JPS58111444A - Optical receiver for digital communication - Google Patents

Abstract

PURPOSE:To receive a multiplex wavelength digital signal with one set of optical receiver, by using a plurality of photodetectors having different sensitivity to light wavelength, and converting the detected signal into an electric signal corresponding one to one to the wavelength of an incident light at a light wavelength/electric signal converting circuit. CONSTITUTION:A digital signal of multiplex wavelength made incident from a digital communication optical cable is received at a photodetector 10 consisting of a one chip element having photo diodes PD1, PD2 having different sensitivity to the wavelength of light. An output of the photo detector 10 is converted into an electric signal corresponding one to one to a short-circuited current ratio of the photo detector 10 and having a prescribed relation with the wavelength at a light wavelength/electric signal conversion circuit 11 comprising logarithmic circuits 111A, 111B and a subtraction circuit 112. The on/off-state of the digital signal is discriminated from the presence/absence of optical signals, lambda1, lambda2 in wavelengths at a signal discrimination circuit 12 comprising comparators C1-C5, AND gates A1-A3, an OR gate N1, resistors R5-R8, and power supplies +V, -V from the converted output, and four states of the incident light are outputted from the gates A1 and A2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to digital optical reception, and more particularly to an optical receiver for digital communication suitable for wavelength multiplexing transmission lines.

Conventional digital optical receivers use one photodiode in the light receiving section, but since the photodiode has a wide sensitivity to light wavelengths, the basic configuration of the wavelength multiplexing transmission line is
It will look like the figure. Optical wavelengths λl, λ3 signals 8s, Sm
Optical transmitters T1. The output of T2 is guided to a multiplexer 1 via an optical cable 3, and after mixing the two wavelengths of light, the output is guided via an optical cable 3 to a receiver. The optical signal is divided into two wavelength optical signals by the demultiplexer 2, and each optical signal is sent to an optical receiver R1゜R2.
The signal enters the circuit, is converted into an electrical signal, and is output.

In this method, as the number of wavelengths for multiplexed transmission increases, the number of optical receivers also increases, resulting in disadvantages such as increased cost and decreased reliability.

An object of the present invention is to electrically regenerate a digital signal of each wavelength from a received optical signal containing digital signals of a plurality of optical wavelengths and output each digital electric signal, thereby achieving low cost and low flaw axis. An object of the present invention is to provide an optical receiver for digital communication that can realize a wavelength division multiplexing digital transmission system.

The % mold of the present invention uses a plurality of photoreceptors with different sensitivities to the wavelength of light as the light-receiving section, and uses a wavelength/electrical conversion circuit to convert the input from the light-receiving section into a one-to-one correspondence with the wavelength of the incident light. By converting it into an electrical output, and using the electrical output, a signal discrimination circuit outputs an electrical signal corresponding to each wavelength signal of the wavelength multiplexed transmission. This makes it possible to receive multiple digital signals.

FIG. 2 is a diagram showing an embodiment of the present invention. The light receiving section IO is formed by integrating two photodiodes PDI and PD2 into one chip, and the cathodes of PDI and P layer 2 are connected to each other in common, and are connected to a ground terminal 6. P.D.I.
, anode terminals 5 and 7 of the P layer 2 are output terminals.

The wavelength/electrical conversion circuit 11 includes logarithmic circuits 111A, 111
B. Consists of the subtraction circuit 112. The logarithmic circuit 111 consists of an operational amplifier OPI and a diode D1. Logarithmic circuit 11
1B consists of an operational amplifier OP2 and a diode D2. The subtraction circuit 112 includes an operational amplifier OP3 and resistors R1-R4. The signal discrimination circuit 12 is a comparator
CI, C2, C3, C4゜C5, and Kate Al, A
2. A3, OR gate Nl, variable resistor R5, l'L6.
)L7. Consists of R8.

FIG. 3 shows the layer structure of the light receiving section 10. As shown in FIG. The light receiving section 10 is composed of a PNP layer, and terminals 5, 7, and N are provided on the two P layers.
Terminals 6 are formed in the layer. When light is incident on the top of the chip of the light receiving section 10, the degree to which the light reaches each layer varies depending on the color (wavelength) of the light. In the figure, 7A is blue light, which reaches only the uppermost P layer. 7B is red light and reaches the N layer. 7C is infrared light and reaches the bottom P layer. That is, the thickness of each layer of PNP acts as an optical filter, and light with a short wavelength is absorbed near the silicon surface (3), and light with a long wavelength reaches a deep part and is absorbed. Therefore, the relationship between input wavelength and relative sensitivity has the characteristics shown in FIG. 3. When light enters each photodiode PDI, PD2, a current (terminal 5
and 6, or when terminals 6 and 7 are short-circuited, a short-circuit current flows, but the relationship shown in this figure is constant regardless of the depth of the incident light. Therefore, the relationship between the short-circuit current ratio (I scs / I act ) of the P layer 2 and PDI and the wavelength λ is as shown in FIG. 5, and is constant regardless of the incident light power.

Therefore, logarithmic circuits 111A and IIIB are provided to perform logarithmic conversion. This logarithmic circuit 111A.

When the output of 111B is subtracted by the subtraction circuit 112, the relationship between the output voltage V and the wavelength λ becomes as shown in FIG. A discrimination circuit 12 discriminates the level of this output.

The signal discrimination circuit 12 will be explained.

The output V(1) of the subtraction circuit 112 is as follows, that is, the output V is the short circuit current ratio (Iscs/l
5c1), and does not depend on the wavelength of the incident light, but has a constant relationship with the wavelength (see No. 6m). - Now, in wavelength multiplex transmission, different wavelengths λ1 and λ are used as signal transmission light. In digital transmission, signals are transmitted by turning on/off light, so there are four states of light incident on the light receiving section as shown in Table 1.

Table 1 Conditions of incident light Among these, in states 2 and 3, the wavelength component of the incident light is one type and the output of the circuit 11 remains unchanged as the relationship shown in FIG. 6 is applied.

In state 4, that is, when the lights of A1 and A3 are mixed and nine lights are incident on the light receiving section, V· can be obtained by the following calculation. Normally, in optical communications, light with a wavelength around 85 Qnm is used, which causes less loss in fibers. Therefore, the two wavelengths are A1 =
The explanation will be made by selecting 750 nm and λ = 900 nm.

λ1. Let the incident intensity of light of λ be pt, P, mW, respectively.
Then, PDI, short circuit current Iacl of P layer 2, I
From FIG. 3, each mcs is as follows.

lIC1=(PIXo, 530P2X0.21)C-(
2) Iscz-(PtX0.66+PsX0.95)C
...(3) However, C is a constant.

The ratio between Pl and pm can be easily determined from the output of the optical transmitter for each wavelength and the loss wavelength characteristics of the optical cable. Here, if we calculate the output of the optical transmitter and the loss in the cable (#j), the short-circuit current ratio is l5cs / l5c
t = Z 1 8 - (4).

Therefore, from FIG. 5, the line fiber wavelength λ of the light-receiving section when a single layer and a λ-rich mixture are found to be 820 nm, and from FIG. 6, Vo in this case is found to be 0.65 V.

Next, in state 1, that is, no signal input, PDl,
Since the output current of PD2 is 0, the logarithmic circuit 111A and 1
The output of 11B becomes negative infinity in terms of salt theory. In the circuit of this embodiment, the output voltage is close to the power supply voltage of -15V. Since the output voltage at this time varies depending on the circuit elements, there is no point in using the output of the subtraction circuit 112 for signal determination. Therefore, in this embodiment, IIIA,
The output of IIIB is I! L connection is used.

Hereinafter, the signal judgment circuit 12 based on the above signal judgment principle will be explained.
The operation of each part is summarized in Table 2.

Table 2 Signals of each part of the signal judgment circuit (Note) 1. Let λ1 be λ2.

2. H is TTL level HIGH, L is TTL level l, OW'f: Blow.

3. Indicates that X can be either H or L.

From the wooden surface, two light wavelengths λ1. It can be seen that the signals of λ, respectively, are correctly reproduced on the digital electrical outputs S 1+ 8 .

+V and -V in the figure are the reference voltages +15V and -15V-, respectively, and the optical wavelength λ1 for multiplex transmission. λ3 is 750nm each
, 900nm, V1+Vs and Vm are respectively 0.2V, (16sV,
There is tlVf.

The comparison voltages of the comparators C1 to C3 are set to ■1 to V
s Ex 4. ．． Set only AV to a small voltage. In this embodiment, ΔV is set to 0.2v.

Comparison voltage of comparator C4, CS ■4 is simply like 11I
It is not only useful for determining l. In this embodiment, as mentioned above, fluctuations in the optical power level (light received) do not affect signal reproduction, but if an extremely small optical signal is received, the influence of the v4- of the diode of the logarithmic circuit and noise may occur. Therefore, the signal may not be reproduced correctly and an erroneous signal may be output. For this reason, v4 also functions as a signal limiter to prevent receiver malfunction, and is useful for increasing receiver reliability.

As described above, this embodiment has the following effects.

(1) Receive and separate digital signals transmitted at two different optical wavelengths, and reproduce and reproduce them as electrical output.

(2) It operates stably regardless of the received light intensity, and does not output a signal to prevent malfunction when receiving a full signal that cannot be regenerated.

(3) Multiple wavelength multiplexed signals can be received with a simple circuit, and costs can be reduced compared to devices that use conventional optical demultiplexers and optical receivers.

In this embodiment, no signal is output when a weak signal is received, but it is also possible to add a signal output or an LED display when a weak signal is received.

In this embodiment, it is sufficient to omit the configuration for two-wavelength multiplexing or to change the comparison logic of the signal judgment circuit for wavelength-multiplexed signals of three or more wavelengths, and the light receiving section 10 and the Sakahan electric conversion circuit are left as they are. That's fine.

In addition, in this embodiment, the light receiving section uses an element that integrates two photodiodes, but multiple photodiodes with different sensitivities to wavelengths (even if the sensitivity is adjusted with an optical filter, there is no difference) are used. You may do so. However, in this case, the efficiency of receiving light from the optical fiber tends to decrease, and if three or more are used, the wavelength/electrical conversion circuit becomes complicated, so this embodiment can easily be implemented using wax.

Further, in this embodiment, a temperature characteristic compensation circuit for the photodiode was not particularly provided, but the output fluctuation is absorbed by Δ■, so there is no need to worry. However, a photodiode temperature characteristic compensation circuit may be added, and it is even better to add a diode temperature characteristic compensation circuit of a logarithmic circuit.

As described above, according to the present invention, a single receiver can receive digital signals at multiple optical wavelengths, so that an optical receiver for wavelength multiplexed digital transmission can achieve The number of receivers is 1/the number of wavelengths used, which has the effect of configuring a wavelength division multiplexing digital transmission system at low cost and with high reliability.

[Brief explanation of the drawing]

Figure 1 is an example of wavelength multiplexing transmission W & wax using a conventional optical receiver, Figure 2 is the circuit configuration of an embodiment of the present invention, the third factor is the structure of the light receiving section, and Figure 4 is the sensitivity of the light receiving element. Figure 5 is a diagram showing the relationship between the short-circuit current ratio of the light receiving element and wavelength, and Figure 6 is a diagram showing the relationship between the output voltage of the wavelength/electric conversion circuit and wavelength. be. 10... Light receiving section, PDI, PD2... Photodiode, 11... Wavelength/electric conversion circuit, IIIJI, 1l
lb...logarithm circuit, 112...subtraction circuit, 12...
・Signal discrimination circuit. Agent Patent attorney Masami Akimoto η ・−11−−−−−1− −−−]r−L−−−−−−
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Bow C2, 'i-t. Do ---"l, h-1"V
111: 〆l. 1': ""-,, J: 111

11 /671, 'RI 11> 11
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1: 1・−−−−−−1・・1 ′″−″+ 1
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Claims (1)

[Claims] 1. Wavelength multiplier incident from optical cable for digital communication 1
A light receiving section that receives converted optical digital signals and generates different outputs depending on the wavelength of the light, and an electrical output that corresponds one-to-one to the received light wavelength recognized by the light receiving section using the output of the cough light receiving section. and a second means for separating wavelength-multiplexed received optical signals using the output from the first means and outputting digital electrical signals corresponding to each wavelength. optical receiver. 2. The scope of the claim that the light receiving section is comprised of a single-chip device consisting of two photodiodes with different sensitivities to the wavelength of light! An optical receiver for digital communication according to item s1.