Patent Application
20220278497
The present invention relates generally to lasers. More specifically, it relates to Titanium-doped sapphire lasers.
Lasers are at the core of a wide range of technologies, scientific research, and medical applications. Titanium-doped sapphire (Ti:Sapphire) laser is unique among other commercially available lasers due to its very wide gain bandwidth. This enables Ti:Sapphire laser to be used as a wide-range (up to 650-1100 nm) tunable coherent source, and, consequently, as a source of ultra-fast pulsed light. The Ti:Sapphire laser is an irreplaceable and very costly tool used for numerous industrial, biomedical, and research applications. The cost of a Ti:Sapphire laser, however, typically ranges between $30,000-200,000, excluding the pump laser. The pump laser for the Ti:Sapphire module is additionally $30,000-50,000. Moreover, such lasers occupy square meters of optical table surface. Therefore, the cost of Ti:Sapphire laser and its physical dimensions remain prohibitively large for wide-spread integration into equipment and devices, impeding further progress.
The prospect of miniaturization and integration of a Ti:Sapphire laser with on chip photonics would revolutionize the field of photonics and have a major impact on many applications, including two-photon microscopy in neuroscience; LIDAR systems where a pulsed source could also be integrated with beam-steering photonics on a single chip, thereby reducing the cost and size and enabling integration with other car sensors; and quantum photonics, where large scale Ti:Sapphire lasers are used to pump quantum emitters to generate single or entangled photon states for quantum information processing. However, up to now, the implementation of a pulsed laser source on chip has been persistently elusive.
This description discloses a fully chip-integrated Ti:Sapphire laser producing ultrafast pulses, which can be driven by an inexpensive infrared diode as driving source. This architecture is a complete microscale Ti:Sapphire laser system, which could fit into a volume on the order of a cubic centimeter, and is thus fully portable (reduction of many orders of magnitude relative to state of the art). Apart from the reduction in size, there would also be orders of magnitude of reduction in cost—to order of $1000 or less for the whole system.
In one aspect, the invention provides a Ti:Sapphire laser device comprising: a substrate (such as quartz, glass, sapphire, or others); a first waveguide resonator composed of a gain medium integrated onto the substrate in a planar technology configuration; a frequency doubler composed of a second order nonlinear material integrated onto the substrate in a planar technology configuration and as a resonant or waveguiding component; a second waveguide resonator composed of a titanium doped sapphire gain medium integrated onto the substrate in a planar technology configuration; wherein the first waveguide resonator is optically coupled to the frequency doubler and is capable of producing laser radiation from pump diode light input to the Ti:Sapphire laser device; wherein the frequency doubler is optically coupled to the second waveguide resonator and is capable of producing frequency doubled radiation from the laser radiation.
In one implementation of the Ti:Sapphire laser device, the first waveguide resonator is a Nd:YVO4 resonator or Nd:YAG resonator.
In one implementation of the Ti:Sapphire laser device, the frequency doubler comprises a SiC ring resonator that frequency doubles the laser radiation via a doubly resonant second-harmonic generation process. An alternative to SiC may be thin film lithium niobite resonator integrated on the same substrate.
In one implementation of the Ti:Sapphire laser device, the second waveguide resonator includes dispersion-engineered laser cavity mirrors.
In one implementation of the Ti:Sapphire laser device, the second waveguide resonator includes low-loss Kerr nonlinear mirror; and one broadband linear mirror and the Kerr nonlinear mirror form the second waveguide laser cavity.
In one implementation of the Ti:Sapphire laser device, the substrate is SiO2 and the Ti:Sapphire laser has a device layer stack comprising YVO on SiO2 on SiC on SiO2 on Ti:Sapphire on the substrate.
In one example, the infrared diode pumps an integrated Nd:YVO4 ring resonator, which produces narrow-band laser light at 1064 nm. The 1064 nm emission is routed onto a SiC ring resonator, which frequency-doubles it to 532 nm via doubly resonant efficient second harmonic generation process. The 532 nm light is routed to the Ti:Sapphire resonator. Combined with a commercial diode pump, the volume of the system is smaller than one cubic centimeter—many orders of magnitude smaller than the state of the art.
The full chip-scale integration of the laser system simultaneously shrinks the size, boosts efficiency, enables low-power operation, and dramatically drops the system costs.
As illustrated in
This embodiment may be realized using various different material systems and resonator configurations. For example, the first waveguide resonator 102 may be a Nd:YVO4 resonator or Nd:YAG resonator. The frequency doubler 104 may be a SiC ring resonator that frequency doubles the laser radiation via a doubly resonant second-harmonic generation process. The second waveguide resonator 106 preferably includes dispersion-engineered laser cavity mirrors.
In one example shown in
In one realization of the Ti:Sapphire laser device, the substrate is SiO2 and the Ti:Sapphire laser has a device layer stack comprising YVO on SiO2 on SiC on SiO2 on Ti:Sapphire on the substrate. A technique for fabricating Silicon Carbide on Insulator devices has been disclosed in U.S. patent application Ser. No. 16/805,073, hereby incorporated by reference in its entirety. The process flow for fabricating Silicon Carbide on Insulator is shown in
The modification of the technique for fabricating Silicon Carbide on Insulator devices disclosed in U.S. patent application Ser. No. 16/805,073 enabling the extension of the technique to Sapphire is the use of a substrate with a matched thermal expansion coefficient: Fabrication of Ti:Sapphire on insulator with a Sapphire handle is used to prevent strain build-up that would result in cracking of the film during thinning and polishing. The versatility of this method enables the stacking of arbitrary layers of highly-pure crystalline materials. This is important for the implementation of on-chip Ti:Sapphire laser. The device layer stack for Ti:Sapphire laser in one embodiment is YVO on SiO2, SiC on SiO2, and Ti:Sapphire on SiO2. The integration of these materials together can be done via bonding them side by side on a chip and using low-loss vertically coupled waveguide interconnects to route light between the different stages of the device.
Sapphire is one of the most difficult dielectric materials to process for patterning nanostructures. We developed a fabrication technique based on photolithography and reactive-ion-etching for low-roughness sapphire etching with good selectivity against photoresist, to enable fabrication of high quality structures in Sapphire. The fabrication is done via utilizing inductively coupled plasma (ICP). In particular, we utilize chemically reactive ions for sapphire, such as BCl3 and/or Cl2, which helps to provide fast and smooth etch. Furthermore, utilizing etch operation under low pressure (e.g., 0.1-0.5 mTorr) condition with high bias (e.g., 400-800 V) and Ar ions, we are also combining ion-induced etching, which further improves etching conditions. With such etching technique, we are able to define waveguide and resonator structures in sapphire simultaneously maintaining a selectivity of 0.3 against photoresist while minimizing redeposition during etch. Redeposition during etching is particularly harmful to low-roughness sidewalls. Finally, partial etching into sapphire, thereby not exposing SiO2 underlayer, allows removal of redeposition via dilute Hydrofluoric acid, producing photonic structures entirely without etch redeposition, shown in
The Ti:Sapphire laser device preferably includes dispersion-engineered laser cavity mirrors in the second waveguide resonator. This can be done via a traditional ring resonator approach (e.g., Nature Photonics, 10, 316-320 (2016)), or via dispersion engineered reflectors The cavity dispersion is one of key parameters that determine temporal width and spectral shape of the pulsed laser output. Precise fabrication technique (
In one embodiment, shown in
The miniaturized and inexpensive Ti:Sapphire laser provided by the present invention may be integrated with on chip photonics and has many applications, such as the following.
1) A low-cost, compact, integratable solution for two-photon microscopy in medical research and neuroscience.
2) LIDAR systems where a pulsed Ti:Sapphire source could also be integrated with beam-steering photonics on a single chip, thereby reducing the cost and size and enabling integration with other car sensors.
3) Optical clocks of unprecedented precision, where frequency-stabilized Ti:Sapphire laser would synthesize a microwave clock signal from atomic or ion transition frequency in an optical trap.
4) Dual-comb spectroscopy—a monolithically integrated, short-acquisition-time solution for high spectral resolution spectroscopy, fully miniaturized.
5) Ultrastable terahertz- and radio-frequency signal generation where Ti:Sapphire mode-locked laser could be used to produce a spectrally pure micro- or terahertz-signal at the frequency of pulse repetition rate, with spectroscopy and imaging applications.
6) Laser-driven dielectric particle accelerators on chip, which are crucial building blocks of on chip X-ray sources which would revolutionize medical applications.
7) Integrated quantum photonics devices. Currently, on-chip quantum photonic devices being developed for quantum computation and quantum repeaters employ large scale Ti:Sapphire lasers to pump the quantum emitters with ultra-fast pulses. Generation of high purity single or entangled photon states for quantum information processing in a compact platform thus requires a compact ultra-fast source.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US20/44560 | 7/31/2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62881174 | Jul 2019 | US |
