Chip integrated titanium: sapphire laser

Abstract

An embodiment of an integrated "titanium:sapphire" laser device includes a substrate [100], a first waveguide resonator [102] consisting of a gain medium integrated onto the substrate using a planar technique, a frequency multiplier [104] consisting of a second-order nonlinear material integrated onto the substrate using a planar technique, and a second waveguide resonator [106] consisting of a titanium-doped sapphire gain medium integrated onto the substrate using a planar technique.

Description

Technical Field

[0001] This invention generally relates to lasers. More specifically, it relates to titanium-doped sapphire lasers. Background Technology

[0002] Lasers are central to a wide range of technological, scientific research, and medical applications. Titanium-doped sapphire (“Ti:Sapphire”) lasers are unique among other commercial lasers due to their exceptionally wide gain bandwidth. This allows Ti:Sapphire lasers to be used as broadband (up to 650-1100 nm) tunable coherent sources and, consequently, as ultrafast pulsed sources. Ti:Sapphire lasers are an indispensable and very expensive tool for numerous industrial, biomedical, and research applications. However, the cost of a typical Ti:Sapphire laser ranges from $30,000 to $200,000, excluding the pump laser. The pump laser used in a Ti:Sapphire module costs an additional $30,000 to $50,000. Furthermore, such lasers occupy several square meters of optical stage surface. Therefore, the cost and physical size of Ti:Sapphire lasers remain too large for widespread integration into devices and equipment, hindering further development.

[0003] The prospect of miniaturization and integration of Ti:sapphire lasers with on-chip photonics will revolutionize the field and have a significant impact on many applications, including two-photon microscopy in neuroscience; lidar systems, where pulsed sources can also be integrated with beam-controlled photonics on a single chip, thereby reducing cost and size and enabling integration with other automotive sensors; and quantum photonics, where large-scale Ti:sapphire lasers are used to pump quantum emitters to generate single-photon states or entangled photon states for quantum information processing. However, the implementation of on-chip pulsed laser sources has remained elusive until now. Summary of the Invention

[0004] This specification discloses a fully integrated Ti:sapphire laser that generates ultrafast pulses and can be driven by an inexpensive infrared diode. This architecture represents a complete miniaturized Ti:sapphire laser system that can be packed into a volume on the order of cubic centimeters, making it entirely portable (orders of magnitude smaller than existing technologies). In addition to the size reduction, the cost will also be reduced by orders of magnitude—the cost of the entire system will be reduced to the order of $1,000 or less.

[0005] In one aspect, the present invention provides a "titanium:sapphire" laser device, comprising: a substrate (such as quartz, glass, sapphire, etc.); a first waveguide resonator composed of a gain medium integrated onto the substrate using a planar configuration; a frequency doubler composed of a second-order nonlinear material integrated onto the substrate using a planar configuration and serving as a resonator or waveguide component; a second waveguide resonator composed of a titanium-doped sapphire gain medium integrated onto the substrate using a planar configuration; wherein the first waveguide resonator is optically coupled to the frequency doubler and is capable of generating laser radiation from pump diode light input to the "titanium:sapphire" laser device; wherein the frequency doubler is optically coupled to the second waveguide resonator and is capable of generating frequency-doubled radiation from the laser radiation.

[0006] In one embodiment of the "Ti:Sapphire" laser device, the first waveguide resonator is an Nd:YVO4 resonator or an Nd:YAG resonator.

[0007] In one embodiment of the "Ti:Sapphire" laser device, the frequency doubler includes a SiC ring resonator that doubles the laser radiation via a double-resonance second-harmonic generation process. An alternative to SiC is a thin-film lithium niobate resonator integrated on the same substrate.

[0008] In one embodiment of the "Ti:Sapphire" laser device, the second waveguide resonator includes a dispersion-engineered laser cavity mirror.

[0009] In one embodiment of the "Ti:Sapphire" laser device, the second waveguide resonator includes a low-loss Kerr nonlinear mirror; and a broadband linear mirror and the Kerr nonlinear mirror form the second waveguide laser cavity.

[0010] In one embodiment of the "Ti:Sapphire" laser device, the substrate is SiO2, and the "Ti:Sapphire" laser has a device layer stack comprising SiO2 on SiC on SiO2 on the substrate and YVO on SiO2.

[0011] In one example, an infrared diode-pumped integrated Nd:YVO4 ring resonator generates a narrowband laser at 1064 nm. The 1064 nm emission is routed to a SiC ring resonator, which is frequency-doubled to 532 nm via a dual-resonance, high-efficiency second-harmonic generation process. The 532 nm light is then routed to a Ti:Sapphire resonator. Combined with a commercially available diode pump, the system volume is less than one cubic centimeter—orders of magnitude smaller than existing technologies.

[0012] The fully chip-level integration of the laser system simultaneously reduces size, improves efficiency, enables low-power operation, and significantly reduces system cost. Attached Figure Description

[0013] Figure 1A The diagram shows the main components and structure of an integrated "titanium:sapphire" laser device according to an embodiment of the present invention.

[0014] Figure 1B This is a conceptual diagram representing a chip-integrated "Ti:sapphire" laser, on the order of 100 μm in size. Combined with a commercial diode pump, its volume is less than one cubic centimeter—orders smaller than existing technologies.

[0015] Figure 1C : A conceptual diagram representing a "Ti:Sapphire" laser cavity including a Kerr nonlinear mirror.

[0016] Figure 2 A process flow for fabricating thin-film silicon carbide on an insulator. The same method can be used to transfer thin YVO films onto an insulator and thin "titanium:sapphire" films onto an insulator, thereby implementing the entire circuit presented in Figure 1.

[0017] Figure 3 This study demonstrates an etched sapphire waveguide using a low-pressure, low-roughness reactive ion etching method for producing integrated sapphire photonic structures. Detailed Implementation

[0018] like Figure 1A As shown, an embodiment of the "Ti:Sapphire" laser device includes a substrate 100, a first waveguide resonator 102 composed of a gain medium integrated onto the substrate using a planar configuration, a frequency doubler 104 composed of a second-order nonlinear material integrated onto the substrate using a planar configuration, and a second waveguide resonator 106 composed of a titanium-doped sapphire gain medium integrated onto the substrate using a planar configuration. The first waveguide resonator 102 is optically coupled to the frequency doubler 104 and is capable of generating laser radiation from the pump diode light 108 input to the "Ti:Sapphire" laser device. The frequency doubler 104 is optically coupled to the second waveguide resonator 106 and is capable of generating frequency-doubled radiation from the laser radiation. The "Ti:Sapphire" laser device outputs laser light 110 from the second waveguide resonator 106.

[0019] This embodiment can be implemented using various different material systems and resonator configurations. For example, the first waveguide resonator 102 may be an Nd:YVO4 resonator or an Nd:YAG resonator. The frequency multiplier 104 may be a SiC ring resonator that doubles the laser radiation frequency via a double-resonance second harmonic generation process. The second waveguide resonator 106 preferably includes a dispersion-engineered laser cavity mirror.

[0020] exist Figure 1BIn one example shown, light 128 generated from an infrared diode (not shown) is input to the device and pumps an integrated Nd:YVO4 ring resonator 122, which generates a narrowband laser at 1064 nm. The 1064 nm emission is routed to a SiC ring resonator 124, which is frequency-doubled to 532 nm via a dual-resonance high-efficiency second-harmonic generation process. The 532 nm light is routed to a Ti:Sapphire resonator 126. The device outputs pulsed light 130. Combined with a commercially available diode pump, the system volume is less than one cubic centimeter—orders smaller than existing technologies.

[0021] In one implementation of a Ti:Sapphire laser device, the substrate is SiO2, and the Ti:Sapphire laser has a device layer stack comprising SiO2 on SiC on SiO2 on the substrate and YVO on SiO2. U.S. Patent Application No. 16 / 805073 discloses a technique for fabricating silicon carbide-on-insulator devices, which is incorporated herein by reference in its entirety. The process flow for fabricating silicon carbide-on-insulator is described in... Figure 2 As shown, the process flows for YVO and "titanium:sapphire" follow very similar procedures. The techniques used for implementing thin-film silicon carbide on insulators can be applied to transfer thin YVO films onto insulators, and also to transfer thin "titanium:sapphire" films onto insulators. For example... Figure 2 As shown, the process begins with substrates 202 and 204 and a bulk active material 200 (YVO or "Ti:Sapphire"). The substrates and active material are fused together at a bonding interface 206 to form material 208. Then, precision grinding 210 thins material 212 to a thickness approximately 1 micrometer greater than the target device thickness. Finally, chemical mechanical polishing 214 removes the last few micrometers of material while producing a surface roughness better than 3 angstroms RMS. The result is a layered material 216.

[0022] A modification to the technique for fabricating silicon carbide-on-insulator devices disclosed in U.S. Patent Application No. 16 / 805073, which enables the extension of this technology to sapphire, is the use of a substrate with a matching coefficient of thermal expansion: "Ti:sapphire" is fabricated on an insulator using a sapphire method to prevent the buildup of tensile stresses that would cause the film to crack during thinning and polishing. The versatility of this method allows for the stacking of arbitrary layers of high-purity crystalline materials. This is important for realizing on-chip "Ti:sapphire" lasers. In one embodiment, the device layer stack for a "Ti:sapphire" laser is YVO on SiO2, SiC on SiO2, and "Ti:sapphire" on SiO2. The integration of these materials can be accomplished by bonding them side-by-side on a chip and using low-loss vertically coupled waveguide interconnects to route light between different stages of the device.

[0023] Sapphire is one of the most difficult dielectric materials to work with for forming nanostructure patterns. We have developed a photolithography-based and reactive ion etching (RIE) fabrication technique for low-roughness sapphire etching with good selectivity to photoresist, enabling the fabrication of high-quality structures in sapphire. This fabrication is accomplished using inductively coupled plasma (ICP). In particular, we use chemically reactive ions, such as BCl3 and / or Cl2, on the sapphire, which helps to provide fast and smooth etching. Furthermore, we combine ion-induced etching with etching operations under high bias (e.g., 400–800 V) and low-pressure (e.g., 0.1–0.5 mTorr) conditions for Ar ions, which further improves the etching conditions. Using this etching technique, we are able to define waveguide and resonator structures in sapphire while maintaining a photoresist selectivity of 0.3 and minimizing redeposition during etching. Redeposition during etching is particularly detrimental to low-roughness sidewalls. Finally, the sapphire is partially etched to avoid exposing the SiO2 underlayer, allowing for removal and redeposition via dilute hydrofluoric acid, thus producing a photonic structure with no etch-redeposition. Figure 3 As shown.

[0024] The "Ti:Sapphire" laser device preferably includes a dispersion-engineered laser cavity mirror in the second waveguide resonator. This can be accomplished using a conventional ring resonator method (e.g., Natural Photonics, 10, 316–320 (2016)) or via a dispersion-engineered reflector. Cavity dispersion is one of the key parameters determining the temporal width and spectral shape of the pulsed laser output. Precision manufacturing techniques ( Figure 2 and Figure 3 Broadband dispersion control can be achieved through various photonic designs. This dispersion engineering technique (e.g., see Optics Letters 19, 3, 201–203 (1994)) can be implemented in such laser devices and plays a crucial role in generating wide-bandwidth pulses. Photonic inverse design methods can be used to implement optimal dispersion engineering. The spectral bandwidth of pulsed lasers is an important metric for applications in microscopy, spectroscopy, optical clocks, and particle accelerators.

[0025] exist Figure 1CIn one embodiment shown, the "Ti:Sapphire" laser device includes a low-loss Kerr nonlinear mirror 154 in a second waveguide resonator. The second waveguide resonator is formed using the Kerr nonlinear mirror 154 and a conventional mirror 152. Mode-locked lasers typically require devices that provide higher gain for short pulses and enable self-starting lasers (turnkey operation). Free-space mode-locked lasers use semiconductor saturable absorbers, Kerr lenses, polarization rotators, etc. (e.g., see IEEE Quantum Electronics Special Issue, 6, 6, 1173–1185 (2000)). However, conventional devices are either not integrable or result in high loss, low damage threshold, and narrow operating bandwidth. The Kerr nonlinear mirror has a broadband linear waveguide mirror 156 and a microring resonator 158. The ring resonator is placed next to the waveguide mirror (e.g., see Natural Photonics, 14, 369–374 (2020)). Alternatives to the ring resonator are photonic crystal resonators or another waveguide resonator. The integrated Kerr nonlinear mirror exhibits higher reflectivity for short pulses, as well as low insertion loss, wide operating bandwidth, and high damage threshold. This device is implemented in the laser device (“Ti:Sapphire” second waveguide resonator) and enables self-starting operation of the mode-locked laser. The low-loss operation of the Kerr nonlinear mirror enables high peak power of the pulsed laser.

[0026] The miniaturized and inexpensive "titanium:sapphire" laser provided by this invention can be integrated with on-chip photonics and has a variety of applications, such as the following.

[0027] 1) A low-cost, compact, and integrable solution for two-photon microscopy in medical research and neuroscience.

[0028] 2) The pulsed "Ti:Sapphire" source can also be integrated with a beam-controlled photonic lidar system on a single chip, thereby reducing cost and size, and enabling integration with other automotive sensors.

[0029] 3) An optical clock with unprecedented precision, in which a frequency-stable “Ti:Sapphire” laser synthesizes a microwave clock signal by transitioning the frequency of atoms or ions in an optical trap.

[0030] 4) Dual-comb spectroscopy – a monolithic, short-acquisition-time solution for high-spectral-resolution spectroscopy, which is fully miniaturized.

[0031] 5) Utilizing ultra-stable terahertz and radio frequency signal generation for spectral and imaging applications, where a “Ti:sapphire” mode-locked laser can be used to generate spectrally pure micro or terahertz signals at pulse repetition rate frequencies.

[0032] 6) Laser-driven on-chip dielectric particle accelerators, a key component of on-chip X-ray sources, will revolutionize medical applications.

[0033] 7) Integrated quantum photonic devices. Currently, on-chip quantum photonic devices being developed for quantum computing and quantum repeaters employ large-scale Ti:sapphire lasers to pump quantum emitters with ultrafast pulses. Therefore, generating high-purity single photon states or entangled photon states for quantum information processing on a compact platform requires compact, ultrafast sources.

Claims

1. A miniature integrated "titanium:sapphire" laser device, comprising: Substrate; A first waveguide resonator is composed of a gain dielectric integrated onto the substrate using a planar technique. A frequency multiplier, wherein the frequency multiplier is composed of a second-order nonlinear material integrated onto the substrate using a planar technique; The second waveguide resonator is composed of a titanium-doped sapphire gain medium integrated onto the substrate using a planar technique. The first waveguide resonator is optically coupled to the frequency multiplier and is capable of generating laser radiation from the pump diode light input to the "Ti:Sapphire" laser device; The frequency multiplier is optically coupled to the second waveguide resonator and is capable of generating frequency-doubled radiation from the laser radiation.

2. The "titanium:sapphire" laser device as described in claim 1, characterized in that, The first waveguide resonator is an Nd:YVO4 resonator or an Nd:YAG resonator.

3. The "titanium:sapphire" laser device as described in claim 1, characterized in that, The frequency multiplier includes a SiC ring resonator, which multiplies the laser radiation frequency via a double-resonance second harmonic generation process.

4. The "titanium:sapphire" laser device as described in claim 1, characterized in that, The frequency multiplier includes a thin-film lithium niobate resonator.

5. The "titanium:sapphire" laser device as described in claim 1, characterized in that, The second waveguide resonator includes a dispersive engineered laser cavity mirror.

6. The "titanium:sapphire" laser device as described in claim 1, characterized in that, The second waveguide resonator includes a low-loss Kerr nonlinear mirror and a broadband linear mirror.

7. The "titanium:sapphire" laser device as described in claim 1, characterized in that, The substrate is SiO2, and the "titanium:sapphire" laser has a device layer stack comprising SiO2 on SiC on SiO2 on the substrate and YVO on SiO2.

8. The "titanium:sapphire" laser device as described in claim 1, characterized in that, The substrate is quartz, glass, or sapphire.

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