GB2225505A - Low noise optoelectronic correlators and mixers - Google Patents
Low noise optoelectronic correlators and mixers Download PDFInfo
- Publication number
- GB2225505A GB2225505A GB8816250A GB8816250A GB2225505A GB 2225505 A GB2225505 A GB 2225505A GB 8816250 A GB8816250 A GB 8816250A GB 8816250 A GB8816250 A GB 8816250A GB 2225505 A GB2225505 A GB 2225505A
- Authority
- GB
- United Kingdom
- Prior art keywords
- signal
- optical
- photo
- transmission line
- conductor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 230000005693 optoelectronics Effects 0.000 title claims description 3
- 230000003287 optical effect Effects 0.000 claims abstract description 18
- 230000005540 biological transmission Effects 0.000 claims abstract description 7
- 239000013307 optical fiber Substances 0.000 claims abstract description 3
- 239000004020 conductor Substances 0.000 claims description 14
- 239000004065 semiconductor Substances 0.000 claims description 6
- 230000002596 correlated effect Effects 0.000 claims description 3
- 238000001514 detection method Methods 0.000 claims description 3
- 239000002184 metal Substances 0.000 claims description 3
- 230000003111 delayed effect Effects 0.000 abstract description 5
- 101150071746 Pbsn gene Proteins 0.000 abstract description 2
- 238000001228 spectrum Methods 0.000 abstract description 2
- 238000000253 optical time-domain reflectometry Methods 0.000 abstract 1
- 230000005855 radiation Effects 0.000 abstract 1
- 239000000835 fiber Substances 0.000 description 6
- 230000001934 delay Effects 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000006798 recombination Effects 0.000 description 2
- 238000005215 recombination Methods 0.000 description 2
- 238000001914 filtration Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
- G01M11/3109—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
- G01M11/3118—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR using coded light-pulse sequences
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2/00—Demodulating light; Transferring the modulation of modulated light; Frequency-changing of light
- G02F2/002—Demodulating light; Transferring the modulation of modulated light; Frequency-changing of light using optical mixing
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H10F30/00—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors
- H10F30/10—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices being sensitive to infrared radiation, visible or ultraviolet radiation, and having no potential barriers, e.g. photoresistors
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Nonlinear Science (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Optical Communication System (AREA)
Abstract
In this invention photo-conductive elements onto which an optical signal with modulation is incident are used to detect and correlate the optical modulation with an electrical r.f. signal all within the same device. This can be used to detect and correlate optical signals which are modulated with pseudo-random codes or spread spectrum codes with reference electrical signals. This can be used in PRBS optical time domain reflectometry for distributed sensor application by launching a PRBS-modulated laser (2) into an optical fibre (12) and correlating at (4) the back-scattered radiation with a delayed version (6) of the original sequence. The device (4) itself consists of a coplanar transmission lie with a gap. <IMAGE>
Description
Low noise optoelectronic correlators and mixers
In this invention a photo-conductive element is used to correlate or mix optical and RF signals to produce a correlated signal or a downconverted
RF signal. The photo-conductor consists of a semiconductor mounted between two metal contacts, as shown in Figure 1. An optical signal with modulation or a number of optical signals are incident on the gap. An electrical RF signal is applied to one of the metal electrodes and the output of the other electrode is the correlation of the modulation and the
RF signal and a subtraction or addition of the modulation frequency and the RF frequency if these are discrete signals. Examples of photo-conductors are shown in Figures 2, 3 and 4. The photoconductors in figures 2 and 3 are coplanar structures where the ground plane and the centre conductor are both on the same side of the semiconductor.In
Figure 2 the centre conductor contains a gap where the electrodes and the semiconductor form the photo-conductor. The optical signal is incident on the semiconductor in the gap. The electical signal is applied to one electrode and the output is taken from the other electrode.
Transmission line tapers are arranged to interface the transmission line to connectors for example OSSM connectors if necessary. In Figure 3 the photoconductor is between the centre line and the ground planes so that the photo-conductor is now in shunt. The photoconductor in Figure 4 is made on microstrip where the ground plane is on one side and the conductor is on the other side. These photo-conductors can be arranged to present different impedances to the electrical or RF signal and the output signal for example lowish impedances at the RF input but act as high impedance sources to drive FET or transimpedance amplifiers by using diplexers or filtering circuits.
In a specific application as described in patent application GB21 901 86A where the system is shown in figure 5 a spread spectrum signal (pseudo-random code) (1) is amplitude modulated onto a laser or light source (2) where this light is launched into a medium such as an optical fibre (12) via a fibre coupler or beam splitter (3). The backscattered light is incident on a photo-detector (4) for example a photo-diode or avalanche photo-diode or photo-multiplier. The electrical output from the photo-ddetector is amplified (5) and applied to a multiplier (8) where the other input is a delayed version of the origional pseudo-random code (6,7). Spatial measurements of backscatter are achieved by scanning the delay of the delayed signal.Chopping techniques as described in
GB2190186A can be used to convert the DC correlation signal into an AC signal by switching between two delays of the pseudo random signal (usually at the end of the sequence) such that there is a correlation within the medium at one delay and no correlation at the other delay by setting the delay to correspond to be a point outside the fibre (medium) producing an AC output from the correlator. This signal is then amplified in a tuned amplifier (9) and lockin amplifier (10) and displayed (11). It can also be amplified and sampled and digitised and processed and displayed.
In the invention described in this application as shown in figure 6 backscatter from the medium or fibre is launched in the same way as in figure 5 but it is now incident on a photo-conductor (4) or photo-detector which performs both the detection of the optical signal and correlation of the modulation on the optical signal with the delayed PRBS signal (6,7) which is applied to one of the electrodes where the output from the other electrode is the correlation. The photo-conductor could be as shown in figures 1,2,3,4. This signal is for example a pseudo-random signal or binary code or code burst or a multi-level signal or multi-colour signal or pulses. The output of the photoconductor is therefore the correlation between the modulation of the optical signal and the electrical signal.
Because the electrical signal is balanced, the Shot noise is reduced. This allows the detection and correlation to be performed all within the same detector. By varying the delay between the launched signal and the delayed signal the spatial variation and hence value of the backscatter can be built up over the whole fibre (medium) and this can be used to measure any parameter of the fibre and any external fields which affect these parameters. Chopping techniques as described in GB21 901 86A can be used to convert the DC correlation signal into an AC signal by switching between two delays of the pseudo random signal such that there is a correlation within the medium at one delay and no correlation at the other delay by setting the delay to correspond to a point outside the fibre (medium) producing an AC output from the correlator.This signal is then amplified in a tuned amplifier (9) and locking amplifier (10) and displayed (11). It can also be amplified, sampled, digitised, processed and displayed.
Because the electrical signal is balanced the Shot noise is reduced.
Further photoconductive gain is achieved where this gain is defined as
G = Tr/Tt where Tr is the recombination time and Tt is the transit time accross the gap. Therefore high gains can be achieved for small gaps and long recombination times.
The modulation is usually amplitude modulation (Amplitude shift Keying) but can be any combination of amplitude or phase or frequency modulation. The detectors can also be used to detect the signal coherently.
The optical signal could be made balanced by using multiple correlating elements. The photo-detector could also consist of two diodes placed in parallel back to back where both photo-diodes are illuminated together.
Claims (6)
- LOW.NOISE OPTO-ELECTRONIC CORRELATORS AND MIXERSCLAIMS 1. A photo-conductive detector comprising a semiconductor with two metal electrodes where the semiconductor is illuminated with a modulated optical signal or many optical signals where one electrode has an input rf signal applied to it where the output from the other electrode is the mixed or correlated or downconverted signal of the optical and electrical signal.
- 2. The input rf signal described in claim 1 is a signal modulated with a pseudo-random code to obtain spatial information about the optical signal by correlating the RF signal with the optical signal which can be from an optical fibre where the output from the other electrode is the correlated signal.
- 3. The photo-conductor described in claim 1 is a coplanar transmission line with a gap in the middle of the transmission line.
- 4. The photo-conductor described in claim 1 is a coplanar transmission line which is illuminated between the centre conductor and the ground plane.
- 5. The photo-conductor described in claim 1 is a microstrip transmission line with a gap in the centre line
- 6. The photoconductor shown in Figures 1 to 4 is used in the system shown in Figure 6 to perform the detection and correlation of the optical signal and the electrical signal to obtain spatial information about the optical signal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8816250A GB2225505A (en) | 1988-07-07 | 1988-07-07 | Low noise optoelectronic correlators and mixers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8816250A GB2225505A (en) | 1988-07-07 | 1988-07-07 | Low noise optoelectronic correlators and mixers |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8816250D0 GB8816250D0 (en) | 1988-08-10 |
| GB2225505A true GB2225505A (en) | 1990-05-30 |
Family
ID=10640082
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8816250A Withdrawn GB2225505A (en) | 1988-07-07 | 1988-07-07 | Low noise optoelectronic correlators and mixers |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2225505A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2243210A (en) * | 1989-08-30 | 1991-10-23 | Jeremy Kenneth Arthur Everard | Distributed optical fibre sensor |
| EP0559102A1 (en) * | 1992-03-03 | 1993-09-08 | Advantest Corporation | Frequency converter |
| US7971368B2 (en) * | 2005-07-26 | 2011-07-05 | Mitsubishi Electric Corporation | Hand drying apparatus |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3491241A (en) * | 1968-02-19 | 1970-01-20 | Inventors & Investors Inc | Modulation of current flow in a semiconductor |
| GB1482954A (en) * | 1973-08-20 | 1977-08-17 | Massachusetts Inst Technology | Electronic device |
-
1988
- 1988-07-07 GB GB8816250A patent/GB2225505A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3491241A (en) * | 1968-02-19 | 1970-01-20 | Inventors & Investors Inc | Modulation of current flow in a semiconductor |
| GB1482954A (en) * | 1973-08-20 | 1977-08-17 | Massachusetts Inst Technology | Electronic device |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2243210A (en) * | 1989-08-30 | 1991-10-23 | Jeremy Kenneth Arthur Everard | Distributed optical fibre sensor |
| EP0559102A1 (en) * | 1992-03-03 | 1993-09-08 | Advantest Corporation | Frequency converter |
| US5352885A (en) * | 1992-03-03 | 1994-10-04 | Advantest Corporation | Frequency converter for varying the frequency of a local signal over a wide band |
| US7971368B2 (en) * | 2005-07-26 | 2011-07-05 | Mitsubishi Electric Corporation | Hand drying apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8816250D0 (en) | 1988-08-10 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |