JP2009522769A - Optical signal source wavelength stabilizer - Google Patents

Abstract

An optical signal output wavelength stabilizing device from the optical signal source (12) couples a control signal out of the optical fiber (14) and the optical fiber (14) arranged to receive the optical signal from the optical signal source (12). The optical tap (16) arrange | positioned so that it may be provided. Optical signal splitter (22) is installed so as to divide the control part into a first portion and a second portion having a wavelength dependent intensity I ₂ having a wavelength dependent intensity I _1. When the control circuit (28) calculates the ratio R = I ₁ / I ₂ and the wavelength shift in the optical signal source (12) causes the ratio R to deviate from the predetermined set point, the optical signal source (12) Installed to send an error signal.

Description

  The present invention relates generally to optical fiber sensors, and more particularly to an optical fiber rotation sensor, also known as an optical fiber gyroscope (FOG). More particularly, the present invention relates to the provision of an optical signal source for an FOG technology application apparatus that has advanced wavelength stabilization over a certain operating temperature range.

（１）
ここでＡは光路の封入面積、Ｎは光ファイバーコイルの巻き数、ｃは真空中における光の速さ、λ_ｃは波長の中心である。この等式（１）から、λ_ｃが変化するとジャイロスケールファクターが影響を受けることがわかる。スケールファクター性能の改善のためには、波長を温度と時間に渡って安定させるか、適宜の情報を収集してジャイロ性能から波長変動を模式化する手段を提供しなければならない。 The broadband light source is mainly used in sensing technology application devices and is a primary signal source used in FOG application technology. The stability of the gyro scale factor (SF _gyro ) is highly dependent on the stability of the wavelength of the signal source, as can be seen from the equation below.

(1)
Here, A is the enclosed area of the optical path, N is the number of turns of the optical fiber coil, c is the speed of light in vacuum, and λ _c is the center of the wavelength. From this equation (1), and λ _c is changed it can be seen that the gyro scale factor is affected. In order to improve the scale factor performance, the wavelength must be stabilized over temperature and time, or appropriate information must be collected to provide a means to model the wavelength variation from the gyro performance.

  The present invention is directed to wavelength stabilization of a broadband optical signal source suitable for use in an optical fiber gyroscope (FOG) system. The invention is applicable to both superfluorescent fibers (SFS) and optical signal sources based on superluminescent diodes (SLD). In any case, the optical signal source spectrum is broad, mainly 20 nm to 50 nm at the 3 dB point, and the center wavelength varies with temperature.

An apparatus according to the present invention for stabilizing the wavelength of an optical signal output from an optical signal source includes an optical fiber arranged for receiving an optical signal from the optical signal source, and an optical arranged so that a control part of the optical signal is taken out from the optical fiber. Includes taps. An optical signal splitter is disposed to divide the control portion into a _first portion having a wavelength dependent intensity I ₁ and a second portion having a wavelength dependent intensity I ₂ . A control circuit is installed to calculate the ratio R = I ₁ / I ₂ and when the wavelength drift of the optical signal source causes the ratio R to deviate from a predetermined set point, an error signal is sent to the optical signal source.

The apparatus further is connected to a control circuit, a first optical detector positioned to produce an electrical signal that represents the wavelength dependent intensity I ₁ is connected to the control circuit, electric representing the wavelength dependent intensity I ₂ And a second photodetector arranged to generate a signal.

The optical signal splitter may include an optical slope filter formed so as to output a transmission part having a wavelength dependent intensity I ₁ and a reflection part having a wavelength dependent intensity I ₂ .

Alternatively, the optical signal splitter may comprise a wavelength independent optical coupler adapted to split the control signal into a first part and a second part, and a first optical edge or bandpass filter. edge or band filter, the first part of the control signal is arranged so as to be incident thereto, is formed so as to transmit light signals I ₁ in the first wavelength band. Second optical edge or band filter, an optical signal I ₂ and the second portion as an incident in the second wavelength band of the control signal may be formed to transmit.

Alternatively, the optical signal splitter includes a first optical fiber to which the control signal is coupled, a first control part that continues to guide the control signal by the first optical fiber, and a second control part that is coupled outside the first optical fiber. And a first optical coupler installed so as to be separated. A second optical coupler is connected to the first optical fiber, the second optical fiber is arranged to receive the first control portion from the second optical coupler, a first fiber Bragg grating is formed in the second optical fiber, and the first wavelength band disposed of so as to form an optical signal I _1, the third optical fiber being disposed from the first optical coupler to receive a second control portion, the second fiber Bragg grating is formed within the third optical fiber and the second it may be installed to form an optical signal I ₂ in the wavelength band.

The optical signal splitter also includes a first optical fiber disposed so that the control signal is coupled, a first control part that continues to guide the control signal by the first optical fiber, and a second control part that is coupled outside the first optical fiber. and the installed optical coupler to separate the light of the second optical frequency to form a fiber optical signal I ₁ of the Bragg grating is a by in the first wavelength band through a first optical frequency, which is formed in the first optical fiber The optical signal I ₂ in the second wavelength band may be reflected back by the coupler and the second optical fiber connected to the optical coupler and installed to receive the optical signal I ₂ may be included.

  Hereinafter, some embodiments according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a spectrum diagram of a typical superluminescent diode (SLD) at two different temperatures. The solid line in FIG. 1 shows the relative intensity as a function of wavelength at a temperature of 17 ° C. The dashed line shows the relative intensity as a function of wavelength at a temperature of 24 ° C. From FIG. 1, it is easily found that a change of about 3 nm occurs in the wavelength of the maximum intensity when the temperature changes by 7 ° C.

  FIG. 2 shows an optical signal source wavelength stabilizing device 10 according to the first embodiment of the present invention. The optical signal source 12 supplies an optical signal to the first optical fiber 14. The optical fiber 14 guides the optical signal from the optical signal source 12 to the optical fiber coupler 16. The optical fiber coupler 16 outputs most of the signal source light to an optical fiber gyroscope (FOG) 18 mainly used in rotation detection application technology. Appropriate configurations of the fiber optic coupler 16 and the FOG 18 are well known in the art and need not be described in detail here.

  The optical fiber coupler 16 couples a part of the signal source light to the second optical fiber 20. The term “tap coupler” is sometimes used for this fiber optic coupler 16. The signal source light partially coupled from the first optical fiber 14 is also referred to as “tap light”. The second optical fiber 20 guides this tap light to the optical slope filter 22, and the optical slope filter 22 transmits the first part (indicated by the arrow 24) of the tap light and reflects the second part (indicated by the arrow 26). . The optical slope filter 22 is configured such that the ratio of the transmitted intensity to the reflected intensity is a function of the light wavelength of the tap light. The optical slope filter is configured such that a predetermined ratio value is set to select a desired wavelength for input to the FOG 18.

The first portion 24 which is transmitted tap light is incident on the first photodetector P _1, the second portion 26 that is reflected is incident on the second photodetector P _2. These photodetectors P ₁ and P ₂ generate electrical signals corresponding to the intensities of the transmitted tap light 24 and the reflected tap light 26, respectively. The first and second photodetectors P ₁ and P ₂ are connected to a control circuit 28, which is configured to generate an error signal indicating that the source wavelength has deviated from the selected wavelength. ing. The error signal is fed back to the optical signal source 12 to adjust the wavelength of the optical signal input to the first optical fiber 14 and the FOG 18.

The ratio of the transmitted tap light intensity to the reflected tap light intensity is set to a fixed set point representing that the signal source light has a selected wavelength. If there is any change in the signal source wavelength, the ratio calculated by the control circuit 28 changes. The difference between the actual ratio determined by the control circuit 28 and the set point is used for generation of the error signal, which is applied to the optical signal source to correct the wavelength change away from the selected value. Provide feedback. It should be noted here that since the ratio of the electrical signals generated by the _first and _second photodetectors P ₁ and P ₂ is used for determining the error signal, fluctuations in the intensity of the signal source signal are optical signals This is not detected by the source wavelength stabilization device 10. Such variations appear in both the transmitted first portion 24 and the reflected second portion 26 and separate from the ratio calculation.

FIG. 3 shows an optical signal source wavelength stabilizing device 30 according to a second embodiment of the present invention. FIG. 3 differs from FIG. 2 only in that the optical slope filter 22 is replaced by an optical coupler 32 and a pair of blue edge and red edge bandpass filters 38 and 42. The tap signal is input from the second optical fiber 20 to the optical coupler 32, where the tap signal is split into two substantially equal signals. It is desirable that the coupling characteristic of the optical coupler 32 is independent of the wavelength of the tap signal. The light remaining in the optical fiber 20 is input to the blue edge band filter 38. The optical coupler 32 couples half of the tap light to the optical fiber 41, and the optical fiber 41 guides the coupled tap light to the red edge band filter 42. The signals output from the blue edge band filter 38 and the red edge band filter 42 are respectively incident on the corresponding photodetectors P ₁ and P ₂ .

The photodetectors P ₁ and P ₂ send electrical signals to the control circuit 28 and indicate the intensity of the optical signals output from the blue edge and red edge bandpass filters 38 and 42. The intensity ratio of these optical signals is set to a fixed value for the selected wavelength output from the optical signal source 12. Deviations of the optical signal source wavelength from the selected wavelength change the intensity ratio. The change in intensity ratio is used to form an error signal that is used to adjust the wavelength of the optical signal source back to a selected value.

  FIG. 4A illustrates the intensity of the optical signal source signal at a selected temperature T as a function of wavelength. FIG. 4A also shows the band characteristics of the blue edge and red edge band filters 38 and 42. Both band-pass filters 38 and 42 are installed so that the intensity passing through them is equal. FIG. 4B is a characteristic diagram of signal intensity versus wavelength of the optical signal source at the temperature T + ΔT. The optical source signal is shifted to the right, which causes a difference in the signal transmitted through both bandpass filters 38 and 42.

  Since the signal source wavelength spectrum usually has a finite bandwidth of 30 to 60 nm, there is a term representing the position on the spectrum shape with respect to the wavelength center. The portion of the spectrum to the left of the wavelength center is called the blue edge component, and the portion of the spectrum to the right of the wavelength center is called the red edge component.

  Both the passband filter and the cut-off filter can be used as blue edge and red edge bandpass filters to affect wavelength transition monitoring in a broadband optical signal source. Shown in FIG. 4A are two passband filters, one applied to the blue edge (left side) of the spectrum, the other applied to the red edge (right side) of the spectrum, and FIG. Same filter in the spectrum.

  Alternatively, a cut-off filter can be used. The transfer function of this filter must have a sharp transition between transmission and non-transmission wavelengths. Shown in FIGS. 4C and 4D are cut-off filters applied to the non-transition signal source spectrum and the transition signal source spectrum, respectively. Functionally, it clearly shows that both passband and cut-off filter approaches result in wavelength stabilization.

FIG. 5 shows an optical signal source wavelength stabilization device 40 according to a third embodiment similar to the embodiments of the present invention shown in FIGS. The optical fiber 20 guides the tapped signal to the optical coupler 50, and the optical coupler 50 distributes the signal equally between the optical fiber 20 and the optical fiber 52. The optical fiber 52 guides a part of the tapped signal branched to the fiber Bragg grating (FBG) 54. The FBG 54 reflects the first selected wavelength band of the signal source spectrum in a direction to return to the optical coupler 50. A portion of the optical signal in the optical fiber 52 that has not been reflected is absorbed by the optical terminator 56 that is arranged to receive the light from the optical fiber 52. Some of the light reflected by the FBG54 is incident through the optical coupler 50 to a photodetector P _1.

Light passing through the optical coupler 50 in the optical fiber 20 propagates through the optical fiber 20 and reaches the optical coupler 58. The optical coupler 58 couples a part of the tapped signal to the optical fiber 60, and the optical fiber 60 is installed so as to guide the optical signal therein to the FBG 62. The FBG 62 reflects the second selected wavelength band of the signal source spectrum in a direction returning to the optical coupler 58. The light that has not been reflected by the FBG 62 is absorbed by the optical terminator 64 that is arranged to receive the optical signal from the optical fiber 60. A part of the tapped signal reflected by the FBG 62 passes through the optical coupler 58 and is guided to the photodetector P ₂ by the optical fiber 60.

Photodetectors P ₁ and P ₂ generates an electrical signal corresponding to the intensity of the first and second selection wavelength band. These electrical signals are processed by the control circuit 28 to generate an error signal that is used to adjust the source wavelength when needed, as described above.

FIG. 6 shows an optical signal source wavelength stabilizing device 70 according to a fourth embodiment using a single temperature-independent FBG 72. The optical fiber 20 guides the tapped signal to the optical coupler 74, and the optical coupler 74 outputs a transmission portion remaining in the optical fiber 20 and a coupling portion coupled to the optical fiber 76. An optical terminator 78 absorbs the binding moiety. The transmission part propagates in the optical fiber 20 to the FBG 72, and the FBG 72 reflects a part of the tapped signal in a direction to return to the optical coupler 74. The part of what optical coupler 74 is reflected by the tap signal coupled to an optical fiber 76, optical fiber 76 for guiding a portion of the reflected tap signal to the optical detector P _1. Some of the tap signals passing through the FBG72 without being reflected is incident on the photodetector P _2. Taking the ratio of the electrical signals generated by the photodetectors P1 and P2 provides information that can be used to generate an error signal that is fed back to the optical signal source 12 to correct for wavelength shifts.

  FIG. 7 is a schematic representation of an optical signal source wavelength stabilization device 80 according to a fifth embodiment using a single FBG 72 and an optical circulator 82. The form seen in FIG. 7 is similar to the optical signal source wavelength stabilization device 70 shown in FIG. The optical coupler 74 independent of the wavelength in FIG. 6 is replaced with a three-port optical circulator 82. The optical circulator 82 has ports 1 to 3. An optical fiber 20 is connected to the port 1 to provide an optical signal from the optical signal source 12 to the optical circulator 82. An optical fiber 84 is connected to port 2 and an optical fiber 86 is connected to port 3. The optical circulator 82 is configured as a three-port device that can be rotated to circulate its input and output. That is, the signal input to port 1 is output from optical circulator 82 at port 2, and the signal input to port 2 is output from port 3. Signals are not allowed to pass from port 1 to port 3 or from port 2 to port 1. This input / output relationship can be expressed as 1⇒2⇒3⇒1. The introduction of an optical circulator is advantageous over the use of a 3 dB coupler in that the loss of light loss is reduced when the optical circulator 82 is used. A typical optical circulator has a loss port to port of about 0.75 dB, while a 3 dB coupler has a loss input to output of 3 dB. In the form shown in FIGS. 6 and 7, the optical loss generated for the power observed by the photodetector P1 is 6 dB and 1.5 dB, respectively.

Thus, the signal input to port 1 of the optical circulator 82 is output from the circulator to the optical fiber 84 at the port 2, and the optical fiber 84 guides this signal to the FBG 88. The first part of the signal input to the FBG 88 is reflected and propagates in the optical fiber 84 to reach the port 2 of the optical circulator 82. The first portion of this signal is then output from optical circulator 82 to optical fiber 86 at port 3. Reflected portion of the signal is detected by the photodetector P _1.

The second portion of the incident signal to FBG88 are transmitted through the optical fiber 84 to the photodetector P _2. The electrical signals generated by photodetectors P ₁ and P ₂ are processed as described above with respect to FIG. 6 to generate an error signal that is used to adjust the wavelength output from optical signal source 12.

FIG. 4 is a diagram illustrating wavelength shift as a function of temperature for a typical optical signal source used in FOG application technology. 1 schematically shows a first embodiment of an optical signal source wavelength stabilization device according to the present invention; 1 schematically shows an embodiment of the present invention using an edge filter for optical signal source stabilization control. The effect of the optical signal source spectral edge filter is shown in a graph. The shifted optical signal source spectrum and the effect of the edge filter are shown in a graph. A spectrum of an optical signal source is shown, and a blue edge filter and a red edge filter are shown. The spectrum of the optical signal source after the frequency transition caused by the temperature change is shown, and the blue edge filter and the red edge filter are shown. 1 schematically illustrates one embodiment of the present invention including a pair of temperature independent fiber Bragg gratings. 1 schematically illustrates one embodiment of the present invention that provides stabilization of an optical signal source using a single fiber Bragg grating. 7 shows an embodiment of the invention similar to that shown in FIG. 6 including an optical circulator instead of an optical coupler.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical signal source wavelength stabilization apparatus 12 Optical signal source 14 1st optical fiber 16 Optical fiber coupler 18 Optical fiber gyroscope (FOG)
DESCRIPTION OF SYMBOLS 20 2nd optical fiber 22 Optical slope filter 24 Transmission 1st part 26 Reflection 2nd part P1, P2 Photodetector 28 Control circuit 30 Optical signal source wavelength stabilization apparatus 32 Optical coupler 38 Blue edge band filter 41 Optical fiber 42 Red edge band filter 40 Optical Signal Source Wavelength Stabilizer 50 Optical Coupler 52 Optical Fiber 54 Fiber Bragg Grating (FBG)
56 optical terminator 58 optical coupler 60 optical fiber 62 FBG
64 Optical Terminator 70 Optical Signal Source Wavelength Stabilizer 72 Heat Impermeable FBG
74 Optical Coupler 76 Optical Fiber 78 Optical Terminator 80 Optical Signal Source Wavelength Stabilizer 82 Optical Circulator 84,86 Optical Fiber 88 FBG

Claims (8)

An optical fiber (14) arranged to receive an optical signal from an optical signal source (12);
An optical tap (16) arranged to couple the control signal from the optical signal guided by the optical fiber (14);
An optical signal splitter (22) installed to split the control signal into a first part having a wavelength dependent intensity I ₁ and a second part having a wavelength dependent intensity I ₂ ;
A control installed to calculate the ratio R = I ₁ / I ₂ and to send an error signal to the optical signal source (12) if the wavelength shift in the optical signal source deviates the ratio R from a predetermined set point. A wavelength stabilization device for an optical signal output from the optical signal source (12), comprising a circuit (28). A first photodetector (P ₁ ) installed to generate an electrical signal connected to the control circuit (28) and exhibiting the wavelength dependent intensity I ₁ , and a wavelength dependency connected to the control circuit (28). The optical signal source wavelength stabilization device of claim 1, further comprising a _second photodetector (P ₂ ) installed to generate an electrical signal indicative of intensity I ₂ . Optical signal splitter (22) is formed as an optical slope filter formed so as to output a reflection portion having a delivery portion and a wavelength dependent intensity I ₂ having a wavelength dependent intensity I _1, claim 2 optical signal Source wavelength stabilizer. The optical signal splitter (22)
A wavelength independent optical coupler (32) installed to split the control signal into a first part and a second part;
Positioned to receive the incident first part of the control signal, a first optical edge filter formed so as to transmit the light signal I ₁ in the first wavelength band (38),
Positioned to receive the incident second portion of the control signals, including the second and optical edge filter (42) which is formed to transmit an optical signal I ₂ in the second wavelength band, according to claim 2 light Signal source wavelength stabilizer. The optical signal splitter (22)
A wavelength independent optical coupler (32) arranged to divide the control signal into a first part and a second part;
Positioned to receive the incident first part of the control signal, a first optical edge filter formed so as to transmit the light signal I ₁ in the first wavelength band (38),
Control signal second portion disposed in to receive incident, including second and optical edge filter (42) which is formed to transmit an optical signal I ₂ in the second wavelength band, the light of claim 1 Signal source wavelength stabilizer. The optical signal splitter (22)
A first optical fiber (20) arranged such that a control signal is coupled;
A first optical coupler (50) installed to split the control signal into a first control part that continues to be guided by the first optical fiber (20) and a second control part that is coupled out of the first optical fiber (20). )When,
A second optical coupler (58) connected to the first optical fiber (20);
A second optical fiber (60) arranged to receive a first control portion from a second optical coupler (58);
First with the fiber Bragg grating (62) disposed so as to form an optical signal I ₁ in the first wavelength band is formed on the second optical fiber (60),
A third optical fiber (52) installed to receive a second control portion from the first optical coupler (50);
Third and a fiber the installed second fiber Bragg grating as formed in (52) to form an optical signal I ₂ in the second wavelength band (54), an optical signal source wavelength stability of claim 1 Device. The optical signal splitter (22)
A first optical fiber (20) arranged such that a control signal is coupled;
An optical coupler (74) installed to split the control signal into a first control portion that continues to be guided by the first optical fiber (20) and a second control portion that is coupled out of the first optical fiber (20);
Is formed on the first optical fiber (20), a second optical frequency while being formed so as to form an optical signal I ₁ in the first wavelength band to transmit a first optical frequency to an optical coupler (74) fiber Bragg grating formed so as to form an optical signal I ₂ in the second wavelength band is reflected and (72),
Including a second and an optical fiber (76) placed therefrom connected to the optical coupler (74) to receive light signals I _2, optical signal source wavelength stabilization apparatus according to claim 1. The optical signal splitter (22)
A first optical fiber (20) arranged such that a control signal is coupled;
A wavelength independent optical circulator (82) installed to divide the control signal into a first control part which continues to be guided by the first optical fiber (20) and a second control part which is coupled outside the first optical fiber (20); ,
Is formed on the first optical fiber (20), a second optical frequency while being formed so as to form an optical signal I ₁ in the first wavelength band to transmit a first optical frequency to an optical circulator (82) fiber Bragg grating formed so as to form an optical signal I ₂ in the second wavelength band is reflected and (88),
Including a second and an optical fiber (86) placed therefrom connected to the optical circulator (82) to receive light signals I _2, optical signal source wavelength stabilization apparatus according to claim 1.

Images