DE1564560C3 - Device for low-noise optical superimposition reception for modulated, coherent optical radiation - Google Patents

Description

The present invention relates to a device for low-noise, optical superimposition reception for modulated, coherent optical radiation, in which the incoming message is in a noise sideband of the local superposition transmitter (local carrier with noise sidebands) which is strong for the purpose of high mixing gain, in which the intermediate frequency noise component Zf _R (intermediate frequency between Local carrier and its own noise is suppressed as far as possible, while the intermediate frequency message _{component Zf N} (intermediate frequency between local carrier and message) has sufficient intensity for demodulation and in which the message superimposed with the local transmitter is fed to two adjustable, non-linear optical mixers out of phase.

It is known that one can demodulate electromagnetic waves, especially at carrier frequencies from the radio wave, microwave or even higher frequency range, the principle is advantageous of the location overlay. The resulting intermediate frequency wave (Z / ^ wave) contains again the transmitted message, which then demodulates with technically simple means, d. H. analyzed, can be.

In the radio and microwave range, polarized radiations are relative to the local superposition sharp lines with sufficient intensity available at the same time - a strong spatial overlay is necessary to achieve the highest possible mixing gain (intensive radiation with Z / carrier wave).

In the optical area, the radiating electron transitions in atoms are superimposed, Molecules or solids in question. This radiation is either polarized or can be simple Means to be polarized.

The required high intensity with the smallest possible line width at the same time is when using of laser beams for local superimposition possible. The noise sidebands of a strong local overlay but are so intense that a weak, intoxicated signal, i.e. H. those with optical Message transmitting carrier frequency that can be covered by the noise sideband.

An optical heterodyne receiver is already described in US Pat. No. 3,191,047 to which a location carrier and the message is fed to a mixer, which is made by means of a partially permeable Mirror (beam splitter) mixes the incoming radiation optically and splits it into two partial beams. In this case, however, no measures are taken to determine the phase positions of the individual noise components to influence such that they are in antiphase or the phase positions of the message components in such a way that they are approximately in phase and therefore intensify.

In the DT-AS 1 564 450 there is already a heterodyne receiver for modulated, coherent signals It has been proposed to use a tunable, optical transmitter as an oscillator to form light Beats with the signal carrier light wave to be received is used. There is a device for converting of the modulated light into an interference fringe pattern with light and dark interference fringes required, as well as a device that is responsive to preselected portions of the interference fringes, to create a couple of signals that indicate the change in the fringe system.

The object of the present invention is to provide a simple device for low-noise, optical To indicate heterodyne reception for modulated, coherent, optical radiation, its Z / noise component is negligibly small compared to the Z / message component, making it special well and easily demodulated, d. H. can be recognized.

Starting from a device of the type mentioned in more detail at the outset, this object is achieved suggested that the two non-linear optical mixers, which are essentially linearly polarized optical beams of the incoming message

and the local superposition transmitter are fed on the input side, have a common mutual intensity adjustment, and that to generate the intermediate frequency components [Zf _K (l), Zj _n (I), Zf _R (U), Zf _N (H)] a waveguide for superimposing the in Z / components generated by the two mixers are provided in which the noise components [Zf _R (l) and Zf ₁₁ (U)] coming from these mixers are approximately in opposite phase due to the different phase position of the radiation falling into the mixer therefore approximately compensate each other in the waveguide, while the message components [ZZn (I) and Z /, _V (II)] are approximately in phase and therefore reinforced in the waveguide by superposition.

Advantageously, only one beam splitter is provided for dividing the two radiations in the superimposed transmitter, between its phase shifts (ψ and φ) caused by reflection or transmission approximately the relationship | ψ - φ

= -γ + ηπ is satisfied with η = integer or zero.

In this embodiment, the required phase condition for the radiation falling into the mixer, ie the required antiphase of the ZZ noise components coming from the mixer [Zf _R (I) and Z / _Ä (II)] is in antiphase with simultaneous in-phase of the ZZ message components [ZZv (I) and Z / _W (II)] achieved in phase.

Further details of the invention, in particular about the properties of the beam splitter mentioned, are in the following description and on the basis of FIG. 1 and 2 explained in more detail:

In Fig. 1 is first of all the schematic structure of the low-noise proposed according to the invention Overlay receiver outlined. Therein mean:

N = radiation of the incoming message, OU = radiation of the local overlay transmitter, I and II = the two non-linear, optical mixers,

3 = device for intensity adjustment,

4 = waveguide to superimpose the Z / -Kom-

components,

Zf _N = ZZ message component; Zf _N (I) or ZZ (II)

In Fig. 2 illustrates the effect of the partially transparent mirror with the required phase control. It means:

N = radiation of the incoming message,
OU = radiation of the local overlay transmitter,

1 = beam splitter with a phase shift ψ

with reflection or φ with transmission (the wavelengths of N and OÜ differ only so little from each other that for

both result in the same phase shift),

2 = deflection mirror for the ver

ongoing partial radiation,

O = additional phase shift due to the path difference between the beams from the beam splitter to the mixers I and II.

The required relationship between the phase shifts ψ and φ for reflection and transmission results from the phase conditions of the ZZ components:

1. Zf _R (I) and ZZfl (II) in opposite phase, that is:

ψ + δ - φ = (2m + 1) π with m = integer or zero;

2. ZZn (I) and Zf _n (II) in phase, that is:

φ + δ - ψ = 2kn with k = integer or zero.

The relation follows directly from this simultaneous system of equations by subtraction. between ψ and φ, so

2 \ ψ— φ \ = π + 2 (m - k) n = π + 2ηπ with

η = whole number or zero or | ψ - φ |

4ο That means: If this relationship applies at the beam splitter 1 between the phase shifts -ψ and φ for reflection or transmission, then the ZZ ^ components Zf _R (l) and ZZ _S (II) in the waveguide 4 as a result of the intensity adjustment 3 between the two mixers, while the Zf _N components Zf _N (1) and Zf _N (H) are additively superimposed, that is, amplified as an intermediate frequency

Zf _N ^ Zf _N (l) + Z

Zf _R = ZZ noise component; Zf _R (I) or ZZs (II).

The arrows at the ZZ components should register their 50 at the output of the arrangement and the demodule phase position suggest. can be lated.

1 sheet of drawings

Claims (2)

Patent claims: 1. Device for low-noise optical superimposition reception for modulated, coherent optical radiation, in which the incoming message is in a noise sideband of the local overlay transmitter (local carrier with noise sidebands) which is strong for the purpose of high mixing gain, in which the intermediate frequency noise component Zf _H (intermediate frequency between local carrier and own noise ) is suppressed as far as possible, while the intermediate frequency message _{component Zf n} (intermediate frequency between local carrier and message) has an intensity sufficient for demodulation and in which the message superimposed with the local transmitter is fed out of phase to two adjustable, non-linear optical mixers, characterized in that the two non-linear optical mixers (I and II), to which the essentially linearly polarized optical beams of the incoming message and the local superimposition transmitter are fed, have a common mutual intensity itätsabgleich (3) and that to generate the intermediate frequency components [Z / _R (I), Zf ₁₁ Q), Z ^ (II), Zf _N (II)] «in waveguide (4) to superimpose the generated in the two mixers Z / components is provided in which, due to the different phase position of the radiation falling into the mixers (I and II), the noise components coming from these mixers [Zf _R (l) and Zf fl (II)] are and are approximately in opposite phase therefore approximately compensate in the waveguide (4), while the message components [ZJ _n (V) and Zf _N (U)] are approximately in phase and therefore reinforced in the waveguide by superposition (Fig. 1). 2. Apparatus according to claim 1, characterized in that only one beam splitter (1) is provided for dividing both radiations in the local overlay transmitter, between its phase shifts (ψ or φ) caused by reflection or transmission approximated Relation \ ψ - φ | = ~ + ηπ with η = whole Number or zero is satisfied. 50