On-chip light combiner

Abstract

On-chip generation of coherent, i.e., laser-like, radiation can be tuned over broadband and / or difficult-to-access wavelength regions in an integrated platform, with targeted spectral coverage beyond what is achievable with existing integrated laser systems.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. §119(e) of co-pending and commonly assigned U.S. Provisional Patent Application No. 63 / 434,015, filed December 20, 2022, CIT-8395-P, Attorney Docket No. 176.0219USP1, entitled "ON-CHIP OPTICAL SYNTHESIZER," to Luis Ledezma, Alireza Marandi, Robert M. Gray and Benjamin Gutierrez, which is incorporated herein by reference.

[0002] [Statement Regarding Government-Funded Research and Development] This invention was made with government support under Grant No. FA9550-20-1-0040 awarded by the Air Force, Grant No. W911NF-18-1-0285 awarded by the U.S. Army, Grant No. 80NMO0018D0004 awarded by NASA, and Grant No. ECCS1846273 awarded by the National Science Foundation. The government has certain rights in this invention. [Technical Field]

[0003] 1. Technical field of the invention The present disclosure relates to integrated circuits that include optical parametric oscillators. [Background technology]

[0004] 2. Description of Related Technology (NOTE: This application refers to several different documents throughout the specification, which are designated by one or more reference numbers in square brackets (e.g., [x]). A list of the different documents, ordered by their reference numbers, is provided below in the "References" section. Each document is incorporated herein by reference.)

[0005] In nanophotonics, widely tunable coherent light sources are desirable for many applications, ranging from communications to sensing. The mid-infrared spectral region (wavelengths above 2 μm) is particularly important for applications relying on molecular spectroscopy. Among tunable light sources, optical parametric oscillators generally offer the widest tuning range; however, their implementation in nanophotonics has been limited to narrow tuning ranges, confined to the visible and near-infrared wavelength ranges. We have already overcome these limitations in dispersion-engineered periodically poled lithium niobate nanophotonics, demonstrating an ultrawideband tunable optical parametric oscillator [1, 2]. With a pump wavelength near 1 μm, we achieve output wavelength tunable from 1.53 μm to 3.25 μm on a single chip, with output powers reaching tens of milliwatts. Our work represents the first octave-spanning tunable light source in nanophotonics extended into the mid-infrared range, potentially useful for numerous integrated photonics applications. Such an optical parametric oscillator (OPO) design is shown in Figures 1A, 1b, 1c, 1d and 1E. Summary of the Invention

[0006] The devices described herein are fabricated on a microchip and are capable of generating tunable coherent radiation across a wide range of the electromagnetic spectrum, including the visible, near-infrared, and mid-infrared wavelength ranges, and are based on optical parametric oscillators (OPOs) with specific control mechanisms.

[0007] Methods for controlling the spectral and / or temporal characteristics of the generated coherent radiation are also described. In some embodiments, the light source is a diode light source, coupled in an optimized geometry into an on-chip waveguide before one of the on-chip OPO embodiments. In further embodiments, the diode cavity is extended onto the chip, and the diode is an external cavity laser diode. In still other embodiments, an actuator is used to synchronize the OPO output to an on-chip and / or off-chip reference. In some embodiments, multiple light sources are used simultaneously to control the on-chip OPO. In still other embodiments, feedback of the input light source alters the behavior of the OPO, providing certain advantages. In other embodiments, feedback from the OPO to the light source achieves mode-locking of the light source. In still other embodiments, an actuator is used to modulate an on-chip light source before one of the on-chip OPO embodiments. In other embodiments, multiple on-chip OPO embodiments are implemented on a single chip. In some embodiments, additional nonlinear processes are also implemented, including, but not limited to, sum frequency generation between the pump and signal / idler and second harmonic generation of the signal / idler wave.

[0008] Representative embodiments of the present invention include, but are not limited to, the following.

[0009] 1. A device comprising a photonic integrated circuit: The photonic integrated circuit comprises: an optical parametric oscillator (OPO) that outputs at least one of a signal or an idler in response to a pump; and at least one of a pump light source, an external injection-locked input, or an auxiliary cavity coupled to the OPO.

[0010] 2. The device of embodiment 1, wherein the photonic integrated circuit further comprises an edge coupler, a grating coupler, or an evanescent coupler arranged to couple the light source to the OPO.

[0011] 3. The device of embodiment 1, wherein the light source comprises a gain medium, such as a semiconductor gain element, and a cavity for forming a laser comprising the gain medium.

[0012] 4. The device of embodiment 3, wherein at least a portion of the laser cavity is within a photonic integrated circuit coupled to the gain medium, and the laser cavity includes a configuration arranged to receive feedback from the photonic integrated circuit to the laser cavity.

[0013] 5. The device of embodiment 4, wherein the OPO comprises an output coupler coupled to output feedback from the OPO to the gain medium and / or the laser cavity.

[0014] 6. The device of embodiment 4, wherein at least a portion of the OPO is within the laser cavity.

[0015] 7. The device of embodiment 4, wherein the photonic integrated circuit comprises at least one of a reflector arranged to reflect the feedback into the laser cavity, an auxiliary resonator coupled to the OPO, at least one OPO actuator coupled to the OPO for tuning the OPO, at least one auxiliary actuator coupled to the auxiliary resonator for tuning the auxiliary resonator, or a light source actuator coupled to the light source for tuning the pump.

[0016] 8. The device of embodiment 7, wherein the reflector is a tunable reflector that is configurable to tune the wavelength of a feedback that controls the wavelength of a pump output from the light source.

[0017] 9. The laser cavity comprising the reflector and the gain medium coupled to the OPO; 8. The device of embodiment 7, further comprising: a light source actuator disposed between the reflector and the gain medium, the light source actuator being configurable to modulate the laser cavity such that the light source comprises a mode-locked laser.

[0018] 10. The reflector includes a wavelength tunable reflector; the light source actuator disposed between the reflector and the gain medium and / or coupled to the reflector; 8. The device of embodiment 7, wherein the actuator is capable of modulating the wavelength of the light source such that the light source comprises a CW laser.

[0019] 11. The photonic integrated circuit includes an auxiliary nonlinear region coupled between the output of the OPO and the gain medium; 4. The device of embodiment 3, wherein the auxiliary nonlinear region is configured to upconvert the frequency of the signal and / or the idler to form feedback that is output to the gain medium and / or laser cavity.

[0020] 12. The device of embodiment 11, wherein the OPO is configurable to output feedback to the laser cavity that self-injection locks the pump.

[0021] 13. The device of embodiment 11, wherein the OPO is configurable to output feedback comprising multiple modes for mode locking of the light source or to provide feedback for spectral narrowing of the pump.

[0022] 14. The auxiliary resonator comprises at least: tuning the frequency of the pump; filtering the frequency of the pump; or 4. The device of embodiment 3, wherein the device is coupled to the photonic integrated circuit so as to self-injection lock the pump of the OPO.

[0023] 15. The auxiliary resonator comprises: resonant at the pump wavelength and coupled to an additional parametric gain region or sharing a parametric gain region with the OPO; or 2. The device of embodiment 1, tuned to filter or modulate the frequency of a mode within the OPO.

[0024] 16. The auxiliary resonator comprises: with a pump resonator; an electro-optic modulator; the pump cavity is pumped by the pump and has at least some overlapping modes with a cavity of the OPO, such that at least some of the overlapping modes are reinforced and recirculated within the pump cavity; 2. The device of embodiment 1, wherein the electro-optic modulator is coupled to the pump resonator to synchronize a mode of the pump resonator to a mode of the pump.

[0025] 17. The auxiliary resonator comprises at least: tuning the frequency of at least one of the signal or the idler; filtering said frequencies, or 2. The device of embodiment 1, configured within the photonic integrated circuit to self-injection lock at least one of the signal or the idler to the OPO.

[0026] 18. The OPO comprises a main cavity coupled to at least one parametric gain region, and the actuator comprises: one or more electro-optic modulators coupled to at least one of the main resonator, the at least one parametric gain region, or the auxiliary resonator and operable to tune the gain and / or oscillation frequency of the pump, signal, and / or idler within the resonator; or 2. The device of embodiment 1, comprising a heater thermally coupled to the parametric gain region such that the thermal output is operable to tune the gain and / or center frequency of at least one of the pump, idler or signal output from the parametric gain region.

[0027] 19. The device of embodiment 1, further comprising one or more external injection locking inputs arranged to couple a seed signal configured for injection locking of the signal and / or the idler.

[0028] 20. The device of embodiment 1, wherein the photonic integrated circuit further comprises an additional OPO and a switch for switching the pump to a different OPO.

[0029] 21. The device of embodiment 1, further comprising a plurality of auxiliary resonators configurable to control the signal and / or idler frequencies within a range in which the OPO can operate without mode hopping.

[0030] 22. The device of embodiment 1, wherein the resonator of the OPO is coupled to one or more auxiliary resonators having different free spectral ranges, such that the combination of modes of the main resonator and the auxiliary resonators selects a single mode or a group of modes that oscillate in the main resonator.

[0031] 23. The device of embodiment 3, further comprising a waveguide coupling the gain medium to an input of the OPO, the waveguide configured to match a mode of the pump to a mode of the OPO.

[0032] 24. The device of embodiment 1, comprising a plurality of said OPOs with parametric gain regions having different spectral responses, such as due to different quasi-phase matching periods.

[0033] 25. The device of embodiment 24, wherein the inputs and outputs of the OPO are coupled, so that by selecting an appropriate combination of the inputs and outputs, signals and / or idlers at one or more outputs are used as pumps at one or more inputs, and a parametric gain region within the OPO generates signals and / or idlers in a wavelength range from the visible to the infrared.

[0034] 26. The device of embodiment 1, wherein the circuit further comprises at least one nonlinear section designed to perform upconversion and / or downconversion of the signal and / or the idler by second harmonic generation and / or sum or difference frequency generation, and may include a pump or auxiliary input to the circuit for the upconversion and / or downconversion.

[0035] 27. A device comprising a photonic integrated circuit, The photonic integrated circuit comprises: an optical parametric oscillator (OPO) comprising a main cavity coupled to a parametric gain region that outputs a signal and an idler in response to a pump using a parametric nonlinear process; and at least one of a tuning circuit or a mode-locking circuit coupled to the OPO.

[0036] Reference will now be made to the drawings, wherein like reference numerals indicate corresponding elements throughout. [Brief explanation of the drawings]

[0037] [Figure 1]Figures 1A, 1B, 1C, 1D, and 1E show an on-chip broadband tunable parametric oscillator. Figure 1A shows that when pumped with a commercially available near-infrared laser, it can generate coherent radiation tunable over an octave. Figure 1B shows that the OPO consists of a master cavity formed by a periodically poled section and a wavelength-selective coupler. Figure 1C shows an image of a fabricated chip containing 16 OPOs. Figure 1D shows an optical microscope image of an individual OPO from the chip in Figure 1C. Figure 1E shows the OPO output wavelength as a function of pump wavelength for four OPOs on the same chip. [Figure 2] Figures 2A, 2B, and 2C show the base OPO. Figure 2A shows the base OPO implemented using a ring resonator. Figure 2B shows the base OPO implemented using a linear resonator with Sagnac loop reflectors on both ends of the cavity. Figure 2C shows the base OPO implemented using a linear resonator with Bragg reflectors on both ends of the cavity. [Figure 3] 3A, 3B and 3C show an on-chip OPO with an intracavity controller. [Figure 4] 4A, 4B and 4C show a pumped resonant on-chip OPO. [Figure 5] 5A, 5B, 5C and 5D show an injection-locked on-chip OPO. [Figure 6] FIG. 6 shows the range extension method. [Figure 7] 7A, 7B, 7C and 7D show diode-integrated on-chip OPOs. [Figure 8] 8A, 8B, 8C, 8D and 8E show device embodiments that further include diode integration. [Figure 9] 9A and 9B show an intracavity on-chip OPO. [Figure 10] FIG. 10A shows an embodiment including a tunable Vernier filter, and FIG. 10B shows an embodiment including an additional auxiliary resonator. [Figure 11] 11A and 11B show a cascade system. [Figure 12] 12A and 12B show mode-locked operation, including laser mode-locking 1. These are two examples of ring cavity architectures where the pulsed operation of the OPO provides strong feedback to the laser, leading to laser mode-locking. [Figure 13] 13A and 13B show mode-locked operation, including laser mode-locking 2. These are two examples of linear cavity architectures in which the pulsed operation of the OPO provides strong feedback to the laser, leading to laser mode-locking. [Figure 14] Figure 14A shows a distributed Bragg reflector (DBR) laser, in which a Bragg grating on the back of the device acts as a wavelength-selective mirror, providing significant feedback over a narrow wavelength range. A cleaved output facet on the front of the device also serves as the other end of the laser cavity. A ridge waveguide, consisting of a stacked structure with one or more high-index quantum wells, runs between the front cleaved facet and the Bragg mirror. Image: JESpencer Own work, CC BY-SA 4.0, https: / / commons.wikimedia.org / w / index.php?curid=34983533. Figure 14B shows the power and wavelength (Δλ = λ - λ) change as a function of injection current for a DBR used to pump an OPO. As the injection current increases, the wavelength monotonically red-shifts between blue-shifted mode hops. Data courtesy of Photodigm, Inc. [Figure 15] The estimated mode shape at the output facet of a commercial DBR laser is shown in Figure 15. Using the manufacturer-provided full-width-at-half-maximum divergence angles (6° horizontal, 28° vertical), the DBR output was modeled as a single-mode elliptical beam with a 3.81 μm and 0.82 μm waist. [Figure 16]Figure 16 shows the estimated power coupling efficiency from the diode laser to the TFLN chip as a function of the TFLN waveguide width. The dashed black trace is the result of the overlap integral of the DBR mode from Figure 15 and the TFLN waveguide mode. The continuous red trace also includes the effect of back reflection due to the effective refractive index difference between the waveguides (assuming neff ≈ 3.5 for the DB waveguide). The insets show the TFLN mode profiles for 2.5 μm and 10 μm widths. [Figure 17] Figures 17A and 17B show the effect of optical feedback on a semiconductor laser. The two main feedback sources are the input and output facets of the OPO chip. The number of modes that can satisfy constructive interference (Δφ = 0) depends on the relative magnitude of the round-trip delay (τ) of the DBR laser cavity to the round-trip delay (τ) of the external cavity formed by the OPO chip. [Figure 18] Figures 18A and 18B show the DBR laser frequency as a function of the injection current with optical feedback. Figure 18A shows the DBR laser frequency when the current is modulated with a triangular wave from 110 mA to 190 mA. As the current changes, the output becomes unstable, exhibiting multiple mode hops in distinct directions. Figure 18B shows that after polishing the output facet at a 7° angle to reduce the optical feedback, the DBR laser frequency stabilizes and changes in a predictable manner, with the expected blue-shifted mode hops. [Figure 19] Figures 19A, 19B, and 19C show the OPO chip coupled to a DBR laser diode. Figure 19A is an image of the OPO chip on the test setup, showing the DBR laser and the output cleaved multimode fiber. The dashed rectangle indicates a single OPO on the chip. Figure 19B is a close-up image of the DBR laser in close contact with the TFLN chip. Two waveguides are visible on the TFLN chip: one is the input to the OPO and the other is a straight waveguide for testing. Figure 19C is a close-up image of the laser diode above threshold. The camera can detect scattered near-infrared light at the interface between the laser and the TFLN chip. [Figure 20] Figures 20A, 20B, and 20C show the spectra of a free-running continuous-wave (CW) OPO driven by a DBR laser diode. Figure 20A shows an example of the output spectrum for a small change in pump wavelength around 1063.7 nm at a DBR injection current of 241 mA (corresponding to approximately 160 mW). Figure 20B shows a close-up of the frequency function of the three spectra. The resolution bandwidth of the optical spectrum analyzer was set to approximately 3.4 GHz, allowing the different cavity modes to be distinguished. The center trace (green) corresponds to the signal / idler single-mode pair, while the other two traces show multimode operation. Figure 20C shows an example of stable operation in the near-degenerate mode, corresponding to the top panel of Figure 20A; the OPO was stable for over 30 minutes without the use of any synchronization techniques or environmental isolation. [Figure 21] FIG. 21 is a flowchart showing a method for manufacturing a device. DETAILED DESCRIPTION OF THE INVENTION

[0038] In the following description of the preferred embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

[0039] Technical Description Described herein are devices fabricated on a microchip based on optical parametric oscillators (OPOs), which further include control mechanisms and / or light sources to enhance the functionality of the on-chip OPOs.

[0040] Base OPO OPOs are fabricated using an optical nonlinear gain section surrounded by an optical cavity. The nonlinear gain section can be implemented on-chip in periodically poled lithium niobate, known as periodically poled lithium niobate (PPLN). The on-chip cavity can be either a ring or linear resonator. Ring resonators rely on a waveguide, or a collection of waveguides, connected by an optical coupler, which surrounds itself to form a single continuous optical path. Linear resonators rely on an on-chip reflector, such as a Sagnac loop reflector, a Bragg reflector, a highly reflective cleaved facet, or any other on-chip device used to reflect electromagnetic radiation back into the same waveguide to form a bidirectional resonator. As used herein, the term "based OPO" refers to an on-chip OPO implemented in this manner.

[0041] 2A, 2B, and 2C illustrate several embodiments of base OPOs. Base OPOs have limited ability to control the coherent radiation generated. The only way to change the characteristics of this radiation in such base OPOs is to modify the characteristics of the resonator and PPLN section. These modifications are static, i.e., fixed after the chip is fabricated, and there is no way to dynamically control the coherent radiation generated. The only way to do this is to completely fabricate a new device. This limits the usefulness of such base OPOs in many applications.

[0042] Control mechanism (actuator, auxiliary resonator, filter, light source) Embodiments of the devices described herein further include a control mechanism that allows for dynamic control of the base OPO. Under the term "control mechanism" or "controller," the actuator, auxiliary resonator, filter, and light source are defined as follows:

[0043] As used herein, the term "actuator" refers to an electro-optic modulator (EOM), an acousto-optic modulator (AOM), a heater, or any on-chip and / or off-chip device and / or mechanism used to dynamically change the refractive index of any portion of the device. Any combination of actuators can be used individually and / or in combination with each other to perform specific dynamic changes in the base OPO that allow control of the output coherent radiation.

[0044] As used herein, the term "auxiliary resonator" refers to any linear or ring resonator implemented in addition to the main OPO resonator. The auxiliary resonator may be separate from the main resonator or may share a portion of the waveguide connected to the main resonator.

[0045] As used herein, the term "filter" refers to any combination of resonators, couplers, or integrated components that allow for spectral selectivity.

[0046] As used herein, the term "light source" refers to an on-chip and / or off-chip device capable of generating electromagnetic radiation to be used as input to an on-chip OPO. This radiation may be coherent or incoherent. The radiation may be pulsed, continuous, or a combination of the two. The light source may be further coupled to the chip using free-space methods, such as end-fire coupling to a chip facet or grating coupler, and / or direct coupling methods, such as butt-coupling to a chip end facet. The light source may also be a diode light source butt-coupled to a waveguide tapered to an optimized shape.

[0047] Illustrative Embodiments a. On-chip OPO with intracavity controller In one embodiment, the device 300 described herein may implement a base OPO further comprising one or more intracavity controllers, which may operate individually and / or simultaneously.

[0048] In one embodiment shown in FIG. 3A, an EOM 310 is implemented in the main cavity 306, and heaters 310 are implemented along the PPLN section. In addition to tuning the cavity modes, the intracavity actuator can also be used to actively synchronize the operation of the OPO 302. This synchronization can be achieved not only by measuring the operation of the OPO itself, but also by comparing the operation to an external reference. External references include passive cavities, either on-chip or off-chip, or atomic or molecular transitions. Additionally, the OPO's generated output can be upconverted or downconverted on-chip to tune to a desired wavelength.

[0049] On-chip OPOs can be combined with an auxiliary resonator or multiple auxiliary resonators that have a different free spectral range (FSR) compared to the main resonator. The coupling to this resonator can be conservative or dissipative (if additional open ports are present). The additional resonators can be of different types, such as ring or linear resonators. The mode combination of the auxiliary and main resonators affects the operation of the OPO. This combination can be configured to oscillate only in a single mode (or a desired set of modes) of the main resonator. The OPO operating principle of such a design can be similar to the use of intracavity etalons in free-space OPOs.

[0050] In one embodiment, the base OPO further comprises an auxiliary resonator 304, a ring resonator conservatively coupled to the main resonator (FIG. 3B). In this embodiment, the overlap of the spectral modes of the main and auxiliary resonators results in single-mode operation of the OPO or selective multimode operation of the OPO. In another related embodiment, both the main and auxiliary resonators 304 further comprise intracavity actuators 310 (FIG. 3C). Thermal and electro-optical actuators are implemented for coarse and / or fine tuning of the oscillation frequency. Heaters are used to adjust the parametric gain center frequency for broadband tuning. Electro-optical modulators on the main and auxiliary resonators are used for fine tuning of the oscillation frequency modes. These actuators can be used to synchronize the OPO output to an on-chip or off-chip reference.

[0051] b. Pumped resonant on-chip OPO In other embodiments, shown in FIGS. 4A, 4B, and 4C, the device 400 described herein may implement a base OPO that further comprises an auxiliary resonator resonating at the pump wavelength. In one embodiment, the auxiliary resonator 406 is a ring resonator that shares the PPLN section 412 of the main resonator 407 (FIG. 4A). In this embodiment, the pump wavelength is also coupled (via a conservative coupler) to the auxiliary resonator 406. This allows for resonant enhancement of the pump field of the OPO cavity, affecting the threshold and efficiency of the on-chip OPO. In another embodiment, the device further comprises actuators 410 within the main resonator, the auxiliary resonator, and along the PPLN section (FIG. 4B). This allows for resonant enhancement of the pump field of the OPO cavity, which can be controlled using the actuator 404 within the pump resonator. In another embodiment, the device further comprises an additional auxiliary resonator 411 coupled to the main resonator to function as a spectrally selective filter. The device may further comprise an actuator 413 within this auxiliary resonator for tuning the resonant frequency mode (FIG. 4C). In another embodiment, the auxiliary resonator can be combined with an additional OPO resonator.

[0052] c. Injection-locked on-chip OPO 5A, 5B, and 5C illustrate that the operation of device 500 can be injection-locked using two or more light sources simultaneously. In some embodiments, two light sources (light source 1 and light source 2) are combined into a single waveguide 504 before being injected into the device (FIGS. 5A, 5B). In other embodiments, light source 502 is injected into device 500 from a different location (FIGS. 5C, 5D). In either case, the additional light source serves to seed the device's operation and synchronize the output coherent radiation to specific operating conditions. Such injection-locking techniques allow the coherence properties of the light source to be transferred to the device's output coherent radiation.

[0053] d. Range expansion method The tuning range of an OPO can be significantly expanded by using multiple OPOs with different quasi-phase-matching periods, which can be driven by the same pump laser using an electro-optical switch integrated on the same chip 600, as shown in Figure 6. In one embodiment, two on-chip OPOs 602 are driven by a single light source 606 with an electro-optical switch 604 routing the pump laser to either of the on-chip OPOs 602 (Figure 6).

[0054] Furthermore, the tuning range of the signal / idler can be used to access new wavelengths through second-harmonic generation on the same chip. Similarly, sum-frequency generation can be used to combine tunable signal / idler and pump waves to generate wavelengths much shorter than the pump, including in the visible wavelength range. All of these processes can be implemented on the same chip.

[0055] e. Diode-integrated on-chip OPO In still other embodiments, the devices described herein can further comprise integration with a semiconductor laser chip (e.g., laser diode 700 or semiconductor gain element) to achieve a fully integrated light source, as shown in Figures 7A, 7B, 7C, and 7D. The semiconductor chip can function as a standalone pump laser, i.e., its operation is independent of the circuitry on the OPO chip and / or may be influenced by circuit elements on the OPO chip 705. All embodiments of the present devices that include a base OPO constitute new device embodiments when further incorporating diode integration. In one embodiment, the semiconductor chip (laser diode) is butt-coupled 702 to the on-chip base OPO. Some embodiments further include additional components, such as a tapered waveguide 704, to optimize the coupling of light from the diode to the OPO chip (Figure 7).

[0056] 8A, 8B, 8C, 8D and 8E show an embodiment of a device 800 further comprising a diode 802 integrated therein.

[0057] f. Intracavity on-chip OPO Diode integration can also enable improved operating capabilities. For example, if the diode is a semiconductor optical amplifier (SOA), as shown in FIGS. 9A-9B, the laser cavity 902 is extended to the OPO chip 901, and a distributed Bragg reflector, Sagnac loop reflector 904, or any other reflective component defines the laser operation. An embodiment of the device 900 is placed within the laser cavity of an external cavity laser diode, resulting in an intracavity OPO. The OPO chip can provide feedback to the laser gain chip, and the laser cavity is external to the semiconductor chip. The feedback mechanism is realized via some kind of reflective mechanism. The reflective mechanism can be placed after the OPO and / or before the OPO. In one embodiment of the device, an SOA, which serves as the input of another embodiment of the device, is butt-coupled to the waveguide, and the device further includes a Sagnac loop reflector 904 placed after the OPO (FIG. 9A). In another related embodiment, the device further includes actuators 907, 908 for tuning the device (FIG. 9B). The laser actuator can also be used to mode-lock the laser cavity to realize an intracavity mode-locked OPO. An output coupler 906 can also be included.

[0058] In another embodiment, the device further includes a tunable Vernier filter 1010 integrated into the Sagnac loop mirror to form a tunable reflector (FIG. 10A). This tunable reflector functions to control the pump laser wavelength, providing another control mechanism for the OPO. In another embodiment, the device further includes an additional auxiliary resonator 1002 coupled to the main resonator to function as a spectrally selective filter, and may further include an actuator 1006 for tuning the resonant frequency mode in the auxiliary resonator (FIG. 10B).

[0059] g. Cascade system In some embodiments, the light source may further include a control mechanism for modulating the light source radiation before being injected into any embodiment of the on-chip OPO. In this manner, the light source can be dynamically controlled, enabling effective dynamic control of the on-chip OPO. In one embodiment, a semiconductor optical amplifier (SOA) is butt-coupled to an on-chip waveguide implementing a Sagnac loop reflector to form an external cavity laser. Figure 11A shows that an EOM 1104 is then placed before the loop reflector 1106 and modulated with the free spectral range of the external cavity laser diode to form an on-chip mode-locked laser. The output of this light source is then used as the input to any embodiment of the on-chip OPO. This embodiment of the device 1100 is then formed by an on-chip mode-locked laser cascaded to an on-chip OPO (Figure 11A). In another embodiment, shown in Figure 11B, an SOA is butt-coupled to a waveguide with a Sagnac loop reflector implementing a tunable Vernier filter 1108. In this embodiment, the tunable Vernier filter is realized by two auxiliary ring resonators placed within the loop reflector and tuned using an EOM. The output of this light source is then used as the input to an optional embodiment of an on-chip OPO. This device embodiment is then formed by a tunable CW laser cascaded to the on-chip OPO (Figure 11B).

[0060] In another embodiment, a laser diode is butt-coupled to a waveguide that further implements an intensity and phase modulator and a dispersion-compensating section of the waveguide to form an on-chip electro-optic frequency comb. An optional embodiment of an on-chip OPO is then cascaded. This device embodiment is then formed by an on-chip electro-optic frequency comb cascaded with an on-chip OPO.

[0061] h. Mode-locked operation The devices described herein may include feedback to the light source, which functions to mode-lock the light source itself. Feedback to the laser may be provided at least in part via the OPO cavity. An embodiment of device 1200 is shown in Figures 12A and 12B. In these configurations, the strength of the feedback to the cavity depends on the strength of the OPO's nonlinearity, e.g., the OPO's conversion efficiency. If the OPO's conversion efficiency is high, the converted wavelength is fed back to the poled region 1202 for upconversion before entering the laser 1204. In such a configuration, the better the OPO performs, the stronger the feedback to the laser, and therefore the laser is expected to self-lock to its best operating mode. This operating mode may be multimode, and mode-locking is expected to occur. In addition to mode-locking, the nonlinear feedback mechanism to the OPO can also result in spectral narrowing of the laser to match the wavelength range required by the OPO. In some embodiments, feedback can also be provided using a linear resonator on the same OPO chip. Examples of such extended resonators are shown in Figures 13A and 13B.

[0062] Example: Laser diode pumped OPO a.Introduction There are several challenges associated with directly driving an on-chip OPO with a compact laser. The most pressing is the large coupling loss encountered with conventional OPOs, which typically exceeds 10 dB when coupling from free space to an on-chip waveguide. For example, for an OPO with a peak power threshold of approximately 30 mW, this would require an off-chip CW power of over 300 mW, which is just enough to reach threshold, assuming the same coupling loss. However, the large input coupling loss is a linear problem that can be solved by optimizing the mode overlap between the incident pump beam and the nanophotonic waveguide. In this example, we demonstrate this optimization when the pump is a compact semiconductor laser diode.

[0063] A second challenge is the sensitivity of laser diodes to optical feedback [4]. Direct butt-coupling of a laser diode to a nanophotonic chip results in back-reflection at each interface, leading to potential instabilities. In fact, the tabletop χ (2) Previous attempts to pump OPOs with laser diodes have required the use of bulky isolators [5], [6] that are incompatible with integrated photonics. Here, we solve this problem by experimentally demonstrating that the main problem arises from reflections at the output facet of the chip, and that reducing these reflections improves the stability of the diode laser sufficiently to achieve stable optical parametric oscillation for tens of minutes without the need for an active synchronization system.

[0064] b.DBR laser A distributed Bragg reflector (DBR) laser consists of a single spatial mode waveguide with a gain region and a passive Bragg grating region (Figure 14A). The gain region has multiple epitaxial layers forming one or more quantum wells that are electrically pumped by current injection. The Bragg grating region forms one end of the laser cavity, providing high reflectivity within a narrow spectral bandwidth. The other end of the laser cavity is provided by a cleaved facet, which typically contains an anti-reflection coating and serves as the laser's output. The output beam is typically nearly diffraction-limited [3].

[0065] The output wavelength of a DBR laser varies with output power and injection current, as shown in Figure 14B for a commercial DBR (PH1064DBR - Photodigm Inc. [3]) that we use to pump an OPO. Increasing the injection current increases the temperature of the gain region, causing thermal expansion and a corresponding redshift of the output wavelength. The temperature of the Bragg region does not change significantly with the injection current into the gain region. Therefore, the reflection bandwidth of a DBR is primarily a function of the temperature of the entire device, not the injection current. After the output mode redshifts by a certain amount with increasing temperature, a combination of gain and reflectivity causes another mode to dominate, resulting in a blueshifted mode hop. This mode hop typically equals the unity free spectral range of the laser cavity. For example, Figure 14B shows a blueshifted mode hop of approximately 20 GHz, corresponding to a cavity length of approximately 1.5 mm. In principle, this tuning behavior allows the output power to be monotonically increased at a fixed wavelength by carefully controlling the device temperature.

[0066] c. Optimizing input coupling Commercially available DBR lasers have a full-width-at-half-maximum (FWHM) output and a horizontal Θ x =6°, vertical Θ y = 28°, which at λ = 1064 nm has horizontal and vertical waists of

number

[0067] The power coupling coefficient between the laser and the TFLN waveguide is

number

number

[0068] Mode overlap γ O is given by [8] as follows:

number

number

[0069] d. Minimizing back reflections All kinds of laser diodes are sensitive to external optical feedback [4][9]. The effects range from unstable behavior and frequent mode hops to linewidth broadening or narrowing. In this case, the two main sources of optical feedback to the pump laser are the two facets of the OPO chip (see Figure 17A). The effect of each facet can be roughly understood as follows: the input facet is in close proximity to the DBR laser facet, and therefore its main effect is the reflection coefficient

number

[0070] A more rigorous analysis can also be performed [4], including the backaction of the laser frequency on the threshold gain and effective refractive index, such that the change in round-trip phase (modulo 2π) is

number

[10] . e <<τ L ), long external cavity feedback (τ e >>τ L A plot of Δφ for ≈ 0.5 is shown in Figure 17B. The zero crossings indicate modes that satisfy the positive feedback round-trip condition.

[0071] This theoretical analysis suggests that reflections from the output facet may play an important role in the stability of DBR lasers. Figure 18A shows the measured spectrum of a DBR laser diode after sweeping the injection current and passing it through a test waveguide on an OPO chip. Discontinuous tuning with frequent mode hops is observed, including in the region of multimode operation. Figure 18B shows the same measurement repeated after polishing the output facet at a 7° angle to reduce the magnitude of reflections. Tuning is monotonic, except for the expected blue-shifted mode hop at approximately 20 GHz. In other cases, the chip's output waveguide intersects the facet at an angle of at least 7°.

[0072] e. Example of operation: Free running OPO results An image of the OPO chip and DBR laser in the test setup is shown in Figure 19A. The OPO chip was mounted on a thermoelectric cooler (TEC), and the output was collected using a cleaved multimode fiber. There were 17 OPOs on this single chip; the red dashed line in Figure 19A highlights a single OPO, approximately 7 mm long and 0.5 mm wide. Figures 19B and 19C show close-up images of the DBR laser in close proximity to the OPO input waveguide. The 1 μm scattered light of the laser above threshold was detected by the camera.

[0073] The OPO crossed threshold at about 120 mA, which corresponds to about 50 mW according to the DBR laser datasheet (see Figure 14B). As the current was increased, several oscillation peaks were observed on the 2 μm photodetector. These peaks were expected because the wavelength of the DBR laser also changes as the current is increased, causing different signal / idler pairs to go in and out of resonance.

[0074] Figure 20A shows three different example spectra when operated at approximately three times the threshold. The OPO could operate in a single-mode signal / idler pair (center panel of Figure 20A) or in the multimode regime (top and bottom panels of Figure 20A). The close-up in Figure 20B has sufficient resolution to reveal the cavity modes with a free spectral range of approximately 9.5 GHz. This on-chip OPO demonstrated significant advantages over tabletop implementations by operating continuously for over 30 minutes without any mode hopping or stabilization or locking techniques (Figure 20C).

[0075] f. Possible improvements The results presented here already demonstrate the feasibility of compact laser sources capable of replacing several individual laser diodes. The tuning range demonstrated here is sufficient for many applications and can be extended by using diode pumps with tuning ranges of more than 10 nm, such as a sampled-grating DBR (SGDBR) design that includes a gain section, a phase section, and front and rear SGDBR mirrors

[11] . Preliminary results show a tuning range of more than 30 nm around 1030 nm

[12] . Another option is to utilize optical feedback from a TFLN chip, creating the first tunable pump from a semiconductor gain chip [1]. Such a pump can be integrated on the same chip as the OPO and be tunable across the entire semiconductor gain bandwidth, essentially eliminating the problem of optical feedback instability.

[0076] In some cases, continuous tuning of the OPO output may require complex algorithms to exploit the interplay of all tuning variables in a doubly resonant OPO. When the tradeoffs between threshold, tunability, and output power are all deemed favorable, as in pulsed applications, utilizing a single-resonant OPO is also an option.

[0077] Applications requiring a single spectral mode with high coherence require refinements to the OPO design. For example, an additional cavity can be added to increase the effective free spectral range and confine the oscillation to a single mode. An electro-optic modulator on the additional cavity enables hopping between adjacent longitudinal modes of the main cavity

[13] . Continuous mode-hop-free tuning of such nested cavities can also be achieved by cooperatively shifting both cavities

[14] .

[0078] OPOs can be used to control the various frequencies involved and additional χ generation, such as sum frequency generation. (2) The process possibilities offer many options in terms of coherence and frequency stabilization. The OPO output can be directly stabilized to a reference cavity, achieving relative stability of several kilohertz over several hours

[15] . It is also possible to perfectly synchronize to atomic transitions; for example, in

[16] , an 852 nm OPO signal was synchronized to a Cs hyperfine transition for several minutes. This method can be extended into the infrared range; for example, the same Cs transition can be used to synchronize a 1704 nm signal via frequency doubling.

[0079] In summary, the results of this example demonstrate that an on-chip OPO can be directly pumped by a compact semiconductor laser without the need for additional bulky components such as high-power amplifiers or isolators, thereby enabling the realization of a fully integrated, broadly tunable light source as described herein.

[0080] g.References The following documents are incorporated herein by reference:

[0081] [1] M. Li, L. Chang, L. Wu, J. Staffa, J. Ling, U. A. Javid, S. Xue, Y. He, R. Lopez-rios, T. J. Morin, H. Wang, B. Shen, S. Zeng, L. Zhu, K. J. Vahala, J. E. Bowers, and Q. Lin, "Integrated Pockels laser," Nature Communications, vol. 13, no. 1, p. 5344, Sep. 2022, ISSN: 2041-1723. DoI: 10.1038 / s41467-022-33101-6. [2] M. Zhang, B. Buscaino, C. Wang, A. Shams-Ansari, C. Reimer, R. Zhu, J. M. Kahn, and M. Loncar, "Broadband electro-optic frequency comb generation in a lithium niobate mirroring resonator," Nature, vol. 568, no. 7752, pp. 373-377, Apr. 2019, ISSN: 1476-4687. Dor: 10.1038 / s41586019-1008-7. [3] Photodigm Inc., PH1064DBR Series, www.photodigm.com. [4] K. Petermann, Laser Diode Modulation and Noise. Springer Science & Business Media, Apr. 1991, ISBN: 978-0-7923-1204-8. [5] I. D. Lindsay, G. A. Turnbull, M. H. Dunn, and M. Ebrahimzadeh, "Doubly resonant continuous-wave optical parametric oscillator pumped by a single-mode diode laser," Optics Letters, vol. 23, no. 24, pp. 1889-1891, Dec. 1998, ISSN: 1539-4794. Dor: 10.1364 / 0L.23.001889. [6] A. J. Henderson, P. M. Roper, L. A. Borschowa, and R. D. Mead, "Stable, continuously tunable operation of a diode-pumped doubly resonant optical parametric oscillator," Optics Letters, vol. 25, no. 17, pp. 1264-1266, Sep. 2000, ISSN: 1539-4794. DOI: 10.1364 / OL.25.001264. [7] M. Achtenhagen, N. V. Amarasinghe, L. Jiang, J. Threadgill, and P. Young, "Spectral properties of high-power distributed bragg reflector lasers," Journal of Lightwave Technology, vol. 27, no. 16, pp. 3433-3437, Aug. 2009, ISSN: 1558-2213. DOI: 10.1109 / JLT. 2008.2005848. [8] A. W. Snyder and J. D. Love, Optical Waveguide Theory (Science Paperbacks 190). London ; New York: Chapman and Hall, 1983, ISBN: 978-0-41209950-2. [9] J. Mork, B. Tromborg, and J. Mark, "Chaos in semiconductor lasers with optical feedback: Theory and experiment," IEEE Journal of Quantum Electronics, vol. 28, no. 1, pp. 93-108, Jan. 1992, issn: 1558-1713. DoI: 10.1109 / 3.119502.

[10] C. Henry, "Theory of the linewidth of semiconductor lasers," IEEE Journal of Quantum Electronics, vol. 18, no. 2, pp. 259-264, Feb. 1982, ISSN: 15581713. DOI: 10.1109 / JQE. 1982.1071522.

[11] P. A. Verrinder, L. Wang, J. Fridlander, F. Sang, V. Rosborough, M. Nickerson, G. Yang, M. Stephen, L. Coldren, and J. Klamkin, "Gallium arsenide photonic integrated circuit platform for tunable laser applications," IEEE Journal of Selected Topics in Quantum Electronics, vol. 28, no. 1, pp. 1-9, 2021.

[12] P. A. Verrinder, L. Wang, J. Fridlander, F. Sang, V. Rosborough, M. Nickerson, G. Yang, M. Stephen, L. Coldren, and J. Klamkin, "Gallium Arsenide Photonic Integrated Circuit Platform for Tunable Laser Applications," IEEE Journal of Selected Topics in Quantum Electronics, vol. 28, no. 1: Semiconductor Lasers, pp. 1-9, Jan. 2022, ISSN: 1558-4542. DOI: 10.1109 / JSTQE . 2021.3086074.

[13] D. J. M. Stothard, I. D. Lindsay, and M. H. Dunn, "Continuous-wave pump-enhanced optical parametric oscillator with ring resonator for wide and continuous tuning of single-frequency radiation," Optics Express, vol. 12, no. 3, pp. 502-511, Feb. 2004, ISSN: 1094-4087. Dor: 10.1364 / OPEX . 12 . 000502.

[14] P. Groβ, I. D. Lindsay, C. J. Lee, M. Nittmann, T. Bauer, J. Bartschke, U. Warring, A. Fischer, A. Kellerbauer, and K.-J. Boller, "Frequency control of a 1163nm singly resonant OPO based on MgO:PPLN," Optics Letters, vol. 35, no. 6, pp. 820-822, Mar. 2010, ISSN: 1539-4794. DoI: 10.1364 / OL.35.000820.

[15] O. Mhibik, T.-H. My, D. Paboeuf, F. Bretenaker, and C. Drag, "Frequency stabilization at the kilohertz level of a continuous intracavity frequency doubled singly resonant optical parametric oscillator," Optics Letters, vol. 35, no. 14, pp. 2364-2366, Jul. 2010, ISSN: 1539-4794. DOI: 10 . 1364 / OL . 35 . Q02364.

[16] S. Zaske, D.-H. Lee, and C. Becher, "Green-pumped cw singly resonant optical parametric oscillator based on MgO:PPLN with frequency stabilization to an atomic resonance," Applied Physics B, vol. 98, no. 4, pp. 729-735, Mar. 2010, ISSN: 1432-0649. DoI: 10.1007 / s00340-009-3871-7.

[17] Luis Ledezma et al., Octave-spanning tunable infrared parametric oscillators in nanophotonics. Sci. Adv. 9, eadf9711 (2023). DOI:10.1126 / sciadv.adf9711

[18] Further information on this example can be found in Ledezma, Luis M. (2023) Towards Universal Integrated Laser Sources with Nonlinear Photonics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907 / ag5t-r511. https: / / resolver.caltech.edu / CaltechTHESIS:05242023-033922764

[0082] Process Steps FIG. 21 is a flowchart showing a method for manufacturing a device.

[0083] Block 2100 represents designing and fabricating (e.g., photolithographically patterning) an OPO with one or more waveguides containing nonlinear material that outputs a signal and an idler in response to a pump using a parametric nonlinear process. The waveguides each have a width and height of less than 5 micrometers. The nonlinear material is phase-matched and dispersion-engineered to control the appropriate group velocity mismatch (GVM) between the pump and signal pulses to provide temporal overlap of the pump and signal pulses. In one or more examples, the lengths of the waveguides range from 10 micrometers to 1 millimeter, with GVM differences of less than 1%. Examples of materials with second-order nonlinearity include, but are not limited to, lithium niobate, lithium tantalate, potassium titanyl phosphate (KTP), aluminum nitride, gallium arsenide, indium phosphide, aluminum gallium arsenide, GaP, or InGaP. In one or more examples, the (e.g., nonlinear) material is patterned on a substrate to form waveguides configured within a photonic integrated circuit. In one or more examples, the substrate comprises lithium niobate on silicon dioxide, and the waveguide is patterned in the lithium niobate (monolithic integration of the waveguide). Other components, such as the laser, injection-locked input, or auxiliary cavity, can be patterned on the same substrate or on a different material substrate bonded to the substrate containing the OPO.

[0084] In one embodiment, the device is fabricated using a commercial wafer with an x-cut, 700 nm thick MgO-doped lithium niobate layer and a silicon oxide buffer layer. Quasi-phase matching is provided by periodic poling over a 5 mm long region. The waveguides are patterned using electron beam lithography and dry-etched to a depth of 250 nm using Ar+ plasma. All OPOs have identical waveguide geometries achieved by dispersion engineering: the input and output waveguides are 2.3 μm wide, tapering (via an adiabatic coupler) to 2.5 μm wide waveguides within the cavity. To maximize the spectral range covered on a single chip, OPOs with poling periods ranging from 5.55 to 5.7 μm in 10 nm increments were fabricated. A straight waveguide is provided next to each OPO for calibration and verification of quasi-phase matching. See Luis Ledezma et al., Octave-spanning tunable infrared parametric oscillators in nanophotonics. Sci. Adv. 9, eadf9711 (2023). DOI:10.1126 / sciadv.adf9711 (this reference is incorporated herein by reference).

[0085] Block 2102 represents the final product, a device, which can be embodied in a variety of forms, including but not limited to the following (see also FIGS. 1-20):

[0086] 1. A device 300, 400, 600, 800, 900, 1000, 1100, 1200, 1300 comprising a photonic integrated circuit 303: The photonic integrated circuit comprises: an optical parametric oscillator (OPO) 302 that outputs at least one of a signal or an idler in response to a pump; A device 300, 400, 600, 800, 900, 1000, 1100, 1200, 1300 comprising a pump light source 700, 408, an external injection locking input 502 or at least one auxiliary cavity 304 coupled to said OPO.

[0087] 2. The device of embodiment 1, wherein the photonic integrated circuit further comprises an edge coupler 700, a grating coupler or an evanescent coupler arranged to couple the light source to the OPO.

[0088] 3. The device of embodiment 1 or 2, wherein the light source comprises a semiconductor gain element 800, a gain medium such as an SOA, and optionally a cavity 902 for forming a laser comprising said gain medium.

[0089] 4. The device of embodiment 3, wherein at least a portion of the laser cavity is within a photonic integrated circuit coupled to the gain medium, and the laser cavity includes a configuration arranged to receive feedback 904 from the photonic integrated circuit to the laser cavity.

[0090] 5. A device as described in any of embodiments 2-4, wherein the OPO comprises an output coupler 906 coupled to output feedback from the OPO to the gain medium and / or the laser cavity.

[0091] 6. A device described in any of embodiments 3-5, wherein at least a portion of the OPO 908 is within the laser cavity.

[0092] 7. A device described in any of embodiments 3-6, wherein the photonic integrated circuit comprises at least one of a reflector 904, 1010 arranged to reflect the feedback into the laser cavity, an auxiliary resonator 1002 coupled to the OPO, at least one OPO actuator 1004 coupled to the OPO for tuning the OPO, at least one auxiliary actuator 1006 coupled to the auxiliary resonator for tuning the auxiliary resonator, or a light source actuator 1008, 908 coupled to the light source for tuning the pump.

[0093] 8. The device of embodiment 7, wherein the reflector 1010 is a tunable reflector that can be configured to tune the wavelength of a feedback that controls the wavelength of a pump output from the light source.

[0094] 9. The laser cavity 902 comprising the reflector 1106 and the gain medium 1110 coupled to the OPO; The device of embodiment 7 or 8, further comprising: a light source actuator 1104 disposed between the reflector and the gain medium and configured to modulate the laser cavity so that the light source comprises a mode-locked laser.

[0095] 10. The reflector includes a wavelength tunable reflector 1108; the light source actuator 1004 disposed between the reflector and the gain medium 1110 and / or coupled to the reflector; 9. The device of embodiment 7 or 8, wherein the actuator is capable of modulating the wavelength of the light source, such that the light source comprises a CW laser.

[0096] 11. The photonic integrated circuit includes an auxiliary nonlinear region 1202 coupled between an output 1206 of the OPO and the gain medium 1204; A device described in any of embodiments 3-10, wherein the auxiliary nonlinear region is configured to upconvert the frequency of the signal and / or the idler to form feedback that is output to the gain medium and / or laser cavity.

[0097] 12. The device of embodiment 11, wherein the OPO is configurable to output feedback to the laser cavity that self-injection locks the pump.

[0098] 13. The device of embodiment 11, wherein the OPO is configurable to output feedback comprising multiple modes for mode locking of the light source or to provide feedback for spectral narrowing of the pump.

[0099] 14. The auxiliary resonators 304, 406, 408 comprise at least: tuning the frequency of the pump; filtering the frequency of the pump; or A device described in any of embodiments 3-13, coupled to the photonic integrated circuit to self-injection lock the pump of the OPO.

[0100] 15. The auxiliary resonators 408, 406: resonant at the pump wavelength and coupled to an additional parametric gain region or sharing a parametric gain region with the OPO; or A device described in any of embodiments 1-14, tuned to filter or modulate the frequency of a mode within the OPO.

[0101] 16. The auxiliary resonator comprises: with a pump resonator; an electro-optic modulator; the pump cavity is pumped by the pump 408 and has at least some overlapping modes with a cavity of the OPO, such that at least some of the overlapping modes are reinforced and recirculated within the pump cavity; A device described in any of embodiments 1-14, wherein the electro-optical modulator is coupled to the pump resonator to synchronize the mode of the pump resonator to the mode of the pump.

[0102] 17. The auxiliary resonator 304 comprises at least: tuning the frequency of at least one of the signal or the idler; filtering said frequencies, or A device described in any of embodiments 1-15, configured within the photonic integrated circuit to self-injection lock at least one of the signal or the idler to the OPO.

[0103] 18. The OPO comprises a main cavity 306 coupled to at least one parametric gain region 308, and an actuator: one or more electro-optic modulators EOM 410 coupled to at least one of the main resonator, the at least one parametric gain region, or the auxiliary resonator and operable to tune the gain and / or oscillation frequency of the pump, signal, and / or idler within the resonator; or A device described in any of embodiments 1-16, comprising a heater 310, 402 thermally coupled to the parametric gain region such that the thermal output is operable to tune the gain and / or center frequency of at least one of the pump, idler or signal output from the parametric gain region.

[0104] 19. A device described in any of embodiments 1-17, further comprising one or more external injection locking inputs 502 arranged to couple a seed signal configured for injection locking of the signal and / or the idler.

[0105] 20. The device of any of embodiments 1-18, wherein the photonic integrated circuit further comprises an additional OPO 602 and a switch 604 for switching the pump 606 to a different OPO.

[0106] 21. A device as described in any of embodiments 1-19, further comprising a plurality of auxiliary resonators 304 configurable to control the frequency of the signal and / or idler within a range in which the OPO can operate without mode hopping.

[0107] 22. A device described in any of embodiments 1-20, wherein the resonator 306 of the OPO is coupled to one or more auxiliary resonators 304 having different free spectral ranges, such that a combination of the modes of the main resonator and the auxiliary resonators selects a single mode or a group of modes that oscillate in the main resonator 306.

[0108] 23. A device described in any of embodiments 3-21, further comprising a waveguide 704 coupling the gain medium to the input of the OPO, the waveguide configured to match the mode of the pump to the mode of the OPO.

[0109] 24. The device of any one of embodiments 1-22, comprising a plurality of the OPOs comprising parametric gain regions 308 having different spectral responses, such as due to different quasi-phase matching periods.

[0110] 25. A device described in any of embodiments 1-23, wherein the inputs and outputs of the OPO are coupled, so that by selecting an appropriate combination of the inputs and outputs, signals and / or idlers at one or more outputs are used as pumps at one or more inputs, and a parametric gain region within the OPO generates signals and / or idlers in a wavelength range from the visible to the infrared.

[0111] 26. The device 600, 1200 of any of embodiments 1-24, wherein the circuit further comprises at least one nonlinear section 1202 designed to perform upconversion and / or downconversion of the signal and / or the idler by second harmonic generation and / or sum frequency generation or difference frequency generation, and may include a pump or auxiliary input to the circuit for the upconversion and / or downconversion.

[0112] 27. A device comprising a photonic integrated circuit 470, The photonic integrated circuit 470 comprises: an optical parametric oscillator (OPO) comprising a main cavity 306 coupled to a parametric gain region 308 that outputs a signal and an idler in response to a pump using a parametric nonlinear process; and at least one of a tuning circuit 304 or a mode-locking circuit 1106 coupled to the OPO.

[0113] A device described in any one of embodiments 1-26, wherein the OPO comprises a waveguide 305.

[0114] conclusion The preferred embodiments of the present invention are described above. The foregoing description of one or more embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, nor is it intended to be exhaustive. Many modifications and variations are possible in light of the above teachings. It is intended that the scope of the present invention be limited not by this detailed description, but rather by the appended claims.

Claims

1. 1. A device comprising a photonic integrated circuit: The photonic integrated circuit comprises: an optical parametric oscillator (OPO) that outputs at least one of a signal or an idler in response to the pump; and at least one of a pump light source, an external injection-locked input, or an auxiliary cavity coupled to the OPO.

2. The device of claim 1 , wherein the photonic integrated circuit further comprises an edge coupler, a grating coupler, or an evanescent coupler positioned to couple the light source to the OPO.

3. The device of claim 1 , wherein the light source comprises a gain medium and / or a cavity for forming a laser comprising the gain medium.

4. 4. The device of claim 3, wherein at least a portion of a laser cavity is within a photonic integrated circuit coupled to the gain medium, the laser cavity including a structure arranged to receive feedback from the photonic integrated circuit to the laser cavity.

5. The device of claim 4 , wherein the OPO comprises an output coupler coupled to output feedback from the OPO to the gain medium and / or the laser cavity.

6. The device of claim 4 , wherein at least a portion of the OPO is within the laser cavity.

7. 5. The device of claim 4, wherein the photonic integrated circuit comprises at least one of a reflector positioned to reflect the feedback into the laser cavity, an auxiliary resonator coupled to the OPO, at least one OPO actuator coupled to the OPO for tuning the OPO, at least one auxiliary actuator coupled to the auxiliary resonator for tuning the auxiliary resonator, or a light source actuator coupled to the light source for tuning the pump.

8. 8. The device of claim 7, wherein the reflector is a tunable reflector configurable to tune a wavelength of feedback that controls a wavelength of a pump output from the light source.

9. the laser cavity comprising the reflector and the gain medium coupled to the OPO; 8. The device of claim 7, further comprising: a light source actuator disposed between the reflector and the gain medium, the light source actuator being configurable to modulate the laser cavity such that the light source comprises a mode-locked laser.

10. the reflector comprising a wavelength tunable reflector; the light source actuator disposed between the reflector and the gain medium and / or coupled to the reflector; The device of claim 7 , wherein the actuator is capable of modulating the wavelength of the light source such that the light source comprises a CW laser.

11. the photonic integrated circuit includes an auxiliary nonlinear region coupled between the output of the OPO and the gain medium; 4. The device of claim 3, wherein the auxiliary nonlinear region is configured to upconvert the frequency of the signal and / or the idler to form feedback output to the gain medium and / or laser cavity.

12. The device of claim 11 , wherein the OPO is configurable to output feedback to the laser cavity that self-injection locks the pump.

13. 12. The device of claim 11, wherein the OPO is configurable to output feedback comprising multiple modes for mode-locking of the light source or to provide feedback for spectral narrowing of the pump.

14. The auxiliary resonator comprises at least: tuning the frequency of the pump; filtering the frequency of the pump; or The device of claim 3 , coupled to the photonic integrated circuit to self-injection lock the pump of the OPO.

15. the auxiliary resonator comprising: resonant at the pump wavelength and coupled to an additional parametric gain region or sharing a parametric gain region with the OPO; or The device of claim 1 , tuned to filter or modulate the frequency of a mode within the OPO.

16. the auxiliary resonator comprising: a pump resonator; an electro-optic modulator; the pump cavity is pumped by the pump and has at least some overlapping modes with a cavity of the OPO, such that at least some of the overlapping modes are reinforced and recirculated within the pump cavity; The device of claim 1 , wherein the electro-optic modulator is coupled to the pump resonator to lock a mode of the pump resonator to a mode of the pump.

17. The auxiliary resonator comprises at least: tuning the frequency of at least one of the signal or the idler; filtering said frequencies, or The device of claim 1 , configured within the photonic integrated circuit to self-injection lock at least one of the signal or the idler to the OPO.

18. the OPO comprising a main cavity coupled to at least one parametric gain region, and an actuator comprising: one or more electro-optic modulators coupled to at least one of the main resonator, the at least one parametric gain region, or the auxiliary resonator and operable to tune the gain and / or oscillation frequency of the pump, signal, and / or idler within the resonator; or a heater thermally coupled to the parametric gain region such that its thermal output is operable to tune the gain and / or center frequency of at least one of the pump, idler, or signal output from the parametric gain region; The device of claim 1 , comprising:

19. The device of claim 1 , further comprising one or more external injection locking inputs arranged to couple a seed signal configured for injection locking of the signal and / or the idler.

20. The device of claim 1 , wherein the photonic integrated circuit further comprises an additional OPO and a switch for switching the pump to a different OPO.

21. The device of claim 1 , further comprising a plurality of auxiliary resonators configurable to control the signal and / or idler frequencies over a range in which the OPO can operate without mode hopping.

22. 10. The device of claim 1, wherein the resonator of the OPO is coupled to one or more auxiliary resonators having different free spectral ranges, such that a combination of modes of the main resonator and the auxiliary resonators selects a single mode or a group of modes that oscillate in the main resonator.

23. The device of claim 3 , further comprising a waveguide coupling the gain medium to an input of the OPO, the waveguide configured to match a mode of the pump to a mode of the OPO.

24. The device of claim 1 comprising a plurality of said OPOs with parametric gain regions having different spectral responses.

25. 25. The device of claim 24, wherein the inputs and outputs of the OPO are coupled so that by selecting an appropriate combination of the inputs and outputs, signals and / or idlers at one or more outputs are used as pumps at one or more inputs, and a parametric gain region within the OPO generates signals and / or idlers in a wavelength range from the visible to the infrared.

26. 10. The device of claim 1, wherein the circuit further comprises at least one nonlinear section designed to perform upconversion and / or downconversion of the signal and / or the idler by second harmonic generation and / or sum or difference frequency generation, and may include a pump or auxiliary input to the circuit for the upconversion and / or downconversion.

27. 1. A device comprising a photonic integrated circuit, The photonic integrated circuit comprises: an optical parametric oscillator (OPO) comprising a master cavity coupled to a parametric gain region that outputs a signal and an idler in response to a pump using a parametric nonlinear process; and at least one of a tuning circuit or a mode-locking circuit coupled to the OPO.

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