JP2901263B2 - Coherent signal processor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a coherent signal processing device using a delay line formed by an optical waveguide.

<Conventional Technology> Optical waveguides, especially optical fibers, have wide fields of use, including transmission lines of optical communication networks, due to their high speed and broadband. In particular, when used for information processing as a delay line, there is an advantage in processing a high-speed optical signal having a wide pass frequency band. The use of a single-mode optical fiber as a delay line for signal processing in this way has already been described in IEEE Transactions on Microelectronics.
"Optical fiber delay-line signal processin" published in Wave Theory and Techniques MTT Vol. 33, No. 3
g ". The tapped delay lines and recirculation delay lines described herein incoherently combine optical signals from each of the taps connected to the delay line. That is, an optical signal from a light source 1 which emits a continuous light wave is modulated by an optical intensity modulator 2 and guided to a delay line composed of an optical waveguide 3 as shown in FIG. I will The optical signals are splitters D ₀ , D ₁ , D ₂ ,... D arranged at equal intervals along the delay line.
the _n-1, the taps _{T 0, T 1, T 2} , is distributed to ... T _n-1, the variable attenuator _{W 0, W 1, W 2} , it is damped by ... W _n-1 to a predetermined value, The addition is performed incoherently by the adder 6. In addition, as shown in FIG. 9, an optical signal from a light source 1 for transmitting a continuous light wave is modulated by an optical intensity modulator 2 and guided to a delay line composed of an optical waveguide 3 as shown in FIG. I will This optical signal is introduced into the input terminal b of the directional coupler 8 and is incoherently coupled with a signal circulating through a delay line provided between the output terminal d and the input terminal a. c and is detected by the optical detector 5.

<Problems to be Solved by the Invention> However, the above-described conventional technique is to combine each signal incoherently, and can realize only a non-negative real number coefficient as a weighting coefficient of a tap, and there is a limitation in signal processing. Was. For example, high-pass filtering characteristics cannot be obtained in frequency characteristics, and differential operation cannot be performed on the time axis.

The present invention has been made in view of the above prior art,
It is an object of the present invention to provide a signal processing device that can use an optical waveguide as a delay line and can coherently couple the signals.

<Means for Solving the Problems> In the coherent signal processing device of the present invention, an optical waveguide is used as a delay line, a plurality of taps arranged in series or in parallel, and an electric field amplitude of an arbitrary branching ratio is applied to each tap. A variable splitter for distributing an optical signal having the phase shifter for performing an arbitrary phase shift on the optical signal distributed to the tap, and an optical coupler for coherently coupling the optical signal, and each tap includes It is characterized in that the divided optical signals are multiplied by an arbitrary weighting coefficient and added.

<Operation> The variable splitter distributes an optical signal having an electric field amplitude having an arbitrary splitting ratio to each tap, and the splitting ratio expresses an absolute value of a weighting coefficient of each tap. The optical signal distributed to each tap is subjected to an arbitrary phase shift by a phase shifter, and is added not only with a non-negative real number coefficient but also with an arbitrary weighting coefficient including a complex number.

<Example> Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows an embodiment according to the first invention of the present application. As shown in the figure, an optical signal from a light source that oscillates a continuous light wave is modulated by a light intensity modulator 2 and guided to a delay line constituted by an optical waveguide 3. Variable splitter S ₀ at equal intervals in the delay _{line, S 1, S 2 ... S} n-1 are arranged, the optical signal is these variable splitter S _{0, S 1, S 2 ... S} n-1 , The electric field amplitudes A ₀ , A ₁ ,
Tap T ₀ as an optical signal having _{A 2 ... A n-1,} T 1, T 2 ... T n-1
Branched to Tap T ₀ ~T _n-1 whereas connected to the delay line through a variable splitter S ₀ ~S _n-1, the tap T _i and T _{i + 1} adjacent connected in parallel to the optical coupler 4 Delay time of delay line τ
Are all equal. Tap T ₀ ~T _n-1 phase shifters P ₀ is _{on, P 1, P 2 ... P} n-1 are arranged respectively tap T ₀ ~T _n-1
Are phase-shifted by the phase shifters P ₀ , P ₁ , P _2, ..., P _{n -1} . After that, the optical signals are combined by the optical coupler 4.

Here, the optical signal has a frequency F of a high frequency of about 2 × 10 ¹⁴ , and its period T (= 1 / F) is generally much smaller than the delay time τ (T≪τ). the position where the position and the taps T ₀ ~T _n-1 subjected to be connected to the optical coupler, the phase of the branched optical signal is shifted. Further, the optical signal is transmitted to the variable splitters S _{0 to} S _n-1 and the optical coupler 4.
, The phase is shifted. For this reason, in the conventional tap delay line having no phase shifters P ₀ , P ₁ , P _2, ..., P _n−1 , the combined optical signal is incoherent. Phase shifter
Unnecessary phase differences of the optical signals between the taps coupled by the optical coupler 4 are canceled by P _{0 to} P _n−1 , and a predetermined desired phase shift is applied. The desired phase shifts performed by the phase shifters P _{0 to} P _n−1 are respectively _denoted by θ ₀ , θ ₁ , θ ₂ .
Assuming θ _n−1 , the weighting coefficients applied to the optical signal passing through each tap are a ₀ = A ₀ exp (jθ ₀ ), a ₁ = A ₁ exp (jθ ₁ ),
a ₂ = A ₂ exp (jθ ₂ )... a _n−1 = A _n−1 exp (jθ _n−1 )

Accordingly, the output optical signal E _out (t) that is coupled by the optical coupler 4 and detected by the optical detector 5 is obtained by multiplying the branched optical signal by the weighting coefficients a _{0 to an -1} as shown in the following equation. It will be added. However, if the optical signal input to the delay line is E
_in (t) and other conditions were omitted.

In order to simplify the explanation of the equation (1), n =
The variable branchers S ₀ , S ₁ ,
The electric field amplitude of the branching ratio by S ₂ … S _n-1 is A ₀ = 1/4 and A ₁ = 1 /, respectively.
2, A ₂ = 1/4, and the phase shifts by the phase shifters P ₀ , P ₁ , P _2, ... P _n-1 are respectively θ ₀ = 0, θ ₁ = π, θ ₂ = 0, weighting coefficient for each tap _{T 0, T 1, T 2} ... T n-1 each
a ₀ = 1/4, a ₁ = 1/2, a ₂ = 1/4. Input optical signal E _in
As (t), an optical signal modulated by a sine wave having an amplitude of 1 and an angular frequency ω (= 2πf), that is, a frequency f
If an optical signal shifted by only (1) is used, the equation (1) is simplified as the following equation. Here, Ω = 2πF.

As described above, according to the present invention, since the weighting coefficient can be made negative, the optical signal can be coherently combined by the optical coupler. Therefore, it is possible to perform signal processing that cannot be performed by the conventional incoherent combination.

For example, the frequency characteristic of the signal processing device having the configuration shown in FIG. 5 is expressed by the following equation, and has a high-pass filtering characteristic, that is, a differential characteristic, as shown in FIG.

I _out ≡ | E _out (t) | ² = ρ in ⁴ π (f + F) τ (3) Accordingly, a kind of intensity-modulated optical signal as shown in FIG. When a multiplexed signal is input, only the high frequency is filtered and obtained as an output signal as shown in FIG.

On the other hand, as a specific embodiment of the variable splitter and the phase shifter, the one shown in FIG. 4 is used. As shown in FIG. 4 (a), the directional coupler 41 is a variable branching device.
An optical switch utilizing an electro-optical effect by providing an electrode 43 at the coupling portion of the optical waveguide is used, and the output of the optical waveguide 42 is as shown in FIG. As a phase shifter, a phase modulator using an electro-optic effect by providing an electrode 43 on an optical waveguide 42 as shown in FIG. 4C is used, and its optical electric field phase is shown in FIG. As shown in FIG.

Next, the second and third inventions of the present application will be described with reference to the embodiment shown in FIG. 2 and FIG.

First, in the embodiment of the second invention shown in FIG. 2, an optical signal from the light source 1 which oscillates a continuous light wave is modulated by an optical intensity modulator and input to the variable branching device S. Taps T ₀ , T ₁ , T _2, ..., T _n−1 are connected in parallel to the variable splitter S, and the variable splitter S outputs a signal input in time series to the absolute value of the weighting coefficient of each tap. Electric field amplitude A ₀ , A ₁ , A ₂ … A _{n-1 of} branching ratio
Branches the optical signal having, distributed to the taps T ₀ ~T _n-1. The taps T _{0 to} T _n−1 have delays 0, τ, 2τ,.
-1) Each phase shift theta ₀ with a delay line comprising a waveguide is disposed with tau, theta _1, the phase shifter P ₀ with _{θ 2 ... θ n-1,} P 1, P 2 ... P n _-1 is provided. Tap T _{0 to} T
_n-1 are connected in parallel to the optical coupler 4, the taps T ₀ through T _n-1
Are divided into weighted coefficients a ₀ = A ₀ ex
p (jθ ₀ ), a ₁ = A ₁ exp (jθ ₁ ), a ₂ = A ₂ exp (jθ ₂ )
... a _n-1 = A _n-1 exp (jθ _n-1 ) is multiplied by the optical coupler 4
Thus, they are added as shown in the above equation (1), are coherently combined, and are detected by the optical detector 5.

In the embodiment of the third invention shown in FIG. 3, a coherently combined optical signal is fed back. That is, similarly to the embodiment of FIG. 1, a delay line composed of an optical waveguide, variable splitters S ₀ , S ₁ ... S _n−1 , a phase shifter P ₀ ,
The optical signals are coherently combined by the optical coupler 4 by P ₁ ... P _n-1 , taps T ₀ , T ₁ ... T _{n-1 and the} like, and further outputted from the light source 1 and modulated by the light intensity modulator 2. It is combined with the optical signal. This embodiment is called a cyclic configuration, while the embodiment shown in FIGS. 1 and 2 is called a non-cyclic configuration.

<Effects of the Invention> As described above in detail with reference to the embodiments, the present invention relates to a signal processing apparatus using a delay line composed of an optical waveguide, in which a variable branching device and a phase shifter are combined to arbitrarily weight. To coherently combine the optical signals. Therefore, it is possible to realize a signal processing function which cannot be performed by the conventional incoherent combination. As a result, the high speed and broadband characteristics of the optical waveguide can be fully utilized, and the optical waveguide can be applied in a wide range of fields such as optical information processing and optical communication.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment according to the first invention of the present application, and FIG.
FIG. 3 is a configuration diagram of an embodiment according to the second invention of the present application, FIG. 3 is a configuration diagram of an embodiment according to the third invention of the present application, FIG.
FIG. 4B is a specific configuration diagram of the variable branching device, FIG. 4B is a graph showing the optical output of FIG. 4A, FIG. 4C is a specific configuration diagram of the phase shifter, and FIG. Is the optical electric field phase θ in FIG.
FIG. 5 is a configuration diagram showing a specific example in which n = 3 in the embodiment shown in FIG. 1, FIG. 6 is a graph showing a frequency characteristic obtained by the configuration shown in FIG. 5, and FIG. (A)
(B) is a graph showing signals input to and output from the signal processing apparatus having the configuration shown in FIG. 5, FIG. 8 is a configuration diagram showing a conventional example of a non-cyclic type, and FIG. 9 is a cyclic type. FIG. 9 is a configuration diagram showing a conventional example. In the drawing, 1 is a light source, 2 is an optical intensity modulator, 3 is an optical waveguide, 4 is an optical coupler, 5 is an optical detector, 6 is an adder, 7 is a signal detector, 8
Are directional couplers, D ₀ , D ₁ ,..., D _n-1 are branching devices, W ₀ , W ₁ ,.
W _n-1 is a variable attenuator, S ₀ , S ₁ ,... S _n-1 is a variable branch, T ₀ ,
T _1, ... T _{n-1 tap, P 0, P 1, ...} P n-1 is phase shifters, A _0,
A ₁ ,... An _n-1 is the electric field amplitude of the optical signal distributed to each tap,
_{θ 0, θ 1, ... θ} n-1 is the phase shift amount to be applied to each tap, a, b is input, c, d is the output end, tau is the unit delay time, 41 directional coupler, 42 Is an optical waveguide, and 43 is an electrode.

Claims (3)

(57) [Claims] 1. A delay line comprising an optical waveguide for transmitting an optical signal whose optical intensity has been modulated, a plurality of taps connected along the delay line, and the plurality of taps arranged at equal intervals on the delay line. A plurality of variable splitters for distributing a delayed optical signal having an electric field amplitude of a splitting ratio that is an absolute value of a weighting coefficient of each tap, and an optical coupler for coherently coupling the optical signals from the plurality of taps. Canceling unnecessary phase differences of optical signals between the respective taps, which are arranged on the plurality of taps and are distributed to the taps and are coupled by the optical coupler, to be coherent and predetermined. A plurality of phase shifters that apply a phase shift to the input optical signal in the optical coupler, wherein the weighting is a product of the absolute value of the weighting coefficient corresponding to each tap and the phase shift. Coherent signal processing apparatus characterized by using addition of the optical signals multiplied by the number. 2. A plurality of taps arranged in parallel, and a branching ratio of an absolute value of a weighting coefficient of each of the plurality of taps connected to an optical waveguide for propagating a light intensity-modulated optical signal. One variable splitter for distributing a delayed optical signal having an electric field amplitude; a delay line including optical waveguides arranged on the plurality of taps and each having a different delay amount; and coherently converting optical signals from the plurality of taps. An optical coupler to be coupled; and a coherent optical signal arranged on each of the plurality of taps and canceling an unnecessary phase difference of an optical signal between the taps coupled by the optical coupler with respect to an optical signal distributed to the tap. And a plurality of phase shifters for performing a predetermined phase shift, the absolute value of the weighting coefficient corresponding to each tap to the input optical signal in the optical coupler and the Coherent signal processing apparatus characterized by using addition of the optical signals multiplied by the weighting factor is the product of the phase shift. 3. A delay line composed of an optical waveguide, a plurality of taps connected along the delay line, and absolute values of weighting coefficients of the taps arranged at equal intervals on the delay line. A plurality of variable splitters for distributing a delayed optical signal having an electric field amplitude of a branching ratio, and a plurality of optical signals from the plurality of taps connected to an optical waveguide for transmitting an optical intensity-modulated optical signal; An optical coupler that coherently couples the optical signal with the modulated optical intensity, and between each tap that is disposed on the plurality of taps and is coupled to the optical signal distributed to the tap by the optical coupler. A plurality of phase shifters for canceling an unnecessary phase difference of the optical signal to make it coherent and to perform a predetermined phase shift; and a predetermined branch connected to the coupler and for dividing the optical signal from the coupler. In the optical coupler, each optical signal obtained by multiplying the input optical signal by a weighting coefficient that is a product of the absolute value of the weighting coefficient corresponding to each tap and the phase shift in the optical coupler. Coherent signal processing device characterized by addition