JPH09287958A - Optical fiber gyroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the scoop-type optical fiber gyroscope, whose characteristics are improved, by applying reverse bias on a photodetector. SOLUTION: In this optical fiber gyroscope, the phase of the branched light by an optical coupler is deviated with a phase modulator, the both right-turning and left-turning beams, which are guided into sensing loops and propagated, respectively, are coupled again with the optical coupler, and thereafter the angular velocity information is detected with a chip-output monitoring photodetector 15, which is provided at the opposite side of the emitting side of a light source 14 and connected to an output resistance value 12. In this case, the output resistance value 12, which is connected to the chip-output monitoring photodetector 15, is set at the specified value so that the anode potential of the photodetector does not become higher than the cathode potential, when the light is applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber gyro, and in particular, it provides signal light after re-combining left and right light traveling in a sensing loop with an optical coupler on the side opposite to the emission side of a light source. The present invention relates to a constant condition of a reverse bias circuit of a photoreceiver which constitutes a so-called scoop type optical fiber gyro for obtaining angular velocity information by detecting the photodetector.

[0002]

2. Description of the Related Art In a conventional general optical fiber gyro, light from a light source is branched by an optical coupler, the branched light is phase-shifted by a phase modulator, and each is guided to a sensing loop and propagated through the sensing loop. Both the left and right lights were recombined by an optical coupler, detected by a photodetector, and angular velocity information was obtained by a signal processing circuit.

An optical fiber gyro having such a structure is
It had the following drawbacks.

(1) The number of parts is large and the cost is high.

(2) Loss occurs in many parts,
It is necessary to increase the amount of light from the light source, resulting in an increase in the light source current and a reduction in the life of the light source.

(3) An angular velocity bias is generated due to the phase difference between the transmission and reflection modes of the optical coupler.

As an optical fiber gyro that has improved the above drawbacks, there is a so-called scoop type optical fiber gyro. FIG. 5 is a schematic explanatory view of a scoop type optical fiber gyro.

The scoop method (Scoop) is Sel
This is an abbreviation for the f-Coupled-Optical-Pickup method and is the method described below.

In FIG. 5, the light from the light source 2 is branched by the optical coupler 3, the branched light is phase-shifted by the phase modulator 4 and guided to the sensing loops 5, respectively. A technique has been proposed in which the light is recombined by the optical coupler 3 and the signal light thereof is detected by the chip output monitor light receiver 1 provided on the side opposite to the emission side of the light source 2. Related to this, Japanese Patent Laid-Open No.
-186043 bulletin

[0010]

In the configuration of the optical fiber gyro of the above system, as shown in FIG. 1, the voltage Va obtained by the light source current flowing through the resistor 11 between the light source driving transistor 13 of the light source driving circuit and the ground, as shown in FIG. And the voltage Vb obtained by the photocurrent flowing through the ground resistance 12 of the DC component of the photodetector 15, the reverse bias voltage of Va-Vb is applied to the photodetector 15.

Therefore, the light receiver 15 and the light source 1
When the direct current component of the monitor current at the time of light output increases due to the characteristics of No. 4 or the loss variation of the optical system, the voltage Vb on the photodetector side increases and the reverse bias voltage applied to the photodetector decreases. , Or a positive bias state. As a result, the frequency characteristic of the photodetector is deteriorated, which adversely affects the characteristic of the optical fiber gyro.

The object of the present invention is to solve the above problems in the prior art, and to optimize the constants of the resistance resistance between the light source and the ground of the light source drive circuit and the ground resistance of the DC component of the light receiver output. The present invention aims to provide an optical fiber gyro that ensures a stable reverse bias condition of a light receiver.

[0013]

In order to achieve the above object, an optical fiber gyro according to the present invention has a structure in which light from a light source is branched by an optical coupler, and the branched light is shifted in phase by a phase modulator, A chip output monitor which is provided on the opposite side of the emission side of the light source and is connected to the output resistance value of the signal light after being led to the sensing loops respectively and the left and right lights traveling through the sensing loops are recombined by the optical coupler. In the optical fiber gyro which detects the angular velocity information by the optical receiver for light, set the output resistance connected to the chip output monitor optical receiver to a predetermined value, and the anode potential of the optical receiver when light is incident is higher than the cathode potential. It is characterized by the fact that it does not happen.

In the optical fiber gyro described in the above paragraph,
It is characterized in that a resistor having a predetermined value is inserted between the light source and the ground so that a reverse bias is applied to the photodetector for the chip output monitor.

A more detailed description will be given.

(1) To increase the cathode side voltage Va of the light receiver, the resistance value between the driven light source of the light source drive circuit and the ground is increased.

(2) To reduce the anode side voltage Vb of the photodetector, the DC ground resistance of the photodetector output is reduced.

(3) According to the above (1) and (2), the reverse bias voltage Vb-Va can be secured.

Regarding the resistance value, (a) the resistance value between the light source and the ground exceeds the value that does not prevent the supply of the necessary light source current within the operating temperature range in order to determine the limiting current of the light source. It goes without saying that there is no such thing.

(B) Since the DC ground resistance value of the photoreceiver output affects the transimpedance gain frequency characteristics of the photoreceiver, the fundamental wave, second harmonic wave, and
It goes without saying that since the harmonic component is detected, the value is not less than the value that does not affect the characteristics of each component.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to FIGS.

FIG. 1 is a drive and light receiving circuit diagram of a scoop type optical fiber gyro according to an embodiment of the present invention.

In the figure, 11 is a grounding resistance between the light source and the ground, 12 is a grounding resistance of the direct current component of the light receiver output, 13 is a light source driving transistor, 14 is a light source, 15 is a chip output monitor light receiver, and 16 is It is an output part.

In FIG. 1, a light source driving transistor 1
3 and the light source 14 are connected in series, and the grounding resistance 11
Are connected in series.

The light source 14 and the ground resistance 1 of this series connection circuit
The photodetector 15 and the output unit 16 are connected to the connection terminal with 1. The ground resistance 12 of the output DC component of the photodetector 15 is inserted between the connection terminal between the photodetector 15 and the output unit 16 and the ground. It is set up.

In the above circuit, the resistance 11 is set to 20 [Ω].
Then, when the current change of the light source 14 is 30 to 80 [mA], the voltage Va obtained by the grounding resistance 11 between the light source 14 of the light source drive circuit and the ground and the light source current flowing through the resistance 11 is ohm. According to the law, 0.6-1.6
[V].

The monitor current of the photodetector 15 is 100 to 2
00 [μA] and the resistance 12 is 2.2 [kΩ], in this case, the voltage Vb obtained from the monitor current of the photodetector 15 and the ground resistance 12 of the DC component of the photodetector output 15
Is 0.22 to 0.44.

From the above, at least the light receiver 15 is
A reverse bias voltage of Va-Vb = 0.6-0.22 = 0.38 [V] is applied, and the photodetector shows stable frequency characteristics.

FIG. 2 is a characteristic diagram of gain and frequency in the circuit diagram of the scoop type optical fiber gyro in FIG. 1, and FIG. 3 is a characteristic of phase and frequency in the circuit diagram of the scoop type optical fiber gyro in FIG. It is a diagram. In the figure, the ground resistance of the DC component of the light receiver output is Rb.

The Rb is changed and selected so as to be in a stable region in accordance with the phase modulation frequency. Needless to say, the limit of the value of the resistor 11 is taken into consideration in the selection.

The present invention is not limited to the above embodiment, and many modifications can be considered. FIG. 4 is a circuit diagram of a scoop type optical fiber gyro according to another embodiment of the present invention.

In the present embodiment, the light source 14 is arranged on the side opposite to the ground of the driving transistor 13, and a voltage of Va and Vbe of the driving transistor 13 are applied.

In each of the above embodiments, the chip output monitor light receiver is provided on the side opposite to the emission side of the light source, but the chip output monitor light receiver may be provided in the light source.

[0034]

As described above in detail, according to the configuration of the present invention, (1) the light source current and the light receiver output current change due to the temperature change, and the light receiver is stable even if the bias condition changes. The fluctuation range can be accommodated in the operation area.

(2) Even when the light source current and the photodetector output current change due to the optical system loss variation and the bias condition also varies, the variation range can be set within the stable operation area of the optical receiver.

(3) By always applying an appropriate reverse bias to the photodetector, the photodetector operates in a good condition,
As a result, the characteristics of the scoop type optical fiber gyro can be improved.

[Brief description of drawings]

FIG. 1 is a drive and light receiving circuit diagram for a scoop type optical fiber gyro according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram of gain and frequency in the circuit of the scoop type optical fiber gyro of FIG.

FIG. 3 is a characteristic diagram of phase and frequency in the circuit of the scoop type optical fiber gyro of FIG.

FIG. 4 is a driving and light receiving circuit diagram of a scoop type optical fiber gyro according to another embodiment of the present invention.

FIG. 5 is a schematic explanatory view of a scoop type optical fiber gyro.

[Explanation of symbols]

 1 Light Source Driving Circuit 2 Light Source 3 Optical Coupler 4 Phase Modulator 5 Sensing Loop 11 Grounding Resistance 12 Grounding Resistance 13 Light Source Driving Transistor 14 Light Source 15 Chip Output Monitor Receiver

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirokazu Soekawa 5-1-1 Hidaka-cho, Hitachi-shi, Ibaraki Hitachi Cable Co., Ltd. Hidaka factory

Claims (2)

[Claims] 1. A light from a light source is branched by an optical coupler, the phase of the branched light is shifted by a phase modulator, each is guided to a sensing loop, and both left and right lights propagating through the sensing loop are recombined by an optical coupler. In a fiber optic gyro that obtains angular velocity information by detecting the signal light after being processed by a photodetector for chip output monitor that is provided on the opposite side of the emission side of the light source and is connected to an output resistor, a chip output monitor photodetector An optical fiber gyro characterized in that the output resistance connected to the optical fiber gyro is set to a predetermined value so that the anode potential of the light receiver does not become higher than the cathode potential when light is incident. 2. The optical fiber gyro according to claim 1, wherein a resistor having a predetermined value is inserted between the light source and the ground, and a reverse bias is applied to a photodetector for chip output monitoring. Fiber optic gyro to do.