Systems and methods for beam steering using a micromirror device
View Patent ↗A beam steering apparatus including a first actuatable micromirror array (AMA) having a pitch, p, adapted to impart a modulation to a wavefront incident on the first AMA by a transition between a first state and a second state, wherein the first AMA has a transition time (T) between the first state and the second state, and at least one light source adapted to provide the incident wavefront having a duration, t, to the first AMA, where t≤T. The AMA may be a MEMS device such as a digital micromirror array. The beam steering apparatus may constitute a portion of LIDAR system.
1. A beam steering apparatus, comprising:
a first actuatable micromirror array (AMA) having a pitch, p, adapted to impart a modulation to a wavefront incident on the first AMA by a transition between a first state and a second state, wherein the first AMA has a transition time (T) between the first state and the second state; and
at least one light source adapted to provide the incident wavefront having a duration, t max , to the first AMA,
where t max ≤T;
wherein
t max ≤T/N Max ,
where N Max is the number of diffraction orders of the incident wavefront supported by the AMA, and is given by,
N
max
=
1
+
floor
p
[
sin
(
2
α
-
β
)
+
sin
(
β
)
]
2
λ
+
floor
p
[
sin
(
-
2
α
-
β
)
+
sin
(
β
)
]
2
λ
where 2α is the phase tilt angle induced by the first AMA for a normal incident wavefront, β is the in-plane angle of incidence of the incident wavefront along which phase is modulated, λ is the wavelength of light from the at least one light source, and the function ‘floor’ rounds N Max down to the nearest integer,
further wherein the first AMA functions as a blazed grating according to the equation
θ
m
=
arcsin
(
2
m
λ
p
-
sin
(
β
)
)
+
β
,
where θ m is a diffraction angle supported by said blazed grating, and m is the diffraction order.
2. The beam steering apparatus of claim 1 , wherein the first state and second state are discrete ON and OFF states, respectively.
3. The beam steering apparatus of claim 1 , wherein the at least one light source comprises a laser.
4. The beam steering apparatus of claim 1 , wherein the at least one light source comprises a plurality of laser diodes.
5. The beam steering apparatus of claim 1 , wherein the at least one light source comprises a plurality of light sources producing at least two different wavelengths.
6. The beam steering apparatus of claim 1 , wherein the incident wavefront is planar.
7. The beam steering apparatus of claim 1 , wherein the at least one light source is configured to produce collimated light.
8. The beam steering apparatus of claim 1 , wherein the at least one light source is configured to produce quasi-collimated light.
9. The beam steering apparatus of claim 1 , wherein the first AMA has only 2 discrete states of operation.
10. The beam steering apparatus of claim 1 , further comprising a second AMA cascaded with the first AMA to receive light from the incident wavefront after is incident on the first AMA.
11. A method for making an effective blazed grating, comprising:
actuating an actuatable micromirror array (AMA) array between a first state and a second state, wherein the AMA has a transition time, T between the first state and the second state; and
directing a wavefront onto the AMA, the wavefront having a duration t,
where t max ≤T, wherein
where t max ≤T, wherein
where N Max is the number of diffraction orders with diffraction efficiency equal to or greater than 50% of the incident wavefront supported by the AMA,
wherein the AMA functions as a blazed grating according to the equation
θ
m
=
arcsin
(
2
m
λ
p
-
sin
(
β
)
)
+
β
,
where θ m is the diffraction angle(s) supported by said blazed grating, λ is the wavelength of the incident wavefront, and m is the diffraction order, β is in-plane angle of incidence of incident wavefront along which phase is modulated.
12. A LIDAR system for detecting an object, comprising:
a first actuatable micromirror array (AMA) having a pitch, p, adapted to impart a modulation to a wavefront incident on the first AMA by a transition between a first state and a second state, wherein the first AMA has a transition time (T) between the first state and the second state;
at least one light source adapted to provide the incident wavefront having a maximum duration, t max , to the first AMA, where t max ≤T; and
a detector positioned to receive light from the wavefront after it is directed onto the object,
wherein
t max ≤T/N Max ,
where N Max is the number of diffraction orders of the incident wavefront supported by the AMA, and is given by,
N
max
=
1
+
floor
❘
"\[LeftBracketingBar]"
p
[
sin
(
2
α
-
β
)
+
sin
(
β
)
]
2
λ
❘
"\[RightBracketingBar]"
+
floor
❘
"\[LeftBracketingBar]"
p
[
sin
(
-
2
α
-
β
)
+
sin
(
β
)
]
2
λ
❘
"\[RightBracketingBar]"
where 2α is the phase tilt angle induced by the first AMA for a normal incident wavefront, β is the in-plane angle of incidence of the incident wavefront along which phase is modulated, λ is the wavelength of light from the at least one light source, and the function ‘floor’ rounds NMax down to the nearest integer,
further wherein the first AMA functions as a blazed grating according to the equation
θ
m
=
arc
sin
(
2
m
λ
p
-
sin
(
β
)
)
+
β
,
where θ m is a diffraction angle supported by said blazed grating, and m is the diffraction order.
13. The LIDAR system of claim 12 , wherein the first state and second state are discrete ON and OFF states, respectively.
14. The LIDAR system of claim 12 , wherein the at least one light source comprises a laser.
15. The beam steering apparatus of claim 12 , wherein the at least one light source comprises a plurality of light sources producing at least two different wavelengths.
16. The beam steering apparatus of claim 12 , wherein the at least one light source is adapted to produce collimated light.
17. The beam steering apparatus of claim 12 , wherein the first AMA has only 2 discrete states of operation.