-guiding structure (43) comprising a fifth optical waveguide (44), The fifth optical waveguide (44) is arranged to optically interconnect the ninth optical output port (36) of the second 1×2 MMI input optical splitter (33) with the eighth optical input port (40) of the third 2×1 MMI output combiner (38), and the fifth optical waveguide structure (43) is configured to provide a fifth optical path length between the ninth optical output port (36) of the second 1×2 MMI input optical splitter (33) and the eighth optical input port (40) of the third 2×1 MMI output combiner (38); and - a sixth light-guiding structure (45), said sixth light-guiding structure (45) comprising a sixth optical waveguide (46), The sixth optical waveguide (46) is arranged to optically interconnect the tenth optical output port (37) of the second 1×2 MMI input splitter (33) with the ninth optical input port (41) of the third 2×1 MMI output combiner (38), and the sixth optical waveguide structure (45) is configured to provide a sixth optical path length between the tenth optical output port (37) of the second 1×2 MMI input splitter (33) and the ninth optical input port (41) of the third 2×1 MMI output combiner (38), wherein the sixth optical path length is different from the fifth optical path length.

6. The semiconductor tunable ring laser (1) according to claim 4, wherein: The optical filter (3) comprises a third MZI-based tunable frequency filter portion (3c), the third MZI-based tunable frequency filter portion (3c) comprising: - a second 1×2 MMI input optical splitter (33), the second 1×2 MMI input optical splitter (33) The invention comprises a fifth multimode waveguide section (34), wherein the fifth multimode waveguide section (34) is provided with: a seventh optical input port (35) arranged to be in optical communication with the eighth optical output port (28) of the second 2×1 MMI output combiner (24) of the second MZI-based tunable frequency filter section (3b), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); A ninth optical output port (36); and A tenth optical output port (37); The fifth multimode waveguide section (34) is configured to achieve a 50 / 50 splitting ratio; - a third 2×1 MMI output combiner (38), the third 2×1 MMI output combiner (38) The invention comprises a sixth multimode waveguide section (39), wherein the sixth multimode waveguide section (39) is provided with: An eighth optical input port (40); A ninth optical input port (41); and an eleventh optical output port (42), the eleventh optical output port (42) being arranged to be in optical communication with the closed-loop optical path of the laser cavity (2); - a fifth light-guiding structure (43), said fifth light-guiding structure (43) comprising a fifth optical waveguide (44), The fifth optical waveguide (44) is arranged to optically interconnect the ninth optical output port (36) of the second 1×2 MMI input optical splitter (33) with the eighth optical input port (40) of the third 2×1 MMI output combiner (38), and the fifth optical waveguide structure (43) is configured to provide a fifth optical path length between the ninth optical output port (36) of the second 1×2 MMI input optical splitter (33) and the eighth optical input port (40) of the third 2×1 MMI output combiner (38); and - a sixth light-guiding structure (45), said sixth light-guiding structure (45) comprising a sixth optical waveguide (46), The sixth optical waveguide (46) is arranged to optically interconnect the tenth optical output port (37) of the second 1×2 MMI input splitter (33) with the ninth optical input port (41) of the third 2×1 MMI output combiner (38), and the sixth optical waveguide structure (45) is configured to provide a sixth optical path length between the tenth optical output port (37) of the second 1×2 MMI input splitter (33) and the ninth optical input port (41) of the third 2×1 MMI output combiner (38), wherein the sixth optical path length is different from the fifth optical path length.

7. The semiconductor tunable ring laser (1) according to claim 5, wherein: The closed-loop optical path of the laser cavity (2) is provided with: - a gain section (47), said gain section (47) comprising: o a tenth optical input port (48) arranged to be in optical communication with the eleventh optical output port (42) of the third 2×1 MMI output combiner (38) of the third MZI-based tunable frequency filter section (3c), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); and o a twelfth optical output port (49); and - a 2×2 MMI output optical splitter (50), the 2×2 MMI output optical splitter (50) comprising a seventh multimode waveguide section (51), the seventh multimode waveguide section (51) being provided with: o a twelfth optical input port (52), the twelfth optical input port (52) being arranged in optical communication with the twelfth optical output port (49) of the gain section (47), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); o a thirteenth optical input port (53), the thirteenth optical input port (53) being arranged in optical communication with an optical reflector (54), the optical reflector (54) being arranged outside the closed-loop optical path of the laser cavity (2); o a thirteenth optical output port (55) arranged to be in optical communication with the first optical input port (6) of the 1×3 MMI input splitter (4) of the first MZI-based tunable frequency filter section (3a), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); and o a fourteenth optical output port (56) configured and arranged to enable optical power to be coupled out of the laser cavity (2) for applications other than wavelength locking and / or power monitoring purposes.

8. The semiconductor tunable ring laser (1) according to claim 6, wherein: The closed-loop optical path of the laser cavity (2) is provided with: - a gain section (47), said gain section (47) comprising: o a tenth optical input port (48) arranged to be in optical communication with the eleventh optical output port (42) of the third 2×1 MMI output combiner (38) of the third MZI-based tunable frequency filter section (3c), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); and o a twelfth optical output port (49); and - a 2×2 MMI output optical splitter (50), the 2×2 MMI output optical splitter (50) comprising a seventh multimode waveguide section (51), the seventh multimode waveguide section (51) being provided with: o a twelfth optical input port (52), the twelfth optical input port (52) being arranged in optical communication with the twelfth optical output port (49) of the gain section (47), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); o a thirteenth optical input port (53), the thirteenth optical input port (53) being arranged in optical communication with an optical reflector (54), the optical reflector (54) being arranged outside the closed-loop optical path of the laser cavity (2); o a thirteenth optical output port (55) arranged to be in optical communication with the first optical input port (6) of the 1×3 MMI input splitter (4) of the first MZI-based tunable frequency filter section (3a), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); and o a fourteenth optical output port (56) configured and arranged to enable optical power to be coupled out of the laser cavity (2) for applications other than wavelength locking and / or power monitoring purposes.

9. The semiconductor tunable ring laser (1) according to claim 1, wherein: The optical filter (3) comprises a second MZI-based tunable frequency filter portion (3b), wherein the second MZI-based tunable frequency filter portion (3b) comprises: - a first 1×2 MMI input optical splitter (19), the first 1×2 MMI input optical splitter (19) The invention comprises a third multimode waveguide portion (20), wherein the third multimode waveguide portion (20) is provided with: a fourth optical input port (21), said fourth optical input port (21) being arranged to be in optical communication with said closed-loop optical path of said laser cavity (2); A sixth optical output port (22); and A seventh optical output port (23); The third multimode waveguide section (20) is configured to achieve a 50 / 50 splitting ratio; - a second 2×1 MMI output combiner (24), said second 2×1 MMI output combiner (24) The invention comprises a fourth multimode waveguide portion (25), wherein the fourth multimode waveguide portion (25) is provided with: A fifth optical input port (26); A sixth optical input port (27); and an eighth optical output port (28) arranged to be in optical communication with the first optical input port (6) of the 1×3 MMI input optical splitter (4) of the first MZI-based tunable frequency filter section (3a), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); - a third light-guiding structure (29), said third light-guiding structure (29) comprising a third optical waveguide (30), The third optical waveguide (30) is arranged to optically interconnect the sixth optical output port (22) of the first 1×2 MMI input optical splitter (19) with the fifth optical input port (26) of the second 2×1 MMI output combiner (24), and the third optical waveguide structure (29) is configured to provide a third optical path length between the sixth optical output port (22) of the first 1×2 MMI input optical splitter (19) and the fifth optical input port (26) of the second 2×1 MMI output combiner (24); and - a fourth light-guiding structure (31), said fourth light-guiding structure (31) comprising a fourth optical waveguide (32), The fourth optical waveguide (32) is arranged to optically interconnect the seventh optical output port (23) of the first 1×2 MMI input splitter (19) and the sixth optical input port (27) of the second 2×1 MMI output combiner (24), and the fourth optical waveguide structure (31) is configured to provide a fourth optical path length between the seventh optical output port (23) of the first 1×2 MMI input splitter (19) and the sixth optical input port (27) of the second 2×1 MMI output combiner (24), and the fourth optical path length is different from the third optical path length.

10. The semiconductor tunable ring laser (1) according to claim 2, wherein: The optical filter (3) comprises a second MZI-based tunable frequency filter portion (3b), wherein the second MZI-based tunable frequency filter portion (3b) comprises: - a first 1×2 MMI input optical splitter (19), the first 1×2 MMI input optical splitter (19) The invention comprises a third multimode waveguide portion (20), wherein the third multimode waveguide portion (20) is provided with: a fourth optical input port (21), said fourth optical input port (21) being arranged to be in optical communication with said closed-loop optical path of said laser cavity (2); A sixth optical output port (22); and A seventh optical output port (23); The third multimode waveguide section (20) is configured to achieve a 50 / 50 splitting ratio; - a second 2×1 MMI output combiner (24), said second 2×1 MMI output combiner (24) The invention comprises a fourth multimode waveguide portion (25), wherein the fourth multimode waveguide portion (25) is provided with: A fifth optical input port (26); A sixth optical input port (27); and an eighth optical output port (28) arranged to be in optical communication with the first optical input port (6) of the 1×3 MMI input optical splitter (4) of the first MZI-based tunable frequency filter section (3a), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); - a third light-guiding structure (29), said third light-guiding structure (29) comprising a third optical waveguide (30), The third optical waveguide (30) is arranged to optically interconnect the sixth optical output port (22) of the first 1×2 MMI input optical splitter (19) with the fifth optical input port (26) of the second 2×1 MMI output combiner (24), and the third optical waveguide structure (29) is configured to provide a third optical path length between the sixth optical output port (22) of the first 1×2 MMI input optical splitter (19) and the fifth optical input port (26) of the second 2×1 MMI output combiner (24); and - a fourth light-guiding structure (31), said fourth light-guiding structure (31) comprising a fourth optical waveguide (32), The fourth optical waveguide (32) is arranged to optically interconnect the seventh optical output port (23) of the first 1×2 MMI input splitter (19) and the sixth optical input port (27) of the second 2×1 MMI output combiner (24), and the fourth optical waveguide structure (31) is configured to provide a fourth optical path length between the seventh optical output port (23) of the first 1×2 MMI input splitter (19) and the sixth optical input port (27) of the second 2×1 MMI output combiner (24), and the fourth optical path length is different from the third optical path length.

11. The semiconductor tunable ring laser (1) according to claim 9, wherein: The optical filter (3) comprises a third MZI-based tunable frequency filter portion (3c), the third MZI-based tunable frequency filter portion (3c) comprising: - a second 1×2 MMI input optical splitter (33), the second 1×2 MMI input optical splitter (33) The invention comprises a fifth multimode waveguide section (34), wherein the fifth multimode waveguide section (34) is provided with: a seventh optical input port (35) arranged to be in optical communication with the fifth optical output port (14) of the first 2×1 MMI output combiner (10) of the first MZI-based tunable frequency filter section (3a), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); A ninth optical output port (36); and A tenth optical output port (37); The fifth multimode waveguide section (34) is configured to achieve a 50 / 50 splitting ratio; - a third 2×1 MMI output combiner (38), the third 2×1 MMI output combiner (38) The invention comprises a sixth multimode waveguide section (39), wherein the sixth multimode waveguide section (39) is provided with: An eighth optical input port (40); A ninth optical input port (41); and an eleventh optical output port (42), the eleventh optical output port (42) being arranged to be in optical communication with the closed-loop optical path of the laser cavity (2); - a fifth light-guiding structure (43), said fifth light-guiding structure (43) comprising a fifth optical waveguide (44), The fifth optical waveguide (44) is arranged to optically interconnect the ninth optical output port (36) of the second 1×2 MMI input optical splitter (33) with the eighth optical input port (40) of the third 2×1 MMI output combiner (38), and the fifth optical waveguide structure (43) is configured to provide a fifth optical path length between the ninth optical output port (36) of the second 1×2 MMI input optical splitter (33) and the eighth optical input port (40) of the third 2×1 MMI output combiner (38); and - a sixth light-guiding structure (45), said sixth light-guiding structure (45) comprising a sixth optical waveguide (46), The sixth optical waveguide (46) is arranged to optically interconnect the tenth optical output port (37) of the second 1×2 MMI input splitter (33) with the ninth optical input port (41) of the third 2×1 MMI output combiner (38), and the sixth optical waveguide structure (45) is configured to provide a sixth optical path length between the tenth optical output port (37) of the second 1×2 MMI input splitter (33) and the ninth optical input port (41) of the third 2×1 MMI output combiner (38), wherein the sixth optical path length is different from the fifth optical path length.

12. The semiconductor tunable ring laser (1) according to claim 10, wherein: The optical filter (3) comprises a third MZI-based tunable frequency filter portion (3c), the third MZI-based tunable frequency filter portion (3c) comprising: - a second 1×2 MMI input optical splitter (33), the second 1×2 MMI input optical splitter (33) The invention comprises a fifth multimode waveguide section (34), wherein the fifth multimode waveguide section (34) is provided with: a seventh optical input port (35) arranged to be in optical communication with the fifth optical output port (14) of the first 2×1 MMI output combiner (10) of the first MZI-based tunable frequency filter section (3a), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); A ninth optical output port (36); and A tenth optical output port (37); The fifth multimode waveguide section (34) is configured to achieve a 50 / 50 splitting ratio; - a third 2×1 MMI output combiner (38), said third 2×1 MMI output combiner (38) comprising a sixth multimode waveguide section (39), said sixth multimode waveguide section (39) being provided with: An eighth optical input port (40); A ninth optical input port (41); and an eleventh optical output port (42), the eleventh optical output port (42) being arranged to be in optical communication with the closed-loop optical path of the laser cavity (2); a fifth optical waveguide structure (43), said fifth optical waveguide structure (43) comprising a fifth optical waveguide (44), said fifth optical waveguide (44) being arranged to optically interconnect said ninth optical output port (36) of said second 1×2 MMI input optical splitter (33) with said eighth optical input port (40) of said third 2×1 MMI output combiner (38), said fifth optical waveguide structure (43) being configured to optically connect said ninth optical output port (36) of said second 1×2 MMI input optical splitter (33) to said eighth optical input port (40) of said third 2×1 MMI output combiner (38). providing a fifth optical path length between the optical input port (40) and the third 2×1 MMI output combiner (38); and a sixth optical waveguide structure (45), the sixth optical waveguide structure (45) comprising a sixth optical waveguide (46), the sixth optical waveguide (46) being arranged to optically interconnect the tenth optical output port (37) of the second 1×2 MMI input optical splitter (33) with the ninth optical input port (41) of the third 2×1 MMI output combiner (38), the sixth optical waveguide structure (45) being configured to optically connect the tenth optical output port (37) of the second 1×2 MMI input optical splitter (33) to the ninth optical input port (41) of the third 2×1 MMI output combiner (38). A sixth optical path length is provided between the optical input port (41) and the ninth optical input port (41) of the third 2×1 MMI output combiner (38), and the sixth optical path length is different from the fifth optical path length.

13. The semiconductor tunable ring laser (1) according to claim 11, wherein: The closed-loop optical path of the laser cavity (2) is provided with: - a gain section (47), said gain section (47) comprising: o a tenth optical input port (48) arranged to be in optical communication with the eleventh optical output port (42) of the third 2×1 MMI output combiner (38) of the third MZI-based tunable frequency filter section (3c), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); and o a twelfth optical output port (49); and - a 2×2 MMI output optical splitter (50), the 2×2 MMI output optical splitter (50) comprising a seventh multimode waveguide section (51), the seventh multimode waveguide section (51) being provided with: o a twelfth optical input port (52), the twelfth optical input port (52) being arranged in optical communication with the twelfth optical output port (49) of the gain section (47), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); o a thirteenth optical input port (53), the thirteenth optical input port (53) being arranged in optical communication with an optical reflector (54), the optical reflector (54) being arranged outside the closed-loop optical path of the laser cavity (2); o a thirteenth optical output port (55) arranged to be in optical communication with the fourth optical input port (21) of the first 1×2 MMI input optical splitter (19) of the second MZI-based tunable frequency filter section (3b), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); and o a fourteenth optical output port (56) configured and arranged to enable optical power to be coupled out of the laser cavity (2) for applications other than wavelength locking and / or power monitoring purposes.

14. The semiconductor tunable ring laser (1) according to claim 9, wherein: The optical filter (3) comprises a third MZI-based tunable frequency filter portion (3c), the third MZI-based tunable frequency filter portion (3c) comprising: - a second 1×2 MMI input optical splitter (33), the second 1×2 MMI input optical splitter (33) The invention comprises a fifth multimode waveguide section (34), wherein the fifth multimode waveguide section (34) is provided with: a seventh optical input port (35), said seventh optical input port (35) being arranged in optical communication with said closed-loop optical path of said laser cavity (2); A ninth optical output port (36); and A tenth optical output port (37); The fifth multimode waveguide section (34) is configured to achieve a 50 / 50 splitting ratio; - a third 2×1 MMI output combiner (38), the third 2×1 MMI output combiner (38) The invention comprises a sixth multimode waveguide section (39), wherein the sixth multimode waveguide section (39) is provided with: An eighth optical input port (40); A ninth optical input port (41); and an eleventh optical output port (42) arranged to be in optical communication with the fourth optical input port (21) of the first 1×2 MMI input optical splitter (19) of the second MZI-based tunable frequency filter section (3b), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); - a fifth light-guiding structure (43), said fifth light-guiding structure (43) comprising a fifth optical waveguide (44), The fifth optical waveguide (44) is arranged to optically interconnect the ninth optical output port (36) of the second 1×2 MMI input optical splitter (33) with the eighth optical input port (40) of the third 2×1 MMI output combiner (38), and the fifth optical waveguide structure (43) is configured to provide a fifth optical path length between the ninth optical output port (36) of the second 1×2 MMI input optical splitter (33) and the eighth optical input port (40) of the third 2×1 MMI output combiner (38); and - a sixth light-guiding structure (45), said sixth light-guiding structure (45) comprising a sixth optical waveguide (46), The sixth optical waveguide (46) is arranged to optically interconnect the tenth optical output port (37) of the second 1×2 MMI input splitter (33) with the ninth optical input port (41) of the third 2×1 MMI output combiner (38), and the sixth optical waveguide structure (45) is configured to provide a sixth optical path length between the tenth optical output port (37) of the second 1×2 MMI input splitter (33) and the ninth optical input port (41) of the third 2×1 MMI output combiner (38), wherein the sixth optical path length is different from the fifth optical path length.

15. The semiconductor tunable ring laser (1) according to claim 14, wherein: The closed-loop optical path of the laser cavity (2) is provided with: - a gain section (47), said gain section (47) comprising: o a tenth optical input port (48) arranged in optical communication with the fifth optical output port (14) of the first 2×1 MMI output combiner (10) of the first MZI-based tunable frequency filter section (3a), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); and o a twelfth optical output port (49); and - a 2×2 MMI output optical splitter (50), the 2×2 MMI output optical splitter (50) comprising a seventh multimode waveguide section (51), the seventh multimode waveguide section (51) being provided with: o a twelfth optical input port (52), the twelfth optical input port (52) being arranged in optical communication with the twelfth optical output port (49) of the gain section (47), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); o a thirteenth optical input port (53), the thirteenth optical input port (53) being arranged in optical communication with an optical reflector (54), the optical reflector (54) being arranged outside the closed-loop optical path of the laser cavity (2); o a thirteenth optical output port (55) arranged to be in optical communication with the seventh optical input port (35) of the second 1×2 MMI input optical splitter (33) of the third MZI-based tunable frequency filter section (3c), and thereby in optical communication with the closed-loop optical path of the laser cavity (2); and o a fourteenth optical output port (56) configured and arranged to enable optical power to be coupled out of the laser cavity (2) for applications other than wavelength locking and / or power monitoring purposes.

16. The semiconductor tunable ring laser (1) according to claim 5, wherein: The first MZI-based tunable frequency filter portion (3a) is configured to have a first free spectral range, the second MZI-based tunable frequency filter portion (3b) is configured to have a second free spectral range, and the third MZI-based tunable frequency filter portion (3c) is configured to have a third free spectral range, the first free spectral range, the second free spectral range, and the third free spectral range being different from each other.

17. The semiconductor tunable ring laser (1) according to claim 11, wherein: The first MZI-based tunable frequency filter portion (3a) is configured to have a first free spectral range, the second MZI-based tunable frequency filter portion (3b) is configured to have a second free spectral range, and the third MZI-based tunable frequency filter portion (3c) is configured to have a third free spectral range, the first free spectral range, the second free spectral range, and the third free spectral range being different from each other.

18. The semiconductor tunable ring laser (1) according to claim 14, wherein: The first MZI-based tunable frequency filter portion (3a) is configured to have a first free spectral range, the second MZI-based tunable frequency filter portion (3b) is configured to have a second free spectral range, and the third MZI-based tunable frequency filter portion (3c) is configured to have a third free spectral range, the first free spectral range, the second free spectral range, and the third free spectral range being different from each other.

19. The semiconductor tunable ring laser (1) according to claim 1, wherein: The semiconductor tunable ring laser (1) is an InP-based tunable ring laser.

20. A photonic integrated circuit (PIC) (100), comprising the semiconductor tunable ring laser (1) according to claim 1, wherein: The PIC (100) is a hybrid integrated PIC or a monolithic integrated PIC.

21. The PIC (100) according to claim 20, wherein The PIC (100) includes an optical radiation monitoring component (110) optically connected to the first optical output port (7) of the 1×3 MMI input optical splitter (4) of the first MZI-based tunable frequency filter portion (3a) of the filter (3) of the semiconductor tunable ring laser (1).

22. A photovoltaic system (200), comprising the PIC (100) according to claim 20, wherein: The optoelectronic system (200) is one of a transmitter, a receiver, a transceiver, a coherent transmitter, a coherent receiver, and a coherent transceiver.

Images