Apparatus and method for measuring characteristics of optical pulses

• US 6,057,919 A
• Filed: 07/11/1997
• Issued: 05/02/2000
• Est. Priority Date: 07/16/1996
• Status: Expired due to Fees

• Current Assignee: Japan Science And Technology Corpration (Japan Science And Technology Agency)
• Original Assignee: Japan Science And Technology Corpration (Japan Science And Technology Agency), Yoshihisa Yamamoto
• Inventors: Jiang, Shudong, Machida, Susumu, Yamamoto, Yoshihisa
• Primary Examiner(s): Kim, Robert H.
• Assistant Examiner(s): LEE, HWA S
• Application Number:
  US08/893,647
• Time in Patent Office: 1,026 Days
• Field of Search: 356/346, 356/349, 356/345
• US Class Current: 356/450
• CPC Class Codes: G01J 11/00 Measuring the characteristics of individual optical pulses or of optical pulse trains
• CPC Class Codes: G04F 13/026 Measuring duration of ultra-short light pulses, e.g. in the pico-second range; particular detecting devices therefor photometry, radiation pyrometry G01J1/00, G01J5/00; non-linear optics G02F1/35

Abstract

In an optical pulse characteristic measuring apparatus, optical pulses to be measured are introduced at the incident end, and split at an beam splitter. A first resultant light beam is reflected by a mirror as a local oscillation light of homodyne detection and is adjusted in a delay element so as to have the same optical path length as that of the second resultant light beam. Subsequently, the first light beam is led to an optical mixer. The second light beam is reflected by a mirror, which is controlled by a signal from a signal generator for modulation of optical path length difference. The second light beam is then reflected by a delay element and is led to the optical mixer. The two light beams combined at the optical mixer are detected by optical detectors. The AC signal component generated by modulation of the optical path length difference is amplified up to a measurable voltage by a differential amplifier. A bandpass filter passes only the AC signal component generated by modulation of the optical path length difference, thereby improving the S-N ratio. By using an AC voltmeter to measure the AC signal component corresponding to the delay of the delay element for correlation length measurement, the auto-correlation signal can be obtained. Accordingly, it is possible to measure the characteristics of optical pulses with high sensitivity and high stability.

Claims

1. An apparatus for measuring characteristics of optical pulses comprising:

(a) a beam splitter for splitting an input beam of optical pulses to be measured into a pair of light beams output therefrom;

(b) means for modulating an optical path length of one of the pair of light beams output from said beam splitter;

(c) means for changing the optical path length of one of said pair of light beams output from said beam splitter relative to the other of said pair of light beams output from said beam splitter;

(d) an optical mixer for mixing the pair of output light beams;

(e) an optical detector for detecting a light beam output from said optical mixer; and

(f) means for measuring the amplitude of an AC signal output from said optical detector.

2. A method for measuring characteristics of optical pulses in an input light beam comprising the steps of:

(a) splitting the input beam of optical pulses to be measured into first and second beams,

b) modulating an optical path length of one of the first and second light beams,

(c) changing an optical path length of one of the first and second light beams relative to the other of said first and second light beams,

(d) mixing the first and second light beams,

(e) detecting a light beam output from said optical mixer, and

(f) measuring the amplitude of an AC signal output from said optical detector;

wherein said modulating the optical path length of one of the first and second light beams and said detecting the light beam from the optical mixer performs heterodyne detection in order to measure the AC signal component which is generated by the modulation of the optical path length.

3. An apparatus for measuring characteristics of optical pulses comprising:

(a) a beam splitter for splitting an input beam of optical pulses to be measured into a pair of light beams output therefrom;

(b) means for modulating the optical path length of one of the pair of light beams output from said beam splitter;

(c) means for changing the optical path length of one of said pair of light beams output from said beam splitter relative to the other of said pair of light beans output from said beam splitter;

(d) means for chopping one of said pair of light beams output from said beam splitter;

(e) an optical mixer for mixing the pair of output light beams;

(f) an optical detector for detecting a light beam from said optical mixer;

(g) detecting means for detecting the amplitude of an AC signal output from said optical detector; and

(h) synchronous detecting means for detecting the amplitude of the output from said detecting means synchronously with the operation of said light chopping means.

4. A method for measuring characteristics of optical pulses in an input light beam comprising the steps of:

(a) splitting the input beam of optical pulses to be measured into first and second beams,

(b) modulating an optical path length of one of the first and second light beams,

(c) changing an optical path length of one of said first and second light beams relative to the other of said first and second light beams,

(d) chopping one of the first and second light beams,

(e) mixing the first and second light beams,

(f) detecting a light beam generated by said mixing,

(g) detecting the amplitude of an AC signal produced from the detecting of the light beam, and

synchronously detecting the amplitude of an AC modulation component in the detected AC signal from the detecting of the light beam in synchronism with the chopping of one of the first and second light beams;

wherein said modulating the optical path length of one off the first and second light beams, said chopping of one of said first and second light beams, said detecting of the amplitude of an AC signal produced from the detecting of the light beam and said synchronously detecting the amplitude of an AC modulation component in the detected AC signal from the detecting of the light beam performs heterodyne detection in order to detect and measure the AC modulation component which is generated by the modulation of the optical path length.