LIDAR SYSTEMS WITH IMPROVED TUNABLE OPTICAL DELAY LINES
A light detection and ranging (LIDAR) system may include a laser and a plurality of single photon avalanche diodes (SPADs) that are triggered by laser light that reflects off a target scene. The LIDAR system may have an optical delay line from which laser light is emitted. It may be desirable to have a tunable optical delay line that has an adjustable delay time. In particular, the tunable optical delay line may include a core layer through which the laser light propagates between cladding layers. One or more of the cladding layers may be formed from electro-optical material that has an adjustable index of refraction when voltage is applied. Due to the adjusted index of refraction, a path length of the light within the delay line may be changed, thereby changing the delay time.
1 . An optical delay line for a light detection and ranging device comprising:
a waveguide comprising:
a first cladding layer,
a second cladding layer that includes electro-optical material, and
a core interposed between the first cladding layer and the second cladding layer; and
an electrode in contact with the second cladding layer.
2 . The optical delay line defined in claim 1 wherein the electrode is configured to apply a voltage to the second cladding layer to change an index of refraction of the second cladding layer.
3 . The optical delay line defined in claim 2 wherein the electrode is a first electrode, the optical delay line further comprising:
a first contact from which the first electrode receives the voltage;
a second electrode that is configured to apply the voltage to the second cladding layer; and
a second contact from which the second electrode receives the voltage.
4 . The optical delay line defined in claim 3 wherein the core has an index of refraction of 1.5.
5 . The optical delay line defined in claim 3 wherein the core is a separate layer formed in a recess of first cladding.
6 . The optical delay line defined in claim 3 wherein the core is diffused in a portion of the first cladding.
7 . The optical delay line defined in claim 2 wherein the first cladding layer includes electro-optical material.
8 . The optical delay line defined in claim 7 wherein the electrode is a first electrode and the voltage is a first voltage, the optical delay line further comprising:
a second electrode that applies a second voltage to the first cladding layer.
9 . The optical delay line defined in claim 8 wherein the second electrode is interposed between the core and the first cladding.
10 . The optical delay line defined in claim 9 further comprising:
a third electrode that is interposed between a substrate and the first cladding.
11 . The optical delay line defined in claim 10 wherein the first, second, and third electrodes are formed from a transparent conductive material.
12 . The optical delay line defined in claim 11 wherein the first, second, and third electrodes are formed from indium tin oxide.
13 . The optical delay line defined in claim 9 wherein the core has a rib-shape, and the first electrode is formed directly on the substrate.
14 . The optical delay line defined in claim 2 wherein the electro-optical material is selected from the group of materials consisting of: lanthanum-modified lead zirconate tantalite (PLZT), lithium niobate (LiNbO3), lithium triborate (LiB3O5), lithium tantalate (LiTaO3), potassium titanyl phosphate (KTiOPO4), β-barium borate (β-BaB2O4), and liquid crystal.
15 . A light detection and ranging device comprising:
a laser;
a tunable optical delay line through which the laser outputs laser light, wherein the laser light propagates in a waveguide in the optical delay line and wherein the waveguide comprises:
a first cladding layer,
a second cladding layer that includes electro-optical material, and
a core interposed between the first cladding layer and the second cladding layer;
control circuitry that adjusts a delay time of the tunable optical delay line;
a single photon avalanche diode that is configured to detect laser light that has been reflected off of external objects; and
peak detection circuitry that determines a time-of-flight based on the delay time and the detection of the reflected laser light.
16 . The light detection and ranging device defined in claim 15 wherein the control circuitry is configured to adjust the delay time of the optical delay line by applying a voltage to the electro-optical material that forms the second cladding layer.
17 . The light detection and ranging device defined in claim 16 wherein the electro-optical material is selected from the group of materials consisting of: lanthanum-modified lead zirconate tantalite (PLZT), lithium niobate (LiNbO3), lithium triborate (LiB3O5), lithium tantalate (LiTaO3), potassium titanyl phosphate (KTiOPO4), β-barium borate (β-BaB2O4), and liquid crystal.
18 . The light detection and ranging device defined in claim 15 wherein the first cladding layer has a first index of refraction, the second cladding layer has a second index of refraction, and the core has a third index of refraction that is less than the first and second indexes of refraction.
19 . A tunable optical delay line for a light detection and ranging device comprising:
a substrate;
a first cladding layer on the substrate;
a second cladding layer that includes electro-optical material;
a core interposed between the first cladding layer and the second cladding layer;
an electrode in contact with the second cladding layer; and
a contact that receives voltage and transfers the voltage to the electrode, wherein the voltage is configured to change an index of refraction of the second cladding layer.
20 . The tunable optical delay line defined in claim 19 wherein the electrode is a first electrode and the first cladding layer comprises electro-optical material, the tunable optical delay line further comprising:
a second electrode in contact with the first cladding layer, wherein the second electrode receives the voltage to change an index of refraction of the first cladding layer.