产品介绍

Newport Nirvana™ 自动平衡光接收器

为了消除与手动平衡参考和信号光束相关的问题，Nirvana 自动平衡光接收器具有内置的低频反馈回路，可控制其中一个接收器的电子增益，并保持信号臂和参考臂之间的自动平衡。您可以有效消除激光强度噪声，并且在不使用锁相放大器和光学斩波器的情况下进行限制散粒噪声的测量。

可将共模噪声降低 50 dB

保持参考臂和信号臂之间的自动直流平衡

自动平衡或手动平衡模式

增益和带宽

非常适用于光谱分析

对比	型号
	1837 GHz Nirvana 自动平衡光接收器，900-1650 nm
	2007 Nirvana 自动平衡光接收器，400-1070 nm，125 kHz，8-32/M4
	2017 Nirvana 自动平衡光接收器，800-1700 nm，125 kHz，8-32/M4

Newport Nirvana™ 自动平衡光接收器产品规格

型号	1837	2007	2017
光输入	FC/APC	FC and Free Space	FC and Free Space
探测器直径		2.5 mm	1 mm
探测器类型	PIN	PIN	PIN
波长范围	900-1650 nm	400-1070 nm	800-1700 nm
3 dB 带宽	100 kHz to 300 MHz	DC to 125 KHz	DC to 125 KHz
共模抑制	25 dB	50 dB	50 dB
上升时间	1 ns	3 µ s	3 µ s
大转换增益	30,000 V/W	5.2 x 105 V/W	1 x 106 V/W
大跨阻抗增益	40,000 V/A	1x106 V/A	1x106 V/A
大射频功率	20 dB THD @ 100 MHz	+12 dBm bei 50 Ω	+12 dBm bei 50 Ω
NEP	15 pW/√Hz	3 pW/√Hz	3 pW/√Hz
峰值响应度	0.75 A/W	0.5 A/W	1.0 A/W
饱和功率	1 mW	1 mW	0.5 mW
大光功率		4 mW	4 mW
输出接头	SMB	Male BNC	Male BNC
输出阻抗	50 Ω	100 Ω	100 Ω
螺纹类型	8-32	8-32	8-32

特征

可将共模噪声降低 50 dB

Nirvana 的zhuan利电路除去了参考和信号光电流，进而消除了这两个通道常有的噪声信号。与单光束实验相比，这使您测量信号功率时，对于 125 kHz 模型，噪声减少了 50 dB；对于 1 GHz 模型，噪声减少了 25 dB。

保持参考臂和信号臂之间的自动直流平衡

与传统的平衡接收器不同，即便两个探测器上的平均光强度不同且会随时间变化，Nirvana 的电子增益补偿也可自动实现平衡探测。自动平衡技术可以消除来自动态变化系统中的背景噪声，包括热漂移和波长依赖性，实现参考光束和信号光束之间的*功率平衡。

400-1070 nm 或 800-1700 nm 版本

我们提供两个 Nirvana 光接收器，涵盖 400-1070 nm 或 800-1700 nm 光谱范围。

自动平衡或手动平衡模式

Nirvana 光接收器可在信号模式、平衡模式或自动平衡模式下工作。光电探测器 (A) 的输出可以表示为 A=(IS – g x IR) x Rf。在这里，IS 是信号光电二极管电流，IR 是参考光电二极管电流，Rf 是反馈电阻的值，g 是电流分流比，用于表示参考电流有多少来自消除节点 (Isub)，有多少来自地面。在信号模式下，g 为零，没有参考光电流来自消除节点。这里，输出 A 仅仅是放大的信号电流。在平衡模式下，g 等于 1，所有参考光电流来自消除节点。在该模式下，A=(IS–IR)•Rf，光电探测器作为普通的平衡光接收器，如果直流光电流相等，则消除激光噪声。在自动平衡模式下，g 由低频反馈回路以电子方式控制，以保持相等的直流光电流，抵消激光噪声，而与光电流的大小无关。

The feedback loop in the Nirvana™ photoreceiver splits the reference photodetector current, IR, to generate the cancellation photocurrent, Isub. When the DC value of Isub equals the signal current, IS, the laser-amplitude noise is cancelled.

Femtosecond Ultrasonics Application Example

The optical components of improved laser-based acoustic set-up for thin film and microstructure metrology.

One example associated with the balanced photodetection technique is femtosecond ultrasonics wherein a femtosecond laser pulse is used to excite an acoustic wave in a material. The length of mechanical (acoustic) wave determines the resolution of ultrasound. Depending upon the materials for test, the velocity of sound, propagating through the media, has a magnitude in the order of 103
m/s. The acoustic wavelength employed in classical ultrasonics locates at around 0.1–10 mm, depending on materials and frequencies. A growing demand of computer chip manufacturers for non-destructive testing of microstructures and thin films has pushed the wavelength scope down to 10–20 nm.

Piezoelectric devices used for production and echo detection of acoustic waves in the macroscopic scale are too rigid in order to resolve signals within time scales of a few picoseconds and corresponding frequencies of 0.30.6 THz. In 1987, researchers at Brown University
proposed the use of laser-generated ultrasound for film thickness measurements. The performance of the laser-based acoustic method has been further improved recently by means of double-frequency modulation, cross-polarization, and balanced photodetection techniques. Shown above
is an improved pump-probe laser-based ultrasonic set-up as it is realized at the Center of Mechanics, Swiss Federal Institute of Technology in Zürich. The specimens (DUTs) consist of aluminum film
on a sapphire substrate.

A Ti:sapphire laser is used in this event to create short laser pulses having durations of less than 70 fs (1015
s) and a wavelength of 810 nm at a repetition rate of 81 MHz. The laser beam is split into a pump beam (carrying 90% of the energy) and a weaker probe beam by a beamsplitter. The short pump pulse hits perpendicular to the surface of the film specimen, and is absorbed within a thin surface layer (less than 10 nm deep). A mechanical stress is generated, which then excites thermo-elastically an acoustic pulse. When the bulk wave propagates and hits a discontinuity of the acoustic impedance (note: the film substrate border represents a strong discontinuity of the acoustic impedance), an echo occurs which is heading back to the surface of the film. Reaching the surface, the echo causes a slight change of the optical reflectivity.

The purpose of the probe pulse is to scan the optical reflectivity at the thin film surface versus time. Therefore, the experiments are constantly repeated at a repetition rate of 81 MHz, while the length of the optical path of the pump beam is varied. This means that the relative time shift between the pump pulse and the probe pulse is varied, and the optical reflectivity at the surface is scanned versus this relative time shift.

Frequency Modulation Spectroscopy Application Example

Diode-laser-based trace gas sensor configuration for continuous NH3 concentration measurements at 1.53 µm.6

In order to interrogate the spectral absorption profile of a sample (such as a noble gas),
frequency modulation spectroscopy
takes advantage of the change in optical absorption as a function of the frequency (wavelength) of light passed through the sample. A tunable laser can be used to generate a beam whose wavelength is time-varying. This beam is then split into two beams for balanced detection, one passing through the sample, and the other going directly into the reference photodiode. This differential measurement is the basis of FM
spectroscopy. Since the time axis of the observed signal is directly related to the optical frequency, the observed signal can easily be couched in terms of optical frequency (hence the name frequency modulation spectroscopy). By using a balanced photoreceiver, any fluctuations of the laser's intensity can be directly eliminated. In addition, the small percentage fluctuations on the DC optical signal due to the time-varying absorption of the sample can be detected with greatly enhanced signal-to-noise by employing a balanced photoreceiver. Light scattering spectroscopy (LSS) detects the scattered electric field interferometrically. It is very sensitive to phase front variations in the scattered wave.