Patent Application
20230387666
N/A
Aspects and embodiments most generally pertain to the field of integrated photonics, more particularly to an integrated photonic laser and microwave apparatus, methods, and applications, and most particularly to an integrated photonic coherent microwave generator, associated methods, and applications.
Spectrally pure microwaves are advantageous for many applications including but not limited to wireless communication, radar, imaging, clock, and high-speed electronics. Compared with electrical approaches, photonic technologies are superior for producing highly coherent microwaves given the high coherence of laser waves and given that optical division and optoelectronic down-conversion significantly suppress the phase noise. To date, a variety of photonic approaches have been developed for microwave generation; e.g., optoelectronic oscillator (OEO), dual-frequency laser, Brillouin laser, Kerr soliton micro-comb, and others known in the art. Optoelectronic oscillators rely on long, low-loss optical delay lines, which are challenging to implement on an integrated chip-scale platform. Although efforts have been reported for developing chip-scale OEOs, their performance is fairly poor compared with table-top counterparts. Microwaves produced via a dual-frequency laser generally exhibit significant phase noise, although their frequency can be widely tunable. Brillouin laser generation relies on an ultra-high-Q silica microdisk resonator or fiber laser, which are not fully integratable on a chip-scale platform. Kerr soliton microcombs can produce highly coherent microwaves that exhibit very low power efficiency.
The inventor has recognized that the related art problems outlined herein above may advantageously be remedied and known challenges mitigated by the enabled aspects and embodiments disclosed herein and as claimed. The apparatus and method disclosed herein enable the following advantageous benefits and improvements over current and past photonic microwave generation approaches. An external laser cavity enables high-speed electro-optic modulation of laser modes directly inside the laser cavity; phase locking of the lasing modes via electro-optic modulation and electro-optic comb generation directly inside the laser cavity; highly coherent microwave generation via phase-locked comb-like lasing modes; an electro-optic modulated III-V phase-locked comb laser fully integrated on a chip-scale platform.
An exemplary aspect is an electrooptic/photonic apparatus enabled to generate a coherent microwave output. The apparatus may be referred to herein as an integrated photonic coherent microwave generator. In an exemplary, non-limiting embodiment the integrated photonic coherent microwave generator includes an integrated external cavity laser that is formed by a high-Q resonator based external cavity on a suitable laser cavity material platform (including driving electrodes), integrated with a III-V gain element. The high-Q resonator laser cavity also includes one or more reflectors. The laser operationally produces a phase-locked laser comb output. Associated electronics are operationally coupled to the integrated photonic external cavity laser, wherein a coherent microwave output is operationally enabled by the apparatus.
In exemplary, non-limiting embodiments the III-V gain element may be edge coupled to the suitable laser cavity platform or heterogeneously integrated on/in a surface of the laser cavity platform. The associated electronics that are operationally coupled to the integrated photonic external cavity laser include an optical detector that converts the beating of laser modes into the RF/microwave regime via down-conversion, and a RF/microwave phase shifter enabling adjustment of the phase of the microwaves. In exemplary, non-limiting embodiments the integrated photonic coherent microwave generator may be comprised as follows and may include the disclosed components, elements, connections, features, implementations, and so on, alone or in various combinations as a PHOSITA would understand:
An exemplary aspect is a method to generate a coherent microwave output on an integrated photonic platform. In an exemplary, non-limiting embodiment the method includes the steps of providing an integrated external cavity laser comprising a suitable material waveguide platform incorporating a high-Q microresonator characterized by a free-spectral range, fR, and an integrated driving electrode and one or more cavity reflectors integrated with a III-V gain element, generating a multi-frequency comb-like laser output with a spectrum that matches the resonance frequencies of the high-Q microresonator, detecting the laser output and down-converting the beats of the lasing modes into a radio-frequency (RF) and/or microwave frequency regime having a comb-like spectrum with frequencies separated by n×fR apart where n is an integer number n=1, 2, 3 . . . , feeding this RF/microwave signal back into the high-Q microresonator to electro-optically modulate the resonator and phase lock the laser modes, which produces a phase-locked laser comb that significantly enhances the coherence of the microwave output and supports regenerative microwave oscillation, and adjusting the phase of the feedback microwave so as to maximize the strength of mode locking by electro-optic modulation.
In an alternative exemplary, non-limiting embodiment the method includes the steps of providing the integrated high-Q laser cavity platform that incorporates a phase modulator with driving electrodes without an incorporated high-Q microresonator, and back-feeding the down-converted electrical signal to the phase modulator. In this case, the laser cavity itself functions as the high-Q resonator. Similarly to the description above, the integrated external-cavity laser produces comb-like lasing modes with frequency mode spacing fR now equal to the free-spectral range of the laser cavity. Electro-optic modulation of the phase modulator with the detected microwave produces phase locking of the laser comb modes resulting in a phase-locked laser comb that in turn enhances the coherence of the produced microwave and supports regenerative microwave oscillation.
In exemplary, non-limiting embodiments the method may be comprised as follows and may include the disclosed steps, components, elements, connections, features, implementations, and so on, alone or in various combinations as a PHOSITA would understand:
A LN external cavity 102 includes a high-Q ring microresonator 108 characterized by a free spectral range fR, that can be tuned and modulated by the electro-optic Pockels effect of LN, with tuning electrodes 110 integrated with the resonator. A Sagnac loop mirror 112 is placed at an output end of the resonator to function as the output end mirror of the laser cavity. Operationally, this novel laser will generate a phase-locked laser comb output 124.
The photonic coherent microwave generator 100-A further includes electrical components 199 operationally connected to the external cavity laser. The electrical components are used to detect the laser comb output from the integrated laser and down-convert it into the RF and/or microwave regime to produce a coherent microwave, which is fed back to electro-optically modulate the laser cavity to introduce and enhance phase locking of the lasing modes that in turn enhances the coherence of the generated microwave output. An optical detector 114 disposed at the laser output down-converts the beating of the phase-locked laser-comb modes into microwaves 125 having a fundamental frequency equal to the free-spectral range fR of the LN ring microresonator 108. A RF/microwave phase shifter 118 is used to adjust the phase of the generated microwaves 125. Optionally, as shown in dotted box, a narrow-band RF/microwave filter 116 may be disposed optically downstream of the detector 114 to cut off broadband noises and pass only the fundamental frequency component at fR. Optionally, as shown in dotted box, a RF/microwave amplifier 120 may be used as necessary to support regenerative microwave oscillation and boost the power of the generated microwave output 125.
As illustrated in
Experimental Verification
We have carried out numerical modeling via a modified Lugiato-Lefever equation by taking into account of the gain and laser actions.
Among other benefits and advantages of the disclosed embodiments, the photonic coherent microwave generator and associated method exhibit significant novel characteristics not present in currently known photonic microwave and optical frequency comb generation approaches. These include, but are not limited to, high-speed electro-optic modulation of laser modes directly inside the laser cavity enabled by the LN external laser cavity; phase locking of the lasing modes via electro-optic modulation and electro-optic comb generation directly inside the laser cavity; spectral broadening of phase-locked comb via enhanced optical Kerr effect inside the microresonator (and/or the laser cavity); phase locking of the laser comb via combined electro-optic comb and optical Kerr comb generation; highly coherent microwave generation via phase-locked comb-like lasing modes; an electro-optic modulated III-V/LN phase-locked comb laser fully integrated on chip-scale platform, and others appreciated by those skilled in the art.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosed embodiments are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein. For example, a range of “less than 10” can include any and all sub-ranges between (and including) the minimum value of zero and the maximum value of 10, that is, any and all sub-ranges having a minimum value of equal to or greater than zero and a maximum value of equal to or less than 10, e.g., 1 to 5.
While various disclosed embodiments have been described above, it should be understood that they have been presented by way of example only and not as a limitation. Numerous changes to the disclosed embodiments can be made in accordance with the specification herein without departing from the spirit or scope of this specification. Thus the breadth and scope of this specification should not be limited by any of the above-described embodiments; rather, the scope of this specification should be defined in accordance with the appended claims and their equivalents.
The instant application claims priority to U.S. Provisional application Ser. 63/345,714 filed May 25, 2022, the subject matter of which is herein incorporated by reference to the fullest extent allowed by applicable laws and rules.
| Number | Date | Country | |
|---|---|---|---|
| 63345714 | May 2022 | US |
