Optical systems, devices, and methods including high performance optical receivers
Optical systems, devices, and methods are provided for determining various characteristics, such as quantity, movement, distance and speed/velocity of an object relative to the system. The system and method includes an optical transmitter to transmit an output optical signal carrying an electrical reference signal and an optical receiver to receive a reflection of the output optical signal. The receiver includes at least one local oscillator providing local oscillator light at a local oscillator frequency, at least one combiner to combine the reflection of the output optical signal with the local oscillator light into a coupled optical signal. An optical-electrical converter converts the coupled optical signal into a first electrical signal, which is rectified via an envelope detector/rectifier to provide a first rectified electrical signal, which is processed by a signal processor along with the reference signal to calculate various characteristics of an object that reflected the output optical signal, such as the quantity, movement, distance, velocity, etc.
1. A system comprising
an electrical reference signal generator to provide an electrical reference signal;
at least one optical transmitter to transmit an output optical signal carrying the electrical reference signal; and
at least one optical receiver to receive a reflection of the output optical signal,
the at least one optical receiver including
at least one local oscillator providing local oscillator light at a local oscillator frequency that is not controlled and offset by a frequency difference from the output optical signal,
a combiner for coupling the reflection of the output optical signal with the local oscillator light into a coupled optical signal,
an optical-electrical converter for converting the coupled optical signal into a first electrical signal,
a rectifier to rectify the first electrical signal to provide a first rectified electrical signal, the optical-electrical converter and rectifier having a bandwidth to receive the coupled optical signal and account for variations resulting from at least one frequency chirp of the output optical signal resulting from directly modulating the optical source and the local oscillator light not being controlled;
an electrical combiner to combine the first rectified electrical signal with the electrical reference signal to generate a detection signal based on differences between the first rectified electrical signal and electrical reference signal; and
a signal processor to calculate a distance traveled by the reflection optical signal based on the first rectified electrical signal and the electrical reference signal.
2. The system of claim 1 , where
the output optical signal is produced by directly modulating a laser with the reference signal.
3. The system of claim 1 , where
the output optical signal is produced by directly modulating a DFB laser with the reference signal.
4. The system of claim 1 , where the signal processor includes
an electrical splitter to split the rectified electrical signal into first and second rectified signals,
first and second electrical combiners to combine the first and second rectified signal with the reference signal and provide first and second rectified reference signals; and
a phase detector to detect phase differences between the first and second rectified reference signals.
5. The system of claim 1 , where the signal processor includes
an analog to digital converter to convert the rectified reference signal into a digital signal; and
a digital signal processor to process the digital signal.
6. The system of claim 1 , where the electrical signal generator is at least one of modulated RF signal from an RF source and a digital signal processor.
7. The system of claim 1 , where
the reflection of the optical signal is from an object, and
the calculation includes calculating the distance of the object from the optical system based on the reflection of the output optical signal.
8. A method of measuring comprising:
providing, by an electrical signal generator, an electrical reference signal;
transmitting, by an optical transmitter, an output optical signal carrying the electrical reference signal;
receiving, by an optical receiver, a reflection of the output optical signal as an input optical signal;
providing, by a local oscillator, local oscillator light at a local oscillator frequency, that is not controlled and offset by a frequency difference from the output optical signal,
combining, by a combiner, the local oscillator light with the received optical signal to provide a coupled optical signal,
converting, by an optical-electrical converter, the coupled optical signal into a first electrical signal,
rectifying, by a rectifier, the first electrical signal to provide a first rectified electrical signal, the optical-electrical converter and rectifier having a bandwidth to receive the coupled optical signal and account for variations resulting from at least one of the frequency chirp of the output optical signal resulting from directly modulating the optical source and the local oscillator light not being controlled;
combining, via an electrical combiner, the first rectified electrical signal with the electrical reference signal to generate a detection signal based on differences between the first rectified electrical signal with the electrical reference signal; and
processing, by a signal processor, the detection signal to calculate a distance traveled by the reflection of the output optical signal.
9. The method of claim 8 , further comprising
filtering, by a high pass filter, the first electrical signal.
10. The method of claim 8 , where processing includes
converting the first rectified electrical signal to a digital signal; and
digitally processing the digital signal.
11. The method of claim 8 , further comprising
amplifying, by a linear amplifier, the first electrical signal.
12. The method of claim 8 , where the reflection of the optical signal is from an object, and
the calculation is at least one of distance and velocity of the object based on the reflection of the output optical signal.
13. The method of claim 8 , where
the electrical reference signal generator is one of an RF source and a digital signal processor.
14. The method of claim 8 , where
the electrical reference signal generator includes a time-stamp.
15. The method of claim 12 , where
the velocity is calculated based on successive distance calculations.
16. The system of claim 1 , where
the optical-electrical converter has a bandwidth of at least 40 GHz.
17. The method of claim 12 , where
the optical-electrical converter has a bandwidth of at least 40 GHz.
18. The system of claim 1 , where
the optical source is directly modulated with a modulation index of less than 1.
19. The system of claim 1 , where
the electrical reference signal generator is an electrically generated frequency-modulated continuous wave (EFMCW) generator.
20. The system of claim 1 , where
the optical source includes a bias current controlled to produce an optical frequency-modulated continuous wave (OFMCW) output optical signal.