System and method for measuring the phase of a modulated optical signal
First Claim
1. An apparatus for determining a range information from a transceiver to an object by measuring a phase of a modulated optical signal, comprising:
- a transmitter transmitting the optical signal modulated with a modulation frequency fm and generating optical pulses of temporal half-width of τ
p towards the object;
a receiver receiving a reflected portion of the modulated optical signal, the receiver contains a single photon sensitive optical receiver with an optical detection efficiency that is modulated at a gate frequency fG with a gate creating a temporal optical detection efficiency half-width of τ
G, the frequency fG=M·
fm where M=I2/I1 and I1 and I2 are relatively prime integers greater than one; and
whereas I2/fG is nearly equal to or larger than the dead time of the optical receiver; and
a processor to determine the range information of the object.
1 Assignment
0 Petitions
Accused Products
Abstract
The invention is related to phase detection in lidar systems using single photon detectors (SPDs). The frequency at which the SPDs are time gated is related to but not an integer multiple of the frequency of the transmitted optical pulses. Each return optical pulse arrives with a particular temporal position with respect to the nearest gate, and thus is detected with a related detection efficiency. The SPD output can be segmented into multiple time-multiplexed signals whose relative detection efficiency reveals the phase of the optical return pulses, and no such phases have negligible detection efficiency for all the time-multiplexed signals. To mitigate the impact of afterpulsing and other saturation effects, when a first optical pulse is detected with high detection efficiency the next optical pulse that is detected with high detection efficiency is separated by a time period about equal to or greater than the detector dead time.
-
Citations
15 Claims
-
1. An apparatus for determining a range information from a transceiver to an object by measuring a phase of a modulated optical signal, comprising:
-
a transmitter transmitting the optical signal modulated with a modulation frequency fm and generating optical pulses of temporal half-width of τ
p towards the object;a receiver receiving a reflected portion of the modulated optical signal, the receiver contains a single photon sensitive optical receiver with an optical detection efficiency that is modulated at a gate frequency fG with a gate creating a temporal optical detection efficiency half-width of τ
G, the frequency fG=M·
fm where M=I2/I1 and I1 and I2 are relatively prime integers greater than one; and
whereas I2/fG is nearly equal to or larger than the dead time of the optical receiver; anda processor to determine the range information of the object. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
-
-
12. A method for determining a range information from a transceiver to an object by measuring a phase of a modulated optical signal, comprising:
-
sending the modulated optical signal comprised of a series of short optical pulses towards the object; receiving a series of short optical pulses at a pulse repetition frequency, a portion of the optical signal being detected in a single photon detector (SPD), the SPD being time gated at a frequency not equal to an integer multiple of the pulse repetition frequency, the SPD preferentially detecting photons during a time gate with a resulting detection efficiency having a known shape as a function of time where the shape of the detection efficiency is used to help measuring the phase of the optical signal; and
whereas the pulse repetition frequency and the gate frequency are such that any two optical pulses that both temporally overlap with time gates are far enough apart in time to keep the photodetector saturation low, thus maintaining a high SPD linearity; andprocessing data on the phase measurement to receive information about the range or velocity of the object. - View Dependent Claims (13, 14, 15)
-
Specification