JP2001108445A - Semiconductor laser, gyro and operation method of gyro - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gyro and its operation method capable of lowering a coupling loss generated when laser light is introduced into a light detector and a noise caused by returning light to a laser from external reflection points. SOLUTION: The gyro has a ring resonance type semiconductor laser where lights circumferentially transmit mutually rcverely to each other, puts in the middle an active layer constituting the semiconductor laser, makes angle αbetween the side surface of a low refractive index layer with lower refractive index than that of the active layer and the active layer surface, satisfys 75 deg.<=α<=105 deg. and detects beat signal generated in the semiconductor laser.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gyro and a method for operating the gyro. More specifically, the present invention relates to a gyro configured using a ring resonator type laser.

[0002]

2. Description of the Related Art Conventionally, as a gyro used for detecting an angular velocity of a moving object, a mechanical gyro having a rotor and a vibrator and an optical gyro are known. In particular, the optical gyro is capable of instantaneous activation and has a wide dynamic range, and is thus innovating in the gyro technical field. The optical gyro includes a ring resonator type laser gyro, an optical fiber gyro, and a passive type ring resonator type gyro. Of these, the first to be developed is a ring resonator type laser gyro using a gas laser, which has already been put to practical use in aircraft applications and the like. Recently, a small and high-precision ring resonator type laser gyro has also been proposed.
-288556.

[0003]

However, the conventional ring resonator type laser gyro emits clockwise laser light and counterclockwise laser light from the laser to the outside of the laser once, and detects both laser lights. And received electrical beats as signals. For this reason, coupling loss has been present when the laser light is incident on the photodetector. In addition, since noise is generated by light returning to the laser from a reflection point outside the laser, it is necessary to use an optical isolator to avoid the noise.

Further, a clockwise laser beam and a counterclockwise laser beam propagating in a circular shape are present inside a semiconductor laser, and the angular velocity of an object is determined by using a beat generated by interference between the laser beams. A technique for achieving this is disclosed in Japanese Patent Application Laid-Open No. 4-174317.

[0005] The laser element described in this publication will be described with reference to FIGS. 34 and 35. FIG.
It is the figure which looked at the element from the upper surface, and FIG. 35 is sectional drawing in AA '.

10 is an InP substrate, 11, 12A, 12
B and 12C are ridge-type optical waveguides, and each corner is provided with a corner mirror for total reflection.

Reference numeral 14 denotes a voltage detection terminal, and 15 denotes a bias current supply terminal.

The total reflection corner mirrors 13A, 13B,
13C and 13D are formed by hollowing out as shown in FIG. 35 by an etching technique.

However, according to the method disclosed in the publication,
Unfavorable in terms of yield when manufacturing industrially,
Further, an element capable of oscillating with lower driving power has been demanded.

The present invention has been made in view of the above points, and the present invention will be described below.

[0011]

SUMMARY OF THE INVENTION A first object of the present invention is to:
It is an object of the present invention to provide a gyro having a semiconductor laser that can be driven at a low current or a low voltage and a method of operating the gyro.

A second object of the present invention is to provide a gyro having no problems such as coupling loss and return light noise, or a greatly reduced gyro, and an operation method thereof.

Still another object of the present invention is to provide a gyro having a compact size and a method of operating the gyro.

A gyro according to a first aspect of the present invention has a ring resonator type semiconductor laser in which light propagates in a counter-rotating circular shape, and has an active layer constituting the semiconductor laser interposed therebetween. An angle α between the side surface of the low refractive index layer having a low refractive index and the active layer surface satisfies 75 ° ≦ α ≦ 105 ° over the entire circumference of the low refractive index layer.

In particular, according to the present invention, the ring resonator type semiconductor laser detects a beat signal generated by rotation as a current flowing through the semiconductor laser, a voltage applied to the semiconductor laser, or a change in impedance of the semiconductor laser. .

Further, the present invention is characterized in that the surface precision of the side surface of the low refractive index layer is equal to or less than half the wavelength in the medium of the active layer.

According to a second method of operating a gyro according to the present invention, an active layer constituting a ring resonator type semiconductor laser is sandwiched between a low refractive index layer side surface having a lower refractive index than the active layer and the active layer surface. The angle α to be formed satisfies 75 ° ≦ α ≦ 105 ° over the entire circumference of the low refractive index layer, and as a signal for determining the magnitude of the angular velocity applied to the ring resonator type semiconductor laser, current, voltage or impedance It is characterized by using change.

Further, the present invention is characterized in that a voltage or a current for driving the ring resonator type semiconductor laser is modulated at a frequency different from the frequency band of the signal.

Further, the present invention is characterized in that the ring resonator type semiconductor laser is rotated clockwise or counterclockwise using a piezoelectric element.

Further, in the semiconductor laser according to the present invention, the angle α between the side surface of the low refractive index layer having a lower refractive index than the active layer and the surface of the active layer sandwiching the active layer is determined by the entire circumference of the low refractive index layer. Over a range of 75 ° ≦ α ≦ 105 °.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a method for detecting an angular velocity using a semiconductor laser according to the present invention will be described with reference to FIG.

In FIG. 1, reference numeral 100 denotes a semiconductor laser;
Denotes an active layer, 102 denotes a substrate, 103 denotes an anode, a line drawn from the anode, and 104 denotes a cathode. 10
5 is an electric terminal. Note that the active layer 101 is sandwiched between cladding layers. A laser beam guided in a ring shape is selectively amplified by injecting current from the anode 103, and laser oscillation occurs when the laser beam exceeds a threshold.

In the ring resonator type laser having the above configuration, light propagates in a circular manner, and there are clockwise laser light and counterclockwise laser light. If the laser is stationary, the oscillation frequency of each laser beam is equal. However, when the laser is rotated, a difference occurs between the oscillation frequencies of the clockwise laser light and the counterclockwise laser light, and the difference Δf is given by the following equation.

Δf = (4S / λL) Ω (1)

Here, S is a closed area surrounded by the optical path, λ is the oscillation wavelength of the laser light, L is the optical path length, and Ω is the angular velocity of rotation. For example, in the case of a laser such as a gas laser or a semiconductor laser that causes a current to flow, there is a one-to-one correspondence between population inversion and laser impedance. If light interferes in the laser, the population inversion changes accordingly, and as a result, the impedance between the electrodes of the laser changes.

This state of change appears as a change in current flowing through the laser when a constant voltage source is used as a drive power source, and as a change in terminal voltage when a constant current source is used. In this case, the state of light interference can be extracted as a signal. More specifically,
A beat signal is detected as a change in the frequency of the current or the voltage.

When a constant voltage source is used, a battery (battery) can be used.
Weight reduction becomes possible.

Of course, it is also possible to directly measure the change in impedance with an impedance meter. In this case, unlike the case where the terminal voltage or the current flowing through the element is measured, the influence of the noise of the driving power supply is reduced.

If it is necessary to prevent surge noise or the like from entering the semiconductor laser from the detection terminal for detecting a change in the terminal voltage of the semiconductor laser, the circuit between the voltage change measurement circuit and the detection terminal is required. It is preferable to provide a protection circuit in the device. As a result, deterioration and destruction of the semiconductor laser due to surge noise or the like can be prevented.

As in the present invention, a ring resonator type laser detects a change in current, voltage or impedance caused by a beat caused by interference of laser beams traveling in opposite directions inside the ring resonator type laser. By providing the terminal, a beat signal corresponding to the rotation can be extracted from the terminal. Therefore, it is possible to obtain a gyro that can omit a photodetector and an optical system for optical coupling, which are essential in the conventional optical gyro.

Hereinafter, the present invention will be described more specifically.

In FIG. 1, low refractive index layers 106 and 107 sandwich the active layer 101 and have lower refractive indexes than the active layer.

For example, InGaAsP having a composition of 1.55 μm is formed as an active layer, and InGaAsP having a composition of 1.3 μm is formed thereon.
Consider a case where an aAsP light guide layer and an InP clad layer are further formed so as to sandwich them.

Since a semiconductor and air have different refractive indexes, reflection occurs at the interface. Assuming that the refractive index of the semiconductor is 3.5,
When the angle between the normal to the interface and the laser beam is 16.6 degrees or more, total reflection occurs. In the mode that receives total reflection, the oscillation threshold value can be reduced by the amount corresponding to the absence of the mirror loss as compared with the other modes, so that oscillation starts at a low injection current level. Moreover, since the gain is concentrated in this oscillation mode, oscillation in other modes is suppressed.

Most of the laser light generated in the active layer 101 seeps into a low-refractive-index layer having a lower refractive index than the active layer, such as a light guide layer and a clad layer, so that light is confined in the active layer. The percentage is small.

For example, InGaAs having a composition of 1.55 μm
When the P active layer is sandwiched between the InGaAsP light guide layer and the IuP clad layer having a composition of 1.3 μm, the ratio of confining the active layer to the light guide layer by laser light is 10%.
It is as follows.

Therefore, in order to prevent loss of light and enable lower current or lower voltage driving, the above-described low refractive index layer 1 is used.
It is necessary to reduce the loss of light at 06 and 107.

Specifically, the angles α ₁ and α ₂ (FIG. 2) formed by the side surface of the low refractive index layer sandwiching the active layer 101 and the active layer surface are 75 ° ≦ α ₁ and α ₂ ≦ 105 °. , 80 ° ≦ α ₁ , α ₂ ≦ 100 °, more preferably 85 ° ≦ α ₁ , α ₂ ≦ 95 °.

By satisfying such a condition, the side surface of the low refractive index layer becomes substantially a total reflection surface and the low refractive index layer 10
Since the loss of light (evanescent light) leaking to 6, 107 can be prevented, the semiconductor laser can be driven with lower current (or lower voltage). In particular, when the thickness of the active layer 101 is about the wavelength of a laser beam, it is necessary to satisfy the above-described conditions α ₁ and α ₂ . That is, in the case of the InP system or the GaAs system, when the active layer thickness is 2 μm or less, the above conditions of α _1,2 are required.

Of course, it is also preferable that the side surface of the semiconductor laser is a total reflection surface. It is preferable that the angle formed by 90% or more of the light exuding region on the total reflection surface with the active layer surface is within the above range.

In particular, it is preferable that the side surface over the entire circumference of the low refractive index layer satisfies the above-mentioned conditions of α ₁ and α ₂ .

In order to prevent light loss due to surface roughness, the surface accuracy of the side surface of the low refractive index layer sandwiching the active layer 101 is determined by the wavelength in the medium in the active layer (wavelength in vacuum / equivalent refractive index of the medium). It is preferably 1/2 or less, more preferably 1/3 or less. Specifically, in the case of an InP system (wavelength: 1.55 μm, equivalent refractive index of the medium: 3.6), the thickness is about 0.22 μm or less, preferably 0.14 μm or less.

In the case of a GaAs system (wavelength: 0.85 μm, equivalent refractive index of the medium: 3.6), it is about 0.12 μm or less, preferably 0.08 μm or less.

The "surface accuracy" indicates the flatness of the side surface of the layer, that is, the height within the surface. This surface accuracy can be considered as a deviation from a perfect circle when the semiconductor laser is circular. Of course, it is desirable that not only the side surface of the low refractive index layer but also the side surface of the active layer be in the above range.

Further, the gyro according to the present invention is characterized in that no reflector is provided within the exudation distance range of the evanescent light generated from the ring resonator type laser.

In the above configuration, if a reflector exists within the exudation distance of the evanescent light, the reflector and the laser are optically coupled to each other, causing not only a loss from the viewpoint of the laser but also a loss from the reflector to the laser. Return light exists and becomes a noise source.

On the contrary, if the reflector does not exist within the exudation distance of the evanescent light of the laser as in the present invention, the laser becomes optically independent of the other reflectors and is affected by the external influence of the laser. In addition to eliminating loss, there is no return optical noise, so that loss due to coupling and return optical noise can be significantly improved.

In the gyro operating method according to the present invention, in the gyro having the above-described configuration, the change in the current, voltage or impedance detected from the terminal is determined by the magnitude of the angular velocity applied to the ring resonant laser. Is used as a signal for determining More specifically, a frequency change such as a current or a voltage is detected. According to this configuration, the conventional optical gyro does not require a photodetector and an optical system for optical coupling, which were essential, and thus can solve the problems of coupling loss and return optical noise caused by these components. , Gyro operation method can be provided.

In the above operation method, it is also preferable that the voltage or current for driving the ring resonator type laser is modulated at a frequency different from the frequency band of the signal due to a change in terminal voltage, current, impedance or the like caused by the beat. It is.

In the gyro having the above configuration,
When the gyro is rotated, a difference appears in the oscillation frequency between the clockwise laser light and the counterclockwise laser light, and the difference Δf is given by Expression (1). When the difference Δf in the oscillation frequencies is small, Due to the non-linearity of the laser medium, the oscillation frequency is pulled in, so that a phenomenon called lock-in, in which Δf = 0, may occur.

However, as shown in the above configuration, the lock-in phenomenon can be avoided if the difference Δf between the oscillation frequencies is always fluctuated.

Conventionally, a method of applying dither (small vibration) has been used as a method of avoiding the lock-in phenomenon, which corresponds to the modulation of the angular velocity Ω in equation (1).

For example, in a semiconductor laser, it is known that the oscillation wavelength varies depending on the magnitude of the current. This is because the refractive index of the semiconductor changes according to the current.

Therefore, by modulating the current of the semiconductor laser, λ of the equation (1) can be modulated.
As a result, a state in which Δf always fluctuates can be created.

Further, by modulating the signal at a frequency in a band different from the signal frequency, lock-in can be avoided without adversely affecting the signal.

Of course, even if the voltage is modulated via the series resistor, the current flowing through the semiconductor laser is modulated,
The same effect is obtained.

Further, even in the case of a gas laser, by modulating the current or the voltage, the Q value of the resonator fluctuates, so that the oscillation wavelength is modulated. This is because the oscillation wavelength of the gas laser is determined by the Q value of the resonance transition of atoms, molecules, or ions and the Q value of the resonator, and this phenomenon is known as drawing of the oscillation wavelength.

Further, in the above operating method, vibration is applied to a gyro provided with the ring-resonant laser at a frequency different from the frequency band of the signal, and a signal is detected from the terminal in synchronization with the vibration, thereby obtaining a vibration. And the magnitude of the terminal voltage can be correlated. For example, when a vibration is applied in the clockwise rotation direction, the terminal voltage increases when the gyro receives clockwise rotation, and conversely, decreases when the gyro receives counterclockwise rotation. Therefore, it is possible to identify whether the gyro is rotating clockwise or counterclockwise. Moreover, by modulating the signal at a frequency in a band different from the signal frequency, the direction of rotation can be detected without adversely affecting the signal.

Hereinafter, the configuration and operation of the gyro according to the present invention and its operating method will be described with reference to the drawings.

(First Embodiment) FIG. 3 is a schematic perspective view showing another example of a gyro provided with a ring resonator type laser in which light propagates in a circular shape according to the present invention.
The case where a quadrangular prism-shaped semiconductor laser is used as the laser is shown. In FIG. 3, reference numeral 305 denotes an electric terminal, 303 denotes an anode, 304 denotes a cathode, 300 denotes a semiconductor laser having a rectangular column shape, 301 denotes an active layer constituting the semiconductor laser,
Reference numeral 02 denotes a substrate on which a semiconductor laser is mounted. And
306 and 307 are low refractive index layers having a lower refractive index than the active layer 301.

Then, the side surface 3 of the low refractive index layer sandwiching the active layer
06 and the layer surface of active layer 301 are at least 75 ° and 10
The element is formed so as to have an angle of 5 ° or less.

Specifically, after depositing each layer constituting the semiconductor laser, not only the portion which becomes the total reflection corner mirror is removed by etching as in the above-mentioned prior art, but the entire side surface of the laser is removed ( The element is formed by, for example, etching.

That is, each layer is formed as shown in FIG. 4 and the entire side surface is etched to produce a square-pillar laser as shown in FIG. FIG. 6 is a view of the same as viewed from above. As an etching method, wet etching, gas etching, plasma etching, sputter etching, reactive ion etching (RIE), and reactive ion beam etching (RIBE) can be used. Of course, a corner portion may be provided as shown in FIG. By removing the entire side surface of the low refractive index layer sandwiching the active layer as in the present invention, the manufacturing process can be simplified.

By satisfying the above-mentioned angle condition, light loss can be prevented and the laser can be oscillated with low driving power. That is, the total reflection surface is substantially formed on the entire peripheral side surface of the low refractive index layer. By driving the semiconductor laser 300 at a constant current and detecting a voltage change applied to the element from the electric terminal 305, a gyro capable of detecting the rotation of an object can be formed.

Of course, constant voltage driving may be used to detect a change in current flowing through the semiconductor laser, or a change in impedance of the semiconductor laser itself.

Further, by providing a protection circuit at the detection terminal of the semiconductor laser, deterioration or destruction of the semiconductor laser can be prevented. FIG. 8 shows an example in which a voltage follower 5005 is connected as a protection circuit. 5000 is
A semiconductor laser, 5002 indicates a current source, 5001 indicates an electric resistance, and 5006 indicates a voltage detection circuit.

When a constant voltage source is used as the power supply, the angular velocity of rotation can be measured as a change in the current flowing through the semiconductor laser. As shown in FIGS. 9 and 10, when the battery 5003 is used as the constant voltage source, the driving system can be reduced in size and weight.

In FIG. 9, the electric resistance is connected in series with the semiconductor laser, and the current flowing through the semiconductor laser is measured as a change in the voltage across the electric resistance. 5007 is a voltmeter. On the other hand, in FIG. 10, an ammeter 5008 is connected in series with the semiconductor laser, and the current flowing through the semiconductor laser is measured directly.

Further, regardless of the type of the constant current, the impedance change of the semiconductor laser can be directly measured by the impedance meter 5009. 5004 is a power supply. In this case, unlike the case where the terminal voltage or the current flowing through the element is measured, the influence of the noise of the driving power supply is reduced. This example is shown in FIG.

Another circuit configuration for detecting a beat signal will be described.

As shown in FIG. 12, an anode of a ring resonator type gas laser 5000 is connected to an operational amplifier 5 for a buffer.
005. Since the signal output from the amplifier 5005 has a frequency corresponding to the angular velocity, the signal is converted into a voltage by a known frequency-voltage conversion circuit (FV conversion circuit) to detect rotation. I do. 5004
Is a constant current source.

Of course, if desired characteristics can be obtained, the operational amplifier 5005 “voltage follower” can be omitted.

FIG. 13 shows an example of a circuit diagram in which the laser is driven at a constant current, a change in the anode potential of the laser 5000 is read, and the rotation is detected.

The anode of the laser 5000 is connected to the output terminal of the operational amplifier 5015 via the protection resistor 5001, and the cathode of the laser 5000 is connected to the operational amplifier 5
015 inverting input terminal.

The resistor 5011 is connected to the operational amplifier 501.
5 between the inverting input terminal and the reference potential.

Here, when a constant potential (Vin) is applied to the non-inverting input terminal of the operational amplifier 5015 from a microcomputer or the like, a constant current drive configuration in which the potential and the current determined by the resistor 5011 flow through the laser 5000 is adopted. The anode of the laser 5000 is connected to the operational amplifier 5005.

The operational amplifier 5005 outputs a signal Vout. Since this signal has a beat frequency proportional to the angular velocity, the signal is converted into a voltage by a known frequency-voltage conversion circuit (FV conversion circuit) or the like, and rotation is detected.

FIG. 14 shows a ring resonator type laser 500.
1 shows an example of a circuit configuration in which 0 is driven at a constant voltage and a beat signal accompanying rotation is detected.

FIG. 14 shows a ring resonator type laser 500.
0 is driven at a constant voltage and the current flowing through the laser is
FIG. 9 shows an example of a circuit diagram which reads as a voltage drop of 001 and detects rotation.

The anode of the laser 5000 has a resistance of 50
01 is connected to the output terminal of the operational amplifier 5015, and the cathode of the laser 5000 is grounded to the reference potential.

When a constant potential (Vin) is applied to the inverting input terminal of the operational amplifier 5015 from a microcomputer or the like, a constant voltage drive configuration in which the potential is always applied to the resistor 5001 and the laser 5000 is adopted.

The electric resistance 5001 is connected to an operational amplifier 5005 for a buffer. The operational amplifier 5005 is
The signal Vout is output. Since this signal has a beat frequency proportional to the angular velocity, the signal is converted into a voltage by a known frequency-voltage conversion circuit (FV conversion circuit) or the like, and rotation is detected. Of course, the rotation detection may be performed by directly inputting the signal of the electric resistance and the equipotential portion to the FV conversion circuit.

Next, FIG. 15 shows a case where the reference of the signal potential is taken to ground by using the subtraction circuit 5025 in addition to the constant voltage drive configuration as in FIG.

A constant potential V ₁ is applied to the inverting input terminal of the operational amplifier 5015 from a microcomputer or the like. 5000 is a ring resonator type laser, 5005 is a voltage follower, 50
01 and 5026 to 5029 are electric resistances;
6 and 5027 and 5028 and 5029 have the same resistance.

The potentials V ₁ and V ₂ at both ends of the electric resistor 5001 are connected to the inverting input terminal and the non-inverting input terminal of the amplifier 5030 through a voltage follower and resistors 5026 and 5028. By doing so, the voltage V ₂ −
A change in V ₁ (= V ₀ ) can be detected. That is, a change in current flowing through the ring resonator type laser 5000 can be detected.

The rotation of the obtained signal is detected through an FV conversion circuit or the like. Of course, a so-called frequency counter circuit or the like can be used.

FIG. 16 shows a frequency-voltage conversion circuit (F
V conversion circuit), but the present invention is not limited to this. This circuit is composed of a transistor, a diode, a capacitor, and a resistor, and the output voltage V _C2 is represented by Expression (2).

[0088]

[Outside 1] Here, E _i is the peak-to-peak value of the input voltage, and f is the beat frequency. C ₂ >> C ₁ , R ₀ C ₂ f <
By designing the circuit parameters to be 1, V _C2 = E _i C ₁ R ₀ f (3) as shown in equation (3), and a voltage output proportional to the beat frequency is obtained. Becomes possible.

When total reflection occurs, there is evanescent light traveling along the interface. When the oscillation wavelength is 1.55 μm, the exudation distance of the evanescent light is 0.074 μm. The intensity of the evanescent light attenuates exponentially.
If it is 10 μm away from a reflector that can be considered with a margin, the effect of the return light can be neglected. That is, the above-described configuration example is an example in the case where the reflector does not exist within 10 μm from the interface of the quadrangular prism of the semiconductor laser 300 in FIG. 3, and is not affected by the return light noise.

It is also preferable to modulate the injection current at a frequency in a band different from the frequency of the beat signal. In this case, it is possible to prevent the signal from being adversely affected.

For example, by modulating the injection current with an amplitude of 0.1 mA and a frequency of 2 kHz, an optical gyro that does not cause a lock-in phenomenon even at the time of rotation according to a frequency as small as a beat frequency of less than 1 Hz. Can also be configured.

The active layer material applicable to this embodiment is GaAs, InP, ZnSe, AlGaAs.
s, InGaAsP, InGaAlP, InGaAs
P, GaAsP, InGaAsSb, AlGaAsS
b, InAsSbP, PbSnTe, GaN, GaAl
N, InGaN, InAlGaN, GaInP, GaI
nAs, SiGe, and the like.

As the cladding layer, those applicable to the above-mentioned active layer can be used. As a specific combination of the active layer and the cladding layer, for example, PbSnTe
(Active layer) / PbSeTe (cladding layer), PbSnS
eTe (active layer) / PbSeTe (cladding layer), Pb
EuSeTe (active layer) / PbEuSeTe, PbEu
SeTe (active layer) / PbTe (cladding layer), InG
aAsSb (active layer) / GaSb (cladding layer), Al
InAsSb (active layer) / GaSb (cladding layer), I
nGaAsP (active layer) / InP (cladding layer), Al
GaAs (active layer) / AlGaAs (cladding layer), A
1GaInP (active layer) / AlGaInP (active layer) can be used.

Further, the configuration of the semiconductor laser is not limited to the bulk type, and the active group may be a single quantum well structure (SQ
W) and a multiple quantum well structure (MQW). When using a quantum well laser,
It is also preferable to adopt a strained quantum well structure. For example, an active layer is formed by eight InGaAsP quantum wells having a compressive strain of about 1% and a barrier layer of InGaAsP. Of course, an MIS structure can also be used.

The substrate may be any substrate on which a desired material can be grown, and may be a GaAs substrate, an InP substrate, a GaSb substrate, an InAs substrate, a PbTe substrate, a Ga
A compound semiconductor such as an N substrate, a ZnSe substrate, or a ZnS substrate, a SiC substrate, a 4H-SiC substrate, a 6H-SiC substrate, a sapphire substrate, a silicon substrate, an SOI substrate, or the like can be used.

For forming an active layer and the like of a semiconductor laser, liquid phase epitaxy (LPE method), molecular beam epitaxy (MBE)
Method), metal organic chemical vapor deposition (MOCVD, MOVPE)
Method), atomic layer growth method (ALE method), metalorganic molecular beam epitaxy (MOMBE), chemical beam epitaxy (CB)
E) can be used.

As the anode electrode, Cr / Au, Ti
/ Pt / Au, AuZn / Ti / Pt / Au or the like can be used. AuGe / Ni as the cathode electrode
/ Au and AuSn / Mo / Au can be used. Of course, it is not limited to these. Further, the arrangement of the electrodes can be appropriately reversed from that shown in the drawings according to the conductivity of the substrate, the active layer, and the like. The same applies to other embodiments. It is also preferable to form a cap layer (contact layer) for reducing contact resistance with an electrode on the clad layer, and then form the above-mentioned electrode material on the cap layer. For example, I
nGaAsP (active layer) / P-type InP (cladding layer) /
This is a configuration of P-type InGaAsP (cap layer) / electrode.

Although the cathode electrode is shown below the substrate in the drawings, the arrangement of the anode and the cathode may be reversed depending on the type of the substrate.

It is also preferable to mount a semiconductor laser chip on a heat radiating material (heat sink) in order to prevent the semiconductor laser from affecting the heat. As a heat sink material, Cu, Si, SiC,
AlN, diamond, or the like can be used. Of course, it is not limited to these. Further, if necessary, a Peltier element can be used for temperature control.

An insulating film (coating film) is formed on the side surface (in a region where light exists) of the semiconductor laser so as to ensure that the semiconductor laser becomes a total reflection surface or to prevent deterioration. Is also preferred.
As the coating material, SiO ₂ , SiN, A
An insulating film such as l ₂ O ₃ or Si ₃ N ₄ or amorphous silicon (α-Si) can be used.

(Second Embodiment) FIG. 17 is a schematic perspective view showing another example of a gyro provided with a link resonator type laser in which light propagates in a circular shape according to the present invention. The difference from the first embodiment (FIG. 3) is that the semiconductor laser used as the laser has a cylindrical shape. The other points were the same as in the first embodiment. Note that 301 is an active layer, and 306 and 307 are low refractive index layers sandwiching the active layer 301. Also in the present embodiment, the angles α ₁ and α ₂ between the layer surface of the active layer 301 and the low refractive index layer are 75 ° ≦ α ₁ and α ₂
When ≦ 105 °, low-current driving becomes possible.

FIG. 18 shows the FE-S of the semiconductor laser when a beat signal is obtained at a drive current of 0.5 mA.
It is sectional drawing by EM.

In FIG. 18, reference numeral 401 denotes an active layer (1.5
InGaAsP having a composition of 5 μm), 422 and 423 are optical guide layers (InGaAsP having a composition of 1.3 μm), 40
6,407 is a cladding layer (InP).

When the angle between the active layer surface and the cladding layers 406 and 407 was measured, α ₁ = 80 ° and α ₂ = 103 °.
Met.

The side surface of the semiconductor laser is formed by RI
Performed using BE. Specifically, the material system is InP or InGaAsP grown on an InP substrate.

The substrate temperature was set to 200 ° C., and chlorine gas was used as an etching gas. The pressure of chlorine gas is 2 × 10
^-4 Torr, microwave power was 120 W, and chlorine ion extraction voltage was 500 V.

Under these conditions, the etching rate is 1.2 μm / min. Met.

Further, the relationship between the surface accuracy of the low refractive index layer and the driving current was examined. As shown in FIG. 19, when the relationship was very close to a perfect circle (in FIG. 19, the maximum value of the error compared to the perfect circle was shown). Is 0.14 μm), a beat signal was obtained with a drive current of 4 mA, but the maximum value of the error compared to a perfect circle was 0.4 μm (greater than one third of the wavelength in the medium) as shown in FIG. At that time, no beat signal was obtained.

The element diameter is 13.4 μm in both cases. The wavelength in the medium is a value obtained by dividing the oscillation wavelength of the semiconductor laser in a vacuum by the equivalent refractive index of the medium (for example, in the case of InGaAsP, the oscillation wavelength is 1.55 μm).
m, the equivalent refractive index of the medium is 3.6, so that the wavelength in the medium is about 0.43 μm).

The active layer is made of GaAs or AlGa.
In the case of As, since the oscillation wavelength is 0.85 μm and the equivalent refractive index of the medium is 3.6, the wavelength in the medium is about 0.24 μm.

(Third Embodiment) FIG. 21 is a schematic perspective view showing another example of a gyro provided with a ring resonator type laser in which light propagates in a circular shape according to the present invention. The difference from the first embodiment is that the semiconductor laser used as the laser is triangular prism instead of square prism. The other points are the same as in the first embodiment.

In FIG. 21, reference numeral 300 denotes a semiconductor laser;
1 is an active layer, 302 is a substrate, 303 is an anode, 305
Is an electric terminal, and the active layer 301 is a low refractive index layer 306;
307.

Also in this embodiment, the angles α ₁ and α ₂ between the active layer surface and the low refractive index layer side surface are 75 ° ≦ α ₁ and α ₂ ≦ 10.
By forming so as to satisfy 5 °, a beat signal can be obtained with low current or low voltage driving.

In the first to third embodiments, the case where the semiconductor laser is cylindrical, quadrangular, or triangular is shown. However, as long as the semiconductor laser has the form of a ring resonator type laser, its shape can be changed. There are no restrictions. For example, the shape may be a disk shape instead of a column shape.

FIG. 22 is a schematic perspective view showing another example of a gyro provided with a ring resonator type laser in which light propagates in a circular shape according to the present invention, and a semiconductor laser used as a laser is formed. The piezoelectric element 3 is provided on the substrate 302.
50.

According to the above configuration, by applying a voltage having a frequency of 20 kHz to the piezoelectric element 350, the clockwise and counterclockwise rotations can be given to the semiconductor laser 300 constituting the gyro. From the terminal 305 to the piezoelectric element 350
By detecting a signal synchronized with the voltage applied to the clock signal, clockwise rotation and counterclockwise rotation can be distinguished. For example, when vibration is applied in the clockwise direction, the terminal voltage increases when the semiconductor laser 300 receives clockwise rotation, and conversely, the terminal voltage decreases when the semiconductor laser 300 receives counterclockwise rotation. . Moreover, by modulating the signal at a frequency in a band different from the signal frequency, the direction of rotation can be detected without adversely affecting the signal. The piezoelectric element is made of, for example, a piezoelectric ceramic such as PZT or lead niobate, or a piezoelectric polymer.

(Example 1) FIG. 23 is a schematic view of a gyro provided with a ring resonator type laser 3000 in which light propagates in a circular shape when viewed from above. It has a rectangular waveguide structure. FIG. 24 shows a cross-sectional view taken along XX '. 3001 is an active layer, 3022 is a light guide layer, 300
2 is a substrate, 3003 is an anode, 3004 is a cathode,
3005 is an electric terminal, 3006 and 3007 are cladding layers (low refractive index layers), and 3040 is a cap layer. Hereinafter, a method for manufacturing the present ring laser will be specifically described.

First, a base having the structure shown in FIG. 25 was prepared.
I do. On an n-GaAs substrate 3002, Al_0.3 Ga
_0.7 Of a multiple quantum well structure composed of three layers of As / GaAs
There is an active layer 3001, and Al is sandwiched between the active layers.
_0.3 Ga_0.7 An As light guide layer 3022 is provided.
Further, the cladding layer (3006 is p-A
l _0.5 Ga_o.5 As, 3007 is n-Al_0.5 Ga_o.5 
As) is formed. 3015 is from n-GaAs
Buffer layer. 3040 is p-GaAs
It is a cap layer composed of: A layer on the cap layer 3040
Cr / Au (or Ti / Pt /
Au) (FIG. 26). And photoresist
After applying 3060, patterning is performed as shown in FIG.
Using patterned photoresist 3060 as a mask
Dry etching is performed on the anode 3003 (see FIG.
28). Next, the semiconductor layer is removed by dry etching.
(FIG. 29), and the photoresist is removed (FIG. 3)
0). Here, the anode is annealed in a hydrogen atmosphere,
Alloy.

Next, if necessary, after polishing the substrate, AuGe
A cathode 3004 made of Ni / Au is deposited (FIG.
1). Anneal again in a hydrogen atmosphere to form an alloy.

FIG. 32 is an enlarged view of the area 3091 in FIG. Active layer 3001 layer surface and cladding layer 3
The angles α ₁ and α ₂ formed by 006 and 3007 are 75 ° ≦ α ₁ ,
α ₂ ≦ 105 ° was satisfied. Actually, α ₁ , = 8
9.0 ° and α ₂ = 88.0 °. Thus, FIG.
An optical gyro having the ring resonator type semiconductor laser shown in FIG.

The length of one side is 400 μm and the oscillation threshold is 4 m
A. When the driving current was set to 5 mA, the camera was shaken or the vehicle was rotated about 30 degrees per second, which was about the vibration of the automobile.
V and a signal of frequency 860 Hz could be obtained.

For comparison, semiconductor lasers having various angles α ₁ and α ₂ between the active layer 3001 and the upper and lower clad layers were manufactured.

For rotations of about 30 degrees per second, α ₁ , α
_{When 2} was 75 ° ≦ α ₁ , α ₂ ≦ 105 °, a beat signal was obtained at 5 mA or less.

However, when the angle between the active layer surface and the side surface of the low refractive index layer exceeded 90 ° ± 15 °, no signal was generated. In the present specification, the low refractive index layer refers to a so-called clad layer, but may be regarded as a low refractive index layer including a light guide layer.

The angle β in FIG. 23 is 45 ± 0.
It is within the range of 01 °, preferably within the range of 45 ° ± 0.001 °. The same applies to the portions corresponding to the other corners. This is a condition necessary for the laser beam to return as close to the starting point as possible when making a round in the optical resonator. Of course, when a semiconductor laser is manufactured by another process, β is desirably within the above range.

FIG. 33 is an enlarged view of the corner 3090 in FIG. 23, but it is preferable to manufacture the corner so that the surface accuracy r is 200 ° or less.

[0127]

As described above, according to the gyro according to the present invention, the ring resonator type laser in which the circulating light of the opposite direction propagates is composed of the active layer surface and the low refractive index layer side surface sandwiching the active layer surface. By controlling the angle of rotation and detecting a beat signal accompanying rotation, a ring laser with small optical loss and a gyro using the same can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a method of detecting an angular velocity using a ring resonator type semiconductor laser according to the present invention.

FIG. 2 is a cross-sectional view for explaining a ring resonator type semiconductor laser according to the present invention.

FIG. 3 is a schematic perspective view of the ring resonator type semiconductor laser according to the first embodiment of the present invention.

FIG. 4 is a diagram for explaining a ring resonator type semiconductor laser according to the first embodiment of the present invention.

FIG. 5 is a diagram for explaining a ring resonator type laser according to the first embodiment of the present invention.

FIG. 6 is a diagram for explaining a ring resonator type laser according to the first embodiment of the present invention.

FIG. 7 is a diagram for explaining a ring resonator type laser according to the first embodiment of the present invention.

FIG. 8 is an example of a circuit diagram for detecting a beat signal according to the present invention.

FIG. 9 is an example of a circuit diagram for detecting a beat signal according to the present invention.

FIG. 10 is an example of a circuit diagram for detecting a beat signal according to the present invention.

FIG. 11 is an example of a circuit diagram for detecting a beat signal according to the present invention.

FIG. 12 is an example of a circuit diagram for detecting a beat signal according to the present invention.

FIG. 13 is an example of a circuit diagram for detecting a beat signal according to the present invention.

FIG. 14 is an example of a circuit diagram for detecting a beat signal according to the present invention.

FIG. 15 is an example of a circuit diagram for detecting a beat signal according to the present invention.

FIG. 16 is a diagram illustrating an example of an FV conversion circuit.

FIG. 17 is a diagram illustrating a ring resonator type laser according to a second embodiment of the present invention.

FIG. 18 is an SEM image of a ring resonator type laser according to a second embodiment of the present invention.

FIG. 19 is an SEM image of the ring resonator type laser according to the second embodiment of the present invention.

FIG. 20 is an SEM image for explaining the present invention.

FIG. 21 is a schematic perspective view showing an example of a gyro provided with a ring resonator type semiconductor laser according to a third embodiment of the present invention.

FIG. 22 is a schematic perspective view showing an example of a gyro provided with the ring resonator type semiconductor laser according to the present invention.

FIG. 23 is a schematic view of a gyro provided with the ring resonator type semiconductor laser according to the present invention when viewed from above.

FIG. 24 is a schematic sectional view of a ring resonator type semiconductor laser according to the present invention.

FIG. 25 is a schematic cross-sectional view for explaining a manufacturing process of the ring resonator type semiconductor laser according to the present invention.

FIG. 26 is a schematic cross-sectional view for explaining a manufacturing process of the ring resonator type semiconductor laser according to the present invention.

FIG. 27 is a schematic cross-sectional view for explaining a manufacturing process of the ring resonator type semiconductor laser according to the present invention.

FIG. 28 is a schematic cross-sectional view for explaining the manufacturing process of the ring resonator type semiconductor laser according to the present invention.

FIG. 29 is a schematic cross-sectional view for explaining the manufacturing process of the ring resonator type semiconductor laser according to the present invention.

FIG. 30 is a schematic sectional view illustrating a ring resonator type semiconductor laser according to the present invention.

FIG. 31 is a schematic sectional view illustrating a ring resonator type semiconductor laser according to the present invention.

FIG. 32 is a schematic sectional view showing an example of a gyro provided with the semiconductor laser according to the present invention.

FIG. 33 is an enlarged view of a partial area of a schematic view when a gyro provided with the ring resonator type semiconductor laser according to the present invention is viewed from above.

FIG. 34 is a diagram for explaining a conventional example.

FIG. 35 is a sectional view taken along AA ′ of FIG. 34;

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 semiconductor laser 101 active layer 102 substrate 103 anode 104 cathode 105 electric terminal 106, 107 low refractive index layer 1350 piezoelectric element

[Procedure amendment]

[Submission date] October 23, 2000 (2000.10.
23)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

A gyro according to a first aspect of the present invention has a ring resonator type semiconductor laser in which light propagates in a counterclockwise circular shape, and sandwiches an active layer having a thickness of 2 μm or less constituting the semiconductor laser. The angle α between the side of the low refractive index layer having a lower refractive index than the active layer and the surface of the active layer satisfies 75 ° ≦ α ≦ 105 ° over the entire circumference of the low refractive index layer, and the semiconductor laser Is characterized by being modulated at a frequency different from the frequency of the beat signal to be detected.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction contents]

According to a second method of operating a gyro according to the present invention, a low-refractive-index layer having a lower refractive index than the active layer is sandwiched by an active layer having a thickness of 2 μm or less constituting a ring resonator type semiconductor laser. And the angle α between the active layer surface and the low refractive index layer satisfies 75 ° ≦ α ≦ 105 ° over the entire circumference, and as a signal for determining the magnitude of the angular velocity applied to the ring resonator type semiconductor laser, It is characterized in that a change in current, voltage or impedance is used, and the drive source of the semiconductor laser is modulated at a frequency different from the frequency of the beat signal to be detected.

Claims (18)

[Claims] 1. A gyro having a ring resonator type semiconductor laser in which light propagates in a counter-rotating circular shape, comprising an active layer forming the semiconductor laser, and having a lower refractive index than the active layer. The angle α between the side of the refractive index layer and the surface of the active layer is 75 ° ≦ α ≦ 1 over the entire circumference of the low refractive index layer.
A gyro characterized by satisfying 05 °. 2. The gyro according to claim 1, wherein the ring resonator type semiconductor laser detects a beat signal generated by rotation as a change in current, voltage, or impedance. 3. The ring resonator type semiconductor laser detects a beat signal generated by rotation as a current flowing through the semiconductor laser, a voltage applied to the semiconductor laser, or an impedance of the semiconductor laser, and changes in respective frequencies. The gyro according to claim 1. 4. The gyro according to claim 1, wherein said gyro has signal detection means for detecting a beat signal generated with rotation. 5. The gyro according to claim 4, wherein said signal detection means is a current detection circuit, a voltage detection circuit, or an impedance detection circuit. 6. The gyro according to claim 4, wherein said signal detection means includes a frequency-voltage conversion circuit or a frequency counter circuit. 7. The gyro according to claim 1, wherein the thickness of the active layer is 2 μm or less. 8. The gyro according to claim 1, wherein an angle α formed between the side surface of the low refractive index layer and the surface of the active layer satisfies 85 ° ≦ α ≦ 95 °. 9. The gyro according to claim 1, wherein the ring resonator type semiconductor laser has a cylindrical shape or a triangular prism shape. 10. The gyro according to claim 1, wherein the surface accuracy of the side surface of the low refractive index layer is equal to or less than half the wavelength of the active layer in the medium. 11. The gyro according to claim 1, wherein the low refractive index layer is a clad layer sandwiching an active layer. 12. The gyro according to claim 1, wherein the low refractive index layer is a light guide layer and a clad layer sandwiching an active layer. 13. The gyro according to claim 1, wherein no reflector is present within a range in which the evanescent light generated from the ring resonator type semiconductor laser exudes. 14. The active layer is made of GaAs, AlGaAs.
The gyro according to claim 1, wherein the gyro is s, InP, or InGaAsP. 15. An angle α between a side surface of a low refractive index layer having a lower refractive index than the active layer and an active layer surface, sandwiching the active layer constituting the ring resonator type semiconductor laser, is defined as the angle of the low refractive index layer. Gyro operation characterized by using a change in current, voltage or impedance as a signal that satisfies 75 ° ≦ α ≦ 105 ° over the entire circumference and determines the magnitude of the angular velocity applied to the ring resonator type semiconductor laser. Method. 16. The gyro operation method according to claim 15, wherein a voltage or a current for driving the ring resonator type semiconductor laser is modulated at a frequency different from a frequency band of the signal. 17. The gyro operation method according to claim 15, wherein the ring resonator type semiconductor laser is rotated clockwise or counterclockwise using a piezoelectric element. 18. An angle α between a side surface of a low refractive index layer having a lower refractive index than the active layer and the surface of the active layer, sandwiching the active layer, is set at 75 ° ≦ α ≦ 105 over the entire circumference of the low refractive index layer. ° semiconductor laser.